HomeMy WebLinkAboutF_RS_Technical_Information_Report_20170517_SIGNED.pdf2017 D. R. STRONG Consulting Engineers Inc. The Pines
Technical Information Report Renton, Washington
TECHNICAL INFORMATION REPORT
for
THE PINES
850 & 870 Monroe Avenue NE, Renton, Washington
____________________________________________________________________________
DRS Project No. 16007
Renton File No. LUA16-000413
Owner/Applicant
Harbour Homes, LLC
400 North 34th Street, Suite 300
Seattle, Washington 98103
Report Prepared by
D. R. STRONG Consulting Engineers, Inc.
620 7th Avenue
Kirkland, WA 98033
(425) 827-3063
Report Issue Date
May 15, 2017
R-3927LUA-16000413
PR-16000372
U-16006592 FINAL
SURFACE WATER UTILITY
rstraka 05/17/2017
DEVELOPMENT ENGINEERING
Ann Fowler 05/17/2017
IN COMPIANCE WITH CITY OF RENTON STANDARDS
2016 D. R. STRONG Consulting Engineers Inc. The Pines
Technical Information Report Renton, Washington
TECHNICAL INFORMATION REPORT
THE PINES
TABLE OF CONTENTS
SECTION I ...................................................................................................................... 1
Project Overview ......................................................................................................... 1
Predeveloped Site Conditions ..................................................................................... 1
Developed Site Conditions .......................................................................................... 1
SECTION II ................................................................................................................... 11
Conditions and Requirements Summary ................................................................... 11
Conditions of Approval............................................................................................... 13
SECTION III .................................................................................................................. 15
Off-Site Analysis ........................................................................................................ 15
Task 1: Define and Map Study Area ...................................................................... 16
Task 2: Resource Review ...................................................................................... 17
Task 3: Field Inspection ......................................................................................... 26
Task 4: Drainage System Description and Problem Descriptions .......................... 27
Task 5: Mitigation of Existing or Potential Problems .............................................. 30
SECTION IV .................................................................................................................. 36
Flow Control Analysis and Water Quality Design ...................................................... 36
Existing Site Hydrology (Part A) ............................................................................. 36
Developed Site Hydrology (Part B) ........................................................................ 38
Performance Standards (Part C) ............................................................................... 41
Flow Control System (Part D) .................................................................................... 41
Flow Control BMP Selection ...................................................................................... 41
Flow Control Facility Design Output........................................................................... 43
Water Quality Treatment System (Part E) ................................................................. 48
SECTION V ................................................................................................................... 50
Conveyance System Analysis and Design ................................................................ 50
SECTION VI .................................................................................................................. 58
Special Reports and Studies ..................................................................................... 58
SECTION VII ................................................................................................................. 59
Other Permits, Variances and Adjustments ............................................................... 59
SECTION VIII ................................................................................................................ 60
CSWPPP Analysis and Design (Part A) .................................................................... 60
SWPPP Plan Design (Part B) .................................................................................... 61
SECTION IX .................................................................................................................. 62
Bond Quantities, Facility Summaries, and Declaration of Covenant .......................... 62
Stormwater Facility Summary Sheet.......................................................................... 63
2016 D. R. STRONG Consulting Engineers Inc. The Pines
Technical Information Report Renton, Washington
SECTION X ................................................................................................................... 65
Operations and Maintenance Manual ........................................................................ 65
APPENDICES ............................................................................................................... 66
Appendix “A” Legal Description ................................................................................. 67
Appendix “B” Bond Quantity Worksheet .................................................................... 68
Appendix “C” CSWPPP ............................................................................................. 69
List of Figures
Figure 1 TIR Worksheet .................................................................................................. 2
Figure 2 Vicinity Map ....................................................................................................... 7
Figure 3 Drainage Basins, Subbasins, and Site Characteristics ..................................... 8
Figure 4 Soils .................................................................................................................. 9
Figure 5 City of Renton Topography Map ..................................................................... 18
Figure 6 City of Renton Coal Mine Hazard Areas Map.................................................. 19
Figure 7 City of Renton Flood Hazards Map ................................................................. 20
Figure 8 City of Renton Streams and Wetlands Map .................................................... 21
Figure 9 City of Renton Landslide Hazards Map ........................................................... 22
Figure 10 City of Renton Seismic Hazard Areas Map ................................................... 23
Figure 11 FEMA Map .................................................................................................... 24
Figure 12 King County iMap Drainage Complaints Map................................................ 25
Figure 13 Offsite Analysis Downstream Map ................................................................ 31
Figure 14 Offsite Analysis Downstream Table .............................................................. 32
Figure 15 Predeveloped Area Map................................................................................ 37
Figure 16 Developed Area Map .................................................................................... 40
Figure 17 Detention & Water Quality Facility Details ..................................................... 49
Figure 18 Backwater Analysis Map ............................................................................... 57
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Technical Information Report Renton, Washington
SECTION I
PROJECT OVERVIEW
The Project is the proposed subdivision of two parcels into 14 single-family residential
lots, per the City of Renton’s (City) subdivision process. The Project is located at 850 &
870 Monroe Avenue NE, Renton, Washington (Site) also known as Tax Parcel Numbers
092305-9116, & -9117. The Project will meet the drainage requirements of the 2009
King County Surface Water Design Manual (Manual), as adopted by the City.
PREDEVELOPED SITE CONDITIONS
The total existing Site area is approximately 107,969 s.f. (2.48 acres). The Site is
currently developed with two single family homes, gravel driveways, one detached
garage, two sheds, a barn, and landscaping. The south-eastern portion of the Site
appears to be undisturbed and in a forested condition with light underbrush.
A high point exists at the eastern property line of the Site creating a shallow grade west
maintaining one Threshold Discharge Areas (TDA). Runoff generated by the TDA
gradually sheet flows east to west towards Monroe Avenue NE. The Natiral Discarge
Area (NDA) of the Site is runoff sheet flow over the west property line. Sheet flow is
captured by the curb and gutter located on the east side of Monroe Ave NE where
runoff then enters one of two, type 1 catch basins creating two downstream paths.
Runoff collected by the two catch basins is conveyed to a 24” diameter pipe where the
two downstream paths converge and flow south through the existing stormwater
system.
DEVELOPED SITE CONDITIONS
The applicant is seeking approval to subdivide 2.48 acres into 14 single–family
residential lots (Project), with lot sizes ranging from approximately 5,000 s.f. to 5,201 s.f.
All existing improvements located on the Site will be demolished or removed during plat
construction.
The Site falls within the Peak Rate Flow Control Standard area matching existing Site
conditions. The Project is required to adhere to basic water quality requirements. A
combined detention/wet vault will be provided to meet detention and water quality
requirements.
The proposed impervious surface areas are as follows: frontage improvements
consisting of a 5’ sidwalk along Monroe Ave NE, Road A, the 14 new single-family
residences and their driveways, Tract B, and Tract D, the detention facility, will generate
approximately 64,927 s.f. of impervious area (1.49 acres). This impervious area
includes the bypass area, but excludes 2,914 s.f. of upstream tributary area. The
remainder of the developed Site will be modeled as till grass 41,487 s.f. (0.95 acre).
A small portion of ROW frontage on Monroe Ave NE, along the north half of the Site will
be bypass. Bypass runoff will continue along its current flow path and converge with the
Site runoff downstream of the detention facility.
(See Section IV).
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FIGURE 1
TIR WORKSHEET
TECHNICAL INFORMATION REPORT (TIR) WORKSHEET
Part 1 PROJECT OWNER AND
PROJECT ENGINEER Part 2 PROJECT LOCATION AND
DESCRIPTION
Project Owner: Harbour Homes, LLC
Phone: (206) 315-8130
Address: 400 North 34th St, Suite 300
Seattle, WA 98103
Project Engineer: Yoshio L. Piediscalzi, P.E.
Company: D. R. STRONG Consulting
Engineers Inc.
Phone: (425) 827-3063
Project Name: The Pines
City Permit#: U 2016-0XXXX
Location:
Township: 23 North
Range: 05 East
Section: 09
Site Address: 850 & 870
Monroe Avenue NE
Renton, WA
Part 3 TYPE OF PERMIT APPLICATION Part 4 OTHER REVIEWS AND PERMITS
Landuse Services
Subdivision / Short Subdivision / UPD
Building Services: M/F / Commercial / SFR
Clearing and Grading
Right-of-Way
Other:
DFW HPA Shoreline Mngmt
COE 404 Structural
DOE Dam Safety Rockery/Vault
FEMA Floodplain ESA Section 7
COE Wetlands
Other:
Part 5 PLAN AND REPORT INFORMATION
Technical Information Report
Type of Drainage Review Full / Targeted /
(circle): Large Site
Date (include revision Decemeber 7th, 2016
dates):
Date of Final:
Site Improvement Plan (Engr. Plans)
Type (circle one): Full / Modified / :
Small Site
Date (include revision
dates):
Date of Final:
Part 6 ADJUSTMENT APPROVALS
Type (circle one): Standard / Complex / Preapplication / Experimental / Blanket
Description: (include conditions in TIR Section 2)
_____________________________________________________________________________________
_____________________________________________________________________________________
____________________________________________________________________________________
Date of Approval:
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Part 7 MONITORING REQUIREMENTS
Monitoring Required: Yes / No
Start Date: TBD
Completion Date
Describe: Monitor discharge location
during construction.
Part 8 SITE COMMUNITY AND DRAINAGE BASIN
Community Plan: Highlands
Special District Overlays: N/A
Drainage Basin: East Lake Washington – Renton
Stormwater Requirements: Peak Rate Flow Control Standard – Matching Existing Site
Conditions and Basic WQ treatment
Part 9 ONSITE AND ADJACENT SENSITIVE AREAS
River/ Stream
Lake
Wetlands
Closed Depression
Floodplain
Other
Steep Slope
Erosion Hazard
Landslide Hazard
Coal Mine Hazard
Seismic Hazard
Habitat Protection
Part 10 SOILS
Soil Type
AmC
Slopes
6-15%
Erosion Potential
Moderate to Severe
High Groundwater Table Sole Source Aquifer
other Seeps/Springs
Additional Sheets Attached
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Part 11 DRAINAGE DESIGN LIMITATIONS
REFERENCE
Core Requirement #2 – Offsite Analysis
SEPA
Additional Sheet Attached
LIMITATION / SITE CONSTRAINT
Part 12 TIR SUMMARY SHEET
Threshold Discharge Area: Site comprised of one TDA
(name or description)
Core Requirements (all 8 apply)
Discharge of Natural Location yes Number of Natural Discharge Locations: 1
Offsite Analysis Level: 1 / 2 / 3 dated: 03/21/16
Flow Control Level: 1 / 2 / 3 or Exemption Number
(incl. facility summary sheet Small Site BMPS N/A
Conveyance System Spill containment located at: TBD
Erosion and Sediment Control ESC Site Supervisor: T/B/D
Contact Phone: T/B/D
After Hours Phone: T/B/D
Maintenance and Operation Responsibility: Private / Public
If Private, Maintenance Log Required: Yes / No
Financial Guarantees and Provided: Yes / No
Liability
Water Quality Type: Basic / Sens Lake / Enhanced Basic / Bog
(include facility summary sheet) or exemption No.
Landscape Management Plan: Yes / No
Special Requirements (as applicable)
Area Specific Drainage Type: CDA / SDO / MDP / BP / LMP / Shared / None
Requirements Name:
Floodplain/Floodway Delineation Type: Major / Minor / Exemption / None
100-year Base Flood Elevation (or range):
Datum:
Flood Protection Facilities Describe: N/A
Source Control Describe Landuse:
(comm. / industrial landuse) Describe any structural controls:
Oil Control High-use Site: Yes / No
Treatment BMP:
Maintenance Agreement: Yes / No
with whom?
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Other Drainage Structures
Describe: Runoff will be collected and conveyed to the combined detention/wet
vault located in Tract D.
Part 13 EROSION AND SEDIMENT CONTROL REQUIREMENTS
MINIMUM ESC REQUIREMENTS
DURING CONSTRUCTION
Clearing Limits
Cover Measures
Perimeter Protection
Traffic Area Stabilization
Sediment Retention
Surface Water Collection
Dewatering Control
Dust control
Flow Control
MINIMUM ESC REQUIREMENTS
AFTER CONSTRUCTION
Stabilize Exposed Surfaces
Remove and Restore Temporary ESC
Facilities
Clean and Remove All Silt and
Debris, Ensure Operations of
Permanent Facilities
Flag Limits of SAO and open space
Preservation areas
Other
Part 14 STORMWATER FACILITY DESCRIPTIONS (Note: Include Facility Summary and Sketch
Flow Control Type/Description Water Quality Type/Description
Detention
Infiltration
Regional
Facility
Shared Facility
Flow Control
BMPs
Other
Vault
Biofiltration
Wetpool
Media Filtration
Oil Control
Spill Control
Flow Control
BMPs
Other
Wet-vault
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Part 15 EASEMENTS/TRACTS Part 16 STRUCTURAL ANALYSIS
Drainage Easement
Covenant
Native Growth Protection Covenant
Tract
Other:
Cast in Place Vault
Retaining Wall
Rockery > 4’ High
Structural on Steep Slope
Other:
Part 17 SIGNATURE OF PROFESSIONAL ENGINEER
I, or a civil engineer under my supervision, have visited the site. Actual site conditions as observed were incorporated into this worksheet and the attached Technical Information Report. To the best of my knowledge the information provided here is accurate.
Signed/Date
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FIGURE 2
VICINITY MAP
The information included on this map has been compiled by King County staff from a variety of sources and is subject to change
without notice. King County makes no representations or warranties, express or implied, as to accuracy, completeness, timeliness,
or rights to the use of such information. King County shall not be liable for any general, special, indirect, incidental, or consequential
damages including, but not limited to, lost revenues or lost profits resulting from the use or misuse of the information contained on
this map. Any sale of this map or information on this map is prohibited except by written permission of King County.
Site
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FIGURE 3
DRAINAGE BASINS, SUBBASINS, AND SITE CHARACTERISTICS
0GRAPHIC SCALE9060301 INCH = 60 FT.
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FIGURE 4
SOILS
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King County Area, Washington
AmC—Arents, Alderwood material, 6 to 15 percent slopes
Map Unit Setting
• National map unit symbol: 1hmsq
• Mean annual precipitation: 35 to 60 inches • Mean annual air temperature: 50 degrees F
• Frost-free period: 150 to 200 days
• Farmland classification: Not prime farmland
Map Unit Composition
• Arents, alderwood material, and similar soils: 100 percent
• Estimates are based on observations, descriptions, and transects of the map unit.
Description of Arents, Alderwood Material
Setting
• Landform: Till plains
• Parent material: Basal till
Typical profile
• H1 - 0 to 26 inches: gravelly sandy loam
• H2 - 26 to 60 inches: very gravelly sandy loam
Properties and qualities
• Slope: 6 to 15 percent
• Depth to restrictive feature: 20 to 40 inches to densic material
• Natural drainage class: Moderately well drained
• Capacity of the most limiting layer to transmit water (Ksat): Very low to moderately low (0.00 to 0.06 in/hr)
• Depth to water table: About 16 to 36 inches
• Frequency of flooding: None
• Frequency of ponding: None • Available water storage in profile: Very low (about 2.3 inches)
Interpretive groups
• Land capability classification (irrigated): None specified
• Land capability classification (nonirrigated): 4s
• Hydrologic Soil Group: B/D
See Appendix B for Geotechnical Engineering Study
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SECTION II
CONDITIONS AND REQUIREMENTS SUMMARY
The Project must comply with the following Core and Special Requirements:
• C.R. #1 – Discharge at the Natural Location: Existing drainage discharges the
Site at one location, maintaining one TDA. The topography indicates that all
stormwater runoff leaves the Site as sheet flow across the west property line.
Runoff is collected by the curb and gutter on the east side of Monroe Avenue NE.
• C.R. #2 – Offsite Analysis: Analysis is included in Section III. The Analysis
describes the Site’s runoff patterns in detail.
• C.R. #3 – Flow Control: The Project is required to adhere to Peak Rate Flow
Control Standard – Matching Existing site conditions. One detention/wet vault will
provide flow control and water quality as required for the new and replaced
impervious and pervious surfaces. The Site is required to “match the developed
peak discharge rates to existing site conditions peak discharge rates for 2, 10 and
100-year return periods.” (City of Renton 2009 Surface Water Design Manual
Amendment, Sec. 1.2.3.1). A combined detention/wet vault will accommodate this
requirement.
• C.R. #4 – Conveyance System: New pipe systems are required to be designed
with sufficient capacity to convey and contain (at minimum) the 25-year peak flow
with a minimum of 6 inches of freeboard between the design water surface and
structure grate, assuming developed conditions for onsite tributary areas and
existing conditions for any offsite tributary areas. Pipe system structures may
overtop for runoff events that exceed the 25-year design capacity, provided the
overflow from a 100-year runoff event does not create or aggravate a “severe
flooding problem” or “severe erosion problem” as defined in C.R. #2. Any overflow
occurring onsite for runoff events up to and including the 100-year event must
discharge at the natural location for the project site. In residential subdivisions, such
overflow must be contained within an onsite drainage easement, tract, covenant or
public right-of-way. The proposed conveyance system was analyzed using the
KCBW program, and is capable of conveying the 100-year peak storm without
overtopping any structures or channels.
• C.R. #5 – Erosion and Sediment Control: The Project will provide the nine
minimum ESC measures.
• C.R. #6 – Maintenance and Operations: Maintenance of the proposed storm
drainage facilities will be the responsibility of the City. An Operation and
Maintenance Manual is included in Section X.
• C.R. #7 – Financial Guarantees: Prior to commencing construction, the Applicant
must post a drainage facilities restoration and site stabilization financial guarantee.
For any constructed or modified drainage facilities to be maintained and operated by
the City, the Applicant must: 1) Post a drainage defect and maintenance financial
guarantee for a period of two years, and 2) Maintain the drainage facilities during the
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two-year period following posting of the drainage defect and maintenance financial
guarantee.
• C.R. #8 – Water Quality: The Project is located in the Basic Water Quality
Treatment area. The combined detention/wet vault will accommodate this
requirement.
• S.R. #1 – Other Adopted Area-Specific Requirements: Not applicable for this
Project.
• S.R. #2 – Floodplain/Floodway Delineation: Not applicable for this Project.
• S.R. #3 – Flood Protection Facilities: Not applicable for this Project.
• S.R. #4 – Source Control: Not applicable for this Project.
• S.R. #5 – Oil Control: Not applicable for this Project.
• S.R. #6 – Aquifer Protection Area: Site not located within zones 1 and 2, therefore
not applicable for this Project.
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CONDITIONS OF APPROVAL
The Pines LUA 16-000413
The proposed preliminary plat, site plan is approved and street modifications are
approved, subject to the following conditions:
1. The applicant shall provide a final detailed landscaping plan compliant with
RMC 4-8-120D at the time of Utility Construction Permit review that provides 15-feet of
landscaping surrounding stormwater Tract D. The vault may encroach into the
landscaping screen, provided the landscaping can still be planted on top of the vault.
The final landscaping plan shall be approved prior to Utility Construction Permit
issuance. All tract landscaping shall be installed and inspected prior to plat recording.
2. The applicant shall provide a final landscaping plan for review and approval by
the Current Planning Project Manager at the time of Utility Construction Permit review
that provides a berm within the 15-foot landscaping screen in stormwater Tract D along
the Monroe Ave NE frontage. The final landscaping plan shall be approved prior to
Utility Construction Permit issuance. The berm shall be installed and inspected prior to
plat recording.
3. The applicant shall be required to create a homeowner’s association for the
shared maintenance and responsibility of the shared tracts and all other shared
improvements of this development. A draft of the document(s) shall be submitted to
Current Planning Project Manager for the review and approval by the City Attorney and
Property Services section prior to the recording of the final plat. The HOA documents
shall be recorded concurrently with the final plat.
4. The applicant shall provide a Road and Grading Plan for review and approval
by the Current Planning Project Manager at the time of Utility Construction Permit
review that provides tree protection measures identified in RMC 4-4-130H9 for offsite
trees with drip lines that are within the subject property; Provided that the “retained”
trees referenced in 4-4-130H9 are construed as trees required to be retained (either by
the applicant or previously by adjoining property owners) by the City’s tree retention
standards.
5. The applicant shall provide a final landscaping plan for review and approval by
the Current Planning Project Manager at the time of Utility Construction Permit review
that provides details of split-rail fencing around Tree Retention Tract A and signage
identifying the tract as tree protection. Split-rail fencing and signage shall be installed
and inspected prior to final plat recording.
6. The applicant shall revise the Preliminary Plat for review and approval by the
Current Planning Project Manager at the time of Utility Construction Permit review that
provides a front yard setback variation for at least one (1) lot for every four (4) abutting
street fronting lots and the varied setbacks shall be provided as a note on the face of
the plat.
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7. The applicant shall provide a plat layout color palette for the new single family
homes for review and approval by the Current Planning Project Manager prior to plat
recording.
8. The applicant shall provide a revised paving plan for review and approval by
the Current Planning Project Manager, at the time of Utility Construction Permit review
identifying the modified Monroe Ave NE street section, as approved through
Modification Request 1.
9. All future homes within the subdivision shall have a fire sprinkler system
approved by the Renton Fire Authority.
10. The applicant shall provide a note on the face of the plat restricting access for
lots 5 and 6 to the shared driveway. The front of the future homes on lots 5 and 6 shall
be oriented to the new residential street (Road A) with garages located on the side or
rear of the homes.
11. The applicant shall submit revised plans for review and approval by the
Current Planning Project Manager at the time of Utility Construction Permit review
removing the four (4) pedestrian ramps facing east along Monroe Ave NE.
12. All proposed street names shall be approved by the City.
13. Side sewer lines shall be installed eight feet (8') into each lot if sanitary sewer
mains are available, or provided with the subdivision development.
14. All utilities designed to serve the subdivision shall be placed underground.
Any utilities installed in the parking strip shall be placed in such a manner and depth to
permit the planting of trees. Those utilities to be located beneath paved surfaces shall
be installed, including all service connections, as approved by the Department of Public
Works. Such installation shall be completed and approved prior to the application of any
surface material. Easements may be required for the maintenance and operation of
utilities as specified by the Department of Public Works.
15. Any cable TV conduits shall be undergrounded at the same time as other
basic utilities are installed to serve each lot. Conduit for service connections shall be
laid to each lot line by Applicant as to obviate the necessity for disturbing the street
area, including sidewalks, or alley improvements when such service connections are
extended to serve any building. The cost of trenching, conduit, pedestals and/or vaults
and laterals as well as easements therefore required to bring service to the
development shall be borne by the developer and/or land owner. The applicant shall be
responsible only for conduit to serve his development. Conduit ends shall be elbowed to
final ground elevation and capped. The cable TV company shall provide maps and
specifications to the applicant and shall inspect the conduit and certify to the City that it
is properly installed.
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SECTION III
OFF-SITE ANALYSIS
An offsite Level One Downstream Analysis was prepared by D.R. STRONG Consulting
Engineers Inc. and is included in this section.
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Level One Downstream Analysis Renton, Washington
LEVEL ONE DOWNSTREAM ANALYSIS
TASK 1: DEFINE AND MAP STUDY AREA
This Offsite Analysis was prepared in accordance with Core Requirement #2, Section
1.2.2 of the 2009 King County Surface Water Design Manual and City Amendments as
adopted by the City of Renton (Manual). The Site is located at 850 & 870 Monroe
Avenue NE, Renton, Washington. The Project is the subdivision of three parcels into 14
single-family lots.
See Figures 1, 2, 3, and 5 for maps of the study area.
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Level One Downstream Analysis Renton, Washington
TASK 2: RESOURCE REVIEW
• Adopted Basin Plans: The City of Renton and King County Department of
Development and Environmental Services (DDES) and Department of Natural
Resources and Parks (DNRP) do not have a specific plan for the East Lake
Washington Drainage Basin.
• Finalized Drainage Studies: No available applicable drainage studies at this time.
• Basin Reconnaissance Summary Reports: None available.
• Comprehensive Plans: Renton’s Comprehensive Plan, adopted on June 22, 2015,
effective July 1, 2015.
• Floodplain/Floodway (FEMA) Map: No floodplains exist on site, See Figure 10.
• Other Offsite Analysis Reports: Albert Balch’s President Park No. 7 & No. 8 and
Skyland Heights No. 2.
• Sensitive Areas Map Folios: See Figures 6-9.
• DNRP Drainage Complaints and Studies: Per King County Water and Land
Resources Division, there were no complaints within the downstream paths, within
approximately one mile from the Site within the last 10 years. See figure 11.
• USDA King County Soils Survey: See Figure 4
• Wetlands Inventory: Vol. 2 East (1990) – No wetlands identified along the
downstream paths in the KC Wetlands Inventory. The City of Renton Mapping
Applications indicates there are also no wetlands along the downstream path. See
Figure 8.
• Migrating River Studies: The Site is not located near the channel migration zones of
Cedar River, Tolt River, Raging River, Snoqualmie River, or Green River.
• King County Designated Water Quality Problems: Per the Washington State Water
Quality Assessment 303(d)/305(b) Integrated Report current as of 2012, there are
no water quality problems within 1 mile downstream of the Site.
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Level One Downstream Analysis Renton, Washington
FIGURE 5
CITY OF RENTON TOPOGRAPHY MAP
Site
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FIGURE 6
CITY OF RENTON COAL MINE HAZARD AREAS MAP
Site
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FIGURE 7
CITY OF RENTON FLOOD HAZARDS MAP
Site
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FIGURE 8
CITY OF RENTON STREAMS AND WETLANDS MAP
Site
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FIGURE 9
CITY OF RENTON LANDSLIDE HAZARDS MAP
Site
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FIGURE 10
CITY OF RENTON SEISMIC HAZARD AREAS MAP
Site
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FIGURE 11
FEMA MAP
Site
(Approximate)
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FIGURE 12
KING COUNTY IMAP DRAINAGE COMPLAINTS MAP
Site
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Level One Downstream Analysis Renton, Washington
TASK 3: FIELD INSPECTION
UPSTREAM TRIBUTARY AREA
Upon evaluation of the upstream area through examining COR topographic map (see
Figure 5) and by conducting field reconnaissance on March 21st 2016, the upstream
tributary area for the Site is considered negligible. Runoff from the north and east is
captured by the developed single-family lots and conveyed to the existing conveyance
systems located in NE 9th St and Olympia Ave NE, respectively. Runoff from the south
is also collected by the developed single-family lots and conveyed to Monroe Ave NE
and south away from the Site.
GENERAL ONSITE AND OFFSITE DRAINAGE DESCRIPTIONS
The Site is contained within one Threshold Discharge Area (TDA). Runoff from the Site
sheet flows over the west property line to the vertical curb and gutter located on the east
side of Monroe Avenue NE. Runoff then flows north via curb and gutter before being
collected by one of two catch basins. Runoff from each catch basin is conveyed to the
24” diameter pipe and catch basin conveyance system within Monroe Avenue NE,
which flows south towards NE 7th St. The conveyance system then turns west at NE 7th
St. and continues to flow that direction for over a quarter-mile downstream of the Site.
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Level One Downstream Analysis Renton, Washington
TASK 4: DRAINAGE SYSTEM DESCRIPTION AND PROBLEM DESCRIPTIONS
DRAINAGE SYSTEM DESCRIPTION
The downstream analysis is further illustrated and detailed in the Downstream Map
Figure 12 and Downstream Table Figure 13. The drainage area is located within the
East Lake Washington - Renton Drainage Basin. The drainage area was evaluated by
reviewing available resources described in task 2, and by conducting a field
reconnaissance on March 21st, 2016 under rainy conditions.
DOWNSTREAM PATH 1
“A1” is the Natural Discharge Area (NDA) for path 1 from the TDA of the Site. It is
located along the western property line (±0).
From Point “A1” to Point “B1”, runoff continues to flow west as sheet flow over
approximately 7.5 feet of till grass and a 6-inch concrete curb. No concentrated flow
was observed (±0’-8’).
Point “B1”, runoff is collected by the concrete gutter located along the east side of
Monroe Avenue NE (±8’).
From Point “B1” to Point “C1”, runoff flows north as channel flow via vertical curb and
gutter. Light flow was observed (±8’-140’).
Point “C1”, runoff enters a Type 1 CB, Facility ID No. 136224 (±140’).
From Point “C1” to Point “D1”, runoff flows northwest as pipe flow via 8” PVC. Trickle
flow was observed (±140’-154’).
Point “D1”, runoff enters a Type 2 CB, Facility ID No. 136225 (±154’).
From Point “D1” to Point “E1”, runoff flows west as pipe flow via 12” CPEP/LCPE.
Moderate flow observed (±154’-182’).
Point “E1”, runoff enters a Type 2 CB, Facility ID No. 135946 (±182’).
From Point “E1” to Point “F1”, runoff flows south as pipe flow via 24” CPEP/LCPE.
Moderate flow was observed (±182’-403’).
Point “F1”, runoff enters a Type 2 CB, Facility ID No 135945 (±403’).
From Point “F1” to Point “G1”, runoff flows south as pipe flow via 24” CPEP/LCPE.
Moderate flow was observed (±403’-553’).
Point “G1”, runoff enters a Type 2 CB, Facility ID No 135942 (±553’).
From Point “G1” to Point “H1”, runoff flows south as pipe flow via 24” CPEP/LCPE.
Moderate flow was observed (±553’-695’).
Point “H1”, runoff enters a Type 2 CB, Facility ID No 136001 (±695’).
From Point “H1” to Point “I1”, runoff flows south as pipe flow via 24” CPEP/LCPE.
Moderate flow was observed (±695’-824’).
Point “I1”, runoff enters a Type 2 CB, Facility ID No 135998 (±824’).
From Point “I1” to Point “J1”, runoff flows south as pipe flow via 24” CPEP/LCPE.
Moderate flow was observed (±824’-958’).
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Level One Downstream Analysis Renton, Washington
Point “J1”, runoff enters a Type 2 CB, Facility ID No 135996 (±958’).
From Point “J1” to Point “K1”, runoff flows south as pipe flow via 24” CPEP/LCPE.
Moderate flow was observed (±958’-1,093’).
Point “K1”, runoff enters a Type 2 CB, Facility ID No 135994. COR Maps incorrectly
identifies the structure as a type 1 (±1,093’).
From Point “K1” to Point “L1”, runoff flows southwest as pipe flow via 24” CPEP/LCPE.
Moderate flow was observed (±1,093’-1,124’).
Point “L1”, runoff enters a Type 2 CB, Facility ID No 135993 (±1,124’).
From Point “L1” to Point “M1”, runoff flows westerly as pipe flow via 24” CPEP.
Moderate flow was observed (±1,124’-1,238’).
Point “M1”, runoff enters a Type 2 CB, Facility ID No 134697 (±1,238’).
From Point “M1” to Point “N1”, runoff flows westerly as pipe flow via 24” CPEP.
Moderate flow was observed (±1,238’-1,300’).
Point “N1”, runoff enters a Type 2 CB, Facility ID No 134696 (±1,300’).
From Point “N1” to Point “O1”, runoff flows westerly as pipe flow via 24” CPEP.
Moderate flow was observed (±1,300’-1,444’).
Point “O1”, runoff enters a Type 2 CB, Facility ID No 134695 (±1,444’).
From Point “O1” to Point “P1”, runoff flows southwesterly as pipe flow via 24” CPEP.
Moderate flow was observed (±1,444’-1,562’).
Point “P1”, runoff enters a Type 2 CB, Facility ID No 134693 (±1,562’).
From Point “P1” to Point “Q1”, runoff flows southwesterly as pipe flow via 24” CPEP.
Moderate flow was observed (±1,562’-1,625’).
Point “Q1”, runoff enters a Type 2 CB, Facility ID No 127707 located in the sidewalk
(±1,625’).
From Point “Q1” to Point “R1”, runoff flows southwest as pipe flow via 24” CPEP.
Moderate flow was observed (±1,625’-1,678’).
Point “R1”, runoff enters a Type 2 CB, Facility ID No 134691 (±1,678’).
From Point “R1” to Point “S1”, runoff flows westerly as pipe flow via 24” CPEP.
Moderate flow was observed (±1,678’-1,806’).
Point “S1”, runoff enters a Type 2 CB, Facility ID No 134688. This concluded the
quarter-mile downstream reconnaissance (±1,806’).
DOWNSTREAM PATH 2
“A2” is the Natural Discharge Area (NDA) for path 2 from the TDA of the Site. It is
located along the west property line of parcel 092305-9116 (±0’).
From Point “A2” to Point “B2”, runoff continues to flow west as sheet flow over
approximately 7.5 feet of till grass and a 6-inch concrete curb. No concentrated flow
was observed (±0’-8’).
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Level One Downstream Analysis Renton, Washington
Point “B2”, runoff is collected by the concrete gutter located along the east side of
Monroe Avenue NE (±8’).
Point “B2” to Point “C2”, runoff flows north as channel flow via vertical curb and gutter.
Light flow was observed (±8’-108’).
Point “C2”, runoff enters a Type 1 CB, Facility ID No. 135944 (±108’).
From Point “C2” to Point “F1”, runoff flows west as pipe flow via 8” PVC. Light flow was
observed (±108’-134’).
Point “F1”, runoff enters a Type 2 CB, Facility ID No. 135945 where runoff from
downstream path 2 converges with runoff downstream path 1 (±134’).
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Level One Downstream Analysis Renton, Washington
TASK 5: MITIGATION OF EXISTING OR POTENTIAL PROBLEMS
A review of the King County Water and Land Resources Division – Drainage Services
Section Documented Drainage Complaints revealed no complaints within one mile of
the downstream flow paths within the last ten years.
The project should not create any problems as specified in Section 1.2.2.1 of the
Manual and therefore is not required to provide Drainage Problem Impact Mitigation
subject to the requirements of Section 1.2.2.2.
A combined detention/wet vault will provide flow control and basic water quality
requirements for the entire Site. During construction, standard sediment and erosion
control methods will be utilized. This will include the use of a stabilized construction
entrance, perimeter silt fencing, and other necessary measures to minimize soil erosion
during construction.
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Level One Downstream Analysis Renton, Washington
FIGURE 13
OFFSITE ANALYSIS DOWNSTREAM MAP
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Level One Downstream Analysis Renton, Washington
FIGURE 14
OFFSITE ANALYSIS DOWNSTREAM TABLE
DOWNSTREAM PATH 1
Symbol Drainage
Component Type,
Name, and Size
Drainage Component
Description
Slope Distance
From site
Discharge
Existing
Problems
Potential
Problems
Observations of field inspector
resource reviewer, or resident
See map
Type: sheet flow, swale,
Stream, channel, pipe,
Pond; Size: diameter
Surface area
drainage basin, vegetation, cover,
depth, type of sensitive area, volume
%
1/4 mile =
1,320 feet
Constrictions, under capacity, ponding,
overtopping, flooding, habitat or
organism destruction, scouring, bank
sloughing, sedimentation, incision, other
erosion
Tributary area, likelihood of problem,
overflow pathways, potential impacts.
A1 Natural discharge area Runoff exits at the NDA along the western
property line of the Site.
–0’ None Observed None Anticipated No concentrated flow observed
A1-B1 West sheet flow Sheet flow over till grass and 6” curb None Observed None Anticipated No concentrated flow observed
B1 6” Vertical curb and
gutter
East side of Monroe Avenue NE –8’ None Observed None Anticipated Light flow observed
B1-C1 North channel flow 6” concrete vertical curb and gutter None Observed None Anticipated Light flow observed
C1 Type 1 CB Renton Facility No. 136224 ±140’ None Observed None Anticipated Light flow observed
C1-D1 Northwest pipe flow 8” Ø PVC None Observed None Anticipated Light flow observed
D1 Type 2 CB Renton Facility No. 136225 ±154’ None Observed None Anticipated Light flow observed
D1-E1 West pipe flow 12” Ø CPEP/LCPE None Observed None Anticipated Moderate flow observed
E1 Type 2 CB Renton Facility No. 135946 ±182’ None Observed None Anticipated Moderate flow observed
E1-F1 South pipe flow 24” Ø CPEP/LCPE None Observed None Anticipated Moderate flow observed
F1 Type 2 CB Renton Facility No. 135945 ±403’ None Observed None Anticipated Moderate flow observed
F1-G1 South pipe flow 24” Ø CPEP/LCPE None Observed None Anticipated Moderate flow observed
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Level One Downstream Analysis Renton, Washington
G1 Type 2 CB Renton Facility No. 135942 ±553’ None Observed None Anticipated Moderate flow observed
G1-H1 South pipe flow 24” Ø CPEP/LCPE None Observed None Anticipated Moderate flow observed
H1 Type 2 CB Renton Facility No. 136001 ±695’ None Observed None Anticipated Moderate flow observed
H1-I1 South pipe flow 24” Ø CPEP/LCPE None Observed None Anticipated Moderate flow observed
I1 Type 2 CB Renton Facility No. 135998 ±824’ None Observed None Anticipated Moderate flow observed
I1-J1 South pipe flow 24” Ø CPEP/LCPE None Observed None Anticipated Moderate flow observed
J1 Type 2 CB Renton Facility No. 135996 ±958’ None Observed None Anticipated Moderate flow observed
J1-K1 South pipe flow 24” Ø CPEP/LCPE None Observed None Anticipated Moderate flow observed
K1 Type 2 CB Renton Facility No. 135994 ±1,093’ None Observed None Anticipated Moderate flow observed
K1-L1 Southwest pipe flow 24” Ø CPEP/LCPE None Observed None Anticipated Moderate flow observed
L1 Type 2 CB Renton Facility No. 135993 ±1,124’ None Observed None Anticipated Moderate flow observed
L1-M1 Westerly pipe flow 24” Ø CPEP None Observed None Anticipated Moderate flow observed
M1 Type 2 CB Renton Facility No. 134697 ±1,238’ None Observed None Anticipated Moderate flow observed
M1-N1 Westerly pipe flow 24” Ø CPEP None Observed None Anticipated Moderate flow observed
N1 Type 2 CB Renton Facility No. 134696 ±1,300’ None Observed None Anticipated Moderate flow observed
N1-O1 Westerly pipe flow 24” Ø CPEP None Observed None Anticipated Moderate flow observed
O1 Type 2 CB Renton Facility No. 134695 ±1,444’ None Observed None Anticipated Moderate flow observed
O1-P1 Southwesterly pipe flow 24” Ø CPEP None Observed None Anticipated Moderate flow observed
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Level One Downstream Analysis Renton, Washington
DOWNSTREAM PATH 2
P1 Type 2 CB Renton Facility No. 134693 ±1,562’ None Observed None Anticipated Moderate flow observed
P1-Q1 Southwesterly pipe flow 24” Ø CPEP None Observed None Anticipated Moderate flow observed
Q1 Type 2 CB Renton Facility No. 134692 located in the
sidewalk
±1,625’ None Observed None Anticipated Moderate flow observed
Q1-R1 Southwesterly pipe flow 24” Ø CPEP None Observed None Anticipated Moderate flow observed
R1 Type 2 CB Renton Facility No. 134691 ±1,678’ None Observed None Anticipated Moderate flow observed
R1-S1 Westerly pipe flow 24” Ø CPEP None Observed None Anticipated Moderate flow observed
S1 Type 2 CB Renton Facility No. 134688. This was the
end of the field reconnaissance at over ¼
mile downstream from the Site.
±1,806’ None Observed None Anticipated Moderate flow observed
Symbol Drainage
Component Type,
Name, and Size
Drainage Component
Description
Slope Distance
From site
Discharge
Existing
Problems
Potential
Problems
Observations of field inspector
resource reviewer, or resident
See map
Type: sheet flow, swale,
Stream, channel, pipe,
Pond; Size: diameter
Surface area
drainage basin, vegetation, cover,
depth, type of sensitive area, volume
%
1/4 mi=1,320
ft
Constrictions, under capacity, ponding,
overtopping, flooding, habitat or
organism destruction, scouring, bank
sloughing, sedimentation, incision, other
erosion
Tributary area, likelihood of problem,
overflow pathways, potential impacts.
A1 Natural discharge area Runoff exits at NDA along the western
property line of parcel 092305-116.
–0’ None Observed None Anticipated No concentrated flow observed
A1-B1 West sheet flow Sheet flow over till grass and 6” curb None Observed None Anticipated No concentrated flow observed
B1 6” Vertical curb and
gutter
East side of Monroe Avenue NE –8’ None Observed None Anticipated Light flow observed
B1-C1 North channel flow 6” concrete vertical curb and gutter None Observed None Anticipated Light flow observed
C1 Type 1 CB Renton Facility No. 135944 ±108’ None Observed None Anticipated Light flow observed
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Level One Downstream Analysis Renton, Washington
C1-F1 West pipe flow 8” Ø PVC None Observed None Anticipated Light flow observed
F1 Type 2 CB Renton Facility No. 135945. Downstream
path 2 combines with downstream path.
–134’ None Observed None Anticipated No concentrated flow observed
2016 D. R. STRONG Consulting Engineers Inc. Page 36 The Pines
Technical Information Report Renton, Washington
SECTION IV
FLOW CONTROL ANALYSIS AND WATER QUALITY DESIGN
EXISTING SITE HYDROLOGY (PART A)
KCRTS was used to model runoff from the Site. The Site falls within the Peak Rate
Flow Control Stadard area matching existing Site conditions. The Site was modeled
with existing forested, pasture and impervious surfaces (see figure 15). Results of the
KCRTS analysis are included in this section.
Modeling Input for the TDA
Pre-Developed KCRTS Modeling Input
Modeling Results
Flow Frequency Analysis
Time Series File:predev.tsf
Project Location:Sea-Tac
---Annual Peak Flow Rates--- -----Flow Frequency Analysis-------
Flow Rate Rank Time of Peak - - Peaks - - Rank Return Prob
(CFS) (CFS) Period
0.181 2 2/09/01 18:00 0.310 1 100.00 0.990
0.077 7 1/05/02 16:00 0.181 2 25.00 0.960
0.170 3 2/28/03 3:00 0.170 3 10.00 0.900
0.030 8 8/26/04 2:00 0.160 4 5.00 0.800
0.097 6 1/05/05 8:00 0.153 5 3.00 0.667
0.160 4 1/18/06 16:00 0.097 6 2.00 0.500
0.153 5 11/24/06 4:00 0.077 7 1.30 0.231
0.310 1 1/09/08 6:00 0.030 8 1.10 0.091
Computed Peaks 0.267 50.00 0.980
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Technical Information Report Renton, Washington
FIGURE 15
PREDEVELOPED AREA MAP
0GRAPHIC SCALE9060301 INCH = 60 FT.
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Technical Information Report Renton, Washington
DEVELOPED SITE HYDROLOGY (PART B)
Soil Type
The soil types are unchanged from predeveloped conditions.
Land covers
KCRTS was used to model the developed peak runoff from the Site. The portions of the
Site within the developable area tributary to the proposed detention facility were
modeled as “Till Grass”, and Impervious as appropriate. Results of the KCRTS analysis
are included in this section.
Modeling Input for DEV Site of the TDA
Developed KCRTS Modeling Input
Modeling Results
Flow Frequency Analysis
Time Series File:dev.tsf
Project Location:Sea-Tac
---Annual Peak Flow Rates--- -----Flow Frequency Analysis-------
Flow Rate Rank Time of Peak - - Peaks - - Rank Return Prob
(CFS) (CFS) Period
0.459 6 2/09/01 2:00 0.930 1 100.00 0.990
0.373 8 1/05/02 16:00 0.586 2 25.00 0.960
0.552 3 2/27/03 7:00 0.552 3 10.00 0.900
0.403 7 8/26/04 2:00 0.487 4 5.00 0.800
0.485 5 10/28/04 16:00 0.485 5 3.00 0.667
0.487 4 1/18/06 16:00 0.459 6 2.00 0.500
0.586 2 10/26/06 0:00 0.403 7 1.30 0.231
0.930 1 1/09/08 6:00 0.373 8 1.10 0.091
Computed Peaks 0.815 50.00 0.980
2017 D. R. STRONG Consulting Engineers Inc. Page 39 The Pines
Technical Information Report Renton, Washington
Modeling Input for the Bypass of the TDA
Developed KCRTS Modeling Input
Modeling Results
Flow Frequency Analysis
Time Series File:bypass.tsf
Project Location:Sea-Tac
---Annual Peak Flow Rates--- -----Flow Frequency Analysis-------
Flow Rate Rank Time of Peak - - Peaks - - Rank Return Prob
(CFS) (CFS) Period
0.004 4 2/09/01 2:00 0.008 1 100.00 0.990
0.003 7 1/05/02 16:00 0.005 2 25.00 0.960
0.005 2 2/27/03 7:00 0.004 3 10.00 0.900
0.003 8 8/26/04 2:00 0.004 4 5.00 0.800
0.004 5 10/28/04 16:00 0.004 5 3.00 0.667
0.004 6 1/18/06 16:00 0.004 6 2.00 0.500
0.004 3 10/26/06 0:00 0.003 7 1.30 0.231
0.008 1 1/09/08 6:00 0.003 8 1.10 0.091
Computed Peaks 0.007 50.00 0.980
The on-site bypass areas satisfy all the requirements set forth in the Manual, Section
1.2.3.2.E. Runoff from the bypass area and the flow control facility converge within a
quarter-mile. The flow control facility is designed to compensate for uncontrolled
bypass. The 100-year discharge from the bypass areas is 0.008 cfs, which is less than
the 0.4 cfs threshold. The bypass area does not contain any pollution generating
impervious surface area. Also, there should be no adverse downstream impacts to the
downstream drainage system created by the runoff from the bypass.
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Technical Information Report Renton, Washington
FIGURE 16
DEVELOPED AREA MAP
0GRAPHIC SCALE9060301 INCH = 60 FT.
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Technical Information Report Renton, Washington
PERFORMANCE STANDARDS (PART C)
The Project is required to adhere to Peak Rate Flow Control Standard – Matching
Existing site conditions. One detention/wet vault will provide flow control and water
quality as required for the new and replaced impervious and pervious surfaces. The
Site is required to “match the developed peak discharge rates to existing site conditions
peak discharge rates for 2, 10 and 100-year return periods.” (City of Renton 2009
Surface Water Design Manual Amendment, Sec. 1.2.3.1). The Project was evaluated
for onsite infiltration and dispersion of roof downspout runoff. A geotechnical analysis
was completed for the Site and the native soils were characterized primarily as Vashon
till. Therefore, the effectiveness of infiltration BMPs would be minimal. The lots have
insufficient space to allow for dispersion of roof runoff and will utilize the reduced
impervious footprint BMP option.
The Basic Water Quality Treatment goal is to remove 80% of TSS for flows or volumes
up to and including the WQ design flow or volume.
Conveyance criteria for the Project require that all new pipes be designed to convey and
contain (at minimum) the 25-year peak flow. The conveyance system will convey the
100-year peak flow with no overtopping.
FLOW CONTROL SYSTEM (PART D)
The Site will utilize a detention vault meeting the Peak Rate Flow Control Standard –
Matching Existing site conditions criteria. The King County Runoff Time Series
(KCRTS) software was used to size the detention facility. The detention vault design
information is included in this section.
FLOW CONTROL BMP SELECTION
Subdivision projects are required to mitigate for impervious surface equal to a minimum
of 10% of each lot area by use of Flow Control Best Management Practices (BMP’s).
The reduced Impervious Surface Credit BMP as described in Appendix C, Section C.2.9
of the KCSWDM will be utilized for the Project. The maximum impervious surface
coverage allowed per zoning code for the total lot area is 65%. The impervious surface
credit is defined as the impervious area restricted below 4,000 s.f. or the maximum
allowed by zoning code. The table on the following page of this report reflects the
maximum impervious restriction and associated credit for each lot. A restricted footprint
covenant shall be recorded on the face of the final plat map.
This satisfies the flow control BMP requirements in Section 1.2.3.3 and 5.2 of the 2009
KCSWDM.
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Technical Information Report Renton, Washington
Lot No.Lot Area Imp Per Zoning (65%)BMP Required Allowable Imp Reduced Imp Credit
1 5001.00 3250.65 500.10 3250.65 2750.00 500.65
2 5001.00 3250.65 500.10 3250.65 2750.00 500.65
3 5001.00 3250.65 500.10 3250.65 2750.00 500.65
4 5001.00 3250.65 500.10 3250.65 2750.00 500.65
5 5201.00 3380.65 520.10 3380.65 2850.00 530.65
6 5201.00 3380.65 520.10 3380.65 2850.00 530.65
7 5000.00 3250.00 500.00 3250.00 2750.00 500.00
8 5002.00 3251.30 500.20 3251.30 2750.00 501.30
9 5001.00 3250.65 500.10 3250.65 2750.00 500.65
10 5001.00 3250.65 500.10 3250.65 2750.00 500.65
11 5001.00 3250.65 500.10 3250.65 2750.00 500.65
12 5001.00 3250.65 500.10 3250.65 2750.00 500.65
13 5001.00 3250.65 500.10 3250.65 2750.00 500.65
14 5001.00 3250.65 500.10 3250.65 2750.00 500.65
Total Required =7041.40 Total Provided =7069.10
BMP
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Technical Information Report Renton, Washington
FLOW CONTROL FACILITY DESIGN OUTPUT
Retention/Detention Facility
Type of Facility: Detention Vault
Facility Length: 56.00 ft
Facility Width: 56.00 ft
Facility Area: 3136. sq. ft
Effective Storage Depth: 6.00 ft
Stage 0 Elevation: 384.00 ft
Storage Volume: 18816. cu. ft
Riser Head: 6.00 ft
Riser Diameter: 12.00 inches
Number of orifices: 3
Full Head Pipe
Orifice # Height Diameter Discharge Diameter
(ft) (in) (CFS) (in)
1 0.00 1.40 0.130
2 3.75 1.25 0.064 4.0
3 5.25 1.75 0.072 4.0
Top Notch Weir: None
Outflow Rating Curve: None
Stage Elevation Storage Discharge Percolation
(ft) (ft) (cu. ft) (ac-ft) (cfs) (cfs)
0.00 384.00 0. 0.000 0.000 0.00
0.01 384.01 31. 0.001 0.006 0.00
0.03 384.03 94. 0.002 0.009 0.00
0.04 384.04 125. 0.003 0.011 0.00
0.06 384.06 188. 0.004 0.013 0.00
0.07 384.07 220. 0.005 0.014 0.00
0.09 384.09 282. 0.006 0.016 0.00
0.10 384.10 314. 0.007 0.017 0.00
0.12 384.12 376. 0.009 0.018 0.00
0.23 384.23 721. 0.017 0.026 0.00
0.35 384.35 1098. 0.025 0.032 0.00
0.47 384.47 1474. 0.034 0.037 0.00
0.59 384.59 1850. 0.042 0.041 0.00
0.71 384.71 2227. 0.051 0.045 0.00
0.82 384.82 2572. 0.059 0.048 0.00
0.94 384.94 2948. 0.068 0.052 0.00
1.06 385.06 3324. 0.076 0.055 0.00
1.18 385.18 3701. 0.085 0.058 0.00
1.29 385.29 4045. 0.093 0.061 0.00
1.41 385.41 4422. 0.102 0.063 0.00
1.53 385.53 4798. 0.110 0.066 0.00
1.65 385.65 5174. 0.119 0.068 0.00
1.76 385.76 5519. 0.127 0.071 0.00
1.88 385.88 5896. 0.135 0.073 0.00
2.00 386.00 6272. 0.144 0.075 0.00
2.12 386.12 6648. 0.153 0.078 0.00
2.23 386.23 6993. 0.161 0.080 0.00
2.35 386.35 7370. 0.169 0.082 0.00
2.47 386.47 7746. 0.178 0.084 0.00
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Technical Information Report Renton, Washington
2.59 386.59 8122. 0.186 0.086 0.00
2.71 386.71 8499. 0.195 0.088 0.00
2.82 386.82 8844. 0.203 0.090 0.00
2.94 386.94 9220. 0.212 0.091 0.00
3.06 387.06 9596. 0.220 0.093 0.00
3.18 387.18 9973. 0.229 0.095 0.00
3.29 387.29 10317. 0.237 0.097 0.00
3.41 387.41 10694. 0.245 0.098 0.00
3.53 387.53 11070. 0.254 0.100 0.00
3.65 387.65 11446. 0.263 0.102 0.00
3.75 387.75 11760. 0.270 0.103 0.00
3.76 387.76 11791. 0.271 0.104 0.00
3.78 387.78 11854. 0.272 0.105 0.00
3.79 387.79 11885. 0.273 0.107 0.00
3.80 387.80 11917. 0.274 0.109 0.00
3.82 387.82 11980. 0.275 0.112 0.00
3.83 387.83 12011. 0.276 0.116 0.00
3.84 387.84 12042. 0.276 0.117 0.00
3.85 387.85 12074. 0.277 0.118 0.00
3.87 387.87 12136. 0.279 0.119 0.00
3.98 387.98 12481. 0.287 0.127 0.00
4.10 388.10 12858. 0.295 0.133 0.00
4.22 388.22 13234. 0.304 0.139 0.00
4.34 388.34 13610. 0.312 0.143 0.00
4.46 388.46 13987. 0.321 0.148 0.00
4.57 388.57 14332. 0.329 0.152 0.00
4.69 388.69 14708. 0.338 0.157 0.00
4.81 388.81 15084. 0.346 0.160 0.00
4.93 388.93 15460. 0.355 0.164 0.00
5.04 389.04 15805. 0.363 0.168 0.00
5.16 389.16 16182. 0.371 0.171 0.00
5.25 389.25 16464. 0.378 0.174 0.00
5.27 389.27 16527. 0.379 0.175 0.00
5.29 389.29 16589. 0.381 0.178 0.00
5.30 389.30 16621. 0.382 0.181 0.00
5.32 389.32 16684. 0.383 0.186 0.00
5.34 389.34 16746. 0.384 0.192 0.00
5.36 389.36 16809. 0.386 0.199 0.00
5.38 389.38 16872. 0.387 0.207 0.00
5.40 389.40 16934. 0.389 0.210 0.00
5.41 389.41 16966. 0.389 0.212 0.00
5.53 389.53 17342. 0.398 0.226 0.00
5.65 389.65 17718. 0.407 0.238 0.00
5.77 389.77 18095. 0.415 0.248 0.00
5.88 389.88 18440. 0.423 0.257 0.00
6.00 390.00 18816. 0.432 0.266 0.00
6.10 390.10 19130. 0.439 0.581 0.00
6.20 390.20 19443. 0.446 1.150 0.00
6.30 390.30 19757. 0.454 1.890 0.00
6.40 390.40 20070. 0.461 2.680 0.00
6.50 390.50 20384. 0.468 2.970 0.00
6.60 390.60 20698. 0.475 3.230 0.00
6.70 390.70 21011. 0.482 3.470 0.00
6.80 390.80 21325. 0.490 3.700 0.00
2016 D. R. STRONG Consulting Engineers Inc. Page 45 The Pines
Technical Information Report Renton, Washington
6.90 390.90 21638. 0.497 3.910 0.00
7.00 391.00 21952. 0.504 4.110 0.00
7.10 391.10 22266. 0.511 4.300 0.00
7.20 391.20 22579. 0.518 4.480 0.00
7.30 391.30 22893. 0.526 4.650 0.00
7.40 391.40 23206. 0.533 4.820 0.00
7.50 391.50 23520. 0.540 4.980 0.00
7.60 391.60 23834. 0.547 5.140 0.00
7.70 391.70 24147. 0.554 5.290 0.00
7.80 391.80 24461. 0.562 5.440 0.00
7.90 391.90 24774. 0.569 5.580 0.00
8.00 392.00 25088. 0.576 5.720 0.00
Hyd Inflow Outflow Peak Storage
Stage Elev (Cu-Ft) (Ac-Ft)
1 0.93 0.29 6.01 390.01 18845. 0.433
2 0.46 0.23 5.52 389.52 17320. 0.398
3 0.46 0.17 5.04 389.04 15803. 0.363
4 0.49 0.16 4.70 388.70 14744. 0.338
5 0.55 0.14 4.30 388.30 13486. 0.310
6 0.29 0.09 3.11 387.11 9744. 0.224
7 0.37 0.07 1.92 385.92 6032. 0.138
8 0.40 0.07 1.57 385.57 4933. 0.113
Hyd R/D Facility Tributary Reservoir POC Outflow
Outflow Inflow Inflow Target Calc
1 0.29 0.01 ******** 0.31 0.30
2 0.23 0.00 ******** ******* 0.23
3 0.17 0.00 ******** 0.17 0.17
4 0.16 0.00 ******** ******* 0.16
5 0.14 0.00 ******** ******* 0.14
6 0.09 0.00 ******** 0.10 0.09
7 0.07 0.00 ******** ******* 0.07
8 0.07 0.00 ******** ******* 0.07
----------------------------------
Route Time Series through Facility
Inflow Time Series File:dev.tsf
Outflow Time Series File:rdout
POC Time Series File:dsout
Inflow/Outflow Analysis
Peak Inflow Discharge: 0.930 CFS at 6:00 on Jan 9 in Year 8
Peak Outflow Discharge: 0.295 CFS at 11:00 on Jan 9 in Year 8
Peak Reservoir Stage: 6.01 Ft
Peak Reservoir Elev: 390.01 Ft
Peak Reservoir Storage: 18845. Cu-Ft
: 0.433 Ac-Ft
Add Time Series:bypass.tsf
Peak Summed Discharge: 0.296 CFS at 11:00 on Jan 9 in Year 8
Point of Compliance File:dsout.tsf
Flow Frequency Analysis
Time Series File:rdout.tsf
2016 D. R. STRONG Consulting Engineers Inc. Page 46 The Pines
Technical Information Report Renton, Washington
Project Location:Sea-Tac
---Annual Peak Flow Rates--- -----Flow Frequency Analysis-------
Flow Rate Rank Time of Peak - - Peaks - - Rank Return Prob
(CFS) (CFS) (ft) Period
0.225 2 2/09/01 19:00 0.295 6.01 1 100.00 0.990
0.074 7 12/28/01 17:00 0.225 5.52 2 25.00 0.960
0.142 5 2/28/03 7:00 0.168 5.03 3 10.00 0.900
0.067 8 8/24/04 0:00 0.157 4.70 4 5.00 0.800
0.094 6 1/05/05 14:00 0.142 4.30 5 3.00 0.667
0.157 4 1/18/06 22:00 0.094 3.10 6 2.00 0.500
0.168 3 11/24/06 7:00 0.074 1.92 7 1.30 0.231
0.295 1 1/09/08 11:00 0.067 1.57 8 1.10 0.091
Computed Peaks 0.272 6.00 50.00 0.980
Flow Frequency Analysis
Time Series File:dsout.tsf
Project Location:Sea-Tac
---Annual Peak Flow Rates--- -----Flow Frequency Analysis-------
Flow Rate Rank Time of Peak - - Peaks - - Rank Return Prob
(CFS) (CFS) Period
0.227 2 2/09/01 19:00 0.296 1 100.00 0.990
0.074 7 12/28/01 17:00 0.227 2 25.00 0.960
0.142 5 2/28/03 7:00 0.169 3 10.00 0.900
0.067 8 8/24/04 0:00 0.158 4 5.00 0.800
0.094 6 1/05/05 13:00 0.142 5 3.00 0.667
0.158 4 1/18/06 22:00 0.094 6 2.00 0.500
0.169 3 11/24/06 7:00 0.074 7 1.30 0.231
0.296 1 1/09/08 11:00 0.067 8 1.10 0.091
Computed Peaks 0.273 50.00 0.980
Evaluating Flow Control Performance (KCSWDM 3.3.2)
• Predeveloped Peaks
2 year = 0.097 cfs
10 year = 0.170 cfs
100 year = 0.310 cfs
• Developed Peaks
2 year = 0.094 cfs
10 year = 0.169 cfs
100 year = 0.296 cfs
2016 D. R. STRONG Consulting Engineers Inc. Page 47 The Pines
Technical Information Report Renton, Washington
Flow Frequency
2017 D. R. STRONG Consulting Engineers Inc. Page 48 The Pines
Technical Information Report Renton, Washington
WATER QUALITY TREATMENT SYSTEM (PART E)
The Project is required to adhere to the City of Renton’s Basic Water Quality treatment
criteria. The treatment goal is 80% removal of total suspend solids (TSS) for a typical
rainfall year, assuming typical pollutant concentrations in urban runoff. A combined
detention/wet vault located in Tract D will be utilized for the Site. The wetvault will
contain 5.5 feet of water quality depth. The water quality portion of the vault was sized
using section 6.4.1.1 of the King County Surface Water Design Manual.
Vr = 2,775.543 c.f.
Ai = 67,339.50 s.f.
Atg = 41,037.50 s.f.
Atf = 0 s.f.
Ao = 0 s.f.
R = 0.039 ft
Vb =3 x 2,775.543 c.f. = 8,327 c.f. required.
The total dead storage volume provided is 8,573 c.f.. See Figure 17 for the combined
detention/wet vault details.
2016 D. R. STRONG Consulting Engineers Inc. Page 49 The Pines
Technical Information Report Renton, Washington
FIGURE 17
DETENTION & WATER QUALITY FACILITY DETAILS
NSERISSEFORPINGOERDETSREENGINELA45232 ORETAT EHAMFOTGNIHASWIDUOJA.
2016 D. R. STRONG Consulting Engineers Inc. Page 50 The Pines
Technical Information Report Renton, Washington
SECTION V
CONVEYANCE SYSTEM ANALYSIS AND DESIGN
Per Core Requirement #4 of the KCSWDM, the conveyance system must be analyzed
and designed for the existing tributary and developed onsite runoff. Pipe systems shall
be designed with sufficient capacity to convey and contain (at minimum) the 25-year
peak flow with a minimum of 6 inches of freeboard between the design water surface
and structure grate. Pipe system structures may overtop for runoff events that exceed
the 25-year design capacity, provided the overflow from a 100-year runoff event does
not create or aggravate a “severe flooding problem” or “severe erosion problem” as
defined in C.R. #2. The Rational Method will be used to calculate the Q-Ratio for each
pipe node.
A conveyance system consisting primarily of pipes and catch basins will be designed for
the Project. Onsite runoff will be collected by the multiple catch basins. Pipes are
typically eight-inch to twelve-inch diameter LCPE material unless noted otherwise.
Storm Water Runoff Variables:
A= Total of Subasin and Tributary Areas
C= Runoff Coefficient (the anticipated proportion of rainfall volume that runs off the area) see 2009 KCSWM Table 3.2.1A
CC= Composite Runoff Coefficient
CC= S(Cn*An)/ATotal
Tc= Time of Concentration (Typically 6.3 minutes which is the minimum value used in calculations)
R= design return frequency
iR= Unit peak rainfall intensity factor
iR= (aR)(Tc)^(-bR)
aR,bR= coefficients from '98 KCSWM Table 3.2.1.B used to adjust the equation for the design storm
IR= Peak rainfall intensity factor for a storm of return frequency 'R'
IR= PR*iR
PR=
total precipitation (inches) for the 24-hour storm event for the given frequency. See Issopluvial Maps in 2009 KCSWM Figures
3.2.1.A - D
QR= peak flow (cfs) for a storm of return frequency 'R'
QR= CC*iR*A
The Q-Ratio describes the ratio of the tributary flow to the main upstream flow.
R= 100 -year storm
aR= 2.61
bR= 0.63
PR= 3.9 inches
Conveyance System Variables:
d= pipe diameter
n= Manning's Number
l= length of pipe
2016 D. R. STRONG Consulting Engineers Inc. Page 51
Technical Information Report
BASIN PIPE CB to CB A1 C1 A2 C2 Cc Tc iR IR Q-ratio d Mat'l n l Slope IE in IE out overflow Q Full V Full Bend CB
sf ac.Basin Total in ft %ft ft ft cfs cfs degree Dia
4 4 4 3 8230 0.9 4590 0.25 12820 0.29 0.67 6.3 0.82 3.19 0.63 0.63 0.00 12 LCPE 0.012 24 0.99 395.21 394.97 398.21 3.84 4.89 0 2
3 3 3 2 8140 0.9 4501 0.25 12641 0.29 0.67 6.4 0.81 3.17 0.61 1.24 0.98 12 LCPE 0.012 201 2.69 394.97 389.58 398.21 6.34 8.08 90 2
14754 0.9 6841 0.25 21595 0.50
13567 0.9 6751 0.25 20318 0.47
2 2 1 28321 0.9 13592 0.25 41913 0.96 0.69 6.8 0.78 3.04 2.02 3.26 1.63 12 LCPE 0.012 171 1.97 389.58 386.2 392.82 5.44 6.92 0 2
14471 0.9 6183 0.25 20654 0.47
8755 0.9 0 0.25 8755 0.20
1 1 Vault 23226 0.9 6183 0.25 29409 0.68 0.76 7.2 0.75 2.93 1.51 4.77 0.46 18 LCPE 0.012 21 20.00 385.70 381.5 390.49 51.03 28.88 90 2
BASIN PIPE CB to CB A1 C1 A2 C2 Cc Tc iR IR Q-ratio d Mat'l n l Slope IE in IE out overflow Q Full V Full Bend CB
sf ac.Basin Total in ft %ft ft ft cfs cfs degree Dia
104 104 104 101 11351 0.9 6183 0.25 17534 0.40 0.67 6.3 0.82 3.19 0.86 0.86 0.00 12 LCPE 0.012 30 0.97 387.77 387.48 390.77 3.82 4.86 0 2
103 103 103 102 1390 0.9 0 0.25 1390 0.03 0.90 6.3 0.82 3.19 0.09 0.09 0.00 12 LCPE 0.012 27 1.00 388.15 387.88 391.15 3.87 4.93 0 2
102 102 102 101 2 0.9 0 0.25 2 0.00 0.90 6.4 0.81 3.16 0.00 0.09 0.00 12 LCPE 0.012 27 1.48 387.88 387.48 391.33 4.71 6.00 45 2
11351 0.9 6183 0.25 17534 0.40
1728 0.9 0 0.25 1728 0.04
101 101 1 13079 0.9 6183 0.25 19262 0.44 0.69 6.5 0.81 3.14 0.96 1.05 10.46 12 LCPE 0.012 25 5.15 387.48 386.2 390.48 8.78 11.18 63 2
14471 0.9 6183 0.25 20654 0.47 0.71
201 201 201 2 14754 0.9 6841 0.25 21595 0.50 0.69 6.3 0.82 3.19 1.10 1.10 0.00 12 LCPE 0.012 24 0.99 389.82 389.58 392.82 3.84 4.89 0 2
101
Run 104-101
Run 101-1
CB#103 TO CB#1
CB#201 TO CB#2
Qr (cfs)
Run 201-2
CB#4 TO INLET 1
At Qr (cfs)
CB#104 TO CB#101
Run 2-12
At
1
Run 103-1
Run 1-INLET 1
2016 D. R. STRONG Consulting Engineers Inc. Page 52 The Pines
Technical Information Report Renton, Washington
BACKWATER COMPUTER PROGRAM FOR PIPES
Pipe data from file:CB#4 TO VAULT.bwp
Surcharge condition at intermediate junctions
Tailwater Elevation:389.52 feet
Discharge Range:0.63 to 4.77 Step of 0.414 [cfs]
Overflow Elevation:398.21 feet
Weir:NONE
Upstream Velocity:0. feet/sec
PIPE NO. 1: 21 LF - 18"CP @ 20.00% OUTLET: 381.50 INLET: 385.70 INTYP: 5
JUNC NO. 1: OVERFLOW-EL: 390.49 BEND: 90 DEG DIA/WIDTH: 2.0 Q-RATIO: 0.46
Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI
*******************************************************************************
0.63 3.84 389.54 * 0.012 0.30 0.12 8.02 8.02 3.83 3.84 0.25
1.04 3.84 389.54 * 0.012 0.39 0.15 8.02 8.02 3.82 3.84 0.38
1.46 3.86 389.56 * 0.012 0.46 0.18 8.02 8.02 3.82 3.86 0.49
1.87 3.88 389.58 * 0.012 0.52 0.20 8.02 8.02 3.83 3.88 0.59
2.29 3.91 389.61 * 0.012 0.58 0.22 8.02 8.02 3.83 3.91 0.69
2.70 3.94 389.64 * 0.012 0.63 0.24 8.02 8.02 3.83 3.94 0.79
3.11 3.98 389.68 * 0.012 0.68 0.26 8.02 8.02 3.84 3.98 0.88
3.53 4.03 389.73 * 0.012 0.72 0.27 8.02 8.02 3.84 4.03 0.98
3.94 4.08 389.78 * 0.012 0.76 0.29 8.02 8.02 3.85 4.08 1.07
4.36 4.13 389.83 * 0.012 0.81 0.30 8.02 8.02 3.85 4.13 1.17
4.77 4.20 389.90 * 0.012 0.84 0.32 8.02 8.02 3.86 4.20 1.27
Q25 = 4.08 cfs
Q100 = 4.77 cfs
PIPE NO. 2: 171 LF - 12"CP @ 1.97% OUTLET: 386.20 INLET: 389.58 INTYP: 5
JUNC NO. 2: OVERFLOW-EL: 392.82 BEND: 0 DEG DIA/WIDTH: 2.0 Q-RATIO: 1.63
Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI
*******************************************************************************
0.43 0.36 389.94 * 0.012 0.28 0.20 3.34 3.34 0.28 ***** 0.36
0.71 0.48 390.06 * 0.012 0.36 0.25 3.34 3.34 0.36 ***** 0.48
1.00 0.58 390.16 * 0.012 0.42 0.30 3.36 3.36 0.42 ***** 0.58
1.28 0.68 390.26 * 0.012 0.48 0.34 3.38 3.38 0.48 ***** 0.68
1.56 0.77 390.35 * 0.012 0.54 0.37 3.41 3.41 0.54 ***** 0.77
1.84 0.93 390.51 * 0.012 0.58 0.41 3.44 3.44 0.59 0.93 0.86
2.13 1.00 390.58 * 0.012 0.63 0.44 3.48 3.48 0.67 1.00 0.95
2.41 1.09 390.67 * 0.012 0.67 0.47 3.53 3.53 0.79 1.09 1.04
2.69 1.31 390.89 * 0.012 0.71 0.50 3.58 3.58 1.04 1.31 1.13
2.98 1.60 391.18 * 0.012 0.74 0.53 3.63 3.63 1.27 1.60 1.22
3.26 1.93 391.51 * 0.012 0.78 0.56 3.70 3.70 1.54 1.93 1.34
Q25 = 2.79 cfs
Q100 = 3.26 cfs
2016 D. R. STRONG Consulting Engineers Inc. Page 53 The Pines
Technical Information Report Renton, Washington
PIPE NO. 3: 200 LF - 12"CP @ 2.69% OUTLET: 389.58 INLET: 394.97 INTYP: 5
JUNC NO. 3: OVERFLOW-EL: 398.21 BEND: 90 DEG DIA/WIDTH: 2.0 Q-RATIO: 0.98
Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI
*******************************************************************************
0.16 0.21 395.18 * 0.012 0.17 0.12 0.36 0.36 0.17 ***** 0.21
0.27 0.28 395.25 * 0.012 0.22 0.15 0.48 0.48 0.22 ***** 0.28
0.38 0.33 395.30 * 0.012 0.26 0.17 0.58 0.58 0.26 ***** 0.33
0.49 0.38 395.35 * 0.012 0.29 0.19 0.68 0.68 0.29 ***** 0.38
0.59 0.43 395.40 * 0.012 0.33 0.21 0.77 0.77 0.33 ***** 0.43
0.70 0.47 395.44 * 0.012 0.35 0.23 0.93 0.93 0.35 ***** 0.47
0.81 0.52 395.49 * 0.012 0.38 0.25 1.00 1.00 0.38 ***** 0.52
0.92 0.56 395.53 * 0.012 0.41 0.26 1.09 1.09 0.41 ***** 0.56
1.03 0.60 395.57 * 0.012 0.43 0.28 1.31 1.31 0.43 ***** 0.60
1.13 0.63 395.60 * 0.012 0.45 0.29 1.60 1.60 0.45 ***** 0.63
1.24 0.67 395.64 * 0.012 0.48 0.31 1.93 1.93 0.48 ***** 0.67
Q25 = 1.06 cfs
Q100 = 1.24 cfs
PIPE NO. 4: 24 LF - 12"CP @ 0.99% OUTLET: 394.97 INLET: 395.21 INTYP: 5
Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI
*******************************************************************************
0.08 0.15 395.36 * 0.012 0.12 0.11 0.21 0.21 0.12 ***** 0.15
0.14 0.20 395.41 * 0.012 0.16 0.13 0.28 0.28 0.16 ***** 0.20
0.19 0.24 395.45 * 0.012 0.18 0.16 0.33 0.33 0.18 ***** 0.24
0.25 0.27 395.48 * 0.012 0.21 0.18 0.38 0.38 0.21 ***** 0.27
0.30 0.30 395.51 * 0.012 0.23 0.19 0.43 0.43 0.23 ***** 0.30
0.35 0.33 395.54 * 0.012 0.25 0.21 0.47 0.47 0.25 ***** 0.33
0.41 0.36 395.57 * 0.012 0.27 0.23 0.52 0.52 0.27 ***** 0.36
0.46 0.43 395.64 * 0.012 0.29 0.24 0.56 0.56 0.30 0.43 0.38
0.52 0.45 395.66 * 0.012 0.30 0.25 0.60 0.60 0.34 0.45 0.41
0.57 0.48 395.69 * 0.012 0.32 0.27 0.63 0.63 0.38 0.48 0.43
0.63 0.51 395.72 * 0.012 0.33 0.28 0.67 0.67 0.42 0.51 0.45
Q25 = 0.54 cfs
Q100 = 0.63 cfs
2016 D. R. STRONG Consulting Engineers Inc. Page 54 The Pines
Technical Information Report Renton, Washington
BACKWATER COMPUTER PROGRAM FOR PIPES
Pipe data from file:CB#103 TO CB#1.bwp
Surcharge condition at intermediate junctions
Tailwater Elevation:389.9 feet
Discharge Range:0.096 to 1.05 Step of 0.096 [cfs]
Overflow Elevation:391.15 feet
Weir:NONE
Upstream Velocity:0. feet/sec
PIPE NO. 1: 24 LF - 12"CP @ 5.15% OUTLET: 386.20 INLET: 387.48 INTYP: 5
JUNC NO. 1: OVERFLOW-EL: 390.48 BEND: 63 DEG DIA/WIDTH: 2.0 Q-RATIO:10.46
Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI
*******************************************************************************
0.10 2.43 389.91 * 0.012 0.13 0.08 3.70 3.70 2.43 2.43 0.14
0.19 2.42 389.90 * 0.012 0.18 0.11 3.70 3.70 2.42 2.42 0.22
0.29 2.42 389.90 * 0.012 0.23 0.13 3.70 3.70 2.42 2.42 0.27
0.38 2.43 389.91 * 0.012 0.26 0.15 3.70 3.70 2.42 2.43 0.32
0.48 2.43 389.91 * 0.012 0.29 0.16 3.70 3.70 2.42 2.43 0.37
0.58 2.44 389.92 * 0.012 0.32 0.18 3.70 3.70 2.43 2.44 0.41
0.67 2.44 389.92 * 0.012 0.35 0.19 3.70 3.70 2.43 2.44 0.45
0.77 2.45 389.93 * 0.012 0.37 0.21 3.70 3.70 2.43 2.45 0.49
0.86 2.46 389.94 * 0.012 0.39 0.22 3.70 3.70 2.43 2.46 0.52
0.96 2.47 389.95 * 0.012 0.42 0.23 3.70 3.70 2.44 2.47 0.56
1.06 2.48 389.96 * 0.012 0.44 0.24 3.70 3.70 2.44 2.48 0.59
Q25 = 0.90 cfs
Q100 = 1.05 cfs
PIPE NO. 2: 26 LF - 12"CP @ 1.48% OUTLET: 387.48 INLET: 387.88 INTYP: 5
JUNC NO. 2: OVERFLOW-EL: 391.33 BEND: 45 DEG DIA/WIDTH: 2.0 Q-RATIO: 0.00
Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI
*******************************************************************************
0.01 2.04 389.92 * 0.012 0.04 0.04 2.43 2.43 2.04 2.04 0.04
0.02 2.02 389.90 * 0.012 0.06 0.05 2.42 2.42 2.02 2.02 0.06
0.03 2.02 389.90 * 0.012 0.07 0.06 2.42 2.42 2.02 2.02 0.08
0.03 2.03 389.91 * 0.012 0.08 0.07 2.43 2.43 2.03 2.03 0.09
0.04 2.03 389.91 * 0.012 0.09 0.07 2.43 2.43 2.03 2.03 0.10
0.05 2.04 389.92 * 0.012 0.10 0.08 2.44 2.44 2.04 2.04 0.12
0.06 2.04 389.92 * 0.012 0.10 0.08 2.44 2.44 2.04 2.04 0.12
0.07 2.05 389.93 * 0.012 0.11 0.09 2.45 2.45 2.05 2.05 0.13
0.08 2.06 389.94 * 0.012 0.12 0.09 2.46 2.46 2.06 2.06 0.14
0.08 2.07 389.95 * 0.012 0.12 0.10 2.47 2.47 2.07 2.07 0.15
0.09 2.08 389.96 * 0.012 0.13 0.10 2.48 2.48 2.08 2.08 0.16
Q25 = 0.08 cfs
Q100 = 0.09 cfs
2016 D. R. STRONG Consulting Engineers Inc. Page 55 The Pines
Technical Information Report Renton, Washington
PIPE NO. 3: 26 LF - 12"CP @ 1.00% OUTLET: 387.88 INLET: 388.15 INTYP: 5
Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI
*******************************************************************************
0.01 1.78 389.93 * 0.012 0.04 0.04 2.04 2.04 1.78 1.78 0.04
0.02 1.75 389.90 * 0.012 0.06 0.05 2.02 2.02 1.75 1.75 0.07
0.03 1.75 389.90 * 0.012 0.07 0.06 2.02 2.02 1.75 1.75 0.08
0.03 1.76 389.91 * 0.012 0.08 0.07 2.03 2.03 1.76 1.76 0.10
0.04 1.76 389.91 * 0.012 0.09 0.08 2.03 2.03 1.76 1.76 0.11
0.05 1.77 389.92 * 0.012 0.10 0.08 2.04 2.04 1.77 1.77 0.12
0.06 1.78 389.93 * 0.012 0.10 0.09 2.04 2.04 1.77 1.78 0.13
0.07 1.78 389.93 * 0.012 0.11 0.10 2.05 2.05 1.78 1.78 0.14
0.08 1.79 389.94 * 0.012 0.12 0.10 2.06 2.06 1.79 1.79 0.15
0.08 1.80 389.95 * 0.012 0.12 0.11 2.07 2.07 1.80 1.80 0.15
0.09 1.81 389.96 * 0.012 0.13 0.11 2.08 2.08 1.81 1.81 0.16
Q25 = 0.08 cfs
Q100 = 0.09 cfs
BACKWATER COMPUTER PROGRAM FOR PIPES
Pipe data from file:CB#104 TO CB#101.bwp
Surcharge condition at intermediate junctions
Tailwater Elevation:389.96 feet
Discharge Range:0.086 to 0.86 Step of 0.086 [cfs]
Overflow Elevation:390.77 feet
Weir:NONE
Upstream Velocity:0. feet/sec
PIPE NO. 1: 29 LF - 12"CP @ 0.97% OUTLET: 387.48 INLET: 387.77 INTYP: 5
Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI
*******************************************************************************
0.09 2.20 389.97 * 0.012 0.12 0.11 2.48 2.48 2.20 2.20 0.16
0.17 2.19 389.96 * 0.012 0.17 0.15 2.48 2.48 2.19 2.19 0.22
0.26 2.19 389.96 * 0.012 0.21 0.18 2.48 2.48 2.19 2.19 0.28
0.34 2.20 389.97 * 0.012 0.25 0.21 2.48 2.48 2.19 2.20 0.33
0.43 2.20 389.97 * 0.012 0.28 0.23 2.48 2.48 2.19 2.20 0.37
0.52 2.21 389.98 * 0.012 0.30 0.25 2.48 2.48 2.20 2.21 0.40
0.60 2.21 389.98 * 0.012 0.33 0.27 2.48 2.48 2.20 2.21 0.44
0.69 2.22 389.99 * 0.012 0.35 0.29 2.48 2.48 2.20 2.22 0.48
0.77 2.22 389.99 * 0.012 0.37 0.31 2.48 2.48 2.20 2.22 0.51
0.86 2.23 390.00 * 0.012 0.39 0.33 2.48 2.48 2.20 2.23 0.54
Q25 = 0.74 cfs
Q100 = 0.86 cfs
2016 D. R. STRONG Consulting Engineers Inc. Page 56 The Pines
Technical Information Report Renton, Washington
BACKWATER COMPUTER PROGRAM FOR PIPES
Pipe data from file:CB#201 TO CB#2.bwp
Surcharge condition at intermediate junctions
Tailwater Elevation:391.51 feet
Discharge Range:0.11 to 1.1 Step of 0.11 [cfs]
Overflow Elevation:392.82 feet
Weir:NONE
Upstream Velocity:0. feet/sec
PIPE NO. 1: 24 LF - 12"CP @ 0.99% OUTLET: 389.58 INLET: 389.82 INTYP: 5
Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI
*******************************************************************************
0.11 1.70 391.52 * 0.012 0.14 0.12 1.93 1.93 1.70 1.70 0.18
0.22 1.69 391.51 * 0.012 0.20 0.17 1.93 1.93 1.69 1.69 0.26
0.33 1.70 391.52 * 0.012 0.24 0.20 1.93 1.93 1.69 1.70 0.32
0.44 1.70 391.52 * 0.012 0.28 0.23 1.93 1.93 1.69 1.70 0.37
0.55 1.71 391.53 * 0.012 0.31 0.26 1.93 1.93 1.69 1.71 0.42
0.66 1.71 391.53 * 0.012 0.34 0.29 1.93 1.93 1.70 1.71 0.46
0.77 1.72 391.54 * 0.012 0.37 0.31 1.93 1.93 1.70 1.72 0.51
0.88 1.73 391.55 * 0.012 0.40 0.33 1.93 1.93 1.70 1.73 0.55
0.99 1.74 391.56 * 0.012 0.42 0.35 1.93 1.93 1.71 1.74 0.59
1.10 1.76 391.58 * 0.012 0.45 0.37 1.93 1.93 1.71 1.76 0.62
Q25 = 0.94 cfs
Q100 = 1.10 cfs
2016 D. R. STRONG Consulting Engineers Inc. Page 57 The Pines
Technical Information Report Renton, Washington
FIGURE 18
BACKWATER ANALYSIS MAP
0GRAPHIC SCALE9060301 INCH = 60 FT.
2016 D. R. STRONG Consulting Engineers Inc. Page 58 The Pines
Technical Information Report Renton, Washington
SECTION VI
SPECIAL REPORTS AND STUDIES
The following report and studies have been provided with this submittal.
Wetland Memo: Re-Align Environmental – April 21st, 2016
Geotechnical Engineering Study: Earth Solutions NW, LLC – April 27, 2016
Traffic Memorandum: Gibson Traffic Consultants, Inc. – July 19, 2016
Arborist Report: Creative Landscape Solutions – July 17, 2016
2016 D. R. STRONG Consulting Engineers Inc. Page 59 The Pines
Technical Information Report Renton, Washington
SECTION VII
OTHER PERMITS, VARIANCES AND ADJUSTMENTS
• Hammerhead turnaround approval at the end of a Dead End provided that all
new homes are fire sprinklered
• Pavement and right-of-way reduction approval for a minor arterial
• Shared driveway approval for rear access on two of the proposed lots
2016 D. R. STRONG Consulting Engineers Inc. Page 60 The Pines
Technical Information Report Renton, Washington
SECTION VIII
CSWPPP ANALYSIS AND DESIGN (PART A)
The Erosion and Sedimentation Control Design will meet the nine minimum King County
requirements:
1. Clearing Limits: Prior to any site clearing or grading, areas to remain
undisturbed during project construction shall be delineated on the project's ESC
plan and physically marked on the project site.
2. Cover Measures: Temporary and permanent cover measures shall be provided
when necessary to protect disturbed areas. The intent of these measures is to
prevent erosion by having as much area as possible covered during any period
of precipitation.
3. Perimeter Protection: Perimeter protection to filter sediment from sheet flow
shall be provided downstream of all disturbed areas prior to upslope grading.
4. Traffic Area Stabilization: Unsurfaced entrances, roads, and parking areas
used by construction traffic shall be stabilized to minimize erosion and tracking of
sediment offsite.
5. Sediment Retention: Surface water collected from all disturbed areas of the site
shall be routed through proposed detention wetvault prior to release from the
site, except those areas at the perimeter of the site small enough to be treated
solely with perimeter protection. Sediment retention facilities shall be installed
prior to grading any contributing area.
6. Surface Water Collection: Surface water collection measures (e.g., ditches,
berms, etc.) shall be installed to intercept all surface water from disturbed areas,
convey it to the detention wetvault, and discharge it downstream of any disturbed
areas. Areas at the perimeter of the site, which are small enough to be treated
solely with perimeter protection, do not require surface water collection.
Significant sources of upstream surface water that drain onto disturbed areas
shall be intercepted and conveyed to a stabilized discharge point downstream of
the disturbed areas. Surface water collection measures shall be installed
concurrently with or immediately following rough grading and shall be designed,
constructed, and stabilized as needed to minimize erosion.
7. Dewatering Control: The water resulting from construction site de-watering
activities must be treated prior to discharge or disposed of as specified.
8. Dust Control: Preventative measures to minimize wind transport of soil shall be
implemented when a traffic hazard may be created or when sediment transported
by wind is likely to be deposited in water resources.
9. Flow Control: Surface water from disturbed areas must be routed through the
project's onsite flow control facility or other provisions must be made to prevent
increases in the existing site conditions 2- year and 10-year runoff peaks
discharging from the project site during construction (flow control BMP areas
(existing or proposed) shall not be used for this purpose).
2016 D. R. STRONG Consulting Engineers Inc. Page 61 The Pines
Technical Information Report Renton, Washington
SWPPP PLAN DESIGN (PART B)
Construction activities that could contribute pollutants to surface and storm water
include the following, with applicable BMP’s listed for each item:
1. Storage and use of chemicals: Utilize source control, and soil erosion and
sedimentation control practices, such as using only recommended amounts of
chemical materials applied in the proper manner; neutralizing concrete wash
water, and disposing of excess concrete material only in areas prepared for
concrete placement, or return to batch plant; disposing of wash-up waters from
water-based paints in sanitary sewer; disposing of wastes from oil-based paints,
solvents, thinners, and mineral spirits only through a licensed waste
management firm, or treatment, storage, and disposal (TSD) facility.
2. Material delivery and storage: Locate temporary storage areas away from
vehicular traffic, near the construction entrance, and away from storm drains.
Material Safety Data Sheets (MSDS) should be supplied for all materials stored,
and chemicals kept in their original labeled containers. Maintenance, fueling,
and repair of heavy equipment and vehicles shall be conducted using spill
prevention and control measures. Contaminated surfaces shall be cleaned
immediately following any spill incident. Provide cover, containment, and
protection from vandalism for all chemicals, liquid products, petroleum products,
and other potentially hazardous materials.
3. Building demolition: Protect stormwater drainage system from sediment-laden
runoff and loose particles. To the extent possible, use dikes, berms, or other
methods to protect overland discharge paths from runoff. Street gutter,
sidewalks, driveways, and other paved surfaces in the immediate area of
demolition must be swept daily to collect and properly dispose of loose debris
and garbage. Spray the minimum amount of water to help control windblown fine
particles such as concrete, dust, and paint chips. Avoid excessive spraying so
that runoff from the site does not occur, yet dust control is achieved. Oils must
never be used for dust control.
4. Sawcutting: Slurry and cuttings shall be vacuumed during the activity to prevent
migration offsite and must not remain on permanent concrete or asphalt paving
overnight. Collected slurry and cuttings shall be disposed of in a manner that
does not violate ground water or surface water quality standards.
The complete CSWPPP can be found in Appendix C.
2016 D. R. STRONG Consulting Engineers Inc. Page 62 The Pines
Technical Information Report Renton, Washington
SECTION IX
BOND QUANTITIES, FACILITY SUMMARIES, AND DECLARATION OF COVENANT
1. Bond Quantity Worksheet – is located in Appendix B
2. The Stormwater Facility Summary Sheet is included in this section
2016 D. R. STRONG Consulting Engineers Inc. Page 63 The Pines
Technical Information Report Renton, Washington
STORMWATER FACILITY SUMMARY SHEET
Development The Pines Date December 15, 2016
Location: 850 & 870 Monroe Ave NE, Renton, Washington 98056
ENGINEER DEVELOPER
Name Yoshio L Piediscalzi, P.E. Name Jamie Waltier
Firm D. R. STRONG Consulting
Engineers, Inc.
Firm Harbour Homes, LLC
Address 620 7th Avenue Address 400 North 34th St, Suite 300
Kirkland, WA 98033 Seattle, WA 98103
Phone (425) 827-3063 Phone (206) 315-8130
Developed Site: 2.509 acres
Number of lots: 14
Number of detention facilities on site: Number of infiltration facilities on site:
___1__ vaults ______ vaults
______ pond ______ ponds
______ tanks ______ tanks
Flow control provided in regional facility (give location)___________________________
No flow control required_____ Exemption number ______________________________
Downstream Drainage Basins
Immediate Major Basin
Basin Renton East Lake Washington
Number & type of water quality facilities on site:
biofiltration swale (regular/wet/ or continuous inflow?)
______ sand filter (basic or large?) ______ sand filter, linear (basic or
large?) ______ CONTECH Stormfilter
__1___ combined detention/WQ vault ______ sand filter vault (basic or large?)
______ combined detention/wetpond ______ stormwater wetland
______ compost filter ______ wetvault (basic or large?)
______ filter strip ______ Wetvault
______ flow dispersion ______ pre-settling pond
______ farm management plan ______ flow-splitter catchbasin
______ landscape management plan
______ oil/water separator (baffle or coalescing plate?)
______ catch basin inserts:
Manufacturer____________________________________________
______ pre-settling structure:
Manufacturer__________________________________________
2016 D. R. STRONG Consulting Engineers Inc. Page 64 The Pines
Technical Information Report Renton, Washington
DESIGN INFORMATION INDIVIDUAL BASIN
Water Quality design flow
Water Quality treated volume
Drainage basin(s) 1
Onsite area (includes frontage) 2.509
Offsite area
Type of Storage Facility Detention
Vault
Live Storage Volume (required) 18,816
Predev Runoff Rate 2-year 0.097
10-year 0.170
100-year 0.310
Developed Runoff Rate 2-year 0.094
(includes bypass) 10-year 0.169
100-year 0.296
Type of Restrictor
Size of orifice/restriction No. 1 1.40” Ø 0.00’
No. 2 1.25” Ø 3.75’
No. 3 1.75” Ø 5.25’
2016 D. R. STRONG Consulting Engineers Inc. Page 65 The Pines
Technical Information Report Renton, Washington
SECTION X
OPERATIONS AND MAINTENANCE MANUAL
The Home Owners Association will be responsible for maintenance of several private
catch basins on various lots as depicted on the plans. Maintenance guidelines set forth
in the 2009 KCSDWDM are included in this section. All other drainage elements are to
be publicly maintained.
APPENDIX A MAINTENANCE REQUIREMENTS FOR FLOW CONTROL, CONVEYANCE, AND WQ FACILITIES
2009 Surface Water Design Manual – Appendix A 1/9/2009 A-9
NO. 5 – CATCH BASINS AND MANHOLES
Maintenance
Component
Defect or Problem Condition When Maintenance is Needed Results Expected When
Maintenance is Performed
Sediment Sediment exceeds 60% of the depth from the
bottom of the catch basin to the invert of the
lowest pipe into or out of the catch basin or is
within 6 inches of the invert of the lowest pipe
into or out of the catch basin.
Sump of catch basin contains no
sediment.
Trash or debris of more than ½ cubic foot which
is located immediately in front of the catch basin
opening or is blocking capacity of the catch basin
by more than 10%.
No Trash or debris blocking or
potentially blocking entrance to
catch basin.
Trash or debris in the catch basin that exceeds 1/3 the depth from the bottom of basin to invert the
lowest pipe into or out of the basin.
No trash or debris in the catch basin.
Dead animals or vegetation that could generate
odors that could cause complaints or dangerous
gases (e.g., methane).
No dead animals or vegetation
present within catch basin.
Trash and debris
Deposits of garbage exceeding 1 cubic foot in
volume.
No condition present which would
attract or support the breeding of
insects or rodents.
Corner of frame extends more than ¾ inch past
curb face into the street (If applicable).
Frame is even with curb.
Top slab has holes larger than 2 square inches or
cracks wider than ¼ inch.
Top slab is free of holes and cracks.
Damage to frame
and/or top slab
Frame not sitting flush on top slab, i.e.,
separation of more than ¾ inch of the frame from
the top slab.
Frame is sitting flush on top slab.
Cracks wider than ½ inch and longer than 3 feet,
any evidence of soil particles entering catch
basin through cracks, or maintenance person
judges that catch basin is unsound.
Catch basin is sealed and
structurally sound.
Cracks in walls or
bottom
Cracks wider than ½ inch and longer than 1 foot
at the joint of any inlet/outlet pipe or any evidence
of soil particles entering catch basin through
cracks.
No cracks more than 1/4 inch wide at
the joint of inlet/outlet pipe.
Settlement/
misalignment
Catch basin has settled more than 1 inch or has
rotated more than 2 inches out of alignment.
Basin replaced or repaired to design
standards.
Damaged pipe joints Cracks wider than ½-inch at the joint of the
inlet/outlet pipes or any evidence of soil entering
the catch basin at the joint of the inlet/outlet
pipes.
No cracks more than ¼-inch wide at
the joint of inlet/outlet pipes.
Structure
Contaminants and
pollution
Any evidence of contaminants or pollution such
as oil, gasoline, concrete slurries or paint.
Materials removed and disposed of
according to applicable regulations.
Source control BMPs implemented if
appropriate. No contaminants
present other than a surface oil film.
Sediment
accumulation
Sediment filling 20% or more of the pipe. Inlet/outlet pipes clear of sediment.
Trash and debris Trash and debris accumulated in inlet/outlet
pipes (includes floatables and non-floatables).
No trash or debris in pipes.
Inlet/Outlet Pipe
Damaged Cracks wider than ½-inch at the joint of the
inlet/outlet pipes or any evidence of soil entering
at the joints of the inlet/outlet pipes.
No cracks more than ¼-inch wide at
the joint of the inlet/outlet pipe.
APPENDIX A MAINTENANCE REQUIREMENTS FLOW CONTROL, CONVEYANCE, AND WQ FACILITIES
1/9/2009 2009 Surface Water Design Manual – Appendix A A-10
NO. 5 – CATCH BASINS AND MANHOLES
Maintenance
Component
Defect or Problem Condition When Maintenance is Needed Results Expected When
Maintenance is Performed
Unsafe grate opening Grate with opening wider than 7/8 inch. Grate opening meets design
standards.
Trash and debris Trash and debris that is blocking more than 20%
of grate surface.
Grate free of trash and debris.
footnote to guidelines for disposal
Metal Grates
(Catch Basins)
Damaged or missing Grate missing or broken member(s) of the grate.
Any open structure requires urgent
maintenance.
Grate is in place and meets design
standards.
Cover/lid not in place Cover/lid is missing or only partially in place.
Any open structure requires urgent
maintenance.
Cover/lid protects opening to
structure.
Locking mechanism
Not Working
Mechanism cannot be opened by one
maintenance person with proper tools. Bolts cannot be seated. Self-locking cover/lid does not
work.
Mechanism opens with proper tools.
Manhole Cover/Lid
Cover/lid difficult to
Remove
One maintenance person cannot remove
cover/lid after applying 80 lbs. of lift.
Cover/lid can be removed and
reinstalled by one maintenance
person.
2016 D. R. STRONG Consulting Engineers Inc. Page 66 The Pines
Technical Information Report Renton, Washington
APPENDICES
2016 D. R. STRONG Consulting Engineers Inc. Page 67 The Pines
Technical Information Report Renton, Washington
APPENDIX “A” LEGAL DESCRIPTION
THE SOUTH 2 ACRES OF THE NORTH 4 ACRES OF THE SOUTHWEST QUARTER
OF THE SOUTHWEST QUARTER OF THE NORTHEAST QUARTER OF SECTION 9,
TOWNSHIP 23 NORTH, RANGE 5 EAST, W.M., IN KING COUNTY, WASHINGTON;
EXCEPT THE EAST 130 FEET THEREOF; AND EXCEPT THE WEST 30 FEET FOR
MONROE AVENUE N.E.; ALSO
THE NORTH 2 ACRES OF THE SOUTHWEST QUARTER OF THE SOUTHWEST
QUARTER OF THE NORTHEAST QUARTER OF SECTION 9, TOWNSHIP 23
NORTH, RANGE 5 EAST, W.M., IN KING COUNTY, WASHINGTON; EXCEPT THE
WEST 30 FEET FOR COUNTY ROAD; EXCEPT THE EAST 130 FEET THEREOF;
AND EXCEPT THE NORTH 48 FEET.
2016 D. R. STRONG Consulting Engineers Inc. Page 68 The Pines
Technical Information Report Renton, Washington
APPENDIX “B” BOND QUANTITY WORKSHEET
Planning Division |1055 South Grady Way – 6 th Floor | Renton, WA 98057 (425) 430-7200
•
•
Section I: Project Information
•
•
•
Section II: Bond Quantities Worksheets
•
•Section II.a EROSION CONTROL (Stabilization/Erosion Sediment Control (ESC))
•Section II.b TRANSPORTATION (Street and Site Improvements)
•Section II.c DRAINAGE (Drainage and Stormwater Facilities):
•Section II.d WATER - ONLY APPLICABLE IF WATER SERVICE IS PROVIDED BY CITY OF RENTON
•Section II.e SANITARY SEWER - ONLY APPLICABLE IF SEWER SERVICE IS PROVIDED BY CITY OF RENTON
•
•
•
•
•
•
Section III. Bond Worksheet
•This section calculates the required Permit Bond for construction permit issuance as well as the required Maintenance Bond for project close-out
submittals to release the permit bond on a project.
All unit prices include labor, equipment, materials, overhead and profit.
Complete the 'Quantity' columns for each of the appropriate section(s). Include existing Right-of-Way (ROW), Future Public Improvements and Private
Improvements.
The 'Quantity Remaining' column is only to be used when a project is under construction. The City allows one (1) bond reduction during the life of the
project with the exception of the maintenance period reduction.
Excel will auto-calculate and auto-populate the relevant fields and subtotals throughout the document. Only the 'Quantity' columns should need
completing.
Additional items not included in the lists can be added under the "write-in" sections. Provide a complete description, cost estimate and unit of measure
for each write-in item.
Note: Private improvements, with the exception of stormwater facilities, are not included in the bond amount calculation, but must be entered on the
form. Stormwater facilities (public and private) are required to be included in the bond amount.
BOND QUANTITY WORKSHEET INSTRUCTIONS
This worksheet is intended to be a "working" copy of the bond quantity worksheet, which will be used throughout all phases of the project, from initial
submittal to project close-out approval.
Submit this workbook, in its entirety, as follows:
The following forms are to be completed by the engineer/developer/applicant as applicable to the project:
The Bond Worksheet form will auto-calculate and auto-populate from the information provided in Section I and Section II.
This section includes all pertinent information for the project
Section II contains a separate spreadsheet TAB for each of the following specialties:
(1) electronic copy (.xlsx format) and (1) hard copy of the entire workbook for civil construction permit submittal. Hard copies are to be included as part
of the Technical Information Report (TIR).
(1) electronic copy (.xlsx format) and (1) hard copy of the entire workbook for final close-out submittal.
This section must be completed in its entirety
Information from this section auto-populates to all other relevant areas of the workbook
Page 1 of 14
Ref 8-H Bond Quantity Worksheet INSTRUCTIONS
Unit Prices Updated: 03/2016
Version: 06/2016
Printed 4/26/2017
Planning Division |1055 South Grady Way – 6 th Floor | Renton, WA 98057 (425) 430-7200
Date Prepared:
Name:
PE Registration No:
Firm Name:
Firm Address:
Phone No.
Email Address:
Project Name: Project Owner:
CED Plan # (LUA):Phone:
CED Permit # (U):Address:
Site Address:
Street Intersection:Addt'l Project Owner:
Parcel #(s):Phone:
Address:
Clearing and grading greater than or equal to 5,000 board feet of timber?
Yes/No:NO Water Service Provided by:
If Yes, Provide Forest Practice Permit #:Sewer Service Provided by:
SITE IMPROVEMENT BOND QUANTITY WORKSHEET
PROJECT INFORMATION
CITY OF RENTON
CITY OF RENTON
1 Select the current project status/phase from the following options:
For Approval - Preliminary Data Enclosed, pending approval from the City;
For Construction - Estimated Data Enclosed, Plans have been approved for contruction by the City;
Project Closeout - Final Costs and Quantities Enclosed for Project Close-out Submittal
Engineer Stamp Required
(all cost estimates must have original wet stamp and signature)
Clearing and Grading Utility Providers
N/A
Project Location and Description Project Owner Information
The Pines
Seattle, Washington, 98103
092305-9116 , 092305-9117
Harbour Homes, LLC
16-000413 (206) 315-8130
4/26/2017
Prepared by:
FOR APPROVALProject Phase 1
yoshio.piediscalzi@drstrong.com
Yoshio L. Piediscalzi
53232
D.R. STRONG Consulting Engineers, Inc.
620 7th Avenue, Kirkland, WA
(425) 827-3063
850 & 870 Monroe Avenue NE
400 N. 34th Street, Suite 300
Monroe Ave. NE & NE 9th St.
U16006592
Abbreviated Legal
Description:
The south 2 acres of the north 4 acres of the southwest quarter of the
southwest quarter of the northeast quarter of Section 9, Township 23
north, Range 5 east, W.M., in King County, Washington;
except the east 130 feet thereof; and
except the west 30 feet for Monroe Avenue N.E.; also
Page 2 of 14
Ref 8-H Bond Quantity Worksheet SECTION I PROJECT INFORMATION
Unit Prices Updated: 06/14/2016
Version: 06/14/2016
Printed 4/26/2017
CED Permit #:U16006592
Unit
Reference #Price Unit Quantity Cost
Backfill & compaction-embankment ESC-1 6.50$ CY
Check dams, 4" minus rock ESC-2 SWDM 5.4.6.3 80.00$ Each 18 1,440.00
Catch Basin Protection ESC-3 35.50$ Each 11 390.50
Crushed surfacing 1 1/4" minus ESC-4 WSDOT 9-03.9(3)95.00$ CY
Ditching ESC-5 9.00$ CY
Excavation-bulk ESC-6 2.00$ CY
Fence, silt ESC-7 SWDM 5.4.3.1 1.50$ LF 1460 2,190.00
Fence, Temporary (NGPE)ESC-8 1.50$ LF 260 390.00
Geotextile Fabric ESC-9 2.50$ SY
Hay Bale Silt Trap ESC-10 0.50$ Each
Hydroseeding ESC-11 SWDM 5.4.2.4 0.80$ SY 8400 6,720.00
Interceptor Swale / Dike ESC-12 1.00$ LF 1100 1,100.00
Jute Mesh ESC-13 SWDM 5.4.2.2 3.50$ SY
Level Spreader ESC-14 1.75$ LF
Mulch, by hand, straw, 3" deep ESC-15 SWDM 5.4.2.1 2.50$ SY
Mulch, by machine, straw, 2" deep ESC-16 SWDM 5.4.2.1 2.00$ SY
Piping, temporary, CPP, 6"ESC-17 12.00$ LF
Piping, temporary, CPP, 8"ESC-18 14.00$ LF
Piping, temporary, CPP, 12"ESC-19 18.00$ LF 50 900.00
Plastic covering, 6mm thick, sandbagged ESC-20 SWDM 5.4.2.3 4.00$ SY
Rip Rap, machine placed; slopes ESC-21 WSDOT 9-13.1(2)45.00$ CY
Rock Construction Entrance, 50'x15'x1'ESC-22 SWDM 5.4.4.1 1,800.00$ Each 1 1,800.00
Rock Construction Entrance, 100'x15'x1'ESC-23 SWDM 5.4.4.1 3,200.00$ Each
Sediment pond riser assembly ESC-24 SWDM 5.4.5.2 2,200.00$ Each
Sediment trap, 5' high berm ESC-25 SWDM 5.4.5.1 19.00$ LF
Sed. trap, 5' high, riprapped spillway berm section ESC-26 SWDM 5.4.5.1 70.00$ LF
Seeding, by hand ESC-27 SWDM 5.4.2.4 1.00$ SY
Sodding, 1" deep, level ground ESC-28 SWDM 5.4.2.5 8.00$ SY
Sodding, 1" deep, sloped ground ESC-29 SWDM 5.4.2.5 10.00$ SY
TESC Supervisor ESC-30 110.00$ HR 80 8,800.00
Water truck, dust control ESC-31 SWDM 5.4.7 140.00$ HR 16 2,240.00
Unit
Reference #Price Unit Quantity Cost
EROSION/SEDIMENT SUBTOTAL:25,970.50
SALES TAX @ 9.5%2,467.20
EROSION/SEDIMENT TOTAL:28,437.70
(A)
SITE IMPROVEMENT BOND QUANTITY WORKSHEET
FOR EROSION & SEDIMENT CONTROL
Description No.
(A)
WRITE-IN-ITEMS
Page 3 of 14
Ref 8-H Bond Quantity Worksheet SECTION II.a EROSION_CONTROL
Unit Prices Updated: 06/14/2016
Version: 06/14/2016
Printed 4/26/2017
CED Permit #:U16006592
Existing Future Public Private
Right-of-Way Improvements Improvements
(D) (E)
Description No. Unit Price Unit Quant.Cost Quant.Cost Quant.Cost Quant.Cost
GENERAL ITEMS
Backfill & Compaction- embankment GI-1 6.00$ CY 485 2,910.00 2250 13,500.00
Backfill & Compaction- trench GI-2 9.00$ CY 150 1,350.00
Clear/Remove Brush, by hand (SY)GI-3 1.00$ SY
Bollards - fixed GI-4 240.74$ Each 2 481.48
Bollards - removable GI-5 452.34$ Each 2 904.68
Clearing/Grubbing/Tree Removal GI-6 10,000.00$ Acre 3 30,000.00
Excavation - bulk GI-7 2.00$ CY 2072 4,144.00 250 500.00
Excavation - Trench GI-8 5.00$ CY 150 750.00 1350 6,750.00
Fencing, cedar, 6' high GI-9 20.00$ LF
Fencing, chain link, 4'GI-10 38.31$ LF
Fencing, chain link, vinyl coated, 6' high GI-11 20.00$ LF
Fencing, chain link, gate, vinyl coated, 20' GI-12 1,400.00$ Each
Fill & compact - common barrow GI-13 25.00$ CY
Fill & compact - gravel base GI-14 27.00$ CY
Fill & compact - screened topsoil GI-15 39.00$ CY
Gabion, 12" deep, stone filled mesh GI-16 65.00$ SY
Gabion, 18" deep, stone filled mesh GI-17 90.00$ SY
Gabion, 36" deep, stone filled mesh GI-18 150.00$ SY
Grading, fine, by hand GI-19 2.50$ SY
Grading, fine, with grader GI-20 2.00$ SY 5000 10,000.00
Monuments, 3' Long GI-21 250.00$ Each 1 250.00 1 250.00
Sensitive Areas Sign GI-22 7.00$ Each 1 7.00
Sodding, 1" deep, sloped ground GI-23 8.00$ SY
Surveying, line & grade GI-24 850.00$ Day 4 3,400.00
Surveying, lot location/lines GI-25 1,800.00$ Acre 3 5,400.00
Topsoil Type A (imported)GI-26 28.50$ CY
Traffic control crew ( 2 flaggers )GI-27 120.00$ HR 8 960.00
Trail, 4" chipped wood GI-28 8.00$ SY
Trail, 4" crushed cinder GI-29 9.00$ SY
Trail, 4" top course GI-30 12.00$ SY
Conduit, 2"GI-31 5.00$ LF
Wall, retaining, concrete GI-32 55.00$ SF
Wall, rockery GI-33 15.00$ SF
SUBTOTAL THIS PAGE:3,310.00 48,840.16 29,407.00
(B)(C)(D)(E)
SITE IMPROVEMENT BOND QUANTITY WORKSHEET
FOR STREET AND SITE IMPROVEMENTS
Quantity Remaining
(Bond Reduction)
(B)(C)
Page 4 of 14
Ref 8-H Bond Quantity Worksheet SECTION II.b TRANSPORTATION
Unit Prices Updated: 06/14/2016
Version: 06/14/2016
Printed 4/26/2017
CED Permit #:U16006592
Existing Future Public Private
Right-of-Way Improvements Improvements
(D) (E)
Description No. Unit Price Unit Quant.Cost Quant.Cost Quant.Cost Quant.Cost
SITE IMPROVEMENT BOND QUANTITY WORKSHEET
FOR STREET AND SITE IMPROVEMENTS
Quantity Remaining
(Bond Reduction)
(B)(C)
ROAD IMPROVEMENT/PAVEMENT/SURFACING
AC Grinding, 4' wide machine < 1000sy RI-1 30.00$ SY 150 4,500.00
AC Grinding, 4' wide machine 1000-2000sy RI-2 16.00$ SY
AC Grinding, 4' wide machine > 2000sy RI-3 10.00$ SY
AC Removal/Disposal RI-4 35.00$ SY 150 5,250.00
Barricade, Type III ( Permanent )RI-5 56.00$ LF
Guard Rail RI-6 30.00$ LF
Curb & Gutter, rolled RI-7 17.00$ LF
Curb & Gutter, vertical RI-8 12.50$ LF 1090 13,625.00
Curb and Gutter, demolition and disposal RI-9 18.00$ LF 96 1,728.00
Curb, extruded asphalt RI-10 5.50$ LF
Curb, extruded concrete RI-11 7.00$ LF
Sawcut, asphalt, 3" depth RI-12 1.85$ LF 230 425.50
Sawcut, concrete, per 1" depth RI-13 3.00$ LF
Sealant, asphalt RI-14 2.00$ LF 230 460.00
Shoulder, gravel, 4" thick RI-15 15.00$ SY
Sidewalk, 4" thick RI-16 38.00$ SY
Sidewalk, 4" thick, demolition and disposal RI-17 32.00$ SY
Sidewalk, 5" thick RI-18 41.00$ SY 525 21,525.00
Sidewalk, 5" thick, demolition and disposal RI-19 40.00$ SY
Sign, Handicap RI-20 85.00$ Each
Striping, per stall RI-21 7.00$ Each
Striping, thermoplastic, ( for crosswalk )RI-22 3.00$ SF 80 240.00
Striping, 4" reflectorized line RI-23 0.50$ LF 460 230.00
Additional 2.5" Crushed Surfacing RI-24 3.60$ SY
HMA 1/2" Overlay 1.5" RI-25 14.00$ SY
HMA 1/2" Overlay 2"RI-26 18.00$ SY
HMA Road, 2", 4" rock, First 2500 SY RI-27 28.00$ SY
HMA Road, 2", 4" rock, Qty. over 2500SY RI-28 21.00$ SY
HMA Road, 4", 6" rock, First 2500 SY RI-29 45.00$ SY
HMA Road, 4", 6" rock, Qty. over 2500 SY RI-30 37.00$ SY
HMA Road, 4", 4.5" ATB RI-31 38.00$ SY 150 5,700.00 1535 58,330.00
Gravel Road, 4" rock, First 2500 SY RI-32 15.00$ SY
Gravel Road, 4" rock, Qty. over 2500 SY RI-33 10.00$ SY
Thickened Edge RI-34 8.60$ LF
SUBTOTAL THIS PAGE:18,063.50 93,950.00
(B)(C)(D)(E)
Page 5 of 14
Ref 8-H Bond Quantity Worksheet SECTION II.b TRANSPORTATION
Unit Prices Updated: 06/14/2016
Version: 06/14/2016
Printed 4/26/2017
CED Permit #:U16006592
Existing Future Public Private
Right-of-Way Improvements Improvements
(D) (E)
Description No. Unit Price Unit Quant.Cost Quant.Cost Quant.Cost Quant.Cost
SITE IMPROVEMENT BOND QUANTITY WORKSHEET
FOR STREET AND SITE IMPROVEMENTS
Quantity Remaining
(Bond Reduction)
(B)(C)
PARKING LOT SURFACING No.
2" AC, 2" top course rock & 4" borrow PL-1 21.00$ SY
2" AC, 1.5" top course & 2.5" base course PL-2 28.00$ SY
4" select borrow PL-3 5.00$ SY
1.5" top course rock & 2.5" base course PL-4 14.00$ SY
SUBTOTAL PARKING LOT SURFACING:
(B)(C)(D)(E)
LANDSCAPING & VEGETATION No.
Street Trees LA-1 200.00$ EA 2 400.00 11 2,200.00
Median Landscaping LA-2
Right-of-Way Landscaping LA-3 50.00$ SY 125 6,250.00 557 27,850.00
Wetland Landscaping LA-4
SUBTOTAL LANDSCAPING & VEGETATION:6,650.00 30,050.00
(B)(C)(D)(E)
TRAFFIC & LIGHTING No.
Signs TR-1 200.00$ EA 5 1,000.00
Street Light System ( # of Poles)TR-2 3,000.00$ EA 2 6,000.00 8 24,000.00
Traffic Signal TR-3
Traffic Signal Modification TR-4
SUBTOTAL TRAFFIC & LIGHTING:6,000.00 25,000.00
(B)(C)(D)(E)
WRITE-IN-ITEMS
SUBTOTAL WRITE-IN ITEMS:
STREET AND SITE IMPROVEMENTS SUBTOTAL:34,023.50 197,840.16 29,407.00
SALES TAX @ 9.5%3,232.23 18,794.82 2,793.67
STREET AND SITE IMPROVEMENTS TOTAL:37,255.73 216,634.98 32,200.67
(B)(C)(D)(E)
Page 6 of 14
Ref 8-H Bond Quantity Worksheet SECTION II.b TRANSPORTATION
Unit Prices Updated: 06/14/2016
Version: 06/14/2016
Printed 4/26/2017
CED Permit #:U16006592
Existing Future Public Private
Right-of-Way Improvements Improvements
(D) (E)
Description No. Unit Price Unit Quant.Cost Quant.Cost Quant.Cost Quant.Cost
DRAINAGE (CPE = Corrugated Polyethylene Pipe, N12 or Equivalent) For Culvert prices, Average of 4' cover was assumed. Assume perforated PVC is same price as solid pipe.)
Access Road, R/D D-1 26.00$ SY 120 3,120.00
* (CBs include frame and lid)
Beehive D-2 90.00$ Each
Through-curb Inlet Framework D-3 400.00$ Each 2 800.00
CB Type I D-4 1,500.00$ Each 1 1,500.00 7 10,500.00 6 9,000.00
CB Type IL D-5 1,750.00$ Each 1 1,750.00
CB Type II, 48" diameter D-6 2,300.00$ Each 2 4,600.00
for additional depth over 4' D-7 480.00$ FT 12 5,760.00
CB Type II, 54" diameter D-8 2,500.00$ Each
for additional depth over 4'D-9 495.00$ FT
CB Type II, 60" diameter D-10 2,800.00$ Each
for additional depth over 4'D-11 600.00$ FT
CB Type II, 72" diameter D-12 6,000.00$ Each
for additional depth over 4'D-13 850.00$ FT
CB Type II, 96" diameter D-14 14,000.00$ Each
for additional depth over 4'D-15 925.00$ FT
Trash Rack, 12"D-16 350.00$ Each
Trash Rack, 15"D-17 410.00$ Each
Trash Rack, 18"D-18 480.00$ Each
Trash Rack, 21"D-19 550.00$ Each
Cleanout, PVC, 4"D-20 150.00$ Each
Cleanout, PVC, 6"D-21 170.00$ Each 8 1,360.00
Cleanout, PVC, 8"D-22 200.00$ Each
Culvert, PVC, 4" (Not allowed in ROW)D-23 10.00$ LF
Culvert, PVC, 6" (Not allowed in ROW)D-24 13.00$ LF 620 8,060.00
Culvert, PVC, 8" (Not allowed in ROW)D-25 15.00$ LF
Culvert, PVC, 12" (Not allowed in ROW)D-26 23.00$ LF
Culvert, PVC, 15" (Not allowed in ROW)D-27 35.00$ LF
Culvert, PVC, 18" (Not allowed in ROW)D-28 41.00$ LF
Culvert, PVC, 24" (Not allowed in ROW)D-29 56.00$ LF
Culvert, PVC, 30" (Not allowed in ROW)D-30 78.00$ LF
Culvert, PVC, 36" (Not allowed in ROW)D-31 130.00$ LF
Culvert, CMP, 8"D-32 19.00$ LF
Culvert, CMP, 12"D-33 29.00$ LF
SUBTOTAL THIS PAGE:11,860.00 16,170.00 18,420.00
(B)(C)(D)(E)
SITE IMPROVEMENT BOND QUANTITY WORKSHEET
FOR DRAINAGE AND STORMWATER FACILITIES
Quantity Remaining
(Bond Reduction)
(B)(C)
Page 7 of 14
Ref 8-H Bond Quantity Worksheet SECTION II.c DRAINAGE
Unit Prices Updated: 06/14/2016
Version: 06/14/2016
Printed 4/26/2017
CED Permit #:U16006592
Existing Future Public Private
Right-of-Way Improvements Improvements
(D) (E)
Description No. Unit Price Unit Quant.Cost Quant.Cost Quant.Cost Quant.Cost
SITE IMPROVEMENT BOND QUANTITY WORKSHEET
FOR DRAINAGE AND STORMWATER FACILITIES
Quantity Remaining
(Bond Reduction)
(B)(C)
DRAINAGE (Continued)
Culvert, CMP, 15"D-34 35.00$ LF
Culvert, CMP, 18"D-35 41.00$ LF
Culvert, CMP, 24"D-36 56.00$ LF
Culvert, CMP, 30"D-37 78.00$ LF
Culvert, CMP, 36"D-38 130.00$ LF
Culvert, CMP, 48"D-39 190.00$ LF
Culvert, CMP, 60"D-40 270.00$ LF
Culvert, CMP, 72"D-41 350.00$ LF
Culvert, Concrete, 8"D-42 42.00$ LF
Culvert, Concrete, 12"D-43 48.00$ LF
Culvert, Concrete, 15"D-44 78.00$ LF
Culvert, Concrete, 18"D-45 48.00$ LF
Culvert, Concrete, 24"D-46 78.00$ LF
Culvert, Concrete, 30"D-47 125.00$ LF
Culvert, Concrete, 36"D-48 150.00$ LF
Culvert, Concrete, 42"D-49 175.00$ LF
Culvert, Concrete, 48"D-50 205.00$ LF
Culvert, CPE, 6" (Not allowed in ROW)D-51 14.00$ LF
Culvert, CPE, 8" (Not allowed in ROW)D-52 16.00$ LF
Culvert, CPE, 12" (Not allowed in ROW)D-53 24.00$ LF
Culvert, CPE, 15" (Not allowed in ROW)D-54 35.00$ LF
Culvert, CPE, 18" (Not allowed in ROW)D-55 41.00$ LF
Culvert, CPE, 24" (Not allowed in ROW)D-56 56.00$ LF
Culvert, CPE, 30" (Not allowed in ROW)D-57 78.00$ LF
Culvert, CPE, 36" (Not allowed in ROW)D-58 130.00$ LF
Culvert, LCPE, 6"D-59 60.00$ LF
Culvert, LCPE, 8"D-60 72.00$ LF
Culvert, LCPE, 12"D-61 84.00$ LF 54 4,536.00 531 44,604.00
Culvert, LCPE, 15"D-62 96.00$ LF
Culvert, LCPE, 18"D-63 108.00$ LF 20 2,160.00
Culvert, LCPE, 24"D-64 120.00$ LF
Culvert, LCPE, 30"D-65 132.00$ LF
Culvert, LCPE, 36"D-66 144.00$ LF
Culvert, LCPE, 48"D-67 156.00$ LF
Culvert, LCPE, 54"D-68 168.00$ LF
SUBTOTAL THIS PAGE:4,536.00 46,764.00
(B)(C)(D)(E)
Page 8 of 14
Ref 8-H Bond Quantity Worksheet SECTION II.c DRAINAGE
Unit Prices Updated: 06/14/2016
Version: 06/14/2016
Printed 4/26/2017
CED Permit #:U16006592
Existing Future Public Private
Right-of-Way Improvements Improvements
(D) (E)
Description No. Unit Price Unit Quant.Cost Quant.Cost Quant.Cost Quant.Cost
SITE IMPROVEMENT BOND QUANTITY WORKSHEET
FOR DRAINAGE AND STORMWATER FACILITIES
Quantity Remaining
(Bond Reduction)
(B)(C)
DRAINAGE (Continued)
Culvert, LCPE, 60"D-69 180.00$ LF
Culvert, LCPE, 72"D-70 192.00$ LF
Culvert, HDPE, 6"D-71 42.00$ LF
Culvert, HDPE, 8"D-72 42.00$ LF
Culvert, HDPE, 12"D-73 74.00$ LF
Culvert, HDPE, 15"D-74 106.00$ LF
Culvert, HDPE, 18"D-75 138.00$ LF
Culvert, HDPE, 24"D-76 221.00$ LF
Culvert, HDPE, 30"D-77 276.00$ LF
Culvert, HDPE, 36"D-78 331.00$ LF
Culvert, HDPE, 48"D-79 386.00$ LF
Culvert, HDPE, 54"D-80 441.00$ LF
Culvert, HDPE, 60"D-81 496.00$ LF
Culvert, HDPE, 72"D-82 551.00$ LF
Pipe, Polypropylene, 6"D-83 84.00$ LF
Pipe, Polypropylene, 8"D-84 89.00$ LF
Pipe, Polypropylene, 12"D-85 95.00$ LF
Pipe, Polypropylene, 15"D-86 100.00$ LF
Pipe, Polypropylene, 18"D-87 106.00$ LF
Pipe, Polypropylene, 24"D-88 111.00$ LF
Pipe, Polypropylene, 30"D-89 119.00$ LF
Pipe, Polypropylene, 36"D-90 154.00$ LF
Pipe, Polypropylene, 48"D-91 226.00$ LF
Pipe, Polypropylene, 54"D-92 332.00$ LF
Pipe, Polypropylene, 60"D-93 439.00$ LF
Pipe, Polypropylene, 72"D-94 545.00$ LF
Culvert, DI, 6"D-95 61.00$ LF
Culvert, DI, 8"D-96 84.00$ LF
Culvert, DI, 12"D-97 106.00$ LF
Culvert, DI, 15"D-98 129.00$ LF
Culvert, DI, 18"D-99 152.00$ LF
Culvert, DI, 24"D-100 175.00$ LF
Culvert, DI, 30"D-101 198.00$ LF
Culvert, DI, 36"D-102 220.00$ LF
Culvert, DI, 48"D-103 243.00$ LF
Culvert, DI, 54"D-104 266.00$ LF
Culvert, DI, 60"D-105 289.00$ LF
Culvert, DI, 72"D-106 311.00$ LF
SUBTOTAL THIS PAGE:
(B)(C)(D)(E)
Page 9 of 14
Ref 8-H Bond Quantity Worksheet SECTION II.c DRAINAGE
Unit Prices Updated: 06/14/2016
Version: 06/14/2016
Printed 4/26/2017
CED Permit #:U16006592
Existing Future Public Private
Right-of-Way Improvements Improvements
(D) (E)
Description No. Unit Price Unit Quant.Cost Quant.Cost Quant.Cost Quant.Cost
SITE IMPROVEMENT BOND QUANTITY WORKSHEET
FOR DRAINAGE AND STORMWATER FACILITIES
Quantity Remaining
(Bond Reduction)
(B)(C)
Specialty Drainage Items
Ditching SD-1 9.50$ CY
Flow Dispersal Trench (1,436 base+)SD-3 28.00$ LF
French Drain (3' depth)SD-4 26.00$ LF
Geotextile, laid in trench, polypropylene SD-5 3.00$ SY
Mid-tank Access Riser, 48" dia, 6' deep SD-6 2,000.00$ Each
Pond Overflow Spillway SD-7 16.00$ SY
Restrictor/Oil Separator, 12"SD-8 1,150.00$ Each 1 1,150.00
Restrictor/Oil Separator, 15"SD-9 1,350.00$ Each
Restrictor/Oil Separator, 18"SD-10 1,700.00$ Each
Riprap, placed SD-11 42.00$ CY
Tank End Reducer (36" diameter)SD-12 1,200.00$ Each
Infiltration pond testing SD-13 125.00$ HR
Permeable Pavement SD-14
Permeable Concrete Sidewalk SD-15
Culvert, Box __ ft x __ ft SD-16
SUBTOTAL SPECIALTY DRAINAGE ITEMS:1,150.00
(B)(C)(D)(E)
STORMWATER FACILITIES (Include Flow Control and Water Quality Facility Summary Sheet and Sketch)
Detention Pond SF-1 Each
Detention Tank SF-2 Each
Detention Vault SF-3 200,000.00$ Each 1 200,000.00
Infiltration Pond SF-4 Each
Infiltration Tank SF-5 Each
Infiltration Vault SF-6 Each
Infiltration Trenches SF-7 Each
Basic Biofiltration Swale SF-8 Each
Wet Biofiltration Swale SF-9 Each
Wetpond SF-10 Each
Wetvault SF-11 Each
Sand Filter SF-12 Each
Sand Filter Vault SF-13 Each
Linear Sand Filter SF-14 Each
StormFilter SF-15 Each
Rain Garden SF-16 Each
SUBTOTAL STORMWATER FACILITIES:200,000.00
(B)(C)(D)(E)
Page 10 of 14
Ref 8-H Bond Quantity Worksheet SECTION II.c DRAINAGE
Unit Prices Updated: 06/14/2016
Version: 06/14/2016
Printed 4/26/2017
CED Permit #:U16006592
Existing Future Public Private
Right-of-Way Improvements Improvements
(D) (E)
Description No. Unit Price Unit Quant.Cost Quant.Cost Quant.Cost Quant.Cost
SITE IMPROVEMENT BOND QUANTITY WORKSHEET
FOR DRAINAGE AND STORMWATER FACILITIES
Quantity Remaining
(Bond Reduction)
(B)(C)
WRITE-IN-ITEMS
WI-1
WI-2
WI-3
WI-4
WI-5
WI-6
WI-7
WI-8
WI-9
WI-10
WI-11
WI-12
WI-13
WI-14
WI-15
SUBTOTAL WRITE-IN ITEMS:
DRAINAGE AND STORMWATER FACILITIES SUBTOTAL:16,396.00 264,084.00 18,420.00
SALES TAX @ 9.5%1,557.62 25,087.98 1,749.90
DRAINAGE AND STORMWATER FACILITIES TOTAL:17,953.62 289,171.98 20,169.90
(B)(C)(D)(E)
Page 11 of 14
Ref 8-H Bond Quantity Worksheet SECTION II.c DRAINAGE
Unit Prices Updated: 06/14/2016
Version: 06/14/2016
Printed 4/26/2017
CED Permit #:U16006592
Existing Future Public Private
Right-of-Way Improvements Improvements
(D) (E)
Description No. Unit Price Unit Quant.Cost Quant.Cost Quant.Cost Quant.Cost
Connection to Existing Watermain W-1 2,000.00$ Each 1 2,000.00
Ductile Iron Watermain, CL 52, 4 Inch Diameter W-2 50.00$ LF
Ductile Iron Watermain, CL 52, 6 Inch Diameter W-3 56.00$ LF
Ductile Iron Watermain, CL 52, 8 Inch Diameter W-4 60.00$ LF 15 900.00 474 28,440.00
Ductile Iron Watermain, CL 52, 10 Inch Diameter W-5 70.00$ LF
Ductile Iron Watermain, CL 52, 12 Inch Diameter W-6 80.00$ LF
Gate Valve, 4 inch Diameter W-7 500.00$ Each
Gate Valve, 6 inch Diameter W-8 700.00$ Each 2 1,400.00
Gate Valve, 8 Inch Diameter W-9 800.00$ Each 1 800.00 1 800.00
Gate Valve, 10 Inch Diameter W-10 1,000.00$ Each 1 1,000.00
Gate Valve, 12 Inch Diameter W-11 1,200.00$ Each
Fire Hydrant Assembly W-12 4,000.00$ Each 2 8,000.00
Permanent Blow-Off Assembly W-13 1,800.00$ Each 1 1,800.00
Air-Vac Assembly, 2-Inch Diameter W-14 2,000.00$ Each
Air-Vac Assembly, 1-Inch Diameter W-15 1,500.00$ Each 1 1,500.00
Compound Meter Assembly 3-inch Diameter W-16 8,000.00$ Each
Compound Meter Assembly 4-inch Diameter W-17 9,000.00$ Each
Compound Meter Assembly 6-inch Diameter W-18 10,000.00$ Each
Pressure Reducing Valve Station 8-inch to 10-inch W-19 20,000.00$ Each
WATER SUBTOTAL:4,700.00 41,940.00
SALES TAX @ 9.5%446.50 3,984.30
WATER TOTAL:5,146.50 45,924.30
(B)(C)(D)(E)
SITE IMPROVEMENT BOND QUANTITY WORKSHEET
FOR WATER
Quantity Remaining
(Bond Reduction)
(B)(C)
Page 12 of 14
Ref 8-H Bond Quantity Worksheet SECTION II.d WATER
Unit Prices Updated: 06/14/2016
Version: 06/14/2016
Printed 4/26/2017
CED Permit #:U16006592
Existing Future Public Private
Right-of-Way Improvements Improvements
(D) (E)
Description No. Unit Price Unit Quant.Cost Quant.Cost Quant.Cost Quant.Cost
Clean Outs SS-1 1,000.00$ Each 14 14,000.00
Grease Interceptor, 500 gallon SS-2 8,000.00$ Each
Grease Interceptor, 1000 gallon SS-3 10,000.00$ Each
Grease Interceptor, 1500 gallon SS-4 15,000.00$ Each
Side Sewer Pipe, PVC. 4 Inch Diameter SS-5 80.00$ LF
Side Sewer Pipe, PVC. 6 Inch Diameter SS-6 95.00$ LF 539 51,205.00
Sewer Pipe, PVC, 8 inch Diameter SS-7 105.00$ LF 476 49,980.00
Sewer Pipe, PVC, 12 Inch Diameter SS-8 120.00$ LF
Sewer Pipe, DI, 8 inch Diameter SS-9 115.00$ LF
Sewer Pipe, DI, 12 Inch Diameter SS-10 130.00$ LF
Manhole, 48 Inch Diameter SS-11 6,000.00$ Each 1 6,000.00 2 12,000.00
Manhole, 54 Inch Diameter SS-13 6,500.00$ Each
Manhole, 60 Inch Diameter SS-15 7,500.00$ Each
Manhole, 72 Inch Diameter SS-17 8,500.00$ Each
Manhole, 96 Inch Diameter SS-19 14,000.00$ Each
Pipe, C-900, 12 Inch Diameter SS-21 180.00$ LF
Outside Drop SS-24 1,500.00$ LS
Inside Drop SS-25 1,000.00$ LS
Sewer Pipe, PVC, ____ Inch Diameter SS-26
Lift Station (Entire System)SS-27 LS
SANITARY SEWER SUBTOTAL:6,000.00 61,980.00 65,205.00
SALES TAX @ 9.5%570.00 5,888.10 6,194.48
SANITARY SEWER TOTAL:6,570.00 67,868.10 71,399.48
(B)(C)(D)(E)
SITE IMPROVEMENT BOND QUANTITY WORKSHEET
FOR SANITARY SEWER
Quantity Remaining
(Bond Reduction)
(B)(C)
Page 13 of 14
Ref 8-H Bond Quantity Worksheet SECTION II.e SANITARY SEWER
Unit Prices Updated: 06/14/2016
Version: 06/14/2016
Printed 4/26/2017
Planning Division |1055 South Grady Way – 6th Floor | Renton, WA 98057 (425) 430-7200
Date:
Name:Project Name:
PE Registration No:CED Plan # (LUA):
Firm Name:CED Permit # (U):
Firm Address:Site Address:
Phone No.Parcel #(s):
Email Address:Project Phase:
Site Restoration/Erosion Sediment Control Subtotal (a)(a)28,437.70$
Existing Right-of-Way Improvements Subtotal (b)(b)48,972.23$
Future Public Improvements Subtotal (c)(c)330,427.38$
Stormwater & Drainage Facilities Subtotal (d)(d)327,295.50$
Bond Reduction (Quantity Remaining)2 (e)(e)-$
Site Restoration
Civil Construction Permit
Maintenance Bond 141,339.02$
Bond Reduction2
Construction Permit Bond Amount 3
Minimum Bond Amount is $10,000.00
1 Estimate Only - May involve multiple and variable components, which will be established on an individual basis by Development Engineering.
2 The City of Renton allows one request only for bond reduction prior to the maintenance period. Reduction of not more than 70% of the original bond amount, provided that the remaining 30% will
cover all remaining items to be constructed.
3 Required Bond Amounts are subject to review and modification by Development Engineering.
* Note: The word BOND as used in this document means any financial guarantee acceptable to the City of Renton.
** Note: All prices include labor, equipment, materials, overhead and profit.
T
(P +R - S)
Prepared by:Project Information
CONSTRUCTION BOND AMOUNT */**
(prior to permit issuance)
(425) 827-3063
yoshio.piediscalzi@drstrong.com
The Pines
16-000413
850 & 870 Monroe Avenue NE
092305-9116 , 092305-9117
FOR APPROVAL
U16006592
620 7th Avenue, Kirkland, WA
1,102,699.21$
P
(a) x 150%
SITE IMPROVEMENT BOND QUANTITY WORKSHEET
BOND CALCULATIONS
4/26/2017
Yoshio L. Piediscalzi
53232
D.R. STRONG Consulting Engineers, Inc.
R
((b)+(c)+(d)) x 150%
EST1
((b) + (c) + (d)) x 20%
-$
MAINTENANCE BOND */**
(after final acceptance of construction)
28,437.70$
48,972.23$
1,060,042.66$
42,656.55$
-$
330,427.38$
327,295.50$
S
(e) x 150%
Page 14 of 14
Ref 8-H Bond Quantity Worksheet SECTION III. BOND WORKSHEET
Unit Prices Updated: 06/14/2016
Version: 06/14/2016
Printed 4/26/2017
2016 D. R. STRONG Consulting Engineers Inc. Page 69 The Pines
Technical Information Report Renton, Washington
APPENDIX “C” CSWPPP
D.R. STRONG Consulting Engineers, Inc. The Pines
Stormwater Pollution Prevention Plan Renton, Washington
Construction Stormwater General Permit
Stormwater Pollution Prevention Plan
(SWPPP)
for
The Pines
Prepared for:
The Washington State Department of Ecology
Northwest Regional Office
3190 160th Avenue SE
Bellevue, WA 98008-5452
Permittee / Owner Developer Operator / Contractor
Harbour Homes, LLC
400 N. 34th Street, Suite 300
Seattle, WA 98103
Harbour Homes, LLC
400 N. 34th Street, Suite 300
Seattle, WA 98103
TBD
850 & 870 Monroe Avenue NE, Renton, Washington
Certified Erosion and Sediment Control Lead (CESCL)
Name Organization Contact Phone Number
TBD Earth Solutions NW (425) 449-4704
SWPPP Prepared By
Name Organization Contact Phone Number
Maher A. Joudi, PE D.R. Strong Consulting
Engineers, Inc.
(425) 827-3063
SWPPP Preparation Date
April 26, 2017
Project Construction Dates
Activity / Phase Start Date End Date
Site Development TBD TBD
D.R. STRONG Consulting Engineers, Inc. The Pines
Stormwater Pollution Prevention Plan Page i Renton, Washington
Table of Contents
1 Project Information ...............................................................................................................2
1.1 Existing Conditions .......................................................................................................2
1.2 Proposed Construction Activities ...................................................................................2
2 Construction Stormwater Best Management Practices (BMPs) ............................................4
2.1 The 12 Elements ...........................................................................................................4
2.1.1 Element 1: Preserve Vegetation / Mark Clearing Limits .........................................4
2.1.2 Element 2: Establish Construction Access .............................................................5
2.1.3 Element 3: Control Flow Rates...............................................................................6
2.1.4 Element 4: Install Sediment Controls .....................................................................7
2.1.5 Element 5: Stabilize Soils.......................................................................................9
2.1.6 Element 6: Protect Slopes....................................................................................10
2.1.7 Element 7: Protect Drain Inlets.............................................................................11
2.1.8 Element 8: Stabilize Channels and Outlets ..........................................................12
2.1.9 Element 9: Control Pollutants ...............................................................................13
2.1.10 Element 10: Control Dewatering ..........................................................................16
2.1.11 Element 11: Maintain BMPs .................................................................................17
2.1.12 Element 12: Manage the Project ..........................................................................18
3 Pollution Prevention Team .................................................................................................20
4 Monitoring and Sampling Requirements ............................................................................21
4.1 Site Inspection ............................................................................................................21
4.2 Stormwater Quality Sampling ......................................................................................21
4.2.1 Turbidity Sampling ...............................................................................................22
4.2.2 pH Sampling ........................................................................................................23
5 Discharges to 303(d) or Total Maximum Daily Load (TMDL) Waterbodies .........................24
5.1 303(d) Listed Waterbodies ..........................................................................................24
5.2 TMDL Waterbodies .....................................................................................................24
6 Reporting and Record Keeping ..........................................................................................25
6.1 Record Keeping ..........................................................................................................25
6.1.1 Site Log Book ......................................................................................................25
6.1.2 Records Retention ...............................................................................................25
6.1.3 Updating the SWPPP ...........................................................................................25
6.2 Reporting ....................................................................................................................25
6.2.1 Discharge Monitoring Reports ..............................................................................25
6.2.2 Notification of Noncompliance ..............................................................................26
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List of Tables
Table 1 – Summary of Site Pollutant Constituents .................................................................2
Table 3 – pH-Modifying Sources ............................................................................................15
Table 5 – Management ............................................................................................................18
Table 7 – Team Information ....................................................................................................20
Table 8 – Turbidity Sampling Method ....................................................................................22
Table 9 – pH Sampling Method ..............................................................................................23
List of Appendices
A. Site Map
B. BMP Detail
C. Correspondence
D. Site Inspection Form
E. Construction Stormwater General Permit (CSWGP)
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List of Acronyms and Abbreviations
Acronym / Abbreviation Explanation
303(d) Section of the Clean Water Act pertaining to Impaired Waterbodies
BFO Bellingham Field Office of the Department of Ecology
BMP(s) Best Management Practice(s)
CESCL Certified Erosion and Sediment Control Lead
CO2 Carbon Dioxide
CRO Central Regional Office of the Department of Ecology
CSWGP Construction Stormwater General Permit
CWA Clean Water Act
DMR Discharge Monitoring Report
DO Dissolved Oxygen
Ecology Washington State Department of Ecology
EPA United States Environmental Protection Agency
ERO Eastern Regional Office of the Department of Ecology
ERTS Environmental Report Tracking System
ESC Erosion and Sediment Control
GULD General Use Level Designation
NPDES National Pollutant Discharge Elimination System
NTU Nephelometric Turbidity Units
NWRO Northwest Regional Office of the Department of Ecology
pH Power of Hydrogen
RCW Revised Code of Washington
SPCC Spill Prevention, Control, and Countermeasure
su Standard Units
SWMMEW Stormwater Management Manual for Eastern Washington
SWMMWW Stormwater Management Manual for Western Washington
SWPPP Stormwater Pollution Prevention Plan
TESC Temporary Erosion and Sediment Control
SWRO Southwest Regional Office of the Department of Ecology
TMDL Total Maximum Daily Load
VFO Vancouver Field Office of the Department of Ecology
WAC Washington Administrative Code
WSDOT Washington Department of Transportation
WWHM Western Washington Hydrology Model
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1 Project Information
Project/Site Name: The Pines
Street/Location: 850 & 870 Monroe Avenue NE
City: Renton State: WA Zip code: 98056
Subdivision: LUA16-000413
Receiving waterbody: Johns Creek
1.1 Existing Conditions
Total acreage (including support activities such as off-site equipment staging yards, material
storage areas, borrow areas).
Total acreage: 2.595
Disturbed acreage: 2.139
Existing structures: 0.108
Landscape topography: 1.666 (estimate)
Drainage patterns: 0.000 (stream channel)
Existing Vegetation: 0.541 (tree retention)
Critical Areas (wetlands, streams,
high erosion risk, steep or
difficult to stabilize slopes):
0.00
Stream and adjacent wetland: 0.00
List of known impairments for 303(d) listed or Total Maximum Daily Load (TMDL) for the
receiving waterbody: None known
Table 1 includes a list of suspected and/or known contaminants associated with the construction
activity.
Table 1 – Summary of Site Pollutant Constituents
Constituent
(Pollutant) Location Depth Concentration
No known contaminants exist on the Site
1.2 Proposed Construction Activities
The applicant has gained approval to create 14 lots with lot sizes ranging from approximately
5,000 s.f. to 5,201 s.f. The 14 single-family residences combined with their driveways will
create approximately 38,700 s.f. of impervious area. The right of way frontage along Monroe
Ave NE will be improved with a 5.7’ dedication that will contain a five-foot sidewalk. One stub
road is proposed, Road A, will contain 26 feet of pavement, vertical curb, gutter, eight-foot
planter strip and five-foot sidewalks. Road A will contain a hammerhead turnaround with a
pavement width of 20’ between lots 5 and 6. The improvements from right-of way and new road
will add approximately 23,058 s.f. of impervious surface. The total developed/disturbed area is
105,463 s.f. of which 64,426 is impervious. 67,340 s.f. of impervious area will be conveyed to
the detention facility due to 2,914 s.f. of non-target right of way area. The remainder of the
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disturbed area (41,037 s.f.) will consist of landscaping and lawns. Bypass areas will consist of
the north half of the frontage improvements along Monroe Ave NE that will be 501 s.f. of
impervious and 450 s.f. of pervious area.
The Project is required to provide Basic Water Quality treatment and Level 2 Flow Control, per
the 2009 KCSWDM (Manual). All surface water runoff from impervious surfaces will be
collected and conveyed to a storm detention/water quality wetvault located in Tract “D”.
Appendix A shows the Site Plan with T.E.S.C. measures.
Final stabilization of the disturbed land will include:
• Asphalt roadway
• Concrete sidewalks
• Formal landscape planting
Contaminated Site Information:
Proposed activities regarding contaminated soils or groundwater (example: on-site treatment
system, authorized sanitary sewer discharge):
Not applicable as no known contamination.
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2 Construction Stormwater Best Management Practices (BMPs)
The SWPPP is a living document reflecting current conditions and changes throughout the life
of the Project. These changes may be informal (i.e., hand-written notes and deletions). Update
the SWPPP when the CESCL has noted a deficiency in BMPs or deviation from original design.
2.1 The 12 Elements
2.1.1 Element 1: Preserve Vegetation / Mark Clearing Limits
To protect adjacent properties and reduce the area of soil exposed to construction, the limits of
construction will be clearly marked before land-disturbing activities begin. Trees that are to be
preserved, as well as all sensitive areas and their buffers, shall be clearly delineated, both in the
field and on the plans.
In general, natural vegetation and native topsoil shall be retained in an undisturbed state to the
maximum extent possible. The BMPs relevant to marking the clearing limits that will be applied
for this project include:
The silt fence will be placed around the perimeter of the developable area of the Site. BMP will
be implemented at the start of construction.
Alternate BMPs for marking clearing limits are included in Appendix C as a quick reference tool
for the onsite inspector in the event the BMP(s) listed above are deemed ineffective or
inappropriate during construction to satisfy the requirements set forth in the General NPDES
Permit (Appendix D). To avoid potential erosion and sediment control issues that may cause a
violation(s) of the NPDES Construction Stormwater permit (as provided in Appendix D), the
CESCL will promptly initiate the implementation of one or more of the alternative BMPs listed in
Appendix C after the first sign that existing BMPs are ineffective or failing.
List and describe BMPs:
High Visibility Plastic or Metal Fence (BMP C103)
Silt Fence (BMP C223)
Installation Schedules:
Installation will occur before all other activity.
Inspection and Maintenance plan:
Weekly
Responsible Staff:
CESCL
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2.1.2 Element 2: Establish Construction Access
Construction access or activities occurring on unpaved areas will be minimized, yet where
necessary, access points shall be stabilized to minimize the tracking of sediment onto public
roads, and wheel washing, street sweeping, and street cleaning shall be employed to prevent
sediment from entering state waters. All wash wastewater shall be controlled on site.
A stabilized construction entrance will be placed along the proposed Road A right-of-way.
List and describe BMPs:
Stabilized Construction Entrance (BMP C105)
Construction Road/Parking Area Stabilization (BMP C107)
Installation Schedules:
Installation will occur after the clearing limits are marked.
Inspection and Maintenance plan:
Weekly
Responsible Staff:
CESCL
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2.1.3 Element 3: Control Flow Rates
In order to protect the properties and waterways downstream of the project site, stormwater
discharges from the site will be controlled. The specific BMPs for flow control that shall be used
on this project include:
• Wetvault
The wetvault will be utilized during construction as a flow control and sedimentation device.
Alternate flow control BMPs are included in Appendix C as a quick reference tool for the onsite
inspector in the event the BMP(s) listed above are deemed ineffective or inappropriate during
construction to satisfy the requirements set forth in the General NPDES Permit (Appendix D).
To avoid potential erosion and sediment control issues that may cause a violation(s) of the
NPDES Construction Stormwater permit (as provided in Appendix D), the Certified Erosion and
Sediment Control Lead will promptly initiate the implementation of one or more of the alternative
BMPs listed in Appendix C after the first sign that existing BMPs are ineffective or failing.
The project site is located west of the Cascade Mountain Crest. As such, the project must
comply with Minimum Requirement 7 (Ecology 2005).
In general, discharge rates of stormwater from the site will be controlled where increases in
impervious area or soil compaction during construction could lead to downstream erosion, or
where necessary to meet local agency stormwater discharge requirements (e.g. discharge to
combined sewer systems).
Will you construct stormwater retention and/or detention facilities?
Yes No
Will you use permanent infiltration ponds or other low impact development (example: rain
gardens, bio-retention, porous pavement) to control flow during construction?
Yes No
List and describe BMPs:
Sediment Traps (BMP C240) (As necessary)
Baker Tanks (As necessary)
Installation Schedules:
Installation will occur before any grading occurs.
Inspection and Maintenance plan:
Weekly
Responsible Staff:
CESCL
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2.1.4 Element 4: Install Sediment Controls
Silt fence will be installed around the perimeter of the Site in areas where runoff could sheet-
flow offsite. This BMP will be installed at the start of construction.
The interceptor swales will be installed during site grading. The interceptor swales will be
directed towards the detention/ water quality wetvault.
Alternate sediment control BMPs are included in Appendix C as a quick reference tool for the
onsite inspector in the event the BMP(s) listed above are deemed ineffective or inappropriate
during construction to satisfy the requirements set forth in the General NPDES Permit
(Appendix D). To avoid potential erosion and sediment control issues that may cause a
violation(s) of the NPDES Construction Stormwater permit (as provided in Appendix D), the
Certified Erosion and Sediment Control Lead will promptly initiate the implementation of one or
more of the alternative BMPs listed in Appendix C after the first sign that existing BMPs are
ineffective or failing.
In addition, sediment will be removed from paved areas in and adjacent to construction work
areas manually or using mechanical sweepers, as needed, to minimize tracking of sediments on
vehicle tires away from the site and to minimize washoff of sediments from adjacent streets in
runoff.
Whenever possible, sediment laden water shall be discharged into onsite, relatively level,
vegetated areas (BMP C240 paragraph 5, page 4-102).
In some cases, sediment discharge in concentrated runoff can be controlled using permanent
stormwater BMPs (e.g., infiltration swales, ponds, trenches). Sediment loads can limit the
effectiveness of some permanent stormwater BMPs, such as those used for infiltration or
biofiltration; however, those BMPs designed to remove solids by settling (wet ponds or detention
ponds) can be used during the construction phase. When permanent stormwater BMPs will be
used to control sediment discharge during construction, the structure will be protected from
excessive sedimentation with adequate erosion and sediment control BMPs. Any accumulated
sediment shall be removed after construction is complete and the permanent stormwater BMP
will be restabilized with vegetation per applicable design requirements once the remainder of
the site has been stabilized.
The following BMPs will be implemented as end-of-pipe sediment controls as required to meet
permitted turbidity limits in the site discharge(s). Prior to the implementation of these
technologies, sediment sources and erosion control and soil stabilization BMP efforts will be
maximized to reduce the need for end-of-pipe sedimentation controls.
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List and describe BMPs:
Baker Tank (As necessary)
Silt Fence (BMP C233)
Interceptor Swale (BMP C200)
Installation Schedules:
These will all be installed before any grading occurs.
Inspection and Maintenance plan:
Weekly
Responsible Staff:
CESCL
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2.1.5 Element 5: Stabilize Soils
Temporary seeding and cover measures may be required for interim grading activity and at soil
stockpiles and the Temporary Sediment Traps. Permanent Seeding will occur as grading is
completed. All stabilized sections will be seeded and vegetated.
Nets and Blankets along with Plastic Covering will be used on all slopes of 2:1 as shown on the
plan.
Dust Control will occur throughout the site as deemed necessary by the contractor and CESCL.
Alternate soil stabilization BMPs are included in Appendix C as a quick reference tool for the
onsite inspector in the event the BMP(s) listed above are deemed ineffective or inappropriate
during construction to satisfy the requirements set forth in the General NPDES Permit
(Appendix D). To avoid potential erosion and sediment control issues that may cause a
violation(s) of the NPDES Construction Stormwater permit (as provided in Appendix D), the
Certified Erosion and Sediment Control Lead will promptly initiate the implementation of one or
more of the alternative BMPs listed in Appendix C after the first sign that existing BMPs are
ineffective or failing.
In general, cut and fill slopes will be stabilized as soon as possible and soil stockpiles will be
temporarily covered with plastic sheeting. All stockpiled soils shall be stabilized from erosion,
protected with sediment trapping measures, and where possible, be located away from storm
drain inlets, waterways, and drainage channels.
West of the Cascade Mountains Crest
Season Dates Number of Days Soils Can
be Left Exposed
During the Dry Season May 1 – September 30 7 days
During the Wet Season October 1 – April 30 2 days
Soils must be stabilized at the end of the shift before a holiday or weekend if needed based on
the weather forecast.
Anticipated project dates: Start date: May 1st 2017 End date:
Will you construct during the wet season?
Yes No
List and describe BMPs:
Temporary and Permanent Seeding (BMP C120)
Nets and Blankets (BMP C122)
Plastic Covering (BMP C123)
Dust Control (BMP C140)
Installation Schedules:
These will all be installed before any grading occurs.
Inspection and Maintenance plan:
Weekly
Responsible Staff:
CESCL
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2.1.6 Element 6: Protect Slopes
Temporary slope protection measures may be required for interim grading activity and at soil
stockpiles and the Temporary Sediment Trap. Permanent Seeding will occur throughout the
site as slopes are stabilized.
Nets and Blankets along with Plastic Covering will be used on all slopes of 2:1 as shown on the
plan.
Checks Dams will be installed every 50’ as shown on the plan.
Alternate slope protection BMPs are included in Appendix C as a quick reference tool for the
onsite inspector in the event the BMP(s) listed above are deemed ineffective or inappropriate
during construction to satisfy the requirements set forth in the General NPDES Permit
(Appendix D). To avoid potential erosion and sediment control issues that may cause a
violation(s) of the NPDES Construction Stormwater permit (as provided in Appendix D), the
Certified Erosion and Sediment Control Lead will promptly initiate the implementation of one or
more of the alternative BMPs listed in Appendix C after the first sign that existing BMPs are
ineffective or failing.
Will steep slopes be present at the site during construction?
Yes No
List and describe BMPs:
Temporary and Permanent Seeding (BMP C120)
Nets and Blankets (BMP C122)
Plastic Covering (BMP C123)
Check Dams (BMP C207)
Installation Schedules:
In general, cut and fill slopes will be stabilized as soon as possible and soil stockpiles
will be temporarily covered with plastic sheeting.
Inspection and Maintenance plan:
Weekly
Responsible Staff:
CESCL
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2.1.7 Element 7: Protect Drain Inlets
All storm drain inlets and culverts made operable during construction shall be protected to
prevent unfiltered or untreated water from entering the drainage conveyance system. However,
the first priority is to keep all access roads clean of sediment and keep street wash water
separate from entering storm drains until treatment can be provided. Storm Drain Inlet
Protection (BMP C220) will be implemented for all drainage inlets and culverts that could
potentially be impacted by sediment-laden runoff on and near the project site. The following inlet
protection measures will be applied on this project:
• Catch Basin Filters
There are several existing catch basins which will require filters.
If the BMP options listed above are deemed ineffective or inappropriate during construction to
satisfy the requirements set forth in the General NPDES Permit (Appendix D), or if no BMPs are
listed above but deemed necessary during construction, the Certified Erosion and Sediment
Control Lead shall implement one or more of the alternative BMP inlet protection options listed
in Appendix C.
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2.1.8 Element 8: Stabilize Channels and Outlets
The project will not discharge to any outlets or channels; therefore, no BMPs are required.
Provide stabilization, including armoring material, adequate to prevent erosion of outlets,
adjacent stream banks, slopes, and downstream reaches, will be installed at the outlets of all
conveyance systems.
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2.1.9 Element 9: Control Pollutants
All pollutants, including waste materials and demolition debris, that occur onsite shall be
handled and disposed of in a manner that does not cause contamination of stormwater. Good
housekeeping and preventative measures will be taken to ensure that the site will be kept clean,
well-organized, and free of debris. If required, BMPs to be implemented to control specific
sources of pollutants are discussed below.
Vehicles, construction equipment, and/or petroleum product storage/dispensing:
• All vehicles, equipment, and petroleum product storage/dispensing areas will be
inspected regularly to detect any leaks or spills, and to identify maintenance needs to
prevent leaks or spills.
• On-site fueling tanks and petroleum product storage containers shall include
secondary containment.
• Spill prevention measures, such as drip pans, will be used when conducting
maintenance and repair of vehicles or equipment.
• In order to perform emergency repairs on site, temporary plastic will be placed
beneath and, if raining, over the vehicle.
• Contaminated surfaces shall be cleaned immediately following any discharge or spill
incident.
Demolition:
• Dust released from demolished sidewalks, buildings, or structures will be controlled
using Dust Control measures (BMP C140).
• Storm drain inlets vulnerable to stormwater discharge carrying dust, soil, or debris
will be protected using Storm Drain Inlet Protection (BMP C220 as described above
for Element 7).
• Process water and slurry resulting from sawcutting and surfacing operations will be
prevented from entering the waters of the State by implementing Sawcutting and
Surfacing Pollution Prevention measures (BMP C152).
Concrete and grout:
• Process water and slurry resulting from concrete work will be prevented from
entering the waters of the State by implementing Concrete Handling measures (BMP
C151).
Sanitary wastewater:
• Portable sanitation facilities will be firmly secured, regularly maintained, and emptied
when necessary.
Solid Waste:
• Solid waste will be stored in secure, clearly marked containers.
Other:
• Other BMPs will be administered as necessary to address any additional pollutant
sources on site.
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The project is not expected to exceed the 1,320 gallon stored-fuel threshold that requires
developing a Spill Prevention, Control, and Countermeasure (SPCC) Plan under the Federal
regulations of the Clean Water Act (CWA).
List and describe BMPs:
Dust Control measures (BMP C140)
Concrete Handling measures (BMP C151)
Sawcutting and Surfacing Pollution Prevention measures (BMP C152)
Storm Drain Inlet Protection (BMP C220)
Installation Schedules: Immediately following or in conjunction with activities.
Inspection and Maintenance plan:
Weekly
Responsible Staff:
CESCL
Will maintenance, fueling, and/or repair of heavy equipment and vehicles occur on-site?
Yes No
List and describe BMPs: N/A
Installation Schedules: N/A
Inspection and Maintenance plan:
Weekly
Responsible Staff:
CESCL
Will wheel wash or tire bath system BMPs be used during construction?
Yes No
List and describe BMPs: Presently not anticipated. SWPPP to be amended if wheel wash
proves necessary.
Installation Schedules: TBD
Inspection and Maintenance plan:
Weekly
Responsible Staff:
CESCL
Will pH-modifying sources be present on-site?
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Yes No
Table 3 – pH-Modifying Sources
None
Bulk cement
Cement kiln dust
Fly ash
Other cementitious materials
New concrete washing or curing waters
Waste streams generated from concrete grinding and sawing
Exposed aggregate processes
Dewatering concrete vaults
Concrete pumping and mixer washout waters
Recycled concrete
Other (i.e., calcium lignosulfate) [please describe: ]
List and describe BMPs: Wash water to be contained and routed to Baker Tank. Specific pH
treatment measures to be determined by contractor and CECSL. Presently, CO2 sparging or
dry ice anticipated approach if pH must be altered.
Installation Schedules: prior to placement of concrete
Inspection and Maintenance plan:
Monitoring will occur at the time of concrete wash operations.
Responsible Staff:
CESCL
Concrete trucks must not be washed out onto the ground, or into storm drains, open ditches,
streets, or streams. Excess concrete must not be dumped on-site, except in designated
concrete washout areas with appropriate BMPs installed.
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2.1.10 Element 10: Control Dewatering
Geotechnical analysis indicates possible perched groundwater at depths of one and one half to
five feet below existing grades. If groundwater is encountered during excavation, then de-
watering measures are to be utilized as needed per geotechnical recommendations.
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2.1.11 Element 11: Maintain BMPs
All temporary and permanent Erosion and Sediment Control (ESC) BMPs shall be maintained
and repaired as needed to ensure continued performance of their intended function.
Maintenance and repair shall be conducted in accordance with each particular BMP
specification (see Volume II of the SWMMWW or Chapter 7 of the SWMMEW).
Visual monitoring of all BMPs installed at the site will be conducted at least once every calendar
week and within 24 hours of any stormwater or non-stormwater discharge from the site. If the
site becomes inactive and is temporarily stabilized, the inspection frequency may be reduced to
once every calendar month.
All temporary ESC BMPs shall be removed within 30 days after final site stabilization is
achieved or after the temporary BMPs are no longer needed.
Trapped sediment shall be stabilized on-site or removed. Disturbed soil resulting from removal
of either BMPs or vegetation shall be permanently stabilized.
Additionally, protection must be provided for all BMPs installed for the permanent control of
stormwater from sediment and compaction. BMPs that are to remain in place following
completion of construction shall be examined and restored to full operating condition. If
sediment enters these BMPs during construction, the sediment shall be removed and the facility
shall be returned to conditions specified in the construction documents.
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2.1.12 Element 12: Manage the Project
Project management will incorporate the key components listed below:
Table 5 – Management
Design the project to fit the existing topography, soils, and drainage patterns
Emphasize erosion control rather than sediment control
Minimize the extent and duration of the area exposed
Keep runoff velocities low
Retain sediment on-site
Thoroughly monitor site and maintain all ESC measures
Schedule major earthwork during the dry season
Other (please describe)
As this project site is located west of the Cascade Mountain Crest, the project will be managed
according to the following key project components:
Phasing of Construction
• The construction project is being phased to the extent practicable in order to prevent soil
erosion, and, to the maximum extent possible, the transport of sediment from the site
during construction.
• Revegetation of exposed areas and maintenance of that vegetation shall be an integral
part of the clearing activities during each phase of construction, per the Scheduling BMP
(C 162).
Seasonal Work Limitations
• From October 1 through April 30, clearing, grading, and other soil disturbing activities
shall only be permitted if shown to the satisfaction of the local permitting authority that
silt-laden runoff will be prevented from leaving the site through a combination of the
following:
o Site conditions including existing vegetative coverage, slope, soil type, and proximity
to receiving waters; and
o Limitations on activities and the extent of disturbed areas; and
o Proposed erosion and sediment control measures.
• Based on the information provided and/or local weather conditions, the local permitting
authority may expand or restrict the seasonal limitation on site disturbance.
• The following activities are exempt from the seasonal clearing and grading limitations:
o Routine maintenance and necessary repair of erosion and sediment control BMPs;
o Routine maintenance of public facilities or existing utility structures that do not
expose the soil or result in the removal of the vegetative cover to soil; and
o Activities where there is 100 percent infiltration of surface water runoff within the site
in approved and installed erosion and sediment control facilities.
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Coordination with Utilities and Other Jurisdictions
• Care has been taken to coordinate with utilities, other construction projects, and the local
jurisdiction in preparing this SWPPP and scheduling the construction work.
Inspection and Monitoring
• All BMPs shall be inspected, maintained, and repaired as needed to assure continued
performance of their intended function. Site inspections shall be conducted by a person
who is knowledgeable in the principles and practices of erosion and sediment control.
This person has the necessary skills to:
o Assess the site conditions and construction activities that could impact the quality of
stormwater, and
o Assess the effectiveness of erosion and sediment control measures used to control
the quality of stormwater discharges.
• A Certified Erosion and Sediment Control Lead shall be on-site or on-call at all times.
• Whenever inspection and/or monitoring reveals that the BMPs identified in this SWPPP
are inadequate, due to the actual discharge of or potential to discharge a significant
amount of any pollutant, appropriate BMPs or design changes shall be implemented as
soon as possible.
Maintaining an Updated Construction SWPPP
• This SWPPP shall be retained on-site or within reasonable access to the site.
• The SWPPP shall be modified whenever there is a change in the design, construction,
operation, or maintenance at the construction site that has, or could have, a significant
effect on the discharge of pollutants to waters of the state.
• The SWPPP shall be modified if, during inspections or investigations conducted by the
owner/operator, or the applicable local or state regulatory authority, it is determined that
the SWPPP is ineffective in eliminating or significantly minimizing pollutants in
stormwater discharges from the site. The SWPPP shall be modified as necessary to
include additional or modified BMPs designed to correct problems identified. Revisions
to the SWPPP shall be completed within seven (7) days following the inspection.
• If BMP(s) are deemed do not satisfy the requirements set forth in the General NPDES
Permit (Appendix D), the CESCL will promptly implement one or more of the alternative
BMPs listed in Appendix C after the first sign that existing BMPs are ineffective or failing.
• Site inspections and monitoring will be conducted in accordance with Special Condition
S4 of the CSWGP. Sampling will occur at the baker tank discharge piping.
• The SWPPP will be updated, maintained, and implemented in accordance with Special
Conditions S3, S4, and S9 of the CSWGP.
• As site work progresses the SWPPP will be modified routinely to reflect changing site
conditions. The SWPPP will be reviewed monthly to ensure the content is current.
• Upon request, contractor shall provide the DOE and City of Sammamish with current
SWPPP.
D.R. STRONG Consulting Engineers, Inc. The Pines
Stormwater Pollution Prevention Plan Page 20 Renton, Washington
3 Pollution Prevention Team
Table 7 – Team Information
Title Name(s) Phone Number
Certified Erosion and
Sediment Control Lead
(CESCL)
TBD TBD
Resident Engineer Yoshi L. Piediscalzi, PE 425-827-3063
Emergency Ecology
Contact
Howard Zorzi 425-649-7130
Emergency Permittee/
Owner Contact
Jamie Waltier 206-315-8130
Non-Emergency Owner
Contact
Jamie Waltier 206-315-8130
Monitoring Personnel TBD TBD
Ecology Regional Office Northwest Regional Office 425-649-7000
City Spill Hotline (8:00 am
to 5:00 pm)
425-430-7400
King County Spill Hotline
(After Hours)
DNRP - Water and Land Resources Division 206-296-8100
D.R. STRONG Consulting Engineers, Inc. The Pines
Stormwater Pollution Prevention Plan Page 21 Renton, Washington
4 Monitoring and Sampling Requirements
Monitoring includes visual inspection, sampling for water quality parameters of concern, and
documentation of the inspection and sampling findings in a site log book. A site log book will be
maintained for all on-site construction activities and will include:
• A record of the implementation of the SWPPP and other permit requirements
• Site inspections
• Stormwater sampling data
File a blank form under Appendix D.
The site log book must be maintained on-site within reasonable access to the site and be made
available upon request to Ecology or the local jurisdiction.
Numeric effluent limits may be required for certain discharges to 303(d) listed waterbodies. See
CSWGP Special Condition S8 and Section 5 of this template.
4.1 Site Inspection
All BMPs will be inspected, maintained, and repaired as needed to assure continued
performance of their intended function. The inspector will be a Certified Erosion and Sediment
Control Lead (CESCL) per BMP C160. The name and contact information for the CESCL is
provided in Section 3 of this SWPPP.
Site inspection will occur in all areas disturbed by construction activities and at all stormwater
discharge points. Stormwater will be examined for the presence of suspended sediment,
turbidity, discoloration, and oily sheen. The site inspector will evaluate and document the
effectiveness of the installed BMPs and determine if it is necessary to repair or replace any of
the BMPs to improve the quality of stormwater discharges. All maintenance and repairs will be
documented in the site log book or forms provided in this document. All new BMPs or design
changes will be documented in the SWPPP as soon as possible.
Site inspections will be conducted at least once every calendar week and within 24 hours
following any discharge from the site. For sites that are temporarily stabilized and inactive, the
required frequency is reduced to once per calendar month.
The site inspector will record each site inspection using the site log inspection forms provided in
Appendix E. The site inspection log forms may be separated from this SWPPP document, but
will be maintained on-site or within reasonable access to the site and be made available upon
request to Ecology or the local jurisdiction.
4.2 Stormwater Quality Sampling
Runoff will be collected and conveyed to the proposed detention/water quality facility in Tract D,
to accommodate Basic Water Quality requirements. The project will collect 100% of the
stormwater generated; however testing will occur as deemed necessary by the CESCL and the
existing downstream catch basins.
D.R. STRONG Consulting Engineers, Inc. The Pines
Stormwater Pollution Prevention Plan Page 22 Renton, Washington
4.2.1 Turbidity Sampling
Requirements include calibrated turbidity meter or transparency tube to sample site discharges
for compliance with the CSWGP. Sampling will be conducted at all discharge points at least
once per calendar week.
Method for sampling turbidity:
Table 8 – Turbidity Sampling Method
Turbidity Meter/Turbidimeter (required for disturbances 5 acres or greater in size)
Transparency Tube (option for disturbances less than 1 acre and up to 5 acres in size)
The benchmark for turbidity value is 25 nephelometric turbidity units (NTU) and a transparency
less than 33 centimeters.
If the discharge’s turbidity is 26 to 249 NTU or the transparency is less than 33 cm but equal to
or greater than 6 cm, the following steps will be conducted:
1. Review the SWPPP for compliance with Special Condition S9. Make appropriate
revisions within 7 days of the date the discharge exceeded the benchmark.
2. Immediately begin the process to fully implement and maintain appropriate source
control and/or treatment BMPs as soon as possible. Address the problems within 10
days of the date the discharge exceeded the benchmark. If installation of necessary
treatment BMPs is not feasible within 10 days, Ecology may approve additional time
when the Permittee requests an extension within the initial 10-day response period.
3. Document BMP implementation and maintenance in the site log book.
If the turbidity exceeds 250 NTU or the transparency is 6 cm or less at any time, the following
steps will be conducted:
1. Telephone the applicable Ecology Region’s Environmental Report Tracking System
(ERTS) number within 24 hours.
• Central Region (Benton, Chelan, Douglas, Kittitas, Klickitat, Okanogan,
Yakima): (509) 575-2490
• Eastern Region (Adams, Asotin, Columbia, Ferry, Franklin, Garfield, Grant,
Lincoln, Pend Oreille, Spokane, Stevens, Walla Walla, Whitman): (509) 329-3400
• Northwest Region (King, Kitsap, Island, San Juan, Skagit, Snohomish,
Whatcom): (425) 649-7000
• Southwest Region (Clallam, Clark, Cowlitz, Grays Harbor, Jefferson, Lewis,
Mason, Pacific, Pierce, Skamania, Thurston, Wahkiakum,): (360) 407-6300
2. Immediately begin the process to fully implement and maintain appropriate source
control and/or treatment BMPs as soon as possible. Address the problems within 10
days of the date the discharge exceeded the benchmark. If installation of necessary
treatment BMPs is not feasible within 10 days, Ecology may approve additional time
when the Permittee requests an extension within the initial 10-day response period
3. Document BMP implementation and maintenance in the site log book.
D.R. STRONG Consulting Engineers, Inc. The Pines
Stormwater Pollution Prevention Plan Page 23 Renton, Washington
4. Continue to sample discharges daily until one of the following is true:
• Turbidity is 25 NTU (or lower).
• Transparency is 33 cm (or greater).
• Compliance with the water quality limit for turbidity is achieved.
o 1 - 5 NTU over background turbidity, if background is less than 50 NTU
o 1% - 10% over background turbidity, if background is 50 NTU or greater
• The discharge stops or is eliminated.
4.2.2 pH Sampling
pH monitoring is required for “Significant concrete work” (i.e., greater than 1000 cubic yards
poured or recycled concrete over the life of the project). The use of engineered soils (soil
amendments including but not limited to Portland cement-treated base [CTB], cement kiln dust
[CKD] or fly ash) also requires pH monitoring.
For significant concrete work, pH sampling will start the first day concrete is poured and
continue until it is cured, typically three (3) weeks after the last pour.
For engineered soils, pH sampling begins when engineered soils are first exposed to
precipitation and continues until the area is fully stabilized.
If the measured pH is 8.5 or greater, the following measures will be taken:
1. Prevent high pH water from entering storm sewer systems or surface water.
2. Adjust or neutralize the high pH water to the range of 6.5 to 8.5 su using appropriate
technology such as carbon dioxide (CO2) sparging (liquid or dry ice).
3. Written approval will be obtained from Ecology prior to the use of chemical treatment
other than CO2 sparging or dry ice.
Method for sampling pH:
Table 9 – pH Sampling Method
pH meter
pH test kit
Wide range pH indicator paper
Not: pH monitoring equipment unknown at this time; to be determined by CESCL
D.R. STRONG Consulting Engineers, Inc. The Pines
Stormwater Pollution Prevention Plan Page 24 Renton, Washington
5 Discharges to 303(d) or Total Maximum Daily Load (TMDL)
Waterbodies
5.1 303(d) Listed Waterbodies
Is the receiving water 303(d) (Category 5) listed for turbidity, fine sediment, phosphorus, or pH?
Yes No
List the impairment(s):
Temperature, Bacteria, Dissolved Oxygen
5.2 TMDL Waterbodies
Waste Load Allocation for CWSGP discharges:
List and describe BMPs:
Discharges to TMDL receiving waterbodies will meet in-stream water quality criteria at the point
of discharge.
The Construction Stormwater General Permit Proposed New Discharge to an Impaired Water
Body form is included in Appendix F.
D.R. STRONG Consulting Engineers, Inc. The Pines
Stormwater Pollution Prevention Plan Page 25 Renton, Washington
6 Reporting and Record Keeping
6.1 Record Keeping
6.1.1 Site Log Book
A site log book will be maintained for all on-site construction activities and will include:
• A record of the implementation of the SWPPP and other permit requirements
• Site inspections
• Sample logs
6.1.2 Records Retention
Records will be retained during the life of the project and for a minimum of three (3) years
following the termination of permit coverage in accordance with Special Condition S5.C of the
CSWGP.
Permit documentation to be retained on-site:
• CSWGP
• Permit Coverage Letter
• SWPPP
• Site Log Book
Permit documentation will be provided within 14 days of receipt of a written request from
Ecology. A copy of the SWPPP or access to the SWPPP will be provided to the public when
requested in writing in accordance with Special Condition S5.G.2.b of the CSWGP.
6.1.3 Updating the SWPPP
The SWPPP will be modified if:
• Found ineffective in eliminating or significantly minimizing pollutants in stormwater
discharges from the site.
• There is a change in design, construction, operation, or maintenance at the construction
site that has, or could have, a significant effect on the discharge of pollutants to waters
of the State.
The SWPPP will be modified within seven (7) days if inspection(s) or investigation(s) determine
additional or modified BMPs are necessary for compliance. An updated timeline for BMP
implementation will be prepared.
6.2 Reporting
6.2.1 Discharge Monitoring Reports
Cumulative soil disturbance is one (1) acre or larger; therefore, Discharge Monitoring
Reports (DMRs) will be submitted to Ecology monthly. If there was no discharge during a given
D.R. STRONG Consulting Engineers, Inc. The Pines
Stormwater Pollution Prevention Plan Page 26 Renton, Washington
monitoring period the DMR will be submitted as required, reporting “No Discharge”. The DMR
due date is fifteen (15) days following the end of each calendar month.
DMRs will be reported online through Ecology’s WQWebDMR System.
6.2.2 Notification of Noncompliance
If any of the terms and conditions of the permit is not met, and the resulting noncompliance may
cause a threat to human health or the environment, the following actions will be taken:
1. Ecology will be immediately notified of the failure to comply by calling the applicable
Regional office ERTS phone number (Regional office numbers listed below).
2. Immediate action will be taken to prevent the discharge/pollution or otherwise stop or
correct the noncompliance. If applicable, sampling and analysis of any noncompliance
will be repeated immediately and the results submitted to Ecology within five (5) days of
becoming aware of the violation.
3. A detailed written report describing the noncompliance will be submitted to Ecology
within five (5) days, unless requested earlier by Ecology.
Anytime turbidity sampling indicates turbidity is 250 NTUs or greater, or water transparency is 6
cm or less, the Ecology Regional office will be notified by phone within 24 hours of analysis as
required by Special Condition S5.A of the CSWGP.
• Central Region at (509) 575-2490 for Benton, Chelan, Douglas, Kittitas, Klickitat,
Okanogan, or Yakima County
• Eastern Region at (509) 329-3400 for Adams, Asotin, Columbia, Ferry, Franklin,
Garfield, Grant, Lincoln, Pend Oreille, Spokane, Stevens, Walla Walla, or Whitman
County
• Northwest Region at (425) 649-7000 for Island, King, Kitsap, San Juan, Skagit,
Snohomish, or Whatcom County
• Southwest Region at (360) 407-6300 for Clallam, Clark, Cowlitz, Grays Harbor,
Jefferson, Lewis, Mason, Pacific, Pierce, Skamania, Thurston, or Wahkiakum
Include the following information:
1. Your name and / Phone number
2. Permit number
3. City / County of project
4. Sample results
5. Date / Time of call
6. Date / Time of sample
7. Project name
In accordance with Special Condition S4.D.5.b of the CSWGP, the Ecology Regional office will
be notified if chemical treatment other than CO2 sparging is planned for adjustment of high pH
water.
D.R. STRONG Consulting Engineers, Inc. The Pines
Stormwater Pollution Prevention Plan Page A-1 Renton, Washington
Appendix A
Site Map
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D.R. STRONG Consulting Engineers, Inc. The Pines
Stormwater Pollution Prevention Plan Page B-1 Renton, Washington
Appendix B
BMP Details
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BMP C101: Preserving Natural Vegetation
Purpose The purpose of preserving natural vegetation is to reduce erosion wherever
practicable. Limiting site disturbance is the single most effective method
for reducing erosion. For example, conifers can hold up to about 50
percent of all rain that falls during a storm. Up to 20-30 percent of this rain may never reach the ground but is taken up by the tree or evaporates. Another benefit is that the rain held in the tree can be released slowly to
the ground after the storm.
Conditions of Use Natural vegetation should be preserved on steep slopes, near perennial
and intermittent watercourses or swales, and on building sites in wooded areas.
• As required by local governments.
• Phase construction to preserve natural vegetation on the project site for
as long as possible during the construction period.
Design and Installation Specifications
Natural vegetation can be preserved in natural clumps or as individual trees, shrubs and vines.
The preservation of individual plants is more difficult because heavy
equipment is generally used to remove unwanted vegetation. The points
to remember when attempting to save individual plants are:
• Is the plant worth saving? Consider the location, species, size, age, vigor, and the work involved. Local governments may also have ordinances to save natural vegetation and trees.
• Fence or clearly mark areas around trees that are to be saved. It is
preferable to keep ground disturbance away from the trees at least as
far out as the dripline.
Plants need protection from three kinds of injuries:
• Construction Equipment - This injury can be above or below the
ground level. Damage results from scarring, cutting of roots, and
compaction of the soil. Placing a fenced buffer zone around plants to
be saved prior to construction can prevent construction equipment injuries.
• Grade Changes - Changing the natural ground level will alter grades,
which affects the plant's ability to obtain the necessary air, water, and
minerals. Minor fills usually do not cause problems although
sensitivity between species does vary and should be checked. Trees can typically tolerate fill of 6 inches or less. For shrubs and other
plants, the fill should be less.
When there are major changes in grade, it may become necessary to
supply air to the roots of plants. This can be done by placing a layer of
gravel and a tile system over the roots before the fill is made. A tile system protects a tree from a raised grade. The tile system should be
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laid out on the original grade leading from a dry well around the tree trunk. The system should then be covered with small stones to allow
air to circulate over the root area.
Lowering the natural ground level can seriously damage trees and
shrubs. The highest percentage of the plant roots are in the upper 12 inches of the soil and cuts of only 2-3 inches can cause serious injury. To protect the roots it may be necessary to terrace the immediate area
around the plants to be saved. If roots are exposed, construction of
retaining walls may be needed to keep the soil in place. Plants can also
be preserved by leaving them on an undisturbed, gently sloping mound. To increase the chances for survival, it is best to limit grade changes and other soil disturbances to areas outside the dripline of the
plant.
• Excavations - Protect trees and other plants when excavating for
drainfields, power, water, and sewer lines. Where possible, the trenches should be routed around trees and large shrubs. When this is not possible, it is best to tunnel under them. This can be done with
hand tools or with power augers. If it is not possible to route the trench
around plants to be saved, then the following should be observed:
Cut as few roots as possible. When you have to cut, cut clean. Paint cut root ends with a wood dressing like asphalt base paint if roots will be exposed for more than 24-hours.
Backfill the trench as soon as possible.
Tunnel beneath root systems as close to the center of the main trunk to
preserve most of the important feeder roots.
Some problems that can be encountered with a few specific trees are:
• Maple, Dogwood, Red alder, Western hemlock, Western red cedar,
and Douglas fir do not readily adjust to changes in environment and
special care should be taken to protect these trees.
• The windthrow hazard of Pacific silver fir and madrona is high, while that of Western hemlock is moderate. The danger of windthrow
increases where dense stands have been thinned. Other species (unless
they are on shallow, wet soils less than 20 inches deep) have a low
windthrow hazard.
• Cottonwoods, maples, and willows have water-seeking roots. These can cause trouble in sewer lines and infiltration fields. On the other
hand, they thrive in high moisture conditions that other trees would
not.
• Thinning operations in pure or mixed stands of Grand fir, Pacific silver
fir, Noble fir, Sitka spruce, Western red cedar, Western hemlock, Pacific dogwood, and Red alder can cause serious disease problems.
Disease can become established through damaged limbs, trunks, roots,
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and freshly cut stumps. Diseased and weakened trees are also susceptible to insect attack.
Maintenance
Standards
Inspect flagged and/or fenced areas regularly to make sure flagging or
fencing has not been removed or damaged. If the flagging or fencing
has been damaged or visibility reduced, it shall be repaired or replaced immediately and visibility restored.
• If tree roots have been exposed or injured, “prune” cleanly with an
appropriate pruning saw or lopers directly above the damaged roots
and recover with native soils. Treatment of sap flowing trees (fir,
hemlock, pine, soft maples) is not advised as sap forms a natural healing barrier.
BMP C102: Buffer Zones
Purpose Creation of an undisturbed area or strip of natural vegetation or an
established suitable planting that will provide a living filter to reduce soil
erosion and runoff velocities.
Conditions of Use Natural buffer zones are used along streams, wetlands and other bodies of water that need protection from erosion and sedimentation. Vegetative
buffer zones can be used to protect natural swales and can be incorporated
into the natural landscaping of an area.
Critical-areas buffer zones should not be used as sediment treatment areas. These areas shall remain completely undisturbed. The local permitting authority may expand the buffer widths temporarily to allow the use of the
expanded area for removal of sediment.
Design and Installation Specifications
• Preserving natural vegetation or plantings in clumps, blocks, or strips
is generally the easiest and most successful method.
• Leave all unstable steep slopes in natural vegetation.
• Mark clearing limits and keep all equipment and construction debris
out of the natural areas and buffer zones. Steel construction fencing is
the most effective method in protecting sensitive areas and buffers.
Alternatively, wire-backed silt fence on steel posts is marginally effective. Flagging alone is typically not effective.
• Keep all excavations outside the dripline of trees and shrubs.
• Do not push debris or extra soil into the buffer zone area because it
will cause damage from burying and smothering.
• Vegetative buffer zones for streams, lakes or other waterways shall be established by the local permitting authority or other state or federal
permits or approvals.
Maintenance
Standards
Inspect the area frequently to make sure flagging remains in place and the
area remains undisturbed. Replace all damaged flagging immediately.
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BMP C103: High Visibility Fence
Purpose Fencing is intended to:
1. Restrict clearing to approved limits.
2. Prevent disturbance of sensitive areas, their buffers, and other areas
required to be left undisturbed.
3. Limit construction traffic to designated construction entrances, exits, or internal roads.
4. Protect areas where marking with survey tape may not provide
adequate protection.
Conditions of Use To establish clearing limits plastic, fabric, or metal fence may be used:
• At the boundary of sensitive areas, their buffers, and other areas required to be left uncleared.
• As necessary to control vehicle access to and on the site.
Design and Installation Specifications
High visibility plastic fence shall be composed of a high-density
polyethylene material and shall be at least four feet in height. Posts for the fencing shall be steel or wood and placed every 6 feet on center (maximum) or as needed to ensure rigidity. The fencing shall be fastened
to the post every six inches with a polyethylene tie. On long continuous
lengths of fencing, a tension wire or rope shall be used as a top stringer to
prevent sagging between posts. The fence color shall be high visibility orange. The fence tensile strength shall be 360 lbs./ft. using the ASTM D4595 testing method.
If appropriate install fabric silt fence in accordance with BMP C233 to
act as high visibility fence. Silt fence shall be at least 3 feet high and
must be highly visible to meet the requirements of this BMP.
Metal fences shall be designed and installed according to the manufacturer's specifications.
Metal fences shall be at least 3 feet high and must be highly visible.
Fences shall not be wired or stapled to trees.
Maintenance Standards If the fence has been damaged or visibility reduced, it shall be repaired or replaced immediately and visibility restored.
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BMP C105: Stabilized Construction Entrance / Exit
Purpose Stabilized Construction entrances are established to reduce the amount of
sediment transported onto paved roads by vehicles or equipment. This is done by constructing a stabilized pad of quarry spalls at entrances and
exits for construction sites.
Conditions of Use Construction entrances shall be stabilized wherever traffic will be entering
or leaving a construction site if paved roads or other paved areas are within 1,000 feet of the site.
For residential construction provide stabilized construction entrances for each residence, rather than only at the main subdivision entrance.
Stabilized surfaces shall be of sufficient length/width to provide vehicle access/parking, based on lot size/configuration.
On large commercial, highway, and road projects, the designer should include enough extra materials in the contract to allow for additional
stabilized entrances not shown in the initial Construction SWPPP. It is difficult to determine exactly where access to these projects will take
place; additional materials will enable the contractor to install them where needed.
Design and Installation
Specifications
See Figure 4.1.1 for details. Note: the 100’ minimum length of the entrance shall be reduced to the maximum practicable size when the size
or configuration of the site does not allow the full length (100’).
Construct stabilized construction entrances with a 12-inch thick pad of 4-
inch to 8-inch quarry spalls, a 4-inch course of asphalt treated base (ATB), or use existing pavement. Do not use crushed concrete, cement,
or calcium chloride for construction entrance stabilization because these products raise pH levels in stormwater and concrete discharge to surface
waters of the State is prohibited.
A separation geotextile shall be placed under the spalls to prevent fine
sediment from pumping up into the rock pad. The geotextile shall meet the following standards:
Grab Tensile Strength (ASTM D4751) 200 psi min.
Grab Tensile Elongation (ASTM D4632) 30% max.
Mullen Burst Strength (ASTM D3786-80a) 400 psi min.
AOS (ASTM D4751) 20-45 (U.S. standard sieve size)
• Consider early installation of the first lift of asphalt in areas that will
paved; this can be used as a stabilized entrance. Also consider the installation of excess concrete as a stabilized entrance. During large
concrete pours, excess concrete is often available for this purpose.
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• Fencing (see BMP C103) shall be installed as necessary to restrict
traffic to the construction entrance.
• Whenever possible, the entrance shall be constructed on a firm,
compacted subgrade. This can substantially increase the effectiveness of the pad and reduce the need for maintenance.
• Construction entrances should avoid crossing existing sidewalks and back of walk drains if at all possible. If a construction entrance must
cross a sidewalk or back of walk drain, the full length of the sidewalk and back of walk drain must be covered and protected from sediment
leaving the site.
Maintenance Standards
Quarry spalls shall be added if the pad is no longer in accordance with
the specifications.
• If the entrance is not preventing sediment from being tracked onto
pavement, then alternative measures to keep the streets free of sediment shall be used. This may include replacement/cleaning of the existing quarry spalls, street sweeping, an increase in the dimensions of the entrance, or the installation of a wheel wash.
• Any sediment that is tracked onto pavement shall be removed by shoveling or street sweeping. The sediment collected by sweeping shall be removed or stabilized on site. The pavement shall not be
cleaned by washing down the street, except when high efficiency sweeping is ineffective and there is a threat to public safety. If it is
necessary to wash the streets, the construction of a small sump to contain the wash water shall be considered. The sediment would then
be washed into the sump where it can be controlled.
• Perform street sweeping by hand or with a high efficiency sweeper. Do
not use a non-high efficiency mechanical sweeper because this creates dust and throws soils into storm systems or conveyance ditches.
• Any quarry spalls that are loosened from the pad, which end up on the roadway shall be removed immediately.
• If vehicles are entering or exiting the site at points other than the construction entrance(s), fencing (see BMP C103) shall be installed to
control traffic.
• Upon project completion and site stabilization, all construction
accesses intended as permanent access for maintenance shall be permanently stabilized.
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Figure 4.1.1 – Stabilized Construction Entrance
Approved as
Equivalent
Ecology has approved products as able to meet the requirements of BMP
C105. The products did not pass through the Technology Assessment
Protocol – Ecology (TAPE) process. Local jurisdictions may choose not to accept this product approved as equivalent, or may require additional testing prior to consideration for local use. The products are available for
review on Ecology’s website at
http://www.ecy.wa.gov/programs/wq/stormwater/newtech/equivalent.html
BMP C106: Wheel Wash
Purpose Wheel washes reduce the amount of sediment transported onto paved
roads by motor vehicles.
Conditions of Use When a stabilized construction entrance (see BMP C105) is not preventing
sediment from being tracked onto pavement.
• Wheel washing is generally an effective BMP when installed with careful attention to topography. For example, a wheel wash can be
detrimental if installed at the top of a slope abutting a right-of-way
where the water from the dripping truck can run unimpeded into the
street.
Driveway shall meet the requirements of the permitting agency
It is recommended that the entrance be crowned so that runoff drains off the pad
Provide full width of ingress/egress area
12” min. thickness
Geotextile
4’ – 8” quarry spalls
Install driveway culvert if there is a roadside ditch present
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• Pressure washing combined with an adequately sized and surfaced pad with direct drainage to a large 10-foot x 10-foot sump can be very
effective.
• Discharge wheel wash or tire bath wastewater to a separate on-site
treatment system that prevents discharge to surface water, such as closed-loop recirculation or upland land application, or to the sanitary sewer with local sewer district approval.
• Wheel wash or tire bath wastewater should not include wastewater
from concrete washout areas.
Design and Installation Specifications
Suggested details are shown in Figure 4.1.2. The Local Permitting Authority may allow other designs. A minimum of 6 inches of asphalt treated base (ATB) over crushed base material or 8 inches over a good
subgrade is recommended to pave the wheel wash.
Use a low clearance truck to test the wheel wash before paving. Either a
belly dump or lowboy will work well to test clearance.
Keep the water level from 12 to 14 inches deep to avoid damage to truck hubs and filling the truck tongues with water.
Midpoint spray nozzles are only needed in extremely muddy conditions.
Wheel wash systems should be designed with a small grade change, 6- to
1-inches for a 10-foot-wide pond, to allow sediment to flow to the low side of pond to help prevent re-suspension of sediment. A drainpipe with a 2- to 3-foot riser should be installed on the low side of the pond to allow
for easy cleaning and refilling. Polymers may be used to promote
coagulation and flocculation in a closed-loop system. Polyacrylamide
(PAM) added to the wheel wash water at a rate of 0.25 - 0.5 pounds per 1,000 gallons of water increases effectiveness and reduces cleanup time. If PAM is already being used for dust or erosion control and is being applied
by a water truck, the same truck can be used to change the wash water.
Maintenance Standards The wheel wash should start out the day with fresh water.
The wash water should be changed a minimum of once per day. On large earthwork jobs where more than 10-20 trucks per hour are expected, the
wash water will need to be changed more often.
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Figure 4.1.2 – Wheel Wash
Notes:
1. Asphalt construction entrance 6 in. asphalt treated base (ATB). 2. 3-inch trash pump with floats on the suction hose.
3. Midpoint spray nozzles, if needed. 4. 6-inch sewer pipe with butterfly valves. Bottom one is a drain. Locate top pipe’s invert 1 foot above bottom
of wheel wash. 5. 8 foot x 8 foot sump with 5 feet of catch. Build so the sump can be cleaned with a trackhoe.
6. Asphalt curb on the low road side to direct water back to pond. 7. 6-inch sleeve under road.
8. Ball valves. 9. 15 foot. ATB apron to protect ground from splashing water.
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BMP C107: Construction Road/Parking Area Stabilization
Purpose Stabilizing subdivision roads, parking areas, and other on-site vehicle
transportation routes immediately after grading reduces erosion caused by
construction traffic or runoff.
Conditions of Use Roads or parking areas shall be stabilized wherever they are constructed, whether permanent or temporary, for use by construction traffic.
• High Visibility Fencing (see BMP C103) shall be installed, if
necessary, to limit the access of vehicles to only those roads and
parking areas that are stabilized.
Design and Installation Specifications
• On areas that will receive asphalt as part of the project, install the first lift as soon as possible.
• A 6-inch depth of 2- to 4-inch crushed rock, gravel base, or crushed
surfacing base course shall be applied immediately after grading or
utility installation. A 4-inch course of asphalt treated base (ATB) may
also be used, or the road/parking area may be paved. It may also be possible to use cement or calcium chloride for soil stabilization. If cement or cement kiln dust is used for roadbase stabilization, pH
monitoring and BMPs (BMPs C252 and C253) are necessary to
evaluate and minimize the effects on stormwater. If the area will not be
used for permanent roads, parking areas, or structures, a 6-inch depth of hog fuel may also be used, but this is likely to require more maintenance. Whenever possible, construction roads and parking areas
shall be placed on a firm, compacted subgrade.
• Temporary road gradients shall not exceed 15 percent. Roadways shall
be carefully graded to drain. Drainage ditches shall be provided on each side of the roadway in the case of a crowned section, or on one side in the case of a super-elevated section. Drainage ditches shall be
directed to a sediment control BMP.
• Rather than relying on ditches, it may also be possible to grade the
road so that runoff sheet-flows into a heavily vegetated area with a well-developed topsoil. Landscaped areas are not adequate. If this area
has at least 50 feet of vegetation that water can flow through, then it is
generally preferable to use the vegetation to treat runoff, rather than a
sediment pond or trap. The 50 feet shall not include wetlands or their
buffers. If runoff is allowed to sheetflow through adjacent vegetated areas, it is vital to design the roadways and parking areas so that no
concentrated runoff is created.
• Storm drain inlets shall be protected to prevent sediment-laden water
entering the storm drain system (see BMP C220).
Maintenance Standards Inspect stabilized areas regularly, especially after large storm events.
Crushed rock, gravel base, etc. shall be added as required to maintain a
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stable driving surface and to stabilize any areas that have eroded.
Following construction, these areas shall be restored to pre-construction
condition or better to prevent future erosion.
Perform street cleaning at the end of each day or more often if necessary.
BMP C120: Temporary and Permanent Seeding
Purpose Seeding reduces erosion by stabilizing exposed soils. A well-established vegetative cover is one of the most effective methods of reducing erosion.
Conditions of Use Use seeding throughout the project on disturbed areas that have reached
final grade or that will remain unworked for more than 30 days.
The optimum seeding windows for western Washington are April 1 through June 30 and September 1 through October 1.
Between July 1 and August 30 seeding requires irrigation until 75 percent
grass cover is established.
Between October 1 and March 30 seeding requires a cover of mulch with
straw or an erosion control blanket until 75 percent grass cover is established.
Review all disturbed areas in late August to early September and complete
all seeding by the end of September. Otherwise, vegetation will not
establish itself enough to provide more than average protection.
• Mulch is required at all times for seeding because it protects seeds from heat, moisture loss, and transport due to runoff. Mulch can be applied on top of the seed or simultaneously by hydroseeding. See BMP C121: Mulching for specifications.
• Seed and mulch, all disturbed areas not otherwise vegetated at final site stabilization. Final stabilization means the completion of all soil disturbing activities at the site and the establishment of a permanent
vegetative cover, or equivalent permanent stabilization measures (such
as pavement, riprap, gabions or geotextiles) which will prevent
erosion.
Design and Installation
Specifications
Seed retention/detention ponds as required.
Install channels intended for vegetation before starting major
earthwork and hydroseed with a Bonded Fiber Matrix. For vegetated
channels that will have high flows, install erosion control blankets
over hydroseed. Before allowing water to flow in vegetated channels, establish 75 percent vegetation cover. If vegetated channels cannot be established by seed before water flow; install sod
in the channel bottom—over hydromulch and erosion control
blankets.
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• Confirm the installation of all required surface water control measures to prevent seed from washing away.
• Hydroseed applications shall include a minimum of 1,500 pounds per
acre of mulch with 3 percent tackifier. See BMP C121: Mulching for
specifications.
• Areas that will have seeding only and not landscaping may need compost or meal-based mulch included in the hydroseed in order to
establish vegetation. Re-install native topsoil on the disturbed soil
surface before application.
• When installing seed via hydroseeding operations, only about 1/3 of the seed actually ends up in contact with the soil surface. This reduces the ability to establish a good stand of grass quickly. To overcome this, consider increasing seed quantities by up to 50 percent.
• Enhance vegetation establishment by dividing the hydromulch operation into two phases:
1. Phase 1- Install all seed and fertilizer with 25-30 percent mulch and tackifier onto soil in the first lift.
2. Phase 2- Install the rest of the mulch and tackifier over the first lift.
Or, enhance vegetation by:
1. Installing the mulch, seed, fertilizer, and tackifier in one lift.
2. Spread or blow straw over the top of the hydromulch at a rate of
800-1000 pounds per acre.
3. Hold straw in place with a standard tackifier.
Both of these approaches will increase cost moderately but will greatly improve and enhance vegetative establishment. The increased cost
may be offset by the reduced need for:
• Irrigation.
• Reapplication of mulch.
• Repair of failed slope surfaces.
This technique works with standard hydromulch (1,500 pounds per
acre minimum) and BFM/MBFMs (3,000 pounds per acre minimum).
• Seed may be installed by hand if:
• Temporary and covered by straw, mulch, or topsoil.
• Permanent in small areas (usually less than 1 acre) and covered
with mulch, topsoil, or erosion blankets.
• The seed mixes listed in the tables below include recommended mixes for both temporary and permanent seeding.
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• Apply these mixes, with the exception of the wetland mix, at a rate of 120 pounds per acre. This rate can be reduced if soil
amendments or slow-release fertilizers are used.
• Consult the local suppliers or the local conservation district for
their recommendations because the appropriate mix depends on a variety of factors, including location, exposure, soil type, slope, and expected foot traffic. Alternative seed mixes approved by the
local authority may be used.
• Other mixes may be appropriate, depending on the soil type and
hydrology of the area.
• Table 4.1.2 lists the standard mix for areas requiring a temporary vegetative cover.
Table 4.1.2 Temporary Erosion Control Seed Mix
% Weight % Purity % Germination
Chewings or annual blue grass
Festuca rubra var. commutata or Poa anna
40 98 90
Perennial rye - Lolium perenne 50 98 90
Redtop or colonial bentgrass
Agrostis alba or Agrostis tenuis
5 92 85
White dutch clover
Trifolium repens
5 98 90
• Table 4.1.3 lists a recommended mix for landscaping seed.
Table 4.1.3 Landscaping Seed Mix
% Weight % Purity % Germination
Perennial rye blend Lolium perenne 70 98 90
Chewings and red fescue blend
Festuca rubra var. commutata
or Festuca rubra
30 98 90
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• Table 4.1.4 lists a turf seed mix for dry situations where there is no need for watering. This mix requires very little maintenance.
Table 4.1.4 Low-Growing Turf Seed Mix
% Weight % Purity % Germination
Dwarf tall fescue (several varieties)
Festuca arundinacea var.
45 98 90
Dwarf perennial rye (Barclay) Lolium perenne var. barclay 30 98 90
Red fescue
Festuca rubra
20 98 90
Colonial bentgrass
Agrostis tenuis
5 98 90
• Table 4.1.5 lists a mix for bioswales and other intermittently wet areas.
Table 4.1.5
Bioswale Seed Mix*
% Weight % Purity % Germination
Tall or meadow fescue
Festuca arundinacea or Festuca
elatior
75-80 98 90
Seaside/Creeping bentgrass
Agrostis palustris
10-15 92 85
Redtop bentgrass
Agrostis alba or Agrostis gigantea
5-10 90 80
* Modified Briargreen, Inc. Hydroseeding Guide Wetlands Seed Mix
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• Table 4.1.6 lists a low-growing, relatively non-invasive seed mix appropriate for very wet areas that are not regulated wetlands. Apply
this mixture at a rate of 60 pounds per acre. Consult Hydraulic Permit
Authority (HPA) for seed mixes if applicable.
Table 4.1.6
Wet Area Seed Mix*
% Weight % Purity % Germination
Tall or meadow fescue
Festuca arundinacea or
Festuca elatior
60-70 98 90
Seaside/Creeping bentgrass
Agrostis palustris
10-15 98 85
Meadow foxtail
Alepocurus pratensis
10-15 90 80
Alsike clover Trifolium hybridum 1-6 98 90
Redtop bentgrass Agrostis alba 1-6 92 85
* Modified Briargreen, Inc. Hydroseeding Guide Wetlands Seed Mix
• Table 4.1.7 lists a recommended meadow seed mix for infrequently
maintained areas or non-maintained areas where colonization by native
plants is desirable. Likely applications include rural road and utility right-of-way. Seeding should take place in September or very early October in order to obtain adequate establishment prior to the winter
months. Consider the appropriateness of clover, a fairly invasive
species, in the mix. Amending the soil can reduce the need for clover.
Table 4.1.7
Meadow Seed Mix
% Weight % Purity % Germination
Redtop or Oregon bentgrass
Agrostis alba or Agrostis
oregonensis
20 92 85
Red fescue
Festuca rubra
70 98 90
White dutch clover
Trifolium repens
10 98 90
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• Roughening and Rototilling:
• The seedbed should be firm and rough. Roughen all soil no matter
what the slope. Track walk slopes before seeding if engineering
purposes require compaction. Backblading or smoothing of slopes
greater than 4H:1V is not allowed if they are to be seeded.
• Restoration-based landscape practices require deeper incorporation than that provided by a simple single-pass rototilling treatment.
Wherever practical, initially rip the subgrade to improve long-term
permeability, infiltration, and water inflow qualities. At a
minimum, permanent areas shall use soil amendments to achieve organic matter and permeability performance defined in engineered soil/landscape systems. For systems that are deeper
than 8 inches complete the rototilling process in multiple lifts, or
prepare the engineered soil system per specifications and place to
achieve the specified depth.
• Fertilizers:
• Conducting soil tests to determine the exact type and quantity of
fertilizer is recommended. This will prevent the over-application
of fertilizer.
• Organic matter is the most appropriate form of fertilizer because it provides nutrients (including nitrogen, phosphorus, and potassium) in the least water-soluble form.
• In general, use 10-4-6 N-P-K (nitrogen-phosphorus-potassium)
fertilizer at a rate of 90 pounds per acre. Always use slow-release
fertilizers because they are more efficient and have fewer environmental impacts. Do not add fertilizer to the hydromulch machine, or agitate, more than 20 minutes before use. Too much
agitation destroys the slow-release coating.
• There are numerous products available that take the place of
chemical fertilizers. These include several with seaweed extracts that are beneficial to soil microbes and organisms. If 100 percent
cottonseed meal is used as the mulch in hydroseed, chemical
fertilizer may not be necessary. Cottonseed meal provides a good
source of long-term, slow-release, available nitrogen.
• Bonded Fiber Matrix and Mechanically Bonded Fiber Matrix:
• On steep slopes use Bonded Fiber Matrix (BFM) or Mechanically
Bonded Fiber Matrix (MBFM) products. Apply BFM/MBFM
products at a minimum rate of 3,000 pounds per acre of mulch
with approximately 10 percent tackifier. Achieve a minimum of 95
percent soil coverage during application. Numerous products are available commercially. Installed products per manufacturer’s
instructions. Most products require 24-36 hours to cure before
rainfall and cannot be installed on wet or saturated soils.
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Generally, products come in 40-50 pound bags and include all necessary ingredients except for seed and fertilizer.
• BFMs and MBFMs provide good alternatives to blankets in most
areas requiring vegetation establishment. Advantages over
blankets include:
• BFM and MBFMs do not require surface preparation.
• Helicopters can assist in installing BFM and MBFMs in remote areas.
• On slopes steeper than 2.5H:1V, blanket installers may require ropes and harnesses for safety.
• Installing BFM and MBFMs can save at least $1,000 per acre compared to blankets.
Maintenance
Standards
Reseed any seeded areas that fail to establish at least 80 percent cover
(100 percent cover for areas that receive sheet or concentrated flows). If
reseeding is ineffective, use an alternate method such as sodding, mulching, or nets/blankets. If winter weather prevents adequate grass
growth, this time limit may be relaxed at the discretion of the local
authority when sensitive areas would otherwise be protected.
• Reseed and protect by mulch any areas that experience erosion after
achieving adequate cover. Reseed and protect by mulch any eroded area.
• Supply seeded areas with adequate moisture, but do not water to the
extent that it causes runoff.
Approved as Equivalent Ecology has approved products as able to meet the requirements of BMP
C120. The products did not pass through the Technology Assessment Protocol – Ecology (TAPE) process. Local jurisdictions may choose not to accept this product approved as equivalent, or may require additional testing
prior to consideration for local use. The products are available for review on
Ecology’s website at
http://www.ecy.wa.gov/programs/wq/stormwater/newtech/equivalent.html
BMP C121: Mulching
Purpose Mulching soils provides immediate temporary protection from erosion.
Mulch also enhances plant establishment by conserving moisture, holding
fertilizer, seed, and topsoil in place, and moderating soil temperatures.
There is an enormous variety of mulches that can be used. This section discusses only the most common types of mulch.
Conditions of Use As a temporary cover measure, mulch should be used:
• For less than 30 days on disturbed areas that require cover.
• At all times for seeded areas, especially during the wet season and
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during the hot summer months.
• During the wet season on slopes steeper than 3H:1V with more than
10 feet of vertical relief.
Mulch may be applied at any time of the year and must be refreshed
periodically.
• For seeded areas mulch may be made up of 100 percent: cottonseed meal; fibers made of wood, recycled cellulose, hemp, kenaf; compost;
or blends of these. Tackifier shall be plant-based, such as guar or alpha
plantago, or chemical-based such as polyacrylamide or polymers. Any
mulch or tackifier product used shall be installed per manufacturer’s instructions. Generally, mulches come in 40-50 pound bags. Seed and fertilizer are added at time of application.
Design and
Installation Specifications
For mulch materials, application rates, and specifications, see Table 4.1.8.
Always use a 2-inch minimum mulch thickness; increase the thickness
until the ground is 95% covered (i.e. not visible under the mulch layer). Note: Thickness may be increased for disturbed areas in or near sensitive areas or other areas highly susceptible to erosion.
Mulch used within the ordinary high-water mark of surface waters should
be selected to minimize potential flotation of organic matter. Composted
organic materials have higher specific gravities (densities) than straw, wood, or chipped material. Consult Hydraulic Permit Authority (HPA) for mulch mixes if applicable.
Maintenance
Standards
• The thickness of the cover must be maintained.
• Any areas that experience erosion shall be remulched and/or protected
with a net or blanket. If the erosion problem is drainage related, then the problem shall be fixed and the eroded area remulched.
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Table 4.1.8
Mulch Standards and Guidelines
Mulch Material Quality Standards Application Rates Remarks
Straw Air-dried; free from undesirable seed and coarse material.
2"-3" thick; 5 bales per 1,000 sf or 2-3 tons per
acre
Cost-effective protection when applied with adequate thickness. Hand-application generally requires greater thickness than blown straw. The thickness of straw may be reduced by half
when used in conjunction with seeding. In windy areas straw
must be held in place by crimping, using a tackifier, or covering
with netting. Blown straw always has to be held in place with a
tackifier as even light winds will blow it away. Straw, however,
has several deficiencies that should be considered when selecting mulch materials. It often introduces and/or encourages the propagation of weed species and it has no significant long-term benefits. It should also not be used within the ordinary high-water elevation of surface waters (due to flotation).
Hydromulch No growth inhibiting factors. Approx. 25-30 lbs per 1,000 sf or 1,500 - 2,000 lbs per acre
Shall be applied with hydromulcher. Shall not be used without seed and tackifier unless the application rate is at least doubled. Fibers longer than about ¾-1 inch clog hydromulch equipment. Fibers should be kept to less than ¾ inch.
Composted
Mulch and
Compost
No visible water or
dust during
handling. Must be
produced in
accordance with WAC 173-350, Solid Waste Handling Standards. .
2" thick min.;
approx. 100 tons
per acre (approx.
800 lbs per yard)
More effective control can be obtained by increasing thickness
to 3". Excellent mulch for protecting final grades until
landscaping because it can be directly seeded or tilled into soil
as an amendment. Composted mulch has a coarser size
gradation than compost. It is more stable and practical to use in wet areas and during rainy weather conditions. Do not use composted mulch near wetlands or near phosphorous impaired water bodies.
Chipped Site Vegetation Average size shall be several inches. Gradations from fines to 6 inches in
length for texture,
variation, and
interlocking
properties.
2" thick min.; This is a cost-effective way to dispose of debris from clearing and grubbing, and it eliminates the problems associated with burning. Generally, it should not be used on slopes above approx. 10% because of its tendency to be transported by
runoff. It is not recommended within 200 feet of surface waters.
If seeding is expected shortly after mulch, the decomposition of
the chipped vegetation may tie up nutrients important to grass
establishment.
Wood-based Mulch or Wood Straw
No visible water or dust during handling. Must be purchased from a supplier with a Solid Waste Handling Permit or one exempt from solid waste regulations.
2” thick min.;
approx. 100 tons per acre (approx. 800 lbs. per cubic yard)
This material is often called “hog or hogged fuel.” The use of
mulch ultimately improves the organic matter in the soil. Special caution is advised regarding the source and composition of wood-based mulches. Its preparation typically does not provide any weed seed control, so evidence of residual vegetation in its composition or known inclusion of weed plants or seeds should be monitored and prevented (or minimized).
Wood Strand
Mulch
A blend of loose,
long, thin wood
pieces derived from
native conifer or
deciduous trees with
high length-to-width ratio.
2” thick min. Cost-effective protection when applied with adequate thickness.
A minimum of 95-percent of the wood strand shall have lengths
between 2 and 10-inches, with a width and thickness between
1/16 and ⅜-inches. The mulch shall not contain resin, tannin, or
other compounds in quantities that would be detrimental to plant life. Sawdust or wood shavings shall not be used as mulch. (WSDOT specification (9-14.4(4))
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BMP C122: Nets and Blankets
Purpose Erosion control nets and blankets are intended to prevent erosion and hold
seed and mulch in place on steep slopes and in channels so that vegetation
can become well established. In addition, some nets and blankets can be
used to permanently reinforce turf to protect drainage ways during high flows. Nets (commonly called matting) are strands of material woven into an open, but high-tensile strength net (for example, coconut fiber matting).
Blankets are strands of material that are not tightly woven, but instead
form a layer of interlocking fibers, typically held together by a
biodegradable or photodegradable netting (for example, excelsior or straw blankets). They generally have lower tensile strength than nets, but cover the ground more completely. Coir (coconut fiber) fabric comes as both
nets and blankets.
Conditions of Use Erosion control nets and blankets should be used:
• To aid permanent vegetated stabilization of slopes 2H:1V or greater and with more than 10 feet of vertical relief.
• For drainage ditches and swales (highly recommended). The
application of appropriate netting or blanket to drainage ditches and
swales can protect bare soil from channelized runoff while vegetation
is established. Nets and blankets also can capture a great deal of sediment due to their open, porous structure. Nets and blankets can be used to permanently stabilize channels and may provide a cost-
effective, environmentally preferable alternative to riprap. 100 percent
synthetic blankets manufactured for use in ditches may be easily
reused as temporary ditch liners.
Disadvantages of blankets include:
• Surface preparation required.
• On slopes steeper than 2.5H:1V, blanket installers may need to be
roped and harnessed for safety.
• They cost at least $4,000-6,000 per acre installed.
Advantages of blankets include:
• Installation without mobilizing special equipment.
• Installation by anyone with minimal training
• Installation in stages or phases as the project progresses.
• Installers can hand place seed and fertilizer as they progress down the slope.
• Installation in any weather.
• There are numerous types of blankets that can be designed with
various parameters in mind. Those parameters include: fiber blend,
mesh strength, longevity, biodegradability, cost, and availability.
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Design and Installation
Specifications
• See Figure 4.1.3 and Figure 4.1.4 for typical orientation and installation of blankets used in channels and as slope protection. Note:
these are typical only; all blankets must be installed per
manufacturer’s installation instructions.
• Installation is critical to the effectiveness of these products. If good ground contact is not achieved, runoff can concentrate under the product, resulting in significant erosion.
• Installation of Blankets on Slopes:
1. Complete final grade and track walk up and down the slope.
2. Install hydromulch with seed and fertilizer.
3. Dig a small trench, approximately 12 inches wide by 6 inches deep along the top of the slope.
4. Install the leading edge of the blanket into the small trench and
staple approximately every 18 inches. NOTE: Staples are metal,
“U”-shaped, and a minimum of 6 inches long. Longer staples are used in sandy soils. Biodegradable stakes are also available.
5. Roll the blanket slowly down the slope as installer walks
backwards. NOTE: The blanket rests against the installer’s legs.
Staples are installed as the blanket is unrolled. It is critical that the
proper staple pattern is used for the blanket being installed. The blanket is not to be allowed to roll down the slope on its own as this stretches the blanket making it impossible to maintain soil
contact. In addition, no one is allowed to walk on the blanket after
it is in place.
6. If the blanket is not long enough to cover the entire slope length, the trailing edge of the upper blanket should overlap the leading edge of the lower blanket and be stapled. On steeper slopes, this
overlap should be installed in a small trench, stapled, and covered
with soil.
• With the variety of products available, it is impossible to cover all the details of appropriate use and installation. Therefore, it is critical that
the design engineer consult the manufacturer's information and that a
site visit takes place in order to ensure that the product specified is
appropriate. Information is also available at the following web sites:
1. WSDOT (Section 3.2.4):
http://www.wsdot.wa.gov/NR/rdonlyres/3B41E087-FA86-4717-
932D-D7A8556CCD57/0/ErosionTrainingManual.pdf
2. Texas Transportation Institute:
http://www.txdot.gov/business/doing_business/product_evaluation/
erosion_control.htm
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• Use jute matting in conjunction with mulch (BMP C121). Excelsior, woven straw blankets and coir (coconut fiber) blankets may be
installed without mulch. There are many other types of erosion control
nets and blankets on the market that may be appropriate in certain
circumstances.
• In general, most nets (e.g., jute matting) require mulch in order to prevent erosion because they have a fairly open structure. Blankets
typically do not require mulch because they usually provide complete
protection of the surface.
• Extremely steep, unstable, wet, or rocky slopes are often appropriate candidates for use of synthetic blankets, as are riverbanks, beaches and other high-energy environments. If synthetic blankets are used, the soil
should be hydromulched first.
• 100-percent biodegradable blankets are available for use in sensitive
areas. These organic blankets are usually held together with a paper or fiber mesh and stitching which may last up to a year.
• Most netting used with blankets is photodegradable, meaning they
break down under sunlight (not UV stabilized). However, this process
can take months or years even under bright sun. Once vegetation is
established, sunlight does not reach the mesh. It is not uncommon to find non-degraded netting still in place several years after installation. This can be a problem if maintenance requires the use of mowers or
ditch cleaning equipment. In addition, birds and small animals can
become trapped in the netting.
Maintenance Standards • Maintain good contact with the ground. Erosion must not occur beneath the net or blanket.
• Repair and staple any areas of the net or blanket that are damaged or
not in close contact with the ground.
• Fix and protect eroded areas if erosion occurs due to poorly controlled
drainage.
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Min. 2“Overlap
Slope surface shall be smooth beforeplacement for proper soil contact.
Stapling pattern as permanufacturer’s recommendations.
Do not stretch blankets/mattings tight -allow the rolls to mold to any irregularities.
For slopes less than 3H:1V, rollsmay be placed in horizontal strips.
If there is a berm at thetop of slope, anchorupslope of the berm.
Anchor in 6"x6" min. Trenchand staple at 12" intervals.
Min. 6" overlap.
Staple overlapsmax. 5" spacing.
Bring material down to a level area, turnthe end under 4" and staple at 12" intervals.
Lime, fertilize, and seed before installation.Planting of shrubs, trees, etc. Should occurafter installation.
Figure 4.1.3 – Channel Installation
Figure 4.1.4 – Slope Installation
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BMP C123: Plastic Covering
Purpose Plastic covering provides immediate, short-term erosion protection to
slopes and disturbed areas.
Conditions of Use Plastic covering may be used on disturbed areas that require cover
measures for less than 30 days, except as stated below.
• Plastic is particularly useful for protecting cut and fill slopes and stockpiles. Note: The relatively rapid breakdown of most polyethylene
sheeting makes it unsuitable for long-term (greater than six months)
applications.
• Due to rapid runoff caused by plastic covering, do not use this method upslope of areas that might be adversely impacted by concentrated runoff. Such areas include steep and/or unstable slopes.
• Plastic sheeting may result in increased runoff volumes and velocities,
requiring additional on-site measures to counteract the increases.
Creating a trough with wattles or other material can convey clean water away from these areas.
• To prevent undercutting, trench and backfill rolled plastic covering
products.
• While plastic is inexpensive to purchase, the added cost of
installation, maintenance, removal, and disposal make this an expensive material, up to $1.50-2.00 per square yard.
• Whenever plastic is used to protect slopes install water collection
measures at the base of the slope. These measures include plastic-
covered berms, channels, and pipes used to covey clean rainwater
away from bare soil and disturbed areas. Do not mix clean runoff from a plastic covered slope with dirty runoff from a project.
• Other uses for plastic include:
1. Temporary ditch liner.
2. Pond liner in temporary sediment pond.
3. Liner for bermed temporary fuel storage area if plastic is not reactive to the type of fuel being stored.
4. Emergency slope protection during heavy rains.
5. Temporary drainpipe (“elephant trunk”) used to direct water.
Design and Installation Specifications
• Plastic slope cover must be installed as follows:
1. Run plastic up and down slope, not across slope.
2. Plastic may be installed perpendicular to a slope if the slope length
is less than 10 feet.
3. Minimum of 8-inch overlap at seams.
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4. On long or wide slopes, or slopes subject to wind, tape all seams.
5. Place plastic into a small (12-inch wide by 6-inch deep) slot trench
at the top of the slope and backfill with soil to keep water from
flowing underneath.
6. Place sand filled burlap or geotextile bags every 3 to 6 feet along seams and tie them together with twine to hold them in place.
7. Inspect plastic for rips, tears, and open seams regularly and repair
immediately. This prevents high velocity runoff from contacting
bare soil which causes extreme erosion.
8. Sandbags may be lowered into place tied to ropes. However, all sandbags must be staked in place.
• Plastic sheeting shall have a minimum thickness of 0.06 millimeters.
• If erosion at the toe of a slope is likely, a gravel berm, riprap, or other
suitable protection shall be installed at the toe of the slope in order to
reduce the velocity of runoff.
Maintenance Standards • Torn sheets must be replaced and open seams repaired.
• Completely remove and replace the plastic if it begins to deteriorate
due to ultraviolet radiation.
• Completely remove plastic when no longer needed.
• Dispose of old tires used to weight down plastic sheeting appropriately.
Approved as
Equivalent
Ecology has approved products as able to meet the requirements of BMP
C123. The products did not pass through the Technology Assessment
Protocol – Ecology (TAPE) process. Local jurisdictions may choose not
to accept this product approved as equivalent, or may require additional testing prior to consideration for local use. The products are available for review on Ecology’s website at
http://www.ecy.wa.gov/programs/wq/stormwater/newtech/equivalent.html
BMP C124: Sodding
Purpose The purpose of sodding is to establish permanent turf for immediate erosion protection and to stabilize drainage ways where concentrated
overland flow will occur.
Conditions of Use Sodding may be used in the following areas:
• Disturbed areas that require short-term or long-term cover.
• Disturbed areas that require immediate vegetative cover.
• All waterways that require vegetative lining. Waterways may also be
seeded rather than sodded, and protected with a net or blanket.
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Design and Installation
Specifications
Sod shall be free of weeds, of uniform thickness (approximately 1-inch thick), and shall have a dense root mat for mechanical strength.
The following steps are recommended for sod installation:
• Shape and smooth the surface to final grade in accordance with the
approved grading plan. The swale needs to be overexcavated 4 to 6 inches below design elevation to allow room for placing soil amendment and sod.
• Amend 4 inches (minimum) of compost into the top 8 inches of the
soil if the organic content of the soil is less than ten percent or the
permeability is less than 0.6 inches per hour. See http://www.ecy.wa.gov/programs/swfa/organics/soil.html for further information.
• Fertilize according to the supplier's recommendations.
• Work lime and fertilizer 1 to 2 inches into the soil, and smooth the
surface.
• Lay strips of sod beginning at the lowest area to be sodded and perpendicular to the direction of water flow. Wedge strips securely
into place. Square the ends of each strip to provide for a close, tight fit.
Stagger joints at least 12 inches. Staple on slopes steeper than 3H:1V.
Staple the upstream edge of each sod strip.
• Roll the sodded area and irrigate.
• When sodding is carried out in alternating strips or other patterns, seed
the areas between the sod immediately after sodding.
Maintenance Standards
If the grass is unhealthy, the cause shall be determined and appropriate
action taken to reestablish a healthy groundcover. If it is impossible to establish a healthy groundcover due to frequent saturation, instability, or some other cause, the sod shall be removed, the area seeded with an
appropriate mix, and protected with a net or blanket.
BMP C125: Topsoiling / Composting
Purpose Topsoiling and composting provide a suitable growth medium for final site stabilization with vegetation. While not a permanent cover practice in
itself, topsoiling and composting are an integral component of providing
permanent cover in those areas where there is an unsuitable soil surface
for plant growth. Use this BMP in conjunction with other BMPs such as
seeding, mulching, or sodding.
Native soils and disturbed soils that have been organically amended not
only retain much more stormwater, but they also serve as effective
biofilters for urban pollutants and, by supporting more vigorous plant
growth, reduce the water, fertilizer and pesticides needed to support
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installed landscapes. Topsoil does not include any subsoils but only the material from the top several inches including organic debris.
Conditions of
Use
• Permanent landscaped areas shall contain healthy topsoil that reduces
the need for fertilizers, improves overall topsoil quality, provides for
better vegetal health and vitality, improves hydrologic characteristics, and reduces the need for irrigation.
• Leave native soils and the duff layer undisturbed to the maximum
extent practicable. Stripping of existing, properly functioning soil
system and vegetation for the purpose of topsoiling during
construction is not acceptable. Preserve existing soil systems in undisturbed and uncompacted conditions if functioning properly.
• Areas that already have good topsoil, such as undisturbed areas, do not
require soil amendments.
• Restore, to the maximum extent practical, native soils disturbed during
clearing and grading to a condition equal to or better than the original site condition’s moisture-holding capacity. Use on-site native topsoil, incorporate amendments into on-site soil, or import blended topsoil to
meet this requirement.
• Topsoiling is a required procedure when establishing vegetation on
shallow soils, and soils of critically low pH (high acid) levels.
• Beware of where the topsoil comes from, and what vegetation was on site before disturbance, invasive plant seeds may be included and could
cause problems for establishing native plants, landscaped areas, or
grasses.
• Topsoil from the site will contain mycorrhizal bacteria that are necessary for healthy root growth and nutrient transfer. These native mycorrhiza are acclimated to the site and will provide optimum
conditions for establishing grasses. Use commercially available
mycorrhiza products when using off-site topsoil.
Design and Installation
Specifications
Meet the following requirements for areas requiring disruption and
topsoiling:
• Maximize the depth of the topsoil wherever possible to provide the
maximum possible infiltration capacity and beneficial growth
medium. Topsoil shall have:
• A minimum depth of 8-inches. Scarify subsoils below the topsoil
layer at least 4-inches with some incorporation of the upper
material to avoid stratified layers, where feasible. Ripping or re-
structuring the subgrade may also provide additional benefits
regarding the overall infiltration and interflow dynamics of the soil system.
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• A minimum organic content of 10% dry weight, and 5% organic matter content in turf areas. Incorporate organic amendments to a
minimum 8-inch depth except where tree roots or other natural
features limit the depth of incorporation.
• A pH between 6.0 and 8.0 or matching the pH of the undisturbed soil.
• If blended topsoil is imported, then fines should be limited to 25
percent passing through a 200 sieve.
• Accomplish the required organic content and pH by either returning
native topsoil to the site and/or incorporating organic amendments.
• To meet the organic content use compost that meets the definition of “composted materials” in WAC 173-350-220. This code is
available online at:
http://apps.leg.wa.gov/WAC/default.aspx?cite=173-350-220.
The compost must also have an organic matter content of 35% to 65%, and a carbon to nitrogen ratio below 25H:1V.
The carbon to nitrogen ratio may be as high as 35H:1V for
plantings composed entirely of plants native to the Puget Sound
Lowlands region.
• For till soils use a mixture of approximately two parts soil to one part compost. This equates to 4 inches of compost mixed to a depth of 12 inches in till soils. Increasing the concentration of compost
beyond this level can have negative effects on vegetal health, while
decreasing the concentrations can reduce the benefits of amended
soils.
• Gravel or cobble outwash soils, may require different approaches. Organics and fines easily migrate through the loose structure of
these soils. Therefore, the importation of at least 6 inches of
quality topsoil, underlain by some type of filter fabric to prevent
the migration of fines, may be more appropriate for these soils.
• The final composition and construction of the soil system will result in
a natural selection or favoring of certain plant species over time. For
example, incorporation of topsoil may favor grasses, while layering
with mildly acidic, high-carbon amendments may favor more woody
vegetation.
• Allow sufficient time in scheduling for topsoil spreading prior to
seeding, sodding, or planting.
• Take care when applying top soil to subsoils with contrasting textures.
Sandy topsoil over clayey subsoil is a particularly poor combination,
as water creeps along the junction between the soil layers and causes the topsoil to slough. If topsoil and subsoil are not properly bonded,
water will not infiltrate the soil profile evenly and it will be difficult to
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establish vegetation. The best method to prevent a lack of bonding is to actually work the topsoil into the layer below for a depth of at least
6 inches.
• Field exploration of the site shall be made to determine if there is
surface soil of sufficient quantity and quality to justify stripping. Topsoil shall be friable and loamy (loam, sandy loam, silt loam, sandy clay loam, and clay loam). Avoid areas of natural ground water
recharge.
• Stripping shall be confined to the immediate construction area. A 4-
inch to 6-inch stripping depth is common, but depth may vary depending on the particular soil. All surface runoff control structures shall be in place prior to stripping.
• Do not place topsoil while in a frozen or muddy condition, when the
subgrade is excessively wet, or when conditions exist that may
otherwise be detrimental to proper grading or proposed sodding or seeding.
• In any areas requiring grading remove and stockpile the duff layer and
topsoil on site in a designated, controlled area, not adjacent to public
resources and critical areas. Stockpiled topsoil is to be reapplied to
other portions of the site where feasible.
• Locate the topsoil stockpile so that it meets specifications and does not interfere with work on the site. It may be possible to locate more than
one pile in proximity to areas where topsoil will be used.
Stockpiling of topsoil shall occur in the following manner:
• Side slopes of the stockpile shall not exceed 2H:1V.
• Between October 1 and April 30:
• An interceptor dike with gravel outlet and silt fence shall
surround all topsoil.
• Within 2 days complete erosion control seeding, or covering
stockpiles with clear plastic, or other mulching materials.
• Between May 1 and September 30:
• An interceptor dike with gravel outlet and silt fence shall
surround all topsoil if the stockpile will remain in place for a
longer period of time than active construction grading.
• Within 7 days complete erosion control seeding, or covering stockpiles with clear plastic, or other mulching materials.
• When native topsoil is to be stockpiled and reused the following
should apply to ensure that the mycorrhizal bacterial, earthworms, and
other beneficial organisms will not be destroyed:
1. Re-install topsoil within 4 to 6 weeks.
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2. Do not allow the saturation of topsoil with water.
3. Do not use plastic covering.
Maintenance
Standards
• Inspect stockpiles regularly, especially after large storm events.
Stabilize any areas that have eroded.
• Establish soil quality and depth toward the end of construction and once established, protect from compaction, such as from large machinery use, and from erosion.
• Plant and mulch soil after installation.
• Leave plant debris or its equivalent on the soil surface to replenish
organic matter.
• Reduce and adjust, where possible, the use of irrigation, fertilizers, herbicides and pesticides, rather than continuing to implement
formerly established practices.
BMP C126: Polyacrylamide (PAM) for Soil Erosion Protection
Purpose Polyacrylamide (PAM) is used on construction sites to prevent soil erosion.
Applying PAM to bare soil in advance of a rain event significantly reduces
erosion and controls sediment in two ways. First, PAM increases the soil’s
available pore volume, thus increasing infiltration through flocculation
and reducing the quantity of stormwater runoff. Second, it increases flocculation of suspended particles and aids in their deposition, thus reducing stormwater runoff turbidity and improving water quality.
Conditions of Use PAM shall not be directly applied to water or allowed to enter a water
body.
In areas that drain to a sediment pond, PAM can be applied to bare soil under the following conditions:
• During rough grading operations.
• In Staging areas.
• Balanced cut and fill earthwork.
• Haul roads prior to placement of crushed rock surfacing.
• Compacted soil roadbase.
• Stockpiles.
• After final grade and before paving or final seeding and planting.
• Pit sites.
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• Sites having a winter shut down. In the case of winter shut down, or where soil will remain unworked for several months, PAM should be
used together with mulch.
Design and Installation Specifications
PAM may be applied with water in dissolved form. The preferred
application method is the dissolved form.
PAM is to be applied at a maximum rate of 2/3 pound PAM per 1,000 gallons water (80 mg/L) per 1 acre of bare soil. Table 4.1.9 can be used to
determine the PAM and water application rate for a disturbed soil area.
Higher concentrations of PAM do not provide any additional effectiveness.
Table 4.1.9
PAM and Water Application Rates
Disturbed Area (ac) PAM (lbs) Water (gal)
0.50 0.33 500 1.00 0.66 1,000
1.50 1.00 1,500 2.00 1.32 2,000
2.50 1.65 2,500 3.00 2.00 3,000
3.50 2.33 3,500 4.00 2.65 4,000
4.50 3.00 4,500 5.00 3.33 5,000
The Preferred Method:
• Pre-measure the area where PAM is to be applied and calculate the amount of product and water necessary to provide coverage at the
specified application rate (2/3 pound PAM/1000 gallons/acre).
• PAM has infinite solubility in water, but dissolves very slowly.
Dissolve pre-measured dry granular PAM with a known quantity of clean water in a bucket several hours or overnight. Mechanical mixing will help dissolve the PAM. Always add PAM to water - not water to
PAM.
• Pre-fill the water truck about 1/8 full with water. The water does not
have to be potable, but it must have relatively low turbidity – in the range of 20 NTU or less.
• Add PAM /Water mixture to the truck
• Completely fill the water truck to specified volume.
• Spray PAM/Water mixture onto dry soil until the soil surface is
uniformly and completely wetted.
An Alternate Method:
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PAM may also be applied as a powder at the rate of 5 lbs. per acre. This must be applied on a day that is dry. For areas less than 5-10 acres, a hand-
held “organ grinder” fertilizer spreader set to the smallest setting will
work. Tractor-mounted spreaders will work for larger areas.
The following shall be used for application of powdered PAM:
• Powered PAM shall be used in conjunction with other BMPs and not in place of other BMPs.
• Do not use PAM on a slope that flows directly into a stream or
wetland. The stormwater runoff shall pass through a sediment control
BMP prior to discharging to surface waters.
• Do not add PAM to water discharging from site.
• When the total drainage area is greater than or equal to 5 acres, PAM
treated areas shall drain to a sediment pond.
• Areas less than 5 acres shall drain to sediment control BMPs, such as a
minimum of 3 check dams per acre. The total number of check dams used shall be maximized to achieve the greatest amount of settlement of sediment prior to discharging from the site. Each check dam shall
be spaced evenly in the drainage channel through which stormwater
flows are discharged off-site.
• On all sites, the use of silt fence shall be maximized to limit the discharges of sediment from the site.
• All areas not being actively worked shall be covered and protected
from rainfall. PAM shall not be the only cover BMP used.
• PAM can be applied to wet soil, but dry soil is preferred due to less
sediment loss.
• PAM will work when applied to saturated soil but is not as effective as
applications to dry or damp soil.
• Keep the granular PAM supply out of the sun. Granular PAM loses its
effectiveness in three months after exposure to sunlight and air.
• Proper application and re-application plans are necessary to ensure total effectiveness of PAM usage.
• PAM, combined with water, is very slippery and can be a safety
hazard. Care must be taken to prevent spills of PAM powder onto
paved surfaces. During an application of PAM, prevent over-spray
from reaching pavement as pavement will become slippery. If PAM powder gets on skin or clothing, wipe it off with a rough towel rather
than washing with water-this only makes cleanup messier and take
longer.
• Some PAMs are more toxic and carcinogenic than others. Only the most environmentally safe PAM products should be used.
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The specific PAM copolymer formulation must be anionic. Cationic PAM shall not be used in any application because of known
aquatic toxicity problems. Only the highest drinking water grade
PAM, certified for compliance with ANSI/NSF Standard 60 for
drinking water treatment, will be used for soil applications. Recent media attention and high interest in PAM has resulted in some entrepreneurial exploitation of the term "polymer." All PAM are
polymers, but not all polymers are PAM, and not all PAM products
comply with ANSI/NSF Standard 60. PAM use shall be reviewed and
approved by the local permitting authority.
• PAM designated for these uses should be "water soluble" or "linear" or "non-crosslinked". Cross-linked or water absorbent PAM, polymerized
in highly acidic (pH<2) conditions, are used to maintain soil moisture
content.
• The PAM anionic charge density may vary from 2-30 percent; a value of 18 percent is typical. Studies conducted by the United States
Department of Agriculture (USDA)/ARS demonstrated that soil
stabilization was optimized by using very high molecular weight (12-
15 mg/mole), highly anionic (>20% hydrolysis) PAM.
• PAM tackifiers are available and being used in place of guar and alpha plantago. Typically, PAM tackifiers should be used at a rate of no more
than 0.5-1 lb. per 1000 gallons of water in a hydromulch machine. Some
tackifier product instructions say to use at a rate of 3 –5 lbs. per acre,
which can be too much. In addition, pump problems can occur at higher rates due to increased viscosity.
Maintenance
Standards
• PAM may be reapplied on actively worked areas after a 48-hour
period.
• Reapplication is not required unless PAM treated soil is disturbed or
unless turbidity levels show the need for an additional application. If PAM treated soil is left undisturbed a reapplication may be necessary after two months. More PAM applications may be required for steep
slopes, silty and clayey soils (USDA Classification Type "C" and "D"
soils), long grades, and high precipitation areas. When PAM is applied
first to bare soil and then covered with straw, a reapplication may not be necessary for several months.
• Loss of sediment and PAM may be a basis for penalties per RCW
90.48.080.
BMP C130: Surface Roughening
Purpose Surface roughening aids in the establishment of vegetative cover, reduces runoff velocity, increases infiltration, and provides for sediment trapping
through the provision of a rough soil surface. Horizontal depressions are
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created by operating a tiller or other suitable equipment on the contour or by leaving slopes in a roughened condition by not fine grading them.
Use this BMP in conjunction with other BMPs such as seeding, mulching,
or sodding.
Conditions for Use • All slopes steeper than 3H:1V and greater than 5 vertical feet require surface roughening to a depth of 2 to 4 inches prior to seeding..
• Areas that will not be stabilized immediately may be roughened to
reduce runoff velocity until seeding takes place.
• Slopes with a stable rock face do not require roughening.
• Slopes where mowing is planned should not be excessively roughened.
Design and
Installation
Specifications
There are different methods for achieving a roughened soil surface on a
slope, and the selection of an appropriate method depends upon the type of
slope. Roughening methods include stair-step grading, grooving, contour
furrows, and tracking. See Figure 4.1.5 for tracking and contour furrows. Factors to be considered in choosing a method are slope steepness, mowing requirements, and whether the slope is formed by cutting or filling.
• Disturbed areas that will not require mowing may be stair-step graded,
grooved, or left rough after filling.
• Stair-step grading is particularly appropriate in soils containing large amounts of soft rock. Each "step" catches material that sloughs from above, and provides a level site where vegetation can become
established. Stairs should be wide enough to work with standard earth
moving equipment. Stair steps must be on contour or gullies will form
on the slope.
• Areas that will be mowed (these areas should have slopes less steep than 3H:1V) may have small furrows left by disking, harrowing,
raking, or seed-planting machinery operated on the contour.
• Graded areas with slopes steeper than 3H:1V but less than 2H:1V
should be roughened before seeding. This can be accomplished in a variety of ways, including "track walking," or driving a crawler tractor
up and down the slope, leaving a pattern of cleat imprints parallel to
slope contours.
• Tracking is done by operating equipment up and down the slope to
leave horizontal depressions in the soil.
Maintenance Standards
• Areas that are graded in this manner should be seeded as quickly as
possible.
• Regular inspections should be made of the area. If rills appear, they
should be re-graded and re-seeded immediately.
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Figure 4.1.5 – Surface Roughening by Tracking and Contour Furrows
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BMP C131: Gradient Terraces
Purpose Gradient terraces reduce erosion damage by intercepting surface runoff
and conducting it to a stable outlet at a non-erosive velocity.
Conditions of Use • Gradient terraces normally are limited to denuded land having a water
erosion problem. They should not be constructed on deep sands or on soils that are too stony, steep, or shallow to permit practical and economical installation and maintenance. Gradient terraces may be
used only where suitable outlets are or will be made available. See
Figure 4.1.6 for gradient terraces.
Design and Installation Specifications
• The maximum vertical spacing of gradient terraces should be determined by the following method:
VI = (0.8)s + y
Where: VI = vertical interval in feet
s = land rise per 100 feet, expressed in feet
y = a soil and cover variable with values from 1.0 to 4.0
Values of “y” are influenced by soil erodibility and cover practices.
The lower values are applicable to erosive soils where little to no
residue is left on the surface. The higher value is applicable only to
erosion-resistant soils where a large amount of residue (1½ tons of straw/acre equivalent) is on the surface.
• The minimum constructed cross-section should meet the design
dimensions.
• The top of the constructed ridge should not be lower at any point than
the design elevation plus the specified overfill for settlement. The opening at the outlet end of the terrace should have a cross section equal to that specified for the terrace channel.
• Channel grades may be either uniform or variable with a maximum
grade of 0.6 feet per 100 feet length (0.6%). For short distances,
terrace grades may be increased to improve alignment. The channel velocity should not exceed that which is nonerosive for the soil type.
• All gradient terraces should have adequate outlets. Such an outlet may
be a grassed waterway, vegetated area, or tile outlet. In all cases the
outlet must convey runoff from the terrace or terrace system to a point
where the outflow will not cause damage. Vegetative cover should be used in the outlet channel.
• The design elevation of the water surface of the terrace should not be
lower than the design elevation of the water surface in the outlet at
their junction, when both are operating at design flow.
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Slope to adequate outlet.
10' min.
• Vertical spacing determined by the above methods may be increased as much as 0.5 feet or 10 percent, whichever is greater, to provide
better alignment or location, to avoid obstacles, to adjust for
equipment size, or to reach a satisfactory outlet. The drainage area
above the terrace should not exceed the area that would be drained by a terrace with normal spacing.
• The terrace should have enough capacity to handle the peak runoff
expected from a 2-year, 24-hour design storm without overtopping.
• The terrace cross-section should be proportioned to fit the land slope.
The ridge height should include a reasonable settlement factor. The ridge should have a minimum top width of 3 feet at the design height. The minimum cross-sectional area of the terrace channel should be
8 square feet for land slopes of 5 percent or less, 7 square feet for
slopes from 5 to 8 percent, and 6 square feet for slopes steeper than
8 percent. The terrace can be constructed wide enough to be maintained using a small vehicle.
Maintenance
Standards
• Maintenance should be performed as needed. Terraces should be
inspected regularly; at least once a year, and after large storm events.
Figure 4.1.6 – Gradient Terraces
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BMP C140: Dust Control
Purpose Dust control prevents wind transport of dust from disturbed soil surfaces
onto roadways, drainage ways, and surface waters.
Conditions of Use • In areas (including roadways) subject to surface and air movement of
dust where on-site and off-site impacts to roadways, drainage ways, or surface waters are likely.
Design and
Installation
Specifications
• Vegetate or mulch areas that will not receive vehicle traffic. In areas
where planting, mulching, or paving is impractical, apply gravel or
landscaping rock.
• Limit dust generation by clearing only those areas where immediate activity will take place, leaving the remaining area(s) in the original condition. Maintain the original ground cover as long as practical.
• Construct natural or artificial windbreaks or windscreens. These may
be designed as enclosures for small dust sources.
• Sprinkle the site with water until surface is wet. Repeat as needed. To prevent carryout of mud onto street, refer to Stabilized Construction Entrance (BMP C105).
• Irrigation water can be used for dust control. Irrigation systems should
be installed as a first step on sites where dust control is a concern.
• Spray exposed soil areas with a dust palliative, following the manufacturer’s instructions and cautions regarding handling and application. Used oil is prohibited from use as a dust suppressant.
Local governments may approve other dust palliatives such as calcium
chloride or PAM.
• PAM (BMP C126) added to water at a rate of 0.5 lbs. per 1,000 gallons of water per acre and applied from a water truck is more effective than water alone. This is due to increased infiltration of water
into the soil and reduced evaporation. In addition, small soil particles
are bonded together and are not as easily transported by wind. Adding
PAM may actually reduce the quantity of water needed for dust control. Use of PAM could be a cost-effective dust control method.
Techniques that can be used for unpaved roads and lots include:
• Lower speed limits. High vehicle speed increases the amount of dust
stirred up from unpaved roads and lots.
• Upgrade the road surface strength by improving particle size, shape, and mineral types that make up the surface and base materials.
• Add surface gravel to reduce the source of dust emission. Limit the
amount of fine particles (those smaller than .075 mm) to 10 to 20
percent.
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• Use geotextile fabrics to increase the strength of new roads or roads undergoing reconstruction.
• Encourage the use of alternate, paved routes, if available.
• Restrict use of paved roadways by tracked vehicles and heavy trucks
to prevent damage to road surface and base.
• Apply chemical dust suppressants using the admix method, blending the product with the top few inches of surface material. Suppressants
may also be applied as surface treatments.
• Pave unpaved permanent roads and other trafficked areas.
• Use vacuum street sweepers.
• Remove mud and other dirt promptly so it does not dry and then turn into dust.
• Limit dust-causing work on windy days.
• Contact your local Air Pollution Control Authority for guidance and
training on other dust control measures. Compliance with the local Air Pollution Control Authority constitutes compliance with this BMP.
Maintenance
Standards
Respray area as necessary to keep dust to a minimum.
BMP C150: Materials on Hand
Purpose Keep quantities of erosion prevention and sediment control materials on the project site at all times to be used for regular maintenance and emergency situations such as unexpected heavy summer rains. Having
these materials on-site reduces the time needed to implement BMPs when
inspections indicate that existing BMPs are not meeting the Construction
SWPPP requirements. In addition, contractors can save money by buying some materials in bulk and storing them at their office or yard.
Conditions of Use • Construction projects of any size or type can benefit from having
materials on hand. A small commercial development project could
have a roll of plastic and some gravel available for immediate
protection of bare soil and temporary berm construction. A large earthwork project, such as highway construction, might have several
tons of straw, several rolls of plastic, flexible pipe, sandbags,
geotextile fabric and steel “T” posts.
• Materials are stockpiled and readily available before any site clearing,
grubbing, or earthwork begins. A large contractor or developer could keep a stockpile of materials that are available for use on several
projects.
• If storage space at the project site is at a premium, the contractor could
maintain the materials at their office or yard. The office or yard must
be less than an hour from the project site.
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Design and Installation
Specifications
Depending on project type, size, complexity, and length, materials and quantities will vary. A good minimum list of items that will cover
numerous situations includes:
Material
Clear Plastic, 6 mil
Drainpipe, 6 or 8 inch diameter
Sandbags, filled
Straw Bales for mulching,
Quarry Spalls
Washed Gravel Geotextile Fabric
Catch Basin Inserts
Steel “T” Posts
Silt fence material
Straw Wattles
Maintenance Standards • All materials with the exception of the quarry spalls, steel “T” posts,
and gravel should be kept covered and out of both sun and rain.
• Re-stock materials used as needed.
BMP C151: Concrete Handling
Purpose Concrete work can generate process water and slurry that contain fine
particles and high pH, both of which can violate water quality standards in
the receiving water. Concrete spillage or concrete discharge to surface waters of the State is prohibited. Use this BMP to minimize and eliminate
concrete, concrete process water, and concrete slurry from entering waters
of the state.
Conditions of Use Any time concrete is used, utilize these management practices. Concrete
construction projects include, but are not limited to, the following:
• Curbs
• Sidewalks
• Roads
• Bridges
• Foundations
• Floors
• Runways
Design and
Installation
• Wash out concrete truck chutes, pumps, and internals into formed
areas only. Assure that washout of concrete trucks is performed off-
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Specifications site or in designated concrete washout areas. Do not wash out concrete trucks onto the ground, or into storm drains, open ditches, streets, or
streams. Refer to BMP C154 for information on concrete washout
areas.
• Return unused concrete remaining in the truck and pump to the originating batch plant for recycling. Do not dump excess concrete on site, except in designated concrete washout areas.
• Wash off hand tools including, but not limited to, screeds, shovels,
rakes, floats, and trowels into formed areas only.
• Wash equipment difficult to move, such as concrete pavers in areas that do not directly drain to natural or constructed stormwater conveyances.
• Do not allow washdown from areas, such as concrete aggregate
driveways, to drain directly to natural or constructed stormwater
conveyances.
• Contain washwater and leftover product in a lined container when no formed areas are available,. Dispose of contained concrete in a manner
that does not violate ground water or surface water quality standards.
• Always use forms or solid barriers for concrete pours, such as pilings,
within 15-feet of surface waters.
• Refer to BMPs C252 and C253 for pH adjustment requirements.
• Refer to the Construction Stormwater General Permit for pH
monitoring requirements if the project involves one of the following
activities:
• Significant concrete work (greater than 1,000 cubic yards poured concrete or recycled concrete used over the life of a project).
• The use of engineered soils amended with (but not limited to)
Portland cement-treated base, cement kiln dust or fly ash.
• Discharging stormwater to segments of water bodies on the 303(d)
list (Category 5) for high pH.
Maintenance Standards
Check containers for holes in the liner daily during concrete pours and
repair the same day.
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BMP C152: Sawcutting and Surfacing Pollution Prevention
Purpose Sawcutting and surfacing operations generate slurry and process water
that contains fine particles and high pH (concrete cutting), both of which
can violate the water quality standards in the receiving water. Concrete
spillage or concrete discharge to surface waters of the State is prohibited. Use this BMP to minimize and eliminate process water and slurry created through sawcutting or surfacing from entering waters of the State.
Conditions of Use Utilize these management practices anytime sawcutting or surfacing
operations take place. Sawcutting and surfacing operations include, but
are not limited to, the following:
• Sawing
• Coring
• Grinding
• Roughening
• Hydro-demolition
• Bridge and road surfacing
Design and
Installation
Specifications
• Vacuum slurry and cuttings during cutting and surfacing operations.
• Slurry and cuttings shall not remain on permanent concrete or asphalt
pavement overnight.
• Slurry and cuttings shall not drain to any natural or constructed drainage conveyance including stormwater systems. This may require temporarily blocking catch basins.
• Dispose of collected slurry and cuttings in a manner that does not
violate ground water or surface water quality standards.
• Do not allow process water generated during hydro-demolition, surface roughening or similar operations to drain to any natural or constructed drainage conveyance including stormwater systems.
Dispose process water in a manner that does not violate ground water
or surface water quality standards.
• Handle and dispose cleaning waste material and demolition debris in a manner that does not cause contamination of water. Dispose of
sweeping material from a pick-up sweeper at an appropriate disposal
site.
Maintenance Standards Continually monitor operations to determine whether slurry, cuttings, or
process water could enter waters of the state. If inspections show that a violation of water quality standards could occur, stop operations and
immediately implement preventive measures such as berms, barriers,
secondary containment, and vacuum trucks.
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BMP C153: Material Delivery, Storage and Containment
Purpose Prevent, reduce, or eliminate the discharge of pollutants to the
stormwater system or watercourses from material delivery and storage. Minimize the storage of hazardous materials on-site, store materials in a
designated area, and install secondary containment.
Conditions of Use These procedures are suitable for use at all construction sites with
delivery and storage of the following materials:
• Petroleum products such as fuel, oil and grease
• Soil stabilizers and binders (e.g. Polyacrylamide)
• Fertilizers, pesticides and herbicides
• Detergents
• Asphalt and concrete compounds
• Hazardous chemicals such as acids, lime, adhesives, paints, solvents and curing compounds
• Any other material that may be detrimental if released to the environment
Design and Installation
Specifications
The following steps should be taken to minimize risk:
• Temporary storage area should be located away from vehicular traffic,
near the construction entrance(s), and away from waterways or storm drains.
• Material Safety Data Sheets (MSDS) should be supplied for all materials stored. Chemicals should be kept in their original labeled
containers.
• Hazardous material storage on-site should be minimized.
• Hazardous materials should be handled as infrequently as possible.
• During the wet weather season (Oct 1 – April 30), consider storing
materials in a covered area.
• Materials should be stored in secondary containments, such as earthen
dike, horse trough, or even a children’s wading pool for non-reactive materials such as detergents, oil, grease, and paints. Small amounts of
material may be secondarily contained in “bus boy” trays or concrete mixing trays.
• Do not store chemicals, drums, or bagged materials directly on the ground. Place these items on a pallet and, when possible, and within secondary containment.
• If drums must be kept uncovered, store them at a slight angle to reduce ponding of rainwater on the lids to reduce corrosion. Domed plastic covers are inexpensive and snap to the top of drums, preventing water from collecting.
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Material Storage Areas and Secondary Containment Practices:
• Liquids, petroleum products, and substances listed in 40 CFR Parts 110, 117, or 302 shall be stored in approved containers and drums and
shall not be overfilled. Containers and drums shall be stored in temporary secondary containment facilities.
• Temporary secondary containment facilities shall provide for a spill containment volume able to contain 10% of the total enclosed
container volume of all containers, or 110% of the capacity of the largest container within its boundary, whichever is greater.
• Secondary containment facilities shall be impervious to the materials stored therein for a minimum contact time of 72 hours.
• Secondary containment facilities shall be maintained free of accumulated rainwater and spills. In the event of spills or leaks,
accumulated rainwater and spills shall be collected and placed into drums. These liquids shall be handled as hazardous waste unless testing determines them to be non-hazardous.
• Sufficient separation should be provided between stored containers to allow for spill cleanup and emergency response access.
• During the wet weather season (Oct 1 – April 30), each secondary containment facility shall be covered during non-working days, prior
to and during rain events.
• Keep material storage areas clean, organized and equipped with an
ample supply of appropriate spill clean-up material (spill kit).
• The spill kit should include, at a minimum:
• 1-Water Resistant Nylon Bag
• 3-Oil Absorbent Socks 3”x 4’
• 2-Oil Absorbent Socks 3”x 10’
• 12-Oil Absorbent Pads 17”x19”
• 1-Pair Splash Resistant Goggles
• 3-Pair Nitrile Gloves
• 10-Disposable Bags with Ties
• Instructions
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BMP C154: Concrete Washout Area
Purpose Prevent or reduce the discharge of pollutants to stormwater from concrete
waste by conducting washout off-site, or performing on-site washout in a
designated area to prevent pollutants from entering surface waters or
ground water.
Conditions of Use Concrete washout area best management practices are implemented on construction projects where:
• Concrete is used as a construction material
• It is not possible to dispose of all concrete wastewater and washout
off-site (ready mix plant, etc.).
• Concrete trucks, pumpers, or other concrete coated equipment are washed on-site.
• Note: If less than 10 concrete trucks or pumpers need to be washed out
on-site, the washwater may be disposed of in a formed area awaiting
concrete or an upland disposal site where it will not contaminate surface or ground water. The upland disposal site shall be at least 50 feet from sensitive areas such as storm drains, open ditches, or water
bodies, including wetlands.
Design and Installation Specifications
Implementation
The following steps will help reduce stormwater pollution from concrete wastes:
• Perform washout of concrete trucks off-site or in designated concrete
washout areas only.
• Do not wash out concrete trucks onto the ground, or into storm drains,
open ditches, streets, or streams.
• Do not allow excess concrete to be dumped on-site, except in designated concrete washout areas.
• Concrete washout areas may be prefabricated concrete washout
containers, or self-installed structures (above-grade or below-grade).
• Prefabricated containers are most resistant to damage and protect against spills and leaks. Companies may offer delivery service and
provide regular maintenance and disposal of solid and liquid waste.
• If self-installed concrete washout areas are used, below-grade
structures are preferred over above-grade structures because they are
less prone to spills and leaks.
• Self-installed above-grade structures should only be used if excavation
is not practical.
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Education
• Discuss the concrete management techniques described in this BMP
with the ready-mix concrete supplier before any deliveries are made.
• Educate employees and subcontractors on the concrete waste
management techniques described in this BMP.
• Arrange for contractor’s superintendent or Certified Erosion and Sediment Control Lead (CESCL) to oversee and enforce concrete
waste management procedures.
• A sign should be installed adjacent to each temporary concrete
washout facility to inform concrete equipment operators to utilize the proper facilities.
Contracts
Incorporate requirements for concrete waste management into concrete
supplier and subcontractor agreements.
Location and Placement
• Locate washout area at least 50 feet from sensitive areas such as storm drains, open ditches, or water bodies, including wetlands.
• Allow convenient access for concrete trucks, preferably near the area
where the concrete is being poured.
• If trucks need to leave a paved area to access washout, prevent track-out with a pad of rock or quarry spalls (see BMP C105). These areas should be far enough away from other construction traffic to reduce
the likelihood of accidental damage and spills.
• The number of facilities you install should depend on the expected
demand for storage capacity.
• On large sites with extensive concrete work, washouts should be placed in multiple locations for ease of use by concrete truck drivers.
On-site Temporary Concrete Washout Facility, Transit Truck
Washout Procedures:
• Temporary concrete washout facilities shall be located a minimum of 50 ft from sensitive areas including storm drain inlets, open drainage
facilities, and watercourses. See Figures 4.1.7 and 4.1.8.
• Concrete washout facilities shall be constructed and maintained in
sufficient quantity and size to contain all liquid and concrete waste
generated by washout operations.
• Approximately 7 gallons of wash water are used to wash one truck
chute.
• Approximately 50 gallons are used to wash out the hopper of a
concrete pump truck.
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• Washout of concrete trucks shall be performed in designated areas only.
• Concrete washout from concrete pumper bins can be washed into
concrete pumper trucks and discharged into designated washout area
or properly disposed of off-site.
• Once concrete wastes are washed into the designated area and allowed to harden, the concrete should be broken up, removed, and disposed of
per applicable solid waste regulations. Dispose of hardened concrete
on a regular basis.
• Temporary Above-Grade Concrete Washout Facility
• Temporary concrete washout facility (type above grade) should be constructed as shown on the details below, with a recommended
minimum length and minimum width of 10 ft, but with sufficient
quantity and volume to contain all liquid and concrete waste
generated by washout operations.
• Plastic lining material should be a minimum of 10 mil polyethylene sheeting and should be free of holes, tears, or other
defects that compromise the impermeability of the material.
• Temporary Below-Grade Concrete Washout Facility
• Temporary concrete washout facilities (type below grade) should be constructed as shown on the details below, with a recommended minimum length and minimum width of 10 ft. The quantity and
volume should be sufficient to contain all liquid and concrete
waste generated by washout operations.
• Lath and flagging should be commercial type.
• Plastic lining material shall be a minimum of 10 mil polyethylene sheeting and should be free of holes, tears, or other defects that
compromise the impermeability of the material.
• Liner seams shall be installed in accordance with manufacturers’
recommendations.
• Soil base shall be prepared free of rocks or other debris that may
cause tears or holes in the plastic lining material.
Maintenance
Standards
Inspection and Maintenance
• Inspect and verify that concrete washout BMPs are in place prior to the commencement of concrete work.
• During periods of concrete work, inspect daily to verify continued
performance.
• Check overall condition and performance.
• Check remaining capacity (% full).
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• If using self-installed washout facilities, verify plastic liners are intact and sidewalls are not damaged.
• If using prefabricated containers, check for leaks.
• Washout facilities shall be maintained to provide adequate holding
capacity with a minimum freeboard of 12 inches.
• Washout facilities must be cleaned, or new facilities must be constructed and ready for use once the washout is 75% full.
• If the washout is nearing capacity, vacuum and dispose of the waste
material in an approved manner.
• Do not discharge liquid or slurry to waterways, storm drains or directly onto ground.
• Do not use sanitary sewer without local approval.
• Place a secure, non-collapsing, non-water collecting cover over the
concrete washout facility prior to predicted wet weather to prevent
accumulation and overflow of precipitation.
• Remove and dispose of hardened concrete and return the structure to a functional condition. Concrete may be reused on-site or hauled
away for disposal or recycling.
• When you remove materials from the self-installed concrete washout,
build a new structure; or, if the previous structure is still intact, inspect for signs of weakening or damage, and make any necessary repairs. Re-line the structure with new plastic after each cleaning.
Removal of Temporary Concrete Washout Facilities
• When temporary concrete washout facilities are no longer required for
the work, the hardened concrete, slurries and liquids shall be removed and properly disposed of.
• Materials used to construct temporary concrete washout facilities shall
be removed from the site of the work and disposed of or recycled.
• Holes, depressions or other ground disturbance caused by the removal
of the temporary concrete washout facilities shall be backfilled, repaired, and stabilized to prevent erosion.
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Figure 4.1.7a – Concrete Washout Area
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Figure 4.1.7b – Concrete Washout Area
Figure 4.1.8 – Prefabricated Concrete Washout Container w/Ramp
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BMP C160: Certified Erosion and Sediment Control Lead
Purpose The project proponent designates at least one person as the responsible
representative in charge of erosion and sediment control (ESC), and water
quality protection. The designated person shall be the Certified Erosion
and Sediment Control Lead (CESCL) who is responsible for ensuring compliance with all local, state, and federal erosion and sediment control and water quality requirements.
Conditions of Use A CESCL shall be made available on projects one acre or larger that
discharge stormwater to surface waters of the state. Sites less than one
acre may have a person without CESCL certification conduct inspections; sampling is not required on sites that disturb less than an acre.
• The CESCL shall:
• Have a current certificate proving attendance in an erosion and
sediment control training course that meets the minimum ESC training and certification requirements established by Ecology (see
details below).
Ecology will maintain a list of ESC training and certification
providers at:
http://www.ecy.wa.gov/programs/wq/stormwater/cescl.html
OR
• Be a Certified Professional in Erosion and Sediment Control
(CPESC); for additional information go to: www.cpesc.net
Specifications • Certification shall remain valid for three years.
• The CESCL shall have authority to act on behalf of the contractor or
developer and shall be available, or on-call, 24 hours per day
throughout the period of construction.
• The Construction SWPPP shall include the name, telephone number, fax number, and address of the designated CESCL.
• A CESCL may provide inspection and compliance services for
multiple construction projects in the same geographic region.
Duties and responsibilities of the CESCL shall include, but are not limited
to the following:
• Maintaining permit file on site at all times which includes the
Construction SWPPP and any associated permits and plans.
• Directing BMP installation, inspection, maintenance, modification,
and removal.
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• Updating all project drawings and the Construction SWPPP with changes made.
• Completing any sampling requirements including reporting results
using WebDMR.
• Keeping daily logs, and inspection reports. Inspection reports should include:
• Inspection date/time.
• Weather information; general conditions during inspection and
approximate amount of precipitation since the last inspection.
• A summary or list of all BMPs implemented, including observations of all erosion/sediment control structures or practices. The following shall be noted:
1. Locations of BMPs inspected.
2. Locations of BMPs that need maintenance.
3. Locations of BMPs that failed to operate as designed or intended.
4. Locations of where additional or different BMPs are required.
• Visual monitoring results, including a description of discharged
stormwater. The presence of suspended sediment, turbid water,
discoloration, and oil sheen shall be noted, as applicable.
• Any water quality monitoring performed during inspection.
• General comments and notes, including a brief description of
any BMP repairs, maintenance or installations made as a result
of the inspection.
• Facilitate, participate in, and take corrective actions resulting from inspections performed by outside agencies or the owner.
BMP C162: Scheduling
Purpose Sequencing a construction project reduces the amount and duration of soil
exposed to erosion by wind, rain, runoff, and vehicle tracking.
Conditions of Use The construction sequence schedule is an orderly listing of all major land-disturbing activities together with the necessary erosion and sedimentation
control measures planned for the project. This type of schedule guides the
contractor on work to be done before other work is started so that serious
erosion and sedimentation problems can be avoided.
Following a specified work schedule that coordinates the timing of land-disturbing activities and the installation of control measures is perhaps the
most cost-effective way of controlling erosion during construction. The
removal of surface ground cover leaves a site vulnerable to accelerated
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erosion. Construction procedures that limit land clearing provide timely installation of erosion and sedimentation controls, and restore protective
cover quickly can significantly reduce the erosion potential of a site.
Design Considerations • Minimize construction during rainy periods.
• Schedule projects to disturb only small portions of the site at any one time. Complete grading as soon as possible. Immediately stabilize the disturbed portion before grading the next portion. Practice staged
seeding in order to revegetate cut and fill slopes as the work
progresses.
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4.2 Runoff Conveyance and Treatment BMPs
This section contains the standards and specifications for Runoff Conveyance and Treatment BMPs. Table 4.2.1, below, shows the
relationship of the BMPs in Section 4.2 to the Construction Stormwater
Pollution Prevention Plan (SWPPP) Elements described in Section 3.3.3.
Table 4.2.1 Runoff Conveyance and Treatment BMPs by SWPPP Element
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BMP C200: Interceptor Dike and Swale
Purpose Provide a ridge of compacted soil, or a ridge with an upslope swale, at the
top or base of a disturbed slope or along the perimeter of a disturbed
construction area to convey stormwater. Use the dike and/or swale to
intercept the runoff from unprotected areas and direct it to areas where erosion can be controlled. This can prevent storm runoff from entering the work area or sediment-laden runoff from leaving the construction site.
Conditions of Use Where the runoff from an exposed site or disturbed slope must be conveyed
to an erosion control facility which can safely convey the stormwater.
• Locate upslope of a construction site to prevent runoff from entering disturbed area.
• When placed horizontally across a disturbed slope, it reduces the
amount and velocity of runoff flowing down the slope.
• Locate downslope to collect runoff from a disturbed area and direct
water to a sediment basin.
Design and Installation
Specifications
• Dike and/or swale and channel must be stabilized with temporary or permanent vegetation or other channel protection during construction.
• Channel requires a positive grade for drainage; steeper grades require
channel protection and check dams.
• Review construction for areas where overtopping may occur.
• Can be used at top of new fill before vegetation is established.
• May be used as a permanent diversion channel to carry the runoff.
• Sub-basin tributary area should be one acre or less.
• Design capacity for the peak flow from a 10-year, 24-hour storm,
assuming a Type 1A rainfall distribution, for temporary facilities. Alternatively, use 1.6 times the 10-year, 1-hour flow indicated by an approved continuous runoff model. For facilities that will also serve on
a permanent basis, consult the local government’s drainage
requirements.
Interceptor dikes shall meet the following criteria:
Top Width 2 feet minimum.
Height 1.5 feet minimum on berm.
Side Slope 2H:1V or flatter.
Grade Depends on topography, however, dike system minimum is
0.5%, and maximum is 1%. Compaction Minimum of 90 percent ASTM D698 standard proctor.
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Horizontal Spacing of Interceptor Dikes:
Average Slope Slope Percent Flowpath Length
20H:1V or less 3-5% 300 feet
(10 to 20)H:1V 5-10% 200 feet
(4 to 10)H:1V 10-25% 100 feet (2 to 4)H:1V 25-50% 50 feet
Stabilization depends on velocity and reach
Slopes <5% Seed and mulch applied within 5 days of dike
construction (see BMP C121, Mulching).
Slopes 5 - 40% Dependent on runoff velocities and dike materials. Stabilization should be done immediately using either sod or riprap or other measures to avoid erosion.
• The upslope side of the dike shall provide positive drainage to the dike
outlet. No erosion shall occur at the outlet. Provide energy dissipation
measures as necessary. Sediment-laden runoff must be released through a sediment trapping facility.
• Minimize construction traffic over temporary dikes. Use temporary
cross culverts for channel crossing.
Interceptor swales shall meet the following criteria:
Bottom Width 2 feet minimum; the cross-section bottom shall be level.
Depth 1-foot minimum.
Side Slope 2H:1V or flatter.
Grade Maximum 5 percent, with positive drainage to a
suitable outlet (such as a sediment pond).
Stabilization Seed as per BMP C120, Temporary and Permanent Seeding, or BMP C202, Channel
Lining, 12 inches thick riprap pressed into the bank
and extending at least 8 inches vertical from the
bottom.
• Inspect diversion dikes and interceptor swales once a week and after
every rainfall. Immediately remove sediment from the flow area.
• Damage caused by construction traffic or other activity must be
repaired before the end of each working day.
Check outlets and make timely repairs as needed to avoid gully formation. When the area below the temporary diversion dike is permanently
stabilized, remove the dike and fill and stabilize the channel to blend with
the natural surface.
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BMP C201: Grass-Lined Channels
Purpose To provide a channel with a vegetative lining for conveyance of runoff.
See Figure 4.2.1 for typical grass-lined channels.
Conditions of Use This practice applies to construction sites where concentrated runoff needs to be contained to prevent erosion or flooding.
• When a vegetative lining can provide sufficient stability for the
channel cross section and at lower velocities of water (normally
dependent on grade). This means that the channel slopes are generally
less than 5 percent and space is available for a relatively large cross section.
• Typical uses include roadside ditches, channels at property boundaries,
outlets for diversions, and other channels and drainage ditches in low
areas.
• Channels that will be vegetated should be installed before major earthwork and hydroseeded with a bonded fiber matrix (BFM). The vegetation should be well established (i.e., 75 percent cover) before
water is allowed to flow in the ditch. With channels that will have high
flows, erosion control blankets should be installed over the hydroseed.
If vegetation cannot be established from seed before water is allowed in the ditch, sod should be installed in the bottom of the ditch in lieu of hydromulch and blankets.
Design and
Installation Specifications
Locate the channel where it can conform to the topography and other
features such as roads.
• Locate them to use natural drainage systems to the greatest extent possible.
• Avoid sharp changes in alignment or bends and changes in grade.
• Do not reshape the landscape to fit the drainage channel.
• The maximum design velocity shall be based on soil conditions, type
of vegetation, and method of revegetation, but at no times shall velocity exceed 5 feet/second. The channel shall not be overtopped by
the peak runoff from a 10-year, 24-hour storm, assuming a Type 1A
rainfall distribution." Alternatively, use 1.6 times the 10-year, 1-hour
flow indicated by an approved continuous runoff model to determine a
flow rate which the channel must contain.
• Where the grass-lined channel will also function as a permanent
stormwater conveyance facility, consult the drainage conveyance
requirements of the local government with jurisdiction.
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• An established grass or vegetated lining is required before the channel can be used to convey stormwater, unless stabilized with nets or
blankets.
• If design velocity of a channel to be vegetated by seeding exceeds 2 ft/sec, a temporary channel liner is required. Geotextile or special mulch protection such as fiberglass roving or straw and netting
provides stability until the vegetation is fully established. See Figure
4.2.2.
• Check dams shall be removed when the grass has matured sufficiently
to protect the ditch or swale unless the slope of the swale is greater
than 4 percent. The area beneath the check dams shall be seeded and mulched immediately after dam removal.
• If vegetation is established by sodding, the permissible velocity for
established vegetation may be used and no temporary liner is needed.
• Do not subject grass-lined channel to sedimentation from disturbed
areas. Use sediment-trapping BMPs upstream of the channel.
• V-shaped grass channels generally apply where the quantity of water is small, such as in short reaches along roadsides. The V-shaped cross
section is least desirable because it is difficult to stabilize the bottom
where velocities may be high.
• Trapezoidal grass channels are used where runoff volumes are large
and slope is low so that velocities are nonerosive to vegetated linings.
(Note: it is difficult to construct small parabolic shaped channels.)
• Subsurface drainage, or riprap channel bottoms, may be necessary on sites that are subject to prolonged wet conditions due to long duration
flows or a high water table.
• Provide outlet protection at culvert ends and at channel intersections.
• Grass channels, at a minimum, should carry peak runoff for temporary
construction drainage facilities from the 10-year, 24-hour storm
without eroding. Where flood hazard exists, increase the capacity according to the potential damage.
• Grassed channel side slopes generally are constructed 3H:1V or flatter
to aid in the establishment of vegetation and for maintenance.
• Construct channels a minimum of 0.2 foot larger around the periphery
to allow for soil bulking during seedbed preparations and sod buildup.
Maintenance Standards During the establishment period, check grass-lined channels after every
rainfall.
• After grass is established, periodically check the channel; check it after
every heavy rainfall event. Immediately make repairs.
• It is particularly important to check the channel outlet and all road crossings for bank stability and evidence of piping or scour holes.
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• Remove all significant sediment accumulations to maintain the
designed carrying capacity. Keep the grass in a healthy, vigorous
condition at all times, since it is the primary erosion protection for the channel.
Figure 4.2.1 – Typical Grass-Lined Channels
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OVERCUTCHANNEL
2'(50mm) TOALLOW
BULKING DURINGSEEDBED
PREPARATION
TYPICAL INSTALLATION
WITHEROSIONCONTROL
BLANKETS OR TURF
REINFORCEMENT MATS Intermittent Check Slot Longitudinal Anchor Trench Shingle-lap spliced ends or begin new roll in an intermittent check slot
Prepare soil and apply seed before installing blankets, mats or other
temporary channel liner system
/
NOTES: 1 Design velocities exceeding 2 ft/sec (0.5m/sec) require temporary blankets, mats or similar liners
to protect seed and soil until vegetation becomes established.
2 Grass-lined channels with design velocities exceeding 6 ft/sec (2m/sec) should include turf reinforcement
mats.
Fig ure 4.2 .2 – Temporary Channel Liners
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BMP C202: Channel Lining
Purpose To protect channels by providing a channel liner using either blankets or
riprap.
Conditions of Use
When natural soils or vegetated stabilized soils in a channel are not adequate
to prevent channel erosion.
• When a permanent ditch or pipe system is to be installed and a
temporary measure is needed.
• In almost all cases, synthetic and organic coconut blankets are more effective than riprap for protecting channels from erosion. Blankets
can be used with and without vegetation. Blanketed channels can be
designed to handle any expected flow and longevity requirement.
Some synthetic blankets have a predicted life span of 50 years or
more, even in sunlight.
• Other reasons why blankets are better than rock include the availability
of blankets over rock. In many areas of the state, rock is not easily
obtainable or is very expensive to haul to a site. Blankets can be
delivered anywhere. Rock requires the use of dump trucks to haul and
heavy equipment to place. Blankets usually only require laborers with hand tools, and sometimes a backhoe.
• The Federal Highway Administration recommends not using flexible
liners whenever the slope exceeds 10 percent or the shear stress
exceeds 8 lbs/ft2.
Design and Installation Specifications
See BMP C122 for information on blankets.
Since riprap is used where erosion potential is high, construction must be
sequenced so that the riprap is put in place with the minimum possible
delay.
• Disturbance of areas where riprap is to be placed should be undertaken
only when final preparation and placement of the riprap can follow immediately behind the initial disturbance. Where riprap is used for
outlet protection, the riprap should be placed before or in conjunction
with the construction of the pipe or channel so that it is in place when
the pipe or channel begins to operate.
• The designer, after determining the riprap size that will be stable under the flow conditions, shall consider that size to be a minimum size and
then, based on riprap gradations actually available in the area, select
the size or sizes that equal or exceed the minimum size. The possibility
of drainage structure damage by children shall be considered in
selecting a riprap size, especially if there is nearby water or a gully in which to toss the stones.
• Stone for riprap shall consist of field stone or quarry stone of
approximately rectangular shape. The stone shall be hard and angular
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and of such quality that it will not disintegrate on exposure to water or weathering and it shall be suitable in all respects for the purpose
intended.
• A lining of engineering filter fabric (geotextile) shall be placed
between the riprap and the underlying soil surface to prevent soil movement into or through the riprap. The geotextile should be keyed in at the top of the bank.
• Filter fabric shall not be used on slopes greater than 1-1/2H:1V as
slippage may occur. It should be used in conjunction with a layer of
coarse aggregate (granular filter blanket) when the riprap to be placed is 12 inches and larger.
BMP C203: Water Bars
Purpose A small ditch or ridge of material is constructed diagonally across a road
or right-of-way to divert stormwater runoff from the road surface, wheel
tracks, or a shallow road ditch. See Figure 4.2.3.
Conditions of use Clearing right-of-way and construction of access for power lines, pipelines, and other similar installations often require long narrow right-of-ways over sloping
terrain. Disturbance and compaction promotes gully formation in these cleared
strips by increasing the volume and velocity of runoff. Gully formation may be
especially severe in tire tracks and ruts. To prevent gullying, runoff can often be diverted across the width of the right-of-way to undisturbed areas by using small predesigned diversions.
• Give special consideration to each individual outlet area, as well as to
the cumulative effect of added diversions. Use gravel to stabilize the
diversion where significant vehicular traffic is anticipated.
Design and Installation
Specifications
Height: 8-inch minimum measured from the channel bottom to the ridge top.
• Side slope of channel: 2H:1V maximum; 3H:1V or flatter when
vehicles will cross.
• Base width of ridge: 6-inch minimum.
• Locate them to use natural drainage systems and to discharge into well vegetated stable areas.
• Guideline for Spacing:
Slope % Spacing (ft)
< 5 125
5 - 10 100
10 - 20 75
20 - 35 50
> 35 Use rock lined ditch
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• Grade of water bar and angle: Select angle that results in ditch slope less than 2 percent.
• Install as soon as the clearing and grading is complete. Reconstruct
when construction is complete on a section when utilities are being
installed.
• Compact the ridge when installed.
• Stabilize, seed and mulch the portions that are not subject to traffic.
Gravel the areas crossed by vehicles.
Maintenance Standards
Periodically inspect right-of-way diversions for wear and after every heavy
rainfall for erosion damage.
• Immediately remove sediment from the flow area and repair the dike.
• Check outlet areas and make timely repairs as needed.
• When permanent road drainage is established and the area above the
temporary right-of-way diversion is permanently stabilized, remove
the dikes and fill the channel to blend with the natural ground, and appropriately stabilize the disturbed area.
Figure 4.2.3 – Water Bar
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BMP C204: Pipe Slope Drains
Purpose To use a pipe to convey stormwater anytime water needs to be diverted
away from or over bare soil to prevent gullies, channel erosion, and
saturation of slide-prone soils.
Conditions of Use Pipe slope drains should be used when a temporary or permanent stormwater conveyance is needed to move the water down a steep slope to avoid erosion (Figure 4.2.4).
On highway projects, pipe slope drains should be used at bridge ends to
collect runoff and pipe it to the base of the fill slopes along bridge
approaches. These can be designed into a project and included as bid items. Another use on road projects is to collect runoff from pavement and pipe it away from side slopes. These are useful because there is generally a
time lag between having the first lift of asphalt installed and the curbs,
gutters, and permanent drainage installed. Used in conjunction with sand
bags, or other temporary diversion devices, these will prevent massive amounts of sediment from leaving a project.
Water can be collected, channeled with sand bags, Triangular Silt Dikes,
berms, or other material, and piped to temporary sediment ponds.
Pipe slope drains can be:
• Connected to new catch basins and used temporarily until all permanent piping is installed;
• Used to drain water collected from aquifers exposed on cut slopes and
take it to the base of the slope;
• Used to collect clean runoff from plastic sheeting and direct it away from exposed soil;
• Installed in conjunction with silt fence to drain collected water to a
controlled area;
• Used to divert small seasonal streams away from construction. They
have been used successfully on culvert replacement and extension
jobs. Large flex pipe can be used on larger streams during culvert
removal, repair, or replacement; and,
• Connected to existing down spouts and roof drains and used to divert water away from work areas during building renovation, demolition,
and construction projects.
There are now several commercially available collectors that are attached
to the pipe inlet and help prevent erosion at the inlet.
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Design and Installation
Specifications
Size the pipe to convey the flow. The capacity for temporary drains shall be sufficient to handle the peak flow from a 10-year, 24-hour storm event,
assuming a Type 1A rainfall distribution. Alternatively, use 1.6 times the
10-year, 1-hour flow indicated by an approved continuous runoff model.
Consult local drainage requirements for sizing permanent pipe slope drains.
• Use care in clearing vegetated slopes for installation.
• Re-establish cover immediately on areas disturbed by installation.
• Use temporary drains on new cut or fill slopes.
• Use diversion dikes or swales to collect water at the top of the slope.
• Ensure that the entrance area is stable and large enough to direct flow into the pipe.
• Piping of water through the berm at the entrance area is a common
failure mode.
• The entrance shall consist of a standard flared end section for culverts
12 inches and larger with a minimum 6-inch metal toe plate to prevent runoff from undercutting the pipe inlet. The slope of the entrance shall be at least 3 percent. Sand bags may also be used at pipe entrances as a
temporary measure.
• The soil around and under the pipe and entrance section shall be
thoroughly compacted to prevent undercutting.
• The flared inlet section shall be securely connected to the slope drain and have watertight connecting bands.
• Slope drain sections shall be securely fastened together, fused or have
gasketed watertight fittings, and shall be securely anchored into the
soil.
• Thrust blocks should be installed anytime 90 degree bends are utilized. Depending on size of pipe and flow, these can be constructed with
sand bags, straw bales staked in place, “t” posts and wire, or ecology
blocks.
• Pipe needs to be secured along its full length to prevent movement. This can be done with steel “t” posts and wire. A post is installed on
each side of the pipe and the pipe is wired to them. This should be
done every 10-20 feet of pipe length or so, depending on the size of
the pipe and quantity of water to divert.
• Interceptor dikes shall be used to direct runoff into a slope drain. The height of the dike shall be at least 1 foot higher at all points than the
top of the inlet pipe.
• The area below the outlet must be stabilized with a riprap apron (see
BMP C209 Outlet Protection, for the appropriate outlet material).
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Dike material compacted90% modified proctor
CPEP or equivalent pipe
Discharge to a stabilizedwatercourse, sediment retentionfacility, or stabilized outlet
Inlet and all sections must besecurely fastened togetherwith gasketed watertight fittings
Provide riprap pador equivalent energydissipation
Interceptor Dike
Standard flaredend section
• If the pipe slope drain is conveying sediment-laden water, direct all flows into the sediment trapping facility.
• Materials specifications for any permanent piped system shall be set
by the local government.
Maintenance Standards
Check inlet and outlet points regularly, especially after storms.
The inlet should be free of undercutting, and no water should be going around the point of entry. If there are problems, the headwall should be
reinforced with compacted earth or sand bags.
• The outlet point should be free of erosion and installed with
appropriate outlet protection.
• For permanent installations, inspect pipe periodically for vandalism and physical distress such as slides and wind-throw.
• Normally the pipe slope is so steep that clogging is not a problem with
smooth wall pipe, however, debris may become lodged in the pipe.
Figure 4.2.4 – Pipe Slope Drain
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BMP C205: Subsurface Drains
Purpose To intercept, collect, and convey ground water to a satisfactory outlet,
using a perforated pipe or conduit below the ground surface. Subsurface
drains are also known as “french drains.” The perforated pipe provides a
dewatering mechanism to drain excessively wet soils, provide a stable base for construction, improve stability of structures with shallow foundations, or to reduce hydrostatic pressure to improve slope stability.
Conditions of Use Use when excessive water must be removed from the soil. The soil
permeability, depth to water table and impervious layers are all factors
which may govern the use of subsurface drains.
Design and Installation
Specifications
Relief drains are used either to lower the water table in large, relatively flat areas, improve the growth of vegetation, or to remove surface water.
Relief drains are installed along a slope and drain in the direction of the
slope.
They can be installed in a grid pattern, a herringbone pattern, or a random pattern.
• Interceptor drains are used to remove excess ground water from a
slope, stabilize steep slopes, and lower the water table immediately
below a slope to prevent the soil from becoming saturated.
Interceptor drains are installed perpendicular to a slope and drain to the side of the slope.
They usually consist of a single pipe or series of single pipes instead of a
patterned layout.
• Depth and spacing of interceptor drains --The depth of an interceptor drain is determined primarily by the depth to which the water table is to be lowered or the depth to a confining layer. For
practical reasons, the maximum depth is usually limited to 6 feet, with
a minimum cover of 2 feet to protect the conduit.
• The soil should have depth and sufficient permeability to permit installation of an effective drainage system at a depth of 2 to 6 feet.
• An adequate outlet for the drainage system must be available either by
gravity or by pumping.
• The quantity and quality of discharge needs to be accounted for in the
receiving stream (additional detention may be required).
• This standard does not apply to subsurface drains for building
foundations or deep excavations.
• The capacity of an interceptor drain is determined by calculating the
maximum rate of ground water flow to be intercepted. Therefore, it is
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good practice to make complete subsurface investigations, including hydraulic conductivity of the soil, before designing a subsurface
drainage system.
• Size of drain--Size subsurface drains to carry the required capacity
without pressure flow. Minimum diameter for a subsurface drain is 4 inches.
• The minimum velocity required to prevent silting is 1.4 ft./sec. The
line shall be graded to achieve this velocity at a minimum. The
maximum allowable velocity using a sand-gravel filter or envelope is 9
ft/sec.
• Filter material and fabric shall be used around all drains for proper bedding and filtration of fine materials. Envelopes and filters should
surround the drain to a minimum of 3-inch thickness.
• The outlet of the subsurface drain shall empty into a sediment pond
through a catch basin. If free of sediment, it can then empty into a receiving channel, swale, or stable vegetated area adequately protected from erosion and undermining.
• The trench shall be constructed on a continuous grade with no reverse
grades or low spots.
• Soft or yielding soils under the drain shall be stabilized with gravel or other suitable material.
• Backfilling shall be done immediately after placement of the pipe. No
sections of pipe shall remain uncovered overnight or during a
rainstorm. Backfill material shall be placed in the trench in such a
manner that the drain pipe is not displaced or damaged.
• Do not install permanent drains near trees to avoid the tree roots that tend to clog the line. Use solid pipe with watertight connections where
it is necessary to pass a subsurface drainage system through a stand of
trees.
• Outlet--Ensure that the outlet of a drain empties into a channel or other watercourse above the normal water level.
• Secure an animal guard to the outlet end of the pipe to keep out
rodents.
• Use outlet pipe of corrugated metal, cast iron, or heavy-duty plastic
without perforations and at least 10 feet long. Do not use an envelope or filter material around the outlet pipe, and bury at least two-thirds of
the pipe length.
• When outlet velocities exceed those allowable for the receiving
stream, outlet protection must be provided.
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Maintenance Standards Subsurface drains shall be checked periodically to ensure that they are free-flowing and not clogged with sediment or roots.
• The outlet shall be kept clean and free of debris.
• Surface inlets shall be kept open and free of sediment and other debris.
• Trees located too close to a subsurface drain often clog the system with their roots. If a drain becomes clogged, relocate the drain or remove the trees as a last resort. Drain placement should be planned to
minimize this problem.
• Where drains are crossed by heavy vehicles, the line shall be checked
to ensure that it is not crushed.
BMP C206: Level Spreader
Purpose To provide a temporary outlet for dikes and diversions consisting of an
excavated depression constructed at zero grade across a slope. To convert
concentrated runoff to sheet flow and release it onto areas stabilized by
existing vegetation or an engineered filter strip.
Conditions of Use Used when a concentrated flow of water needs to be dispersed over a large area with existing stable vegetation.
• Items to consider are:
1. What is the risk of erosion or damage if the flow may become
concentrated?
2. Is an easement required if discharged to adjoining property?
3. Most of the flow should be as ground water and not as surface
flow.
4. Is there an unstable area downstream that cannot accept additional
ground water?
• Use only where the slopes are gentle, the water volume is relatively low, and the soil will adsorb most of the low flow events.
Design and
Installation Specifications
Use above undisturbed areas that are stabilized by existing vegetation.
If the level spreader has any low points, flow will concentrate, create
channels and may cause erosion.
• Discharge area below the outlet must be uniform with a slope flatter
than 5H:1V.
• Outlet to be constructed level in a stable, undisturbed soil profile (not
on fill).
• The runoff shall not re-concentrate after release unless intercepted by another downstream measure.
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Densely vegetated for aMin. of 100' and slopeless than 5:1
Pressure-Treated 2"x10"
1' Min.2:1 Max.3' Min.
• The grade of the channel for the last 20 feet of the dike or interceptor entering the level spreader shall be less than or equal to 1 percent. The
grade of the level spreader shall be 0 percent to ensure uniform
spreading of storm runoff.
• A 6-inch high gravel berm placed across the level lip shall consist of washed crushed rock, 2- to 4-inch or 3/4-inch to 1½-inch size.
• The spreader length shall be determined by estimating the peak flow
expected from the 10-year, 24-hour design storm. The length of the
spreader shall be a minimum of 15 feet for 0.1 cfs and shall increase
by 10 feet for each 0.1 cfs thereafter to a maximum of 0.5 cfs per spreader. Use multiple spreaders for higher flows.
• The width of the spreader should be at least 6 feet.
• The depth of the spreader as measured from the lip should be at least 6
inches and it should be uniform across the entire length.
• Level spreaders shall be setback from the property line unless there is an easement for flow.
• Level spreaders, when installed every so often in grassy swales, keep
the flows from concentrating. Materials that can be used include sand
bags, lumber, logs, concrete, and pipe. To function properly, the
material needs to be installed level and on contour. Figures 4.2.5Figure425 and 4.2.6 provide a cross-section and a detail of a level spreader. A capped perforated pipe could also be used as a spreader.
Maintenance
Standards
The spreader should be inspected after every runoff event to ensure that it
is functioning correctly.
• The contractor should avoid the placement of any material on the structure and should prevent construction traffic from crossing over the structure.
• If the spreader is damaged by construction traffic, it shall be
immediately repaired.
Figure 4.2.5 – Cross Section of Level Spreader
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Figure 4.2.6 – Detail of Level Spreader
BMP C207: Check Dams
Purpose Construction of small dams across a swale or ditch reduces the velocity of concentrated flow and dissipates energy at the check dam.
Conditions of Use Where temporary channels or permanent channels are not yet vegetated,
channel lining is infeasible, and/or velocity checks are required.
• Check dams may not be placed in streams unless approved by the State Department of Fish and Wildlife. Check dams may not be placed in wetlands without approval from a permitting agency.
• Do not place check dams below the expected backwater from any
salmonid bearing water between October 1 and May 31 to ensure that
there is no loss of high flow refuge habitat for overwintering juvenile salmonids and emergent salmonid fry.
• Construct rock check dams from appropriately sized rock. The rock
used must be large enough to stay in place given the expected design
flow through the channel. The rock must be placed by hand or by
mechanical means (no dumping of rock to form dam) to achieve complete coverage of the ditch or swale and to ensure that the center of the dam is lower than the edges.
• Check dams may also be constructed of either rock or pea-gravel filled
bags. Numerous new products are also available for this purpose. They
tend to be re-usable, quick and easy to install, effective, and cost efficient.
• Place check dams perpendicular to the flow of water.
• The dam should form a triangle when viewed from the side. This
prevents undercutting as water flows over the face of the dam rather
than falling directly onto the ditch bottom.
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• Before installing check dams impound and bypass upstream water flow away from the work area. Options for bypassing include pumps,
siphons, or temporary channels.
• Check dams in association with sumps work more effectively at
slowing flow and retaining sediment than just a check dam alone. A deep sump should be provided immediately upstream of the check dam.
• In some cases, if carefully located and designed, check dams can
remain as permanent installations with very minor regrading. They
may be left as either spillways, in which case accumulated sediment would be graded and seeded, or as check dams to prevent further sediment from leaving the site.
• The maximum spacing between the dams shall be such that the toe of
the upstream dam is at the same elevation as the top of the downstream
dam.
• Keep the maximum height at 2 feet at the center of the dam.
• Keep the center of the check dam at least 12 inches lower than the
outer edges at natural ground elevation.
• Keep the side slopes of the check dam at 2H:1V or flatter.
• Key the stone into the ditch banks and extend it beyond the abutments a minimum of 18 inches to avoid washouts from overflow around the dam.
• Use filter fabric foundation under a rock or sand bag check dam. If a
blanket ditch liner is used, filter fabric is not necessary. A piece of
organic or synthetic blanket cut to fit will also work for this purpose.
• In the case of grass-lined ditches and swales, all check dams and accumulated sediment shall be removed when the grass has matured
sufficiently to protect the ditch or swale - unless the slope of the swale
is greater than 4 percent. The area beneath the check dams shall be
seeded and mulched immediately after dam removal.
• Ensure that channel appurtenances, such as culvert entrances below
check dams, are not subject to damage or blockage from displaced
stones. Figure 4.2.7 depicts a typical rock check dam.
Maintenance Standards Check dams shall be monitored for performance and sediment
accumulation during and after each runoff producing rainfall. Sediment shall be removed when it reaches one half the sump depth.
• Anticipate submergence and deposition above the check dam and
erosion from high flows around the edges of the dam.
• If significant erosion occurs between dams, install a protective riprap
liner in that portion of the channel.
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Approved as Equivalent Ecology has approved products as able to meet the requirements of BMP C207. The products did not pass through the Technology Assessment
Protocol – Ecology (TAPE) process. Local jurisdictions may choose not
to accept this product approved as equivalent, or may require additional
testing prior to consideration for local use. The products are available for review on Ecology’s website at http://www.ecy.wa.gov/programs/wq/stormwater/newtech/equivalent.html
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Figure 4.2.7 – Rock Check Dam
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BMP C208: Triangular Silt Dike (TSD) (Geotextile-Encased Check Dam)
Purpose Triangular silt dikes may be used as check dams, for perimeter protection,
for temporary soil stockpile protection, for drop inlet protection, or as a
temporary interceptor dike.
Conditions of use • May be used on soil or pavement with adhesive or staples.
• TSDs have been used to build temporary:
1. sediment ponds;
2. diversion ditches;
3. concrete wash out facilities;
4. curbing;
5. water bars;
6. level spreaders; and,
7. berms.
Design and Installation Specifications
Made of urethane foam sewn into a woven geosynthetic fabric.
It is triangular, 10 inches to 14 inches high in the center, with a 20-inch to 28-inch base. A 2–foot apron extends beyond both sides of the triangle along its standard section of 7 feet. A sleeve at one end allows attachment
of additional sections as needed.
• Install with ends curved up to prevent water from flowing around the
ends.
• The fabric flaps and check dam units are attached to the ground with wire staples. Wire staples should be No. 11 gauge wire and should be
200 mm to 300 mm in length.
• When multiple units are installed, the sleeve of fabric at the end of the
unit shall overlap the abutting unit and be stapled.
• Check dams should be located and installed as soon as construction will allow.
• Check dams should be placed perpendicular to the flow of water.
• When used as check dams, the leading edge must be secured with
rocks, sandbags, or a small key slot and staples.
• In the case of grass-lined ditches and swales, check dams and
accumulated sediment shall be removed when the grass has matured
sufficiently to protect the ditch or swale unless the slope of the swale
is greater than 4 percent. The area beneath the check dams shall be
seeded and mulched immediately after dam removal.
Maintenance • Triangular silt dams shall be inspected for performance and sediment
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Standards accumulation during and after each runoff producing rainfall. Sediment shall be removed when it reaches one half the height of the
dam.
• Anticipate submergence and deposition above the triangular silt dam
and erosion from high flows around the edges of the dam. Immediately repair any damage or any undercutting of the dam.
BMP C209: Outlet Protection
Purpose Outlet protection prevents scour at conveyance outlets and minimizes the
potential for downstream erosion by reducing the velocity of concentrated
stormwater flows.
Conditions of use Outlet protection is required at the outlets of all ponds, pipes, ditches, or other conveyances, and where runoff is conveyed to a natural or manmade
drainage feature such as a stream, wetland, lake, or ditch.
Design and Installation Specifications
The receiving channel at the outlet of a culvert shall be protected from
erosion by rock lining a minimum of 6 feet downstream and extending up the channel sides a minimum of 1–foot above the maximum tailwater elevation or 1-foot above the crown, whichever is higher. For large pipes
(more than 18 inches in diameter), the outlet protection lining of the
channel is lengthened to four times the diameter of the culvert.
• Standard wingwalls, and tapered outlets and paved channels should also be considered when appropriate for permanent culvert outlet protection. (See WSDOT Hydraulic Manual, available through
WSDOT Engineering Publications).
• Organic or synthetic erosion blankets, with or without vegetation, are
usually more effective than rock, cheaper, and easier to install. Materials can be chosen using manufacturer product specifications. ASTM test results are available for most products and the designer can
choose the correct material for the expected flow.
• With low flows, vegetation (including sod) can be effective.
• The following guidelines shall be used for riprap outlet protection:
1. If the discharge velocity at the outlet is less than 5 fps (pipe slope
less than 1 percent), use 2-inch to 8-inch riprap. Minimum
thickness is 1-foot.
2. For 5 to 10 fps discharge velocity at the outlet (pipe slope less than
3 percent), use 24-inch to 48-inch riprap. Minimum thickness is 2 feet.
3. For outlets at the base of steep slope pipes (pipe slope greater than
10 percent), an engineered energy dissipater shall be used.
• Filter fabric or erosion control blankets should always be used under
riprap to prevent scour and channel erosion.
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• New pipe outfalls can provide an opportunity for low-cost fish habitat improvements. For example, an alcove of low-velocity water can be
created by constructing the pipe outfall and associated energy
dissipater back from the stream edge and digging a channel, over-
widened to the upstream side, from the outfall. Overwintering juvenile and migrating adult salmonids may use the alcove as shelter during high flows. Bank stabilization, bioengineering, and habitat features
may be required for disturbed areas. This work may require a HPA.
See Volume V for more information on outfall system design.
Maintenance Standards • Inspect and repair as needed.
• Add rock as needed to maintain the intended function.
• Clean energy dissipater if sediment builds up.
BMP C220: Storm Drain Inlet Protection
Purpose Storm drain inlet protection prevents coarse sediment from entering drainage systems prior to permanent stabilization of the disturbed area.
Conditions of Use Use storm drain inlet protection at inlets that are operational before
permanent stabilization of the disturbed drainage area. Provide protection
for all storm drain inlets downslope and within 500 feet of a disturbed or construction area, unless conveying runoff entering catch basins to a sediment pond or trap.
Also consider inlet protection for lawn and yard drains on new home
construction. These small and numerous drains coupled with lack of
gutters in new home construction can add significant amounts of sediment into the roof drain system. If possible delay installing lawn and yard drains until just before landscaping or cap these drains to prevent sediment from
entering the system until completion of landscaping. Provide 18-inches of
sod around each finished lawn and yard drain.
Table 4.2.2 lists several options for inlet protection. All of the methods for storm drain inlet protection tend to plug and require a high frequency of maintenance. Limit drainage areas to one acre or less. Possibly provide
emergency overflows with additional end-of-pipe treatment where
stormwater ponding would cause a hazard.
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Table 4.2.2
Storm Drain Inlet Protection
Type of Inlet
Protection
Emergency
Overflow
Applicable for Paved/ Earthen
Surfaces Conditions of Use Drop Inlet Protection Excavated drop inlet protection Yes, temporary flooding will occur
Earthen Applicable for heavy flows. Easy to maintain. Large area Requirement: 30’ X 30’/acre
Block and gravel drop inlet protection Yes Paved or Earthen Applicable for heavy concentrated flows. Will not pond. Gravel and wire drop inlet protection No Applicable for heavy concentrated flows. Will pond. Can withstand traffic. Catch basin filters Yes Paved or Earthen Frequent maintenance required.
Curb Inlet Protection Curb inlet protection with a wooden weir Small capacity overflow Paved Used for sturdy, more compact installation. Block and gravel curb inlet protection
Yes Paved Sturdy, but limited filtration.
Culvert Inlet Protection Culvert inlet sediment trap 18 month expected life.
Design and Installation Specifications
Excavated Drop Inlet Protection - An excavated impoundment around the storm drain. Sediment settles out of the stormwater prior to entering the storm drain.
• Provide a depth of 1-2 ft as measured from the crest of the inlet
structure.
• Slope sides of excavation no steeper than 2H:1V.
• Minimum volume of excavation 35 cubic yards.
• Shape basin to fit site with longest dimension oriented toward the
longest inflow area.
• Install provisions for draining to prevent standing water problems.
• Clear the area of all debris.
• Grade the approach to the inlet uniformly.
• Drill weep holes into the side of the inlet.
• Protect weep holes with screen wire and washed aggregate.
• Seal weep holes when removing structure and stabilizing area.
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• Build a temporary dike, if necessary, to the down slope side of the structure to prevent bypass flow.
Block and Gravel Filter - A barrier formed around the storm drain inlet
with standard concrete blocks and gravel. See Figure 4.2.8.
• Provide a height of 1 to 2 feet above inlet.
• Recess the first row 2-inches into the ground for stability.
• Support subsequent courses by placing a 2x4 through the block
opening.
• Do not use mortar.
• Lay some blocks in the bottom row on their side for dewatering the pool.
• Place hardware cloth or comparable wire mesh with ½-inch openings
over all block openings.
• Place gravel just below the top of blocks on slopes of 2H:1V or flatter.
• An alternative design is a gravel donut.
• Provide an inlet slope of 3H:1V.
• Provide an outlet slope of 2H:1V.
• Provide a1-foot wide level stone area between the structure and the
inlet.
• Use inlet slope stones 3 inches in diameter or larger.
• Use gravel ½- to ¾-inch at a minimum thickness of 1-foot for the outlet slope.
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Figure 4.2.8 – Block and Gravel Filter
Gravel and Wire Mesh Filter - A gravel barrier placed over the top of the inlet. This structure does not provide an overflow.
• Use a hardware cloth or comparable wire mesh with ½-inch openings.
• Use coarse aggregate.
• Provide a height 1-foot or more, 18-inches wider than inlet on all
sides.
• Place wire mesh over the drop inlet so that the wire extends a minimum of 1-foot beyond each side of the inlet structure.
• Overlap the strips if more than one strip of mesh is necessary.
Ponding Height
Notes: 1. Drop inlet sediment barriers are to be used for small, nearly level drainage areas. (less than 5%) 2. Excavate a basin of sufficient size adjacent to the drop inlet. 3. The top of the structure (ponding height) must be well below the ground elevation downslope to prevent
runoff from bypassing the inlet. A temporary dike may be necessary on the downslope side of the structure.
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• Place coarse aggregate over the wire mesh.
• Provide at least a 12-inch depth of gravel over the entire inlet opening
and extend at least 18-inches on all sides.
Catchbasin Filters – Use inserts designed by manufacturers for
construction sites. The limited sediment storage capacity increases the amount of inspection and maintenance required, which may be daily for heavy sediment loads. To reduce maintenance requirements combine a
catchbasin filter with another type of inlet protection. This type of inlet
protection provides flow bypass without overflow and therefore may be a
better method for inlets located along active rights-of-way.
• Provides 5 cubic feet of storage.
• Requires dewatering provisions.
• Provides a high-flow bypass that will not clog under normal use at a
construction site.
• Insert the catchbasin filter in the catchbasin just below the grating.
Curb Inlet Protection with Wooden Weir – Barrier formed around a curb inlet with a wooden frame and gravel.
• Use wire mesh with ½-inch openings.
• Use extra strength filter cloth.
• Construct a frame.
• Attach the wire and filter fabric to the frame.
• Pile coarse washed aggregate against wire/fabric.
• Place weight on frame anchors.
Block and Gravel Curb Inlet Protection – Barrier formed around a curb
inlet with concrete blocks and gravel. See Figure 4.2.9.
• Use wire mesh with ½-inch openings.
• Place two concrete blocks on their sides abutting the curb at either side
of the inlet opening. These are spacer blocks.
• Place a 2x4 stud through the outer holes of each spacer block to align
the front blocks.
• Place blocks on their sides across the front of the inlet and abutting the
spacer blocks.
• Place wire mesh over the outside vertical face.
• Pile coarse aggregate against the wire to the top of the barrier.
Curb and Gutter Sediment Barrier – Sandbag or rock berm (riprap and aggregate) 3 feet high and 3 feet wide in a horseshoe shape. See Figure
4.2.10.
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• Construct a horseshoe shaped berm, faced with coarse aggregate if using riprap, 3 feet high and 3 feet wide, at least 2 feet from the inlet.
• Construct a horseshoe shaped sedimentation trap on the outside of the
berm sized to sediment trap standards for protecting a culvert inlet.
Maintenance Standards • Inspect catch basin filters frequently, especially after storm events. Clean and replace clogged inserts. For systems with clogged stone filters: pull away the stones from the inlet and clean or replace. An
alternative approach would be to use the clogged stone as fill and put
fresh stone around the inlet.
• Do not wash sediment into storm drains while cleaning. Spread all excavated material evenly over the surrounding land area or stockpile and stabilize as appropriate.
Approved as
Equivalent
Ecology has approved products as able to meet the requirements of BMP
C220. The products did not pass through the Technology Assessment
Protocol – Ecology (TAPE) process. Local jurisdictions may choose not to accept this product approved as equivalent, or may require additional testing prior to consideration for local use. The products are available for
review on Ecology’s website at
http://www.ecy.wa.gov/programs/wq/stormwater/newtech/equivalent.html
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Figure 4.2.9 – Block and Gravel Curb Inlet Protection
A
Plan View
Wire Screen orFilter Fabric Catch Basin
Curb Inlet
Concrete Block
Ponding Height
Overflow
2x4 Wood Stud(100x50 Timber Stud)
Concrete Block
Wire Screen orFilter Fabric
Curb Inlet
¾" Drain Gravel(20mm)
¾" Drain Gravel(20mm)Section A - A
Back of Curb Concrete Block
2x4 Wood Stud
Catch BasinBack of Sidewalk
NOTES:1. Use block and gravel type sediment barrier when curb inlet is located in gently sloping street segment, where water can pond and allow sediment to separate from runoff.2. Barrier shall allow for overflow from severe storm event.3. Inspect barriers and remove sediment after each storm event. Sediment and gravel must be removed from the traveled way immediately.
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Figure 4.2.10 – Curb and Gutter Barrier
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If required, drape filter fabricover brush and secure in 4"x4"min. trench with compactedbackfill.
Min. 5' wide brush barrier withmax. 6" diameter woody debris.Alternatively topsoil strippingsmay be used to form the barrier.
Anchor downhill edge offilter fabric with stakes,sandbags, or equivalent.
2' Min. Height
BMP C231: Brush Barrier
Purpose The purpose of brush barriers is to reduce the transport of coarse sediment from a construction site by providing a temporary physical barrier to sediment and reducing the runoff velocities of overland flow.
Conditions of Use • Brush barriers may be used downslope of all disturbed areas of less than one-quarter acre.
• Brush barriers are not intended to treat concentrated flows, nor are
they intended to treat substantial amounts of overland flow. Any concentrated flows must be conveyed through the drainage system to a sediment pond. The only circumstance in which overland flow can be treated solely by a brush barrier, rather than by a sediment pond, is when the area draining to the barrier is small.
• Brush barriers should only be installed on contours.
Design and Installation Specifications
• Height 2 feet (minimum) to 5 feet (maximum).
• Width 5 feet at base (minimum) to 15 feet (maximum).
• Filter fabric (geotextile) may be anchored over the brush berm to
enhance the filtration ability of the barrier. Ten-ounce burlap is an adequate alternative to filter fabric.
• Chipped site vegetation, composted mulch, or wood-based mulch (hog fuel) can be used to construct brush barriers.
• A 100 percent biodegradable installation can be constructed using 10-ounce burlap held in place by wooden stakes. Figure 4.2.11 depicts a typical brush barrier.
Maintenance Standards • There shall be no signs of erosion or concentrated runoff under or around the barrier. If concentrated flows are bypassing the barrier, it must be expanded or augmented by toed-in filter fabric.
• The dimensions of the barrier must be maintained.
Figure 4.2.11 – Brush Barrier
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BMP C232: Gravel Filter Berm
Purpose A gravel filter berm is constructed on rights-of-way or traffic areas within
a construction site to retain sediment by using a filter berm of gravel or
crushed rock.
Conditions of Use Where a temporary measure is needed to retain sediment from rights-of-way or in traffic areas on construction sites.
Design and
Installation
Specifications
• Berm material shall be ¾ to 3 inches in size, washed well-grade gravel
or crushed rock with less than 5 percent fines.
• Spacing of berms:
− Every 300 feet on slopes less than 5 percent
− Every 200 feet on slopes between 5 percent and 10 percent
− Every 100 feet on slopes greater than 10 percent
• Berm dimensions:
− 1 foot high with 3H:1V side slopes
− 8 linear feet per 1 cfs runoff based on the 10-year, 24-hour design
storm
Maintenance Standards • Regular inspection is required. Sediment shall be removed and filter
material replaced as needed.
BMP C233: Silt Fence
Purpose Use of a silt fence reduces the transport of coarse sediment from a
construction site by providing a temporary physical barrier to sediment and reducing the runoff velocities of overland flow. See Figure 4.2.12 for
details on silt fence construction.
Conditions of Use Silt fence may be used downslope of all disturbed areas.
• Silt fence shall prevent soil carried by runoff water from going
beneath, through, or over the top of the silt fence, but shall allow the water to pass through the fence.
• Silt fence is not intended to treat concentrated flows, nor is it intended
to treat substantial amounts of overland flow. Convey any
concentrated flows through the drainage system to a sediment pond.
• Do not construct silt fences in streams or use in V-shaped ditches. Silt fences do not provide an adequate method of silt control for anything
deeper than sheet or overland flow.
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Figure 4.2.12 – Silt Fence
Design and
Installation Specifications
• Use in combination with sediment basins or other BMPs.
• Maximum slope steepness (normal (perpendicular) to fence line)
1H:1V.
• Maximum sheet or overland flow path length to the fence of 100 feet.
• Do not allow flows greater than 0.5 cfs.
• The geotextile used shall meet the following standards. All geotextile
properties listed below are minimum average roll values (i.e., the test
result for any sampled roll in a lot shall meet or exceed the values shown in Table 4.2.3):
Table 4.2.3 Geotextile Standards
Polymeric Mesh AOS (ASTM D4751) 0.60 mm maximum for slit film woven (#30 sieve). 0.30 mm maximum for all other geotextile types (#50 sieve).
0.15 mm minimum for all fabric types (#100 sieve).
Water Permittivity (ASTM D4491) 0.02 sec-1 minimum
Grab Tensile Strength (ASTM D4632) 180 lbs. Minimum for extra strength fabric.
100 lbs minimum for standard strength fabric.
Grab Tensile Strength
(ASTM D4632)
30% maximum
Ultraviolet Resistance
(ASTM D4355)
70% minimum
• Support standard strength fabrics with wire mesh, chicken wire, 2-inch x 2-inch wire, safety fence, or jute mesh to increase the strength of the
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fabric. Silt fence materials are available that have synthetic mesh backing attached.
• Filter fabric material shall contain ultraviolet ray inhibitors and
stabilizers to provide a minimum of six months of expected usable
construction life at a temperature range of 0°F. to 120°F.
• One-hundred percent biodegradable silt fence is available that is strong, long lasting, and can be left in place after the project is
completed, if permitted by local regulations.
• Refer to Figure 4.2.12 for standard silt fence details. Include the
following standard Notes for silt fence on construction plans and specifications:
1. The contractor shall install and maintain temporary silt fences at
the locations shown in the Plans.
2. Construct silt fences in areas of clearing, grading, or drainage prior
to starting those activities.
3. The silt fence shall have a 2-feet min. and a 2½-feet max. height above the original ground surface.
4. The filter fabric shall be sewn together at the point of manufacture
to form filter fabric lengths as required. Locate all sewn seams at
support posts. Alternatively, two sections of silt fence can be overlapped, provided the Contractor can demonstrate, to the satisfaction of the Engineer, that the overlap is long enough and
that the adjacent fence sections are close enough together to
prevent silt laden water from escaping through the fence at the
overlap.
5. Attach the filter fabric on the up-slope side of the posts and secure with staples, wire, or in accordance with the manufacturer's
recommendations. Attach the filter fabric to the posts in a manner
that reduces the potential for tearing.
6. Support the filter fabric with wire or plastic mesh, dependent on the properties of the geotextile selected for use. If wire or plastic
mesh is used, fasten the mesh securely to the up-slope side of the
posts with the filter fabric up-slope of the mesh.
7. Mesh support, if used, shall consist of steel wire with a maximum
mesh spacing of 2-inches, or a prefabricated polymeric mesh. The strength of the wire or polymeric mesh shall be equivalent to or
greater than 180 lbs. grab tensile strength. The polymeric mesh
must be as resistant to the same level of ultraviolet radiation as the
filter fabric it supports.
8. Bury the bottom of the filter fabric 4-inches min. below the ground surface. Backfill and tamp soil in place over the buried portion of
the filter fabric, so that no flow can pass beneath the fence and
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scouring cannot occur. When wire or polymeric back-up support mesh is used, the wire or polymeric mesh shall extend into the
ground 3-inches min.
9. Drive or place the fence posts into the ground 18-inches min. A
12–inch min. depth is allowed if topsoil or other soft subgrade soil is not present and 18-inches cannot be reached. Increase fence post min. depths by 6 inches if the fence is located on slopes of 3H:1V
or steeper and the slope is perpendicular to the fence. If required
post depths cannot be obtained, the posts shall be adequately
secured by bracing or guying to prevent overturning of the fence due to sediment loading.
10. Use wood, steel or equivalent posts. The spacing of the support
posts shall be a maximum of 6-feet. Posts shall consist of either:
• Wood with dimensions of 2-inches by 2-inches wide min. and a 3-feet min. length. Wood posts shall be free of defects such as knots, splits, or gouges.
• No. 6 steel rebar or larger.
• ASTM A 120 steel pipe with a minimum diameter of 1-inch.
• U, T, L, or C shape steel posts with a minimum weight of 1.35
lbs./ft.
• Other steel posts having equivalent strength and bending
resistance to the post sizes listed above.
11. Locate silt fences on contour as much as possible, except at the
ends of the fence, where the fence shall be turned uphill such that
the silt fence captures the runoff water and prevents water from
flowing around the end of the fence.
12. If the fence must cross contours, with the exception of the ends of the fence, place gravel check dams perpendicular to the back of the
fence to minimize concentrated flow and erosion. The slope of the
fence line where contours must be crossed shall not be steeper than
3H:1V.
• Gravel check dams shall be approximately 1-foot deep at the
back of the fence. Gravel check dams shall be continued
perpendicular to the fence at the same elevation until the top of
the check dam intercepts the ground surface behind the fence.
• Gravel check dams shall consist of crushed surfacing base course, gravel backfill for walls, or shoulder ballast. Gravel
check dams shall be located every 10 feet along the fence
where the fence must cross contours.
• Refer to Figure 4.2.13 for slicing method details. Silt fence installation using the slicing method specifications:
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1. The base of both end posts must be at least 2- to 4-inches above the top of the filter fabric on the middle posts for ditch checks to drain
properly. Use a hand level or string level, if necessary, to mark
base points before installation.
2. Install posts 3- to 4-feet apart in critical retention areas and 6- to 7-feet apart in standard applications.
3. Install posts 24-inches deep on the downstream side of the silt
fence, and as close as possible to the filter fabric, enabling posts to
support the filter fabric from upstream water pressure.
4. Install posts with the nipples facing away from the filter fabric.
5. Attach the filter fabric to each post with three ties, all spaced within the top 8-inches of the filter fabric. Attach each tie
diagonally 45 degrees through the filter fabric, with each puncture
at least 1-inch vertically apart. Each tie should be positioned to
hang on a post nipple when tightening to prevent sagging.
6. Wrap approximately 6-inches of fabric around the end posts and secure with 3 ties.
7. No more than 24-inches of a 36-inch filter fabric is allowed above
ground level.
Compact the soil immediately next to the filter fabric with the front wheel of the tractor, skid steer, or roller exerting at least 60 pounds per square inch. Compact the upstream side first and then each side
twice for a total of four trips. Check and correct the silt fence
installation for any deviation before compaction. Use a flat-bladed
shovel to tuck fabric deeper into the ground if necessary.
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Figure 4.2.13 – Silt Fence Installation by Slicing Method
Maintenance Standards
• Repair any damage immediately.
• Intercept and convey all evident concentrated flows uphill of the silt fence to a sediment pond.
• Check the uphill side of the fence for signs of the fence clogging and
acting as a barrier to flow and then causing channelization of flows
parallel to the fence. If this occurs, replace the fence or remove the
trapped sediment.
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• Remove sediment deposits when the deposit reaches approximately
one-third the height of the silt fence, or install a second silt fence.
• Replace filter fabric that has deteriorated due to ultraviolet breakdown.
BMP C234: Vegetated Strip
Purpose Vegetated strips reduce the transport of coarse sediment from a
construction site by providing a temporary physical barrier to sediment
and reducing the runoff velocities of overland flow.
Conditions of Use • Vegetated strips may be used downslope of all disturbed areas.
• Vegetated strips are not intended to treat concentrated flows, nor are they intended to treat substantial amounts of overland flow. Any
concentrated flows must be conveyed through the drainage system to a
sediment pond. The only circumstance in which overland flow can be
treated solely by a strip, rather than by a sediment pond, is when the
following criteria are met (see Table 4.2.4):
Table 4.2.4
Contributing Drainage Area for Vegetated Strips
Average Contributing area Slope Average Contributing area Percent Slope Max Contributing area Flowpath Length 1.5H:1V or flatter 67% or flatter 100 feet
2H:1V or flatter 50% or flatter 115 feet
4H:1V or flatter 25% or flatter 150 feet 6H:1V or flatter 16.7% or flatter 200 feet 10H:1V or flatter 10% or flatter 250 feet
Design and Installation Specifications
• The vegetated strip shall consist of a minimum of a 25-foot flowpath length continuous strip of dense vegetation with topsoil. Grass-
covered, landscaped areas are generally not adequate because the
volume of sediment overwhelms the grass. Ideally, vegetated strips
shall consist of undisturbed native growth with a well-developed soil
that allows for infiltration of runoff.
• The slope within the strip shall not exceed 4H:1V.
• The uphill boundary of the vegetated strip shall be delineated with
clearing limits.
Maintenance Standards
• Any areas damaged by erosion or construction activity shall be
seeded immediately and protected by mulch.
• If more than 5 feet of the original vegetated strip width has had
vegetation removed or is being eroded, sod must be installed.
• If there are indications that concentrated flows are traveling across the
buffer, surface water controls must be installed to reduce the flows
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entering the buffer, or additional perimeter protection must be installed.
BMP C235: Wattles
Purpose Wattles are temporary erosion and sediment control barriers consisting of
straw, compost, or other material that is wrapped in biodegradable tubular plastic or similar encasing material. They reduce the velocity and can spread the flow of rill and sheet runoff, and can capture and retain
sediment. Wattles are typically 8 to 10 inches in diameter and 25 to 30 feet
in length. Wattles are placed in shallow trenches and staked along the
contour of disturbed or newly constructed slopes. See Figure 4.2.14 for typical construction details. WSDOT Standard Plan I-30.30-00 also provides information on Wattles
(http://www.wsdot.wa.gov/Design/Standards/Plans.htm#SectionI)
Conditions of Use • Use wattles:
• In disturbed areas that require immediate erosion protection.
• On exposed soils during the period of short construction delays, or over winter months.
• On slopes requiring stabilization until permanent vegetation can be
established.
• The material used dictates the effectiveness period of the wattle. Generally, Wattles are typically effective for one to two seasons.
• Prevent rilling beneath wattles by properly entrenching and abutting
wattles together to prevent water from passing between them.
Design Criteria • Install wattles perpendicular to the flow direction and parallel to the
slope contour.
• Narrow trenches should be dug across the slope on contour to a depth of 3- to 5-inches on clay soils and soils with gradual slopes. On loose
soils, steep slopes, and areas with high rainfall, the trenches should be
dug to a depth of 5- to 7- inches, or 1/2 to 2/3 of the thickness of the
wattle.
• Start building trenches and installing wattles from the base of the slope
and work up. Spread excavated material evenly along the uphill slope
and compacted using hand tamping or other methods.
• Construct trenches at intervals of 10- to 25-feet depending on the
steepness of the slope, soil type, and rainfall. The steeper the slope the closer together the trenches.
• Install the wattles snugly into the trenches and abut tightly end to end.
Do not overlap the ends.
• Install stakes at each end of the wattle, and at 4-foot centers along
entire length of wattle.
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• If required, install pilot holes for the stakes using a straight bar to drive holes through the wattle and into the soil.
• Wooden stakes should be approximately 3/4 x 3/4 x 24 inches min.
Willow cuttings or 3/8-inch rebar can also be used for stakes.
• Stakes should be driven through the middle of the wattle, leaving 2 to 3 inches of the stake protruding above the wattle.
Maintenance
Standards
• Wattles may require maintenance to ensure they are in contact with
soil and thoroughly entrenched, especially after significant rainfall on
steep sandy soils.
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Figure 4.2.14 – Wattles
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• Inspect the slope after significant storms and repair any areas where wattles are not tightly abutted or water has scoured beneath the
wattles.
Approved as Equivalent Ecology has approved products as able to meet the requirements of BMP
C235. The products did not pass through the Technology Assessment Protocol – Ecology (TAPE) process. Local jurisdictions may choose not to accept this product approved as equivalent, or may require additional
testing prior to consideration for local use. The products are available for
review on Ecology’s website at
http://www.ecy.wa.gov/programs/wq/stormwater/newtech/equivalent.html
BMP C236: Vegetative Filtration
Purpose Vegetative Filtration may be used in conjunction with BMP C241
Temporary Sediment Ponds, BMP C206 Level Spreader and a pumping
system with surface intake to improve turbidity levels of stormwater
discharges by filtering through existing vegetation where undisturbed forest floor duff layer or established lawn with thatch layer are present. Vegetative Filtration can also be used to infiltrate dewatering waste from
foundations, vaults, and trenches as long as runoff does not occur.
Conditions of Use • For every five acre of disturbed soil use one acre of grass field, farm
pasture, or wooded area. Reduce or increase this area depending on project size, ground water table height, and other site conditions.
• Wetlands shall not be used for filtration.
• Do not use this BMP in areas with a high ground water table, or in
areas that will have a high seasonal ground water table during the use
of this BMP.
• This BMP may be less effective on soils that prevent the infiltration of
the water, such as hard till.
• Using other effective source control measures throughout a
construction site will prevent the generation of additional highly turbid
water and may reduce the time period or area need for this BMP.
• Stop distributing water into the vegetated area if standing water or
erosion results.
Design Criteria • Find land adjacent to the project that has a vegetated field, preferably a
farm field, or wooded area.
• If the project site does not contain enough vegetated field area consider obtaining permission from adjacent landowners (especially
for farm fields).
• Install a pump and downstream distribution manifold depending on the
project size. Generally, the main distribution line should reach 100 to
200-feet long (many large projects, or projects on tight soil, will
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require systems that reach several thousand feet long with numerous branch lines off of the main distribution line).
• The manifold should have several valves, allowing for control over the
distribution area in the field.
• Install several branches of 4” schedule 20, swaged-fit common septic tight-lined sewer line, or 6” fire hose, which can convey the turbid water out to various sections of the field. See Figure 4.2.15.
• Determine the branch length based on the field area geography and
number of branches. Typically, branches stretch from 200-feet to
several thousand feet. Always, lay branches on contour with the slope.
• On uneven ground, sprinklers perform well. Space sprinkler heads so that spray patterns do not overlap.
• On relatively even surfaces, a level spreader using 4-inch perforated
pipe may be used as an alternative option to the sprinkler head setup.
Install drain pipe at the highest point on the field and at various lower elevations to ensure full coverage of the filtration area. Pipe should be place with the holes up to allow for a gentle weeping of stormwater
evenly out all holes. Leveling the pipe by staking and using sandbags
may be required.
• To prevent the over saturation of the field area, rotate the use of branches or spray heads. Do this as needed based on monitoring the spray field.
• Monitor the spray field on a daily basis to ensure that over saturation
of any portion of the field doesn’t occur at any time. The presence of
standing puddles of water or creation of concentrated flows visually signify that over saturation of the field has occurred.
• Since the operator is handling contaminated water, physically monitor
the vegetated spray field all the way down to the nearest surface water,
or furthest spray area, to ensure that the water has not caused overland
or concentrated flows, and has not created erosion around the spray nozzle.
• Monitoring usually needs to take place 3-5 times per day to ensure
sheet-flow into state waters. Do not exceed water quality standards for
turbidity.
• Ecology strongly recommends that a separate inspection log be developed, maintained and kept with the existing site logbook to aid
the operator conducting inspections. This separate “Field Filtration
Logbook” can also aid the facility in demonstrating compliance with
permit conditions.
Maintenance Standards
• Inspect the spray nozzles daily, at a minimum, for leaks and plugging from sediment particles.
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• If erosion, concentrated flows, or over saturation of the field occurs, rotate the use of branches or spray heads or move the branches to a
new field location.
• Check all branches and the manifold for unintended leaks.
Flowpath Guidelines for Vegetative Filtration
Average Slope Average Area % Slope Estimated Flowpath
Length (ft)
1.5H:1V 67% 250
2H:1V 50% 200
4H:1V 25% 150
6H:1V 16.7% 115
10H:1V 10% 100
Figure 4.2.15 – Manifold and Braches in a wooded, vegetated spray field
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BMP C240: Sediment Trap
Purpose A sediment trap is a small temporary ponding area with a gravel outlet
used to collect and store sediment from sites cleared and/or graded during
construction. Sediment traps, along with other perimeter controls, shall be
installed before any land disturbance takes place in the drainage area.
Conditions of Use Prior to leaving a construction site, stormwater runoff must pass through a sediment pond or trap or other appropriate sediment removal best
management practice. Non-engineered sediment traps may be used on-site
prior to an engineered sediment trap or sediment pond to provide
additional sediment removal capacity.
It is intended for use on sites where the tributary drainage area is less than 3 acres, with no unusual drainage features, and a projected build-out time
of six months or less. The sediment trap is a temporary measure (with a
design life of approximately 6 months) and shall be maintained until the
site area is permanently protected against erosion by vegetation and/or structures.
Sediment traps and ponds are only effective in removing sediment down
to about the medium silt size fraction. Runoff with sediment of finer
grades (fine silt and clay) will pass through untreated, emphasizing the
need to control erosion to the maximum extent first.
Whenever possible, sediment-laden water shall be discharged into on-site, relatively level, vegetated areas (see BMP C234 – Vegetated Strip). This
is the only way to effectively remove fine particles from runoff unless
chemical treatment or filtration is used. This can be particularly useful
after initial treatment in a sediment trap or pond. The areas of release must be evaluated on a site-by-site basis in order to determine appropriate locations for and methods of releasing runoff. Vegetated wetlands shall
not be used for this purpose. Frequently, it may be possible to pump water
from the collection point at the downhill end of the site to an upslope
vegetated area. Pumping shall only augment the treatment system, not replace it, because of the possibility of pump failure or runoff volume in
excess of pump capacity.
All projects that are constructing permanent facilities for runoff quantity
control should use the rough-graded or final-graded permanent facilities
for traps and ponds. This includes combined facilities and infiltration facilities. When permanent facilities are used as temporary sedimentation
facilities, the surface area requirement of a sediment trap or pond must be
met. If the surface area requirements are larger than the surface area of the
permanent facility, then the trap or pond shall be enlarged to comply with
the surface area requirement. The permanent pond shall also be divided into two cells as required for sediment ponds.
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Either a permanent control structure or the temporary control structure (described in BMP C241, Temporary Sediment Pond) can be used. If a
permanent control structure is used, it may be advisable to partially restrict
the lower orifice with gravel to increase residence time while still allowing
dewatering of the pond. A shut-off valve may be added to the control structure to allow complete retention of stormwater in emergency situations. In this case, an emergency overflow weir must be added.
A skimmer may be used for the sediment trap outlet if approved by the
Local Permitting Authority.
Design and Installation Specifications
• See Figures 4.2.16 and 4.2.17 for details.
• If permanent runoff control facilities are part of the project, they
should be used for sediment retention.
• To determine the sediment trap geometry, first calculate the design surface area (SA) of the trap, measured at the invert of the weir. Use the following equation:
SA = FS(Q2/Vs)
where
Q2 = Design inflow based on the peak discharge from the developed 2-year runoff event from the contributing drainage area as computed in the hydrologic analysis. The
10-year peak flow shall be used if the project size, expected
timing and duration of construction, or downstream
conditions warrant a higher level of protection. If no hydrologic analysis is required, the Rational Method may be used.
Vs = The settling velocity of the soil particle of interest. The
0.02 mm (medium silt) particle with an assumed density of
2.65 g/cm3 has been selected as the particle of interest and has a settling velocity (Vs) of 0.00096 ft/sec.
FS = A safety factor of 2 to account for non-ideal settling.
Therefore, the equation for computing surface area becomes:
SA = 2 x Q2/0.00096 or
2080 square feet per cfs of inflow
Note: Even if permanent facilities are used, they must still have a
surface area that is at least as large as that derived from the above
formula. If they do not, the pond must be enlarged.
• To aid in determining sediment depth, all sediment traps shall have a
staff gauge with a prominent mark 1-foot above the bottom of the trap.
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Surface area determinedat top of weir
Note: Trap may be formed by berm or bypartial or complete excavation
Discharge to stabilizedconveyance, outlet, orlevel spreader
¾" - 1.5"Washed gravel
Geotextile
Flat Bottom
1' Min. Overflow
1' Min.
4' Min.
RipRap2"-4" Rock
1' Min.
1.5' Min.
3.5'-5'
3H
:
1
V
M
a
x
.
• Sediment traps may not be feasible on utility projects due to the limited work space or the short-term nature of the work. Portable tanks
may be used in place of sediment traps for utility projects.
Maintenance Standards
• Sediment shall be removed from the trap when it reaches 1-foot in
depth.
• Any damage to the pond embankments or slopes shall be repaired.
Figure 4.2.16 – Cross Section of Sediment Trap
Figure 4.2.17 – Sediment Trap Outlet
Native soil orcompacted backfill
Geotextile
Min. 1' depth2"-4"' rock
Min. 1' depth 3/4"-1.5"washed gravel
6' Min.
1' Min. depth overflow spillway
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BMP C241: Temporary Sediment Pond
Purpose Sediment ponds remove sediment from runoff originating from disturbed
areas of the site. Sediment ponds are typically designed to remove
sediment no smaller than medium silt (0.02 mm). Consequently, they
usually reduce turbidity only slightly.
Conditions of Use Prior to leaving a construction site, stormwater runoff must pass through a sediment pond or other appropriate sediment removal best management
practice.
A sediment pond shall be used where the contributing drainage area is 3
acres or more. Ponds must be used in conjunction with erosion control practices to reduce the amount of sediment flowing into the basin.
Design and
Installation
Specifications
• Sediment basins must be installed only on sites where failure of the
structure would not result in loss of life, damage to homes or
buildings, or interruption of use or service of public roads or utilities.
Also, sediment traps and ponds are attractive to children and can be very dangerous. Compliance with local ordinances regarding health and safety must be addressed. If fencing of the pond is required, the
type of fence and its location shall be shown on the ESC plan.
• Structures having a maximum storage capacity at the top of the dam of
10 acre-ft (435,600 ft3) or more are subject to the Washington Dam Safety Regulations (Chapter 173-175 WAC).
• See Figures 4.2.18, 4.2.19, and 4.2.20 for details.
• If permanent runoff control facilities are part of the project, they
should be used for sediment retention. The surface area requirements
of the sediment basin must be met. This may require temporarily enlarging the permanent basin to comply with the surface area requirements. The permanent control structure must be temporarily
replaced with a control structure that only allows water to leave the
pond from the surface or by pumping. The permanent control structure
must be installed after the site is fully stabilized. .
• Use of infiltration facilities for sedimentation basins during
construction tends to clog the soils and reduce their capacity to
infiltrate. If infiltration facilities are to be used, the sides and bottom of
the facility must only be rough excavated to a minimum of 2 feet
above final grade. Final grading of the infiltration facility shall occur only when all contributing drainage areas are fully stabilized. The
infiltration pretreatment facility should be fully constructed and used
with the sedimentation basin to help prevent clogging.
• Determining Pond Geometry
Obtain the discharge from the hydrologic calculations of the peak flow for the 2-year runoff event (Q2). The 10-year peak flow shall be used if
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the project size, expected timing and duration of construction, or downstream conditions warrant a higher level of protection. If no
hydrologic analysis is required, the Rational Method may be used.
Determine the required surface area at the top of the riser pipe with the
equation:
SA = 2 x Q2/0.00096 or 2080 square feet per cfs of inflow
See BMP C240 for more information on the derivation of the surface
area calculation.
The basic geometry of the pond can now be determined using the following design criteria:
• Required surface area SA (from Step 2 above) at top of riser.
• Minimum 3.5-foot depth from top of riser to bottom of pond.
• Maximum 3H:1V interior side slopes and maximum 2H:1V exterior
slopes. The interior slopes can be increased to a maximum of 2H:1V if fencing is provided at or above the maximum water surface.
• One foot of freeboard between the top of the riser and the crest of the
emergency spillway.
• Flat bottom.
• Minimum 1-foot deep spillway.
• Length-to-width ratio between 3:1 and 6:1.
• Sizing of Discharge Mechanisms.
The outlet for the basin consists of a combination of principal and
emergency spillways. These outlets must pass the peak runoff
expected from the contributing drainage area for a 100-year storm. If, due to site conditions and basin geometry, a separate emergency spill-way is not feasible, the principal spillway must pass the entire peak
runoff expected from the 100-year storm. However, an attempt to
provide a separate emergency spillway should always be made. The
runoff calculations should be based on the site conditions during construction. The flow through the dewatering orifice cannot be
utilized when calculating the 100-year storm elevation because of its
potential to become clogged; therefore, available spillway storage
must begin at the principal spillway riser crest.
The principal spillway designed by the procedures contained in this standard will result in some reduction in the peak rate of runoff.
However, the riser outlet design will not adequately control the basin
discharge to the predevelopment discharge limitations as stated in
Minimum Requirement #7: Flow Control. However, if the basin for a
permanent stormwater detention pond is used for a temporary
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Riser pipe(principal spillway)open at top withtrash rackper Fig 4.4.4E
Dewatering device(see riser detail)
Wire-backed silt fencestaked haybales wrappedwith filter fabric, orequivalent divider
Dewateringorifice Concrete base(see riser detail)
Discharge to stabilizedconveyance outlet orlevel spreader
Embankment compacted 95%pervious materials such asgravel or clean sand shallnot be used
6' min. WidthCrest ofemergency spillway
Key divider into slopeto prevent flowaround sides
The pond length shall be 3 to 6times the maximum pond width Emergency overflowspillway
Discharge to stabilizedconveyance, outlet, orlevel spreader
Note: Pond may be formed by berm orby partial or complete excavation
Inflow
Pond length
Silt fence orequivalent divider
Riser pipe
sedimentation basin, the control structure for the permanent pond can be used to maintain predevelopment discharge limitations. The size of
the basin, the expected life of the construction project, the anticipated
downstream effects and the anticipated weather conditions during
construction, should be considered to determine the need of additional discharge control. See Figure 4.2.21 for riser inflow curves.
Figure 4.2.18 – Sediment Pond Plan View
Figure 4.2.19 – Sediment Pond Cross Section
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Perforated polyethylenedrainage tubing, diametermin. 2" larger thandewatering orifice.Tubing shall comply with ASTM F667 and AASHTO M294
Polyethylene cap Provide adequatestrapping
Dewatering orifice, schedule,40 steel stub min.Diameter as per calculations
Alternatively, metal stakesand wire may be used toprevent flotation
2X riser dia. Min.
Concrete base
Corrugatedmetal riser
Watertightcoupling
18" min.
6" min.
Tack weld
3.5" min.
Figure 4.2.20 – Sediment Pond Riser Detail
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Figure 4.2.21 – Riser Inflow Curves
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Principal Spillway: Determine the required diameter for the principal spillway (riser pipe). The diameter shall be the minimum necessary to pass
the site’s 15-minute, 10-year flowrate. If using the Western Washington
Hydrology Model (WWHM), Version 2 or 3, design flow is the 10-year (1
hour) flow for the developed (unmitigated) site, multiplied by a factor of 1.6. Use Figure 4.2.21 to determine this diameter (h = 1-foot). Note: A permanent control structure may be used instead of a temporary riser.
Emergency Overflow Spillway: Determine the required size and design
of the emergency overflow spillway for the developed 100-year peak flow
using the method contained in Volume III.
Dewatering Orifice: Determine the size of the dewatering orifice(s) (minimum 1-inch diameter) using a modified version of the discharge
equation for a vertical orifice and a basic equation for the area of a circular
orifice. Determine the required area of the orifice with the following
equation:
5.0
5.0
3600x6.0
)2(
Tg
hAAso=
where Ao = orifice area (square feet)
As = pond surface area (square feet)
h = head of water above orifice (height of riser in feet)
T = dewatering time (24 hours) g = acceleration of gravity (32.2 feet/second2)
Convert the required surface area to the required diameter D of the orifice:
ooAADx54.13x24==π
The vertical, perforated tubing connected to the dewatering orifice must be
at least 2 inches larger in diameter than the orifice to improve flow
characteristics. The size and number of perforations in the tubing should
be large enough so that the tubing does not restrict flow. The orifice should control the flow rate.
• Additional Design Specifications
The pond shall be divided into two roughly equal volume cells by a
permeable divider that will reduce turbulence while allowing
movement of water between cells. The divider shall be at least one-half the height of the riser and a minimum of one foot below the top of the riser. Wire-backed, 2- to 3-foot high, extra strength filter fabric
supported by treated 4"x4"s can be used as a divider. Alternatively,
staked straw bales wrapped with filter fabric (geotextile) may be used.
If the pond is more than 6 feet deep, a different mechanism must be proposed. A riprap embankment is one acceptable method of
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separation for deeper ponds. Other designs that satisfy the intent of this provision are allowed as long as the divider is permeable, structurally
sound, and designed to prevent erosion under or around the barrier.
To aid in determining sediment depth, one-foot intervals shall be
prominently marked on the riser.
If an embankment of more than 6 feet is proposed, the pond must comply with the criteria contained in Volume III regarding dam safety
for detention BMPs.
• The most common structural failure of sedimentation basins is caused
by piping. Piping refers to two phenomena: (1) water seeping through fine-grained soil, eroding the soil grain by grain and forming pipes or tunnels; and, (2) water under pressure flowing upward through a
granular soil with a head of sufficient magnitude to cause soil grains to
lose contact and capability for support.
The most critical construction sequences to prevent piping will be:
1. Tight connections between riser and barrel and other pipe connections.
2. Adequate anchoring of riser.
3. Proper soil compaction of the embankment and riser footing.
4. Proper construction of anti-seep devices.
Maintenance Standards • Sediment shall be removed from the pond when it reaches 1–foot in depth.
• Any damage to the pond embankments or slopes shall be repaired.
BMP C250: Construction Stormwater Chemical Treatment
Purpose This BMP applies when using stormwater chemicals in batch treatment or flow-through treatment.
Turbidity is difficult to control once fine particles are suspended in
stormwater runoff from a construction site. Sedimentation ponds are
effective at removing larger particulate matter by gravity settling, but are
ineffective at removing smaller particulates such as clay and fine silt. Traditional erosion and sediment control BMPs may not be adequate to
ensure compliance with the water quality standards for turbidity in
receiving water.
Chemical treatment can reliably provide exceptional reductions of
turbidity and associated pollutants. Chemical treatment may be required to meet turbidity stormwater discharge requirements, especially when
construction is to proceed through the wet season.
Conditions of Use Formal written approval from Ecology is required for the use of chemical
treatment regardless of site size. The Local Permitting Authority may also
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require review and approval. When approved, the chemical treatment systems must be included in the Construction Stormwater Pollution
Prevention Plan (SWPPP).
Design and Installation Specifications
See Appendix II-B for background information on chemical treatment.
Criteria for Chemical Treatment Product Use: Chemically treated stormwater discharged from construction sites must be nontoxic to aquatic organisms. The Chemical Technology Assessment Protocol (CTAPE)
must be used to evaluate chemicals proposed for stormwater treatment.
Only chemicals approved by Ecology under the CTAPE may be used for
stormwater treatment. The approved chemicals, their allowable application techniques (batch treatment or flow-through treatment), allowable application rates, and conditions of use can be found at the
Department of Ecology Emerging Technologies website:
http://www.ecy.wa.gov/programs/wq/stormwater/newtech/technologies.ht
ml.
Treatment System Design Considerations: The design and operation of a chemical treatment system should take into consideration the factors that
determine optimum, cost-effective performance. It is important to
recognize the following:
• Only Ecology approved chemicals may be used and must follow approved dose rate.
• The pH of the stormwater must be in the proper range for the polymers
to be effective, which is typically 6.5 to 8.5
• The coagulant must be mixed rapidly into the water to ensure proper
dispersion.
• A flocculation step is important to increase the rate of settling, to produce the lowest turbidity, and to keep the dosage rate as low as
possible.
• Too little energy input into the water during the flocculation phase
results in flocs that are too small and/or insufficiently dense. Too much energy can rapidly destroy floc as it is formed.
• Care must be taken in the design of the withdrawal system to minimize
outflow velocities and to prevent floc discharge. Discharge from a
batch treatment system should be directed through a physical filter
such as a vegetated swale that would catch any unintended floc discharge. Currently, flow-through systems always discharge through
the chemically enhanced sand filtration system.
• System discharge rates must take into account downstream
conveyance integrity.
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Polymer Batch Treatment Process Description:
A batch chemical treatment system consists of the stormwater collection
system (either temporary diversion or the permanent site drainage system),
a storage pond, pumps, a chemical feed system, treatment cells, and
interconnecting piping.
The batch treatment system shall use a minimum of two lined treatment cells in addition to an untreated stormwater storage pond. Multiple
treatment cells allow for clarification of treated water while other cells are
being filled or emptied. Treatment cells may be ponds or tanks. Ponds
with constructed earthen embankments greater than six feet high or which impound more than 10 acre-feet require special engineering analyses. The Ecology Dam Safety Section has specific design criteria for dams in
Washington State (see
http://www.ecy.wa.gov/programs/wr/dams/GuidanceDocs.html ).
Stormwater is collected at interception point(s) on the site and is diverted by gravity or by pumping to an untreated stormwater storage pond or other untreated stormwater holding area. The stormwater is stored until
treatment occurs. It is important that the holding pond be large enough to
provide adequate storage.
The first step in the treatment sequence is to check the pH of the stormwater in the untreated stormwater storage pond. The pH is adjusted by the application of carbon dioxide or a base until the stormwater in the
storage pond is within the desired pH range, 6.5 to 8.5. When used, carbon
dioxide is added immediately downstream of the transfer pump. Typically
sodium bicarbonate (baking soda) is used as a base, although other bases may be used. When needed, base is added directly to the untreated stormwater storage pond. The stormwater is recirculated with the
treatment pump to provide mixing in the storage pond. Initial pH
adjustments should be based on daily bench tests. Further pH adjustments
can be made at any point in the process.
Once the stormwater is within the desired pH range (dependant on
polymer being used), the stormwater is pumped from the untreated
stormwater storage pond to a treatment cell as polymer is added. The
polymer is added upstream of the pump to facilitate rapid mixing.
After polymer addition, the water is kept in a lined treatment cell for clarification of the sediment-floc. In a batch mode process, clarification
typically takes from 30 minutes to several hours. Prior to discharge
samples are withdrawn for analysis of pH, flocculent chemical
concentration, and turbidity. If both are acceptable, the treated water is
discharged.
Several configurations have been developed to withdraw treated water
from the treatment cell. The original configuration is a device that
withdraws the treated water from just beneath the water surface using a
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float with adjustable struts that prevent the float from settling on the cell bottom. This reduces the possibility of picking up sediment-floc from the
bottom of the pond. The struts are usually set at a minimum clearance of
about 12 inches; that is, the float will come within 12 inches of the bottom
of the cell. Other systems have used vertical guides or cables which constrain the float, allowing it to drift up and down with the water level. More recent designs have an H-shaped array of pipes, set on the
horizontal.
This scheme provides for withdrawal from four points rather than one.
This configuration reduces the likelihood of sucking settled solids from the bottom. It also reduces the tendency for a vortex to form. Inlet diffusers, a long floating or fixed pipe with many small holes in it, are also
an option.
Safety is a primary concern. Design should consider the hazards
associated with operations, such as sampling. Facilities should be designed to reduce slip hazards and drowning. Tanks and ponds should have life rings, ladders, or steps extending from the bottom to the top.
Polymer Batch Treatment Process Description:
At a minimum, a flow-through chemical treatment system consists of the
stormwater collection system (either temporary diversion or the permanent site drainage system), an untreated stormwater storage pond, and the chemically enhanced sand filtration system.
Stormwater is collected at interception point(s) on the site and is diverted
by gravity or by pumping to an untreated stormwater storage pond or other
untreated stormwater holding area. The stormwater is stored until treatment occurs. It is important that the holding pond be large enough to provide adequate storage.
Stormwater is then pumped from the untreated stormwater storage pond to
the chemically enhanced sand filtration system where polymer is added.
Adjustments to pH may be necessary before chemical addition. The sand filtration system continually monitors the stormwater for turbidity and pH.
If the discharge water is ever out of an acceptable range for turbidity or
pH, the water is recycled to the untreated stormwater pond where it can be
retreated.
For batch treatment and flow-through treatment, the following equipment should be located in a lockable shed:
• The chemical injector.
• Secondary containment for acid, caustic, buffering compound, and
treatment chemical.
• Emergency shower and eyewash.
• Monitoring equipment which consists of a pH meter and a
turbidimeter.
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System Sizing:
Certain sites are required to implement flow control for the developed
sites. These sites must also control stormwater release rates during
construction. Generally, these are sites that discharge stormwater directly,
or indirectly, through a conveyance system, into a fresh water. System sizing is dependent on flow control requirements.
Sizing Criteria for Batch Treatment Systems for Flow Control
Exempt Water Bodies:
The total volume of the untreated stormwater storage pond and treatment
ponds or tanks must be large enough to treat stormwater that is produced during multiple day storm events. It is recommended that at a minimum the untreated stormwater storage pond be sized to hold 1.5 times the
runoff volume of the 10-year, 24-hour storm event. Bypass should be
provided around the chemical treatment system to accommodate extreme
storm events. Runoff volume shall be calculated using the methods presented in Volume 3, Chapter 2. Worst-case land cover conditions (i.e., producing the most runoff) should be used for analyses (in most cases, this
would be the land cover conditions just prior to final landscaping).
Primary settling should be encouraged in the untreated stormwater storage
pond. A forebay with access for maintenance may be beneficial.
There are two opposing considerations in sizing the treatment cells. A larger cell is able to treat a larger volume of water each time a batch is
processed. However, the larger the cell the longer the time required to
empty the cell. A larger cell may also be less effective at flocculation and
therefore require a longer settling time. The simplest approach to sizing the treatment cell is to multiply the allowable discharge flow rate times the desired drawdown time. A 4-hour drawdown time allows one batch per
cell per 8-hour work period, given 1 hour of flocculation followed by two
hours of settling.
If the discharge is directly to a flow control exempt receiving water listed in Appendix I-E of Volume I or to an infiltration system, there is no
discharge flow limit.
Ponds sized for flow control water bodies must at a minimum meet the
sizing criteria for flow control exempt waters.
Sizing Criteria for Flow-Through Treatment Systems for Flow Control Exempt Water Bodies:
When sizing storage ponds or tanks for flow-through systems for flow
control exempt water bodies, the treatment system capacity should be a
factor. The untreated stormwater storage pond or tank should be sized to
hold 1.5 times the runoff volume of the 10-year, 24-hour storm event minus the treatment system flowrate for an 8-hour period. For a chitosan-
enhanced sand filtration system, the treatment system flowrate should be
sized using a hydraulic loading rate between 6-8 gpm/ft². Other hydraulic
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loading rates may be more appropriate for other systems. Bypass should be provided around the chemical treatment system to accommodate
extreme storms. Runoff volume shall be calculated using the methods
presented in Volume 3, Chapter 2. Worst-case land cover conditions (i.e.,
producing the most runoff) should be used for analyses (in most cases, this would be the land cover conditions just prior to final landscaping).
Sizing Criteria for Flow Control Water Bodies:
Sites that must implement flow control for the developed site condition
must also control stormwater release rates during construction.
Construction site stormwater discharges shall not exceed the discharge durations of the pre-developed condition for the range of pre-developed discharge rates from ½ of the 2-year flow through the 10-year flow as
predicted by an approved continuous runoff model. The pre-developed
condition to be matched shall be the land cover condition immediately
prior to the development project. This restriction on release rates can affect the size of the storage pond and treatment cells.
The following is how WWHM can be used to determine the release rates
from the chemical treatment systems:
1. Determine the pre-developed flow durations to be matched by entering
the existing land use area under the “Pre-developed” scenario in WWHM. The default flow range is from ½ of the 2-year flow through the 10-year flow.
2. Enter the post developed land use area in the “Developed
Unmitigated” scenario in WWHM.
3. Copy the land use information from the “Developed Unmitigated” to “Developed Mitigated” scenario.
4. While in the “Developed Mitigated” scenario, add a pond element
under the basin element containing the post-developed land use areas.
This pond element represents information on the available untreated
stormwater storage and discharge from the chemical treatment system. In cases where the discharge from the chemical treatment system is
controlled by a pump, a stage/storage/discharge (SSD) table
representing the pond must be generated outside WWHM and
imported into WWHM. WWHM can route the runoff from the post-
developed condition through this SSD table (the pond) and determine compliance with the flow duration standard. This would be an iterative
design procedure where if the initial SSD table proved to be
inadequate, the designer would have to modify the SSD table outside
WWHM and re-import in WWHM and route the runoff through it
again. The iteration will continue until a pond that complies with the flow duration standard is correctly sized.
Notes on SSD table characteristics:
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• The pump discharge rate would likely be initially set at just below
½ of the 2-year flow from the pre-developed condition. As runoff
coming into the untreated stormwater storage pond increases and
the available untreated stormwater storage volume gets used up, it would be necessary to increase the pump discharge rate above ½ of the 2-year. The increase(s) above ½ of the 2-year must be such that
they provide some relief to the untreated stormwater storage needs
but at the same time will not cause violations of the flow duration
standard at the higher flows. The final design SSD table will identify the appropriate pumping rates and the corresponding stage and storages.
• When building such a flow control system, the design must ensure
that any automatic adjustments to the pumping rates will be as a
result of changes to the available storage in accordance with the final design SSD table.
5. It should be noted that the above procedures would be used to meet the
flow control requirements. The chemical treatment system must be
able to meet the runoff treatment requirements. It is likely that the
discharge flow rate of ½ of the 2-year or more may exceed the treatment capacity of the system. If that is the case, the untreated
stormwater discharge rate(s) (i.e., influent to the treatment system)
must be reduced to allow proper treatment. Any reduction in the flows
would likely result in the need for a larger untreated stormwater
storage volume.
If the discharge is to a municipal storm drainage system, the allowable
discharge rate may be limited by the capacity of the public system. It may
be necessary to clean the municipal storm drainage system prior to the
start of the discharge to prevent scouring solids from the drainage system. If the municipal storm drainage system discharges to a water body not on
the flow control exempt list, the project site is subject to flow control
requirements. Obtain permission from the owner of the collection system
before discharging to it.
If system design does not allow you to discharge at the slower rates as described above and if the site has a retention or detention pond that will
serve the planned development, the discharge from the treatment system may
be directed to the permanent retention/detention pond to comply with the flow control requirement. In this case, the untreated stormwater storage pond and treatment system will be sized according to the sizing criteria for flow-
through treatment systems for flow control exempt water bodies described
earlier except all discharge (water passing through the treatment system and
stormwater bypassing the treatment system) will be directed into the permanent retention/detention pond. If site constraints make locating the untreated stormwater storage pond difficult, the permanent
retention/detention pond may be divided to serve as the untreated stormwater
storage pond and the post-treatment flow control pond. A berm or barrier must be used in this case so the untreated water does not mix with the treated
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water. Both untreated stormwater storage requirements, and adequate post-
treatment flow control must be achieved. The post-treatment flow control
pond’s revised dimensions must be entered into the WWHM and the WWHM must be run to confirm compliance with the flow control requirement.
Maintenance Standards
Monitoring: At a minimum, the following monitoring shall be
conducted. Test results shall be recorded on a daily log kept on site.
Additional testing may be required by the NPDES permit based on site
conditions.
Operational Monitoring:
• Total volume treated and discharged.
• Flow must be continuously monitored and recorded at not greater than
15-minute intervals.
• Type and amount of chemical used for pH adjustment.
• Amount of polymer used for treatment.
• Settling time.
Compliance Monitoring:
• Influent and effluent pH, flocculent chemical concentration, and
turbidity must be continuously monitored and recorded at not greater
than 15-minute intervals. pH and turbidity of the receiving water.
Biomonitoring:
Treated stormwater must be non-toxic to aquatic organisms. Treated
stormwater must be tested for aquatic toxicity or residual chemicals.
Frequency of biomonitoring will be determined by Ecology.
Residual chemical tests must be approved by Ecology prior to their use.
If testing treated stormwater for aquatic toxicity, you must test for acute
(lethal) toxicity. Bioassays shall be conducted by a laboratory accredited
by Ecology, unless otherwise approved by Ecology. Acute toxicity tests
shall be conducted per the CTAPE protocol.
Discharge Compliance: Prior to discharge, treated stormwater must be sampled and tested for compliance with pH, flocculent chemical concentration, and turbidity limits. These limits may be established by
the Construction Stormwater General Permit or a site-specific discharge
permit. Sampling and testing for other pollutants may also be necessary at
some sites. pH must be within the range of 6.5 to 8.5 standard units and not cause a change in the pH of the receiving water of more than 0.2
standard units. Treated stormwater samples and measurements shall be
taken from the discharge pipe or another location representative of the
nature of the treated stormwater discharge. Samples used for determining
compliance with the water quality standards in the receiving water shall not be taken from the treatment pond prior to decanting. Compliance with
the water quality standards is determined in the receiving water.
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Operator Training: Each contractor who intends to use chemical treatment shall be trained by an experienced contractor . Each site using
chemical treatment must have an operator trained and certified by an
organization approved by Ecology.
Standard BMPs: Surface stabilization BMPs should be implemented on site to prevent significant erosion. All sites shall use a truck wheel wash to prevent tracking of sediment off site.
Sediment Removal and Disposal:
• Sediment shall be removed from the storage or treatment cells as
necessary. Typically, sediment removal is required at least once during a wet season and at the decommissioning of the cells. Sediment remaining in the cells between batches may enhance the settling
process and reduce the required chemical dosage.
• Sediment that is known to be non-toxic may be incorporated into the
site away from drainages.
BMP C251: Construction Stormwater Filtration
Purpose Filtration removes sediment from runoff originating from disturbed areas
of the site.
Background Information:
Filtration with sand media has been used for over a century to treat water and wastewater. The use of sand filtration for treatment of stormwater has developed recently, generally to treat runoff from streets, parking lots, and
residential areas. The application of filtration to construction stormwater
treatment is currently under development.
Conditions of Use Traditional BMPs used to control soil erosion and sediment loss from sites under development may not be adequate to ensure compliance with the water quality standard for turbidity in the receiving water. Filtration may
be used in conjunction with gravity settling to remove sediment as small
as fine silt (0.5 µm). The reduction in turbidity will be dependent on the
particle size distribution of the sediment in the stormwater. In some circumstances, sedimentation and filtration may achieve compliance with
the water quality standard for turbidity.
The use of construction stormwater filtration does not require approval
from Ecology as long as treatment chemicals are not used. Filtration in
conjunction with polymer treatment requires testing under the Chemical Technology Assessment Protocol – Ecology (CTAPE) before it can be
initiated. Approval from the appropriate regional Ecology office must be
obtained at each site where polymers use is proposed prior to use. For
more guidance on stormwater chemical treatment see BMP C250.
Volume II – Construction Stormwater Pollution Prevention - August 2012
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Design and Installation
Specifications
Two types of filtration systems may be applied to construction stormwater treatment: rapid and slow. Rapid sand filters are the typical system used
for water and wastewater treatment. They can achieve relatively high
hydraulic flow rates, on the order of 2 to 20 gpm/sf, because they have
automatic backwash systems to remove accumulated solids. In contrast, slow sand filters have very low hydraulic rates, on the order of 0.02 gpm/sf, because they do not have backwash systems. Slow sand filtration
has generally been used to treat stormwater. Slow sand filtration is
mechanically simple in comparison to rapid sand filtration but requires a
much larger filter area.
Filtration Equipment. Sand media filters are available with automatic backwashing features that can filter to 50 µm particle size. Screen or bag
filters can filter down to 5 µm. Fiber wound filters can remove particles
down to 0.5 µm. Filters should be sequenced from the largest to the
smallest pore opening. Sediment removal efficiency will be related to particle size distribution in the stormwater.
Treatment Process Description. Stormwater is collected at interception
point(s) on the site and is diverted to an untreated stormwater sediment
pond or tank for removal of large sediment and storage of the stormwater
before it is treated by the filtration system. The untreated stormwater is pumped from the trap, pond, or tank through the filtration system in a rapid sand filtration system. Slow sand filtration systems are designed as
flow through systems using gravity.
Maintenance Standards Rapid sand filters typically have automatic backwash systems that are
triggered by a pre-set pressure drop across the filter. If the backwash water volume is not large or substantially more turbid than the untreated stormwater stored in the holding pond or tank, backwash return to the
untreated stormwater pond or tank may be appropriate. However, other
means of treatment and disposal may be necessary.
• Screen, bag, and fiber filters must be cleaned and/or replaced when they become clogged.
• Sediment shall be removed from the storage and/or treatment ponds as
necessary. Typically, sediment removal is required once or twice
during a wet season and at the decommissioning of the ponds.
Sizing Criteria for Flow-Through Treatment Systems for Flow Control Exempt Water Bodies:
When sizing storage ponds or tanks for flow-through systems for flow
control exempt water bodies the treatment system capacity should be a
factor. The untreated stormwater storage pond or tank should be sized to
hold 1.5 times the runoff volume of the 10-year, 24-hour storm event minus the treatment system flowrate for an 8-hour period. For a chitosan-
enhanced sand filtration system, the treatment system flowrate should be
sized using a hydraulic loading rate between 6-8 gpm/ft². Other hydraulic
Volume II – Construction Stormwater Pollution Prevention - August 2012
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loading rates may be more appropriate for other systems. Bypass should be provided around the chemical treatment system to accommodate
extreme storms. Runoff volume shall be calculated using the methods
presented in Volume 3, Chapter 2. Worst-case conditions (i.e., producing
the most runoff) should be used for analyses (most likely conditions present prior to final landscaping).
Sizing Criteria for Flow Control Water Bodies:
Sites that must implement flow control for the developed site condition
must also control stormwater release rates during construction.
Construction site stormwater discharges shall not exceed the discharge durations of the pre-developed condition for the range of pre-developed discharge rates from 1/2 of the 2-year flow through the 10-year flow as
predicted by an approved continuous runoff model. The pre-developed
condition to be matched shall be the land cover condition immediately
prior to the development project. This restriction on release rates can affect the size of the storage pond, the filtration system, and the flow rate through the filter system.
The following is how WWHM can be used to determine the release rates
from the filtration systems:
1. Determine the pre-developed flow durations to be matched by entering the land use area under the “Pre-developed” scenario in WWHM. The default flow range is from ½ of the 2-year flow through the 10-year
flow.
2. Enter the post developed land use area in the “Developed
Unmitigated” scenario in WWHM.
3. Copy the land use information from the “Developed Unmitigated” to “Developed Mitigated” scenario.
4. There are two possible ways to model stormwater filtration systems:
a. The stormwater filtration system uses an untreated stormwater
storage pond/tank and the discharge from this pond/tank is pumped to one or more filters. In-line filtration chemicals would be added
to the flow right after the pond/tank and before the filter(s).
Because the discharge is pumped, WWHM can’t generate a
stage/storage /discharge (SSD) table for this system. This system is
modeled the same way as described in BMP C250 and is as follows:
While in the “Developed Mitigated” scenario, add a pond element
under the basin element containing the post-developed land use
areas. This pond element represents information on the available
untreated stormwater storage and discharge from the filtration system. In cases where the discharge from the filtration system is
controlled by a pump, a stage/storage/discharge (SSD) table
representing the pond must be generated outside WWHM and
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imported into WWHM. WWHM can route the runoff from the post-developed condition through this SSD table (the pond) and
determine compliance with the flow duration standard. This would
be an iterative design procedure where if the initial SSD table
proved to be out of compliance, the designer would have to modify the SSD table outside WWHM and re-import in WWHM and route the runoff through it again. The iteration will continue until a pond
that enables compliance with the flow duration standard is
designed.
Notes on SSD table characteristics:
• The pump discharge rate would likely be initially set at just below ½ if the 2-year flow from the pre-developed condition.
As runoff coming into the untreated stormwater storage pond
increases and the available untreated stormwater storage
volume gets used up, it would be necessary to increase the pump discharge rate above ½ of the 2-year. The increase(s) above ½ of the 2-year must be such that they provide some
relief to the untreated stormwater storage needs but at the same
time they will not cause violations of the flow duration
standard at the higher flows. The final design SSD table will identify the appropriate pumping rates and the corresponding stage and storages.
• When building such a flow control system, the design must
ensure that any automatic adjustments to the pumping rates
will be as a result of changes to the available storage in accordance with the final design SSD table.
b. The stormwater filtration system uses a storage pond/tank and the
discharge from this pond/tank gravity flows to the filter. This is
usually a slow sand filter system and it is possible to model it in
WWHM as a Filter element or as a combination of Pond and Filter element placed in series. The stage/storage/discharge table(s) may
then be generated within WWHM as follows:
(i) While in the “Developed Mitigated” scenario, add a Filter
element under the basin element containing the post-developed
land use areas. The length and width of this filter element would have to be the same as the bottom length and width of
the upstream untreated stormwater storage pond/tank.
(ii) In cases where the length and width of the filter is not the same
as those for the bottom of the upstream untreated stormwater
storage tank/pond, the treatment system may be modeled as a Pond element followed by a Filter element. By having these
two elements, WWHM would then generate a SSD table for
the storage pond which then gravity flows to the Filter element.
The Filter element downstream of the untreated stormwater
Volume II – Construction Stormwater Pollution Prevention - August 2012
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storage pond would have a storage component through the media, and an overflow component for when the filtration
capacity is exceeded.
WWHM can route the runoff from the post-developed condition through the treatment systems in 4b and determine compliance with the flow duration standard. This would be an iterative design
procedure where if the initial sizing estimates for the treatment system
proved to be inadequate, the designer would have to modify the
system and route the runoff through it again. The iteration would continue until compliance with the flow duration standard is achieved.
5. It should be noted that the above procedures would be used to meet the
flow control requirements. The filtration system must be able to meet the
runoff treatment requirements. It is likely that the discharge flow rate of ½ of the 2-year or more may exceed the treatment capacity of the system. If that is the case, the untreated stormwater discharge rate(s) (i.e., influent
to the treatment system) must be reduced to allow proper treatment. Any
reduction in the flows would likely result in the need for a larger
untreated stormwater storage volume.
If system design does not allow you to discharge at the slower rates as described above and if the site has a retention or detention pond that will
serve the planned development, the discharge from the treatment system may
be directed to the permanent retention/detention pond to comply with the flow control requirements. In this case, the untreated stormwater storage pond and treatment system will be sized according to the sizing criteria for flow-
through treatment systems for flow control exempt waterbodies described
earlier except all discharges (water passing through the treatment system and
stormwater bypassing the treatment system) will be directed into the permanent retention/detention pond. If site constraints make locating the
untreated stormwater storage pond difficult, the permanent
retention/detention pond may be divided to serve as the untreated stormwater
discharge pond and the post-treatment flow control pond. A berm or barrier must be used in this case so the untreated water does not mix with the treated water. Both untreated stormwater storage requirements, and adequate post-
treatment flow control must be achieved. The post-treatment flow control
pond’s revised dimensions must be entered into the WWHM and the WWHM
must be run to confirm compliance with the flow control requirement.
Volume II – Construction Stormwater Pollution Prevention - August 2012
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BMP C252: High pH Neutralization Using CO2
Purpose When pH levels in stormwater rise above 8.5 it is necessary to lower the
pH levels to the acceptable range of 6.5 to 8.5, this process is called pH
neutralization. pH neutralization involves the use of solid or compressed
carbon dioxide gas in water requiring neutralization. Neutralized stormwater may be discharged to surface waters under the General Construction NPDES permit.
Neutralized process water such as concrete truck wash-out, hydro-
demolition, or saw-cutting slurry must be managed to prevent discharge to
surface waters. Any stormwater contaminated during concrete work is considered process wastewater and must not be discharged to surface waters.
Reason for pH Neutralization:
A pH level range of 6.5 to 8.5 is typical for most natural watercourses, and
this neutral pH is required for the survival of aquatic organisms. Should the pH rise or drop out of this range, fish and other aquatic organisms may become stressed and may die.
Calcium hardness can contribute to high pH values and cause toxicity that
is associated with high pH conditions. A high level of calcium hardness in
waters of the state is not allowed.
The water quality standard for pH in Washington State is in the range of 6.5 to 8.5. Ground water standard for calcium and other dissolved solids in
Washington State is less than 500 mg/l.
Conditions of Use Causes of High pH:
High pH at construction sites is most commonly caused by the contact of stormwater with poured or recycled concrete, cement, mortars, and other Portland cement or lime containing construction materials. (See BMP
C151: Concrete Handling for more information on concrete handling
procedures). The principal caustic agent in cement is calcium hydroxide
(free lime).
Advantages of CO2 Sparging:
• Rapidly neutralizes high pH water.
• Cost effective and safer to handle than acid compounds.
• CO2 is self-buffering. It is difficult to overdose and create harmfully
low pH levels.
• Material is readily available.
Volume II – Construction Stormwater Pollution Prevention - August 2012
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The Chemical Process:
When carbon dioxide (CO2) is added to water (H2O), carbonic acid
(H2CO3) is formed which can further dissociate into a proton (H+) and a
bicarbonate anion (HCO3-) as shown below:
CO2 + H2O ↔ H2CO3 ↔ H+ + HCO3-
The free proton is a weak acid that can lower the pH. Water temperature
has an effect on the reaction as well. The colder the water temperature is the slower the reaction occurs and the warmer the water temperature is the
quicker the reaction occurs. Most construction applications in Washington
State have water temperatures in the 50°F or higher range so the reaction
is almost simultaneous.
Design and Installation Specifications
Treatment Process:
High pH water may be treated using continuous treatment, continuous
discharge systems. These manufactured systems continuously monitor
influent and effluent pH to ensure that pH values are within an acceptable
range before being discharged. All systems must have fail safe automatic
shut off switches in the event that pH is not within the acceptable discharge range. Only trained operators may operate manufactured
systems. System manufacturers often provide trained operators or training
on their devices.
The following procedure may be used when not using a continuous
discharge system:
1. Prior to treatment, the appropriate jurisdiction should be notified in
accordance with the regulations set by the jurisdiction.
2. Every effort should be made to isolate the potential high pH water in
order to treat it separately from other stormwater on-site.
3. Water should be stored in an acceptable storage facility, detention pond, or containment cell prior to treatment.
4. Transfer water to be treated to the treatment structure. Ensure that
treatment structure size is sufficient to hold the amount of water that is
to be treated. Do not fill tank completely, allow at least 2 feet of
freeboard.
5. The operator samples the water for pH and notes the clarity of the
water. As a rule of thumb, less CO2 is necessary for clearer water. This
information should be recorded.
6. In the pH adjustment structure, add CO2 until the pH falls in the range
of 6.9-7.1. Remember that pH water quality standards apply so adjusting pH to within 0.2 pH units of receiving water (background
pH) is recommended. It is unlikely that pH can be adjusted to within
0.2 pH units using dry ice. Compressed carbon dioxide gas should be
introduced to the water using a carbon dioxide diffuser located near
Volume II – Construction Stormwater Pollution Prevention - August 2012
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the bottom of the tank, this will allow carbon dioxide to bubble up through the water and diffuse more evenly.
7. Slowly discharge the water making sure water does not get stirred up
in the process. Release about 80% of the water from the structure
leaving any sludge behind.
8. Discharge treated water through a pond or drainage system.
9. Excess sludge needs to be disposed of properly as concrete waste. If
several batches of water are undergoing pH treatment, sludge can be
left in treatment structure for the next batch treatment. Dispose of
sludge when it fills 50% of tank volume.
Sites that must implement flow control for the developed site must also control stormwater release rates during construction. All treated
stormwater must go through a flow control facility before being released
to surface waters which require flow control.
Maintenance Standards Safety and Materials Handling:
• All equipment should be handled in accordance with OSHA rules and regulations.
• Follow manufacturer guidelines for materials handling.
Operator Records:
Each operator should provide:
• A diagram of the monitoring and treatment equipment.
• A description of the pumping rates and capacity the treatment
equipment is capable of treating.
Each operator should keep a written record of the following:
• Client name and phone number.
• Date of treatment.
• Weather conditions.
• Project name and location.
• Volume of water treated.
• pH of untreated water.
• Amount of CO2 needed to adjust water to a pH range of 6.9-7.1.
• pH of treated water.
• Discharge point location and description.
A copy of this record should be given to the client/contractor who should
retain the record for three years.
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BMP C253: pH Control for High pH Water
Purpose When pH levels in stormwater rise above 8.5 it is necessary to lower the
pH levels to the acceptable range of 6.5 to 8.5, this process is called pH
neutralization. Stormwater with pH levels exceeding water quality
standards may be treated by infiltration, dispersion in vegetation or compost, pumping to a sanitary sewer, disposal at a permitted concrete batch plant with pH neutralization capabilities, or carbon dioxide sparging.
BMP C252 gives guidelines for carbon dioxide sparging.
Reason for pH Neutralization:
A pH level range of 6.5 to 8.5 is typical for most natural watercourses, and this pH range is required for the survival of aquatic organisms. Should the pH rise or drop out of this range, fish and other aquatic organisms may
become stressed and may die.
Conditions of Use Causes of High pH:
High pH levels at construction sites are most commonly caused by the contact of stormwater with poured or recycled concrete, cement, mortars, and other Portland cement or lime containing construction materials. (See
BMP C151: Concrete Handling for more information on concrete handling
procedures). The principal caustic agent in cement is calcium hydroxide
(free lime).
Design and Installation
Specifications
Disposal Methods:
Infiltration
• Infiltration is only allowed if soil type allows all water to infiltrate (no
surface runoff) without causing or contributing to a violation of
surface or ground water quality standards.
• Infiltration techniques should be consistent with Volume V, Chapter 7
Dispersion
Use BMP T5.30 Full Dispersion
Sanitary Sewer Disposal
• Local sewer authority approval is required prior to disposal via the sanitary sewer.
Concrete Batch Plant Disposal
• Only permitted facilities may accept high pH water.
• Facility should be contacted before treatment to ensure they can accept
the high pH water.
Stormwater Discharge
Any pH treatment options that generate treated water that must be
discharged off site are subject to flow control requirements. Sites that
must implement flow control for the developed site must also control
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stormwater release rates during construction. All treated stormwater must go through a flow control facility before being released to surface waters
which require flow control.
D.R. STRONG Consulting Engineers, Inc. The Pines
Stormwater Pollution Prevention Plan Page C-1 Renton, Washington
Appendix C
Correspondence
D.R. STRONG Consulting Engineers, Inc. The Pines
Stormwater Pollution Prevention Plan Page D-1 Renton, Washington
Appendix D
Site Inspection Form
The results of each inspection shall be summarized in an inspection report or checklist that is
entered into or attached to the site log book. It is suggested that the inspection report or
checklist be included in this appendix to keep monitoring and inspection information in one
document, but this is optional. However, it is mandatory that this SWPPP and the site
inspection forms be kept onsite at all times during construction, and that inspections be
performed and documented as outlined below.
At a minimum, each inspection report or checklist shall include:
Inspection date/times
Weather information: general conditions during inspection, approximate amount of precipitation
since the last inspection, and approximate amount of precipitation within the last 24 hours.
A summary or list of all BMPs that have been implemented, including observations of all
erosion/sediment control structures or practices.
The following shall be noted:
locations of BMPs inspected,
locations of BMPs that need maintenance,
the reason maintenance is needed,
locations of BMPs that failed to operate as designed or intended, and
locations where additional or different BMPs are needed, and the reason(s) why
A description of stormwater discharged from the site. The presence of suspended sediment,
turbid water, discoloration, and/or oil sheen shall be noted, as applicable.
A description of any water quality monitoring performed during inspection, and the results of that
monitoring.
General comments and notes, including a brief description of any BMP repairs, maintenance or
installations made as a result of the inspection.
A statement that, in the judgment of the person conducting the site inspection, the site is either
in compliance or out of compliance with the terms and conditions of the SWPPP and the
NPDES permit. If the site inspection indicates that the site is out of compliance, the inspection
report shall include a summary of the remedial actions required to bring the site back into
compliance, as well as a schedule of implementation.
Name, title, and signature of person conducting the site inspection; and the following statement:
“I certify under penalty of law that this report is true, accurate, and complete, to the best of my
knowledge and belief”.
D.R. STRONG Consulting Engineers, Inc. The Pines
Stormwater Pollution Prevention Plan Page D-2 Renton, Washington
When the site inspection indicates that the site is not in compliance with any terms and
conditions of the NPDES permit, the Permittee shall take immediate action(s) to: stop, contain,
and clean up the unauthorized discharges, or otherwise stop the noncompliance; correct the
problem(s); implement appropriate Best Management Practices (BMPs), and/or conduct
maintenance of existing BMPs; and achieve compliance with all applicable standards and permit
conditions. In addition, if the noncompliance causes a threat to human health or the
environment, the Permittee shall comply with the Noncompliance Notification requirements in
Special Condition S5.F of the permit.
Construction Stormwater Site Inspection Form
D.R. STRONG Consulting Engineers, Inc. The Pines
Stormwater Pollution Prevention Plan Page D-3 Renton, Washington
Project Name Permit #: Date: Time:
Name of Certified Erosion Sediment Control Lead (CESCL) or qualified inspector if less than one acre
Print Name:
Approximate rainfall amount since the last inspection (in inches):
Approximate rainfall amount in the last 24 hours (in inches):
Current Weather Clear Cloudy Mist Rain Wind Fog
A. Type of inspection: Weekly Post Storm Event Other
B. Phase of Active Construction (check all that apply):
Pre Construction/installation of erosion/sediment controls Clearing/Demo/Grading Infrastructure/storm/roads
Concrete pours Vertical Construction/buildings Utilities
Offsite improvements Site temporary stabilized Final stabilization
C. Questions:
1. Were all areas of construction and discharge points inspected? Yes No
2. Did you observe the presence of suspended sediment, turbidity, discoloration, or oil sheen Yes No
3. Was a water quality sample taken during inspection? (refer to permit conditions S4 & S5) Yes No
4. Was there a turbid discharge 250 NTU or greater, or Transparency 6 cm or less?* Yes No
5. If yes to #4 was it reported to Ecology? Yes No
6. Is pH sampling required? pH range required is 6.5 to 8.5. Yes No
If answering yes to a discharge, describe the event. Include when, where, and why it happened; what action was taken,
and when.
*If answering yes to # 4 record NTU/Transparency with continual sampling daily until turbidity is 25 NTU or less/
transparency is 33 cm or greater.
Sampling Results: Date:
Parameter Method (circle one) Result Other/Note
NTU cm pH
Turbidity tube, meter, laboratory
pH Paper, kit, meter
Construction Stormwater Site Inspection Form
D.R. STRONG Consulting Engineers, Inc. The Pines
Stormwater Pollution Prevention Plan Page D-4 Renton, Washington
D. Check the observed status of all items. Provide “Action Required “details and dates.
Element # Inspection BMPs
Inspected
BMP needs
maintenance
BMP
failed
Action required
(describe in
section F) yes no n/a
1
Clearing
Limits
Before beginning land disturbing
activities are all clearing limits, natural
resource areas (streams, wetlands,
buffers, trees) protected with barriers
or similar BMPs? (high visibility
recommended)
2
Construction
Access
Construction access is stabilized with
quarry spalls or equivalent BMP to
prevent sediment from being tracked
onto roads?
Sediment tracked onto the road way
was cleaned thoroughly at the end of
the day or more frequent as necessary.
3
Control Flow
Rates
Are flow control measures installed to
control stormwater volumes and
velocity during construction and do
they protect downstream properties
and waterways from erosion?
If permanent infiltration ponds are
used for flow control during
construction, are they protected from
siltation?
4
Sediment
Controls
All perimeter sediment controls (e.g.
silt fence, wattles, compost socks,
berms, etc.) installed, and maintained
in accordance with the Stormwater
Pollution Prevention Plan (SWPPP).
Sediment control BMPs (sediment
ponds, traps, filters etc.) have been
constructed and functional as the first
step of grading.
Stormwater runoff from disturbed
areas is directed to sediment removal
BMP.
5
Stabilize Soils
Have exposed un-worked soils been
stabilized with effective BMP to
prevent erosion and sediment
deposition?
Are stockpiles stabilized from erosion,
protected with sediment trapping
measures and located away from drain
inlet, waterways, and drainage
channels?
Have soils been stabilized at the end of
the shift, before a holiday or weekend
if needed based on the weather
forecast?
Construction Stormwater Site Inspection Form
D.R. STRONG Consulting Engineers, Inc. The Pines
Stormwater Pollution Prevention Plan Page D-5 Renton, Washington
Element # Inspection BMPs Inspected BMP needs
maintenance
BMP
failed
Action required
(describe in
section F) yes no n/a
6
Protect
Slopes
Has stormwater and ground water
been diverted away from slopes and
disturbed areas with interceptor dikes,
pipes and or swales?
Is off-site storm water managed
separately from stormwater generated
on the site?
Is excavated material placed on uphill
side of trenches consistent with safety
and space considerations?
Have check dams been placed at
regular intervals within constructed
channels that are cut down a slope?
7
Drain Inlets
Storm drain inlets made operable
during construction are protected.
Are existing storm drains within the
influence of the project protected?
8
Stabilize
Channel and
Outlets
Have all on-site conveyance channels
been designed, constructed and
stabilized to prevent erosion from
expected peak flows?
Is stabilization, including armoring
material, adequate to prevent erosion
of outlets, adjacent stream banks,
slopes and downstream conveyance
systems?
9
Control
Pollutants
Are waste materials and demolition
debris handled and disposed of to
prevent contamination of stormwater?
Has cover been provided for all
chemicals, liquid products, petroleum
products, and other material?
Has secondary containment been
provided capable of containing 110%
of the volume?
Were contaminated surfaces cleaned
immediately after a spill incident?
Were BMPs used to prevent
contamination of stormwater by a pH
modifying sources?
Wheel wash wastewater is handled
and disposed of properly.
10
Control
Dewatering
Concrete washout in designated areas.
No washout or excess concrete on the
ground.
Dewatering has been done to an
approved source and in compliance
with the SWPPP.
Were there any clean non turbid
dewatering discharges?
Construction Stormwater Site Inspection Form
D.R. STRONG Consulting Engineers, Inc. The Pines
Stormwater Pollution Prevention Plan Page D-6 Renton, Washington
Element # Inspection BMPs Inspected BMP needs
maintenance
BMP
failed
Action required
(describe in
section F)
yes no n/a
11
Maintain
BMP
Are all temporary and permanent
erosion and sediment control BMPs
maintained to perform as intended?
12
Manage the
Project
Has the project been phased to the
maximum degree practicable?
Has regular inspection, monitoring and
maintenance been performed as
required by the permit?
Has the SWPPP been updated,
implemented and records maintained?
E. Check all areas that have been inspected.
All in place BMPs All discharge locations All concrete wash out areas All construction
entrances/exits
All disturbed soils All material storage areas All equipment storage areas
F. Elements checked “Action Required” (section D) describe corrective action to be taken. List the element number;
be specific on location and work needed. Document, initial, and date when the corrective action has been completed
and inspected.
Element
#
Description and Location Action Required Completion
Date
Initials
Attach additional page if needed
Sign the following certification:
“I certify that this report is true, accurate, and complete, to the best of my knowledge and belief”
Inspected by:
Print Signature
Title/Qualification of Inspector Date
D.R. STRONG Consulting Engineers, Inc. The Pines
Stormwater Pollution Prevention Plan Page F-1 Renton, Washington
Appendix E
Construction Stormwater General Permit (CSWGP)
Construction Stormwater General Permit
Page 2
TABLE OF CONTENTS
LIST OF TABLES ...........................................................................................................................3
SUMMARY OF PERMIT REPORT SUBMITTALS .....................................................................4
SPECIAL CONDITIONS ................................................................................................................5
S1. PERMIT COVERAGE ........................................................................................................5
S2. APPLICATION REQUIREMENTS ...................................................................................8
S3. COMPLIANCE WITH STANDARDS .............................................................................12
S4. MONITORING REQUIREMENTS, BENCHMARKS, AND
REPORTING TRIGGERS ................................................................................................13
S5. REPORTING AND RECORDKEEPING REQUIREMENTS .........................................20
S6. PERMIT FEES...................................................................................................................23
S7. SOLID AND LIQUID WASTE DISPOSAL ....................................................................23
S8. DISCHARGES TO 303(d) OR TMDL WATERBODIES ................................................23
S9. STORMWATER POLLUTION PREVENTION PLAN...................................................27
S10. NOTICE OF TERMINATION .........................................................................................37
GENERAL CONDITIONS ...........................................................................................................38
G1. DISCHARGE VIOLATIONS ...........................................................................................38
G2. SIGNATORY REQUIREMENTS.....................................................................................38
G3. RIGHT OF INSPECTION AND ENTRY .........................................................................39
G4. GENERAL PERMIT MODIFICATION AND REVOCATION ......................................39
G5. REVOCATION OF COVERAGE UNDER THE PERMIT .............................................39
G6. REPORTING A CAUSE FOR MODIFICATION ............................................................40
G7. COMPLIANCE WITH OTHER LAWS AND STATUTES .............................................40
G8. DUTY TO REAPPLY .......................................................................................................40
G9. TRANSFER OF GENERAL PERMIT COVERAGE .......................................................41
G10. REMOVED SUBSTANCES .............................................................................................41
G11. DUTY TO PROVIDE INFORMATION ...........................................................................41
G12. OTHER REQUIREMENTS OF 40 CFR ...........................................................................41
G13. ADDITIONAL MONITORING ........................................................................................41
G14. PENALTIES FOR VIOLATING PERMIT CONDITIONS .............................................41
G15. UPSET ...............................................................................................................................42
G16. PROPERTY RIGHTS ........................................................................................................42
Construction Stormwater General Permit
Page 3
G17. DUTY TO COMPLY ........................................................................................................42
G18. TOXIC POLLUTANTS.....................................................................................................42
G19. PENALTIES FOR TAMPERING .....................................................................................43
G20. REPORTING PLANNED CHANGES .............................................................................43
G21. REPORTING OTHER INFORMATION ..........................................................................43
G22. REPORTING ANTICIPATED NON-COMPLIANCE .....................................................43
G23. REQUESTS TO BE EXCLUDED FROM COVERAGE UNDER THE PERMIT ..........44
G24. APPEALS ..........................................................................................................................44
G25. SEVERABILITY ...............................................................................................................44
G26. BYPASS PROHIBITED ....................................................................................................44
APPENDIX A – DEFINITIONS ...................................................................................................47
APPENDIX B – ACRONYMS .....................................................................................................55
LIST OF TABLES
Table 1: Summary of Required Submittals ................................................................................... 4
Table 2: Summary of Required On-site Documentation............................................................... 4
Table 3: Summary of Primary Monitoring Requirements .......................................................... 15
Table 4: Monitoring and Reporting Requirements ..................................................................... 17
Table 5: Turbidity, Fine Sediment & Phosphorus Sampling and Limits for
303(d)-Listed Waters .................................................................................................... 25
Table 6: pH Sampling and Limits for 303(d)-Listed Waters ...................................................... 26
Construction Stormwater General Permit
Page 4
SUMMARY OF PERMIT REPORT SUBMITTALS
Refer to the Special and General Conditions within this permit for additional submittal
requirements. Appendix A provides a list of definitions. Appendix B provides a list of acronyms.
Table 1: Summary of Required Submittals
Permit
Section
Submittal Frequency First Submittal Date
S5.A and
S8
High Turbidity/Transparency Phone
Reporting
As Necessary Within 24 hours
S5.B Discharge Monitoring Report Monthly* Within 15 days following
the end of each month
S5.F and
S8
Noncompliance Notification –
Telephone Notification
As necessary Within 24-hours
S5.F Noncompliance Notification –
Written Report
As necessary Within 5 Days of non-
compliance
S9.C Request for Chemical Treatment
Form
As necessary Written approval from
Ecology is required prior to
using chemical treatment
(with the exception of dry
ice or CO2 to adjust pH)
G2 Notice of Change in Authorization As necessary
G6 Permit Application for Substantive
Changes to the Discharge
As necessary
G8 Application for Permit Renewal 1/permit cycle No later than 180 days
before expiration
G9 Notice of Permit Transfer As necessary
G20 Notice of Planned Changes As necessary
G22 Reporting Anticipated Non-
compliance
As necessary
SPECIAL NOTE: *Permittees must submit electronic Discharge Monitoring Reports (DMRs) to the Washington
State Department of Ecology monthly, regardless of site discharge, for the full duration of permit coverage. Refer to
Section S5.B of this General Permit for more specific information regarding DMRs.
Table 2: Summary of Required On-site Documentation
Document Title
Permit Conditions
Permit Coverage Letter See Conditions S2, S5
Construction Stormwater General Permit See Conditions S2, S5
Site Log Book See Conditions S4, S5
Stormwater Pollution Prevention Plan (SWPPP) See Conditions S9, S5
Construction Stormwater General Permit
Page 5
SPECIAL CONDITIONS
S1. PERMIT COVERAGE
A. Permit Area
This Construction Stormwater General Permit (CSWGP) covers all areas of Washington
State, except for federal operators and Indian Country as specified in Special Condition
S1.E.3.
B. Operators Required to Seek Coverage Under this General Permit:
1. Operators of the following construction activities are required to seek coverage
under this CSWGP:
a. Clearing, grading and/or excavation that results in the disturbance of one or
more acres (including off-site disturbance acreage authorized in S1.C.2) and
discharges stormwater to surface waters of the State; and clearing, grading
and/or excavation on sites smaller than one acre that are part of a larger
common plan of development or sale, if the common plan of development or
sale will ultimately disturb one acre or more and discharge stormwater to
surface waters of the State.
i. This includes forest practices (including, but not limited to, class IV
conversions) that are part of a construction activity that will result in the
disturbance of one or more acres, and discharge to surface waters of the
State (that is, forest practices that prepare a site for construction
activities); and
b. Any size construction activity discharging stormwater to waters of the State that
the Washington State Department of Ecology (Ecology):
i. Determines to be a significant contributor of pollutants to waters of the
State of Washington.
ii. Reasonably expects to cause a violation of any water quality standard.
2. Operators of the following activities are not required to seek coverage under this
CSWGP (unless specifically required under Special Condition S1.B.1.b. above):
a. Construction activities that discharge all stormwater and non-stormwater to
ground water, sanitary sewer, or combined sewer, and have no point source
discharge to either surface water or a storm sewer system that drains to surface
waters of the State.
b. Construction activities covered under an Erosivity Waiver (Special Condition
S2.C).
c. Routine maintenance that is performed to maintain the original line and grade,
hydraulic capacity, or original purpose of a facility.
Construction Stormwater General Permit
Page 6
C. Authorized Discharges:
1. Stormwater Associated with Construction Activity. Subject to compliance with the
terms and conditions of this permit, Permittees are authorized to discharge
stormwater associated with construction activity to surface waters of the State or to
a storm sewer system that drains to surface waters of the State. (Note that “surface
waters of the State” may exist on a construction site as well as off site; for
example, a creek running through a site.)
2. Stormwater Associated with Construction Support Activity. This permit also
authorizes stormwater discharge from support activities related to the permitted
construction site (for example, an on-site portable rock crusher, off-site equipment
staging yards, material storage areas, borrow areas, etc.) provided:
a. The support activity relates directly to the permitted construction site that is
required to have an NPDES permit; and
b. The support activity is not a commercial operation serving multiple unrelated
construction projects, and does not operate beyond the completion of the
construction activity; and
c. Appropriate controls and measures are identified in the Stormwater Pollution
Prevention Plan (SWPPP) for the discharges from the support activity areas.
3. Non-Stormwater Discharges. The categories and sources of non-stormwater
discharges identified below are authorized conditionally, provided the discharge is
consistent with the terms and conditions of this permit:
a. Discharges from fire-fighting activities.
b. Fire hydrant system flushing.
c. Potable water, including uncontaminated water line flushing.
d. Hydrostatic test water.
e. Uncontaminated air conditioning or compressor condensate.
f. Uncontaminated ground water or spring water.
g. Uncontaminated excavation dewatering water (in accordance with S9.D.10).
h. Uncontaminated discharges from foundation or footing drains.
i. Uncontaminated water used to control dust. Permittees must minimize the
amount of dust control water used.
j. Routine external building wash down that does not use detergents.
k. Landscape irrigation water.
The SWPPP must adequately address all authorized non-stormwater discharges, except
for discharges from fire-fighting activities, and must comply with Special Condition S3.
Construction Stormwater General Permit
Page 7
At a minimum, discharges from potable water (including water line flushing), fire
hydrant system flushing, and pipeline hydrostatic test water must undergo the following:
dechlorination to a concentration of 0.1 parts per million (ppm) or less, and pH
adjustment to within 6.5 – 8.5 standard units (su), if necessary.
D. Prohibited Discharges:
The following discharges to waters of the State, including ground water, are prohibited.
1. Concrete wastewater.
2. Wastewater from washout and clean-up of stucco, paint, form release oils, curing
compounds and other construction materials.
3. Process wastewater as defined by 40 Code of Federal Regulations (CFR) 122.2
(see Appendix A of this permit).
4. Slurry materials and waste from shaft drilling, including process wastewater from
shaft drilling for construction of building, road, and bridge foundations unless
managed according to Special Condition S9.D.9.j.
5. Fuels, oils, or other pollutants used in vehicle and equipment operation and
maintenance.
6. Soaps or solvents used in vehicle and equipment washing.
7. Wheel wash wastewater, unless managed according to Special Condition S9.D.9.
8. Discharges from dewatering activities, including discharges from dewatering of
trenches and excavations, unless managed according to Special Condition S9.D.10.
E. Limits on Coverage
Ecology may require any discharger to apply for and obtain coverage under an
individual permit or another more specific general permit. Such alternative coverage will
be required when Ecology determines that this CSWGP does not provide adequate
assurance that water quality will be protected, or there is a reasonable potential for the
project to cause or contribute to a violation of water quality standards.
The following stormwater discharges are not covered by this permit:
1. Post-construction stormwater discharges that originate from the site after
completion of construction activities and the site has undergone final stabilization.
2. Non-point source silvicultural activities such as nursery operations, site
preparation, reforestation and subsequent cultural treatment, thinning, prescribed
burning, pest and fire control, harvesting operations, surface drainage, or road
construction and maintenance, from which there is natural runoff as excluded in 40
CFR Subpart 122.
3. Stormwater from any federal operator.
Construction Stormwater General Permit
Page 8
4. Stormwater from facilities located on “Indian Country” as defined in 18
U.S.C.§1151, except portions of the Puyallup Reservation as noted below.
Indian Country includes:
a. All land within any Indian Reservation notwithstanding the issuance of any
patent, and, including rights-of-way running through the reservation. This
includes all federal, tribal, and Indian and non-Indian privately owned land
within the reservation.
b. All off-reservation Indian allotments, the Indian titles to which have not been
extinguished, including rights-of-way running through the same.
c. All off-reservation federal trust lands held for Native American Tribes.
Puyallup Exception: Following the Puyallup Tribes of Indians Land
Settlement Act of 1989, 25 U.S.C. §1773; the permit does apply to land within
the Puyallup Reservation except for discharges to surface water on land held
in trust by the federal government.
5. Stormwater from any site covered under an existing NPDES individual permit in
which stormwater management and/or treatment requirements are included for all
stormwater discharges associated with construction activity.
6. Stormwater from a site where an applicable Total Maximum Daily Load (TMDL)
requirement specifically precludes or prohibits discharges from construction
activity.
S2. APPLICATION REQUIREMENTS
A. Permit Application Forms
1. Notice of Intent Form/Timeline
a. Operators of new or previously unpermitted construction activities must submit
a complete and accurate permit application (Notice of Intent, or NOI) to
Ecology.
b. Operators must apply using the electronic application form (NOI) available on
Ecology’s website http://www.ecy.wa.gov/programs/wq/stormwater/
construction/index.html. Permittees unable to submit electronically (for
example, those who do not have an internet connection) must contact Ecology
to request a waiver and obtain instructions on how to obtain a paper NOI.
Department of Ecology
Water Quality Program - Construction Stormwater
PO Box 47696
Olympia, Washington 98504-7696
Construction Stormwater General Permit
Page 9
c. The operator must submit the NOI at least 60 days before discharging
stormwater from construction activities and must submit it on or before the date
of the first public notice (see Special Condition S2.B below for details). The 30-
day public comment period begins on the publication date of the second public
notice. Unless Ecology responds to the complete application in writing, based
on public comments, or any other relevant factors, coverage under the general
permit will automatically commence on the thirty-first day following receipt by
Ecology of a completed NOI, or the issuance date of this permit, whichever is
later; unless Ecology specifies a later date in writing as required by WAC173-
226-200(2).
d. If an applicant intends to use a Best Management Practice (BMP) selected on
the basis of Special Condition S9.C.4 (“demonstrably equivalent” BMPs), the
applicant must notify Ecology of its selection as part of the NOI. In the event
the applicant selects BMPs after submission of the NOI, it must provide notice
of the selection of an equivalent BMP to Ecology at least 60 days before
intended use of the equivalent BMP.
e. Permittees must notify Ecology regarding any changes to the information
provided on the NOI by submitting an updated NOI. Examples of such changes
include, but are not limited to:
i. Changes to the Permittee’s mailing address,
ii. Changes to the on-site contact person information, and
iii. Changes to the area/acreage affected by construction activity.
f. Applicants must notify Ecology if they are aware of contaminated soils and/or
groundwater associated with the construction activity. Provide detailed
information with the NOI (as known and readily available) on the nature and
extent of the contamination (concentrations, locations, and depth), as well as
pollution prevention and/or treatment BMPs proposed to control the discharge
of soil and/or groundwater contaminants in stormwater. Examples of such detail
may include, but are not limited to:
i. List or table of all known contaminants with laboratory test results
showing concentration and depth,
ii. Map with sample locations,
iii. Temporary Erosion and Sediment Control (TESC) plans,
iv. Related portions of the Stormwater Pollution Prevention Plan (SWPPP)
that address the management of contaminated and potentially
contaminated construction stormwater and dewatering water,
v. Dewatering plan and/or dewatering contingency plan.
Construction Stormwater General Permit
Page 10
2. Transfer of Coverage Form
The Permittee can transfer current coverage under this permit to one or more new
operators, including operators of sites within a Common Plan of Development,
provided the Permittee submits a Transfer of Coverage Form in accordance with
General Condition G9. Transfers do not require public notice.
B. Public Notice
For new or previously unpermitted construction activities, the applicant must publish a
public notice at least one time each week for two consecutive weeks, at least 7 days
apart, in a newspaper with general circulation in the county where the construction is to
take place. The notice must contain:
1. A statement that “The applicant is seeking coverage under the Washington State
Department of Ecology’s Construction Stormwater NPDES and State Waste
Discharge General Permit”.
2. The name, address and location of the construction site.
3. The name and address of the applicant.
4. The type of construction activity that will result in a discharge (for example,
residential construction, commercial construction, etc.), and the number of acres to
be disturbed.
5. The name of the receiving water(s) (that is, the surface water(s) to which the site
will discharge), or, if the discharge is through a storm sewer system, the name of
the operator of the system.
6. The statement: “Any persons desiring to present their views to the Washington
State Department of Ecology regarding this application, or interested in Ecology’s
action on this application, may notify Ecology in writing no later than 30 days of
the last date of publication of this notice. Ecology reviews public comments and
considers whether discharges from this project would cause a measurable change in
receiving water quality, and, if so, whether the project is necessary and in the
overriding public interest according to Tier II antidegradation requirements under
WAC 173-201A-320. Comments can be submitted to: Department of Ecology,
PO Box 47696, Olympia, Washington 98504-7696 Attn: Water Quality Program,
Construction Stormwater.”
Construction Stormwater General Permit
Page 11
C. Erosivity Waiver
Construction site operators may qualify for an erosivity waiver from the CSWGP if the
following conditions are met:
1. The site will result in the disturbance of fewer than 5 acres and the site is not a
portion of a common plan of development or sale that will disturb 5 acres or
greater.
2. Calculation of Erosivity “R” Factor and Regional Timeframe:
a. The project’s rainfall erosivity factor (“R” Factor) must be less than 5 during the
period of construction activity, as calculated (see the CSWGP homepage
http://www.ecy.wa.gov/programs/wq/stormwater/construction/index.html for a
link to the EPA’s calculator and step by step instructions on computing the “R”
Factor in the EPA Erosivity Waiver Fact Sheet). The period of construction
activity starts when the land is first disturbed and ends with final stabilization.
In addition:
b. The entire period of construction activity must fall within the following
timeframes:
i. For sites west of the Cascades Crest: June 15 – September 15.
ii. For sites east of the Cascades Crest, excluding the Central Basin:
June 15 – October 15.
iii. For sites east of the Cascades Crest, within the Central Basin: no additional
timeframe restrictions apply. The Central Basin is defined as the portions
of Eastern Washington with mean annual precipitation of less than 12
inches. For a map of the Central Basin (Average Annual Precipitation
Region 2), refer to http://www.ecy.wa.gov/programs/wq/stormwater/
construction/resourcesguidance.html.
3. Construction site operators must submit a complete Erosivity Waiver certification
form at least one week before disturbing the land. Certification must include
statements that the operator will:
a. Comply with applicable local stormwater requirements; and
b. Implement appropriate erosion and sediment control BMPs to prevent violations
of water quality standards.
4. This waiver is not available for facilities declared significant contributors of
pollutants as defined in Special Condition S1.B.1.b. or for any size construction
activity that could reasonably expect to cause a violation of any water quality
standard as defined in Special Condition S1.B.1.b.ii.
5. This waiver does not apply to construction activities which include non-
stormwater discharges listed in Special Condition S1.C.3.
Construction Stormwater General Permit
Page 12
6. If construction activity extends beyond the certified waiver period for any reason,
the operator must either:
a. Recalculate the rainfall erosivity “R” factor using the original start date and a
new projected ending date and, if the “R” factor is still under 5 and the entire
project falls within the applicable regional timeframe in Special Condition
S2.C.2.b, complete and submit an amended waiver certification form before the
original waiver expires; or
b. Submit a complete permit application to Ecology in accordance with Special
Condition S2.A and B before the end of the certified waiver period.
S3. COMPLIANCE WITH STANDARDS
A. Discharges must not cause or contribute to a violation of surface water quality standards
(Chapter 173-201A WAC), ground water quality standards (Chapter 173-200 WAC),
sediment management standards (Chapter 173-204 WAC), and human health-based
criteria in the National Toxics Rule (40 CFR Part 131.36). Discharges not in compliance
with these standards are not authorized.
B. Prior to the discharge of stormwater and non-stormwater to waters of the State, the
Permittee must apply all known, available, and reasonable methods of prevention,
control, and treatment (AKART). This includes the preparation and implementation of
an adequate SWPPP, with all appropriate BMPs installed and maintained in accordance
with the SWPPP and the terms and conditions of this permit.
C. Ecology presumes that a Permittee complies with water quality standards unless
discharge monitoring data or other site-specific information demonstrates that a
discharge causes or contributes to a violation of water quality standards, when the
Permittee complies with the following conditions. The Permittee must fully:
1. Comply with all permit conditions, including planning, sampling, monitoring,
reporting, and recordkeeping conditions.
2. Implement stormwater BMPs contained in stormwater management manuals
published or approved by Ecology, or BMPs that are demonstrably equivalent to
BMPs contained in stormwater technical manuals published or approved by
Ecology, including the proper selection, implementation, and maintenance of all
applicable and appropriate BMPs for on-site pollution control. (For purposes of
this section, the stormwater manuals listed in Appendix 10 of the Phase I
Municipal Stormwater Permit are approved by Ecology.)
D. Where construction sites also discharge to ground water, the ground water discharges
must also meet the terms and conditions of this CSWGP. Permittees who discharge to
ground water through an injection well must also comply with any applicable
requirements of the Underground Injection Control (UIC) regulations, Chapter 173-218
WAC.
Construction Stormwater General Permit
Page 13
S4. MONITORING REQUIREMENTS, BENCHMARKS, AND REPORTING
TRIGGERS
A. Site Log Book
The Permittee must maintain a site log book that contains a record of the implementation
of the SWPPP and other permit requirements, including the installation and maintenance
of BMPs, site inspections, and stormwater monitoring.
B. Site Inspections
The Permittee’s site inspections must include all areas disturbed by construction
activities, all BMPs, and all stormwater discharge points under the Permittee’s
operational control. (See Special Conditions S4.B.3 and B.4 below for detailed
requirements of the Permittee’s Certified Erosion and Sediment Control Lead [CESCL].)
Construction sites one acre or larger that discharge stormwater to surface waters of the
State must have site inspections conducted by a certified CESCL. Sites less than one
acre may have a person without CESCL certification conduct inspections.
1. The Permittee must examine stormwater visually for the presence of suspended
sediment, turbidity, discoloration, and oil sheen. The Permittee must evaluate the
effectiveness of BMPs and determine if it is necessary to install, maintain, or repair
BMPs to improve the quality of stormwater discharges.
Based on the results of the inspection, the Permittee must correct the problems
identified by:
a. Reviewing the SWPPP for compliance with Special Condition S9 and making
appropriate revisions within 7 days of the inspection.
b. Immediately beginning the process of fully implementing and maintaining
appropriate source control and/or treatment BMPs as soon as possible,
addressing the problems no later than within 10 days of the inspection. If
installation of necessary treatment BMPs is not feasible within 10 days, Ecology
may approve additional time when an extension is requested by a Permittee
within the initial 10-day response period.
c. Documenting BMP implementation and maintenance in the site log book.
2. The Permittee must inspect all areas disturbed by construction activities, all BMPs,
and all stormwater discharge points at least once every calendar week and within
24 hours of any discharge from the site. (For purposes of this condition, individual
discharge events that last more than one day do not require daily inspections. For
example, if a stormwater pond discharges continuously over the course of a week,
only one inspection is required that week.) The Permittee may reduce the
inspection frequency for temporarily stabilized, inactive sites to once every
calendar month.
Construction Stormwater General Permit
Page 14
3. The Permittee must have staff knowledgeable in the principles and practices of
erosion and sediment control. The CESCL (sites one acre or more) or inspector
(sites less than one acre) must have the skills to assess the:
a. Site conditions and construction activities that could impact the quality of
stormwater, and
b. Effectiveness of erosion and sediment control measures used to control the
quality of stormwater discharges.
4. The SWPPP must identify the CESCL or inspector, who must be present on site or
on-call at all times. The CESCL must obtain this certification through an approved
erosion and sediment control training program that meets the minimum training
standards established by Ecology (see BMP C160 in the manual referred to in
Special Condition S9.C.1 and 2).
5. The Permittee must summarize the results of each inspection in an inspection
report or checklist and enter the report/checklist into, or attach it to, the site log
book. At a minimum, each inspection report or checklist must include:
a. Inspection date and time.
b. Weather information, the general conditions during inspection and the
approximate amount of precipitation since the last inspection, and precipitation
within the last 24 hours.
c. A summary or list of all implemented BMPs, including observations of all
erosion/sediment control structures or practices.
d. A description of the locations:
i. Of BMPs inspected;
ii. Of BMPs that need maintenance and why;
iii. Of BMPs that failed to operate as designed or intended; and
iv. Where additional or different BMPs are needed, and why.
e. A description of stormwater discharged from the site. The Permittee must note
the presence of suspended sediment, turbidity, discoloration, and oil sheen, as
applicable.
f. Any water quality monitoring performed during inspection.
g. General comments and notes, including a brief description of any BMP repairs,
maintenance or installations made following the inspection.
h. A summary report and a schedule of implementation of the remedial actions that
the Permittee plans to take if the site inspection indicates that the site is out of
compliance. The remedial actions taken must meet the requirements of the
SWPPP and the permit.
Construction Stormwater General Permit
Page 15
i. The name, title, and signature of the person conducting the site inspection, a
phone number or other reliable method to reach this person, and the following
statement: “I certify that this report is true, accurate, and complete to the best of
my knowledge and belief.”
Table 3: Summary of Primary Monitoring Requirements
Size of Soil
Disturbance1
Weekly Site
Inspections
Weekly
Sampling w/
Turbidity
Meter
Weekly
Sampling w/
Transparency
Tube
Weekly pH
Sampling2
CESCL
Required for
Inspections?
Sites that disturb
less than 1 acre, but
are part of a larger
Common Plan of
Development
Required Not Required Not Required Not Required No
Sites that disturb 1
acre or more, but
fewer than 5 acres
Required Sampling Required –
either method3
Required Yes
Sites that disturb 5
acres or more
Required Required Not Required4 Required Yes
1 Soil disturbance is calculated by adding together all areas that will be affected by construction activity.
Construction activity means clearing, grading, excavation, and any other activity that disturbs the surface of the
land, including ingress/egress from the site.
2 If construction activity results in the disturbance of 1 acre or more, and involves significant concrete work (1,000
cubic yards of poured over the life of a project) or the use of recycled concrete or engineered soils (soil amendments
including but not limited to Portland cement-treated base [CTB], cement kiln dust [CKD], or fly ash), and
stormwater from the affected area drains to surface waters of the State or to a storm sewer stormwater collection
system that drains to other surface waters of the State, the Permittee must conduct pH sampling in accordance with
Special Condition S4.D.
3 Sites with one or more acres, but fewer than 5 acres of soil disturbance, must conduct turbidity or transparency
sampling in accordance with Special Condition S4.C.
4 Sites equal to or greater than 5 acres of soil disturbance must conduct turbidity sampling using a turbidity meter in
accordance with Special Condition S4.C.
Construction Stormwater General Permit
Page 16
C. Turbidity/Transparency Sampling Requirements
1. Sampling Methods
a. If construction activity involves the disturbance of 5 acres or more, the
Permittee must conduct turbidity sampling per Special Condition S4.C.
b. If construction activity involves 1 acre or more but fewer than 5 acres of soil
disturbance, the Permittee must conduct either transparency sampling or
turbidity sampling per Special Condition S4.C.
2. Sampling Frequency
a. The Permittee must sample all discharge points at least once every calendar
week when stormwater (or authorized non-stormwater) discharges from the site
or enters any on-site surface waters of the state (for example, a creek running
through a site); sampling is not required on sites that disturb less than an acre.
b. Samples must be representative of the flow and characteristics of the discharge.
c. Sampling is not required when there is no discharge during a calendar week.
d. Sampling is not required outside of normal working hours or during unsafe
conditions.
e. If the Permittee is unable to sample during a monitoring period, the Permittee
must include a brief explanation in the monthly Discharge Monitoring Report
(DMR).
f. Sampling is not required before construction activity begins.
g. The Permittee may reduce the sampling frequency for temporarily stabilized,
inactive sites to once every calendar month.
3. Sampling Locations
a. Sampling is required at all points where stormwater associated with
construction activity (or authorized non-stormwater) is discharged off site,
including where it enters any on-site surface waters of the state (for example, a
creek running through a site).
b. The Permittee may discontinue sampling at discharge points that drain areas of
the project that are fully stabilized to prevent erosion.
c. The Permittee must identify all sampling point(s) on the SWPPP site map and
clearly mark these points in the field with a flag, tape, stake or other visible
marker.
d. Sampling is not required for discharge that is sent directly to sanitary or
combined sewer systems.
Construction Stormwater General Permit
Page 17
e. The Permittee may discontinue sampling at discharge points in areas of the
project where the Permittee no longer has operational control of the construction
activity.
4. Sampling and Analysis Methods
a. The Permittee performs turbidity analysis with a calibrated turbidity meter
(turbidimeter) either on site or at an accredited lab. The Permittee must record
the results in the site log book in nephelometric turbidity units (NTUs).
b. The Permittee performs transparency analysis on site with a 1¾-inch-diameter,
60-centimeter (cm)-long transparency tube. The Permittee will record the results
in the site log book in centimeters (cm).
Table 4: Monitoring and Reporting Requirements
Parameter Unit Analytical Method Sampling
Frequency
Benchmark
Value
Phone
Reporting
Trigger Value
Turbidity NTU SM2130 Weekly, if
discharging
25 NTUs 250 NTUs
Transparency cm Manufacturer
instructions, or
Ecology guidance
Weekly, if
discharging
33 cm 6 cm
5. Turbidity/Transparency Benchmark Values and Reporting Triggers
The benchmark value for turbidity is 25 NTUs or less. The benchmark value for
transparency is 33 centimeters (cm). Note: Benchmark values do not apply to
discharges to segments of water bodies on Washington State’s 303(d) list
(Category 5) for turbidity, fine sediment, or phosphorus; these discharges are
subject to a numeric effluent limit for turbidity. Refer to Special Condition S8 for
more information.
a. Turbidity 26 – 249 NTUs, or Transparency 32 – 7 cm:
If the discharge turbidity is 26 to 249 NTUs; or if discharge transparency is
less than 33 cm, but equal to or greater than 6 cm, the Permittee must:
i. Review the SWPPP for compliance with Special Condition S9 and make
appropriate revisions within 7 days of the date the discharge exceeded the
benchmark.
ii. Immediately begin the process to fully implement and maintain
appropriate source control and/or treatment BMPs as soon as possible,
addressing the problems within 10 days of the date the discharge
exceeded the benchmark. If installation of necessary treatment BMPs is
not feasible within 10 days, Ecology may approve additional time when
the Permittee requests an extension within the initial 10-day response
period.
Construction Stormwater General Permit
Page 18
iii. Document BMP implementation and maintenance in the site log book.
b. Turbidity 250 NTUs or greater, or Transparency 6 cm or less:
If a discharge point’s turbidity is 250 NTUs or greater, or if discharge
transparency is less than or equal to 6 cm, the Permittee must complete the
reporting and adaptive management process described below.
i. Telephone or submit an electronic report to the applicable Ecology
Region’s Environmental Report Tracking System (ERTS) number (or
through Ecology’s Water Quality Permitting Portal [WQWebPortal] –
Permit Submittals when the form is available) within 24 hours, in
accordance with Special Condition S5.A.
Central Region (Okanogan, Chelan, Douglas, Kittitas, Yakima,
Klickitat, Benton): (509) 575-2490
Eastern Region (Adams, Asotin, Columbia, Ferry, Franklin, Garfield,
Grant, Lincoln, Pend Oreille, Spokane, Stevens, Walla Walla,
Whitman): (509) 329-3400
Northwest Region (Kitsap, Snohomish, Island, King, San Juan,
Skagit, Whatcom): (425) 649-7000
Southwest Region (Grays Harbor, Lewis, Mason, Thurston, Pierce,
Clark, Cowlitz, Skamania, Wahkiakum, Clallam, Jefferson, Pacific):
(360) 407-6300
Links to these numbers and the ERTS reporting page are located on the
following web site:
http://www.ecy.wa.gov/programs/wq/stormwater/construction/index.html.
ii. Review the SWPPP for compliance with Special Condition S9 and make
appropriate revisions within 7 days of the date the discharge exceeded the
benchmark.
iii. Immediately begin the process to fully implement and maintain
appropriate source control and/or treatment BMPs as soon as possible,
addressing the problems within 10 days of the date the discharge
exceeded the benchmark. If installation of necessary treatment BMPs is
not feasible within 10 days, Ecology may approve additional time when
the Permittee requests an extension within the initial 10-day response
period.
iv. Document BMP implementation and maintenance in the site log book.
v. Sample discharges daily until:
a) Turbidity is 25 NTUs (or lower); or
b) Transparency is 33 cm (or greater); or
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c) The Permittee has demonstrated compliance with the water quality
limit for turbidity:
1) No more than 5 NTUs over background turbidity, if background
is less than 50 NTUs, or
2) No more than 10% over background turbidity, if background is
50 NTUs or greater; or
d) The discharge stops or is eliminated.
D. pH Sampling Requirements – Significant Concrete Work or Engineered Soils
If construction activity results in the disturbance of 1 acre or more, and involves
significant concrete work (significant concrete work means greater than 1000 cubic
yards poured concrete used over the life of a project ) or the use of recycled concrete or
engineered soils (soil amendments including but not limited to Portland cement-treated
base [CTB], cement kiln dust [CKD], or fly ash), and stormwater from the affected area
drains to surface waters of the State or to a storm sewer system that drains to surface
waters of the State, the Permittee must conduct pH sampling as set forth below. Note: In
addition, discharges to segments of water bodies on Washington State’s 303(d) list
(Category 5) for high pH are subject to a numeric effluent limit for pH; refer to Special
Condition S8.
1. For sites with significant concrete work, the Permittee must begin the pH sampling
period when the concrete is first poured and exposed to precipitation, and continue
weekly throughout and after the concrete pour and curing period, until stormwater
pH is in the range of 6.5 to 8.5 (su).
2. For sites with recycled concrete, the Permittee must begin the weekly pH sampling
period when the recycled concrete is first exposed to precipitation and must
continue until the recycled concrete is fully stabilized and stormwater pH is in the
range of 6.5 to 8.5 (su).
3. For sites with engineered soils, the Permittee must begin the pH sampling period
when the soil amendments are first exposed to precipitation and must continue
until the area of engineered soils is fully stabilized.
4. During the applicable pH monitoring period defined above, the Permittee must
obtain a representative sample of stormwater and conduct pH analysis at least once
per week.
5. The Permittee must sample pH in the sediment trap/pond(s) or other locations that
receive stormwater runoff from the area of significant concrete work or engineered
soils before the stormwater discharges to surface waters.
6. The benchmark value for pH is 8.5 standard units. Anytime sampling indicates that
pH is 8.5 or greater, the Permittee must either:
Construction Stormwater General Permit
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a. Prevent the high pH water (8.5 or above) from entering storm sewer systems or
surface waters; or
b. If necessary, adjust or neutralize the high pH water until it is in the range of pH
6.5 to 8.5 (su) using an appropriate treatment BMP such as carbon dioxide
(CO2) sparging or dry ice. The Permittee must obtain written approval from
Ecology before using any form of chemical treatment other than CO2 sparging
or dry ice.
7. The Permittee must perform pH analysis on site with a calibrated pH meter, pH
test kit, or wide range pH indicator paper. The Permittee must record pH sampling
results in the site log book.
S5. REPORTING AND RECORDKEEPING REQUIREMENTS
A. High Turbidity Reporting
Anytime sampling performed in accordance with Special Condition S4.C indicates
turbidity has reached the 250 NTUs or more (or transparency less than or equal to 6 cm)
high turbidity reporting level, the Permittee must either call the applicable Ecology
Region’s Environmental Report Tracking System (ERTS) number by phone within 24
hours of analysis or submit an electronic ERTS report (or submit an electronic report
through Ecology’s Water Quality Permitting Portal (WQWebPortal) – Permit Submittals
when the form is available). See the CSWGP web site for links to ERTS and the
WQWebPortal: http://www.ecy.wa.gov/programs/wq/stormwater/construction/
index.html. Also, see phone numbers in Special Condition S4.C.5.b.i.
B. Discharge Monitoring Reports (DMRs)
Permittees required to conduct water quality sampling in accordance with Special
Conditions S4.C (Turbidity/Transparency), S4.D (pH), S8 (303[d]/TMDL sampling),
and/or G13 (Additional Sampling) must submit the results to Ecology.
Permittees must submit monitoring data using Ecology's WQWebDMR web application
accessed through Ecology’s Water Quality Permitting Portal. To find out more
information and to sign up for WQWebDMR go to: http://www.ecy.wa.gov/programs/
wq/permits/paris/portal.html.
Permittees unable to submit electronically (for example, those who do not have an
internet connection) must contact Ecology to request a waiver and obtain instructions on
how to obtain a paper copy DMR at:
Department of Ecology
Water Quality Program - Construction Stormwater
PO Box 47696
Olympia, Washington 98504-7696
Permittees who obtain a waiver not to use WQWebDMR must use the forms provided to
them by Ecology; submittals must be mailed to the address above. Permittees shall
Construction Stormwater General Permit
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submit DMR forms to be received by Ecology within 15 days following the end of each
month.
If there was no discharge during a given monitoring period, all Permittees must submit a
DMR as required with “no discharge" entered in place of the monitoring results. DMRs
are required for the full duration of permit coverage (from issuance date to termination).
For more information, contact Ecology staff using information provided at the following
web site: www.ecy.wa.gov/programs/wq/permits/paris/contacts.html.
C. Records Retention
The Permittee must retain records of all monitoring information (site log book, sampling
results, inspection reports/checklists, etc.), Stormwater Pollution Prevention Plan, copy
of the permit coverage letter (including Transfer of Coverage documentation), and any
other documentation of compliance with permit requirements for the entire life of the
construction project and for a minimum of three years following the termination of
permit coverage. Such information must include all calibration and maintenance records,
and records of all data used to complete the application for this permit. This period of
retention must be extended during the course of any unresolved litigation regarding the
discharge of pollutants by the Permittee or when requested by Ecology.
D. Recording Results
For each measurement or sample taken, the Permittee must record the following
information:
1. Date, place, method, and time of sampling or measurement.
2. The first and last name of the individual who performed the sampling or
measurement.
3. The date(s) the analyses were performed.
4. The first and last name of the individual who performed the analyses.
5. The analytical techniques or methods used.
6. The results of all analyses.
E. Additional Monitoring by the Permittee
If the Permittee monitors any pollutant more frequently than required by this permit
using test procedures specified by Special Condition S4 of this permit, the results of this
monitoring must be included in the calculation and reporting of the data submitted in the
Permittee’s DMR.
F. Noncompliance Notification
In the event the Permittee is unable to comply with any part of the terms and conditions
of this permit, and the resulting noncompliance may cause a threat to human health or
the environment (such as but not limited to spills of fuels or other materials, catastrophic
pond or slope failure, and discharges that violate water quality standards), or exceed
Construction Stormwater General Permit
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numeric effluent limitations (see S8. Discharges to 303(d) or TMDL Waterbodies), the
Permittee must, upon becoming aware of the circumstance:
1. Notify Ecology within 24-hours of the failure to comply by calling the applicable
Regional office ERTS phone number (refer to Special Condition S4.C.5.b.i. or
www.ecy.wa.gov/programs/wq/stormwater/construction/turbidity.html
for Regional ERTS phone numbers).
2. Immediately take action to prevent the discharge/pollution, or otherwise stop or
correct the noncompliance, and, if applicable, repeat sampling and analysis of any
noncompliance immediately and submit the results to Ecology within five (5) days
of becoming aware of the violation.
3. Submit a detailed written report to Ecology within five (5) days, of the time the
Permittee becomes aware of the circumstances, unless requested earlier by
Ecology. The report must be submitted using Ecology’s Water Quality Permitting
Portal (WQWebPortal) - Permit Submittals, unless a waiver from electronic
reporting has been granted according to S5.B. The report must contain a
description of the noncompliance, including exact dates and times, and if the
noncompliance has not been corrected, the anticipated time it is expected to
continue; and the steps taken or planned to reduce, eliminate, and prevent
reoccurrence of the noncompliance.
The Permittee must report any unanticipated bypass and/or upset that exceeds any
effluent limit in the permit in accordance with the 24-hour reporting requirement
contained in 40 C.F.R. 122.41(l)(6).
Compliance with these requirements does not relieve the Permittee from
responsibility to maintain continuous compliance with the terms and conditions of
this permit or the resulting liability for failure to comply. Upon request of the
Permittee, Ecology may waive the requirement for a written report on a case-by-
case basis, if the immediate notification is received by Ecology within 24 hours.
G. Access to Plans and Records
1. The Permittee must retain the following permit documentation (plans and records)
on site, or within reasonable access to the site, for use by the operator or for on-site
review by Ecology or the local jurisdiction:
a. General Permit
b. Permit Coverage Letter
c. Stormwater Pollution Prevention Plan (SWPPP)
d. Site Log Book
2. The Permittee must address written requests for plans and records listed above
(Special Condition S5.G.1) as follows:
Construction Stormwater General Permit
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a. The Permittee must provide a copy of plans and records to Ecology within 14
days of receipt of a written request from Ecology.
b. The Permittee must provide a copy of plans and records to the public when
requested in writing. Upon receiving a written request from the public for the
Permittee’s plans and records, the Permittee must either:
i. Provide a copy of the plans and records to the requester within 14 days of
a receipt of the written request; or
ii. Notify the requester within 10 days of receipt of the written request of the
location and times within normal business hours when the plans and
records may be viewed; and provide access to the plans and records
within 14 days of receipt of the written request; or
iii. Within 14 days of receipt of the written request, the Permittee may
submit a copy of the plans and records to Ecology for viewing and/or
copying by the requester at an Ecology office, or a mutually agreed
location. If plans and records are viewed and/or copied at a location other
than at an Ecology office, the Permittee will provide reasonable access to
copying services for which a reasonable fee may be charged. The
Permittee must notify the requester within 10 days of receipt of the
request where the plans and records may be viewed and/or copied.
S6. PERMIT FEES
The Permittee must pay permit fees assessed by Ecology. Fees for stormwater discharges
covered under this permit are established by Chapter 173-224 WAC. Ecology continues to
assess permit fees until the permit is terminated in accordance with Special Condition S10
or revoked in accordance with General Condition G5.
S7. SOLID AND LIQUID WASTE DISPOSAL
The Permittee must handle and dispose of solid and liquid wastes generated by construction
activity, such as demolition debris, construction materials, contaminated materials, and
waste materials from maintenance activities, including liquids and solids from cleaning
catch basins and other stormwater facilities, in accordance with:
A. Special Condition S3, Compliance with Standards
B. WAC 173-216-110
C. Other applicable regulations
S8. DISCHARGES TO 303(d) OR TMDL WATERBODIES
A. Sampling and Numeric Effluent Limits For Certain Discharges to 303(d)-listed
Waterbodies
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1. Permittees who discharge to segments of waterbodies listed as impaired by the
State of Washington under Section 303(d) of the Clean Water Act for turbidity,
fine sediment, high pH, or phosphorus, must conduct water quality sampling
according to the requirements of this section, and Special Conditions S4.C.2.b-f
and S4.C.3.b-d, and must comply with the applicable numeric effluent limitations
in S8.C and S8.D.
2. All references and requirements associated with Section 303(d) of the Clean Water
Act mean the most current listing by Ecology of impaired waters (Category 5) that
exists on January 1, 2016, or the date when the operator’s complete permit
application is received by Ecology, whichever is later.
B. Limits on Coverage for New Discharges to TMDL or 303(d)-listed Waters
Operators of construction sites that discharge to a TMDL or 303(d)-listed waterbody are
not eligible for coverage under this permit unless the operator:
1. Prevents exposing stormwater to pollutants for which the waterbody is impaired,
and retains documentation in the SWPPP that details procedures taken to prevent
exposure on site; or
2. Documents that the pollutants for which the waterbody is impaired are not present
at the site, and retains documentation of this finding within the SWPPP; or
3. Provides Ecology with data indicating the discharge is not expected to cause or
contribute to an exceedance of a water quality standard, and retains such data on
site with the SWPPP. The operator must provide data and other technical
information to Ecology that sufficiently demonstrate:
a. For discharges to waters without an EPA-approved or -established TMDL, that
the discharge of the pollutant for which the water is impaired will meet in-
stream water quality criteria at the point of discharge to the waterbody; or
b. For discharges to waters with an EPA-approved or -established TMDL, that
there is sufficient remaining wasteload allocation in the TMDL to allow
construction stormwater discharge and that existing dischargers to the
waterbody are subject to compliance schedules designed to bring the waterbody
into attainment with water quality standards.
Operators of construction sites are eligible for coverage under this permit if
Ecology issues permit coverage based upon an affirmative determination that the
discharge will not cause or contribute to the existing impairment.
C. Sampling and Numeric Effluent Limits for Discharges to Water Bodies on the 303(d)
List for Turbidity, Fine Sediment, or Phosphorus
1. Permittees who discharge to segments of water bodies on the 303(d) list (Category
5) for turbidity, fine sediment, or phosphorus must conduct turbidity sampling in
accordance with Special Condition S4.C.2 and comply with either of the numeric
effluent limits noted in Table 5 below.
Construction Stormwater General Permit
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2. As an alternative to the 25 NTUs effluent limit noted in Table 5 below (applied at
the point where stormwater [or authorized non-stormwater] is discharged off-site),
Permittees may choose to comply with the surface water quality standard for
turbidity. The standard is: no more than 5 NTUs over background turbidity when
the background turbidity is 50 NTUs or less, or no more than a 10% increase in
turbidity when the background turbidity is more than 50 NTUs. In order to use the
water quality standard requirement, the sampling must take place at the following
locations:
a. Background turbidity in the 303(d)-listed receiving water immediately upstream
(upgradient) or outside the area of influence of the discharge.
b. Turbidity at the point of discharge into the 303(d)-listed receiving water, inside
the area of influence of the discharge.
3. Discharges that exceed the numeric effluent limit for turbidity constitute a
violation of this permit.
4. Permittees whose discharges exceed the numeric effluent limit shall sample
discharges daily until the violation is corrected and comply with the non-
compliance notification requirements in Special Condition S5.F.
Table 5: Turbidity, Fine Sediment & Phosphorus Sampling and Limits for 303(d)-Listed Waters
Parameter identified
in 303(d) listing
Parameter
Sampled
Unit Analytical
Method
Sampling
Frequency
Numeric Effluent
Limit1
Turbidity
Fine Sediment
Phosphorus
Turbidity NTU SM2130 Weekly, if
discharging
25 NTUs, at the
point where
stormwater is
discharged from the
site; OR
In compliance with
the surface water
quality standard for
turbidity (S8.C.2.a)
1Permittees subject to a numeric effluent limit for turbidity may, at their discretion, choose either numeric effluent
limitation based on site-specific considerations including, but not limited to, safety, access and convenience.
D. Discharges to Water Bodies on the 303(d) List for High pH
1. Permittees who discharge to segments of water bodies on the 303(d) list (Category
5) for high pH must conduct pH sampling in accordance with the table below, and
comply with the numeric effluent limit of pH 6.5 to 8.5 su (Table 6).
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Table 6: pH Sampling and Limits for 303(d)-Listed Waters
Parameter identified in
303(d) listing
Parameter
Sampled/Units
Analytical
Method
Sampling
Frequency
Numeric Effluent
Limit
High pH pH /Standard
Units
pH meter Weekly, if
discharging
In the range of 6.5
– 8.5
2. At the Permittee’s discretion, compliance with the limit shall be assessed at one of
the following locations:
a. Directly in the 303(d)-listed waterbody segment, inside the immediate area of
influence of the discharge; or
b. Alternatively, the Permittee may measure pH at the point where the discharge
leaves the construction site, rather than in the receiving water.
3. Discharges that exceed the numeric effluent limit for pH (outside the range of 6.5 –
8.5 su) constitute a violation of this permit.
4. Permittees whose discharges exceed the numeric effluent limit shall sample
discharges daily until the violation is corrected and comply with the non-
compliance notification requirements in Special Condition S5.F.
E. Sampling and Limits for Sites Discharging to Waters Covered by a TMDL or Another
Pollution Control Plan
1. Discharges to a waterbody that is subject to a Total Maximum Daily Load
(TMDL) for turbidity, fine sediment, high pH, or phosphorus must be consistent
with the TMDL. Refer to http://www.ecy.wa.gov/programs/wq/tmdl/
TMDLsbyWria/TMDLbyWria.html for more information on TMDLs.
a. Where an applicable TMDL sets specific waste load allocations or requirements
for discharges covered by this permit, discharges must be consistent with any
specific waste load allocations or requirements established by the applicable
TMDL.
i. The Permittee must sample discharges weekly or as otherwise specified
by the TMDL to evaluate compliance with the specific waste load
allocations or requirements.
ii. Analytical methods used to meet the monitoring requirements must
conform to the latest revision of the Guidelines Establishing Test
Procedures for the Analysis of Pollutants contained in 40 CFR Part 136.
Turbidity and pH methods need not be accredited or registered unless
conducted at a laboratory which must otherwise be accredited or
registered.
b. Where an applicable TMDL has established a general waste load allocation for
construction stormwater discharges, but has not identified specific requirements,
Construction Stormwater General Permit
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compliance with Special Conditions S4 (Monitoring) and S9 (SWPPPs) will
constitute compliance with the approved TMDL.
c. Where an applicable TMDL has not specified a waste load allocation for
construction stormwater discharges, but has not excluded these discharges,
compliance with Special Conditions S4 (Monitoring) and S9 (SWPPPs) will
constitute compliance with the approved TMDL.
d. Where an applicable TMDL specifically precludes or prohibits discharges from
construction activity, the operator is not eligible for coverage under this permit.
2. Applicable TMDL means a TMDL for turbidity, fine sediment, high pH, or
phosphorus that is completed and approved by EPA before January 1, 2016, or
before the date the operator’s complete permit application is received by Ecology,
whichever is later. TMDLs completed after the operator’s complete permit
application is received by Ecology become applicable to the Permittee only if they
are imposed through an administrative order by Ecology, or through a modification
of permit coverage.
S9. STORMWATER POLLUTION PREVENTION PLAN
The Permittee must prepare and properly implement an adequate Stormwater Pollution
Prevention Plan (SWPPP) for construction activity in accordance with the requirements of
this permit beginning with initial soil disturbance and until final stabilization.
A. The Permittee’s SWPPP must meet the following objectives:
1. To implement best management practices (BMPs) to prevent erosion and
sedimentation, and to identify, reduce, eliminate or prevent stormwater
contamination and water pollution from construction activity.
2. To prevent violations of surface water quality, ground water quality, or sediment
management standards.
3. To control peak volumetric flow rates and velocities of stormwater discharges.
B. General Requirements
1. The SWPPP must include a narrative and drawings. All BMPs must be clearly
referenced in the narrative and marked on the drawings. The SWPPP narrative
must include documentation to explain and justify the pollution prevention
decisions made for the project. Documentation must include:
a. Information about existing site conditions (topography, drainage, soils,
vegetation, etc.).
b. Potential erosion problem areas.
c. The 13 elements of a SWPPP in Special Condition S9.D.1-13, including BMPs
used to address each element.
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d. Construction phasing/sequence and general BMP implementation schedule.
e. The actions to be taken if BMP performance goals are not achieved—for
example, a contingency plan for additional treatment and/or storage of
stormwater that would violate the water quality standards if discharged.
f. Engineering calculations for ponds, treatment systems, and any other designed
structures.
2. The Permittee must modify the SWPPP if, during inspections or investigations
conducted by the owner/operator, or the applicable local or state regulatory
authority, it is determined that the SWPPP is, or would be, ineffective in
eliminating or significantly minimizing pollutants in stormwater discharges from
the site. The Permittee must then:
a. Review the SWPPP for compliance with Special Condition S9 and make
appropriate revisions within 7 days of the inspection or investigation.
b. Immediately begin the process to fully implement and maintain appropriate
source control and/or treatment BMPs as soon as possible, addressing the
problems no later than 10 days from the inspection or investigation. If
installation of necessary treatment BMPs is not feasible within 10 days, Ecology
may approve additional time when an extension is requested by a Permittee
within the initial 10-day response period.
c. Document BMP implementation and maintenance in the site log book.
The Permittee must modify the SWPPP whenever there is a change in design,
construction, operation, or maintenance at the construction site that has, or could
have, a significant effect on the discharge of pollutants to waters of the State.
C. Stormwater Best Management Practices (BMPs)
BMPs must be consistent with:
1. Stormwater Management Manual for Western Washington (most current approved
edition at the time this permit was issued), for sites west of the crest of the Cascade
Mountains; or
2. Stormwater Management Manual for Eastern Washington (most current approved
edition at the time this permit was issued), for sites east of the crest of the Cascade
Mountains; or
3. Revisions to the manuals listed in Special Condition S9.C.1. & 2., or other
stormwater management guidance documents or manuals which provide an
equivalent level of pollution prevention, that are approved by Ecology and
incorporated into this permit in accordance with the permit modification
requirements of WAC 173-226-230; or
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4. Documentation in the SWPPP that the BMPs selected provide an equivalent level
of pollution prevention, compared to the applicable Stormwater Management
Manuals, including:
a. The technical basis for the selection of all stormwater BMPs (scientific,
technical studies, and/or modeling) that support the performance claims for the
BMPs being selected.
b. An assessment of how the selected BMP will satisfy AKART requirements and
the applicable federal technology-based treatment requirements under 40 CFR
part 125.3.
D. SWPPP – Narrative Contents and Requirements
The Permittee must include each of the 13 elements below in Special Condition
S9.D.1-13 in the narrative of the SWPPP and implement them unless site
conditions render the element unnecessary and the exemption from that element is
clearly justified in the SWPPP.
1. Preserve Vegetation/Mark Clearing Limits
a. Before beginning land-disturbing activities, including clearing and grading,
clearly mark all clearing limits, sensitive areas and their buffers, and trees that
are to be preserved within the construction area.
b. Retain the duff layer, native topsoil, and natural vegetation in an undisturbed
state to the maximum degree practicable.
2. Establish Construction Access
a. Limit construction vehicle access and exit to one route, if possible.
b. Stabilize access points with a pad of quarry spalls, crushed rock, or other
equivalent BMPs, to minimize tracking sediment onto roads.
c. Locate wheel wash or tire baths on site, if the stabilized construction entrance is
not effective in preventing tracking sediment onto roads.
d. If sediment is tracked off site, clean the affected roadway thoroughly at the end
of each day, or more frequently as necessary (for example, during wet weather).
Remove sediment from roads by shoveling, sweeping, or pickup and transport
of the sediment to a controlled sediment disposal area.
e. Conduct street washing only after sediment removal in accordance with Special
Condition S9.D.2.d. Control street wash wastewater by pumping back on site or
otherwise preventing it from discharging into systems tributary to waters of the
State.
3. Control Flow Rates
a. Protect properties and waterways downstream of development sites from
erosion and the associated discharge of turbid waters due to increases in the
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velocity and peak volumetric flow rate of stormwater runoff from the project
site, as required by local plan approval authority.
b. Where necessary to comply with Special Condition S9.D.3.a, construct
stormwater retention or detention facilities as one of the first steps in grading.
Assure that detention facilities function properly before constructing site
improvements (for example, impervious surfaces).
c. If permanent infiltration ponds are used for flow control during construction,
protect these facilities from siltation during the construction phase.
4. Install Sediment Controls
The Permittee must design, install and maintain effective erosion controls and
sediment controls to minimize the discharge of pollutants. At a minimum, the
Permittee must design, install and maintain such controls to:
a. Construct sediment control BMPs (sediment ponds, traps, filters, infiltration
facilities, etc.) as one of the first steps in grading. These BMPs must be
functional before other land disturbing activities take place.
b. Minimize sediment discharges from the site. The design, installation and
maintenance of erosion and sediment controls must address factors such as the
amount, frequency, intensity and duration of precipitation, the nature of
resulting stormwater runoff, and soil characteristics, including the range of soil
particle sizes expected to be present on the site.
c. Direct stormwater runoff from disturbed areas through a sediment pond or other
appropriate sediment removal BMP, before the runoff leaves a construction site
or before discharge to an infiltration facility. Runoff from fully stabilized areas
may be discharged without a sediment removal BMP, but must meet the flow
control performance standard of Special Condition S9.D.3.a.
d. Locate BMPs intended to trap sediment on site in a manner to avoid interference
with the movement of juvenile salmonids attempting to enter off-channel areas
or drainages.
e. Provide and maintain natural buffers around surface waters, direct stormwater to
vegetated areas to increase sediment removal and maximize stormwater
infiltration, unless infeasible.
f. Where feasible, design outlet structures that withdraw impounded stormwater
from the surface to avoid discharging sediment that is still suspended lower in
the water column.
5. Stabilize Soils
a. The Permittee must stabilize exposed and unworked soils by application of
effective BMPs that prevent erosion. Applicable BMPs include, but are not
limited to: temporary and permanent seeding, sodding, mulching, plastic
covering, erosion control fabrics and matting, soil application of polyacrylamide
Construction Stormwater General Permit
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(PAM), the early application of gravel base on areas to be paved, and dust
control.
b. The Permittee must control stormwater volume and velocity within the site to
minimize soil erosion.
c. The Permittee must control stormwater discharges, including both peak flow
rates and total stormwater volume, to minimize erosion at outlets and to
minimize downstream channel and stream bank erosion.
d. Depending on the geographic location of the project, the Permittee must not
allow soils to remain exposed and unworked for more than the time periods set
forth below to prevent erosion:
West of the Cascade Mountains Crest
During the dry season (May 1 - September 30): 7 days
During the wet season (October 1 - April 30): 2 days
East of the Cascade Mountains Crest, except for Central Basin*
During the dry season (July 1 - September 30): 10 days
During the wet season (October 1 - June 30): 5 days
The Central Basin*, East of the Cascade Mountains Crest
During the dry season (July 1 - September 30): 30 days
During the wet season (October 1 - June 30): 15 days
*Note: The Central Basin is defined as the portions of Eastern
Washington with mean annual precipitation of less than 12 inches.
e. The Permittee must stabilize soils at the end of the shift before a holiday or
weekend if needed based on the weather forecast.
f. The Permittee must stabilize soil stockpiles from erosion, protected with
sediment trapping measures, and where possible, be located away from storm
drain inlets, waterways, and drainage channels.
g. The Permittee must minimize the amount of soil exposed during construction
activity.
h. The Permittee must minimize the disturbance of steep slopes.
i. The Permittee must minimize soil compaction and, unless infeasible, preserve
topsoil.
6. Protect Slopes
a. The Permittee must design and construct cut-and-fill slopes in a manner to
minimize erosion. Applicable practices include, but are not limited to, reducing
continuous length of slope with terracing and diversions, reducing slope
steepness, and roughening slope surfaces (for example, track walking).
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b. The Permittee must divert off-site stormwater (run-on) or ground water away
from slopes and disturbed areas with interceptor dikes, pipes, and/or swales.
Off-site stormwater should be managed separately from stormwater generated
on the site.
c. At the top of slopes, collect drainage in pipe slope drains or protected channels
to prevent erosion.
i. West of the Cascade Mountains Crest: Temporary pipe slope drains must
handle the peak 10-minute flow rate from a Type 1A, 10-year, 24-hour
frequency storm for the developed condition. Alternatively, the 10-year,
1-hour flow rate predicted by an approved continuous runoff model,
increased by a factor of 1.6, may be used. The hydrologic analysis must
use the existing land cover condition for predicting flow rates from
tributary areas outside the project limits. For tributary areas on the project
site, the analysis must use the temporary or permanent project land cover
condition, whichever will produce the highest flow rates. If using the
Western Washington Hydrology Model (WWHM) to predict flows, bare
soil areas should be modeled as "landscaped area.”
ii. East of the Cascade Mountains Crest: Temporary pipe slope drains must
handle the expected peak flow rate from a 6-month, 3-hour storm for the
developed condition, referred to as the short duration storm.
d. Place excavated material on the uphill side of trenches, consistent with safety
and space considerations.
e. Place check dams at regular intervals within constructed channels that are cut
down a slope.
7. Protect Drain Inlets
a. Protect all storm drain inlets made operable during construction so that
stormwater runoff does not enter the conveyance system without first being
filtered or treated to remove sediment.
b. Clean or remove and replace inlet protection devices when sediment has filled
one-third of the available storage (unless a different standard is specified by the
product manufacturer).
8. Stabilize Channels and Outlets
a. Design, construct and stabilize all on-site conveyance channels to prevent
erosion from the following expected peak flows:
i. West of the Cascade Mountains Crest: Channels must handle the peak
10-minute flow rate from a Type 1A, 10-year, 24-hour frequency storm
for the developed condition. Alternatively, the 10-year, 1-hour flow rate
indicated by an approved continuous runoff model, increased by a factor
of 1.6, may be used. The hydrologic analysis must use the existing land
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cover condition for predicting flow rates from tributary areas outside the
project limits. For tributary areas on the project site, the analysis must use
the temporary or permanent project land cover condition, whichever will
produce the highest flow rates. If using the WWHM to predict flows, bare
soil areas should be modeled as "landscaped area.”
ii. East of the Cascade Mountains Crest: Channels must handle the expected
peak flow rate from a 6-month, 3-hour storm for the developed condition,
referred to as the short duration storm.
b. Provide stabilization, including armoring material, adequate to prevent erosion
of outlets, adjacent stream banks, slopes, and downstream reaches at the outlets
of all conveyance systems.
9. Control Pollutants
Design, install, implement and maintain effective pollution prevention measures to
minimize the discharge of pollutants. The Permittee must:
a. Handle and dispose of all pollutants, including waste materials and demolition
debris that occur on site in a manner that does not cause contamination of
stormwater.
b. Provide cover, containment, and protection from vandalism for all chemicals,
liquid products, petroleum products, and other materials that have the potential
to pose a threat to human health or the environment. On-site fueling tanks must
include secondary containment. Secondary containment means placing tanks or
containers within an impervious structure capable of containing 110% of the
volume contained in the largest tank within the containment structure. Double-
walled tanks do not require additional secondary containment.
c. Conduct maintenance, fueling, and repair of heavy equipment and vehicles
using spill prevention and control measures. Clean contaminated surfaces
immediately following any spill incident.
d. Discharge wheel wash or tire bath wastewater to a separate on-site treatment
system that prevents discharge to surface water, such as closed-loop
recirculation or upland land application, or to the sanitary sewer with local
sewer district approval.
e. Apply fertilizers and pesticides in a manner and at application rates that will not
result in loss of chemical to stormwater runoff. Follow manufacturers’ label
requirements for application rates and procedures.
f. Use BMPs to prevent contamination of stormwater runoff by pH-modifying
sources. The sources for this contamination include, but are not limited to: bulk
cement, cement kiln dust, fly ash, new concrete washing and curing waters,
recycled concrete stockpiles, waste streams generated from concrete grinding
and sawing, exposed aggregate processes, dewatering concrete vaults, concrete
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pumping and mixer washout waters. (Also refer to the definition for "concrete
wastewater" in Appendix A--Definitions.)
g. Adjust the pH of stormwater or authorized non-stormwater if necessary to
prevent an exceedance of groundwater and/or surface water quality standards.
h. Assure that washout of concrete trucks is performed off-site or in designated
concrete washout areas only. Do not wash out concrete trucks or concrete
handling equipment onto the ground, or into storm drains, open ditches, streets,
or streams. Do not dump excess concrete on site, except in designated concrete
washout areas. Concrete spillage or concrete discharge to surface waters of the
State is prohibited.
i. Obtain written approval from Ecology before using any chemical treatment,
with the exception of CO2 or dry ice used to adjust pH.
j. Uncontaminated water from water-only based shaft drilling for construction of
building, road, and bridge foundations may be infiltrated provided the
wastewater is managed in a way that prohibits discharge to surface waters. Prior
to infiltration, water from water-only based shaft drilling that comes into contact
with curing concrete must be neutralized until pH is in the range of 6.5 to 8.5
(su).
10. Control Dewatering
a. Permittees must discharge foundation, vault, and trench dewatering water,
which have characteristics similar to stormwater runoff at the site, into a
controlled conveyance system before discharge to a sediment trap or sediment
pond.
b. Permittees may discharge clean, non-turbid dewatering water, such as well-
point ground water, to systems tributary to, or directly into surface waters of the
State, as specified in Special Condition S9.D.8, provided the dewatering flow
does not cause erosion or flooding of receiving waters. Do not route clean
dewatering water through stormwater sediment ponds. Note that “surface waters
of the State” may exist on a construction site as well as off site; for example, a
creek running through a site.
c. Other dewatering treatment or disposal options may include:
i. Infiltration.
ii. Transport off site in a vehicle, such as a vacuum flush truck, for legal
disposal in a manner that does not pollute state waters.
iii. Ecology-approved on-site chemical treatment or other suitable treatment
technologies (see S9.D.9.i. regarding chemical treatment written
approval).
iv. Sanitary or combined sewer discharge with local sewer district approval,
if there is no other option.
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v. Use of a sedimentation bag with discharge to a ditch or swale for small
volumes of localized dewatering.
d. Permittees must handle highly turbid or contaminated dewatering water
separately from stormwater.
11. Maintain BMPs
a. Permittees must maintain and repair all temporary and permanent erosion and
sediment control BMPs as needed to assure continued performance of their
intended function in accordance with BMP specifications.
b. Permittees must remove all temporary erosion and sediment control BMPs
within 30 days after achieving final site stabilization or after the temporary
BMPs are no longer needed.
12. Manage the Project
a. Phase development projects to the maximum degree practicable and take into
account seasonal work limitations.
b. Inspection and monitoring – Inspect, maintain and repair all BMPs as needed to
assure continued performance of their intended function. Conduct site
inspections and monitoring in accordance with Special Condition S4.
c. Maintaining an updated construction SWPPP – Maintain, update, and
implement the SWPPP in accordance with Special Conditions S3, S4 and S9.
13. Protect Low Impact Development (LID) BMPs
The primary purpose of LID BMPs/On-site LID Stormwater Management BMPs is
to reduce the disruption of the natural site hydrology. LID BMPs are permanent
facilities.
a. Permittees must protect all Bioretention and Rain Garden facilities from
sedimentation through installation and maintenance of erosion and sediment
control BMPs on portions of the site that drain into the Bioretention and/or Rain
Garden facilities. Restore the facilities to their fully functioning condition if
they accumulate sediment during construction. Restoring the facility must
include removal of sediment and any sediment-laden Bioretention/Rain Garden
soils, and replacing the removed soils with soils meeting the design
specification.
b. Permittees must maintain the infiltration capabilities of Bioretention and Rain
Garden facilities by protecting against compaction by construction equipment
and foot traffic. Protect completed lawn and landscaped areas from compaction
due to construction equipment.
c. Permittees must control erosion and avoid introducing sediment from
surrounding land uses onto permeable pavements. Do not allow muddy
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construction equipment on the base material or pavement. Do not allow
sediment-laden runoff onto permeable pavements.
d. Permittees must clean permeable pavements fouled with sediments or no longer
passing an initial infiltration test using local stormwater manual methodology or
the manufacturer’s procedures.
e. Permittees must keep all heavy equipment off existing soils under LID facilities
that have been excavated to final grade to retain the infiltration rate of the soils.
E. SWPPP – Map Contents and Requirements
The Permittee’s SWPPP must also include a vicinity map or general location map (for
example, a USGS quadrangle map, a portion of a county or city map, or other
appropriate map) with enough detail to identify the location of the construction site and
receiving waters within one mile of the site.
The SWPPP must also include a legible site map (or maps) showing the entire
construction site. The following features must be identified, unless not applicable due to
site conditions:
1. The direction of north, property lines, and existing structures and roads.
2. Cut and fill slopes indicating the top and bottom of slope catch lines.
3. Approximate slopes, contours, and direction of stormwater flow before and after
major grading activities.
4. Areas of soil disturbance and areas that will not be disturbed.
5. Locations of structural and nonstructural controls (BMPs) identified in the
SWPPP.
6. Locations of off-site material, stockpiles, waste storage, borrow areas, and
vehicle/equipment storage areas.
7. Locations of all surface water bodies, including wetlands.
8. Locations where stormwater or non-stormwater discharges off-site and/or to a
surface waterbody, including wetlands.
9. Location of water quality sampling station(s), if sampling is required by state or
local permitting authority.
10. Areas where final stabilization has been accomplished and no further construction-
phase permit requirements apply.
11. Location or proposed location of LID facilities.
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S10. NOTICE OF TERMINATION
A. The site is eligible for termination of coverage when it has met any of the following
conditions:
1. The site has undergone final stabilization, the Permittee has removed all temporary
BMPs (except biodegradable BMPs clearly manufactured with the intention for the
material to be left in place and not interfere with maintenance or land use), and all
stormwater discharges associated with construction activity have been eliminated;
or
2. All portions of the site that have not undergone final stabilization per Special
Condition S10.A.1 have been sold and/or transferred (per General Condition G9),
and the Permittee no longer has operational control of the construction activity; or
3. For residential construction only, the Permittee has completed temporary
stabilization and the homeowners have taken possession of the residences.
B. When the site is eligible for termination, the Permittee must submit a complete and
accurate Notice of Termination (NOT) form, signed in accordance with General
Condition G2, to:
Department of Ecology
Water Quality Program – Construction Stormwater
PO Box 47696
Olympia, Washington 98504-7696
When an electronic termination form is available, the Permittee may choose to submit a
complete and accurate Notice of Termination (NOT) form through the Water Quality
Permitting Portal rather than mailing a hardcopy as noted above.
The termination is effective on the thirty-first calendar day following the date Ecology
receives a complete NOT form, unless Ecology notifies the Permittee that the
termination request is denied because the Permittee has not met the eligibility
requirements in Special Condition S10.A.
Permittees are required to comply with all conditions and effluent limitations in the
permit until the permit has been terminated.
Permittees transferring the property to a new property owner or operator/Permittee are
required to complete and submit the Notice of Transfer form to Ecology, but are not
required to submit a Notice of Termination form for this type of transaction.
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GENERAL CONDITIONS
G1. DISCHARGE VIOLATIONS
All discharges and activities authorized by this general permit must be consistent with the
terms and conditions of this general permit. Any discharge of any pollutant more frequent
than or at a level in excess of that identified and authorized by the general permit must
constitute a violation of the terms and conditions of this permit.
G2. SIGNATORY REQUIREMENTS
A. All permit applications must bear a certification of correctness to be signed:
1. In the case of corporations, by a responsible corporate officer;
2. In the case of a partnership, by a general partner of a partnership;
3. In the case of sole proprietorship, by the proprietor; or
4. In the case of a municipal, state, or other public facility, by either a principal
executive officer or ranking elected official.
B. All reports required by this permit and other information requested by Ecology
(including NOIs, NOTs, and Transfer of Coverage forms) must be signed by a person
described above or by a duly authorized representative of that person. A person is a duly
authorized representative only if:
1. The authorization is made in writing by a person described above and submitted to
Ecology.
2. The authorization specifies either an individual or a position having responsibility
for the overall operation of the regulated facility, such as the position of plant
manager, superintendent, position of equivalent responsibility, or an individual or
position having overall responsibility for environmental matters.
C. Changes to authorization. If an authorization under paragraph G2.B.2 above is no longer
accurate because a different individual or position has responsibility for the overall
operation of the facility, a new authorization satisfying the requirements of paragraph
G2.B.2 above must be submitted to Ecology prior to or together with any reports,
information, or applications to be signed by an authorized representative.
D. Certification. Any person signing a document under this section must make the
following certification:
“I certify under penalty of law, that this document and all attachments
were prepared under my direction or supervision in accordance with a
system designed to assure that qualified personnel properly gathered and
evaluated the information submitted. Based on my inquiry of the person or
persons who manage the system, or those persons directly responsible for
gathering information, the information submitted is, to the best of my
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knowledge and belief, true, accurate, and complete. I am aware that there
are significant penalties for submitting false information, including the
possibility of fine and imprisonment for knowing violations.”
G3. RIGHT OF INSPECTION AND ENTRY
The Permittee must allow an authorized representative of Ecology, upon the presentation of
credentials and such other documents as may be required by law:
A. To enter upon the premises where a discharge is located or where any records are kept
under the terms and conditions of this permit.
B. To have access to and copy – at reasonable times and at reasonable cost – any records
required to be kept under the terms and conditions of this permit.
C. To inspect – at reasonable times – any facilities, equipment (including monitoring and
control equipment), practices, methods, or operations regulated or required under this
permit.
D. To sample or monitor – at reasonable times – any substances or parameters at any
location for purposes of assuring permit compliance or as otherwise authorized by the
Clean Water Act.
G4. GENERAL PERMIT MODIFICATION AND REVOCATION
This permit may be modified, revoked and reissued, or terminated in accordance with the
provisions of Chapter 173-226 WAC. Grounds for modification, revocation and reissuance,
or termination include, but are not limited to, the following:
A. When a change occurs in the technology or practices for control or abatement of
pollutants applicable to the category of dischargers covered under this permit.
B. When effluent limitation guidelines or standards are promulgated pursuant to the CWA
or Chapter 90.48 RCW, for the category of dischargers covered under this permit.
C. When a water quality management plan containing requirements applicable to the
category of dischargers covered under this permit is approved, or
D. When information is obtained that indicates cumulative effects on the environment from
dischargers covered under this permit are unacceptable.
G5. REVOCATION OF COVERAGE UNDER THE PERMIT
Pursuant to Chapter 43.21B RCW and Chapter 173-226 WAC, the Director may terminate
coverage for any discharger under this permit for cause. Cases where coverage may be
terminated include, but are not limited to, the following:
A. Violation of any term or condition of this permit.
B. Obtaining coverage under this permit by misrepresentation or failure to disclose fully all
relevant facts.
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C. A change in any condition that requires either a temporary or permanent reduction or
elimination of the permitted discharge.
D. Failure or refusal of the Permittee to allow entry as required in RCW 90.48.090.
E. A determination that the permitted activity endangers human health or the environment,
or contributes to water quality standards violations.
F. Nonpayment of permit fees or penalties assessed pursuant to RCW 90.48.465 and
Chapter 173-224 WAC.
G. Failure of the Permittee to satisfy the public notice requirements of WAC 173-226-
130(5), when applicable.
The Director may require any discharger under this permit to apply for and obtain
coverage under an individual permit or another more specific general permit. Permittees
who have their coverage revoked for cause according to WAC 173-226-240 may request
temporary coverage under this permit during the time an individual permit is being
developed, provided the request is made within ninety (90) days from the time of
revocation and is submitted along with a complete individual permit application form.
G6. REPORTING A CAUSE FOR MODIFICATION
The Permittee must submit a new application, or a supplement to the previous application,
whenever a material change to the construction activity or in the quantity or type of
discharge is anticipated which is not specifically authorized by this permit. This application
must be submitted at least sixty (60) days prior to any proposed changes. Filing a request for
a permit modification, revocation and reissuance, or termination, or a notification of planned
changes or anticipated noncompliance does not relieve the Permittee of the duty to comply
with the existing permit until it is modified or reissued.
G7. COMPLIANCE WITH OTHER LAWS AND STATUTES
Nothing in this permit will be construed as excusing the Permittee from compliance with
any applicable federal, state, or local statutes, ordinances, or regulations.
G8. DUTY TO REAPPLY
The Permittee must apply for permit renewal at least 180 days prior to the specified
expiration date of this permit. The Permittee must reapply using the electronic application
form (NOI) available on Ecology’s website. Permittees unable to submit electronically (for
example, those who do not have an internet connection) must contact Ecology to request a
waiver and obtain instructions on how to obtain a paper NOI.
Department of Ecology
Water Quality Program - Construction Stormwater
PO Box 47696
Olympia, Washington 98504-7696
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G9. TRANSFER OF GENERAL PERMIT COVERAGE
Coverage under this general permit is automatically transferred to a new discharger,
including operators of lots/parcels within a common plan of development or sale, if:
A. A written agreement (Transfer of Coverage Form) between the current discharger
(Permittee) and new discharger, signed by both parties and containing a specific date for
transfer of permit responsibility, coverage, and liability (including any Administrative
Orders associated with the Permit) is submitted to the Director; and
B. The Director does not notify the current discharger and new discharger of the Director’s
intent to revoke coverage under the general permit. If this notice is not given, the transfer
is effective on the date specified in the written agreement.
When a current discharger (Permittee) transfers a portion of a permitted site, the current
discharger must also submit an updated application form (NOI) to the Director
indicating the remaining permitted acreage after the transfer.
G10. REMOVED SUBSTANCES
The Permittee must not re-suspend or reintroduce collected screenings, grit, solids, sludges,
filter backwash, or other pollutants removed in the course of treatment or control of
stormwater to the final effluent stream for discharge to state waters.
G11. DUTY TO PROVIDE INFORMATION
The Permittee must submit to Ecology, within a reasonable time, all information that
Ecology may request to determine whether cause exists for modifying, revoking and
reissuing, or terminating this permit or to determine compliance with this permit. The
Permittee must also submit to Ecology, upon request, copies of records required to be kept
by this permit [40 CFR 122.41(h)].
G12. OTHER REQUIREMENTS OF 40 CFR
All other requirements of 40 CFR 122.41 and 122.42 are incorporated in this permit by
reference.
G13. ADDITIONAL MONITORING
Ecology may establish specific monitoring requirements in addition to those contained in
this permit by administrative order or permit modification.
G14. PENALTIES FOR VIOLATING PERMIT CONDITIONS
Any person who is found guilty of willfully violating the terms and conditions of this permit
shall be deemed guilty of a crime, and upon conviction thereof shall be punished by a fine of
up to ten thousand dollars ($10,000) and costs of prosecution, or by imprisonment at the
discretion of the court. Each day upon which a willful violation occurs may be deemed a
separate and additional violation.
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Any person who violates the terms and conditions of a waste discharge permit shall incur, in
addition to any other penalty as provided by law, a civil penalty in the amount of up to ten
thousand dollars ($10,000) for every such violation. Each and every such violation shall be a
separate and distinct offense, and in case of a continuing violation, every day’s continuance
shall be deemed to be a separate and distinct violation.
G15. UPSET
Definition – “Upset” means an exceptional incident in which there is unintentional and
temporary noncompliance with technology-based permit effluent limitations because of
factors beyond the reasonable control of the Permittee. An upset does not include
noncompliance to the extent caused by operational error, improperly designed treatment
facilities, inadequate treatment facilities, lack of preventive maintenance, or careless or
improper operation.
An upset constitutes an affirmative defense to an action brought for noncompliance with
such technology-based permit effluent limitations if the requirements of the following
paragraph are met.
A Permittee who wishes to establish the affirmative defense of upset must demonstrate,
through properly signed, contemporaneous operating logs or other relevant evidence that: 1)
an upset occurred and that the Permittee can identify the cause(s) of the upset; 2) the
permitted facility was being properly operated at the time of the upset; 3) the Permittee
submitted notice of the upset as required in Special Condition S5.F, and; 4) the Permittee
complied with any remedial measures required under this permit.
In any enforcement proceeding, the Permittee seeking to establish the occurrence of an upset
has the burden of proof.
G16. PROPERTY RIGHTS
This permit does not convey any property rights of any sort, or any exclusive privilege.
G17. DUTY TO COMPLY
The Permittee must comply with all conditions of this permit. Any permit noncompliance
constitutes a violation of the Clean Water Act and is grounds for enforcement action; for
permit termination, revocation and reissuance, or modification; or denial of a permit renewal
application.
G18. TOXIC POLLUTANTS
The Permittee must comply with effluent standards or prohibitions established under Section
307(a) of the Clean Water Act for toxic pollutants within the time provided in the
regulations that establish those standards or prohibitions, even if this permit has not yet been
modified to incorporate the requirement.
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G19. PENALTIES FOR TAMPERING
The Clean Water Act provides that any person who falsifies, tampers with, or knowingly
renders inaccurate any monitoring device or method required to be maintained under this
permit shall, upon conviction, be punished by a fine of not more than $10,000 per violation,
or by imprisonment for not more than two years per violation, or by both. If a conviction of
a person is for a violation committed after a first conviction of such person under this
condition, punishment shall be a fine of not more than $20,000 per day of violation, or
imprisonment of not more than four (4) years, or both.
G20. REPORTING PLANNED CHANGES
The Permittee must, as soon as possible, give notice to Ecology of planned physical
alterations, modifications or additions to the permitted construction activity. The Permittee
should be aware that, depending on the nature and size of the changes to the original permit,
a new public notice and other permit process requirements may be required. Changes in
activities that require reporting to Ecology include those that will result in:
A. The permitted facility being determined to be a new source pursuant to 40 CFR
122.29(b).
B. A significant change in the nature or an increase in quantity of pollutants discharged,
including but not limited to: for sites 5 acres or larger, a 20% or greater increase in
acreage disturbed by construction activity.
C. A change in or addition of surface water(s) receiving stormwater or non-stormwater
from the construction activity.
D. A change in the construction plans and/or activity that affects the Permittee’s monitoring
requirements in Special Condition S4.
Following such notice, permit coverage may be modified, or revoked and reissued pursuant
to 40 CFR 122.62(a) to specify and limit any pollutants not previously limited. Until such
modification is effective, any new or increased discharge in excess of permit limits or not
specifically authorized by this permit constitutes a violation.
G21. REPORTING OTHER INFORMATION
Where the Permittee becomes aware that it failed to submit any relevant facts in a permit
application, or submitted incorrect information in a permit application or in any report to
Ecology, it must promptly submit such facts or information.
G22. REPORTING ANTICIPATED NON-COMPLIANCE
The Permittee must give advance notice to Ecology by submission of a new application or
supplement thereto at least forty-five (45) days prior to commencement of such discharges,
of any facility expansions, production increases, or other planned changes, such as process
modifications, in the permitted facility or activity which may result in noncompliance with
permit limits or conditions. Any maintenance of facilities, which might necessitate
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unavoidable interruption of operation and degradation of effluent quality, must be scheduled
during non-critical water quality periods and carried out in a manner approved by Ecology.
G23. REQUESTS TO BE EXCLUDED FROM COVERAGE UNDER THE PERMIT
Any discharger authorized by this permit may request to be excluded from coverage under
the general permit by applying for an individual permit. The discharger must submit to the
Director an application as described in WAC 173-220-040 or WAC 173-216-070,
whichever is applicable, with reasons supporting the request. These reasons will fully
document how an individual permit will apply to the applicant in a way that the general
permit cannot. Ecology may make specific requests for information to support the request.
The Director will either issue an individual permit or deny the request with a statement
explaining the reason for the denial. When an individual permit is issued to a discharger
otherwise subject to the construction stormwater general permit, the applicability of the
construction stormwater general permit to that Permittee is automatically terminated on the
effective date of the individual permit.
G24. APPEALS
A. The terms and conditions of this general permit, as they apply to the appropriate class of
dischargers, are subject to appeal by any person within 30 days of issuance of this
general permit, in accordance with Chapter 43.21B RCW, and Chapter 173-226 WAC.
B. The terms and conditions of this general permit, as they apply to an individual
discharger, are appealable in accordance with Chapter 43.21B RCW within 30 days of
the effective date of coverage of that discharger. Consideration of an appeal of general
permit coverage of an individual discharger is limited to the general permit’s
applicability or nonapplicability to that individual discharger.
C. The appeal of general permit coverage of an individual discharger does not affect any
other dischargers covered under this general permit. If the terms and conditions of this
general permit are found to be inapplicable to any individual discharger(s), the matter
shall be remanded to Ecology for consideration of issuance of an individual permit or
permits.
G25. SEVERABILITY
The provisions of this permit are severable, and if any provision of this permit, or
application of any provision of this permit to any circumstance, is held invalid, the
application of such provision to other circumstances, and the remainder of this permit shall
not be affected thereby.
G26. BYPASS PROHIBITED
A. Bypass Procedures
Bypass, which is the intentional diversion of waste streams from any portion of a
treatment facility, is prohibited for stormwater events below the design criteria for
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stormwater management. Ecology may take enforcement action against a Permittee for
bypass unless one of the following circumstances (1, 2, 3 or 4) is applicable.
1. Bypass of stormwater is consistent with the design criteria and part of an approved
management practice in the applicable stormwater management manual.
2. Bypass for essential maintenance without the potential to cause violation of permit
limits or conditions.
Bypass is authorized if it is for essential maintenance and does not have the
potential to cause violations of limitations or other conditions of this permit, or
adversely impact public health.
3. Bypass of stormwater is unavoidable, unanticipated, and results in noncompliance
of this permit.
This bypass is permitted only if:
a. Bypass is unavoidable to prevent loss of life, personal injury, or severe property
damage. “Severe property damage” means substantial physical damage to
property, damage to the treatment facilities which would cause them to become
inoperable, or substantial and permanent loss of natural resources which can
reasonably be expected to occur in the absence of a bypass.
b. There are no feasible alternatives to the bypass, such as the use of auxiliary
treatment facilities, retention of untreated wastes, maintenance during normal
periods of equipment downtime (but not if adequate backup equipment should
have been installed in the exercise of reasonable engineering judgment to
prevent a bypass which occurred during normal periods of equipment downtime
or preventative maintenance), or transport of untreated wastes to another
treatment facility.
c. Ecology is properly notified of the bypass as required in Special Condition S5.F
of this permit.
4. A planned action that would cause bypass of stormwater and has the potential to
result in noncompliance of this permit during a storm event.
The Permittee must notify Ecology at least thirty (30) days before the planned date
of bypass. The notice must contain:
a. A description of the bypass and its cause.
b. An analysis of all known alternatives which would eliminate, reduce, or
mitigate the need for bypassing.
c. A cost-effectiveness analysis of alternatives including comparative resource
damage assessment.
d. The minimum and maximum duration of bypass under each alternative.
e. A recommendation as to the preferred alternative for conducting the bypass.
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f. The projected date of bypass initiation.
g. A statement of compliance with SEPA.
h. A request for modification of water quality standards as provided for in WAC
173-201A-110, if an exceedance of any water quality standard is anticipated.
i. Steps taken or planned to reduce, eliminate, and prevent reoccurrence of the
bypass.
5. For probable construction bypasses, the need to bypass is to be identified as early
in the planning process as possible. The analysis required above must be
considered during preparation of the Stormwater Pollution Prevention Plan
(SWPPP) and must be included to the extent practical. In cases where the probable
need to bypass is determined early, continued analysis is necessary up to and
including the construction period in an effort to minimize or eliminate the bypass.
Ecology will consider the following before issuing an administrative order for this
type bypass:
a. If the bypass is necessary to perform construction or maintenance-related
activities essential to meet the requirements of this permit.
b. If there are feasible alternatives to bypass, such as the use of auxiliary treatment
facilities, retention of untreated wastes, stopping production, maintenance
during normal periods of equipment down time, or transport of untreated wastes
to another treatment facility.
c. If the bypass is planned and scheduled to minimize adverse effects on the public
and the environment.
After consideration of the above and the adverse effects of the proposed bypass
and any other relevant factors, Ecology will approve, conditionally approve, or
deny the request. The public must be notified and given an opportunity to
comment on bypass incidents of significant duration, to the extent feasible.
Approval of a request to bypass will be by administrative order issued by Ecology
under RCW 90.48.120.
B. Duty to Mitigate
The Permittee is required to take all reasonable steps to minimize or prevent any
discharge or sludge use or disposal in violation of this permit that has a reasonable
likelihood of adversely affecting human health or the environment.
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APPENDIX A – DEFINITIONS
AKART is an acronym for “all known, available, and reasonable methods of prevention, control,
and treatment.” AKART represents the most current methodology that can be reasonably
required for preventing, controlling, or abating the pollutants and controlling pollution associated
with a discharge.
Applicable TMDL means a TMDL for turbidity, fine sediment, high pH, or phosphorus, which
was completed and approved by EPA before January 1, 2016, or before the date the operator’s
complete permit application is received by Ecology, whichever is later.
Applicant means an operator seeking coverage under this permit.
Benchmark means a pollutant concentration used as a permit threshold, below which a pollutant
is considered unlikely to cause a water quality violation, and above which it may. When
pollutant concentrations exceed benchmarks, corrective action requirements take effect.
Benchmark values are not water quality standards and are not numeric effluent limitations; they
are indicator values.
Best Management Practices (BMPs) means schedules of activities, prohibitions of practices,
maintenance procedures, and other physical, structural and/or managerial practices to prevent or
reduce the pollution of waters of the State. BMPs include treatment systems, operating
procedures, and practices to control: stormwater associated with construction activity, spillage or
leaks, sludge or waste disposal, or drainage from raw material storage.
Buffer means an area designated by a local jurisdiction that is contiguous to and intended to
protect a sensitive area.
Bypass means the intentional diversion of waste streams from any portion of a treatment facility.
Calendar Day A period of 24 consecutive hours starting at 12:00 midnight and ending the
following 12:00 midnight.
Calendar Week (same as Week) means a period of seven consecutive days starting at 12:01
a.m. (0:01 hours) on Sunday.
Certified Erosion and Sediment Control Lead (CESCL) means a person who has current
certification through an approved erosion and sediment control training program that meets the
minimum training standards established by Ecology (see BMP C160 in the SWMM).
Chemical Treatment means the addition of chemicals to stormwater and/or authorized non-
stormwater prior to filtration and discharge to surface waters.
Clean Water Act (CWA) means the Federal Water Pollution Control Act enacted by Public
Law 92-500, as amended by Public Laws 95-217, 95-576, 96-483, and 97-117; USC 1251 et seq.
Combined Sewer means a sewer which has been designed to serve as a sanitary sewer and a
storm sewer, and into which inflow is allowed by local ordinance.
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Common Plan of Development or Sale means a site where multiple separate and distinct
construction activities may be taking place at different times on different schedules and/or by
different contractors, but still under a single plan. Examples include: 1) phased projects and
projects with multiple filings or lots, even if the separate phases or filings/lots will be constructed
under separate contract or by separate owners (e.g., a development where lots are sold to separate
builders); 2) a development plan that may be phased over multiple years, but is still under a
consistent plan for long-term development; 3) projects in a contiguous area that may be unrelated
but still under the same contract, such as construction of a building extension and a new parking
lot at the same facility; and 4) linear projects such as roads, pipelines, or utilities. If the project is
part of a common plan of development or sale, the disturbed area of the entire plan must be used
in determining permit requirements.
Composite Sample means a mixture of grab samples collected at the same sampling point at
different times, formed either by continuous sampling or by mixing discrete samples. May be
"time-composite" (collected at constant time intervals) or "flow-proportional" (collected either as
a constant sample volume at time intervals proportional to stream flow, or collected by
increasing the volume of each aliquot as the flow increases while maintaining a constant time
interval between the aliquots.
Concrete Wastewater means any water used in the production, pouring and/or clean-up of
concrete or concrete products, and any water used to cut, grind, wash, or otherwise modify
concrete or concrete products. Examples include water used for or resulting from concrete
truck/mixer/pumper/tool/chute rinsing or washing, concrete saw cutting and surfacing (sawing,
coring, grinding, roughening, hydro-demolition, bridge and road surfacing). When stormwater
comingles with concrete wastewater, the resulting water is considered concrete wastewater and
must be managed to prevent discharge to waters of the State, including ground water.
Construction Activity means land disturbing operations including clearing, grading or
excavation which disturbs the surface of the land. Such activities may include road construction,
construction of residential houses, office buildings, or industrial buildings, site preparation, soil
compaction, movement and stockpiling of topsoils, and demolition activity.
Contaminant means any hazardous substance that does not occur naturally or occurs at greater
than natural background levels. See definition of “hazardous substance” and WAC 173-340-200.
Contaminated Groundwater means groundwater which contains contaminants, pollutants, or
hazardous substances that do not occur naturally or occur at levels greater than natural
background.
Contaminated Soil means soil which contains contaminants, pollutants, or hazardous
substances that do not occur naturally or occur at levels greater than natural background.
Demonstrably Equivalent means that the technical basis for the selection of all stormwater
BMPs is documented within a SWPPP, including:
1. The method and reasons for choosing the stormwater BMPs selected.
Construction Stormwater General Permit
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2. The pollutant removal performance expected from the BMPs selected.
3. The technical basis supporting the performance claims for the BMPs selected, including
any available data concerning field performance of the BMPs selected.
4. An assessment of how the selected BMPs will comply with state water quality standards.
5. An assessment of how the selected BMPs will satisfy both applicable federal technology-
based treatment requirements and state requirements to use all known, available, and
reasonable methods of prevention, control, and treatment (AKART).
Department means the Washington State Department of Ecology.
Detention means the temporary storage of stormwater to improve quality and/or to reduce the
mass flow rate of discharge.
Dewatering means the act of pumping ground water or stormwater away from an active
construction site.
Director means the Director of the Washington State Department of Ecology or his/her
authorized representative.
Discharger means an owner or operator of any facility or activity subject to regulation under
Chapter 90.48 RCW or the Federal Clean Water Act.
Domestic Wastewater means water carrying human wastes, including kitchen, bath, and laundry
wastes from residences, buildings, industrial establishments, or other places, together with such
ground water infiltration or surface waters as may be present.
Ecology means the Washington State Department of Ecology.
Engineered Soils means the use of soil amendments including, but not limited, to Portland
cement treated base (CTB), cement kiln dust (CKD), or fly ash to achieve certain desirable soil
characteristics.
Equivalent BMPs means operational, source control, treatment, or innovative BMPs which
result in equal or better quality of stormwater discharge to surface water or to ground water than
BMPs selected from the SWMM.
Erosion means the wearing away of the land surface by running water, wind, ice, or other
geological agents, including such processes as gravitational creep.
Erosion and Sediment Control BMPs means BMPs intended to prevent erosion and
sedimentation, such as preserving natural vegetation, seeding, mulching and matting, plastic
covering, filter fences, sediment traps, and ponds. Erosion and sediment control BMPs are
synonymous with stabilization and structural BMPs.
Federal Operator is an entity that meets the definition of “Operator” in this permit and is either
any department, agency or instrumentality of the executive, legislative, and judicial branches of
Construction Stormwater General Permit
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the Federal government of the United States, or another entity, such as a private contractor,
performing construction activity for any such department, agency, or instrumentality.
Final Stabilization (same as fully stabilized or full stabilization) means the establishment of a
permanent vegetative cover, or equivalent permanent stabilization measures (examples of
permanent non-vegetative stabilization methods include, but are not limited to riprap, gabions or
geotextiles) which prevents erosion.
Ground Water means water in a saturated zone or stratum beneath the land surface or a surface
waterbody.
Hazardous Substance means any dangerous or extremely hazardous waste as defined in RCW
70.105.010 (5) and (6), or any dangerous or extremely dangerous waste as designated by rule under
chapter 70.105 RCW; any hazardous substance as defined in RCW 70.105.010(10) or any
hazardous substance as defined by rule under chapter 70.105 RCW; any substance that, on the
effective date of this section, is a hazardous substance under section 101(14) of the federal cleanup
law, 42 U.S.C., Sec. 9601(14); petroleum or petroleum products; and any substance or category of
substances, including solid waste decomposition products, determined by the director by rule to
present a threat to human health or the environment if released into the environment. The term
hazardous substance does not include any of the following when contained in an underground
storage tank from which there is not a release: crude oil or any fraction thereof or petroleum, if the
tank is in compliance with all applicable federal, state, and local law.
Injection Well means a well that is used for the subsurface emplacement of fluids. (See Well.)
Jurisdiction means a political unit such as a city, town or county; incorporated for local self-
government.
National Pollutant Discharge Elimination System (NPDES) means the national program for
issuing, modifying, revoking and reissuing, terminating, monitoring, and enforcing permits, and
imposing and enforcing pretreatment requirements, under sections 307, 402, 318, and 405 of the
Federal Clean Water Act, for the discharge of pollutants to surface waters of the State from point
sources. These permits are referred to as NPDES permits and, in Washington State, are
administered by the Washington State Department of Ecology.
Notice of Intent (NOI) means the application for, or a request for coverage under this general
permit pursuant to WAC 173-226-200.
Notice of Termination (NOT) means a request for termination of coverage under this general
permit as specified by Special Condition S10 of this permit.
Operator means any party associated with a construction project that meets either of the
following two criteria:
The party has operational control over construction plans and specifications, including
the ability to make modifications to those plans and specifications; or
Construction Stormwater General Permit
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The party has day-to-day operational control of those activities at a project that are
necessary to ensure compliance with a SWPPP for the site or other permit conditions
(e.g., they are authorized to direct workers at a site to carry out activities required by the
SWPPP or comply with other permit conditions).
Permittee means individual or entity that receives notice of coverage under this general permit.
pH means a liquid’s measure of acidity or alkalinity. A pH of 7 is defined as neutral. Large
variations above or below this value are considered harmful to most aquatic life.
pH Monitoring Period means the time period in which the pH of stormwater runoff from a site
must be tested a minimum of once every seven days to determine if stormwater pH is between
6.5 and 8.5.
Point Source means any discernible, confined, and discrete conveyance, including but not
limited to, any pipe, ditch, channel, tunnel, conduit, well, discrete fissure, and container from
which pollutants are or may be discharged to surface waters of the State. This term does not
include return flows from irrigated agriculture. (See Fact Sheet for further explanation.)
Pollutant means dredged spoil, solid waste, incinerator residue, filter backwash, sewage,
garbage, domestic sewage sludge (biosolids), munitions, chemical wastes, biological materials,
radioactive materials, heat, wrecked or discarded equipment, rock, sand, cellar dirt, and
industrial, municipal, and agricultural waste. This term does not include sewage from vessels
within the meaning of section 312 of the CWA, nor does it include dredged or fill material
discharged in accordance with a permit issued under section 404 of the CWA.
Pollution means contamination or other alteration of the physical, chemical, or biological
properties of waters of the State; including change in temperature, taste, color, turbidity, or odor
of the waters; or such discharge of any liquid, gaseous, solid, radioactive or other substance into
any waters of the State as will or is likely to create a nuisance or render such waters harmful,
detrimental or injurious to the public health, safety or welfare; or to domestic, commercial,
industrial, agricultural, recreational, or other legitimate beneficial uses; or to livestock, wild
animals, birds, fish or other aquatic life.
Process Wastewater means any water which, during manufacturing or processing, comes into
direct contact with or results from the production or use of any raw material, intermediate
product, finished product, byproduct, or waste product. If stormwater commingles with process
wastewater, the commingled water is considered process wastewater.
Receiving Water means the waterbody at the point of discharge. If the discharge is to a storm
sewer system, either surface or subsurface, the receiving water is the waterbody to which the
storm system discharges. Systems designed primarily for other purposes such as for ground
water drainage, redirecting stream natural flows, or for conveyance of irrigation water/return
flows that coincidentally convey stormwater are considered the receiving water.
Construction Stormwater General Permit
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Representative means a stormwater or wastewater sample which represents the flow and
characteristics of the discharge. Representative samples may be a grab sample, a time-
proportionate composite sample, or a flow proportionate sample. Ecology’s Construction
Stormwater Monitoring Manual provides guidance on representative sampling.
Responsible Corporate Officer for the purpose of signatory authority means: (i) a president,
secretary, treasurer, or vice-president of the corporation in charge of a principal business
function, or any other person who performs similar policy- or decision-making functions for the
corporation, or (ii) the manager of one or more manufacturing, production, or operating facilities,
provided, the manager is authorized to make management decisions which govern the operation
of the regulated facility including having the explicit or implicit duty of making major capital
investment recommendations, and initiating and directing other comprehensive measures to
assure long term environmental compliance with environmental laws and regulations; the
manager can ensure that the necessary systems are established or actions taken to gather
complete and accurate information for permit application requirements; and where authority to
sign documents has been assigned or delegated to the manager in accordance with corporate
procedures (40 CFR 122.22).
Sanitary Sewer means a sewer which is designed to convey domestic wastewater.
Sediment means the fragmented material that originates from the weathering and erosion of
rocks or unconsolidated deposits, and is transported by, suspended in, or deposited by water.
Sedimentation means the depositing or formation of sediment.
Sensitive Area means a waterbody, wetland, stream, aquifer recharge area, or channel migration
zone.
SEPA (State Environmental Policy Act) means the Washington State Law, RCW 43.21C.020,
intended to prevent or eliminate damage to the environment.
Significant Amount means an amount of a pollutant in a discharge that is amenable to available
and reasonable methods of prevention or treatment; or an amount of a pollutant that has a
reasonable potential to cause a violation of surface or ground water quality or sediment
management standards.
Significant Concrete Work means greater than 1000 cubic yards poured concrete used over the
life of a project.
Significant Contributor of Pollutants means a facility determined by Ecology to be a
contributor of a significant amount(s) of a pollutant(s) to waters of the State of Washington.
Site means the land or water area where any "facility or activity" is physically located or
conducted.
Source Control BMPs means physical, structural or mechanical devices or facilities that are
intended to prevent pollutants from entering stormwater. A few examples of source control
Construction Stormwater General Permit
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BMPs are erosion control practices, maintenance of stormwater facilities, constructing roofs over
storage and working areas, and directing wash water and similar discharges to the sanitary sewer
or a dead end sump.
Stabilization means the application of appropriate BMPs to prevent the erosion of soils, such as,
temporary and permanent seeding, vegetative covers, mulching and matting, plastic covering and
sodding. See also the definition of Erosion and Sediment Control BMPs.
Storm Drain means any drain which drains directly into a storm sewer system, usually found
along roadways or in parking lots.
Storm Sewer System means a means a conveyance, or system of conveyances (including roads
with drainage systems, municipal streets, catch basins, curbs, gutters, ditches, manmade
channels, or storm drains designed or used for collecting or conveying stormwater. This does not
include systems which are part of a combined sewer or Publicly Owned Treatment Works
(POTW) as defined at 40 CFR 122.2.
Stormwater means that portion of precipitation that does not naturally percolate into the ground
or evaporate, but flows via overland flow, interflow, pipes, and other features of a stormwater
drainage system into a defined surface waterbody, or a constructed infiltration facility.
Stormwater Management Manual (SWMM) or Manual means the technical Manual
published by Ecology for use by local governments that contain descriptions of and design
criteria for BMPs to prevent, control, or treat pollutants in stormwater.
Stormwater Pollution Prevention Plan (SWPPP) means a documented plan to implement
measures to identify, prevent, and control the contamination of point source discharges of
stormwater.
Surface Waters of the State includes lakes, rivers, ponds, streams, inland waters, salt waters,
and all other surface waters and water courses within the jurisdiction of the State of Washington.
Temporary Stabilization means the exposed ground surface has been covered with appropriate
materials to provide temporary stabilization of the surface from water or wind erosion. Materials
include, but are not limited to, mulch, riprap, erosion control mats or blankets and temporary
cover crops. Seeding alone is not considered stabilization. Temporary stabilization is not a
substitute for the more permanent “final stabilization.”
Total Maximum Daily Load (TMDL) means a calculation of the maximum amount of a
pollutant that a waterbody can receive and still meet state water quality standards. Percentages
of the total maximum daily load are allocated to the various pollutant sources. A TMDL is the
sum of the allowable loads of a single pollutant from all contributing point and nonpoint sources.
The TMDL calculations must include a "margin of safety" to ensure that the waterbody can be
protected in case there are unforeseen events or unknown sources of the pollutant. The
calculation must also account for seasonable variation in water quality.
Construction Stormwater General Permit
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Transfer of Coverage (TOC) means a request for transfer of coverage under this general permit
as specified by General Condition G9 of this permit.
Treatment BMPs means BMPs that are intended to remove pollutants from stormwater. A few
examples of treatment BMPs are detention ponds, oil/water separators, biofiltration, and
constructed wetlands.
Transparency means a measurement of water clarity in centimeters (cm), using a 60 cm
transparency tube. The transparency tube is used to estimate the relative clarity or transparency
of water by noting the depth at which a black and white Secchi disc becomes visible when water
is released from a value in the bottom of the tube. A transparency tube is sometimes referred to
as a “turbidity tube.”
Turbidity means the clarity of water expressed as nephelometric turbidity units (NTUs) and
measured with a calibrated turbidimeter.
Uncontaminated means free from any contaminant. See definition of “contaminant” and WAC
173-340-200.
Waste Load Allocation (WLA) means the portion of a receiving water’s loading capacity that
is allocated to one of its existing or future point sources of pollution. WLAs constitute a type of
water quality based effluent limitation (40 CFR 130.2[h]).
Water-only Based Shaft Drilling is a shaft drilling process that uses water only and no
additives are involved in the drilling of shafts for construction of building, road, or bridge
foundations.
Water quality means the chemical, physical, and biological characteristics of water, usually
with respect to its suitability for a particular purpose.
Waters of the State includes those waters as defined as "waters of the United States" in 40 CFR
Subpart 122.2 within the geographic boundaries of Washington State and "waters of the State" as
defined in Chapter 90.48 RCW, which include lakes, rivers, ponds, streams, inland waters,
underground waters, salt waters, and all other surface waters and water courses within the
jurisdiction of the state of Washington.
Well means a bored, drilled or driven shaft, or dug hole whose depth is greater than the largest
surface dimension. (See Injection well.)
Wheel Wash Wastewater means any water used in, or resulting from the operation of, a tire
bath or wheel wash (BMP C106: Wheel Wash), or other structure or practice that uses water to
physically remove mud and debris from vehicles leaving a construction site and prevent track-
out onto roads. When stormwater comingles with wheel wash wastewater, the resulting water is
considered wheel wash wastewater and must be managed according to Special Condition S9.D.9.
Construction Stormwater General Permit
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APPENDIX B – ACRONYMS
AKART All Known, Available, and Reasonable Methods of Prevention, Control,
and Treatment
BMP Best Management Practice
CESCL Certified Erosion and Sediment Control Lead
CFR Code of Federal Regulations
CKD Cement Kiln Dust
cm Centimeters
CTB Cement-Treated Base
CWA Clean Water Act
DMR Discharge Monitoring Report
EPA Environmental Protection Agency
ERTS Environmental Report Tracking System
ESC Erosion and Sediment Control
FR Federal Register
LID Low Impact Development
NOI Notice of Intent
NOT Notice of Termination
NPDES National Pollutant Discharge Elimination System
NTU Nephelometric Turbidity Unit
RCW Revised Code of Washington
SEPA State Environmental Policy Act
SWMM Stormwater Management Manual
SWPPP Stormwater Pollution Prevention Plan
TMDL Total Maximum Daily Load
UIC Underground Injection Control
USC United States Code
USEPA United States Environmental Protection Agency
WAC Washington Administrative Code
WQ Water Quality
WWHM Western Washington Hydrology Model
D.R. STRONG Consulting Engineers, Inc. The Pines
Stormwater Pollution Prevention Plan Page F-1 Renton, Washington
Appendix F
Engineering Calculations
EXISTING SITE HYDROLOGY
KCRTS was used to model runoff from the Site. The Site falls within the Peak Rate
Flow Control Stadard area matching existing Site conditions. The Site was modeled
with existing forested, pasture and impervious surfaces (see figure 15). Results of the
KCRTS analysis are included in this section.
Modeling Input
Table 1 Pre-Developed KCRTS Modeling Input
Modeling Results
SITE
Flow Frequency Analysis
Time Series File:predev.tsf
Project Location:Sea-Tac
---Annual Peak Flow Rates--- -----Flow Frequency Analysis-------
Flow Rate Rank Time of Peak - - Peaks - - Rank Return Prob
(CFS) (CFS) Period
0.181 2 2/09/01 18:00 0.310 1 100.00 0.990
0.077 7 1/05/02 16:00 0.181 2 25.00 0.960
0.170 3 2/28/03 3:00 0.170 3 10.00 0.900
0.030 8 8/26/04 2:00 0.160 4 5.00 0.800
0.097 6 1/05/05 8:00 0.153 5 3.00 0.667
0.160 4 1/18/06 16:00 0.097 6 2.00 0.500
0.153 5 11/24/06 4:00 0.077 7 1.30 0.231
0.310 1 1/09/08 6:00 0.030 8 1.10 0.091
Computed Peaks 0.267 50.00 0.980
D.R. STRONG Consulting Engineers, Inc. The Pines
Stormwater Pollution Prevention Plan Page F-2 Renton, Washington
Facility Sizing
The Site will utilize the proposed detention vault for sediment control. The maximum discharge
rate for the site is 0.0485 cfs (50% of the 2-year predeveloped peak).