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CIVIL ENGINEERING �AND SURVEYING PROJECT MANAGEMENT ( STORMWATER MANAGEMENT TRANSPORTATION I LAND PLANNING LANDSCAPE ARCHITECTURE
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ROSEWOOD HIGHLAHDS
Technical Information Report
December 22. 2010
Prepared for
Gladco Development, L.L.C.
P.O. Box 1830
Renton, Washington 98056
Submitted by
ESM Consulting Engineers, LLC
181 South 333�d Street '
Building C. Suite 210 '
Federal Way, WA 98003 '',
253-838-6113te1 I�
253-838-7104fax I
www.esmcivil.com
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ROSEWOOD HIGHLANDS
Technicat information Report
Prepared for
Gladco Development L.L.C. '
P.O. Box 1830
Renton, WA 98056
Submitted by '
ESM Consulting Engineers, LLC �
20021 120'h Avenue NE Suite 103
Bothell, WA 98011
Job No: 1352-001-006
Prepared by: I
Trevor Stiff. P.E.
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ESM JOB# 1352-001-006 Rosewood Highlands
Figure1 - TIR Worksheet........................................................................................................................................................1
1. PROJECT OVERVIEW..........................................................................................................................................................6
Proj e ct:...............................................................................................................................................................................................6
SiteLocation:..............................................................................................................................................................................6
AdjacentDevelopment:....................................................................................................................................................6
ExistingConditions:.............................................................................................................................................................6
So i I s:....................................................................................................................................................................................................7
Figure2 - Vicinity Map.....................................................................................................................................................8
Figure3 - Existing Conditions Map....................................................................................................................9
Figure4 - Offsite Basins Map................................................................................................................................10
Figure5 - Soils Map........................................................................................................................................................11
DevelopedConditions:..................................................................................................................................................12
DesignStandards:..............................................................................................................................................................13
Fgure6 - Developed Conditions Map........................................................................................................14
2. CONDITIONS AND REQUIREMENTS SUMMARY................................................................................15
King County Surface Water Design Manual Special Requirements:.............................16
3. OFFSITE ANALYSIS.............................................................................................................................................................17
Fgure 7 - Downstream Analysis........................................................................................................................19
Table 1 - Offsite Analysis Drainage System Table...........................................................................20
4. FLOW CONTROL AND WATER QUALJTY FACILITY ANALYSIS AND DESIGN.........21
ExistingHydrology:............................................................................................................................................................21
Precipitation:.............................................................................................................................................................................22
Fgure8 - Topographic Map..................................................................................................................................23
Figure9 - Existing Hydrology Map...................................................................................................................24
DevelopedHydrology:....................................................................................................................................................25
Table 2 - Individual Lot BMPs Flow Control BMPs Credits:...................................................26
Fgure 10 - Developed Hydrology Map.......................................................................................................28
FlowControl System:.......................................................................................................................................................29
WaterQuality System:.....................................................................................................................................................35
5. CONVEYANCE SYSTEM ANALYSIS AND DESIGN..............................................................................36
6. SPECIAL REPORTS AND STUDIES.....................................................................................................................37
7. OTHER PERMITS..................................................................................................................................................................38
8. ESC ANALYSIS AND DESIGN...................................................................................................................................39
9. BOND QUANTITIES, FACILITY SUMMARIES, DECLARATION OF COVENANT .....40 '
10. MAINTENANCE AND OPERATIONS MANUAL....................................................................................41
APPENDICIES:
A - Additional Reports
B - Downstream Analysis Information
C - Runoff Control and Water Quality Calculations
D - Conveyance Calculations
- i -
KING COUNTY. Vl'ASHINGTON, SURFACE �'�ATER DESIGN MANUAL '
TECHNICAL INFORMATION REPORT (TIR) WORKSHEET
Part 1 PRoJECT OWNER AND Part 2 PROJECT LOCATION AND
PROJECT ENGINEER DESCRIPTION ,
Project Owner Gladco Development, LLC Project Name Rosewood Highlands
Phone (206) 799-8504 DDES Permit# N/A
Address PO Box 1830 Location Township 23N
Renton, WA 98056 Range 5E
Project Engineer Trevor S t i f f, PE Section 15
Company ESM Consulting Eng, LLC SiteAddress 230 Union Ave NE
Phone 253-838-6113 Renton, WA 98059
Part 3 TYPE OF PERMIT APPLICATION Part 4 OTHER REVIEWS AND PERMITS
� Landuse Services ❑ DFW HPA ❑ Shoreline
Subdivison / Short Subd. / UPD Management
❑ COE 404
❑ Building Services ❑ DOE Dam Safery � Structural
M/F/Commerical / SFR Rockery/VaulU
❑ FEMA Floodplain
� Clearing and Grading ❑ ESA Section 7
❑ Right-of-Way Use
❑ COE Wetlands
❑ Other ❑ Other
Part 5 PLAN AND REPORT INFORMATION
Technical Information Report Site Improvement Plan (Engr. Plans)
Type of Drainage Review Full / Targeted / Type(circle one): Full / Modified /
(circle): Large Site Small Site
Date(include revision 12/0 6/2 O 10 Date(include revision 12/0 6/2 O 10
dates): dates):
Date of Final: Date of Final:
Part 6 ADJUSTMENT APPROVALS
Type(circle one): Standard / Complex / Preapplication / Experimental / Blanket
Description: (include conditions in TIR Section 2)
N/A
Date of Approval: N/A
2009 Surface Water Design Manua] 1,'9i2009
1
KING COUNTY. WASHINGTON. SURFACE ��JATER DESIGN MANUAL
TECHNICAL INFORMATION REPORT (TIR) WORKSHEET
Part 7 MONITORING REQUIREMENTS
Monitoring Required: Yes / No Describe:
Start Date:
Completion Date:
Part 8 SITE COMMUNiTY AND DRAINAGE BASIN
Community Plan : Newcastle
Special District Overlays: N A
Drainage Basin: Lower Cedar River
Stormwater Requirements: Level 2 Detention '
Part 9 ONSITE AND ADJACENT SENSITIVE AREAS
� River/Stream Maplewood Creek ❑ Steep Slope
❑ Lake ❑ Erosion Hazard '
� Wetlands ❑ Landslide Hazard I
❑ Closed Depression ❑ Coal Mine Hazard
❑ Floodplain ❑ Seismic Hazard
❑ Other ❑ Habitat Protection
❑
Part 10 SOILS I
Soil Type Slopes Erosion Potential
AgC 6-15% slow to medium
❑ High Groundwater Table(within 5 feet) ❑ Sole Source Aquifer
❑ Other ❑ Seeps/Springs
❑ Additional Sheets Attached
2009 Surface Water Design Manual l/'9/2Q09
2
KING COUNTY. WASHINGTON, SURFACE WATER DESIGN MANUAL
TECHNICAL INFORMATION REPORT (TIR) WORKSHEET
Part 11 DRAINAGE DESIGN LIMITATIONS
REFERENCE LIMITATION/SITE CONSTRAINT
� Core 2—Offsite Analvsis none
� Sensitive/CriticalAreas Roofs of 5 houses to buffer
� SEPA none
❑ Other
❑
❑ Additional Sheets Attached
Part 12 TIR SUMMARY SHEET ( rovide one TIR Summa Sheet erThreshold Dischar e Area
Threshold Discharge Area:
name or descri tion site
Core Requirements (all 8 apply)
Dischar e at Natural Location Number of Natural Dischar e Locations: 1
Offsite Analysis Level: 1 / 2 / 3 dated: 02 02 07
Flow Control Level: 1 / 2 3 or Exemption Number
incl. facili summa sheet Small Site BMPs
Conveyance System Spill containment located at:
Erosion and Sediment Control ESC Site Supervisor:
Contact Phone:
After Hours Phone:
Maintenance and Operation Responsibility: Private / Public
If Private, Maintenance Lo Re uired: Yes /No
Financial Guarantees and Provided: Yes / No
Liabilit
Water Quality Type: Basic / Sens. Lake / Enhanced Basicm / Bog
(include facility summary sheet) or Exemption No. N/A
Landsca e Mana ement Plan: Yes / No
S ecial Re uirements as a licable
Area Specific Drainage Type: CDA/SDO/MDP/ BP 1 LMP/Shared Fac. I None
Re uirements Name:
Floodplain/Floodway Delineation Type: Major / Minor / Exemption / None
100-year Base Flood Elevation (or range): N/A
Datum:N/A
Flood Protection Facilities Describe: N/A
Source Control Describe landuse: N/A
(comm./industrial land use)
Describe any structural controls: N/A
2009 Surface Water Design Manual l!9!'2009
3
KING COU?�TY. VvASHI'��GTON, SURFACE WATER DESIGN MANUAL
TECHNICAL INFORMATION REPORT (TIR) WORKSHEET
Oil Control High-use Site: Yes / No
Treatment BMP: N/A
Maintenance Agreement: Yes / No
with whom? N A
Other Draina e Structures
Describe:
Part 13 EROSION AND SEDIMENT CONTROL REQUIREMENTS
MINIMUM ESC REQUIREMENTS MINIMUM ESC REQUIREMENTS
DURING CONSTRUCTION AFTER CONSTRUCTION
� Clearing Limits � Stabilize Exposed Surfaces
� Cover Measures � Remove and Restore Temporary ESC Facilities
� Perimeter Protection � Clean and Remove Ail Silt and Debris, Ensure
0 Traffic Area Stabilization Operation of Permanent Facilities
� Sediment Retention � Flag Limits of SAO and open space
preservation areas
� Surface Water Collection ❑ Other
� Dewatering Control
� Dust Controi
� Flow Control
Part 14 STORMWATER FACILITY DESCRIPTIONS Note: include Facili Summa and Sketch
Flow Control T e/Descri tion Water Qualit T e/Descri tion
� Detention Vault ❑ Biofiltration
❑ Infiltration � Wetpool Vault
❑ Regional Facility ❑ Media Filtration
❑ Shared Facility ❑ Oil Control
❑ Flow Control ❑ Spill Control
BMPs
❑ Flow Control BMPs
❑ Other
❑ Other
2009 Surface Water Design Manual 1/9/2009
4
KING COLNTI'. �'��ASHINGTO\. SLRFACE 1�'ATER DESIGN MANUAL
TECHNICAL INFORMATION REPORT (TIR) WORKSHEET
Part 15 EASEMENTSrfRACTS Part 16 STRUCTURAL ANALYSIS
❑ Drainage Easement � Cast in Place Vault
❑ C�venant ❑ Retaining Wall
❑ Native Growth Protection Covenant ❑ Rockery >4' High
� Tract ❑ Structural on Steep Slope
❑ Other ❑ 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
knowled pro ided here is accurate.
/Z G �v
Si ned/Date
2009 Surface Water Design Manual 1;'912009
5
ESM JOBr 1352-001-006 Rosewood Hiphlands
1 . PROJECT OVERVIEW
Project:
The proposed project is the development of a 4.39-acre site into 27 single-family lots with
associated roads, utilities, a detention vault, and a wetland / sensitive area tract. Included
with the development are improvements to NE 2�d Place.
Project Name: Rosewood Highlands
ESM Job number: 1352-001-006
Site Location:
The project site is located within a portion of the NW 1/4 of Section 15, Township 23
North, and Range 5 East of the Willamette Meridian. The site address is 230 Union
Avenue NE in the City of Renton, Washington Refer to Figure 2 - Viciniiy Map for a map
of the location of the site.
Adjacent Developments: I
Developments adjacent to the site include the following: ��
North - Single-family homes and an undeveloped gravel lot ',
West - Union Avenue NE '
South - NE 2"d Place �
East - Maplewood Creek and Single-family homes '
Existing Conditions:
The project site is comprised of six parcels totaling 4.39-acres. Parcels 518210-0069,
518210-0073, and 518210-0079 contain single-family homes with detached garages.
Parcels 518210-0068 and 512810-0081 are undeveloped and contain pasture with some
forested areas and light underbrush. Parcel 518210-005 is the access road area along
the southern boundary, which is known as NE 2�d Place. Refer to Figure 3 - Existing
Conditions Map, Access to the single-family homes is from driveways off of Union
Avenue NE and along NE 2"d Place along the south boundary.
Topography for the site generally slopes from west to east with a slope along the
northeastern corner of the site. Maplewood Creek runs southerly along the east boundary
of the site. Stormwater runoff from the site sheet flows east with slopes ranging from 3%
in the west to 23% in the east. Stormwater runoff either sheet flows sheet flows directly in
to Maplewood Creek, or flows to a Class III wetland in the northeast corner of the site that
drains to Maplewood Creek.
Included with the site development plan is to improve NE 2�d Place along the southern
edge of the site. This existing asphalt road varies in width from 10 - 17 feet and slopes
easterly around 5%. Access to the road is off of Union Avenue NE. Stormwater runoff
from the road currently sheet flows east toward Maplewood Creek.
- 6 -
ESM JOB� 1352-001-006 Rosewood Highlands
Two offsite basins contribute flow to the site. The first area, referred to as Basin A on
Figure 4, is the undeveloped parcel north of the site that extends to NE 4th Street This
runoff from this basin flows through the onsite wetland and Maplewood Creek along the '
east side of the site. This runoff bypasses the site and does not contribute to the
proposed storm system.
The other offsite basin, referred to as Basin B on Figure 4, is a portion of the single-family
lot northwest of the site. This runoff is collected via a trench drain along the side of lot 17
and conveyed to the proposed storm drainage system.
Frontage along Union Avenue NE that drains to the site consists of a small amount of
asphalt at the entrance to NE 2"d Place.
SOIIS:
Per the Natural Resources Conservation Service (NRCS), onsite soils are Alderwood
Gravelly Sandy Loam, 6 to 15 percent slopes (AgC). Refer to Figure 5 for the Soils Map.
Refer to the Geotechnical Report prepared by Pacific Geo Engineering included in
Appendix A of this report.
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VICINITY MAP
PROJECT: ROSEWOOD HIGHLANDS SCALE: N.T.S.
JOB N0. 1352-001—Q06 DATE : 02/14/07
DRAWING NAME : EN-01 DRAWN : ECN
CON3ULTINO ENQINEER9 LLC
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BO�Y� WA 88� fEDERAL WAY (253J 838-6173
BOfMELL (4I5) 115-61aa FI G U R E 2
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Publ'c Works I Project Monogement I Londscape Arch�tecture
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CONSULTING ENGINEERS LLC EXISTING CONDITIONS MAP
181 S 333rd St,Bldg C,Suite 21 O I � I � I � I
Federal Way.WA 98003
FtiOERAL WAY (257�838-811J
EVERETT (415)197-9900
www.esmcivil.com ELLENSBURG (509)997-7808
C�vil Engineering Land Surveyfng Land Planning R OS E WOO D H I G H LAN D S
Public Works I Project Management I Lantlscape Arch�tecture
JOB NO. 1752-001-006 DATE: 10/Y6/2010 FlGURE 3
�RAWN: ECN SHF_ET � OF 1
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ESM JOB# 1352-001-006 Rosewood Highlands
Developed Conditions:
Out of the 4.39 acre site, 3.86 acres are being developed in to 27 single-family residential
lots, 1190 lineal feet of public roadway, 212 linear feet of private residential roadway, 83
linear feet of joint use driveway, and an underground stormwater vault. Refer to Figure 6 -
Developed Conditions Map.
The remaining 0.47 acres of wetland, stream and buffers will remain undeveloped and
placed in a sensitive area tract. The 0.06 acres at the east end of existing NE 2"d Place,
south of the proposed stormwater, vault is currently paved and will not be improved
The proposed Vashon Avenue NE and NE 2�d Court consist of 347 lineal feet of 42 foot
right-of-way with 32 foot wide crowned asphalt roadway, vertical curb and gutter, and 5
foot sidewalks on both sides. 212 lineal feet of Vashon Place NE and a 344 lineal feet of
NE 2�d Court and consist of a 26 foot wide tract with 20 foot wide asphalt road that is
sloped to one side, vertical curb and gutter, and a 5 foot sidewalk on one side. The joint
use driveways consist of a 20-foot wide tract containing an 18 foot wide inverted crown
asphalt roadway. Northeast 2�d Place is an existing road along the south boundary of the
site. It will receive half street improvements consisting of 340 lineal feet of 26 foot right-of-
way containing a 20 foot crowned asphalt roadway, vertical curb and gutters, and a 5 foot
sidewalk on the north side. �I
In addition, a portion of Union Avenue NE (0.03 acres) flows onto Northeast 2nd Place and �
is collected in the proposed storm system.
Stormwater Detention/Dispersion
Stormwater runoff from a majority of the site (roads, landscaped areas, and buildings) is
collected and conveyed, via a closed pipe conveyance system, to the proposed
detention/water quality vault in the southeast corner of the site. The facility releases
detained and treated stormwater runoff onto a riprap pad to sheet flow east in to the
buffer of Maplewood Creek.
The runoff from the four lots along the east boundary (lots 24 through 27) will discharge to
the adjacent stream buffer via flow dispersion trenches. The runoff from lot 23 will
discharge to the adjacent wetland buffer via a flow dispersion trench. According to the
wetland biologist Chad Armour, the release of stormwater runoff from the lots to the buffer
area will help maintain the existing wetland and stream hydrology. This was discussed in
a letter dated January 31, 2008 and a Wetland Hydrology Report dated November 18,
2010. Copies are included in Appendix A of this report
There are two offsite basins that flow on to the site. Refer to Figure 4 - Offsite Basin Map.
Runoff from the large basin to the north, Basin A, will continue to flow through the
sensitive area tract (Class III Wetland) in the northeast corner of the site as it currently
does. Offsite flow from 0.15 acres of the adjacent parcel, Basin B, is collected along the
west side of lot 17. This runoff will combine with the onsite conveyance system, and be
conveyed to the stormwater vault.
- 1z -
ESM JOB� 1352-001-0�6 Rosewood Highlands
Design Standards:
The project is designed in accordance with the City of Renton Amendments to the 2005
King County Surface Water Design Manual (KCSWDM).
- 13 -
F��e:\\EsmB\ENGR\ESM-JO85\1J52\001\006\exhibils\EN-04.dwg ,
Plottetl: 12/21/2010 1:46 PM Plotted By: Trevor SGtI
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DRAWING:EN-0�
C 0 N S U L T I N G E N G I N E E R g L C
�8� S 333rd St, Bldg C, Suite �1�• I � I � I Gladco Development LLC
Federol Woy, WA 98003
reoEqAL w�r (7»)e3e-6��3
EVEREIT (�75)797-9900
www.esmcivil.com ELLENSBURC (509)96]-2608
Civil Engineering Lond Surveyinq Lontl Plonninq R o s ewo o d H i g h I a n d s
Pubfic Works I Project Monog�m�nt I LondxoDe ArChiteclure
�aa No. „Sz-��-� DATE: 12/06/2010 Developed Conditions Map
DRAWN: T�S SNEET 1 OF 1
ESM JOB# 1352-001-006 Rosewood Highlands
2. CONDITIONS AND REQUIREMENTS SUMMARY
King County Surface Water Design Manual Core Requirements:
1. Discharge at the Natural Location:
Stormwater runoff is released at the natural discharge location to the extent
possible. In order to maintain existing wetland/stream hydrology, stormwater runoff
is releases to the sensitive area tract along the east side of the site.
2. Otfsite Analysis:
An offsite analysis was performed by ESM. See Section 3 of this report.
3. Flow Control:
The site is located in a flow control Flow Control Duration Standard Matching
Forested Site Conditions or Conservation FC Area. See Section 4 of this report.
4. Conveyance System:
The stormwater conveyance system collects stormwater runoff and conveys it, via
a closed pipe system, to the stormwater vault. Refer to Section 5 of this report for
the conveyance system analysis.
5. Erosion and Sediment Control:
Erosion and Sediment Controls (ESC) are provided for the site. A Temporary
Erosion and Sediment Control Plan (TESC Plan) is created and is found in the
construction plan set. Refer to Section 8 of this report for the ESC analysis and
design.
6. Maintenance and Operations:
The Maintenance and Operation Manual for the stormwater system is included in
Section 10 of this report.
7. Financial Guarantees and Lrability:
The Bond Quantities Worksheet is included in Section 9 of this report.
8. Water Quality:
Per the King County Water Quality Map, the site is in the Basic Water Quality
treatment area. Water quality is provided via dead storage in the detention vault.
Refer to Section 4 of this report for the water quality analysis and design.
- 15 -
ESM JOB� 1352-001-006 Rosewood Hiqhlands I
King County Surface Water Design Manual Special Requirements:
1. Other Adopted Area-Specific Requirements
The project is not known to be located in within a Critical Drainage Area, a Master ,
Drainage Plan, a Basin Plan, a Salmon Conservation Plan, a Stormwater
Compliance Plan, a Lake Management Plan, a Flood Hazard Reduction Plan nor a
Shared Faciliry Drainage Plan area. '
2. Flood Hazard Area Delineation: '
The project is not known to be located within the 100-year floodplain or within a
floodway area. In addition, the project site is not located adjacent to a lake, nor a
closed depression. '
3. Flood Protection Facilities:
The project does not contain nor is adjacent to a levee and / or revetments. ,
4. Source Control:
The project is a residential subdivision and is not subjected to this requirement
5. Oi! Control:
The project is not a high-use site development, does not propose $100,000 or
more to an existing high-use site, and is not subjected to this requirement
( ,
- 16 -
ESM JOB# 1352-001-006 Rosewood Highlands
3. OFFSITE ANALYSIS
ESM performed a Level 1 downstream analysis for the Plat of Rosewood Highlands. The
downstream drainage information was reviewed for one mile downstream of the site and
the downstream system analysis is examined one-quarter mile downstream of the site.
The following five tasks (outlined in the KCSWDM) were completed in an effort to identify
any negative downstream impacts to the existing drainage system.
Task 1 - Study Area Definition and Maps
The project is located within the Lower Cedar River drainage basin. See Fgure 7-
Downstream Analysis Map for an overview of the basin study area.
Task 2 - Resource Review
The following resources have been reviewed in conjunction with the downstream analysis
for the development:
Adopted basin plans
• The site is located in the Lower Cedar River drainage basin and the Cedar River /
Lake Washington watershed.
Sensitive Areas Folio
• Wetlands - A wetlands report was prepared by Chad Armour, LLC and has been
submitted to the City. A wetland is located on the northeast section of the properry
and is rated as Class III.
• Streams and 100-Year Floodplains - Mapfewood Creek runs north-south along the
east boundary of the site.
• Erosion Hazard Areas - None mapped.
• Landslide Hazard Areas - None mapped.
• Seismic Hazard Areas - None mapped.
• Coal Mine Hazard Areas - None mapped.
Drainage Complaints
• The closest drainage complaint was less than a quarter mile downstream;
however, the development will not aggravate the site for the reason that the
property lies on the opposite side of the Maplewood Creek bank.
U.S. Department of Agriculture, King County Soils Survey
• The soils of the project site were obtained from the National Resources
Conservation Society (See Figure 5).
Flow Control Applications Map
• The proposed site is located within a Flow Control Duration Standard Matching
Forested Site Condition or Conservation FC Area.
Water Quality Applications Map
- �� -
ESM JOB# 1352-001-006 Rosewood Hiqhlands
• The site is located in a basic water quality treatment area per the King County
SWDM
Task 3 - Field Inspection
A site reconnaissance was performed on February 2, 2007, the purpose of analyzing the
proposed project site and its upstream and downstream corridors. The weather
conditions were dry, 50 degrees Fahrenheit and cloudy. The field inspection documented
in this report will have all descriptions and referenced labels coincide with Figure 7-
Downstream Analysis, and Table 1-Offsite Analysis Drainage System Table.
Stormwater from the site sheet flows to the eastern section of the property and is
collected by the enhanced Maplewood Creek. At the time of the downstream analysis
there was no water observed in the creek immediately east of the project site.
Maplewood Creek has the appearance of having a man-made cut which can better serve
stormwater conveyance of large upstream flows.
Maplewood Creek proceeds to flow south collecting runoff from various developments
along its conveyance path {Label P�. Maplewood Creek did not have any indications of
erosion or scour. About an eighth of a mile downstream from the site, the creek drains to
a large open area where drainage disperses (Label B). Within the open area,
groundwater was observed seeping from the ground and filling the creek with the first
signs of a surface flows.
After the large open area, drainage again converges into Maplewood Creek and is
directed towards a 12-inch storm pipe before Bremerton Place NE (Label C). No
sediment was observed in the pipe. The pipe connects to a 48 inch catch basin. This
catch basin includes a debris cage at the surface to allow high flows to enter the catch
basin, The catch basin has 36 inch outlet pipe that conveys flows under Bremerton Place
NE (Label D). Across the street, the pipe outfalls into a deep draw with large rocks lining
the channel (Label E). This completed the quarter mile downstream analysis,
Task 4 - Drainage System Description and Problem Descriptions
The current drainage system appeared to be adequate to convey the largest stormwater
events. The large culvert at Bremerton Place Northeast appeared to be an improvement
to address any past drainage problems that may have arisen. The drainage system
appeared to be in good shape with no visible signs of conveyance problems.
Task 5 - Mitigation of Existing or Potential Problems
The site is located within a Conservation Flow Control Area with Level 2 Flow Control.
This standard requires the developed discharge durations to match the predeveloped
durations between 50% of the 2-year peak flow up to the full 50-year peak flow. Also
match developed peak discharge rates to the predeveloped peak discharge rates for the
2-year and 10-year return periods. By detaining stormwater runoff from the site and
releasing per the Level 2 standard, the development should not aggravate existing
downstream drainage problems
- 18 -
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ORAWING:�N-lp" ..�� `\ / I����� �
�oNS��T�NG ENGINEERS LLC DOWNSTREAM ANALYSIS MAP
181 S 333rd St,Bldc�C,Suite 21 O I � I � I � I
Fetleral Way,WA 98003
FEOFRAL WAV (257)83B-fi11]
EVERET� (475)297-9900
www.esmcivil.com ELLENSBURC (509)982-2608
C�vil Engineering Land Surveying Land Planning R O S E W 00 D H I G H LA N D S
Public Works I Project Managemmt I Landacape Architecture
JOB NO. 1352-001-OOE DATE: 10/28/2010 FlGURE 7
DRAWN: ECN SHEET 1 OF�
TABLE 1 - OFF-SiTE ANALYSIS DRAINAGE SYSTF.M TABLE
SURFACE WATER DF,SiGN MANUAL, CORE REQUIRF,MFNT#Z
Basin: Lower C,edar River Subbasin Name: Subbasin Number:
Symbol Drainage Drainage Slope Distance Existing Potential Observations of field
Component Type, Component from site Problems Problems inspector, resource
Name, and Size Descri tion dischar e reviewer, or resident
see map Type:sheet flow,swale, dralnage basin,vegetation, % Y,ml=1.320 ft. constrictions,under capacity,ponding, tributary area,likelihood of problem,
stream,channel,plpe, cover,depth,type of sensitive overtopping,flooding,habitat or organism overFlow pathways,potential impacts
pond;Size:diameter, area,volume destruction,scouring,bank sloughing,
surface area sedimentation,incision,other erosion
----- —..__ __
--- -- — ---._.__ _. — --.___
Nc� water observed. Creck
A Maplewood Creek Site discharge 3 0 None None appeared to have man-made
cut.
B Open dispersion 5 600 None Nonc Groundwater seeping from
area ground.
12" Culvert
C 5 900 None None
48" Catch Basin
D 36" Culvert 5 1280 None None
E Rock lined outfall 5 1320 Nonc None
ESM JOB� 1352-001-006 Rosewood Highlands
4. FLOW CONTROL AND WATER QUALITY FACILITY ANALYSIS AND
DESIGN I
Existing Hydrology:
Vegetation cover on the site is split up mainly between the eastern and western sections.
Refer to Figure 9 - Existing Hydrology Map. In the western section, there are three single-
family homes with outbuildings and the vegetation is mainly grass / pasture. In the
eastern section, the vegetation is mostly pasture with some forested areas having light '�
underbrush.
Stormwater runoff irom the site sheet flows from west to east through the vegetation and
either into the Class III Wetland along the northeastern corner of the site, or into
Maplewood Creek. Rows out of the wetland also flow into Maplewood Creek. Roof
runoff from the existing buildings flows along the surface toward the creek.
Stormwater runoff from the existing pavement on NE 2�d Place sheet flows easterly down
the road and into Maplewood Creek.
Offsite stormwater runoff contributing to the site from Offsite Basin B, the single-family lot
northwest of the site, will be collected by a trench along the west side of lot 17, and
conveyed to the proposed stormwater vault.
Pre-developed conditions are modeled as historic conditions (forested), The offsite Basin
B and tributary area from Union Avenue is modeled as current developed conditions. The
table below shows the breakdown of the areas for existing condition.
Existing conditions of area tributary to storm vault (PREDEV basin in KCRTS)
PREDEV Impervious Till-Grass Till-Pasture Till-Forest Total
(ac) (ac) (ac) (ac) (ac)
Site - - ' - � 3.86 3,86
Offsite Basin B 0.02 � 0.13 � - 0.15
Fronta e (Union Avenue) 0.03 - - - 0.03
Total 0.05 - 0.13 3.86 4.04
The remainder of the site is undeveloped and not included in the storm drainage
calculations
Undeveloped Impervious Till-Grass � Till-Pasture Till-Forest Total
(ac) (ac) (ac) (ac) (ac)
Sensitive Areas Tract - - - 0.47 0.47
East end of existing NE 0.03 0.03 - - 0.06
2"d PI '
Total 0.03 0.03 - 0.47 0.53
- zi -
ESM JOB# 1352-001-006 Rosewood Hiqhlands
Precipitation:
Precipitation amounts are found from the Isopluvial maps in Chapter 3 of the SWDM. The
24-hour precipitation values for specific year events and the rainfall regions and scale
factor are listed below.
Year 2 10 25 100
24-Hour Precip. 2.00-inches 2.90-inches 3.40-inches 3.90-inches
Rainfall Region = Sea-Tac
Scale Factor = 1.0
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DRAWING:EN-05 ...... .............
CONSULTING ENGINEERS LLC
181 S333rdSt,BldgC,Suite2101 • I � I � I EXISTING HYDROLOGY MAP
Federal Way,WA 98003
�o�w�v (253)B78-B113
EVEHErr (azs) zs�-ssoo
www.esmcivil.com ELLENSBURG �S�A�sb�-26�8
Civil Engineering Lond Surveyinq Land Planning R O S E W 00 D H I G H LA N D S
Public Works I ProJect Management I Landscape Architecture
JOB NO. 1352-001-008 DATE: 10/28/2010 FIGURE 9
DRAWN: ECN SHEET 1 OF 1
ESM JOBa 1352-001-006 Rose�vood Hiqhlands '
Developed Hydrology:
The proposed developed site will consist of impervious areas from roadways, homes, and
sidewalks; and pervious area from landscaping and lawns (See Figure 10 - Developed
Hydrology Map).
Stormwater runoff from most of the site (roads, landscaped areas, and buildings) are
collected and conveyed, via a closed pipe conveyance system, to the detention/water
quality vault.
The runoff from the easterly four lots (lots 24-27) will released to the adjacent stream
buffers via gravel filled flow dispersion trenches. The runoff from lot 23 will be discharged
to the adjacent wetland via a gravel filled flow dispersion trench. Stormwater runoff will
sheet flow easterly into the adjacent sensitive area tract This area bypasses the
detention facility; therefore, it is modeled as a bypass basin and a downstream point of
compliance is used in sizing the detention facility.
Individual Lot BMPs Sizing Credits
Per the Section 1.2.3.2.0 of the KCSWDM, sizing credits will be given to the different
individual lot fiow control BMPs that are being proposed. These BMPs will be used:
Restricted Footprint, Basic Dispersion and Perforated Pipe connection. Refer to Table 2 -
Individual Lot Flow Control BMPs Credits included in this section of the report. Below is a
summary on how the credits have been applied.
• Restricted Footprint (Section C2.9.2) - The impervious area for each lot will be
limited to 2,300 square feet via a recorded covenant
� Basic Dispersion (Section C.2.4) - The runoff from the lots 23-27 will be discharged
to the wetland and stream buffer via individual lot flow dispersion trenches. These
lots meet the requirements because there will be at least a 25' flow path within the
natural vegetation within the sensitive area buffer. The gravel filled trenches for lots
24-27 will be 35' long, based on the manual's recommended sizing of 10' per 700
square feet of impervious. The gravel filled trench for lot 23 will be 50' long to
provide a more dispersed flow to enter the wetland buffer.
• Perforated Pipe Connection (Section C.2.11) - For the lots where flow dispersion is
not an option (lots 1-22) perforated pipe connections will be used for the
connection of the roof drains to the road drainage system.
- 25 -
Table 2 - Individual Lot Flow Control BMP Credits
Lot Area Restricted Footprint Calculation Basic Dispersion Credit Total
Lot (A) (B) (C) (D) (E) (H) (I) (7) (K)
Number Lot Area Max Imp Max House Dwy and Total Imp Roof 50% Roof 50% Till Grass Imp
(sf) (75% of lot (sf) Patio (sf) Till Grass Imp (sf) (sf)
up to 4000 (sf) (sf) (sf)
Ax75% =C+D =Cx50% =Cx50% =A-K =E-I
1 5,023 3,767 1,800 500 2,300 2,723 2,300
2 3,825 2,869 1,800 500 2,300 1,525 2,300
3 3,555 2,666 1,800 500 2,300 1,255 2,300
4 3,555 2,666 1,800 500 2,300 1,255 2,300
5 5,223 3,917 1,800 500 2,300 2,923 2,300
6 4,950 3,713 1,800 500 2,300 2,650 2,300
7 4,296 3,222 1,800 500 2,300 1,996 2,300
8 3,771 2,828 1,800 500 2,300 1,471 2,300
9 4,345 3,259 1,800 500 2,300 2,045 2,300
10 3,466 2.600 1,800 500 2,300 1,166 2,300
11 3,200 2,400 1,800 500 2,300 900 2,300
12 3,739 2,804 1,800 500 2,300 1,439 2,300
13 3,739 2,804 1,800 500 2,300 1,439 2,300
14 3,200 2,400 1,800 500 2,300 900 2,300
15 3,352 2,514 1,800 500 2,300 1,052 2,300
16 4,994 3,746 1,800 500 2,300 2,694 2,300
17 5,168 3,876 1,800 500 2,300 2,868 2,300
18 3,505 2,629 1,800 500 2,300 1,205 2,300
19 4,373 3,280 1,800 500 2,300 2,073 2,300
20 4,124 3,093 1,800 500 2,300 1,824 2,300
21 4,272 3,204 1,800 500 2,300 1,972 2,300
22 4,161 3,121 1,800 500 2,300 1,861 2,300
23 5,660 4,000 1,800 500 2,300 900 900 4,260 1,400
24 5,353 4,000 1,800 500 2,300 900 900 3,953 1,400
25 3,600 2,700 1,800 500 2,300 900 900 2,200 1,400
26 3,600 2,700 1,800 500 2,300 900 900 2,200 1,400
27 3,600 2,700 1,800 500 2,300 900 900 2,200 1,400
Total(Ac) � • •
ESM JOE� 1352-Q�1-006 ______ ____ __Rose����o�d HiahlUn_c__s
The developed conditions, including the frontage improvement area, are as follows.
Developed area tributary to storm vault (DEV basin in KCRTS)
Till-Grass ' Till-Pasture Impervious Total
DEV (ac) (ac) (ac) (ac)
Lots 1-9 0.41 - 0.48 0.89
Lots 10-15 0.16 � -� 0.32 0.48
Lots 16-22 0.33 - 0.37 0.70
Lots 23 * 0.10 - 0.03 0.13
Lots 24-27 * 0.24 - 0.13 0.37
Plat Roads 0.01 - 1.11 1.12
Storm Vault Tract 0.18 - - 0.18
Offsite Basin B - 0.13 0.02 0.15
Frontage -Union - �- 0 03 0.03
Ave
Total 1.43 0.13 2.49 4.05
'` Basic flow dispersion credit has been applied. Refer to Table 2 for area
calculations.
- 27 -
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ESM JOB# 1352-001-006 Rosewood Highlands
Flow Control System:
Calculations for the proposed project are based on the 2005 KCSWDM and the City of
Renton amendments. Detention and water quality treatment is to be provided for in a
stormwater vault located in the southeastern corner of the site
The project is located in a Flow Control Duration Standard Matching Forested Site
Conditions. This is also referred to as Conservation FC Area or Level 2 Flow Control in the
King County Manual
In accordance with the FC Duration Standard, the design intent for the detention facility is
to match the developed duration levels to the existing duration levels for the following
ranges:
• 2-year developed to 50% of the historic 2-year duration and
• 50-year developed to the historic 50-year duration.
In addition, you have to match the peak flows for the developed facility to the existing
flows for the following ranges:
• 2-year developed peak to the historic 2-year peak and
• 10-year developed peak to the historic 10-year peak.
The pre-developed basin has been modeled as forested conditions.
Existinq Basin Flows:
Existing basin data is entered into KCRTS for the site to obtain individual time series.
Below is a summary of the peak flows. '
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
G .264 2 2/09/O1 18:00 0.350 1 100.00 0.990
0 . 078 7 1/05/02 16:00 0.264 2 25.00 0.960
0 .204 4 2/28/03 3:00 0 .205 3 10.00 0.900
0 . 013 8 8/26/04 2:00 0 .204 4 5.00 0.800
0. 121 6 1/05/05 8:00 0.180 5 3 .00 0.667
0.205 3 1/18/06 20:00 0.121 6 2.00 0.500
0. 180 5 11/24/06 4:00 0.078 7 1.30 0.231
0. 350 1 1/09/08 9:00 0.013 8 1.10 0.091
Computed Peaks 0.322 50. 00 0. 980 ��
- 29 -
ESM JOB� 1352-001-006 Rosewood Highlands II
Developed Basin Flows: I
The basin data is entered into KCRTS for the site to obtain a time series. Below is a
summary of the peak flows.
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
0.735 6 2/09/O1 2 :00 1.49 1 100.00 0.990
0.598 8 1/05/02 16:00 0.938 2 25.00 0 .960
0 .883 3 2/27/03 7:00 0.883 3 10.00 0.900
0 .645 7 8/26/04 2:00 0.781 4 5.00 0.800
0 .777 S 10/28/04 16:00 0.777 5 3.00 0.667
0 .781 4 1/18/06 16:00 0.735 6 2.00 0.500
0 . 938 2 10/26/06 0:00 0.645 7 1.30 0.231
1.49 1 1/09/08 6:00 0.598 8 1.10 0 .091
Ccmputed Peaks 1.31 50.00 0. 980
Facilitv Desiqn:
The following is the output from the KCRTS detention design.
Retention/Detention Facility
Type of Facility: Detention Vault
Facility Length: 78.00 ft
Facility Width: 78. 00 ft
Facility Area: 6084. sq. ft
Effective Storage Depth: 7.46 ft
Stage 0 Elevation: 100. 00 ft
Storage Volume: 45387. cu. ft
Riser Head: 7.46 ft
Riser Diameter: 18. 00 inches
Nuriber of orifices: 3
Full Head Pipe �
Orifice # Height Diameter Discharge Diameter
{ft) (in) (CFS) (in)
1 0.00 1. 00 0. 074
2 4 .45 1. 55 0. 113 4 .0
3 5.55 1.25 0.059 4 .0
Top Notch Weir: None
Outflow Rating Curve: None
Stage Elevation Storage Discharge Percolation
(ft) (ft) (cu. ft) (ac-ft) (cfs) (cfs)
0. 00 100. 00 0. 0. 000 0. 000 0. 00
0 . 01 100. 01 61. 0. 001 0. 003 0. 00
0 . 02 100.02 122 . 0.003 0. 004 0. 00
0 . 03 100.03 183 . 0 . 004 0. 005 0. 00
0 . 04 100.04 243 . 0 . 006 0 .006 0.00
0 . 05 100. 05 304 . 0 . 007 0 . 006 0. 00
0 . 06 100 . 06 365. 0 . 008 0 . 007 0. 00
- 30 -
ESM JOBTM 1352-001-006 _ __ __ ____ Rosewood Hi.hl�
G . �7 �CG . G7 425 . � . C10 O . 007 C. 00
0. 08 100.08 487 . 0. 011 0. 008 0. 00
0. 09 100.09 548 . 0 . 013 0. 008 0. 00
0. 24 100.24 1460. 0. 034 0. 013 0.00
a. 39 100.39 2373 . 0 . 054 0. 017 0. 00
0 . 53 100.53 3225. 0 . 074 0. 020 0. 00
0 .68 100.68 4137. 0. 095 0. 022 0.00
0 . 83 100.83 5050. 0. 116 0. 025 0. 00
0 . 97 100.97 5902. 0. 135 0. 027 0. 00
1. 12 101.12 6814. 0. 156 0. 029 0. 00
1.26 101.26 7666. 0.176 0. 030 0. 00
1.41 101.41 8578. 0. 197 0. 032 0. 00
1. 56 101.56 9491. 0.218 0. 034 0.00
1. 70 101.70 10343 . 0.237 0. 035 0. 00
1. 85 101.85 11255. 0.258 0. 037 0. 00
2. 00 102.00 12168 . 0.279 0. 038 0. 00
2 . 14 102.14 13�20 . 0.299 0 . 040 0. 00
2 .29 102 .29 13932 . 0.320 0 . 041 0. 00
2 .43 102.43 14784. 0.339 0. 042 0. 00
2 . 58 102.58 15697. 0.360 0. 044 0. 00
2 . 73 102.73 16609. 0.381 0.045 0. 00
2 . 87 102 .87 17461. 0.401 0. 046 0. 00
3 . 02 103 .02 18374. 0.422 0. 047 0. 00
3 . 17 103 .17 19286. 0.443 0.048 0. 00
3 .31 103 .31 20138. 0.462 0. 049 0. 00
, 3 .46 103 .46 21051. 0.483 0.050 0. 00
3 . 60 103 .60 21902 . 0. 503 0.051 0. 00
3 . 75 103 .75 22815. 0. 524 0 .053 0. 00
3 . 90 103 .90 23728 . 0. 545 0 .054 0. 00
4 . 04 104.04 24579 . 0. 564 0 .055 0. 00
4 . 19 104 .19 25492 . 0 .585 0 . 056 0. 00
4 .34 104 .34 26405. 0 .606 0 . 056 0. 00
4 .45 104 .45 27074. 0. 622 0 . 057 0. 00
4 .47 104 .47 27195. 0. 624 0. 058 0. 00
4 .48 104 .48 27256. 0.626 0.059 O. OQ
4 . 50 104 .50 27378. 0.629 0.062 0. 00
4. 51 104 .51 27439. 0.630 0.066 0. 00
4 . 53 104 .53 27561. 0.633 0.070 0. 00
4 .55 104 .55 27682 . 0. 635 0.075 0. 00
4.56 104 .56 27743 . 0. 637 0 . 080 0. 00
4.58 104.58 27865. 0.640 0 . 081 0. 00
' 4. 60 104.60 27986 . 0 .642 0 .083 0. 00
4 . 74 104 .74 28838 . 0 .662 0 .094 0. 00
4 . 89 104 .89 29751. 0 . 683 0.103 0. 00
5. 03 105.03 30603 . 0.703 0.111 0. 00
5. 18 105.18 31515. 0. 723 0.117 0. 00
5. 33 105.33 32428. 0. 744 0.124 0. 00
5.47 105.47 33279. 0.764 0.129 0. 00
5. 55 105.55 33766. 0.775 0.132 0. 00
5. 56 105.56 33827. 0. 777 0.133 0. 00
5. 58 105.58 33949. 0. 779 0. 134 O. CO
5. 59 105.59 34010. 0. 781 0.137 0. 00
5. 60 105.60 34070. 0 . 782 0 . 139 0. 00
5. 62 105.62 34192 . 0 . 785 0 . 143 0. 00
- 31 -
ESM JOBn 1352-001-006 Rosewood Hiqhlands
5 . 63 105 . 63 34253 . 0. 786 0. 147 0. 00
5. 64 105.64 34314 . 0. 788 0.148 0. 00
5 . 65 105.65 34375. 0. 789 0.150 0. 00
5 . 80 105. 80 35287 . 0.810 0.162 O. GC
5. 95 105. 95 36200 . 0.831 0. 173 O. 00
6. 09 106 .09 37052 . 0.851 0. 182 O. 00
6.24 106 .24 37964 . 0. 872 0. 190 O. 00
6 .39 106.39 38877. 0. 892 0. 198 O. 00
6. 53 106 .53 39729. 0. 912 0. 205 O. CC
6. 68 106 .68 40641. 0. 933 0. 212 O. GC
6. 82 106.82 41493 . 0. 953 0.219 O. CO
6. 97 106. 97 42405. 0. 973 0.226 0. 00
7. 12 107 . 12 43318 . 0. 994 0.232 0. 00
7.26 107 .26 44170. 1. 014 0.238 O. CO
7.41 107 .41 45082. 1. 035 0.244 O. CO
7.46 107 .46 45387. 1. 042 0.246 0. 00
7. 56 107 .56 45995. 1. 056 0 .712 0. 00
7. 66 107.66 46603 . 1. 070 1.560 0. 00
7. 76 107.76 47212. 1. 084 2 .660 0. 00
7. 86 107.86 47820. 1.098 3 . 960 0. 00
7 . 96 107.96 48429. 1.112 5.430 0. 00
8 . 06 108. 06 49037. 1.126 6 .860 0. 00
8 .16 108 .16 49645. 1. 140 7.390 0. 00
8 .26 108.26 50254 . 1.154 7.890 0. 00
8 .36 108 .36 50862 . 1. 168 8.350 0. 00
8 .46 108 .46 51471. 1. 182 8.790 0. 00
8 .56 108 .56 52079. 1. 196 9.210 0. 00
8 .66 108.66 52687. 1.210 9.61Q 0. 00
8 . 76 108 .76 53296 . 1.224 9.990 O. 00
8 .86 108.86 53904 . 1.237 10.360 0. 00
8 . 96 108 .96 54513 . 1.251 10.720 0. 00
9. 06 109. 06 55121. 1. 265 11. 060 0. 00
9. 16 109 .16 55729. 1.279 11.400 0. 00
9.26 109 .26 56338. 1.293 11. 720 0. 00
Hyd Inflow Outflow Peak Storage
Target Calc Stage Elev (Cu-Ft) (Ac-Ft)
1 1.49 0.35 1. 00 7 . 59 107. 59 46199. 1. 061
2 0 .74 ******* 0.24 7 .41 107.41 45a63 . 1. 035
3 0 .74 ******* 0.21 6 .55 106. 55 39861. 0.915
4 0.88 ******* 0. 20 6 .34 106. 34 38570. 0.885
5 0.78 ******* 0. 13 5.47 105.47 33308 . 0.765
6 0.46 ******* 0. 08 4 . 62 104. 62 28127 . 0.646
7 0.60 ******* 0. 06 4.16 104 .16 25314 . 0.581
8 0. 64 ******* 0. 05 2. 95 102. 95 17920. 0.411
----------------------------------
- 32 -
ESM JOBn 1352-�01-006 Rosewood Hiphlands �
Route Time Series through Facility
Inflow Time Series File:dev.tsf
Outflow Time Series File:rdout
Inflow/Outflow Analysis
Peak Inflow Discharge: 1.49 CFS at 6: 00 on Jan 9 in Year 8 ,
Peak Outflow Discharge: 0. 997 CFS at 9: 00 on Jan 9 in Year 8
Peak Reservoir Stage: 7 .59 Ft
Peak Reservoir Elev: 107.59 Ft
PeaK Reservoir Storaae: 46199. Cu-Ft
. 1. 061 Ac-Ft
Flow Duratior. �rom Time Series File:rdout.tsf
Cutoff Count Frequency CDF Exceedence_Probability '
C F S % °s °s '
0 . 004 31627 51.577 51. 577 48 .423 0.484E+00
0 . 012 7868 12 .831 64 .408 35.592 0.356E+00
0 . 019 5988 9. 765 74 . 173 25.827 0.258E+00
0 . 027 5468 8 . 950 83 . 123 16. 877 0. 169E+00
0 . 035 4893 7 .979 91.102 8 . 898 0. 890E-01
G . 043 2100 3 .425 94.527 5.473 0.547E-01
0 . 050 1745 2.846 97 .373 2 .627 0.263E-01
0 . 058 1157 1.887 99 .260 0 .740 0. 740E-�2 �
0. 066 48 0.078 99.338 0.662 0. 662E-02
0. 074 34 0 .055 99.393 0 .607 0.607E-02
0. 081 21 0. 034 99.428 0 .572 0.572E-02
0. 089 41 0. 067 99.494 0.506 0.506E-02
0 . 097 44 0.072 99.566 0.434 0.434E-02
0 . 105 39 0. 064 99.630 0.370 0.370E-02
0 . 112 36 0.059 99. 689 0.311 0.311E-02
0 . 120 28 0.046 99. 734 0.266 0.266E-02
0 . 128 39 0.064 99 .798 0.202 0.202E-02
0 . 136 28 0.046 99 .843 0.157 0. 157E-02
0 . 143 8 0.013 99 .856 0 .144 0. 144E-02
0 . 151 4 0.007 99.863 0.137 0. 137E-02
C . 159 5 0 .008 99.871 0.129 0. 129E-02
0 . 166 7 0. 011 99.883 0 .117 0. 117E-02
0 . 174 7 0.011 99.894 0 .106 0. 106E-02
0 . 182 8 0.013 99.907 0. 093 0. 930E-03
0 . 190 8 0.013 99. 920 0. 080 0. 799E-03
0 . 197 15 0.024 99. 945 0. 055 0.554E-03
0 .205 12 0.020 99. 964 0.036 0.359E-03
0 .213 5 0.008 99 .972 0. 028 0.277E-03
0 .221 3 0. 005 99 .977 0.023 0.228E-03
0 .228 2 O.OQ3 99 .980 0. 020 0. 196E-03
0 .236 5 0.008 99.989 0. 011 0.114E-03
0 . 244 4 0 .007 99.995 0. 005 0.489E-04
0 . 252 2 0. 003 99. 998 0 .002 0.163E-�4
0 .259 0 0. 000 99.998 0.002 0. 163E-04
0 .267 0 0.000 99.998 0. 002 0. 163E-04
0 .275 0 0 . 000 99 . 998 0. 002 0 . 163E-04
- 3 3 -
ESM JOB� 1352-001-006 Rosewood Hiqhlands
Duration CompGrison Pnaylsis
Base File: predev.tsf
New File: rdout. tsf
Cutoff Units: Discharge in CFS
-----Fraction of Time----- ---------Check of Tolerance------
Cutoff Base New oChange Probability Base New oChange
0. 060 � 0. 87E-02 0. 71E-02 -18 .7 I 0.87E-02 0. 060 0. 057 -6 . 0
0. 076 I 0. 61E-02 0.60E-02 -2 .7 I 0.61E-02 0. 076 0. 072 -4 .4
0. 091 I 0.47E-02 0.48E-02 1.7 I 0.47E-02 0. 091 0. 092 0 .7
0 .107 I 0.36E-02 0.35E-02 -3 .6 � 0 .36E-02 0. 107 0. 105 -1.8
0 . 123 I 0.27E-02 0.25E-02 -7.7 � 0.27E-02 0. 123 0. 119 -3 .1
0 . 138 I 0.21E-02 0.15E-02 -26. 0 � 0.21E-02 0. 138 0. 127 -7 . 9
0 . 154 I 0.14E-02 0.13E-02 -3 .5 � 0.14E-02 0. 154 0.150 -2.5
0 . 170 � 0.99E-03 0.11E-02 14 . 8 � 0.99E-03 0. 170 0.178 4 . 9
0 . 185 � 0.60E-03 0.88E-03 45. 9 ( 0.60E-03 0. 185 0.195 5.3
0 .201 I 0.34E-03 0.46E-03 33 .3 I 0.34E-03 0. 201 0.206 2 .4
0 .217 � 0.20E-03 0.26E-03 33 . 3 � 0.20E-03 0. 217 0.228 5.4
0.232 I 0.15E-03 0.15E-03 0. 0 � 0.15E-03 0.232 0.233 0.2
0.248 � 0. 82E-04 0.16E-04 -80. 0 ( 0. 82E-04 0.248 0.241 -2 . 8
0.264 I 0. 16E-04 0.16E-04 0. 0 � 0. 16E-04 0 . 264 0 .275 4 .5
Maximum positive excursion = 0. 014 cfs ( 8. 1%)
occurring at 0.175 cfs on the Base Data:predev.tsf
and at 0.189 cfs on the New Data:rdout.tsf
Maximum negative excursion = 0. 009 cfs (-13 . 1�)
occurring at 0.068 cfs on the Base Data:predev. tsf
and at 0. 059 cfs on the New Data:rdout.tsf
The proposed detention facility has a volume of 46,550 cubic feet which is larger than the
required 45,387 cubic feet
Control Structure:
The control structure is an 18-inch diameter Frop-T standpipe structure with three orifices.
Orifice sizes are listed above in the KCRTS printout.
Orifice 1: 1.00" EI = 384.75
Orifice 2: 1.55" EI = 389.20
Orifice 3: 1.25" EI = 390.30
- 34 -
ESM JOB# 1352-001-006 Rosewood Hi4hlands
Water Quality System:
The project is located in the Basic Water Quality Treatment Area per the King County
Water Quality Applications Map. The water quality treatment will be achieved in the form
of dead storage in the bottom of the stormwater vault.
The design intent for the water quality facility is 80 percent removal of total suspended
solids (TSS).
Facilitv Desiqn:
The facility is sized per Chapter 6.4 of the 2005 KCSWDM using a Basic Wetpond design.
The following equations are used to size the water quality facility.
Calculation of the mean annual storm is as follows.
V,. _ (0.9A; +O.ZSA,� +O.l 0A�� +O.OIAo)x R
Where:
A; = 108,100 (2.48 Ac of impervious surface)
A,Q = 67,354sf (1.56 Ac of till grass & till pasture surface)
.9„ = 0 sf (Area of till forest surface)
.9oQ = 0 sf (Area of outwash grass surface)
R = 0.039ft (Rainfall from mean annual storm = 0.47")
i; =Volume of runoff from mean annual storm (cfl
I', _ �(0.9 x 108,100)+(0.25 x 67.354)+(0.10 x 0)+(0.01 x 0)k0.47)/12
I', = 4,451 cf
Calculate wetpool volume is as follows.
ib = fxV.
f =3 (Basic Wetpond)
i; = 4,451 cf (Calculated above)
i�, = Minimum pond volume (cfl
ih = 3x4.451 = 13.353cf
The provided dead storage volume in the bottom of the proposed vault is 24,960 cubic
feet, which is greater than the 13,353 cubic feet required.
- 3 5 -
ESM JOB= 1352-001-006 Rosewood Highiands
5. CONVEYANCE SYSTEM ANALYSIS AND DESIGN
Per the KCSWDM Core Requirement #4, Section 1.2.4, new conveyance systems must be
designed to convey and contain the 25-year peak flow (at a minimum) providing that the
overflow from the 100-year storm event does not create or aggravate a severe fiooding
problem.
Per Table 3.2 of the KCSWDM, un-detained areas with tributary areas less than 10-acres
are required to use the Rational Method to obtain conveyance flows.
As directed by KCSWDM, the conveyance analysis for the 25-year and 100-year peak flow
has been calculated using the Rational Method. The backwater analysis was performed
using the calculations described in Figure 4.2.1.1 of the KCSWDM. The calculations are
included in this section of the TIR,
See Appendix D for conveyance calculations. The calculations show that the system has
adequate capacity to convey the 25-year and 100-year storm event without backwater
issues.
- 36 -
ESM JOB# 1352-001-006 Rosewood Hiqhlands
6. SPECIAL REPORTS AND STUDIES
The following lists are the known reports and studies done for the project These reports
may be found in Appendix A.
Report / Study ; By ' Dated
January 24,
Wetland Report Chad Armour, LLC 2007
Letter discussing discharging Chad Armour, LLC January 31,
storm to stream buffer * 2008
November 18,
Wetland Hydrology Report * Chad Armour, LLC 2010
Geotech Report * Pacific Geo February 15,
Engineering, LLC 2007
Geotech Report for Storm Vault Pacific Geo February 8,
En ineerin , LLC 2008
* These reports may be found in Appendix A.
- 37 -
ESM JOB# 1352-001-006 Rosewood Hi,hlcL ands
7. OTHER PERMITS I
Known permits required for the project include:
• Grading Permit from the City of Renton
• NPDES Construction Stormwater Discharge Permit from Department of Ecology
• Building permit for construction of stormwater vault
- 38 -
ESM JOB# 1352-001-0o6 Rosewood Highlands
8. ESC ANALYSIS AND DESIGN
A Wet Season Erosion and Sediment Control (ESC) Plan has been prepared for the site.
A copy of this plan is included in Appendix E of this report.
i
,
- 39 -
ESM JOB# 1352-001-006 Rosewood Hiahlands
9. BOND QUANTITIES, FACILITY SUMMARIES, AND DECLARATION OF
COVENANT
Bond quantities, facility summaries, and declaration of covenant will be provided at time
of final submittal.
- 40 -
ESM JOBN 1352-001-006 Rosewood Highlands
10. OPERATIONS AND MAINTENANCE MANUAL
The following pages are maintenance standards for the stormwater vault and drainage
systems.
;
- 41 -
APPENDIX A MAINTENANCE REQiJIREMEI�'TS FLOW CONIROL,CONVEYANCE,,SND WQ FACIL•IIIES
N4. 3-DETENTtON TANKS AND VAULTS
AAaintenance Defect or Problem Conditions When Maintenance is Needed Results Expected When
Component Maintenance is Performed
Storage Area Plugged Air Vents One-half of the oross section of a vent is blocked Vents free of debris and sediment
at any point with debris and sediment.
Debris and Sediment Accum�lated sediment depth exceeds 10%of All sediment and debris removed
the diameter oi the storage area for Yz length of from storage area.
storage vault or any pant depth exceeds 15%of
diameter. Example:72-incfi storage tank would
require cleaning when sediment reaches depth of
7 inches for more than'/:length of taMc.
Joints Between My crack allowing material to be transporied into All joint between tanklpipe sections
TanklPipe Sec6on facility. are sealed
Tank Pipe Bent Out of Any part of tanklpipe is bent out of shape more Tanklpipe repaired or replaced to
Shape than 10%of its design shape. design.
Vau�t Structure Damage to Wall, Cracks wider than'/rinch and any evidence of Vault replaced or repaired to design
Frame,Bottom, soil particles entering the structure through the specifcations
and/or Top Slab cracks,or maintenance inspection personnel
determines that fhe vauri is not sVucturatly
sound.
Damaged Pipe Joints Cradcs wider thart'/rinch at the joint of any No cracks more than Y.-inch wide at
infetloutlet pipe or arey evidence of soil particles the joini of the inleUoutlet pipe.
entering the vauft through the walls.
Manhole Cover Not in Place Cover is missing or only partially in place Any Manhole is Gosed.
open manhole requires maintenance.
Locking Mechanism Mechanism cannot be opened by one Mechanism opens with proper tools.
Not Working mainlenance person with proper tools.Bolts into
frame have less than%,inch of thread(may not
apply to self-locking lids.}
Cover Difficult to One maintenance psrson cannot remove tid after Cover can be removed and
Remove applying 80Ibs of lift. Intent is to keep cover irom reinstalled by one maintenancs
seafing off access to maintenance. person.
Ladder Rungs Unsafe King County Safety Office and/or maintenance Ladder meets design standards
person judges that ladder is unsafe due to Allows maintenance person safe
missing rungs,misalignment,rust,or cracks access.
Large access Gaps, Doesn't Cover Large access doors not flat andlor access hole Doors closes flat and covers access
doors/plate Completely not completely covered. NOTE however that hole completely
grated doors are accepbble
lifting R9ngs Missing Lifting rings not capable of lifting weight of door Lifting rings sufficient to remrne lid
Rusted or lid.
1/24/2005 2005 Surface WaterDesign Manual—Appendix A
A-4
APPE1`TDtX A MA]7TTE?�ANCE RLQi;IRE�fE1TS FOR FLOW CONTROL,C01�VEYA�ICE,AND VJQ rACILIT{ES
{d0. 4—CONTROL STRUCTURE/FLOW RESTRICTOR
Maintenance Defect or Problem Condition When Malntenance is Needed Resuits Expected When
Component Malntenance is Performed
General Trash and Debris Distance between debris build-up and bottom of All trash and debris removed.
(Inr.fudes Sedime�t) orifice plate is fess than 1.5 feet-
Structural Damage Shucture is not securely attached to manhole Structure securely attached to wail
wall and outlet pipe structure should support at and outlet pipe
least 1,000 Ibs of up or down pressure.
Strudure is not in upright position(allow up to Structure in correct posKion
10%from plumb).
Connections to outlet pipe are not watertight and Connections to ouUet pipe are water
show signs of rust. tight;structure repaired or repiaoed
and wo�lcs as designed.
Any holes�ther than designed holes�--+n the Structure has no hoEes other than
sVucture. designed holes.
Cleanout Gate Damaged or Missing Cleanout gate is not wate�tight or is missing Gate is watertight and works as
designed.
Gate cannot be moved up and down by one Gate moves up and dawn easily and
maintenance person. fs watertight
Chain/rod lead9ng to gate is missing or damaged Chain is in place and works as
designed.
Gate is rusted over 50%of its surface area Gate is repaired or replaced to meet
design standards.
prifice Plate Damaged or Missing Control device is not working properiy due to Plate is in place and works as
missing,out of place,or bent o�ca plate. designed.
Obstructions Any trash,debris, sedimeM or vegetation Plate is free of all obstructions and
blocking the plate wnrks as designed.
Overflow Pipe Obstructions Any trash or debris blocking(or having the Pipe is iree of all obstructions and
potential of blocking)the overflow pipe. works as designed,
Ntanhole See'Detention Tanks See`Detention Tanks and Vaults'Table No.3 See"Detenlion Tanks and Vaults°
and Vaults° Table No.3
2005 Surface Water Design Manual—Appendix A 1/'L4/20Q5
A-5
APPENDIX A MAINIENANCE REQUIREMENIS FL,OW CONIROL,CONVEYANCE,AND WQ FAC]L11IES
NO. 5-CATCH BASINS
Maintenance Defect or Problem Conditions When Maintenance is Needed Resutts Expected When
Component Maintenance is pertormed
General Trash&Debris Trash or debris of more than'�cubic foot which No Trash or debns located
(]nckudes Sediment) is located immediatety in iror►t of the catch basin immediately in frait of catch basin
opening or is blocking capacity of the basin by opening
more than 10°�.
Trash or debris(in the basin)that exceeds'is the No trash or debris in the catch
depth from the bottom of basin to invert the basin
lowest pipe into or out of the basin.
Trash or debris in any inlet or outlet pipe blocking Inlet and outlet pipes free of trash or
more than�/3 of its height debris.
Dead animals or vegetation that could generate No dead animals or vegetation
odors that could cause complaints or dangerous present within the catch basin
gases(e.g.,methane).
Qeposits of garbage exceeding 1 cubic foot in No condition present which wouid
volume attract or support the Dreeding of
inseccs or rodents.
Structure Damage to Comer of frame extends more than'/.inch past Frame is even with curb
Frame and/or Top curb face into the street(If applicable}.
Slab
"fop slab has holes larger than 2 square inches 7op slab is free of holes and cracks
or cracks wider than'/.inch(intent is to make
sure all material is running inEo basin).
Frame not sitting 8ush on top slab,i e., Frame is sitting flush on top slab.
separation of more than'/.inch of the frame from
the top slab.
Cracks in Basin Cracks wider than Yz inch and longer than 3 feei Basin replaced or repaired to design
Wa1lsBotlorn any evidence of soil partides entering catch standards
basin through cracks,or maintenanoe person
judges that structure is unsound.
Cracks wider than'/:inch and longer than't foot No cracks more than'!<inch wide at
at the joint of any inleUoutlet pipe or any the joirrt of inleVoutlet pipe.
evidence of soil partiGes entering catch basin
through cracks
SettlemenU Basin has setUed more than 1 inch or has rotated Basin replaced or repaired to design
Misalignment more than 2 inches out of alignment. standards.
Fire Hazard Presence of chemicals such as natural gas oil !Jo flammable cfiemicals present.
and gasoline.
Vegetation Vegetation growing across and blocking more No vegetation blocking opening to
than 1 D%of ihe basin opening basin.
Vegetation growing in inleUoutlet pipe joints that No vegetation or root growth
is more than 6 inches ta11 and less than 6 inches present
apart.
Pollution Nonflammable chemicals of more than%2 cubic No pollution present other ihan
fiot per three feet of basin length su►iace film.
Catch Basin Cover Cover Not in Place Cover is miss9ng or only partially in place Any Catch basin cover is closed
open catch basin requlres maintenance.
Locking Mechanism Mechanism cannot be opened by on Mechanism opens with proper tools.
Not Working maintenance person with proper tools.Botts into
frame have less than h ii►ch of thread.
Cover Difficuft to One maintenance person cannot remove lid after Cover can be removed by one
Remove applying 80 Ibs of lift;intent is keep cover from maintenance person.
sealing off acoess to maintenance.
Ladder Ladder Rungs Unsafe Ladder is unsafe due to missing rungs, Ladder meets design standards and
misalignment rust.cracks or sharp edges albws maintenance person safe
access.
1l24/2Q05 2005 Surface Water Design Manual-Appendix A
A-6
.s.PPETDIX A A4AT?�'IENAhCE REQUIREME?�TS FUR FIOti��CO'�IROL,CO;VVE�'ANCE,AND WQ FACIIITIES
NO. 5-CATCH BASINS
Malntenance Defect or Problem Conditiorts When Maintenance is Needed Resalts Expected When
Component Maintenance is performed
Metal Grates Unsafe Grate Grate with opening wider than'!a inch Grate opening meets design I
{If Applicable) Opening standards I
Trash and Debris Trash and debris that is blocking more than 20% Grate free of trash and debris
of grate surface.
Damaged or Missing Grate missing or broken member(s)of the grate Grate is in ptace and meets design '
standards.
NO. 6- DEBRiS BARRfERS E.G.,TRASH RACKS) I,
�
Maintenance Defect or Problem Condition When Maintenance is Needed Results Expected When
Component Maintenance is Performed. I
Genera! Trash and Debris Trash or debris that is plugging more than 20°k Barrier clear to receive capacity
of the openings in the barrier flow. '
Metal Damaged/Missing Bars are bent out of shape more than 3 inches Bars in place with no bends more
Bars than'/.inch.
Bars are missing or entire barrier missing. Bars in place according to design.
Bars are loose and rust is causing 50% Repair or replace barrier to design
deterioration to any part of barrier, standards
NO. 7-ENERGY DISSIPATERS
Maintenance Defect or Problem Conditions When Maintenance is Needed Resutts Ezpected When
Component Malntenance Is Pertormed.
Exiemai:
Rock Pad Missing or Nbved Only ane layer of rock exists above native soil in Replace rocks to design standards
Rock area five square feet or larger or any exposure
of nafive soil.
Dispersion Tre�ch Pipe Plugged with Accumulated sediment that exceeds 20%oT the Pipe Geaned/flushed so that it
Sediment design depth. matches design.
Not Discharging Visual evidence oi water discharging at Trench must be redesigned or
Water Properly concentrated points along trench(normal rebuiti to standards
condition is a"sheet flovJ'of water atong trench).
{ntent is to prevent erosion damage.
Per(orations Plugged. Over%:of perforations in pipe are plugged with Clean or replace perforated pipe
debris and sediment.
Water Flows Out Top Maintenance person observes water flowing out Facility must be rebuilt or
of'Distributor'Catch during any storm less than the design storm a redesigned to standards
Basin, its causing or appears likely to cause damage.
Receiving Area Over- Water in receiving area is causing or has No danger of landslides.
Saturated potentlal oi causing landslide problems.
Intemal:
tvlanhole/Chamber Wom or Damaged Structure dissipating flow detsriorates to Y�or Replace strucFure to design
Post. Baffles Side of original size or any concentrated wom spot standards
Chamber exceeding one square foot which would make
struclure unsound.
2005 Surface Water Design Manval-Appendix A ]/24/2005
A-7
APPENDIX A MAINTENANCE REQUIREMEI�7S FLOW CONTROL.,CONVEYANCE,AND WQ FACILITIES
NO. 8- FENCING
Mairrtenance Defect or Prabiem Conditions When Mairrtenance is Needed Results Expeded When
Component Maintenance is Performed
General Missi�g or Broken Any defect in the fence that permits easy entry to Parts in place to provide adequate
Parts a faciliry. secunty.
Erosion Erosion more than 4 inches high and 12-18 No opening under the fence that
inches wide permitting an opening under a fence. exceeds 4 inches in he+ght
Wire Fences Damaged Pafts Post out of plumb more than fi inches. Post plumb to within 1'/z inches.
Top rails bent more than 6 inches Top rail free of bends greater than
1 inch.
Any part of fence(including post,top raiis,and Fence is aligned and meets design
fabric}more than 1 foot out of design alignment. standards.
Missing or loose tension wire 7ension wire in place and holding
fabric.
Mssing or loose barbed wire that is sagging Bari�ed wire in pface with less than
more than 2Y=inches between posts. '1.inch sag between post.
Extens9on arm missing broken,or bent out of Exter�sion arm in place with no
shape more than 1 h inches. bends farger than'/.inch.
Deteriorated Paint or Part or parts that have a rusting or scaling Structurally adequate posts or parts
Protective Coating condition that has aflected structural adequacy. with a unifomi protective coating.
Openings in Fabric Openings in fabric are such that an 8-inch No openings in fabric
diameter ball could fit through.
No. s-GATES
Maintenance Defect or Prob{em Conditions When Maintenance is Needed Results Expected When
Component Maintenance is Performed
General Damaged or Missing Missing gate or locking devices Gates and Locking devices in place
Members
Broken or missing hinges such that gate cannot Hinges intact and lubed Gate is
be easily opened and closed by a mairrtenance working freely
person.
Gate is out o!plumb more than 6 inches and Gate is aligned and vertical
more than 1 foot out oi design aEignment
Missing stretcher bar,stretcher bands,and ties. Stretcher bar,bands,and ties in
place.
Openings in Fabric Sse"Fencing`Table No 8 See"Fencing°Table No.8
� ,
i
!
1/24/2005 2005 Surface Water Design Manual—Appendix A
A-8
APPENDIX A MAINrENANCE REQU[REMEN7S FOR FL.OW CONTROL,CONVEYANCE,AND WQ FACILI?IES
Id0. 10—CONVEYANCE PIPES AND DtTCHES
Maintenance Defsct or Problero Conditions When Maintenance is Needed Resutts Expected When
Component Malntenance is Performed
Pipes 5ediment 8 Debris Accumulated sediment that exceeds 20%of the Pipe Geaned of all sediment and
diameter of the pipe. debris.
Vegetation VegetaUon that reduces free movement of water All vegetation removed so water
ttxough pipes ftows freely thra�gh pipes.
Damaged Protective coating is damaged;rust is causing Pipe repaired or reptaced
more than 50%deterioration to any part of pipe.
Any dent that decreases the cross section area Pipe re�aired or replaced
of pipe by more than 20%
Open Dftches Trash&Debris Trash and debris eweesds 1 cubic foot per 1 000 Trash and debns Geared from
square teet of ditch and slopes. ditches.
Sed9ment Accumulated sediment that exceeds 20%of the Ditch cleaned/fiushed of ap
design depth. sediment and debris so that it
matches design.
Vegetation Vegetation that reduces free movement of water Water flows freely through d�tches
tfirough ditches.
Erosion Damage to See°Detention Ponds'Table No 1 See"Detention Ponds"Table No 1
5lopes
Rock Lining Out�f Maintenance person can see native soil beneath Replace rocks to design standards.
Place or Nlissing{If the rock lining.
Applicable).
N0. 11 —GROUNDS (LANDSCAPING)
Maintenance Defect or Probfem Conditions When IJlaintenance is Needed Results Expected When
Component Maintenance is Pertormed
General Weeds Weeds growing in more than 20°�ot the Weeds present in less than 5%of
(Nonpoisonous not landscaped area(trees and shrubs only) the Iandscaped area
nobous)
Safety Hazard Any presence of poison ivy or other poisonous No poisonous vegetation present in
vegetation. landscaped area.
Trash or Litter Paper,cans bottles. totaling more than 1 cubic Area clear of litter
foot within a landscaped area(trees and shrubs
only)of 1,000 square feei.
7rees and 5hrubs Damaged limbs or parts of trees or shrubs that are split or Trees and shrubs with less than 5%
broken which affect more than 25%of the total of total foliage with split or broken
foliage of the tree or shrub limbs
Trees or shrubs that have been blown down or Tree or shrub in place free of injury
knocked over
Trees or shrubs which are not adequately Tree or shrub in place and
supported or are{eaning over causing exposure adequately supported;remove any
of the roots dead or diseased trees
2005 Surface Water Design Manual—Appendix A I/24/2005
A-9
APPEND3X A MAiNTENANCE REQLJTREivlETTS FLOW CONTROL,CONV�YANCE,AND R'Q�ACIIITIES
NO. '!2-ACCESS ROADS
Maintenante Defecf ot Probiem CondFtion When Maintenance is Needed itesuEts Expecfed When
Cornponent Maintenance is Pertormed
General Trash and Debris Trash and debris exceeds 1 cubic foot per 1,000 Roadway free of debris which could
square#ee!(i e. trash and debris would fill up damage tires.
one standards size garbage can).
BlocEced Roadway Debris which could damage vehicle tires(g4ass Roadway free of debris which could
or meta!). damage tires.
Any obstrudion which reduces clearance above Roadway overhead clear to 14 feet
road surface to less than 14 feet. high.
Any obstruction restricting the access to a 10-to Obstniction removed to allow at
12-foot width for a distance of more than t2 feet keast a 12 foof access.
or any point restrioting access to less tF�an a 10-
fopt width.
Road Surface Setttement,Potholes, When any surtace defect exceeds 6 inches in Road surface uniformly smooth with
Mush Spots Ruts deptti and 6 square feet in area (n generat any no evidence oi settlement,potholes,
t
surface defect which hinders or prevents mush spots or ruis
maintenance access.
Vegetation in Road Weeds growing in the road surface that are more Road surFace free of weeds taller
Surtace than fi inches tall and tess than 6 inches tall and than 2 inches
fess than 6 inches aparl within a 400-square foot
area.
Modular Grid Build-up of sediment mildly contaminated with Removal of sediment and disposal
Pavement petroleum hydrocarbons in keeping with Health Department
recommendations for mildly
contaminated soils or catch basin
sediments.
5houlders and Erosion Damage Erosion wifhin 1 foot of tEie roadway more than 8 Shoulder free of erosion and
Ditches inches wide and 6 inches deep. matching the sunounding road.
Weeds and Brush Weeds and brush exceed 18 inches in height or Weeds and brush cut to 2 inches in
hinder maintenance access height or cleared in such a way as to
allow maintenance access.
t/24/2005 2005 SurEace Water Design Manuai—Appendix A
A-10
APPENDU+A MAINrEI�AI�CE REQL'IREMENIS FLOW CO:v7ROL,CONVEYANCE,AhD WQ FACII.IIIES
N0. 17-WE7VAULT
Maintsnance Defect or Problem CondiHon When Maintenance is Needed Recommended Maintenance to
Component Correct Problem
Vault Area TrashJDebris Trash and debris accumufated in vault(inGudes Remove trash and debris
Accumulation floatab{es and non-floatables)
Sediment Sediment accumulation in vault bottom exceeds Remove sediment from vault.
Accumulation the depth of the sediment zone plus 6 inches.
Veniilation Ventilation area blocked or plugged Remove or Gear blocking material
from ve�ilation area A specified%
of the vault surface area must
provide ventllation to the vault
interior(see p 6-82 for required%}.
Vault Structure Damage to Wa11, Gacks wider than%rinch and any evidence of Vault repfaced or repaired to design
Frame, Bottom, sal partiGes entering the structure through the specifications
andlor 7op Slab cracks,or maintenance inspection personnel
detertnines that the vault is not structuratly
sound.
Damaged PiF�e Joints Cracks wider than'/rinch at the joint of any No aacks more than Y.-inch wide at
inleUoutlet pipe or any evidenoe of soil particles the joint of the inleUouqet pipe.
entering the vautt through the walls.
Bafiles Damaged/Dafective Baffles corroding,cracking warping andlor Repair or replace baifles to
showing signs of failure as determined by spe�cations
maintenance�nspedion staff.
In1eU0ullet damaged Pipes InleUoutlei piping damaged or broken and in Pipe repaired and/or replaced.
need of repair.
Trash/Debris Trash and debris accumulated in pipe or Remove trash and debris
Accumulation inleUouclet{indudes floatables and non-
floatables). ,
Access Cover Damaged/Not Cover cannot be opened a removed espeaalty Pipe repaired or replaced to proper
Working by one person. working specifications.
, Access Ladder Damaged Ladder is corroded or deteriorated,not Ladder replaced or repaired to
function9ng properly, missing rungs has cracics specifications,and 9s safe to use as
and/or misafigned Confined space waming sign deteRnined by inspection personnel
missing Replace sign waming of confined
space entry requirements.
i
1/242005 2005 Surface Water Design Manual—Appendix A
A-l4
APPENDIX A MAINIENANCE REQUIREMENIS FLOW CON7R01,CONVEYANCE,AND WQ FACILITIES
NO. 24-CATCHBASIN INSERT
Maintenance Defect or Probiem Conditions When Maintenance is Needed ResulEs Expected When
Component Maintenance fs Performed
Catch Basin Inspection ]nspection of inedia insert is required. Effluent water from media insert is
free of oils and has no visible sheen.
Sediment When sediment forms a cap over ihe insert No sediment cap on the insert
Accumulation media of the inseh and/or unit, media and its unit.
Trash and Debris Trash and debris accumulates on insert unit Trash and debris removed from
Accumuiation creating a blockage/restriction insert unit Runoff freely flows into
r,atch basin.
Media lnsert Water Saturated Catch basin inser[is saturated with water,which Remove and replace media insert
no ionger has the capacity to absorb.
Oil Saturated AAedia oil saturated due to petroleum spill that Remove and replace media insert
drains into catch basin.
Service Life F�cceeded Regular interval replacement due to typical Remove and replace media at
average lite of inedia insert product regular intervals,depending on
insert product.
1/'L4/2005 2005 Surface Water Design Manual—Appendix A
A-20
APPENDIX A
Additional Reports
Letter discussing direct storm discharge of lots 24-27
Prepared by: Chad Armour, LLC ,
Date: 1 /31/2008 ',
CHAD ARMOUR, LLC 6500126�hAvenueS.E.
Bellevue,Washington 98006-3941
(425)641-9743 Office (425)643-3499 Fax
chad@chadarmour.com
January 31, 2008
Job No. 07-001
Mr. Michael Gladstein
American Classic Homes
P. O. Box 1830
Renton, Washington 98055
Subject: Response to City November 30, 2007 Plan Review Letter
Rosewood Highlands Preliminary Plat (Plan Review U070148)
Renton, Washington
Dear Mr. Gladstein:
Your representative, ESM Consulting Engineers, asked us to review the above-
referenced letter and address comments related to Storm Drainage Report Item 4.
We understand that the drainage plan for the Rosewood Highlands Plat includes a
stormwater management system designed to capture and route precipitation that falls on
impervious surfaces to a storm vault in Tract E. The vault will discharge to the stream by
way of the buffer. We also understand that drainage from precipitation falling on the
rooftops of Lots 24 through 27 will be dispersed by splash blocks. Further precipitation
falling on pervious backyard surfaces on these four lots will sheet flow in the direction of
the stream buffer and is thus not part of the drainage system.
The surface of the plat slopes gently to the east. In the winter when prolonged periods
of precipitation are typical the soil is saturated throughout its profile. A till layer some 2
to 4 feet below ground surface impedes downward migration of shallow groundwater.
Most of the shallow groundwater on the plat likely flows eastward discharging to the
stream. Precipitation falling on parts of Lots 21 though 23 that becomes shallow
groundwater likely discharges to the wetland to the north.
It seems that most if not all of the precipitation falling on the site did and will continue to
drain to the stream. A small area of the plat could drain to the wetland. This area is
found in the back yards of Lots 21 through 23. Assuming that this area becomes lawn
and/or landscaping, it is likely that precipitation falling in this area will continue to make
its way to the wetland. Thus the drainage plan is not likely to adversely affect wetland
hydrology.
C:/ESMlRoselResponse to City Letter.doc 1 01/31/08
Chad Armour, LLC
Response to City's Nov 30, 2007 Letter Rosewood Highlands Preliminary Plat
Renton, Washington
Any questions regarding our work and this letter, the presentation of the information, and
the interpretation of the data are welcome and should be referred to the undersigned.
Sincerely,
Chad Armour, LLC
i�*b�-
Chad Armour
Principal
cc: Robert Ludwig, ESM Consulting Engineers
C:/ESMlRoseJResponse to City Letter.doc 2 01/31/08
Chad Armour, LLC
Wetland Hydrology Report
Prepared by: Chad Armour, LLC
Date: 11 /18/2010
C H AD AR l�lf Of U R, L LC 6500 126�h Avenue S.E.
Bellevue,Washington 98006-3941
(425) 641-9743 Office (425) 643-3499 Fax
chad@chadarmour.com
November 18, 2010
Job No. 10-007
Mr. Michael Gladstein
American Classic Homes
2821 Northup Way, Suite 100
Bellevue, Washington 98004
Subject: Wetland Hydrology Report - Revised
Rosewood Highlands Project
Renton, Washington
Dear Mr. Gladstein:
We are pleased to present the results of our revised wetland hydrology assessment for
the above-referenced property located in Renton, Washington. The work was
accomplished in accordance with our proposal (No. 388) dated October 25, 2010.
BACKGROUND INFORMATION
We understand that in their May 12, 2008 plan review letter, the City of Renton (City)
asked for additional stormwater management information. Among other things, they
asked that you address potential impacts to wetlands as a result of the proposed project.
Specifically, they requested that the analyses address both existing and development
wetland hydrological conditions and follows Guide Sheet 2B Wetland Hvdroloqv
Protection Guideline in the reference section found in the 2005 King County Design
Manual. Our analysis utilized information gleaned from our February 26, 2007 critical
areas assessment and delineation report as well as reports and drawings provided by
ESM Consulting Engineers (ESM).
After reviewing our October 26'h letter, the City asked us to revise our analysis to
address potential short-term impacts to the on-site wetland. Specifically they asked us
to conduct a hydrological assessment using existing conditions for the 2-year storm
event. Previously we evaluated the potential hydrological impact to the wetland
assuming forested conditions for the 2-, 10-, and 100-year storm events.
Wetland and Buffer
The on-site wetland is a part of a larger wetland located off of the site to the north
(Attachment A— Figure 4). The on-site portion of the wetland covers 1,543 square feet
(sf). Although we did not survey the entire wetland, based on the information provided
by ESM and found on the King County iMap for Parcel No.518210-0022 (the parcel that
contains the wetland), it appears the wetland covers an estimated 50,000 sf.
The buffer subject to this analysis is composed of approximately 25% forest and 75%
pasture.
C:/ESM/RoselWetland Hydrology Report(rev}.doc 1 11/18/10
Chad Armour, LLC
Revised Wetland Hydrology Report Rosewood Highlands Project
Renton, Washington
Hydrology
The site is located at the upper reaches of west branch of Maplewood Creek, which
flows south along the eastern portion of the site. The drainage basin upgradient of the
site drains a small area bounded by NE 4th Street (north), Union Street(east), and the
Post Office (west). This basin includes two smaller on-site sub-basins, both of which
discharge to Maplewood Creek (Figure 9). Most of the site (->90%)drains to
Maplewood Creek and the remaining about <10% of the site drains to the wetland which
in-turn drains to Maplewood Creek.
Portions of future Lots 20 through 23 are located in the sub-basin that currently drains to
the wetland. We understand that with the exception of L�ts 23 through 27, all of the
precipitation that falls on impervious surfaces will be directed to the stormwater vault.
Precipitation that falls on the roofs and rear yards of Lots 24 through 27 will bypass the
stormwater management system and be directed to the stream. Precipitation that falls
on the roof and rear yard of Lot 23 will be directed to the wetland (Figure 11).
Soils
The King County soil survey indicates that the site supports one soil type, Alderwood
gravelly sandy loam. Alderwood soils are made up of moderately well drained soils
underlain by a dense till layer typically two to 3.5 feet(ft) below the surface. The
geotechnical engineering report confirmed that glacial till underlies the site, but to a
depth ranging from 5 to more than 10 ft below the ground surface. The same report
indicates that the north and eastern portions of the site have been filled with 3.5 to 9.5 ft
of fill, including all or part of Lots 17 through 27.
Analysis
Using the King County Runoff Time Series (KCRTS) method for estimating runoff and
volume, the City will require 44,286 cubic feet(cf) of storage to detain the runoff from the
developed site. An underground water quality/detention vault will be constructed in the
southeast corner of the site.
The developed estimated runoff and 30-day volume for the portion of the site draining to
the wetland project pre-development for the 2-year event for Lots 20 through 23 is 0.003
cfs and 417 cf for a 30-day storm. Post-development runoff for Lot 23 will be 0.014 cfs
and 1,431 cf .
Estimated runoff from the Rosewood Hei hts pro'ect �
Condition 2-Year Storm Intensit a j
Flow Volumed �
Pre-Developmentb 0.003 cfs 417 cf
Post-Develo ment` 0.014 cfs 1431 cf
a data provided by ESM Consulting Engineers
b Lots 20 through 23
` Lot 23 only
d 30-day storm
C:/ESM/RoseJWetland Hydrology Report(rev).doc 2 11/18/10
Chad Armour, LLC
Revised Wetland Hydrology Report Rosewood Highlands Project
Renton, Washington
� Conclusions
We understand that the City requires discharge runoff from the site post-development to
be roughly equivalent to pre-development conditions. As indicated on the previous tabie
runoff to the wetland will slightly increase after the site is developed. From an ecological
perspective this increase should have a negligible effect on the wetland, particularly
because the wetland is connected to Maplewood Creek. The additional water will flow
through the wetland and as such site development should have no detrimental '�
hydrological effect on the wetland. ,,
Because there will be little if any effect on wetland hydrology from the site post- I''
development, the development should have no cumulative hydrological effect on the
wetland. Similarly, because the stormwater captured on the site, detained in a
stormwater vault, and released per the requirements of the stormwater design manual,
we anticipate no cumulative hydrological effect on the watershed.
LIMITATIONS
Work for this project was performed, and this letter report prepared, in accordance with
generally accepted professional practices for the nature and conditions of the work
completed in the same or similar localities, at the time the work was performed. It is
intended for the exclusive use of American Classic Homes and their assigns for specific
application to the referenced property. This report is not meant to represent a legal
opinion. No other warranty, express or implied, is made.
It should be noted that Chad Armour relied on information provided by others indicated
previously. Chad Armour can only relay this information and cannot be responsible for
its accuracy or completeness. Also note that assessing wetland hydrology is an inexact
science. Biological professionals may disagree on the mechanics of this function.
Accordingly, the wetland hydrology assessment perFormed for this study, as well as the
conclusions drawn in this report, should be reviewed by the appropriate permitting
authority prior to committing to detailed planning and design activities.
Any questions regarding our work and this report, the presentation of the information,
and the interpretation of the data are welcome and should be referred to the
undersigned.
Sincerely,
Chad Armour, LLC
Chad Armour
Principal
Attachments:
References
Attachment A— Figure 4
— Figure 9
— Figure 11
C:IESM/Rose/Wetland Hydrology Report(rev).doc 3 11/18/10
Chad Armour, LLC
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,,`ti '
Geotechnical Report
Prepared by: Pacific Geo Engineering, LLC
Date: 2/15/2007
i
� GEOTECHNICAL ENGINEERING STUDY
I
For
�
I UNION AVENUE PROPERTY
RENTON, K1NG COUNTY, WASHINGTON
�
(
Prepared For
�
AMERICAN CLASSIC HOMES, LLC ,
P.O. BOX 1830
RENTON, WA 98055
Prepared By
Pacific Geo Engineering, LLC
P.O. BOX 1419
ISSAQUAH, WASHINGTON 98027
PGE PROJECT NUMBER 0701146
February 15, 2007
�acific Geo Engineering LLC
Geotechnical Engineering, Consulring & Inspection
February I 5, 200 i
American Classic Homes, LLC
P.O. Box ]83U
Renton, WA 98055
Attn.: Mr. Michael Gladstein
Re: Geotechnical Engineering Stud��
Union Avenue Property
230, 242, & 224 Union Avenue '�E
Renton, King County; Washington
Parcel Nos. 518210-0068, -0069,-0073,-0079,-0081
PGE Proiect No. 0701146
Dear Mr. Gladstein:
Pacific Geo Engineering, LLC (PGE) has completed a Geotechnical Engineering study for
the referenced project. This report includes the results of our subsurface exploration and
engineering evaluation, and provides recommendations for the geotechnical aspects of the design
and development of the project.
We trust the infonnation presented in this report is sufficient for your current needs. VVe
appreciate the opportunity to pro��ide the geotechnical services at this phase of the project and ]ook
forward to continued participation during the design and construction phase of this project. Should
you have any questions or concerns, which have not been addressed, or if we may be of additional
assistance, please do not hesitate to call us at 425-218-9316 or 425-643-2616.
Respectfully submitted, "
Pacific Geo Frtgineering, �LC ��V�
�w �
�, ���
SQ�� � �
� �
Santanu Vlo�var, MSCE, P.E. �'
� 37;�3
�`�f�NAL
D:`,Gcc�ccl;nical,.�00?-pro;'�.07�1 I a6rP; p�—O I—O S
P.O .Box 1419 . Issaquah . WA . 98027 . (Tel) 425-643-2616 . (Fax) 425-643-0436
TABLE OF CONTEITS
Page No.
1.0 IVTRODUCTIOn.............................................................................................................................................. ]
Z.0 PROPOSED DEVELOPME?�'T...................................................................................................................... l
?.0 SCOPE OF SERVICES..................................................................................................................................... 2
3 1 Field Im�estigation............................................................................................................................... 2
;.2 Laboratory Testing.............................................................................................................................. 3
�.s EngineeringEvaivation....................................................................................................................... 3
4 0 SL'RFACE AiVD SUBSURFACE FEATURES.............................................................................................. 4
4 1 Site Location......................................................................................................................................... 4
-i ? Site Descriptions................................................................................................................................... 4
-"� 3 Reeional Geology ................................................................................................................................. 5
-I.4 Soil Descriptions per Soil Conservation Survey(SCS)Map ............................................................. 5
�.� Visual Soil Descriptions........................................................................................................................ 6
�.6 Groundwater Conditions....................................................................................................................... 7
_ ..
`.�_, CON Al\ : � A ......................................................................................... 7
5.1 General................................................................................................................................................ 7
�.2 Site Prepararion.................................................................................................................................. 9
5.2.1 Clearing and Grubbing........................................................................................................ 9
�.2.2 Subgrade Prepazation.......................................................................................................... 10
5.2.3 Reuse of On-Site Soils......................................................................................................... 10
5.2.4 Dry Vi'eather Construction................................................................................................... 11
5.2.5 Wet Weather Constnzction.................................................................................................. 11
5.2.6 Structural Fills..................................................................................................................... 12
5.2.7 Fill Placement&Compaction Requirements.............................................................
......... 13
�.2.8 Temporary Excavation Slopes .......................................................................................... 13
�.2.9 Permanent Cut and Fill Slopes ........................................................................................... 16
5.2.10 Construcrion Dewatering................................................................................
.................... 16
5.2.11 Construction Monitoring..................................................................................................... 16
�.� Foundation Recommendations............................................................................................................ 17
�.4 Floor Slabs........................................................................................................................................... 18
� � Site Drainage....................................................................................................................................... 19
ti.6 litiliry Support and Backfill................................................................................................................ 19
ti.- Pavement Thickness............................................................................................................................ 21
�.8 Geologic Hazards................................................................................................................................ 22
� 8.1 Erosion Hazard..................................................................................................................... 22
5.8.2 Seismic Hazard..................................................................................................................... 22
5.8.3 Landslide Hazard.................................................................................................................. 23
5.9 Infiltrarion Potential Evaluation ......................................................................................................... 23
6.0 REPORT LIMITATIONS................................................................................................................................ 24
?.0 ADDITIONAL SERVICES............................................................................................................................... 24
i
LIST OF FIGURES LIST OF APPENDICES
Figure 1 Vicinity Map Appendix A Soil Test Pit Logs
Figure 2 Preliininary Plat Plan Appendix B Laboratory Test Results ��
Figure 3 Topographic Survey& Exploration Plan '
Figure 4 Soi] Consen�ation�1ap
(ii)
Pacific Geo Enqineerinq, ttC
Geotechnica�Eraineerinp, Consui,abon&Inspecticn
Union Avenue Propern
Project No Q?01 1�16
Februarv 15. 24(1?
Page 1 of<4
1.0 I\TRODL:�CTIO'�
This repart presents the findings of our subsurface exploration and geotechnical engineering
evaluation for a proposed residential development, to be located in Renton, King County, VVashington.
The general location of the site is show�n on the Vicinity Map, Figure 1. This study was accomplished in
general accordance with our proposal No. 701199, dated January 10, 2007, and was granted to proceed b}�
w�-itten authorization of Mr. I�•'Iichael Gladstein on the same day.
2.0 PROPOSED DEVELOPAZE�'T
The development plan calls for constructing a residential community with several single-family
residences and associated drive�vays and road���ays. Based on the preliminary p�at plan prepared by ESM
the site encompasses approximately 4 acres of land. A total of 27 dwelling units will be built in the
subject development. A storm vault system will be built at the southeastern comer of the site by cut into
the present grades to manage the stormwater runoff of the proposed development. The proposed ]ots,
roads, and the storm vault are shown on the Preliminary Road, Grading and Utility Plan, Figure 2.
Based on our experience with similar projects, we anticipate that the houses will be double-story
wood-framed structures with loading carried primarily by a system of bearing walls. We expect bearing
«-all loads will be in the range of 2 to 3 kips per lineal foot, isolated column loads in the range of 30 to 40
kips, and slab-on-grade floor loads of 150 pounds per square foot (ps fl. We further expect that the first
floor levels of the buildings will be constructed at grade or framed over a crawl space area.
Based on the Preliminary Road, Grading and Utility Plan, Figure 2, we understand that the site
will have some cuts and fills to achieve the final grades. Based on this plan, there will be minor cuts of
approximately 2 to 4 feet along the proposed Road C between Lot 9 and 16 to reduce the existing slopes
to milder gradients. Also, in other areas of the site there will be some minor cuts in the range of 2 to 4
feet to achieve the fina] lot grades. There will be regarding of the existing slopes in lot 25, 26, and 27
area located along the eastern edge slope of the site. The proposed development will include several
asphalt-paved driveways. We anticipate vehicle traffic will primarily consist of passenger cars and
oecasional waste management trucks.
The conclusions and recommendations contained in this report are based upon our understanding
of the above design features of the development. We recommend that PGE should be allowed to revie��-
the final grades and the actual features after the final construction plans are prepared so that the
conclusions and recommendations contained in this report may be re-evaluated and modified; if
necessary.
Pacific Geo Enc7ineerinq, LLC
Geo[echnica!fnqinee�inq,Consul[ation&Inspec[ion
linion Avenue Property
Project T�o. 070t 146
February 15,200 i
Page 2 of 24
3.0 SCOPE OF SERVICES
The purpose of this study��ras to evaluate the geotechnical aspects of the proposed development,and
to identify and address the geotechnical issues that may impact the proposed site development. The scope of
this geotechnical study included field explorations, laboratory testing, geologic literature revie«-, and
engineering evaluation of the field and laboratory data. This study also included interpretation of this
information to generate pertinent geotechnical recommendations and conclusions that may be used for the
design and construction of the development.
The scope of our work did not include any wetland study, or any environmental analysis or
evaluation to find the presence of any hazardous or toxic materials in the soil, surface water;groundwater,or
air in or around this site.
3.1 Field Investigation
We explored the surface and subsurface conditions at the project site on Januaiy 19, 2007. Seven i,
(7) test pits were excavated to depths of about 6 to 10 feet below the existing grades, and were backfilled
with loosely compacted excavated soils.
The test pits were completed using a backhoe provided by a subcontractor. The specific number,
locations, and depths of the test pits were selected in relation to the existing and proposed site features,
accessibility, underground utility conflicts, purpose of evaluation, and budget considerations. The
proposed locations of the test pits were estimated by measuring from existing site features and should be
considered accurate only to the degree implied by the method used. The approximate test pit locations are
shown on the Boundary and Topographic Survey and Exploration Plan, Figure 3.
A professional geotechnical engineer from our firm observed the excavations, continually logged
the subsurface conditions in each test pit, collected representative bulk samples from different soil layers;
and observed pertinent site features. Samples were designated according to the test pit number and depth,
stored in watertight plastic containers, and later on transported to our laboratory for further visual
examination and testing.
Results of the field investigation are presented on the test pit logs, which are presented on Pages
A-1 through A-4 of Appendix A. The final logs are modified based on the interpretation of our field logs,
laboratory test results, and visual examination of the samples in the laboratory.
Pacific Geo Enuineerinq, LLC
Geofechnical Enoineerinq,Consultatfon&Inspecfion
Union.Avenue Property
Praject No. 0701 146
February I5,2007
Page 3 of 24
3.2 Laborator�� Testing
The bulk samples ���ere visually classified in the field and laboratory, and later on supplemented
by grain size analyses to evaluate the general physical properties and engineering characteristics of the
soils encountered. Sieve analysis «�as performed on one (1) selected samples in accordance with the
ASTM D-422 and D-2487 pr�cedures. The result of the sieve analysis with the USCS classification of
the soil is presented on the grain-size distribution graph B-1 enclosed in Appendix B.
3.3 Engineering Evaluation
The results from the field and laboratory tests were evaluated and engineering analyses ���ere
performed to provide pertinent information and recommendations on the following geotechnica] aspects of
the proposed site development:
• Soil and groundwater conditions of the site.
• Foundation types and allowable bearing capacity for supporting the proposed residences.
• Settlement due to the recommended bearing capacity and observed soil conditions.
• Frictional and passive values for the resistance of lateral forces.
• Subgrade preparation for slab-on-grade. '
• General recommendations on retaining walls.
• Earth�vork, including site preparation, excavation, and placement of compacted fill.
• Use of the on-site soils as structural fill.
• Dry weather construction.
• Wet weather construction.
• Seismic design considerations, including the site coefficient per 1BC 2003.
• Site drainage including permanent subsurface drainage systems and temporary ground«�ater
control measures, if necessary. '
• Erosion control.
• Geologic hazards: as per the City of Renton Critical Area Ordinances.
• Infiltration potential of native soils.
_ -�
Pacific Geo Enqineerinq, c�c
Geotechnica/Enqineerinq,Consultation&lnsp=cfion
Union ,4��enue Property
Project No. 0701 146
February I5;2007 ,
Paee 4 of 24 '
4.0 SURFACE AND SUBSURFACE FEATURES 'I
4.1 Site Location I�'
The proposed development is to be located at 230, 242, and 224 Union Avenue NE in Renton,
king County, Washington. The legai description of the site is N�� �4 oT N�iV 'i< of Section I5, Township
23 N, and Range 5 E. The parcel numbers recorded for the site are 518210-0068, -0069; -0073, -0079,
and -0081. The north boundary of the site is bounded partially by residences and partly by existing storm ,
pond, the south boundary by I�TE 2nd Place, the west boundary by Union Avenue NE, and the east I
boundan� Lv a strezm. The �eneral location of the si:e is sho��:, o:: the ��'icini�� \9�p. Figure 1.
4.2 Site Descriptions
The project site is located «rithin a region dominated by residences. The majority of the site is �
currently open and used as pasture areas covered with grasses and few scattered trees, and the remaining i
areas of the site are occupied with several structures used for residential purposes. The site has an access 'I
via a gravel driveway from the Union Avenue':�TE. '
The majority of the site is almost level ground, except the southwestern areas, where the site has
higher ground areas relative to the remaining portions of the site. The site, in general, slopes downward '
to its south and east boundary. The east edge of the site has slopes that run down to the stream located '
east of the site. I
Based on the topography of the site, prepared by ESM, and represented in Figure 3, the genera] I'I
elevations in the level ground areas of the site range approximately from 398 feet to 402 feet, and the
elevations in the higher ground areas range from 410 feet adjacent to the Union Avenue NE to
approximately 402 feet around the toe of the higher g-round areas. Based on the elevation differences
across the toe of the higher ground areas the native grades have drops in the range of 6 to 10 feet and the
slopes along the eastern edge have drops in the range of 6 to 14 feet. These drops have generated
gradients of approximately 6 to 50 percent. The above elevations and the associated drops and the
gradients across the site are sho�;�n on Figure 3.
During our field study, we attempted to notice the firmness and the stability of the slopes along
the higher ground areas as well as any evidences of geologic phenomena like previous landslides, erosion,
and presence of any groundwater seepage or streams across the slopes. No such phenomena were visible
on the slopes at the time of our observations of the slopes. Based on our visual observations of the soils
in the exploratory test pits the slopes are appeared to be stable and firm at their present conditions.
However, due to the dense nature of the vegetations it was not possible to make such observations along
the slopes of the eastern edge of the site.
Pacific Geo Enaineerinq, LLC
. Gecfechnica/Enqineerinq, Consultation&Inspecfion
Union Avenue Property
Project No. 0701 146
February 1 S, 200 i
Paee 5 of 24
4.3 Regional Geology
The site is in the Puget Sound Lowland, a north-south trending structural and topographic
depression lying between Olympic Mountains on the west and Cascade Mountains on the east. The
lowland depression experienced successive glaciation and nonglaciation activities over the time of
Pleistocene period. During the most recent Fraser glaciation, which advanced from and retreated to
British Columbia between 13,000 and 20,000 years ago, the ]owland depression was buried under about
3,000 feet of continenta] glacial ice. During the successive glacial and nonglacial intervals, the lowland
depression, which is underlain by Tertiary volcanic and sedimentary bedrock, was filled up above the
bedrocks to the present-day land surface with Quaternary sediments, which consisted of Pleistocene
glacial and nonglacial sediments. The glacial deposits include concrete-like lodgement till, ]acustrine silt,
fine sand and clay, advance and recessional outwash composed of sand or sand and gravel, and some
glaciomarine materials. The nonglacial deposits include largely fluvial sand and gravel, overback silt and
clay deposits, and peat attesting to the sluggish stream environments that were apparently ���idespread
during nonglacial times.
4.4 SCS Soil Descriptions
According to the United States Department of Agriculture Soil Conservation Survey (SCS} for i
King County, VVashington, the site of its upper 60 inches consists of the soil units `Alderwood Gravelly �,
Sandy Loam (AgC)'. The site location with respect to the horizontal boundaries of the above soil unit is ;
shown on the Soil Conservation Map, Fig. 4. A typical soil profile for these units are as follo���s: �I
Table 1: Alderwood Gravelly Sandy Loam (AgC)
Depth, inch USDA Texture USCS Soil Definition
0— 27 Gravelly sandy loam SM
27 Weakly to strongly consolidated till
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4.5 �'isual Soil Descriptions
The average thicicness of the topsoils ���as found about 6 inches; which was composed of bro«-n
silt «ith roots and organic materials.
Tcst Pit I, 2, and 6
The topsoi]s �vere underlain by grayish brown silty sandy gravels that extended upto
approximately 5 feet below the existing grades. This deposit was then underlain by bluish gray tills in
Test Pit 1 and 2. In Test Pit 3; the topsoils ��rere underlain by tills. The tills were continued upto the
bottom of the test pits. The deposits aUove the tills w�ere medium dense and the tills were partly cemented �i�
and very dense. The soils «�ere in moist conditions. I
"I'est Pit 3, 4, 5, and 7 '
The topsoils were underlain by fills consisted of decayed wood debris, concrete and asphalt
chunks, and metal and plastic pieces. The fills had strong organic odor, and were in moist and medium
dense conditions. It should be noted that in Test Pit 7,the fill within its bottom 2 feet depth was consisted
of«�et and soft silt containing significant amounts of decayed wood debris. The fill thiclrness varied from I
6 to 10 feet below the existing grades. In our opinion, the fills are considered to be of uncontrolled
nature. �
The fills in Test Pit 5 and 7 were underlain by native soils consisted of very dense bluish gray
tills, which continued upto the bottom of the test pits. However, in Test Pit 3 and 4, the fills were
continued upto the bottom of the test pits therefore the depths of the fills in these test pits were unknown
during our exploration. The actual depths of the fills in the vicinity of these test pits should be
determined when the construction ���ill talce place in this site. The depths of fills in the test pits are shown
on Figure 3.
During our field explorations we had an opportunity to converse with one of the dweller of this
properry, and according to his recollection we came to lrnow that at some point in the past fills were
brought in into this site and «�ere placed primarily where the fills were encountered during our
explorations.
The preceding discussion on the subsurface conditions of the site is intended as a general review
to highlight the major subsurface stratification features and material characteristics. For more complete
and specific information at individual test pit locations, please review the Test Pit Logs (Pages A-1
through A-4) included in Appendix A. These logs include soil descriptions, stratification, and location of
the samples and laboratory test data. It should be noted that the stratification lines shown on the
individual loQs represent the approximate boundaries bet«reen various soi] strata; actual transitions may
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Geofechnrcal Enc:neerinq,Consul:a6on&Inspec[;on
Union Avenue Property
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be more gradual or inore severe. The subsurface conditions depicted in the logs are for the test pit
locations indicated only, and it should not necessarily be expected that these conditions are representative
at other locations of the site.
4.6 Ground�izater Conditions
No �-oundwater or seepage was encountered in Test Pit 1, 3, 4, and 5. However; minor perched
water seepage was encountered in Test Pit 2 and 3, and heavy seepage was encountered in Test Pit 7.
It is to be noted that seasonal fluctuations in the groundwater elevations and the variations in the
presence of perched water seepage in the permeable loams may be expected in the amount of rainfall,
surface runoff, and other factors not apparent at the time of our exploration. Typically, the groundwater
levels rise higher and the seepage flow rates increase during the wet winter months in the Puget Sound
area. The possibility of groundwater level fluctuations and the presence of perched water must be
considered when designing and developing the proposed development and the stormwater management
system in this site.
5.0 CONCLUSIONS AND RECOMMENDATIONS '
5.1 General
As mentioned above, portion of the site has native soils at the present grades and portion of the
site has existing fills at the present grades. Depending on such conditions the following recommendations
are provided.
Existing Fill Areas (Test Pit 3, 4, 5, and 7)
Based on the findings of our field explorations, the portion of the site is underlain by fills of
approximately 6 to 10 feet thiclrness above the native soils. The fills are considered uncontrolled in
nature because of the presence of significant amounts of debris in the fills. Based on our engineering
evaluation the existing fills under the sustained loadings from the new buildings and any ne«� fills may
undergo some amount of differential settlement due to the rearrangements of the debris. Due to the
uncontrolled nature and varying depths of the existing fills across the site the amount of differential
settlement cannot be computed accurately, and also the amount of such settlement are expected to be
variable across the fill areas. Considering the above geological factor, and the current development plan
of the site, «re evaluated the follo«�ing foundation options, which may be considered feasible for ,
supporting the residences in this site. The options are discussed below.
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O�tion i: Shallo��- spi-ead footings on existing fills
The building footings could be placed on the ehisting fills considering the possibility o: the
differential settlement of the footings of unlmown amount as described above. Therefore, if this option is
cliosen then the owner and the contractor must be willing to assume some risks associated with the impact
of such settlement of the existing fills to the building footings. As a result; such settlement related impact
might adversely affect the performances of the buildings during the life of these structures.
The amount of differential settlement of the buildings could be reduced if the footings are ali tied
up lilce a framed structure using a grade or tie beam. We recommend that the structural engineer must
consider the possibility of such differential settlement and provide adequate reinforcement in the footings
to account for such settlement.
Option 2: Shallow spread footings on new fills
Alternative to the above option, the problem associated «-ith the differential settlement of
unlcnown amount may be eliminated by supporting the footings on the new structural fills placed above
the finn native soils. In this option, we recommend that the existing fills underneath the footing areas
must be overexcavated completely upto the firm native soils and then backfilled the void areas with ne�v
adequately compacted structural fills upto the final footing subgrades. The footings should then be placed
on the new �lls. It should be noted that the depth of the overexcavation would be determined during the
actual construction of the footings based on the fill thiclrness encountered at a particular footine area.
Option 3: Removal of all existing fills from the site
Another option to eliminate the possibility of differential settlement of unlrnown amount is to
overexcavate the existing fills from this site completely upto the firm native soils and then backfill the
void areas with new adequately compacted structural fills placed upto the final footing subgrades. The
footings, pavements and any additional ne«�fills may then be placed above the new fills.
Similar to the footings, the floor slabs, the pavements; and any additional new fills placed above
the existing fills may also undergo some amount of differential settlement however with lesser degree in
comparison to the footings. �We recommend that a thorough proofrolling with a loaded dump truck must
be done prior to considering the placing of floor slabs, pavements, or new additional fills above the
existing fills. For first two options, the floor slabs could be of either slab-on-grade type or of structural
type depending on the amount of risks and the impact associated «�ith the differential settlement of the
existing fills on the floor slabs could be taken by the owrner and the contractor.
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We recommend that the edge of the existing fill embankment along the stream should be rebuild
by removing the existing fills completely and then replaced with ne�v adequately compacted structural
fills upto the desired final grades. The rebuilding��-idth should be determined based on the fill conditions
encountered during the actual construction to be taken in this area. V�'e belie��e that the existing fills along
the edge of the embanlanent «�ere possibly not compacted adequately. Therefore, the possible inadeq_uate
coinpaction accoinpanying with the saturated condition of the existing fills due to their proximiry to the
stream may cause the existing fill embankment edge to fail or slide during the construction activities, or
under the loadings of new buildings or any new additiona] fills placed adjacent to the existing fill
embankment edge.
We recommend that the decision of removal depths of the existing fills in this site would be
determined during the mass grading activities by a representative of PGE.
Native Soil Areas (Test Pit 1, 2, and 6)
In native soils areas of the site, the footings, the floor slabs,the pavement, and any new additional
fills may be placed on the firm native grades following the site preparation procedures described in the
following section 5.2. The native soils are very dense in condition therefore they are capable of providing
adequate support for the above structures. The proposed residences may be suppo�ted on conventional
shallow footing foundations placed above the firm native soils or on the new structural fills placed over
the firm native soils. The floor slabs if slab-on-grade type is chosen may also bear on similar type of soils
described above.
The remainder of this section (5.0) presents specific engineering recommendations on the
pertinent geotechnical aspects that are anticipated for the design and construction of the proposed
development. These reconvnendations should be incorporated into the final design and drawings, and
construction specifications.
5.2 Site Preparation !
Preparation of the site should involve removal of existing structures, temporary drainage, II'�
clearing; strip�ing, cutting, filling, exca�-ations, dewatering, and subgrade proofrolling. The following �
paragraphs provide specific recommendations on these issues. I
5.2.1 Clearing and Grubbing �
Initial site preparation for construction of new buildings and driveway areas should include �
stripping of vegetation and topsoil from the site. Based on the topsoil thickness encountered at our test pit '
locations, we anticipate topsoil stripping depths of about 6 inches, however, thicker layers of topsoil may
Ue present in unexplored portions of the site. It should be realized that if the stripping operation takes �
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place during wet winter months, it is typical a greater stripping depth might be necessary to remove the
near-surface moisture-sensiti��e soils disturbed during the stripping; therefore, stripping is best perforn�ed
dui-ing dry weather period. Stripped vegetation debris should be removed from the site. Stripped organic
topsoils will not be suitable for use as structural fill but may be used for future landscaping purposes.
5.2.2 Subgrade Preparation
After the site clearing and site stripping, cut and fill operations can be initiated to establish
desired pavement and building grades. Any exposed subgrades that are intended to provide direct support
for new construction and/or require new fills should be adequately proofrolled to evaluate their condition.
Proofrolling should be done with a loaded dump truck or front-end loader under the supervision of a
geotechnical engineer from PGE, and/or must be probed with a T-probe by the geotechnical engineer to
identify the presence of any isolated soft and yielding areas and to verify that stable subgrades are
achieved to support the buildings, driveways, and the new �lls. If any subgrade area ruts and pumps
excessively and cannot be stabilized in place by compaction, the affected soils should be over-excavated
completely to firm and unyielding suitable bearing materials, and replaced with new structural fills to
desired final subgrade levels. If the depth of overexcavation to remove unstable soils becomes excessive,
a geotextile fabric, such as Mirafi SOOX or equivalent in conjunction with structural fills may be
considered. Such decision should be made on-site by a geotechnical engineer from PGE during the actual
construction of the project.
The loosely backfilled soils in the areas of exploratory test pits should be overexcavated
, completely upto the firn� native soils and backfilled with adequately compacted nev�� structural fills upto
the final grades. If any underground utilities are encountered or are to be abandoned those lines should be
plugged in order to prevent the lines from becoming conduits for the infiltration of water under the
, building area. Tree stumps and large root balls should be removed completely and backfilled with new
structural fills to the desired subgrade levels.
5.2.3 Reuse of On-Site Soils
The ability to use native soils obtained from the site excavations as structural fills depends on the
gradation, moisture content of the soils; and the prevailing weather conditions exist during the grading
activities. As the fines content (that portion passing the U.S. No. 200 sieve) of a soil increases, it
becomes increasingly sensitive to small changes in moisture content, and adequate compaction becomes
rnore difficult or impossible to achieve. Soils containing more than about 5 percent fines by weight
cannot be consistently compacted to the recommend degree when the moisture content is more than about
2 percent above or belo��� the optimum.
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The near-surface native soils in this site contain a significant percentage of�nes (24%), and are
thei-efore considered moisture sensitive soils. These soils may be used as structural fill only during the
dry season and if the optimum moisture content of these soils can be maintained during the compaction.
Because of the higher fines content, these soils wil] pose problems during their compaction if they are
used as structural fill during the ���et season. During wet weather periods, typically between October and
May, increases in the moisture content of these soils can cause significant reduction in the soils strength
and support capabilities. In addition, when these soils become wet they may be slo«� to dry and thus
significantly retard the progress of grading and compaction activities. It ���ill; therefore, be advantageous
to perforn� the earthwork consh-uction activities, during the dry season, typically from July through
September, so that earthwor]<costs can be significantly reduced over wet weather construction.
In the event that ���hether the fill materials are to be imported to the site, or if on-site soils are to
be reused as a fill, we reconunend that the potential fill materials be verified and approved by the project
geotechnical engineer prior to their use.
5.2.4 Drv ��'eatlier Construction
The presence of high fines content (24%) in the near surface soils may contribute erosion related
proUlems in this site. This may particularly happen, ���hen uncontrolled surface runoff is allowed to flow
over unprotected excavation areas during the wet winter months. We therefore recommend that the
proposed construction be completed during the dry season of the year. This will help eliminating erosion ,
related problems.
5.2.5 VVet Weather Construction
If the construction takes place during the wet weather, the near surface silty soils will be found
vei�� ��ret and disturbed; and these soils could not be adequately compacted. Therefore, it may be
necessary to adopt some remedial measures to enhance the subgrade conditions in this site if the
construction takes place in the winter. The contractor should include a contingency in the earthwork
budget for this possibility. The appropriate remedial measure be best determined by the geotechnical
engineer during the actual construction of the project. The following remedial measures may be
considered in this regard:
(i) the earth contractoi- must use reasonable care during site pt-eparation and excavation so that the
subgrade soils are remain firm, unyielding, and stable
(ii) removal of the affected soil to expose suitable bearing subgrades and replacemen: «�ith
imported free-draining materials as structural fills that can be compacted.
(iii) aeration of the surficial materials during favorable dry weather by methods such as scariTying
or windrowing repeatedl} and expose to sunlight to dry near optimum moisture content prio:- to
placement and compaction
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(i�-) chemical modification of the subgrades �vith admixtures like hydrated lime or Portland
cement; depending on the soi] type.
(v) mechanical stabilization ��-ith a coarse crushed aggregate (such as sand and gravel, crushed
rock, or quarry spalls) compacted into the subgrade, possibly in conjunction «rith a geotextile
fabric. such as Mirafi SQOX.
In the event earth��-ork takes place during the wet season, we recommend that special
precautionary measurements shoulci be adopted to minimize [he impact of water and construction
activities on the moisture sensitive soils. It is recorrunended that earthwork be progressed part by part in
small sections to minimize the soil's exposure to wet weather. Traversing of construction equipment can
cause considerable disturbance to the exposed subgrades, therefore; should be restricted within the
specific drive areas. This will also prevent excessive widespread disturbance of the subgrades.
Construction of a new working surface from an advancing working surface could be used to a��oid
trafficking the exposed subgrade soils. Any excavations or rei�noval of unsuitable soils should be
immediately followed by the placement of backfill or concrete in footings. At the end of each day, no
loose on-site soils and exposed subgrades be left uncompacted or properly tamped, which will help seal
the subgrade and thereby to minimize the potential for moisture infiltration into the underlying layers of
fil]s or subgrades.
In case site filling must proceed during wet weather the contractor should include a contingency
in the earthwork budget for the possibility of using imported clean, granular fill instead of the on-site
native silty soils. For general structural fill purposes, we recommend that using well-graded sand and
�-avel, such as `Ballast' or `Gravel Bon-ow' per WSDOT Standard Specifications 9-039(1) and 9-
03.14(1), respectively. Alternatively, `free-draining' soil similar to the one described in the following
section (5.2.6; Table 6) may also be considered suitable as filling material for the wet weather
construction. This type of fill refers to soils that have a fines content of 5 percent or less (by ���eight)
based on the minus '/<-inch soil fraction.
5.2.6 Structural Fills
Structural fill is defined as non-organic soil, free of deleterious materials, and well-graded and
free-draining granular material, with a maximum of 5 percent passing the No. 200 sieve by weight, and
not exceeding 6 inches for any individual particle. A typical gradation for structural fill is presented in
the following table.
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Table 2: Structural Fill
U.S. Standard Sieve Size Percent Passing by Dr����'eight
3 inch 100
'/4 inch 50—100
No. 4 25 —65
No. 10 10 —SO
'�o. 40 0 —20
No. 200 5 Maximum*
* Based on the'/4 inch fraction.
Other materials may be suitable for use as structural fill provided they are approved by the project
geotechnica] engineer. Such materials typically used include clean, well-graded sand and gravel (pit-run);
clean sand; various mixtures of gravel; crushed rock; controlled-density-fill (CDF); and lean-mix concrete
(LMC). Recycled asphalt, concrete, and glass, which are derived from pulverizing the parent materials
are also potentially useful as structural fill in certain applications. These materials must be thoroughly
crushed to a size deemed appropriate by the geotechnical engineer (usually less than 2 inches). The top ,
12 inches of compacted structural fill should have a maximum 2 to 3-inch particle diameter and all
underlying fill a maximum 4 to 6-inch diameter unless specifically approved by the geotechnical
engineer.
5.2.7 Fill Placement and Compaction Requirements
Generally, quairy spalls, controlled density fills (CDF), ]ean mix concrete (LMC) do not require
special placement and compaction procedures. In contrast, clean sand, crushed rock, soi] mixtures and
recycled materials should be placed under special placement and compaction procedures and
specifications described here. Such structural fills under structural elements should be placed in uniform
loose lifts not exceeding 12 inches in thiclmess for heavy compactors and 4 inches for hand held
compaction equipment. Each lift should be compacted to a minimum of 95 percent of the soil's
laboratory maximum dry density as determined by ASTM Test Designation D-1557 (Modified Proctor)
method, or to the applicable minimum City or County standard, whichever is the more conservative. The
fill should be moisture conditioned such that its final moisture content at the time of compaction should
be at or near (typically within about 2 percent) of its optimum moisture content, as determined by the
ASTM method. If the fill materia]s are on the wet side of optimum, they can be dried by periodic
windro«�ing and aeration or by intennixing lime or cement powder to absorb excess moisture.
In-place density tests should be performed to verify compaction and moisture content of the fills
and base materials. Each lift of fill or base material should be tested and approved by the soils engineer
prior to placement of subsequent lifts. As a guideline, it is recommended that field density tests be
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perfornled at a frequency of not less than 1 test per 2,000 square feet of surface area per lift in the
buildine and pavement areas.
If field density tests indicate that the last lift of compacted fills has not been achieved the required
pe:-ce,-�t of compaction oi- the surface is pun.ping and weaving under loading, then the fill should be
�canfied, moisiure-conditioned to near optimum moisture content, re-compacted, and re-tested prior to
;�lacing additional lifts.
5.2.8 Temporarv Excavation Slopes
.As we understand from the project plan that the proposed site development does not likely to
imol�-e excavations of any significant depth, with the possible exception of utility trench and the
overexcavation of existing fills if perfom�ed. The o«-ner and the contractor should be aware that in no
case should the excavation slopes be greater than the limits specified in local, state, and federa] safety
regulations, particularly, the Occupationa] Safety and Health Administration (OSHA) regulations in the
"Construction Standards for Excavations, 29 CFR; part 1926, Subpart P, dated October 31, 1989" of the
Federal Register, Volume 54, the United States Department of Labor. As mentioned above, we also
recommend that the owner and the contractor should follow the local and state regulations such as
�t�'SDOT section 2-09.3(3) B, Washington Industrial Safety and Health Act (WISHA), Chapter
49.17RCW, and Washington Administrative Code (WAC) Chapter 296-11 S, Part N. These documents
are to better insure the safety of construction worker entering trenches or excavation. It is mandated by
these regulations that excavations, whether they are for utility trenches or footings, be constructed in
accordance with the guidelines provided in the above documents. ��'e understand that these regulations
are being strictly enforced and, if they are not closely followed, both the owner and the contractor could
be liable for substantial penalties.
S±ability of temporary excavations is a function of many factors including the presence of and
abundance of groundv��ater and seepage, the type and density of the various soil strata, the depth of
excavation, surcharge loadings adjacent to the excavation, and the length of time and weather conditions
while the excavation remains open. It is exceedingly difficult under these unknown and variable
circumstances to pre-establish a safe and maintenance-free temporary excavation slope angle at this time
of the study. We therefore, strongly recommend that all temporary, as ���ell as permanent, cuts and
excavations in excess of 4 feet be examined bv a representative of PGE during the actua] construction to
verify that the recommended slope inclinations in this section are appropriate for the actual soil and
groundwater seepage conditions exposed in the cuts. If the conditions observed during the actual
construction are different than anticipated during this study then, the proper inclination of the excavation
and cut slopes or requirements of temporary shoring should be deternzined depending on the condition of
the excavations and the slopes.
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As a general rule, all teinporary soil cuts greater than 4 feet in height associated with site
regarding or excavations should be adequately sloped back or properly shored to prevent sloughing and I,
collapse. As for the estimation purposes, in our opinion, for temporary excavations within the 8 to 10 feet ,
depths, the side slopes should be laid back at a minimum slope inclination of 3:1 (Horizontal:Vertical).
The recommended inclinations assumes that the ground surface behind the cut slopes is level, that surface
loads from equipment and materials are kept a sufficient distance a«�ay from the top of the slope. If these
assuinptions are not valid, we should be contacted for additional recomrnendations. Flatter slopes may be
required if soils are loose or caving andior ���ater; are encountered along the slope faces. If such
— conditions occur and the excavation cannot stand by itself, or the excavation slope cannot be flattened
because of the space limitations between the excavation line and the boundary of the property, temporary
shoring may be considered. The shoring will assist in preventing slopes from failure and provide
protection to field personnel during excavation. Because of the diversity available of shoring stems and
construction techniques, the design of temporary shoring is most appropriately left up to the contractor
engaged to complete the installation. ��'e can assist in designing the shoring system by providing with
detailed shoring design parameters including earth-retaining parameters, if required.
�'lThere sloped embankments are used, the top of the slopes should be barricaded to prevent
vehicles and storage loads within 10 feet of the top of the slopes. Greater setbacks may be necessary
when considering heavy vehicles, such as concrete trucks and cranes. If the temporary construction
embankments are to be maintained during the rainy season, berms are suggested along the top of the
slopes to prevent runoff water from entering the excavation and eroding the slope faces. All temporary
slopes should be protected from swface water runoff.
The abo�re information is provided solely for the benefit of the owner and other design
consultants, and under no circumstances should not be construed to imply that PGE assumes '
responsibility for construction site safety or the contractor's activities; such responsibility is not being
implied and should not be inferred. Therefore, the contractor is solely responsible for designing and
constructing stable; temporary excavations and should shore, slope, or bench the sides of the excavations ,
as required to maintain stability of both the exca��ation sides and bottom. The contractor's "responsible
person", as defined in 29 CFR Part 1926, should evaluate the soil exposed in the excavations as part of
the contractor's safety procedures.
��e expect that the excavation can be completed using conventional equipments such as
bulldozers or backhoes. �
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5.2.9 Permanent Cut and Fill Slopes
For permanent cut slopes in the native soils the side slopes should be laid back at a minimum
slope inclination of 3:1. �'�There the above slopes are not feasible, protecti�-e facings and�or retaining
structures should be considered. Temporary erosion protection described latter on in section 5.8.1 of this
report should be used until permanent protection is established. Cut slopes should be re-vegetated as soon
as practical to reduce the surface erosion and sloughing.
�L`e recommend that any pennanent fill slope be constructed no steeper than 2H:1 V. To achieve
uniforn� compaction, we recominend that fill slopes be overbuilt slightly and subsequently cut back to
expose well compacted fill. We recommend that a pernlanent berm, swale; or curb be constructed along
the top edge of all permanent slopes to intercept surface flow. Also, a hardy vegetative groundcover
should be established as soon as feasible, to further protect the slopes from runoff water erosion.
Alternatively, permanent slopes could be armored with quairy spalls or a geosynthetic mat. This
recoinmendation is particularly applicable for the new fills to be placed along the eastern edge of the site.
5.2.10 Construction Dewatering
If the regional groundwater levels rise above the planned excavation base during the ���inter and
spring months, the contractor should be prepared to dewater the excavations especially the underground
utility trenches.
If localized (perched) groundwater or minor seepage is encountered, we anticipate that internal
collection ditches directing water inflow to sumpholes and then removal of water by conventional filtered
sump pumps will be adequate to temporarily dewater the excavations and to maintain a relatively dry
���orking area for construction purposes.
The de«�atering must remain in operation to maintain a dry worlcing condition throughout the
construction period in the trenches. If severe water conditions encountered, more specialized dewatering
techniques, such as ��acuum «-ells, well points, etc., may be needed. However, these more extensive
dewatering techniques can lead to settlement of the ground surface in the surrounding vicinity when the
groundwater is drawn down. If such dewatering techniques are contemplated a geotechnica] engineer
should be consulted for specific design and consh�uction recommendations for the excavation areas.
5.2.11 Construction Monitoring
Problems associated with earthwork and construction can be avoided or corrected during the
progress of the construction if proper inspection and testing services are provided. It is recommended that
site preparation activities including but not limited to stripping, cut and filling, final subgrade preparation
for foundation, floor slab, and pavement be monitored by a representative from our firm. PGE can assist
Pacific Geo Enqineerinq, LLC
Geo[echnical Enqineenrlq,Consul[atior,&Inspecfion
l;nion.Avenue Proper:y
Project No. 0701 146
February I�, 20a i
Paec I?of 24 �
the o��-ner before construction begins to develop an appropriate monitoring and testing plan to aid in
accomplishing a fast and cost-effective construction process.
5.3 Foundations Recommendations
S�read FootinQ
Based on the subsurface conditions encountered in our test pits, it is our opinion that the proposed
residences can be supported on conventional shallow strip and spread footings. The footings may be
supported on the soils described in pre��ious sections 5.1 and 5.2.2 of this report.
The new structural fills may be consisted of���ell-graded sands and gravels, such as `Ballast' per
WSDOT Standard Specifications 9-039(1), or uniformly graded crushed rock, such as `Crushed
Surfacing Base Course' per WSDOT Standard Specifications 9-03.9(3), structural fills described earlier in
section 5.2.6 (Table 6}. If the construction takes place during dry summer period and if the optimum
moisture content of these soils is maintained during the compaction the on-site silty soil could also be
used as building pad materials. All bearing pad soils should be compacted to at least 95 percent of the
Modified Proctor maximum dry density value (ASTM:D-1557). Controlled density fills (CDF) and lean
mix concrete (LMC) should be used ior higher bearing pressure (more than 2�00 ps fl footing in order to
maintain adequate bearing capacities.
' For the design of shallo��� footing foundation supported on the firm native soils or properly
compacted ne��� structural fills placed above the firm native soils ���e recommend using a maximum net
allowable bearing capacity of 2,500 pounds per square foot(psfl. For short-term loads, such as wind and
seismic, a 1/3 increase in this allo���able capacity can be used. We recommend that continuous footings
� have a minimum width of 12; 15, and 18 inches for 1-, 2-, and 3-strory residential structures as presented
in the Table 1805.4.2 of 2003 Intemational Building Code (IBC). `�Je recommend a minimum width of
24 inches for the individual column footings.
Based on our settlement potential evaluation of the footings placed on the firm native soils or on the
properly compacted new structural fills placed above the firm native soils, we anticipate that properly
designed and constructed foundations supported on these soils should experience total and differential
settlements of less than 1 inch and 1/2 inch; respectively. Most of these settlements are expected to occur
invnediately following the building loads are applied. The predicted settlement values may be expected
larger if soft, loose, organic soil is encountered, or if the foundation subgrade is disturbed and becomes soft
during construction. The settlement evaluation was done without the aid of any laboratory consolidation test
data,and on the basis of our experience with similar types of structures and subsoil conditions.
Pacific Geo Enqineerinq, tcc
Geo:echrica!Enqrneermq Cersultation 8 Inspecbe�
Union Avenue Property
Project No. 0701146
February I 5; 2U0 i
Page I 8 of 24
Lateral foundation ]oads can be resisted by friction between the foundation base and ,he
supporting soil, and by passive earth pressure acting on the face of the embedded portion of the
foundation. We recommend using a coefficient of friction of 0.4 to calculate friction between the
concrete, and the native soils or the structural fills. For passive earth pressure, the available resistance
may be dete�n�ined using an ec�uivalent fluid pressure of 300 pcf, ���hich includes a factor of safery of ].5.
This value assumes the foundations are cast "neat" against the undisturbed native soils or structura] fills
placed and compacted as reco�nmend in section 5.2 of this report. We recommend to disregard the upper
12 inches of soil while computing the passive resistance value because this depth can be affected byr
weather or disturbed by future grading activity. To achieve the adequate passive resistance from the
eir�bedded soils as well as for fi-ost and erosion protection, we recommend that all exterior footings must
be embedded at least ]8 inches below the final adjacent outside grades consisted of either the undisturbed
native soils or structural fills placed and com�acted as recommend in section 5.2 of this report. The
interior footings may be embedded only 12 inches below the surrounding slab surface level.
Variations in the quality and strength of these potential bearing soils can occur with depth and
distance between the test pits. Therefore, careful evaluation of the appropriate bearing materials is
recommended at the time of construction to verify their suitability to support the above recommended
bearing pressure. ��'e recommend that a PGE representative examine the bearing materials prior to
placing forms or rebar.
The footing bearing pads if constructed with new structural fills need to be extended beyond the
actual outer edges of the footings. This is because footing stresses are transferred outw-ard as well as
downward into the bearing pad soils. All footing bearing pads should extend horizontally outward from
the edge of the footing a distance equal to the bearing pad thickness (1H:1V). This is particularly
applicable if the foundation option 2 described earlier in section 5.1 is chosen. For bearing pads
composed of controlled density fills (CDF) or lean mix concrete (LMC) the horizontal distance should be
at least half of the fill depth. This is particularl}-applicable if the foundation option 2 described earlier in
section 5.1 is chosen.
5.4 Floor Slabs
If slab-on-grade option is chosen for the buildings then the slab-on-grade floors should bear on
the properly prepared subgrades as discussed in previous section 5.1 and 5.2.2. All soil-supported slab-
on-�-ade floors should bear on firnz, unyielding native soils or on suitable properly compacted structural
fill. After subgrade preparation is completed, the slab should be provided with a capillary break to retard
the upv.-ard wicking of ground moisture beneath the floor slab. The capillary break ���ould consist of a
minimum of 6-inch thick clean, free-draining sand or pea gravel. The structural fill requirements
specified in Table 3 could be used as capillary break materials except that there should be no more than 2
percent of fines passing the �io. 200 sieve. Alternatively, `Gravel Backfill for Drains' per WSDOT
Standard Specifications 9-03.12(4) can be used as capillary break materials. Where moisture by vapor
Pacific Geo Engineerinq, ccc
Geotechr,ica/Enqmee�inq Consul[a[ion&Inspec[ion
Union Avenue Property
Project No. 0701 146
February 15, 2007
Paee 19 of 24
transmission is undesirable, ��-e recommend the use of a vapor barrier such as a layer of durable plastic
sheeting (suc11 as Crossstuff, Moistop; or Visqueen) between the capillary break and the floor slab to
pre��ent the up���ard migration of ground moisture vapors through the slab. During the casting of the slab,
care should be taken to avoid puncturing the vapor barrier. At ov�mer's or architecture's discretion, the
membrane may be covered ��-ith 2 inches of clean, moist sand as a `curing course' to guard against
damage during construction and to facilitate uniform curing of the overlying concrete slab. The addition
of 2 inches of sand over the vapor barrier is a non-structural recommendation. Based on the subgrade
preparation as described in section 5.2 of this report, a modulus of subgrade reaction value of about 150
pounds per cubic inch (pci) can be used to estimate slab deflections, which could arise due to elastic
compression of the subgrades.
�.5 Site Drainage
Surface DrainaQe
The final site grades must be such that surface runoff will flow by gravity away from the
structures, and should be directed to suitable collection points. We recommend providing a minimum
drainage �radient of about 3% for a minimum distance of about 10 feet from the building perimeter. A
combination of using positive site surface drainage and capping of the building surroundings by concrete,
asphalt, or low penneability silty soils will help minimize or preclude surface water infiltration around the
perimeter of the buildings and beneath the floor slabs. Driveways should be graded to direct runoff to
catch basins and or other collection facilities. Collected water should be directed to the on-site drainage
facilities by means of properly sized smooth walled PVC pipe. Interceptor ditches or trenches or low
earthen benns should be installed along the upgrade perimeters of the site to prevent surface water runoff
from precipitation or other sources entering the site. Surface water collection facilities should be
desi��ed by a professional civil engineer.
Footing Excavation Drain
VVater must not be allowed to pond in the foundation excavations or on prepared subgrades either
during or after construction. If due to the seasonal fluctuations, ground«rater seepage is encountered
«-ithin footing depths, we recommend that the bottom of excavation should be sloped toward one corner
to facilitate removal of any collected rainwater, groundwater, or surface runoff, and then direct the water
to ditches, and to collect it in prepared sump pits from which the water can be pumped and discharged
into an approved stonn drainage system.
Footing Drain
Footing drains should be used where (1) crawl spaces or basements will be below a structure, (2)
a slab below the outside grade, and (3) the outside grade does not slope downward from a building. The
drains must be laid with a gradient sufficient to promote positive flow to a controlled point of approved
Pacific Geo Enqineerinq, �tc
GeotechNcal EnqLveerinq,ConsuJfation&Inspectren
Union Avenue Property
Project No. 0701 14C
Februan 15. =00�
Page �'i of 24
d�schar�e. The foundatioil d�ains �hould 'oe t:�h:lmed separateiv Tro�n t};e roo?d�ain� .o lhis discharge
point. Footing drains should consist of at least 4-inch diameter perfoi-ated PVC pipe. The pipe should be
placed in a free-draining sand and gravel backfill. Either the pipe or the pipe and free-draining backfill
should be wrapped in a non-woven geotextile filter fabric to limit the ingress of fines. Cleanouts should
be provided. In the flatter areas of the site the d►-ains should be located on the outside of the spread
footings. In sloped areas of the site, the footing drains should be installed at the inner base of the lo���er
perimeter footings and at the outer base of the upper and t�e side perimeter footings.
Downspout or Roof Drain
These should be installed once the building roof in place. They should discharge in tightlines to a
positive, pernzanent drain system. Under no circums±ances connect these tightlines to the perimeter
footing drains.
5.6 Utility Support and Backfill
Based on the soils encountered at the site within the exploration depths; the majority of the soils
appear to be adequate for supporting utility ]ines; ho���ever, softer soils inay be encountered at isolated
locations, where, it should be removed to a depth that will provide adequate support for the utiliry. A
major concern with utility ]ines is generally related to the settlement of trench backfill along utility
alignments and pavements. Therefore, it is important that each section of utility be adequately supported
on proper bedding material and propei-ly bacl<lilled.
It is recon�unend that utility trenchir,g, lnstallation, and backfilling confonn to all applicable
Federal, State, and local regulations such as WISHA and OSHA for open excavations. Utility bedding
should be placed in accordance with manufacturer's recoinmendations and local ordinances. Bedding
inaterial for rigid and flexible pipe should conform to Sections 9-03.15 and 9-03.16, respectively, of the
]994 Vl�'SDOTiAPWA (American Public `�orks Association) Standard Specifications for Road, Bridge,
and Municipal Construction. For site utilities located within the City of Renton right-of-ways, bedding
and backfill should be completed in accordance «rith the Ciry of Renton specifications. As a minimum,
Si8 inch pea gravel or c]ean sand may be used for bedding and backfill materials. The bedding materials
should be hand tamped to ensure support is provided around the pipe haunches. Trench backfill should be
carefully placed and hand tamped to about 12 inches above the crown of the pipe before any hea��}�
compaction equipment is brought into use. The remainder of the trench backfill should be placed in lifts
having a loose thickness of]ess than 12 inches and compacted to 90 percent of the maximum dry density
per ASTM Test Designation D-1557 (Modified Proctor) except for the uppermost foot of backfill ���hich
should be compacted to 95 percent of the maximum dry density per ASTM Test Designation D-I55�
(I�-lodified Proctor).
Pacific Geo EnaineerinA, ttc
Gectechrica/Enqineerirq,Consulta[ro�8 lnspec[ion
Union Avenue Property �
Project No. 0701 146 �
February I5, 2007
Page 21 of 24 ,
The utility trenches should not be left open for extended periods to prevent water entry and
softening of the subgrade. Should soft soils be encountered at the bottom of the trench, it should be i
overexcavated and replaced ���ith select fills. As an alternative to undercutting, a Geotextile fabric or II
crushed rock may be used to stabilize the trench subgrade. Where water is encountered in the trench j
excavations, it should be removed prior to fill placement. Altematively, quarry spalls or pea gravel could '
be used belo«� the water le�-e1 if allowed in the project specifications. ,
5.7 Pavement Thickness I�
:� properly prepared subgrade is very important for the life and performance of the driveway II
pavements. Therefore, we recommend that all driveway areas be prepared as described in section 5.2 of
this report. Subgrades should either be comprised of adequately proofrolled competent undisturbed native '
soils, or be comprised of a minimum of one foot of granular structural fill that is compacted adequately. I
The structural fill should be compacted to 95 percent of the maximum dry density as determined by I
Modified Proctor (ASTM `Test Designation D-1557). It is possible that some localized areas of yielding �
and weak subgrade may still exist after this process. If such conditions occur, crushed rock or other
qualified materials as addressed in section 5.2 may be used to stabilize these localized areas. ��I
We assumed that the traffic would mostly consist of passenger cars and occasional waste I'�
management trucks, which is typical for a residential community. Two h�pes of pavement sections may I
be considered for such traffic, the minimum thicknesses of which are as follows: �',
' I
• 2 inches of Asphalt Concrete (AC) over 2 inches of Crushed Surface Top Course (CSTC) over a �i
' 6 inches of Granular Subbase, or
• 2 inches of Asphalt Concrete (AC) over 3 inches of Asphalt Treated Base (ATB)material.
The 1998 Standard Specifications for Washington State Department of Transpartation (WSDOT)
and American Public Works Association (APWA) should be applicable to our recommendations that
aggregate for AC should meet the Class-B grading requirements as specified in 9-03.8(6). For the
Crushed Surfacing Top Course (CSTC}, we recommend using imported, clean, crushed rock per WSDOT
Standard Specifications 9-03.9(3). For the sub base course, we recommend using imported; clean, well-
graded sa�ld and gravel, such as Ballast or Gravel Borrow per��SDOT Standard Specifications 9-o39(1)
and 9-03.14, respectively. For the asphalt treated base course (ATB) the aggregate should be consistent
«�ith V�'SDOT Standard Specifications 9-Q3.b (2).
Long-term performance of the pavement will depend on its surface drainage. A poorly-drained
pavement section will deteriorate faster due to the infiltration of surface water into the subgrade soils,
thereby reducing their supporting capability. Therefore, we recommend using a minimum surfacir.g
drainage gradient of about 1% to minimize this problem and to enhance the pavement performance. Also,
regular maintenance of the pavement must be considered.
Pacific Geo Enqineerinq, c�c
Gectec'�ical Enqineermq, Censu�fatr;^&:nspe,t,:,:
Union A��enue Propert�:
Project No.07(�; I,G
February I5,2�)'�?
Page 22 of 24
5.8 Geologic Hazards
5.8.1 Erosion Hazard
Uncontrolled surface ��-ater ���ith runoff over unprotected site surfaces during construction
activities is considered the single most important factor that impacts the erosion po�ential of a site. The
erosion process may be accelerated for soils ���ith high fines, especially when construction activities take
place in the wet winter montlls. Taking into consideration of the fines content (24%) in the near surface
native soils, the project site will have severe impact due to erosion. The erosion hazard can be mitigated if
the mass grading activities and the earthwork can be completed within the dry summer period. Also.
measurements such as the contro( of surface water must be maintained during construction, and a tempoi-ar�
erosion and sedimentary control (TESC) plan, as a part of the Best Management Practices (BMP) must be
developed and implemented as ���ell. The TESC plan should include the use of geotextile barriers (silt
fences) along any do���n-slope, stra�;� bales to de-energize downward flow; controlled surface grading,
lim�ted worl< areas, equipment washing, storm drain inlet protection, and sediment traps. A permanent
erosion control plan is to be implemented following the completion of the construction.
5.8.2 Seismic Hazard
Structural design oi� the buildings at the project site should follow 2003 International Buildine
Code (IBC) standards. Based on our evaluations of the subsurface conditions and review of Table
1615.].1 of IBC, we interpret the underlying bearing soils to conespond to `C',which refers to very dense
soils. According to the IBC standards, the mapped spectral response accelerations SS = 1.5 and S, = 0.5,
and corresponding site co-efficient �-alues F, = 1.0 and F,, = 1.3, respectively, should be used far the
design of the buildings.
As part of the seisinic evaluation of the site, the liquefaction potential of the site was also
evaluated. Liquefaction is a phenomenon, which takes place due to the reduction or comp]ete loss of so;l
strengtll due to increased pore water pressure during a major earthquake event. Liquefaction primaril}
affects geologically recent deposits of fine-grained sands that are below the groundwater table. Based or,
the soil and groundwater conditions, it is our opinion that the on-site soils are not prone to liquefactior,
therefore, potential for widespread liquefaction and its associated hazards over the site during a seismic
event is none. Therefore, subsurface conditions do not ���arrant additional mitigation techniques relating
to seismic hazards.
_ _
Pacific Geo Enqineerinq, �LC !
Ge�[ecY,mcal Er,Grneerinc,Corsu'raGor,&InsCectron
L'nion .A�enue Proper,y
Project No. 0701 146 i
February I5, 2007
Paee 23 of 24
5.8.3 Landslide Hazard
As mentioned earlier, the majoriry of the site is almost level ground, with some exceptions in the
southwestern areas and along the east edge of the site, where the present grades have some slopes with
elevations drop in the range of 6 to l4 feet generating gradients of approximately 6 to 50 percent. The
above ele��ations and the associated d►-ops and the gradients across the site are shown on Figure 3.
According to the City of Renton Title IV, Chapter 3, Section 4.3.O�O.J, Geologic Hazards
ordinances, some of the slopes «�ith gradients exceeding 40% and drops less than 15 feet qualify as
sensitive slopes with high ]andslide hazards (LH).
As mentioned earlier in section 4.2, during our field observations the slopes within the site (in
southwestern area) were appeared to be stable and firm at their present conditions. In addition to that, due
to the regarding of the native grades in this area as shown on the Preliminary Road, Grading and Utility
Plan, Figure 2, the native slopes will be reduced to milder slopes from their present gradients. In our ,
opinion, considering the above conditions, the slopes in this area at their present as well as in their post-
consti-tiction conditions would not be considered potentials for any landslide hazard.
As recommended earlier in section 5.1, if the edge of the existing fill embankment along the �',
stream are rebuild then in our opinion the final slopes in this area could be considered not potentials for
any landslide hazard. Due to the criticality involved in regarding the finat grades and rebuilding the fina]
slope in this area we recommend that a PGE engineer must be involved by the owner or the contractor
during such operations to observe and monitor that the recommendations provided in this report are
properly understood, interpreted, and followed.
��'e recommend that houses adjacent to the edge of the existing fill embankments along the
stream must maintain a minimum buffer distance equal to 15 feet from the crest of the edge of the final
fill embankments.
In our opinion, the proposed development is feasible in this site, without anticipating any adverse
impact to the stability of the slopes within the perimeter of the subject site. Our conclusion is based on
the considerations that the recommendations in this report are incorporated and implemented during the
design and the construction phases of the development.
5.9 Infilh-ation Potential Evaluation
The native soils encountered in this site are very low penneable soils. Such characteristic would
hinder the consideration of installing any type of infiltration system in these soils to manage the storm and
rooftop water. Due to the limitations of the native soils, in our opinion, the stormwater facility with
Pacific Geo Enqineerinq, LLC
_ 6ecre� —�F�_-e= ,:�4, co - 'b - --.
llnion Avenue Pro�e�t.
Proiect No. 0701 14C
February I5,20C-
Page 24 of 24
surface storage capability (e.g., detention pond) should be �on�idered fo: manag;r:�� ;he s�o-m��ater �:nd
t'.�e -oo':�top ���ater runoff of the proposed de��e!opmen:.
6.0 REPORT LI�1IT.�TIO\S
The analyses, conclusions, and recommendations presented in this report are based upon the
information available from our subsurface exploration, and project details furnished by the client. If there
are any revisions to the plans for this project or if variations in the subsurface conditions noted during this
study are encountered later on during construction, PGE should be notified immediately of these revisions
and variations so that necessary amendment of our geotechnical recommendations can be made. If such
changes or variations are not notified to PGE, no responsibilin� should be implied on PGE for the impact
of those changes or variations on the project.
PGE wanants that this report including its �ndings, recoinmendations, specifications, or
professional advice has been prepared in accordance with generally accepted professional geotechnical
engineer practices in the ]ocal area. No other warranty, expressed or implied, is made.
This report is the property of Pacific Geo Engineering, and has been prepared for the exclusive
use of American Classic Homes, LLC and his authorized representatives for the specific app]ication to the
proposed development at the subject site in Renton, King Counn, �'Vashington.
7.0 .4llllITIONAL SERVICES
As the geotechnical engineel� of record for the proposed development, PGE should be retained to
perfonn a review of the project plans and specifications to verify that the geotechnica] recommendations
of this report have been properly interpreted and incorporated into the project design and specifications.
PGE should also be retained to provide geotechnical consultation, material testing, and construction
monitoring services during the construction of the project. These services are important for the project to
confinn that the earthwork and the general site development are in compliance with the general intent of
design concepts, specifications, and the geotechnical recommendations presented in this report. Also.
participation of PGE during the construction �vill help PGE engineers to make on-site engineering
decisions in the event that any variations in subsurface conditions are encountered or any revisions in
design and plan are made.
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VICINITY MAP
Nor to scale
Pro,ject No: 070114(i
Date: February 15, 2007 PROJECT Pacific Geo Enqineerinq,LLC
Geotechnicaf Engineering, Consultinq&Inspecfion
Drawn by: SM Union Avenue Property
230, 242, & 224 Llnion Avenue NE Fi�ure 1
Ciient: Amcrican Classic Homes, LLC' Renton, i<ing Cou��ty, Washington
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PREI,iMINARY PLAT PLAN
Not to Scale
Project No.: 070114(
PROJECT Pacific Geo Er�Qineerin ,LLC
Date: February 15, 2007 g
Geotechnical Engineering, Consu/ting&Inspection
Drawn By: SM Union Avcnuc Property
Client: American Classic I�omes, LLC �30, 242, & 224 Union Avenue NE F�Qure 2 �i
Renton, Washington
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BOUNDARY & TOPOGRAPHIC SURVEY, & EXPLORATION PLAN
Not to Scale
LEGEND:
Projcct No.: 0701146
� Approximate Test pate: February 15, 2007 PRO.iECT Pacific Geo EnQineerinq,LLC
Pic r_.oca�ion
Geotechnical Engineering, Consulting&Inspec[ion
Drawn By: SM Union Avenue Property
230, 242, & 224 Union Avenue NF, Figure 3
Client: American Classic Ilo�nes, LLC Renton, wasi�ingto��
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N
SOIL CONSI;RVATION SURVEY MAP
Not. to Scalc
Project No.: 0701146
Date: February 15, 2007 YROJF,CT Pacific Geo Enqineerinq,�cc
Geotechn7cal Engineering, Consulting&Inspection
Drawn By: SM Union Avenue Vroperty ��,
230, 242 & 224 Union Avenue NE Figure 4
Client: American Classic Homes, LLC Renton, King County, Washiti�ton
Appendix A
Soil Test Pit Logs
i
�
i-�
Pac��'�c �ea Eng�r�ee�r�r�gLLC
Geotechr�lcal Englneering, Consulting & Inspectlon
KEY TO EXPLORATION LOGS
Sample Descriptlons:
Classif�cation of soifs �n this report is based on visuai field and laboratory observations, which include densitylcons�stency, moislure cond�t�on,
grain size, and plastic�ty estimates, and should not be construed to imply field or laboratory testing unless presented herein. Visual-manuai
classification methods in accordance with ASTM 0-2488 were used as an identification guide. WheFe laboratory data available, soil
classifications are in general accordance with ASTM D2487. Soil density/consistency in borings is related primarily to the Standard Penetralion
Resistance values. Soii densitylconsistency in test pits is estimated based on visual observations of excavations. Undrained shear strength =Yz
unconfined compressior strength.
RELATIVE DENSITY OR CONSITENCY VS. SPT N-VALUE �
,
COARSE GRAINED SOIIS: SAND OR GRAVEL FINE GRAINED SOILS: SILT OR CLAY
Density N (Biowslft.) Approx. Relative Density(%) � Consistency N(Blowslft.) Approx.Undrained
� Shear Stren lh s(
Very Loose 0-4 0- 15 Very Soft 0-2 <250
Loose 4-10 15-35 Soft 2-4 250-500
! Medium Dense 10-30 35-65 Medium Stiff 4-8 500- 1000
� Dense 30-50 65-85 Stifi 8-15 1000-2000
! Very Dense >50 85-100 Very Stiff 15-30 2000-4�00
Hard > 50 >4000
MOISTIfRE CONTENT DEFINITIONS
pry { Absence of moisture,dusty,dry to the touch
�
Moist Damp but no visible water
• Wet Visible free water,from below water tabie
I
DESCRIPTIONS FOR SOIL STRATA AND STRUCTURE
General Thickness or Spacing Structure General Attitude
Parting < 1/16 in Pocket Erratic,discontinuous deposit of limited extent Near Horizontal C- 10 deg
Seam 1/16- 1!2 in Lens Lenticutar deposit Low Angle 10-45 deg
Layer Yz- 12 in I Varved Altemating seams of silt and clay High Angle 45-80 deg
I
Stratum > 12 in Laminated Altemating seams Near Vertical 80-90 deg
Scattered < 1 per fl Interbedded Altemating Layers
i
� Numerous > 1 per ft Fractured Breaks easily along definite fractured planes
Slickensided Poiished,glossy,fractured pianes i
Blocky, Diced Breaks easily into small angular lumps I
Sheared Disturbed texture,mix of strengths
Homogeneous Same color and appearance throughout
Pacific Geo Ennineerinq,LLC
Geo[ech.nlcal Fn�ineerrnq, Ccnsv�tahon B/nspection
Union A�-enue Property
Renton; 1�1'ashington
Pro�ect No.0701 146
January 22, 2007
Page.A-I
SOIL TEST PIT LOGS
TEST PIT - 1
Date of Excavation: 01/19/07 ,
i
Depth, Ft. � USCS ' Soil Descriptions ! Sample No./ A'Ioisture -#200 %
� ; Depth,Ft. Content °/a
0—0.5 Topsoil: 6"thick Brn. Silt wl'Organics&Roots
� 0.5 —5 SM Grayish Bm. Silty Sandy Gravel S1?2 24.4
Moist,?vled. Dense
(GraphB-I) ;
5 —7 SM Bluish Gray Silty Sandy Gravel(Till) S2/6
Partly cemented,Difficult digging
! Moist, V. Dense
I \'ote: Test pit was ternunated at approximately 7 feet below the existing ground surfaces.
, ?�o groundwater or seepage was encountered within the exploratory depth.
No mottling was noticed within the explorarion depth.
No caving was noticed within the exploration depth.
,� TEST PIT - 2
Date of Excavation: 01I19/07
II Depth,Ft. USCS i Soil Descriptions Sample No./ '.Vloisture -#200 %
Depth,Ft. Content %
0—0.5 Topsoil: 6"thick Brn. Silt w/Organics&Roots �
0.5 — 5 SM Grayish Brn. Silty Sandy Gravel S1/3
Moist, Med. Dense
� — 7 SM Bluish Gray Silty Sandy Gravel(Till) S2?6
Partly cemented, Difficult digging
I Moist, V. Dense
i
1�ote: Test pit was tenninated at approximately 7 feet below the existing ground surfaces.
Perclled water seepage was encountered at 4 feet below the existing grades.
; No mottling was noticed within the exploration depth.
No caving was noticed within the exploration depth.
Pacific Geo EnaineerinA,LLC
Geote�`=•cai Enoroeenno,Consc.;'ta[ion&Inspec c-
Union Avenue Property
Renton, Washington
Project T�o. 0?Ol !:G
Januan 22, ''(il;,,
Paee .:-,
ITEST PIT - 3
Date of Excavation: O1;]9107
Depth, Ft. tiSCS Soil Descriptions Sample no./ � hloisture -#200 % �
� Depth, Ft. Content % ��
0—0.5 ' Topsoil: 6"thick Brn. Silt wi Organics&Roots
0.5 — 10 Fills: Brn. Silty Sandy Gravel w/ decayed wood S1/5
debris, concrete chunks,and meta]pieces '
, � Organic odor
Moist, Med. Dense
l�ote: Test pit was tenninated at approximately 10 feet below the existing ground surfaces.
Native soil was not encountered with the exploration depth. �
No groundwater or seepage was encountered within the exploratory depth.
No mottling was noticed within the exploration depth. �I
No caving was noticed within the exploration depth. I
T�ST PIT - 4
Date of Excavation: O1/19/07
Depth, Ft. USCS Soil Descriptions Sample No./ Moisture -#200 %
Depth, Ft. Content %
0—O.S Topsoil: 6" thick Brn. Silt�v'Organics &Roots
0.5— 10 Fills: Bm. Silty Sandy Gravel w; no visible S I!5 I
debris such as «�ood, metal, asphalt, plastic, or �
I concrete pieces
Organic odor
Moist, Med. Dense �
�
i
� Note: Test pit was temunated at approximately 10 feet below the existing ground surfaces.
No groundwater or seepage was encountered within the exploratory depth. I
No mottling was noticed within the exploration depth.
No caving was noticed within the exploration depth.
Pacific Geo Engineerinq,LLC
Geotechn�ca7 Enqineerinq, Consultallon&Ir,soecG�n
linion Avenue Property
Renron,Washineton
Project No. 0701 146
)anuary 22,2007
Page A-3
TEST PIT - 5
Date of Excavation: Ol/19/0 i
�
Depth, Ft. L;SCS Soil Descriptions Sample No./ hloisture -#200 °/a
� Depth, Ft. Content % ,
0—0.5 Topsoil: 6"thick Brn. Silt w/Organics &Roots '
Q.5 —4 Fills: Bm. Silry Sandy Gra�-el w/ large size S 1/2
� asphalt chunlcs and small plastic pieces
Organic odor �
' Moist, Med. Dense
�
i
4 —6 SM Native Soils: Grayish Brn. Silty Sandy Gravel S2/5
Moist. Med. Dense
6— 8 SM Bluish Gray Silty Sandy Gravel(Til])
?vloist, Dense
I note: Test pit was terminated at approximately 8 feet below the existing ground surfaces.
No groundwater or seepage was encountered within the exploratory depth. � '
i I�o mottling was noticed���ithin the exploration depth. '
No caving �vas noticed within the exploration depth.
!I TEST PIT - 6
Date ofExcavation: O1/19;07
Depth,Ft. USCS Soil Descriptions Sample No./ Moisture -#200 %
� Depth,Ft. Content %
0—0.5 Topsoil: 6"thick Brn. Silt wi Organics&Roots
� �
j 0.5— 8 SM Bluish Gray Silty Sandy Gravel(Till) S1/4
i Partly cemented,Difficult digging
V. Moist, V. Dense
i
note: Test pit was terntinated at approximately 8 feet below the existing ground surfaces.
Perched water seepage was encountered at 3 feet and 6 feet below the existing grades.
No mottling was noticed within the exploration depth.
\'o caving�vas noticed within the exploration depth.
Pacific Geo En�c ineering,LLC
Ge�tecn,�:�a:f��.,ee�.^e C_^s::'tah��&!�s�ec��;.
Union Avcnue Propert�
Renton, ��v'ashineror,
Project No- 0?�:�I '=6
Januar� '". �(1i��
PaEe .�,-�1
TEST PIT - 7 il
Date of Excavation: 01 i 19/07 ��
Depth, Ft. I;SCS Soil Descriptions Sample No./ :14oisture -#200 % '
Depth, Ft. ' Content % �
0—0.5 Topsoil: 6"thick Bm. Silt�v!Organics&Roots j �
0.5—6 Filis: Brn. Silty Sandy Gravel w/ ]arge size S1/3
asphalt ct�unks and small plastic pieces
Sh�ong organic odor
Moist, Med. Dense
6—8 Fills: Drk. Brn. Silt w/ significant amount of S2/7 '
decayed wood debris i
Strong organic odor
�
V. Vl'et. Soft
�
� 8— 10 S'.v1 Native Soils: Bluish Gray Silty Sandy Gravel S3/9 '�
Moist,Med. Dense
�
Note: Test pit was terminated at approximately 10 feet below the existing ground surfaces.
Heavy seepage was encountered @ 6 feet below the existing grades.
' No mottling was noticed witllin the exploration depth.
Caving�vas noticed between 6 to 8 feet below the existing grades.
Appendix B
Laboratory Test Result
_ ;
P�c�fic C�a Ertgir��er�ngLLC
Geotechnica! Engineering, Consulting & Inspection
UNIFIED SOIL CLASSIFICATION SYSTEM
Soil Classitication
Griteria for Assignfng Group Symbols and Group Names Using Laboratory Tests" —
Group Group NameB
Symbol
Coarse-Grained Soils Gravels Clean Gravels Cu a a and 1 s Cc s 3E GW We11-graded gravelF
More than 50% retained on More than 50% of coarse Less than 5°/a fines�
No.200 sieve fraction retained on Cu < 4 andlor 1 > Cc > 3E GP Poorly graded gravelF
No.4 sieve Fines classify as ML or MH GM Silty gravelF,c.M
Gravels with Fines
More Ihan 72°/a fines� Fines classify as CL or CH GC Clayey gravelF,�,H
Sands Clean Sands Cu � 6 and 1 < Cc s 3E SW Well•graded sand'
50% or more ot coarse Less ihan 5°/a finesE —
traclion passes Cu < 6 andlor 1> Cc > 3E SP Poorly graded sand�
No. 4 sieve Fines classify as ML or MH SM Silty sandc � �
Sands with Fines _
More than 12% fines° Fines classi(y as CL or CH SC Clayey sandc.H,i
Fine-Grained Soils Silts and Clays inorganic PI > 7 and plots on or above"A"line� CL Lean clayK�M
50% or more passes the Liquid limit less than 50
No.200 sieve PI < 4 or plots below "A" line� ML SIIIK,L M
9 Liquid limit — oven dried < 075 OL Organic clayK,�""."
or anic
Liquid limit — not dried Organic siltK�M,o
Silts and Clays inorganic PI plots on or above "A"line CH Fat clayK�M
Liquid limit 50 or more
PI plots below"A" line MH Elastic siltK,�,M
9 Liquid limit — oven dried � 0.75 OH Organic clayK,�,M,P
or anic
Liquid limit — not dried Organic si11K�"',o
Highly organic soils Primarily organic matter,dark in color,and organic odor PT Peat
"BaseG on the material passing the 3-in. E (D�� Klf soil contai�s 15 to 29% plus No. 200,add
(75•mm)sieve. Cu = D�lO�a Cc = D x D "with sand"or"with gravel",whichever is
Blf field sample contained cobbles or F o 10 � predominant.
boulders,or both, add "with cobbies or If soil contains >_ 15/o sand, add "with sand" 10 ��� soii contains >_ 30% plus. No.200
boulders,or both"to rou name. 9�oup name.
g p � predominantly sand,add "sandy" to group
�Gravels with 5 to 12% tines require dual If fines classify as CL-ML,use dual symbol GC- name. •
symbols: MGM,or SC�SM. ""If soil contains z 30°/. plus No.200,
GW-GM welt• raded ravel with siH If tines are organic, add "with organic fines"to redominantl ravel,add" ravell to rou
9 9 P Y 9 9 Y" 9 P
GWGC well•graded gravel with clay group name. name.
GP-GM poorly graded gravel with silt �If soil contalns >_ 15% gravel, add "with gravel"to "PI > 4 and plots on or above "A" line.
GP•GC poorly graded gravel with clay group name. °pl < 4 or plots below"A" line.
°Sands with 5 to 12% fines require dual �It Atterberg limits plot in shaded area,soil is a CL• Pp� p�ots on or above "A" line.
symbols: ML, silty clay. °pl lots below "A" tine.
SW-SM well-graded sand with silt P
SW-SC well•graded sand with clay �o
SP•SM poorly graded sand wlth silt ca ow.in�.uo�o�n�.y�,i�•a sou.
SP-SC poorly graded sand with clay �nOMnyrNnW Ir�cllonoleoxs� ,/
� pr4nW wib _ _ _
�4�`--_..__—_..
EOwtlon ol'A"�nne �\��� \�(p —�
Ho�liontel al PI .�lo LL=255. I O•,,.•P�
a tMn PI-0.7J(LL�201 'J� �' I
wa �Eaua,ion ol'V"�une ��P — --*'---- -----
p veAical at Ll- t6 to P�. 7.
Z IhM PI:0.9�LL�8j ,� G �
} 30 __"_'__._ � .i
_.___._ —_ _____ _.___F .._..� _— __
� I / _._. �__ .
U �/�pO� -
N �1 I ,
g - --- /��-G P j MH.oa OH � -
,o — -- -� / -- —_:_ _. I _ � _ �
7 _ 1
� � M L oa OL I ' �
o '
0 t0 t6 20 ]0 �0 50 60 70 !0 90 100 »0
LIQUID LIMIT(LL)
Number oi Mesh per Inch
Size of Opernng In Inches Grain Size in Millimetres �
(US Standard)
� C m N o m p 8 �p p � N � O O� S p p
N cD v N '- .- f`�' ifi� -�- M o � N o � O N O O O O O O O
l I Iljl � I I .j l Iltl l I I I I 1111 I I I I I IIII I � I I I ill I I I I I I I
8 8 8m � Q � � o � � < � N � � � e � N � S � � � o � 8 � S 8 S S
^ Grain Size in Millimetres
Cobble Coarse � Fine Coarse Medium Fine
, � Gravel Sand Silt andlor Clay
Particle Size Distribution Report
_ - - - � oo � � � �
- - - - _ _ _ $ �
,oo ; !! ; , , ;
' ! � � ' i , j i , ; ! j � I � �'
9Q -r I---j- ,- J-:j� �-� � -t---�.I� � I� � I , , I I � I �I I --
� ! � , ��, . I�I '���1 1 � � i � , 'i i � � I I �
; I � ; , ; . ;� j � �� � , � � : I �i ; ; :
' ��� � , . : I I � I . , , (� i ; , , ',
80 ----- ---r-'-r '�T - ' -+--�-- t � T�—�i ,-�-�--1-- __ _
� �; � �i� �r � ; � � ,'I I I �
i i I �I � I� � � I �� � � , I : I ' i I I I 1
�
, ' t � ` I , I i �'I I i ; i i
� I
,
' t � �--
. :_ ,_ .
70 -� �-_. _ ��- I ,- . � -F+ r--• _4_—�_���i �_I �- _
I ,. +. I:I i I �. ,��I �,I � 'I , , '��+'� ! I I ' � i�! ' f ',
� I � , I � I � I' , I � ' I � I I I ' i *I
W 6C . , �r.l � 3_-; � -I - �1 fT �•-!- -�- ---� i --;- '--- --- fii-1- ----
� ; � -� � � ,► f � ; _r_ � �__
� i : '; I , „ i l ' � � � ; ; ;� � � I I � I i
' � � . , ; ! , I
� -��--- ; � i ' �-1 ;�:--- ,- i ,' ;i ;, �{�' � '+I _r.
� � I i � � i �
z Sp a- �:-- � ,-- - --- ;i , T-� �,-.. - -
� i I ; I I I i I I i � i I i I, � I ; I I I �I
I � I
� , ��� ' . I . ; ,, � �� � .i . � �, ; i
W 40 _ �i; I-�'- --���._ r�,� -��--1-- -�-t i—— .. -
� i; , ; , i� I ' ;-} , ; -I_ � ; ; , -�-1— �--; ;
r" ' ! ! � j I i ' i� , �
I� i'' � � i- ' � �' ' �' ' ' ' � -t-
30 -1-- ------- I-+-I-; -�—rt---:- -'r - ----- -- -�----�� -- --
� i, , � ! i. . . I I�� , ., .
, I i I � � , , j I, , i j
� ' �i!�� �. , � �I I � , � � � . �
i
� I
� l i l � I i ' ' '
��, i i � , , , , I �
2o i �- - y- - — -----
, -- , -�--..-.N-;.}r--�.._ , 1�- ; 1 � ; ; ', ' -t� . ;
; H � ' � � �� , i; • � , , I ' � ; i ; '
i i I i' iI� { �, , , � I �
,o --� -{ --�--.----���;� I�I-+: : i - ; ; T- --i--�---
; , : � , � � ! , � � j �
� 'I I � ' � � ' ' i �, �
p il � � i . � , , i I
S00 100 �0 1 0.1 0.01 OA01
GRAIN S►ZE - mm
°/a GRAVEL � %SAND %FINES
% COBBLES CRS. FINE CRS. MEDIUM FINE SILT CLAY
0.0 39.G 11.� 5.3 6.7 12.7 24.4
SIEVE PERCENT SPEC.� PASS? Soil Description
SIZE FINER � PERCENT (X=NO) Silty Gravel with Sand
3 in. 100.0
2.5 in. �8.4
I.5 in. j 73.8 �
3/4 in. b0.4 � Atterberq Limits
I/2 in. 53.7 PL= LL= P1=
�4 49.I
�! 10 43.8 Coefficients
�#40 37.I D - 59.2 D 18.7 D 6.73
t� 10� 28.1 85- 60- 50-
�' 200 24.4 �30= 0.190 D15= D�p=
C�= C�=
Classification
USCS= GM AASHTO=
I
� Remarks
I
I
� (no,p�cificaUun provided)
Sample No.: S I Source of Sample: Nacive Soil I Date: OI/22i2007
Location: "i'cst Pit 2 EIev./Depth: 2 ft.
Client: American Classic Homes, LLC
Paeifie Geo Enqineering, LLC Project: Union Avenue Property
Geo[echnrca/Engineeriny,Consultation 8 Inspection
Project No: 0701146 Plate B-1
APPENDIX B
Downstream Analysis Information
� .
� �t ��� � � ' F� ��'� �� ' , �
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N � * � I� .
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�w
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APPEtVDIX C
Runoff Control & Water Quality Calculations �
Plat of Rosewood Highlands DetentionNVater Quality Calcs 12!22;2010
Detention/Water Quality Calcs
Plat of Rosewood Highlands
�aTE: 12/22/10
�oa No. 1352-001-006
ESM CONSULTING ENGINEERS, LLC. COMP BY: TLS
181 South 338rd St, Bldb C,Ste 210 cHK�sY: �
Federal Way,WA 98003 ,
253-838-6113 FAX: 253-838-7104
Location!Parcels:
�The site is located at 230 Union Avenue NE, Renton.
"N.W. 1!4 of Sect. 15, Twn. 23, Rge. 05 East, W.M.
'Parcel numbers are:
518210-0068
518210-0069
518210-0073
518210-0079
518210-0081
518210-0085
Jurisdictions:
City of Renton
Codes:
Runoff Control-2005 KCSWDM
Water Quality control-2005 KCSWDM
Site Information:
`Zoned R-10(Residential)
'Site area is 4.39 AC.
"Off-site tributary area is 0.18 AC.
"Soils are Alderwood Gravelly Sandy Loam, 6 to 15%(AgC).
'Per KCSWDM soils are classified as Alderwoods= C, Till.
'Existing use is single-family residences.
'NE 2nd PI is included in site boundary.
"There is one drainage basin on the site.
'`Areas are obtained using AutoCAD.
'Individual lot flow control BMPs are being used and credits are being utilized
to calculate lot impervious area
'Assumed some off-site flows are collected and conveyed to the proposed storm vault.
The remaining offsite basin bypasses the development by flowing through
the wetland/stream buffer.
`The City of Renton specifies Conservation FC Areas.
Detention Requirements:
Match durations for 50°/a 2-yr through 50-year and historic
2-yr and 10-yr peaks.
"There is a small section of Union Ave that is assumed to drain toward the site.
ESM Job#: 1352-001-006 1 of 3
Plat of Rosewood Highlands Detention/Water Quality Calcs 12/22/2010
SITE •
Site area: Total Site Area 4.39 Ac
- Undeveloped Sensitive Area and Buffer 0.47 Ac
- Undeveloped east end of NE 2nd Place 0.06 Ac
= Total Developed Site Area 3.86 Ac
Offsite: Union Ave Frontage 0.03 Ac
+ Portion of Parcel to the NW (Basin B) 0.15 Ac
= Total Offsite Areas 0.18 Ac
Total Total Developed Site Area 3.86 Ac
+ Total Offsite Area 0.18 Ac
= Total Area Contributing to Storm Vault 4.04 Ac
PREDEVELOPED SITE CONDITIONS
Refered to as PRE-DEV in the KCRTS model
Predeveloped site conditions modeled in KCRTS
Assumed historic site conditions(Forested)for developed site and current conditions
for offsite contributing area.
Total Till Forest Till Pasture Impervious
Develo ed Site 3.86 3.86 - -
Offsite Area 0.15 - 0.13 0.02
Frontage 0.03 - - 0.03
Total 4.04 3.86 0.13 0.05
DEVELOPED SITE CONDTIONS I
Refered to as DEV in the KCRTS
Lots will be limited to 2,300 sf of impervious
The runoff from Lots 23 through 27 will be discharged to the adjacent sensitive area
buffer via dispersion trenches. Basic dispersion credit will be applied
and the roof impervious area is modeled as 50% impervious, 50%Till Grass.
Developed Site Tributary to Storm Vault
Till Grass Till Pasture Impervious Total
Lots 1-9 0.41 - 0.48 0.89
Lots 10-15 0.16 - 0.32 0.48
Lots 16-22 0.33 - 0.37 0.70
� Lot 23 0.10 0.03 0.13
Lots 24-27 0.24 0.13 0.37
Plat Roads 0.01 - 1.11 1.12
Offsite Area - 0.13 0.02 0.15
Fronta e - - 0.03 0.03
Storm Tract 0.18 - - 0.18
Total 1.43 0.13 2.48 4.05
ESM Job#: 1352-001-006 2 of 3
Plat of Rosewood Highlands Detention/Water Quality Calcs 12/22/2010
DETENTION DESIGN:
*Program used is KCRTS
*The detention facility will be a vault.
*Per Water Quality Assessment for Washington Map,the site is not phosphorus control.
'Site is within Sea-Tac 1.0.
Minimum live storage elevation = 384.75 ft
Maximum live storage elevation = 392.21 ft
Distance from top of live surface to Finish Grade= 2.79 ft
Total �ive storage depth = 7.46 ft
Minimum finish grade for facility= 395 ft
Required volume area = 45,387 sf
Proposed volume area= 46,550 sf
Percent oversized 3%
Bottom orifice elevation = 384.75 ft
Bottom orifice diameter= 1 in
Second orifice distance= 4.45 ft
Second orifice elevation = 389.20 ft
Second orifice diameter= 1.55 in
Third orifice distance= 5.55 ft
Third orifice etevation = 390.30 ft
Third orifice diameter= 1.25 in
WATER QUALITY
Vr={(0.9 'Ai)+ (0.25`Atg)+ (0.10 'Atf)+ (0.01 'Ao)} " R
Vb=f'Vr
Ai= 2.48 Ac = 108,100 sf
Atg= 1.56 Ac = 67,997 sf
Atf= 0 Ac = - sf
Ao = 0 Ac = - sf
R = 0.039 ft
Vr= {(�.9* 108,100)+ (0.25`67,354)+(0.10'`0)+ (0.01 '`0)}*0.039
Vr=4,451 cf
Vb =f'Vr
f=3
Vb =3"'4,451
Vb = 13,353 cf
ESM Job#: 1352-001-006 3 of 3 II
APPENDIX D
Conveyance Calculations
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STORM SEWER DESIGN CALCULATIONS (by Rational Method)
PROJECT: Rosewood Highlands
DATE: December 6, 2010
Runoff Coefficients "C"Values for the Rational Method
Grass/Landscape area 0.25
Road Impervious Area 0.90
Coefficients for the Rational Method "iR" Equation
25-year Design Storm a R 2.66
25-year Design Storm bR 0.65
100-year Design Storm a R 2.61 I,
100-year Design Storm bR 0.63 '
25-year Precipitation PR PR�z5� = 3.40
100-year Precipitation PR PR��oo� = 3•90
T�(min) T�= 6.30
25-year i R r R�Zs� = 0.80
100-year iR �R��oo� = 0•82
25-year Intensity lR�25� = 2.73
100-year Intensity lR��oo� = 3.19
Basin Area and Flow Summary
Basin Flow Composite
Calculations Runoff 25-year 100-year
Rational Impervious Pervious Total Coefficient Q=CIA Q=CIA
Method sf Ac sf Ac sf Ac C� cfs cfs
DA-01 1,178 0.03 - 0.00 1,178 0.03 0.90 0.07 0.08
DA-02 3,242 0.07 - 0.00 3,242 0.07 0.90 0.18 0.21
DA-03 4,585 0.11 1,465 0.03 6,050 0.14 0.74 0.28 0.33
DA-04 7,755 0.18 2,166 0.05 9,921 0.23 0.76 0.47 0.55
DA-05 - 0.00 - 0.00 - 0.00 0.00 0.00 �.00
DA-06 13,813 0.32 6,941 0.16 20,754 0.48 0.68 0.89 1.04
DA-07 3,989 0.09 586 0.01 4,575 0.11 0.82 0.23 0.27
DA-08 9,279 0.21 3,570 0.08 12,850 0.29 0.72 0.58 0.68
DA-09 3,195 0.07 2,071 0.05 5,266 0.12 0.64 0.21 0.25
DA-10 5,132 0.12 2,654 0.06 7,786 0.18 0.68 0.33 0.39
DA-11 2,881 0.07 1,702 0.04 4,583 0.11 0.66 0.19 0.22
DA-12 198 0.00 - 0.00 198 0.00 0.90 0.01 0.01
DA-13 12,432 0.29 5,407 0.12 17,839 0.41 0.70 0.79 0.92
DA-14 3,751 0.09 1,465 0.03 5,216 0.12 0.72 0.23 0.27
DA-15 3,285 0.08 1,078 0.02 4,363 0.10 0.74 0.20 0.24
DA-16 8,991 0.21 10,898 0.25 19,889 0.46 0.54 0.68 0.79
DA-17 3,342 0.08 926 0.02 4,268 0.10 0.76 0.20 0.24
DA-18 5,155 0.12 859 0.02 6,015 0.14 0.81 0.30 0.36
DA-19 4,159 0.10 2,948 0.07 7,107 0.16 0.63 0.28 0.33
DA-20 6,492 0.15 9,456 0.22 15,948 0.37 0.51 0.52 0.60
102,856 2.36 54,192 1.24 157,047 3.61 6.66 7.78
25-year and 100-year Conve ance Anal sis
e ocity year year
Pipe Pipe Wet Hydraulic @ full % %
Pipe Segment Diameter Diameter Area perimeter Radius Capacity 25 year flow Capacity 100 year Capacity Contributing Pipes&
Pipe CB to CB (in) (ft) (ftz) (ft) (ft) Slope(ft/ft) Pipe n (cfs) flow(cfs) (ft/sec) (cfs) flow(cis) (cfs) Basins
P-19 CB-19-CB-20 12 1.00 0.79 3.14 0.250 0.0163 0.013 4.56 0.?8 5.81 6% 0.33 7% DA-19
P-20 CB-20-CB-10 12 1.00 0.79 3.14 0.250 0.0425 0.013 7.36 0.80 9.38 11% 0.93 13% P-19,DA-19
P-10 CB-10-CB-09 12 1.00 0.79 3.14 0.250 0.0235 0.013 5.48 1.13 6.97 21% 1.32 24% P-19,DA-10
P-17 CB-17-CB-09 12 1.00 0.79 3.14 0.250 0.0203 0.013 5.09 0.20 6.48 4% 024 5% DA-17
P-09 CB-09-CB-08 12 1.00 0.79 3.14 0.250 0.0529 0.013 8.22 1.54 10.46 19% 1.80 22% P-10,P-17,DA-09
P-08 CB-08-CB-05 12 1.00 0.79 3.14 0.250 0.0100 0.013 3.57 2.12 4.55 59% 2.4II 69% P-09,DA-08
P-16 CB-16-CB-15 12 1.00 0.79 3.14 0.250 0.0100 0.013 3.57 0.68 4.55 19% 0.79 22% DA-16
P-15 CB-15-CB-14 12 1.00 0.79 3.14 0.250 0.0237 0.013 5.50 0.88 7.00 16% 1.03 19% P-16,DA-15
P-14 CB-14-CB-12 12 1.00 0.79 3.14 0.250 0.0378 0.013 6.95 1.12 8.84 16% 1.30 19% P-15,DA-14
P-13 CB-11 -CB-11 12 1.00 0.79 3.14 0.250 0.0125 0.013 3.99 0.79 5.09 20% 0.92 23% DA-13
P-12 CB-12-CB-11 12 1.00 0.79 3.14 0.250 0.0161 0.013 4.53 1.91 5.77 42% 224 49% P-13,P-14,DA-12
P-11 CB-11 -CB-01 12 1.00 0.79 3.14 0.250 0.1202 0.013 12.39 2.10 15.77 17% 2.46 20% P-12,DA-11
P-07 CB-07-CB-06 12 1.00 0.79 3.14 0.250 0.0182 0.013 4.82 0.23 6.14 5% 027 6% DA-07
P-06 CB-06-CB-05 12 1.00 0.79 3.14 0.250 0.0518 0.013 8.13 1.12 10.35 14% 1.31 16% P-07,DA-06
P-05 CB-OS-CB-04 15 1.25 1.23 3.93 0.313 0.0195 0.013 9.04 3.25 7.37 36% 3.79 42% P-08,P-06,DA-05
P-04 CB-04-CB-03 15 1.25 1.23 3.93 0.313 0.0240 0.013 10.03 3.72 8.18 37% 4.34 43% P-O5,DA-04
P-03 CB-03-CB-02 15 1.25 1.23 3.93 0.313 0.0312 0.013 11.44 4.00 9.32 35% 4.67 41% P-03,DA-03
P-02 CB-02-CB-01 18 1.50 1.77 4.71 0.375 0.1848 0.013 45.28 4.19 25.62 9% 4.89 11% P-03,DA-02
P-18 CB-18-CB-01 12 1.00 0.79 3.14 0.250 0.0755 0.013 9.82 0.30 12.50 3% 0.36 4% DA-18
P-01 CB-01 -Vault 24 2.00 3.14 6.28 0.500 0.2857 0.013 121.24 6.59 38.59 5% 7.70 6% P-02,P-18,P-11,DA-01
25-year Backwater Analysis (1 of 2)
1 2 3 4 5 6 7 8 9 10 11
arre
25-year Pipe Pipe Hydraulic Outlet Inlet Barrel Barrel Velocity Tailwater
Pipe Segment Q=CIA Length Slope Diameter Radius Elevation Elevation Area Velocity Head Elevation Friction
Pipe Run CB to CB (cfs) (ft) (ft/ft) (ft) (ft) Pipe n (ft) (ft) (ft2) (ft/s) (ft) (ft) Loss(ft)
P-19 CB-19-CB-20 0.28 128 0.0163 1.00 0.250 0.013 402.42 404.51 0.79 0.36 0.002 403.22 0.01
P-20 CB-20-CB-10 0.80 85 0.0425 1.00 0.250 0.013 398.80 402.42 0.79 1.01 0.016 399.72 0.04
P-10 CB-10- CB-09 1.13 53 0.0235 1.00 0250 0.013 397.56 398.80 0.79 1.44 0.032 398.57 0.05
P-17 CB-17- CB-09 0.20 31 0.0203 1.00 0.250 0.013 397.56 398.18 0.79 0.26 0.001 398.57 0.00
P-09 CB-09-CB-08 1.54 91 0.0529 1.00 0.250 0.013 392.76 397.56 0.79 1.97 0.060 394.44 0.17
P-08 CB-08-CB-05 2.12 22 0.0100 1.00 0.250 0.013 392.54 392.76 0.79 2.70 0.114 394.08 0.08
P-16 CB-16-CB-15 0.68 34 0.0100 1.00 0.250 0.013 397.54 397.88 0.79 0.86 0.012 398.37 0.01
P-15 CB-15-CB-14 0.88 70 0.0237 1.00 0.250 0.013 395.88 397.54 0.79 1.12 0.020 396.76 0.04
P-14 CB-14-CB-12 1.12 45 0.0378 1.00 0.250 0.013 394.18 395.88 0.79 1.42 0.031 395.32 0.04
P-13 CB-11 -CB-11 0.79 30 0.0125 1.00 0.250 0.013 394.18 394.56 0.79 1.00 0.016 395.32 0.01
P-12 CB-12-CB-11 1.91 106 0.0161 1.00 0.250 0.013 392.47 394.18 0.79 2.44 0.092 393.56 0.30
P-11 CB-11 -CB-01 2.10 64 0.1202 1.00 0.250 0.013 384.78 392.47 0.79 2.68 0.111 392.18 022
P-07 CB-07-CB-06 0.23 33 0.0182 1.00 0250 0.013 397.72 398.32 0.79 0.30 0.001 398.64 0.00
P-06 CB-06-CB-05 1.12 100 0.0518 1.00 0.250 0.013 392.54 397.72 0.79 1.43 0.032 394.08 0.10
P-05 CB-05-CB-04 3.25 57 0.0195 1.25 0.313 0.013 389.18 392.29 1.23 2.65 0.109 393.62 0.14
P-04 CB-04-CB-03 3.72 83 0.0240 1.25 0.313 0.013 389.19 391.18 1.23 3.03 0.143 392.99 0.27
P-03 CB-03-CB-02 4.00 25 0.0312 1.25 0.313 0.013 388.41 389.19 1.23 3.26 0.165 392.45 0.10
P-02 CB-02-CB-01 4.19 21 0.1848 1.50 0.375 0.013 384.28 388.16 1.77 2.37 0.087 392.18 0.03
P-18 CB-18-CB-01 0.30 44 0.0755 1.00 0.250 0.013 384.78 388.10 0.79 0.39 0.002 392.18 0.00
P-01 CB-01 -Vault 6.59 7 0.2857 2•0� 0.500 0.013 381.75 383.78 3.14 2.10 0.068 391.95 0.01
25-year Backwater Analysis (2 of 2)
12 13 14 15 16 17 18 19 20
Entrance Entrance Outlet Inlet Appr. Bend Junction Upstream CB Grate
HGL Head Control Control Velocity Head Head HW CB Grate Elev. -
Pipe Segment Elevation Loss Exit Head Elevation Elevation Head Loss Loss Elevation Elevation HW Elev.
Pipe Run CB to CB (ft) (ft) Loss(ft) (ft) Q/AD°5 (ft) (ft) (ft) Q Ratio (ft) (ft) (ft) (ft)
P-19 CB-19- CB-20 403.23 0.00 0.00 403.24 1.24 405.22 0.00 0.00 0.00 0.00 405.22 408.01 2.79
P-20 CB-20- CB-10 399.77 0.01 0.02 399.79 3.51 403.21 0.02 0.00 0.00 0.00 403.22 407.42 4.20
P-10 CB-10-CB-09 398.62 0.02 0.03 398.67 4.97 399.66 0.03 0.04 0.00 0.00 399.72 402.25 2.53
P-17 CB-17-CB-09 398.57 0.00 0.00 398.57 0.90 398.88 0.00 0.00 0.00 0.00 398.88 401.52 2.64
P-09 CB-09-CB-08 394.61 0.03 0.06 394.70 6.81 398.47 0.06 0.00 1.00 0.03 398.57 401.51 2.94
P-08 CB-08- CB-05 394.15 0.06 0.11 394.32 9.37 393.80 0.11 0.00 0.00 0.00 394.44 395.75 1.31
P-16 CB-16-CB-15 398.38 0.01 0.01 398.40 2.99 398.66 0.01 0.01 0.00 0.00 398.68 401.85 3.17
P-15 CB-15-CB-14 396.80 0.01 0.02 396.83 3.89 398.35 0.02 0.00 0.00 0.00 398.37 401.47 3.10
P-14 CB-14-CB-12 395.36 0.02 0.03 395.41 4.92 396.73 0.03 0.00 0.00 0.00 396.76 399.67 2.91
P-13 CB-11 -CB-11 395.34 0.01 0.02 395.36 3.47 395.36 0.02 0.02 0.00 0.00 395.40 398.59 3.19
P-12 CB-12-CB-11 393.86 0.05 0.09 394.00 8.44 395.18 0.09 0.00 1.00 0.05 395.32 398.59 3.27
P-11 CB-11 -CB-01 392.40 0.06 0.11 392.57 9.28 393.45 0.11 0.00 0.00 0.00 393.56 396.39 2.83
P-07 CB-07-CB-06 398.64 0.00 0.00 398.64 1.03 399.02 0.00 0.00 0.00 0.00 399.02 402.21 3.19
P-06 CB-06-CB-05 394.18 0.02 0.03 394.22 4.96 398.56 0.03 0.04 0.00 0.00 398.64 401.73 3.09
P-05 CB-05-CB-04 393.77 0.05 0.11 393.93 8.20 393.52 0.11 0.00 0.53 0.04 394.08 396.80 2.72
P-04 CB-04-CB-03 393.27 0.07 0.14 393.48 9.39 392.47 0.14 0.00 0.00 0.00 393.62 395.39 1.77
P-03 CB-03- CB-02 392.55 0.08 0.17 392.79 10.10 390.51 0.17 0.03 0.00 0.00 392.99 393.58 0.59
P-02 CB-02-CB-01 392.22 0.04 0.09 392.35 6.70 389.43 0.09 0.02 0.00 0.00 392.45 392.89 0.44
P-18 CB-18- CB-01 392.19 0.00 0.00 392.19 1.34 388.79 0.00 0.00 0.00 0.00 392.19 392.90 0.71
P-01 CB-01 -Vault 391.96 0.03 0.07 392.06 5.14 385.24 0.07 0.00 1.99 0.06 392.18 392.46 0.28
100-year Backwater Analysis (1 of 2)
1 2 3 4 5 6 7 8 9 10 11
arre
100-year Pipe Pipe Hydraulic Outlet Inlet Barrel Barrel Velocity Tailwater
Pipe Segment Q=CIA Length Slope Diameter Radius Elevation Elevation Area Velocity Head Elevation Friction
Pipe Ru CB to CB (cfs) (ft) (ft/ft) (ft) (ft) Pipe n (ft) (ft) (ft2) (ft/s) (ft) (ft) Loss(ft)
P-19 CB-19-CB-20 0.33 128 0.0163 1.00 0.250 0.013 402.42 404.51 0.79 0.42 0.003 403.25 0.01
P-20 CB-20-CB-10 0.93 85 0.0425 1.00 0.250 0.013 398.80 402.42 0.79 1.18 0.022 399.77 0.06
P-10 CB-10-CB-o9 1.32 53 0.0235 1.00 0250 0.013 397.56 398.80 0.79 1.68 0.044 398.65 0.07
P-17 CB-17-CB-09 0.24 31 0.0203 1.00 0.250 0.013 397.56 398.18 0.79 0.30 0.001 398.65 0.00
P-09 CB-09-CB-08 1.80 91 0.0529 1.00 0.250 0.013 392.76 397.56 0.79 2.30 0.082 395.32 0.23
P-08 CB-08-CB-05 2.48 22 0.0100 1.00 0.250 0.013 392.54 392.76 0.79 3.16 0.155 394.83 0.11
P-16 CB-16-CB-15 0.79 34 0.0100 1.00 0.250 0.013 397.54 397.88 0.79 1.01 0.016 398.41 0.02
P-15 CB-15-CB-14 1.03 70 0.0237 1.00 0.250 0.013 395.88 397.54 0.79 1.31 0.027 396.80 0.06
P-14 CB-14-CB-12 1.30 45 0.0378 1.00 0.250 0.013 394.18 395.88 0.79 1.66 0.043 395.43 0.06
P-13 CB-11 -CB-11 0.92 30 0.0125 1.00 0.250 0.013 394.18 394.56 0.79 1.17 0.021 395.43 0.02
P-12 CB-12-CB-11 2.24 106 0.0161 1.00 0.250 0.013 392.47 394.18 0.79 2.85 0.126 393.66 0.41
P-11 CB-11 -CB-01 2.46 64 0.1202 1.00 0.250 0.013 384.78 392.47 0.79 3.13 0.152 392.27 0.30
P-07 CB-07-CB-06 0.27 33 0.0182 1.00 0.250 0.013 397.72 398.32 0.79 0.35 0.002 398.68 0.00
P-06 CB-06-CB-o5 1.31 100 0.0518 1.00 0.250 0.013 392.54 397.72 0.79 1.67 0.043 394.83 0.13
P-05 CB-05-CB-04 3.79 57 0.0195 1.25 0.313 0.013 389.18 392.29 1.23 3.09 0.148 394.21 0.19
P-04 CB-04-CB-03 4.34 83 0.0240 125 0.313 0.013 389.19 391.18 1.23 3.54 0.195 393.35 0.37
P-03 CB-03-CB-02 4.67 25 0.0312 125 0.313 0.013 388.41 389.19 1.23 3.81 0.225 392.63 0.13
P-02 CB-02-CB-01 4.89 21 0.1848 1.50 0.375 0.013 384.28 388.16 1.77 2.77 0.119 392.27 0.05
P-18 CB-18-CB-01 0.36 44 0.0755 1.00 0250 0.013 384.78 388.10 0.79 0.45 0.003 392.27 0.00
P-01 CB-01 -Vault 7.70 7 0.2857 2.00 0.500 0.013 381.75 383.78 3.14 2.45 0.093 391.95 0.01
100-year Backwater Analysis (2 of 2)
12 13 14 15 16 17 18 19 20
pstrea
Entrance Entrance Outlet Inlet Appr. Bend Junction m CB Grate
HGL Head Exit Control Control Velocity Head Head HW Grate Elev.-
Pipe Pipe Segment Elevation Loss Head Elevation Elevation Head Loss Loss Elevation Elevation HW Elev.
Run CB to CB (ft) (ft) Loss(ft) (ft) Q/AD°5 (ft) (ft) (ft) Q Ratio (ft) (ft) (ft) (ft)
P-19 CB-19- CB-20 403.26 0.00 0.00 403.27 1.45 405.23 0.00 0.00 0.00 0.00 405.23 408.01 2.78
P-20 CB-20- CB-10 399.83 0.01 0.02 399.86 4.10 403.23 0.02 0.00 0.00 0.00 40325 407.42 4.17
P-10 CB-10- CB-09 398.72 0.02 0.04 398.78 5.81 399.69 0.04 0.04 0.00 0.00 399.77 402.25 2.48
P-17 CB-17- CB-09 398.65 0.00 0.00 398.65 1.05 398.88 0.00 0.00 0.00 0.00 398.88 401.52 2.64
P-09 CB-09- CB-08 395.55 0.04 0.08 395.68 7.95 398.52 0.08 0.00 1.00 0.05 398.65 401.51 2.86
P-08 CB-08-CB-05 394.94 0.08 0.15 395.17 10.94 393.86 0.15 0.00 0.00 0.00 395.32 395.75 0.43
P-16 CB-16-CB-15 398.42 0.01 0.02 398.45 3.50 398.68 0.02 0.01 0.00 0.00 398.71 401.85 3.14
P-15 CB-15-CB-14 396.86 0.01 0.03 396.90 4.54 398.38 0.03 0.00 0.00 0.00 398.41 401.47 3.06
P-14 CB-14-CB-12 395.49 0.02 0.04 395.55 5.75 396.76 0.04 0.00 0.00 0.00 396.80 399.67 2.87
P-13 CB-11 -CB-11 395.45 0.01 0.02 395.48 4.05 395.39 0.02 0.02 0.00 0.00 395.52 398.59 3.07
P-12 CB-12 -CB-11 394.08 0.06 0.13 394.26 9.86 395.23 0.13 0.00 1.00 0.07 395.43 398.59 3.16
P-11 CB-11 -CB-01 392.57 0.08 0.15 392.80 10.84 393.51 0.15 0.00 0.00 0.00 393.66 396.39 2.73
P-07 CB-07-CB-06 398.68 0.00 0.00 398.69 1.21 399.03 0.00 0.00 0.00 0.00 399.03 402.21 3.18
P-06 CB-06-CB-05 394.96 0.02 0.04 395.03 5.79 398.59 0.04 0.04 0.00 0.00 398.68 401.73 3.05
P-05 CB-05-CB-04 394.41 0.07 0.15 394.63 9.58 393.59 0.15 0.00 0.53 0.05 394.83 396.80 1.97
P-04 CB-04-CB-03 393.73 0.10 0.19 394.02 10.97 392.55 0.19 0.00 0.00 0.00 394.21 395.39 1.18
P-03 CB-03-CB-02 392.76 0.11 0.23 393.10 11.80 390.59 0.23 0.03 0.00 0.00 393.35 393.58 0.23
P-02 CB-02-CB-01 392.31 0.06 0.12 392.49 7.82 389.49 0.12 0.02 0.00 0.00 392.63 392.89 0.26
P-18 CB-18-CB-01 392.27 0.00 0.00 392.28 1.57 388.79 0.00 0.00 0.00 0.00 392.28 392.90 0.62
P-01 CB-01 -Vault 391.96 0.05 0.09 392.10 6.00 385.31 0.09 0.00 1.99 0.08 392.27 392.46 0.19
APPENDIX E
Wet Season ESC Plan �
ROSEWOOD HIGHLANDS
Wet Season ESC Plan
Prepared for
Gtadco Development L.L.C. ',
P.O. Box 1830 �'
Renton, WA 98056
Submitted by
ESM Consulting Engineers, LLC
181 South 333�d Street
Building C, Suite 210
Federal Way. WA 98003
Job No: 1352-001-006
December 6, 2010
Prepared by:
Trevor Stiff, P.E.
ESM JOBr 1352-001-006 ___ Rosewood Highlands
Sections:
1. INTRODUCTION........................................................................................................................................................................1
2. PROJECT OVERVIEW..........................................................................................................................................................1
3. SITE SPECIFIC BMPs...........................................................................................................................................................2
4. WET SEASON SPECIAL PROVISIONS................................................................................................................2
5. CONSTRUCTION SEQUENCE...................................................................................................................................3
6. SEDIMENT POND DESIGN............................................................................................................................................4
APPENDICIES:
A - TESC and Grading Plans
B - City of Renton TESC Details
C - King County TESC Details
- i -
ESM JOB= 1352-001-006 Rosewood Hiyhlands
1 . INTRODUCTION
Project:
The proposed Rosewood Highlands project would like to propose construction to start
during the winter of 2010/2011. Because this construction would occur during the
wet season (October 1 to April 30) additional erosion and sediment control (ESC)
measures will be required. This "Wet Season ESC Plan" will outline these measures. I
In addition to this Wet Season ESC Plan, a Stormwater Pollution Prevention Plan I
(SWPPP) will be prepared prior to construction as part of the NPDES stormwater permit
requirements. The SWPPP will include a full description of the TESC measures, along
with the inspection/monitoring measures and recordkeeping.
2. PROJECT OVERVIEW
Project:
The proposed Rosewood Highlands project is the development of a 4.39-acre site into
27 single-family lots with associated roads, utilities, a detention vault, and a wetland /
sensitive area tract Included with the development are improvements to Northeast
2�d Place.
Site Location:
The project site is located at 230 Union Avenue Northeast in the City of Renton,
Washington 98059. More generally, the site is located within a portion of the NW 1/4
of Section 15, Township 23 North, and Range 5 East of the Willamette Meridian.
Existing Conditions:
The project site is comprised of six parcels totaling 4.39-acres. The site currently
contains single-family, undeveloped pasture with some forested areas and light
underbrush. There is an existing access road along the southern boundary.
Topography for the site generally slopes from west to east with a steep slope along
the northeastern comer of the site. Maplewood Creek runs southerly along the
eastern boundary of the site. Stormwater runoff from the site sheet flows easterly with
slopes ranging from 3% in the west to 23% in the east Stormwater runoff either sheet
flows into a Class III wetland along the northeastern comer of the site and then into
Maplewood Creek, or sheet flows directly into Maplewood Creek.
SOIIS:
Per the Natural Resources Conservation Service (NRCS), onsite soils are Alderwood
Gravelly Sandy Loam, 6 to 15 percent slopes (AgC). Refer to the geotech report
prepared by Pacific Geo Engineering for further information.
1
ESM JOB� 1352-001-006 Rosewood Highlands
Developed Conditions:
Out of the 4.39-acres, 0.47 acres in the wetland / sensitive area tract are remaining
undisturbed and. The remaining 3.95-acres are being developed with 27 single-family
homes, approximately 340 linear feet of public residential roadway, 554 linear feet of
private residential roadway and 83 linear feet of joint use driveway.
Stormwater runoff from a majority of the site (roads, landscaped areas, and buildings)
is collected and conveyed via a closed pipe conveyance system to the
detention/water quality vault in the southeastern corner of the site.
Design Standards:
The Wet Season ESC plan is designed in accordance with the 2005 City of Renton
Amendments to the King County Surface Water Design Manual.
3. SITE SPECIFlC BMPs
Details of site specific BMPs are included in Appendix B of this report The following is
a list of the included details, and the City of Renton standard plan number.
Std Plan # Description
• 213.30 Plastic Covering
• 214.00 Silt Fence
• 215.10 Stabilized Construction Entrance
• 216.00 Sediment Pond
• 216.10 Sediment Pond Riser Detail
• 216.30 Catch Basin Filter
• 217.00 Interceptor Dike
• 217.10 Interceptor Swale
• 217.40 Check Dam Spacing and Cross Section
A TESC and grading plan has been prepare for the site showing the location of the
required BMPs. A copy of these plans is included in Appendix A of this report.
4. WET SEASON SPECIAL PROVISIONS
In addition to the standard requirements for erosion control during the dry season, the
following special provisions are required for construction during the wet season.
Excerpts from Appendix D of the 2005 King County SWDM, which includes the
associated BMPs and TESC measures, are included in Appendix C of this report I
2
ESM JOB� 1352-001-006 Rosewood Hiqhlands
1. The aliowed time that a disturbed area may remain unworked without cover
measures is reduced to two consecutive working days, rather than seven,
(Section D.3.2 - Cover Measures)
2. Stockpiles and steep cut and fill slopes are to be protected if unworked for
more than 12 hours. (Section D.3.2 - Cover Measures)
3, Cover materials sufficient to cover all disturbed areas shall be stockpiled on
site. (Section D.3.2 - Cover Measures)
4. All areas that are to be unworked during the wet season shall be seeded within
one week of the beginning of the wet season. (Section D.3.2.6 - Temporary
and Permanent Seeding)
5. Mulch is required to protect all seeded areas. (Section D.3.2.2 - Mulching)
6. A minimum of 220 linear feet of silt fence. (Fifty linear per acre) and the
necessary stakes must be stockpiled on site. (Section D.3.3.1 - Silt Fence)
7. Construction road and parking lot stabilization are required. (Section D.3.4.2 -
Construction Road/Parking Stabilization)
8. Sediment retention (TESC Pond) is required. (Section D.3.5.2.
9. Surface water controls (ditches and interceptor swales) are required. (Section
D.3.6)
10. Phasing and more conservative BMPs must be evaluated for construction
activity near the surface waters. (Section D.5.3 - Critical Areas Restrictions)
11.Any runoff generated by dewatering may be required to discharge to the
sanitary sewer (with appropriate discharge authorization), portable sand filter
systems, or holding tanks,
12.The frequency of maintenance review increases from monthly to weekly.
(Section D.5.4 - Maintenance Requirements)
5. CONSTRUCTION SEQUENCE
The developer is proposing to begin construction January 1, 2011 and estimates the
construction activities would be complete in 90 days (April 1, 2011). The following is
the proposed construction sequence.
1. Schedule a pre-construction sequence with the City of Renton.
2. Pre-construction meeting.
3. Post sign with name and phone number of TESC supervisor (may be
consolidated with the required notice of construction sign).
4. Flag or fence clearing limits.
5. Install catch basin protection on existing structures if required.
� 6. Grade and install construction entrance{s}.
� 7. Install perimeter protection (silt fence, brush barrier, etc.).
8. Excavate TESC pond and install pond riser outlet
9. Grade and stabilize construction roads,
10. Construct surface water controls (interceptor dikes, pipe slope drains, etc.)
simultaneously with clearing and grading for project development.
11, Maintain erosion control measures in accordance with city of Renton standards
and manufacturer's recommendations.
3
�I _ _
ESM JOBr 1352-001-006 Rosewood Hiqhlands
12. Relocate erosion control measures or install new measures so that as site
conditions change the erosion and sediment control is always in accordance
with the city of Renton erosion and sediment control standards,
13. Cover all areas that will be unworked for more than seven days during the dry
season or two days during the wet season with straw, wood fiber mulch,
compost, plastic sheeting or equivalent.
14.Stabilize all areas that reach flnal grade within seven days.
15.Seed or sod any areas to remain unworked for more than 30 days.
16. Install storm drainage system with temporary catch basin protection.
17. Excavate and construct stormwater vault
18. Install all other utilities, curb, gutter, sidewalk and paving.
19. Clean detention system as necessary.
20. Upon completion of the project, all disturbed areas must be stabilized and
BMPs removed if appropriate.
6. CONDITIONS FOR WET SEASON CONSTRUCTION
The following conditions are set by the City for construction during the wet season.
1. Any construction that will result in disturbed areas on or within a critical area or
associated buffer, shall be subject to the "Critical Area Restrictions" contained
in the Erosion Sedimentation Control (ESC) Standards. These provisions
include phasing the project whenever possible so that construction in these
areas is limited to the dry season.
2. During construction, ESC plans shall be revised as necessary by the ESC
supervisor or as directed by the City to address changing site conditions.
unexpected storm events, or non-compliance with the ESC performance criteria
in Section D.4.1 (p. D-69). If non-compliance with the ESC performance criteria
occurs, the plan must be updated within 48 hours of inspections or
investigations. Implementation of the onsite changes must occur within 5 days.
• All ESC measures shall be maintained and reviewed on a regular basis as
prescribed in the maintenance requirements for each BMP and in this section.
The ESC supervisor shall review the site at least weekly during the wet season,
and within 24 hours of significant storms. In general, a significant storm is one
with more than 0.5 inches of rain in 24 hours or less. A written record of these
reviews shall be kept on site with copies submitted to City of Renton
Development Services Division within 48 hours.
4
ESM JOB# 1352-001-006 Rosewood Highlands
7. SEDIMENT POND DESIGN
The TESC pond was designed in accordance with Appendix D of the 2005 King
County SWDM.
The TESC pond has been sized per the following requirements:
• The design flows are based on the developed conditions of the site and
calculated using the KCRTS program.
• The pond was sized based on the developed site 10-year, 15-minute storm
event to provide a higher level of protection.
• The pond has been designed with a length to width ratio of 3:1,
Sediment Pond Sizing Calculations:
Developed Basin
Impervious = 2.67 ac
Till Grass = 1.35 ac
Till Pasture = 0.13 ac
Total = 4.15 ac
The developed basin includes 0.20 tributary from offsite. The remaining
0.44 acres of the total 4.59 acres consist of the sensitive areas that will
not be disturbed.
KCRTS Output:
Flow Frequency Analysis
Time series File:rosewood-tesc.tsf
Project Location:5ea-Tac
---Annual Peak Flow Rates--- -----Flow Frequency Analysis-------
Flow Rate Rank Time of Peak - - Peaks - - Rank rteturn Prob
(CFS) (CFS) Period
1.27 6 8/27/O1 18:00 3.86 1 100.00 0.990
0.898 8 1/05/02 15:00 2.72 2 25.00 0.960
2.72 2 12/08/02 17:15 1.77 3 10.00 0.900
1.02 7 8/23/04 14:30 1.52 4 5.00 0.800
1.52 4 11/17/04 5:00 1.51 5 3.00 0.667
1.51 5 10/27/OS 10:45 1.27 6 2.00 0.500
1.77 3 10/25/06 22:45 1.02 7 1.30 0.231
3.86 1 1/09/O8 6:30 0.898 8 1.10 0.091
Computed Peaks 3.48 50.00 0.980
Q,o = 1.77 cfs (Developed 15 min, 10-yr storm flow)
*
SA = � Q�o ���
0.00096
5
ESM JOB� 1352-001-006 Rosewood Highlands I�
Where: II
sa = Minimum surface area (sfl
SA = 2*1'�� = 3,542 sf
0.00096
Required depth = 3.5 feet
The TESC pond shown on the plans provides 3,675 square feet of surface area at the
water elevation.
Dewatering Orifice Sizing Calculations:
:90=4.81*10-6 *AS * h
Where:
.ao = Orifice area (sfl
:�is = 3,542 sf (Minimum surface area)
1� = 3.> ft (Minimum head of water above orifice)
Ao = 4.81 *10-`' *3,54?" 3.5 = 0.0319 sf
The orifice diameter is as follows,
D = 13.54*Aoo�
Where:
D = Dewatering orifice (inches)
.90 = 0.0319 Sf (Orifice area)
D = 13.54*(0.0319)°5 � 2.42 inches
Use the closest standard hole diameter opening, which is 2.44 inches or
2-7/16''
Dewatering Riser Pipe Sizing:
The riser pipe (Frop-T) is sized to convey the developed 10-year, 15-minute, flow. Per
Figure 5.3.4.H (pg. D-50) of the KCSWDM, the lowest value from the following two
equations is used to size the outlet riser (see Appendix C - KCSWDM Figure 5,3.4H
Riser Inflow Curves and 15-minute time step tables).
�
Q = 3.782*D' *H'
Q =9.739*D*H-'
6
ESM JOB= 1352-0Q1_-006 ___ R_osE���ood Hiqh�ands
Where:
D= 1.0 ft (Diameter of Riser Pipe)
H =0.5 ft (Design head measured from crest of riser)
Q= Flow able to be conveyed (cfs)
Q=3.782*(l.0)` *(0.5)' =2.67 cfs
z
Q = 9.739"(1.0) *(0.5)' _ �.44Cfs
The 12" riser pipe can convey 2.67 cfs, which is more than the developed 10-year, 15-
minute flow rate of 1.77 cfs; therefore, the 12-inch diameter riser pipe can adequately
handle the flow.
Emergency Overflow Spillway Sizing:
The emergency overflow spillway shall convey the 100 year, developed design storm
event (Q100 = 3.50 cfs). Minimum spillway width (W) required is 6.00 feet.
Q,00
W = , , - 2.4H
(3.21)(H - j
Q,oa = 3.86 cfs, H = 0.5 ft, therefore W=2.20 ft
Use 6.0 ft for the emergency spillway width.
7
APPENDIX A
TESC and Grading Plans
� A PORTION OF THF NW 1/4 OF SFCTION 15.TWP.23 N. RGF.5 E�W.M.,KING COUNTY,WASHINGTON '
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SECTIO\' D.$ ESC 1�4PLEh9EVTATlO'� REQUIREMENTS
D.5.2 WET SEASON REQUIREMENTS
Any site�y�ith exposed soils during the wet season(October ] to April 30) shall be subject to the special
provisions belo«-. In addition to the ESC cover measures (see Section D3.2,p. D-]0),these provisions
include covering any newly seeded areas with mulch and identifying and seeding as much disturbed area
as possible prior to September 23 in order to pro��ide grass cover for the«-et season. A "wet season ESC
plan"must be submitted and approved b�-tlle Counn before ��ork proceeds or continues.
Wet Season Special Provisions
All of the following provisions for wet season construction are detailed in the referenced sections. These
requirements are listed here for the convenience of the designer and the reviewer.
1. The allowed time that a disturbed area may remain unworked without cover measures is reduced to
hvo consecutive working days,rather than seven(Section D.3.2).
2. Stockpiles and steep cut and fiil slopes are to be protected if unworked for more than 12 hours
(Section D.3.2).
3. Cover materials sufficient to cover all disturbed areas shall be stockpiled on site(Section D.3.2).
4. All areas that are to be unworked during the wet season shall be seeded within one«�eek of the
beginning of the�vet season(Section D3.2.5).
5. Mulch is required to protect all seeded areas(Section D3.2.1).
6. Fifty linear feet of silt fence(and the necessary stakes)per acre of disturbance must be stockpiled on
site(Section D.3.3.1).
7. Construction road and parking lot stabilization are required for all sites unless the site is underlain b}
coarse-grained soil (Section D.3.4.2).
8. Sediment retention is required unless no offsite discharge is anticipated for the specified design flo�
(Section D.3.5).
9. Surface water controls are required unless no offsite discharge is anticipated for the specified desien
flow(Section D.3.6).
10. Phasing and more conservative BMPs must be evaluated for construction activity near surface waters
(Section D.5.3).
11. Any runoff generated by dewatering may be required to discharge to the sanitary sewer(«-ith
appropriate discharge authorization),portable sand filter systems,or holding tanks.
12. The frequency of maintenance review increases from monthly to weekly(Section D.5.4).
D.5.3 CRITICAL AREAS RESTRICTIONS
Any construction that will result in disturbed areas on or���ithin a stream or associated buffer. a�vetland or
associated buffer,or within 50 feet of a lake shall be subject to the special provisions below. These
provisions include,whenever possible,phasing the project so that construction in these areas is limited to
the dry season. The County may require more conservative BMPs, including more stringent cover
requirements,in order to protect surface water quality: Any project proposing work within 50 feet of a
steep slope hazard area shall evaluate the need for diverting runoff that mieht flow over the top of the
slope.
Critical Areas Special Provisions
Any project that disturbs areas on or within a stream or associated buffer,wetland or a�sociated buffer, or
within 50 feet of a lake has the potential to seriously damage water resources,even if the project is
1!9'2009 2009 Surface Water Design'�9anual—.Appendix D
D-74
D.5.3 CRITICAL ARE.4S RESTRICTIONS I
relatively small. While it i�difficult to require specific measures for such projects because the ESC plan
must be very site specific,the following recommendations shall be incorporated into the plan where
appropriate:
1. Whenever possible,phase all or part of the project so that it occurs dunng the dry season. If this is
impossible,November through February shall be avoided since this is the most likely period for]arge,
high-intensity storms.
2. All projects shall be completed and stabilized as quickly as possible. Limiting the size and duration
of a project is probably the most effective form of erosion control.
3. Where appropriate,sandbags or an equivalent barrier shall be constructed between the project area
and the surface water in order to isolate the construction area from high water that might result due to
precipitation.
4. Additional perimeter protection shal]be considered to reduce the likelihood of sediment entering the
surface waters. Such protection might include multiple silt fences, silt fences with a higher AOS,
construction of a berm,or a thick layer of organic mulch upslope of a silt fence. i
5. If work is to occur within the ordinary high water mark of a stream,most projects must isolate the �I
work area from the stream by diverting the stream or constructing a cofferdam. Certain small projects ,
that propose only a small amount of grading may not require isolation since diversions typically result '
in disturbance and the release of some sediment to the stream. For such small projects,the potential
impacts from construction with and without a diversion must be weighed.
6. If a stream must be crossed,a temporary bridge shall be considered rather than allowing equipment to
utilize the streambed for a crossing. '
For projects in or near a salmonid stream,it may be appropriate to monitor the composition of any
spawning gravels within a quarter-mile of the site with a McNeil sampler or similar method approved by
King County before,during,and after construction. The purpose of such monitoring would be to
determine if the fine content of the gravels increases as a result of construction impacts. Monitoring
results could be used to guide erosion control efforts during construction and as a threshold for replacing
spawning gravels if the fine content nses significantly.
D.5.4 MAINTENANCE REQUIREMENTS ��
All ESC measures shall be maintained and reviewed on a regular basis as prescribed in the maintenance
requirements for each BMP and in this section. The ESC supervisor shall review the site at least twice a
month during the dry season,weekly during the wet season,and within 24 hours of significant storms. �
The Counry may require that a�r�ritten record of these reviews be kept on site with copies submitted to
DDES within 48 hours. �
Documentation II
If DDES requires that a written record be maintained,a standard ESC Maintenance Report, included in
Section 0(p. D-95),may be used. A copy of all the required maintenance reports shall be kept on site
throughout the duration of construction. Detailed maintenance requirements for each ESC measure are
provided in Section D.3.
Review Timing
During the wet season,weekly reviews shall be carried out every 6 to 8 calendar days. During the dry
season,monthly reviews shall be carried out within 3 days of the calendar day for the last inspection(e.g.,
if an inspection occurred on June 6,then the next inspection must occur between July 3 and July 9).
Reviews shall also take place within 24 hours of significant storms. In general,a significant storm is one
with more than 0.5 inches of rain in 24 hours or less. Other indications that a storm is"significant" are if
the sediment ponds or traps are filled�vith water,or if gullies form as a result of the runoff.
2009 Surface Water Design Manual—Appendix D I1�)2009
D-75
-�
SECTI01�D.5 ESC l�-iPLE�9ENTATION REQUIREMEVTS ',
,�'ote: The site is to be ir� compliance 11•ith the regulations of this appendix at al/times. The reguirement �',
for periodre�•e��iews does not remove the applicant's responsibilit}�for having the site constantly in ',
compliance ivith Core Reyuii•ement#S and the requireme�its o�'this appendix. The revieK�s ar-e a I
nzechanism to ensure that ull measures are thoroughly checked on a regular basis and that there is
documentation of compliance. Tlre requirement for these 1•e��iervs does not mean that ESC is�o be ignored
i��behveen.
D.5.5 FINAL STABILIZATION
Prior to obtaining fina]construction approval,the site shall be stabilized,the structural ESC measures, ,
such as silt fences and sediment traps,removed,and drainage facilities cleaned. The remova]of ESC
measures is not required for those projects, such as plats,that will be followed by additional construction
under a different permit. In these circumstances, the need for removing or retaining the measures must be
e��aluated on a site-specific basis.
To obtain final construction approval,the following conditions must be met:
I. All disturbed areas of the site shall be vegetated or otherwise permanently stabilized. At a
minimum, disturbed areas shall be seeded and mulched(see Section D.3.2.5)with a high likelihood
that su�cient cover will develop shortly after final approval. Mulch without seeding is not adequate
to allow final approval of the permit,except for small areas of mulch used for landscaping. The only
erceptions to these reyuirements are lots within a plat that are to be developed under an approved
residential permit immediately following plat appro��al. In these cases,mulch and.�or temporary
seeding are adequate for cover.
2. Structural measures such as,but not limited to,silt fences,pipe slope drains,construction entrances,
storm drain inlet protection,and sediment traps and ponds shall be removed from the site. Measures
that will quickly decompose,such as brush barriers and organic mulches,may be left in place. In the
case of silt fences,it may be best to remove fences in conjunction with the seeding,since it may be
necessary to bring machinery back in to remove them. This will result in disturbed soils that will
again require protection. The DDES inspector must approve an applicant's proposal to remove
fencing prior to the establishment of vegetation. In some cases,such as residential building following
plat development,it shall be appropriate to leave some or all ESC measures for use during subsequent
development. This shall be determined on a site-specific basis.
3. All permanent surface water facilities,including catch basins,manholes,pipes,ditches,channels,
flow control facilities,and water quality facilities,shall be cleaned. Any offsite catch basin that
required protection during construction(see Section D.3.53)shall also be cleaned.
4. If only the infrastructure of the site has been developed(e.g.,subdivisions and short plats)with
building construction to occur under a different permit,then the critical area buffers,Critical Area
Tracts,or Critical Area Setback Areas shall be clearly marked as described in Section D3.1 (p. D-8)
in order to alert future buvers and builders.
1:�9�2009 20�9 Surface 1Vater Desien Manual—Appendix D
D-76
APPENDIX B
City of Renton TESC Details ,
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TOE IN SHEETING IN � I—I I I i I I I �����'
MINIMUM a'X4"TRENCH � I � � I—I I �
III III—I
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—III—III—
—III—III 1
PROVIDEENERGYDISSIPATION � I—I I I—I I I - � �
AT TOE WHEN NEEDED — � � � � .
� � �— — �—I� �— .
INOTES
i1. CONDITION OF USE ,
1.1. PLASTIC COVERING MAY BE USED ON DISTURBED AREAS THAT REQUIRED COVER MEASURES FOR LESS THAN 30 DAYS.
I 1.2. PLASTIC IS PARTICULARLY USEFUL FOR PROTECTING CUT AND FILL SLOPES AND STOCKPILES.
1.3. CLEAR PLASTIC SHEETING MAY BE USED OVER NEWLY-SHEEDED AREAS TO CREATE A GREENHOUSE EFFECT AND ENCOURAGE GRASS
, GROWTH.CLEAR PLASTIC SHOULD NOT BE USED FOR THIS PURPOSE DURING THE SUMMER MONTHS
I 1.4. THIS METHOD SHALL NOT BE USED UPSLOPE OF AREAS THAT MIGHT BE ADVERSELY IMPACTED BY RUNOFF.SUCH AREAS INCLUDE STEEP AND
UNSTABLE SLOPES
I .
: 2. DESIGN AND INSTALLATION SPECIFICATIONS
2.1. PLASTIC SHEETING SHOULD HAVE A MINIMUM THICKNESS OF 0.03 MILLIMETERS.
2.2. 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.
3. MAINTENANCE STANDARDS
3.1. TORN SHEETS MOST BE REPLACED AND OPEN SEAMS REPAIRED.
3.2. IF THE PLASTIC BEGINS TO DETERIORATE DIE TO ULTRAVIOLET RADIATION,IT MOST BE COMPLETELY REMOVED AND REPLACED.
3.3. WHEN THE PLASTIC IS NO LONGER NEEDED,IT SHALL BE COMPLETELY REMOVES.
���i��,� STD. PLAN - 213.30
i.s� � PUBLIC WORKS PLASTIC COVERING
�,�`�$ DEPARTMENT
�N.�O hSARCH 2O08
a
JOINTS IN FILTER FABRIC SHALL BE SPLICED
1
AT POSTS.USE STAPLES.WIRE RINGS,OR
a 2`x2"BY 14 Ga.WIRE OR
s EQUIVALENT TO ATTACH FABRIC TO POSTS.
EQUIVALENT,IF STANDARD
3 STRENGTH FABRIC USED I
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FILTER FA6RIC-� I
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6'MAX. MINIMUM 4'x4'TRENCH � �ii �
/ BACKFILL TRENCH WITH /
POST SPACING MAY BE INCREASED
NATIVE SOIL
TO 8'IF WIRE BACKING IS USE�
2"x4'WOOD POSTS.STEEL FENCE
POSTS,REBAR,OR EQUIVALENT
NOTES
1. CONDITION OF USE
1.1. SILT FENCE MAY BE USED DOWNSLOPE OF ALL DISTURBED AREAS.
1.2. SILT FENCE IS NOT INTENDED TO TREAT CONCENTRATED FLOWS,NOR IS INTENDED TO TREAT SUBSTANTIAL AMOUNTS OF OVERLAND FLOW.
ANY CONCENTRATED FLOW MOST BE CONVEYED THROUGH THE DRAINAGE SYSTEM TO A SEDIMENT TRAP OR POND.
2. DESIGN AND INSTALLATION SPECIFICATIONS
2.1. THE GEOTEXTILE USED MOST MET THE STANDARD LISTED BELLOW.A COPY OF THE MANUFACTURER'S FABRIC SPECIFICATIONS MOST BE
AVAILABLE ON SITE.
AOS(ASTM D4751) 3D-10051EVE SRE(0.6PO.15MM)FOR SILT FlLM
50-10051EVE SIZE(030-015MM)FOR OTHER FABRICS
WATERPERMITTIVITY�ASTMD491) 0.02SEC^-1MINIMUM
GRABTENSILESTRENCHT�ASTM D4632) 180LBS.MIN.FORE%TRASTRENGH FABRIC
100 LBS.MIN.FOR STANDARD STRENGM FABRIC
GRAB TENSI LE ELONGATION(ASTM D4632)30%MAX. �
ULTRAVIOIATE RESISTANCE(ASTM D43551 7094,tdlN.
2.2. STANDARD STRENGTH FABRIC REQUIRES WIRE BACKING TO INCREASE THE STRENGTH OF THE FENCE.WIRE BACKING OR CLOSER POST
SPACING MAY BE REQUIRED FOR EXTRA STRENGTH FABRIC IF FIELD PERFORMANCE WARRANTS A STRONGER FENCE.
2.3. WHERE THE FENCE IS INSTALLED,THE SLOPE SHALL NOT BE STEEPER THAN 2H:1V
2.4. IF A TYPICAL SILT FENCE IS USED,THE STANDARD 4X4 TRENCH MAY NOT BE REDUCED AS LONG AS THE BOTTOM 8 INCHES OF THE SILT FENCE
IS WELL BURIED AND SECURE IN A TRENCH THAT STABILIZES THE FENCE AND DOES NOT ALLOW WATER TO BYPASS OR UNDERMINE THE SILT
FENCE.
3. MAINTENANCE STANDARDS
3.1. ANY DAMAGE SHALL BE REPAIR IMMEDIATELY.
3.2. IF CONCENTRATED FLOES ARE EVIDENT UPHILL OD THE FENCE,THEY MUST BE INTERCEPTED AND CONVEYED TO A SEDIMENT TRAP OR POND.
3.3. IT IS IMPORTANT TO 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 REMOVED THE TRAP
SEDIMENT.
3.4. SEDIMENT MOST BE REMOVED WHEN SEDIMENT IS 6 INCHES HIGH. I
3.5. IF THE FILTER FABRIC(GEOTEXTILE)HAS DETERIORATED DUE TO ULTRAVIOLET BREAKDOWN,IT SHALL BE REPLACED. �
ti`tY O _
+��� PUBLIC WORKS SILT FENCE
STD. PLAN 214.Q0
,�,�$ DEPARTMENT
�NTO MARCH 2O08
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z DRIVEWAVS SHALL BE PAVED TO THE EDGE
e P OF R-6W PRIOR TO INSTALLATION OF THE
o Ey'�Sj,NGRo 0 / DAMAG NG OFOT ENROADWAVO AVOID
IT IS RECOMMENDED THAT THE I�
R=25'MIN. ENTRANCE BE CROWNED SO THAT '�
RUNOFF DRAINS OFF THE PAD �
�OQ
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INSTALL DRIVEWAY CUWERT IF THERE \�
IS A ROADSIDE DITCH PRESENT,AS
PER CITY ROAD STANDARDS
4'-8"�UARRY SPALLS
GEOTEXIILE
���
� \ ,�6
12'MIN.THICKNESS \ �� PROVIDE FUIL WIDTH OF
NOTES INGRESS/EGRESS AREA
1. CONDITION OF USE
1.1. CONSTRUCTION ENTRANCE SHALL BE STABILIZED WHEREVER TRAFFIC WILL BE LEAVING A CONSTRUCTION SITE AND TRAVELING ON
PAVED ROADS OR OTHER PAVED AREAS WITHIN 1,000 FEET OF THE SITE.
GRABTENSILESTREBNGTH�ASTMD4751) 200PSIMIN.
GRAB TENSILE ELONGATION(ASTM D4632) 30%MAX.
MULLEN BURSTSTRENGTH(ASTM D3786-80A) QOOPSI MIN.
AOS(ASTM D4751) 20-45(U.S.STANDARD SIEVE SIZE)
2. DESIGN AND INSTALLATION SPECIFICATIONS
2.1. HOG FUEL(WOOD BASED MULCH)MAY BE SUBSTITUTED FOR OR COMBINED WITH QUARRY SPALLS IN ARES THAT WILL BOT BE USED
FOR PERMANENT ROADS.HOG FUEL IS NOT RECOMMENDED FOR ENTRANCE STABILIZATION IN URBAN AREAS.THE INSPECTOR MAY
AT ANY TIME REQUIRE THE USE OF QUARRY SPALLS IF THE HOG FUEL IS NOT PREVENTING SEDIMENT FROM BEING TRACKED ONTO
PAVEMENT OR IF THE HOG FUEL IS BEING CARRIED ONTO PAVEMENT.
2.2. FENCING SHALL BE INSTALLED AS NECESSARY TO RESTRICT TRAFFIC TO THE CONSTRUCTION ENTRANCE.
2.3. 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.
3. MAINTENANCE STANDARDS
3.1. QUARRY SPALLS SHALL BE ADDED IF THE PAD IS NO LONGER IN ACCORDANCE WITH THE SPECIFICATIONS.
3.2. IF THE ENTRANCE IS NOT PREVENTING SEDIMENT BEING TRACKED ONTO PAVEMENT,THEN ALTERNATIVE MEASURES TO KEEP THE
STREETS FREE OF SEDIMENT SHALL BE USED.THIS MAY INCLUDE STREET SWEEPING,AN INCREASE IN THE DIMENSIONS OF THE
ENTRANCE,OR THE INSTALLATION OF THE WHEEL WASH.IF WASHING IS USED,IT SHALL BE DONE ON AN AREA COVERED WITH
CRUSHED ROCK,AND WASHED WATER SHALL DRAIN TO A SEDIMENT TRAP OR POND.
3.3. ANY SEDIMENT THAT IS TRACKED ONTO PAVEMENT SHALL BE REMOVED IMMEDIATELY BY 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 SWEEPING IS INEFFECTIVE AND THERE IS A THREAT TO PUBLIC SAFETY.IF IT NECESSARY TO WASH THE STREETS,A
SMALL SUMP MUST BE CONDUCTED.THE SEDIMENT WOULD THEN BE WASHED INTO THE SUMP WHERE IT CAN BE CONTROLLED AND
DISCHARGED APPROPRIATELY.
3.4. ANY QUARRY SPALLS THAT ARE LOOSENED FROM THE PAD AND END UP ON THE ROADWAY SHALL BE REMOVED IMMEDIATELY.
3.5. IF VEHICLES ARE ENTERING OR EXITING THE SITES AT POINTS OTHER THAN THE CONSTRUCTION ENTRANCE(S),FENCING SHALL BE
INSTALLED TO CONTROL TRAFFIC.
��Y � STD. PLAN — 215.10
��,���' PUBLic woRxs STABILIZED
���`�$ DEPARTMENT CONSTRUCTION ENTRANCE h4ARCH 2O08
�NT�
Y
ai TO PREVENR I�NLTOO�SLOPE
� AROUND SID S
�
m THE POND LENGTH SHALL BE 3 TO 6
� TIMES THE MAXIMUM POND WIDTH
p EME SPILN�WaOVERF�O's/
a � /
°°' �°�°
0
OND LENGT ���
INFLOW �O C
SILT FENCE OR RISER PIPE DISCHARGE TO STABILIZED
EQUIVALENT DIVIDER I CONVEYANCE OUTLET OR
I1 LEVELSPREAdER
!
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i
RISER PIPE CREST OF 6'MIN.WIDTH
(PRINCIPAL SPILLWAY) EMERGENCY SPILLWAY�
OPEN AT TOP WITH
TRASH RACK
I—I I I—= I � � �•M�N EMBANIQ,4ENT COMPACTED 95°h.
-I I I—�I I.=I I I—I - PERVIOUS MATERIALS SUCH AS '�.
DEWATERING DEVICE � ___-_-__-__� GRAVEL OR CLEAN SAND SHALL
I I I i "'S (SEE RISER DETAIL) -------- NOT BE USED. ��
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POLYETHYLENE CAP �
PROVIDE ADEQUATE
�� /STRAPPING I
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PERFORATED POLYETHYLENE � �` �II',
DRAINAGE TUBING,DIAMETER � CORRUGATED '�,
MIN.2"LARGER THAN ; METAL RISER '
DEWATERING ORIFICE.� �I
TUBING SHALL COMPLY '
'JJITH ASTM F667 AND � 3.5' MIN. ��.
AASHTO M294. �� .
�--�--y WATERTIGHT DEWATERING ORIFICE,SCHEDULE ,,
� -� COUPUNG I
F--� 40 STEEL STUB MIN.
�____� � TACK WELD
� DIAMETER AS PER CALCULATIONS ,
I
� 6'MIN.
18' MIN �
ALTERNATIVELY.METALSTAKES
� AND WIRE tv1AY BE USED TO
CONCRETE BASE PREVENTFLOTATION
� 2X RISER DIA. MIN. -►{
I
�Y STD. PLAN - 216.10
�'�.���' PUBLIC WORKS SEDIMENT POND
��``��,� DEPARTMENT RISER DETAIL MARCH 2O08
5"MAX.
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3 1
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� SEDIMENT AND DEBRIS
i .a o .
�. -. OVERFLOW BYPASS
0
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�D o � BELOW INLET GRATE DEVICE
U v
% �� Fl�TERED�
I I WATER �
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G ' Q
' p ' , ° � ' ' D
SECTION VIEW
DRAINAGE GRATE
—RECTANGULAR GR,4TE SHOWN � RETRIEVAL SYSTEM(TYP.)
\
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BELOW INLET GRATE DEVICE OVERFLOW BYPASS(TYP.)
/
ISOMETRIC VIEW
NOTES
1. Size the Below Inlet Grate Device(BIGD)for the storm water structure it will service.
2. The BIGD shall have a built-in high-flow relief system(overflow bypass).
3. The retrieval system must allow removal of the BIGD without spilling the coliected material.
4. Perform maintenance in accordance with Standard Specification 8-01.3(15).
Y �
���� PUBLIC WORKS CATCH BASIN FILTER i �' P� - 218.30
�\`` �,$ DEPARTMENT I �
F�,TO , �4ARCH 2O08
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f° 2:1 MAX.SLOPE
; DIKE MATERIAL COMPACTED i
¢ 90'h MODIFIED PROCTOR \ j �\
0
; 2'MIN. !! \1`
' -18'MIN. \ I -I I I
r - � -_� � �_
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-I I I-I I I-I I I DIKE SPACING DEPENDS ON SLOPE GRADIENT
NOTES
1. CONDITION OF USE
1.1. REQUIRED AT:
1.1.1. THE TOP OF ALL SLOPES IN EXCESS OF 3H:1 V AND WITH MORE THAN 20 FEET OF VERTICAL RELIEF.
1.1.2. AT INTERVALS ON ANY SLOPES THAT EXCEEDS THE DIMENSIONS SPECIFIED BELLOW.
AVERAGE SLOPE SLOPE PERCENT FLOWPATH LENGTH
20H:1V 3-5% 300 FEET
(10T020)H:1V 5-10% 200FEET
(4T010)H:1V 1a25% 100FEET
(2T04)H:1V 25-50% 50FEET
2. DESIGN AND INSTALLATION SPECIFICATIONS
2.1. FOR SLOPES STEEPER THAN 2H:1V WITH MORE THAN 10 FEET OF VERTICAL RELIEF,BENCHES MAY BE CONSTRUCTED OR CLOSER SPACED
INTERCEPTOR DIKES MAY BE USED.THE DESIRE MEASURE MOST BE DESIGNED BY AN ENGINEER TO EFFECTIVELY INTERCEPT THE HIGH
VELOCITY RUNOFF TO A SEDIMENT POND OR TRAP.
2.2. CONSTRUCTION TRAFFIC OVER TEMPORARY DiKES SHALL BE MINIMIZED.
3. MAINTENANCE STANDARDS
3.1. DAMAGE RESULTING FROM RUNOFF OR CONSTRUCTION ACTIVITY SHALL BE REPAIRED IMMEDIATELY.
3.2. IF THE FACILITY DO NOT REGULARLY RETAIN STORM RUNOFF,THE CAPACITY ANDlOR FREQUENCY OF THE DIKES SHALL BE INCREASED.
��Y � STD. PLAN - 217.00
,�� PUBLIC titi'ORKS INTERCEPTOR DIKE
,P��� DEPARTMENT
��p MARCH 2O08
Q
= 2:1 MAX.SLOPE
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�I I i�., !_I-1 I 1= ; , ,_
I��,III- � -
=I 1-� '
2'MIN.
SWALE SPACING DEPENDS ON SLOPE GRADIENT
NOTES
1. CONDITION OF USE
1.1. REQUIRED AT:
1.1.1. THE TOP OF ALL SLOPES IN EXCESS OF 3H:1V AND WITH MORE THAN 20 FEET OF VERTICAL RELIEF.
1.1.2. AT INTERVALS ON ANY SLOPES THAT EXCEEDS THE DIMENSIONS SPECIFIED BELLOW.
AVERAGE SLOPE SLOPE PERCENT FLOWPATH LENGTH
20H:1V 3-59�0 300FEET
(1OT020)H:1V 5-1096 200fEET
(4TOl0�H:1V 10-25% 100FEEf
(2 TO 4)H:1V 25-50% SO FEET
2. DESIGN AND INSTALLATION SPECIFICATIONS
2.1. FOR SLOPES STEEPER THAN 2H:1V WITH MORE THAN 10 FEET OF VERTICAL RELIEF,BENCHES MAY BE CONSTRUCTED OR CLOSER
SPACED INTERCEPTOR SWALES MAY BE USED.THE DESIRE MEASURE MOST BE DESIGNED BY AN ENGINEER TO EFFECTIVELY
INTERCEPT THE HIGH VELOCITY RUNOFF TO A SEDIMENT POND OR TRAP.
2.2. CONSTRUCTION TRAFFIC OVER TEMPORARY SWALES SHALL BE MINIMIZED.
3. MAINTENANCE STANDARDS
3.1. DAMAGE RESULTING FROM RUNOFF OR CONSTRUCTION ACTIVITY SHALL BE REPAIRED IMMEDIATELY.
3.2. IF THE FACILITY DO NOT REGULARLY RETAIN STORM RUNOFF,THE CAPACITY AND/OR FREQUENCY OF THE SWALES SHALL BE
INCREASED.
+���Y STD. PLAN — 217.10
� PUBLIC woRKs INTERCEPTOR SWALE
'`` DEPARTMENT
�'�N,tp'$ MARCH 2O08
S
� ROCK MUST COMPLETELY COVER THE
BOTTOM AND SIDES OF THE DITCH
z
3
<
o �� 6"MIN. ��� � ���.
���a�a ������ �
�O��� ^-�� � � Q 24"MIN.
,n ����� ���� � I�
� �,�-��� 0 �
2:1 SLOPES
i1
�
� 1
�p� � ��oO� L=TA AND B AREEOF EQUA LELE�VATION z�-4�ROCK
-111= �'
,�A B
' � � '-1 I I=���—��— , ` aa�
���—�ii-1 !_,;,i l 1,=� � __— o�� �a
i '=i I 1-1 I 1-1 I —___—_� ��op,�
- ' -I -� I I_ I- -
' �� � '_� � =i =� � �_
NOTES
1. CONDITION OF USE
1.1. WERE CONCENTRATED RUNOFF FROM DISTURBED AREAS TO AND FROM PONDS OR TRAPS.
1.2. TO CONVEY RUNOFF INTERCEPTED FROM UNDISTURBED AREAS AROUND THE SITE TO A NON-EROSIVE DISCHARGE POINT.
2. MAINTENANCE STANDARDS
2.1. ANY SEDIMENT DEPOSITION OF MORE THAN 0.5 FEET SHALL BE REMOVED SO THAT THE CHANNEL IS RESTORED TO ITS ORIGINAL
DESIGN CAPACITY.
2.2. THE CHECK DAMS SHALL BE EXAMINED FOR SIGNS OF SCOURING AND EROSION OF THE BED AND BANKS.IF SCOURING AND EROSION
HAS OCCURRED,AFFECTED AREAS SHALL BE PROTECTED BY RIPRAP OR AN EROSION CONTROL BLANKET.
�Y S'I'D. PLAN - 217.40
ti o
��4 PUBLIC WORKS CHECK DAMS SPACING AND
,Q�_�/$ DEPARTMENT CROSS SECTIONS
�N,�p MARCH 2O08
APPENDIX C
King County TESC Details
KING COL\Tl'. \�'.ASHINGTOT�, Sl RFACE V4'ATER DESIGT� '�1.ANU.4L
D.3 ESC MEASURES
This section details the ESC measures that are required to minimize erosion and sediment transport off a
construction site. These ESC measures represent Best Management Practices(BMPs%6 for the control of
erosion and entrained sediment as well as other impacts related to consrruction such as increased runoff
due to land disturbing activities. The measures and practices are grouped into nine sections corresponding
to each of the nine categories of ESC measures in Core Requirement#5, Section 12.5 of the King Count}% I
Surface YVate��Design Manual. The introductory paragraphs at the beginning each section present the ��
basic requirement for that category of ineasures,the purpose of those measures, installation requirements I
relative to construction activity, guidclines for the conditions of use,and other infonnation relevant to all I
measures in the sectionlcategory. Compliance with each of the nine categories of the ESC measures,to ,
the extent applicable and necessary to meet the performance criteria in Section D.4,and compliance with I
the ESC implementation requirements in Section D.S,constitutes overall compliance with King County's
ESC Standards. Note:Additional measures shall be required by the County if the existing standards are
insufficient to protect adjacent properties, drainage facilities, or water resou�•ces.
The standards for each indi�ridual ESC measure are divided into four sections:
1. Purpose
2. Conditions of Use
3. Design and Installation Specifications
4. Maintenance Requirements. I,
A code and symbol for each measure have also been included for ease of use on ESC plans. Note that the II
� "Conditions of Use"always refers to site conditions. As site conditions change,ESC measures must be I�
changed to remain in compliance with the requirements of this appendix. '
Whenever compliance with King County ESC Standards is required, all of the following categories of
ESC measures must be considered for application to the project site as detailed in the following sections:
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 a sediment pond or trap 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 a sediment pond or trap,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
6 Best Management Practices(BMPs)means the best available and reasonable physical,structural,managerial,or behavioral
activities,that when singly or in combination,eliminate or reduce the contamination of surface and/or ground waters.
2009 Surfacc`'l'ater Design Manual—Appendix D I!9,�2009
D-7
SECTIO'�D.3 ESC MEASURES
conveyed to a stabilized discharge point downstream of the disturbed areas. Surface water collection
ineasures shall be installed concurrently��ith or immediately follo���ing rough grading and shall be
designed, constructed,and stabilized as needed to minimize erosion.
7. Dewatering Control: The���ater resulting from construction site de-watering activities must be
treated prior to discharge or disposed of as specified.
8. Dust Control: Pre�entative 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 made to prevent increases in the existing site conditions 2-
year and 10-year runoff peaks discharging from the project site during construction.
� D.3.1 CLEARING LIMITS
Prior to any site clearing or grading, those areas that are to remain undisturbed during project construction
shall be delineated. At a minimum,clearing limits shall be installed at the edges of all critical area buffers
and any other areas required to be left uncleared such as portions of the site subject to clearing limits
under KCC 16.82.150, areas around significant trees identified to be retained,and other areas identified to
be left undisturbed to protect sensitive features.
Purpose: The purpose of clearing limits is to prevent disturbance of those areas of the project site that are
not designated for clearing or grading. This is important because limiting site disturbance is the single
most effective method for reducing erosion. Clearing limits may also be used to control construction
traffic,thus reducing the disturbance of soil and limiting the amount of sediinent tracked off site. ',
� � VVhen to Install: Clearing limits shall be installed prior to the clearing and/or grading of the site. I
Measures to Use: Marking clearing limits by delineating the site with a continuous length of brighth-
colored survey tape is soinetimes sufficient. The tape may be supported by vegetation or stakes, and it
shall be 3 to 6 feet high and highly visible. Critical areas and their buffers require more substantial
protection and shall be delineated with plastic or meta] safety fences or stake and wire fences. Fencing
may be required at the County's discretion to contro] construction rraffic or at any location where greater
protection is warranted. Permanent fencing may also be used if desired by the applicant. Silt fence, in
coinbination with survey flagging, is also an acceptable method of marking critical areas and their buffers.
D.3.11 PLASTIC OR METAL FENCE
~ Code: FE Symbol: �h r .;�''�rr r,:i2Y'%�'' x �x
Purpose
Fencing is intended to (I)restrict clearing to approved limits; (2)prevent disturbance of critical areas,
their buffers, and other areas required to be left undisturbed; (3)limit construction traffic to designated
construction entrances or roads; and (4) protect areas�vhere marking with survey tape may not provide
adequate protection.
Conditions of Use
To establish clearing limits,plastic or metal fence may be used:
1. At the boundary of critical areas,their buffers,and other areas required to be left uncleared.
2. As necessary to control �ehicle access to and on the site (see Sections D.3.4.1 and D.3.4.2).
]-9i?009 2009 Surface�'�'ater Design h4anual—Appendix D
D-8
D.�.l CLEARING LIM17"S
Design and Installation Specifications
1. The fence shall be designed and installed according to the manufacturer's specifications.
2. The fence shall be at least 3 feet high and must be highly visible.
3. The fence shall not be«�ired or stapled to trees.
Maintenance Requirements
1. If the fence has been damaged or visibility reduced;it shall be repaired or replaced immediately and
visibility restored.
2. Disturbance of a critical area, critica] area buffer,native growth retention area, or any other area
required to be left undisturbed shall be reported to the Count} for resolution.
D.3.1.2 STAKE A'�1D «'IRE FEI�CE
_:� -
;S,;,,F�,
Code: S�b'F Sr'mbal: �%
Purpose
Fencing is intended to(1)restrict clearing to approved limits; (2)prevent disturbance of critical areas,
their buffers, and other areas required to be left undisturbed; (3)limit construction traffic to designated
construction entrances or roads; and(4)protect any areas where marking with survey tape may not
� provide adequate protection.
Conditions of Use
To establish clearing limits,stake or wire fence may be used: °
1. At the boundary of critical areas,their buffers,and other areas required to be left uncleared.
?. As necessary,to control vehicle access to and on the site(see Sections D.3.4.1 and D.3.4.2).
Design and Installation Specifications
See Figure D.3.].A for details.
Maintenance Requirements
1. If the fence has been damaged or visibility reduced, it shall be repaired or replaced immediately and
visibility restored.
2. Disturbance of a critical area,critical area buffer,native growth retention area,or other area required
to be left undisturbed shall be reported to the County for resolution.
3. The County may require more substantial fencing if the fence does not prevent encroachment into
those areas that are not to be disturbed.
2009 Surface Water Design Manual—Appendix D lr9%2009
D-9
SECTION D3 ESC MEASURES
FIGURE D.31.A STAKE Al�D WIRE FENCE
DO NOT NAIL OR STAPLE
SURVEY FLAGGING �gqLING WIRE WIRE TO TREES
l '
� ; Ii
�,
3' MIN.
I 10'—20'�
METAL
FENCE POST
I ' I -I I I- ; _� '=1 I I I I-�i I I-I ' I-I I I- ! I I I 1- �
-� �- ���-���-�� ���-� �-�-���-���-����- � �-�
12" MIN.
� 1 �
D.3.2 COVER MEASURES
Temporary and permanent cover measures shall be provided to protect all disturbed areas, including the
faces of cut and fill slopes. Temporary cover shall be installed if an area is to remain unworked for more
than seven days during the dry season(May 1 to September 30)or for more than two consecutive working
days during the wet season(October 1 to April 30). These time limits may be relaxed if an area poses a
low risk of erosion due to soil type, slope gradient, anticipated weather conditions,or other factors.
Conversely,the County may reduce these time limits if site conditions wanant greater protection (e.g.,
adjacent to significant aquatic resources or highly erosive soils)or if significant precipitation(see Section
D.5.2)is expected. Any area to reinain unw�orked for more than 30 days shall be seeded or sodded,unless
the County determines that winter weather makes vegetation establishment infeasible. During the wet
season,slopes and stockpiles at 3H:I V or steeper and with more than ten feet of vertical relief shall be
covered if they are to remain unworked for more than 12 hours. Also during the wet season,the material
necessary to cover all disturbed areas must be stockpiled on site. The intent of these cover requirements is
to have as much area as possible covered during any period of precipitation.
Purpose: The purpose of covering exposed soils is to prevent erosion,thus reducing reliance on less
effective methods that remove sediment after it is entrained in runoff. Cover is the only practical method
of reducing turbidity in runoff. Structural measures, such as silt fences and sediment ponds, are only
capable of removing coarse particles and in most circumstances have little to no effect on hzrbidity.
When to Install: Any exposed soils that will remain unworked for more than the time limit set above
shall be covered by the end of the working day. If the exposed area is to remain unworked for more than
30 days,the area shall be seeded with the temporary seed mix or an equivalent mix that will provide rapid
protection(see Section D.3.2.5). If the disturbed area is to remain unworked for a year or more or if the
area has reached final grade,permanent seed mix or an equivalent mix shall be applied.
Measures to Use: Cover methods include the use of surface roughening,mulch,erosion control nets and
blankets,plastic covering,seeding,and sodding. Mulch and plastic sheeting are primarily intended to
protect disturbed areas for a short period of time,typically days to a few months. Seeding and sodding are
measures for areas that are to remain un��orked for months. Erosion nets and blankets are to be used in
conjunction with seeding steep slopes. The choice of ineasures is left to the designer;however,there are
restrictions on the use of these methods,which are listed in the"Conditions of Use" and the"Design and
Installation Specifications" sections for each measure.
l 19i2009 2009 Surface l'�'ater Design 1�4anual—.Appendix D
D-10
D.i2 CO�'ER�4EASURES
The methods listed are by no means exhaustive. Variations on the standards presented here are
encouraged if other cost-effective products or methods provide substantially equi��alent or superior
perfonnance. Also,the details of installation can,and should,��ary with the site conditions. A useful
reference on the application of cover measures in the Puget Sound area is Horner,Guedrey,and Kortenhof
(1990).
D.3.2.1 SURFACE ROUGHENI�'G
Purpose
The purpose of surface roughenin� is to aid in the establishment of�egetati�e co�er and to reduce runoff
velocity,increase infiltration,and provide for sediment trapping through the provision of a rough soil
surface. The rough soil surface may be created by operating a tiller or other equipment on the contour to
fonn horizontal depressions or by leaving slopes in a roughened condition by not fine grading.
Conditions of Use
1. All slopes steeper than 3:1 and greater than 5 vertical feet require surface roughening.
2. Areas with grades steeper than 3:1 should be roughened to a depth of 2 to 4 inches priar to seeding.
3. Areas that will not be stabilized immediately may be roughened to reduce runoff�•elocity until
seeding takes place.
4. Slopes with a stable rock face do not require roughening.
5. 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 D.3.2.A for infonnation on tracking and contour
furrov��s. Factors to be considered in choosing a method are slope steepness,mowing requirements, and
whether the slope is forn�ed by cutting or filling. Sole reliance on roughening for teinporary erosion
control is of limited effectiveness in intense rainfall events. Stair-step grading may not be practical for
sandy, steep, or shallow soils.
1. Disturbed areas that will not require mowing may be stair-step graded,grooved,or left rough after
filling
2. 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 mo�-ing equipment.
Stair steps must be on contour or gullies will form on the slope.
3. Areas that will be mowed(slopes less steep than 3:1)may have small furrows left by disking,
harrowing,raking,or seed-planting machinery operated on the contour.
4. Graded areas with slopes greater than 3:1 but less than 2:1 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.
5. Tracking is done by operating equipment up and down the slope to leave horizontal depressions in the
soil.
2009 Surface 1�'ater Desien 'vlanual—Appendix D 1 r'y,2009
D-11
D.3.2 COVER�9E.ASURES
D.3.2.2 MULCHING
� '
_-- �- �
Code: MU Svmbol: `�
Purpose
The purpose of mulching soils is to provide immediate teinporary 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 enonnous variety of mulches that may be used. Only the most
common types are discussed in this section.
Conditions of Use
As a temporary cover measure,mulch should be used:
1. On disturbed areas that require cover rneasures for less than 30 days
2. As a cover for seed during the wet season and during the hot summer months
3. During the wet season on slopes steeper than 3H:1 V with more than 10 feet of vertical relief.
Design and Installation Specifications
For mulch materials,application rates,and specifications, see Table D.3.2.A. 11�ote: Thicknesses niay be
incr-eased for disturbed areas in or near•critical areas or other areas highly susceptible to erosion.
Maintenance Standards
]. The thickness of the cover must be maintained.
2. 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 drainage problem shall be assessed and alternate
drainage such as interceptor swales may be needed to fix the problem and the eroded area remulched.
�__
f
I �
2009 Surface Water Design Manual—Appendix D 1 i9.r2009
D-13
SECTION D.3 ESC MEASL'RES
TABLE D.3Z.A i�IULCH STANDARDS AND GUIDELIl�'ES
Mulch Quality Standards Application Rates Remarks
Material
Straw Air-dried;free from 2"-3"thick; 2-3 Cost-effective protection when applied with adequate ;
undesirable seed and bales per 1000 sf thickness. Hand-application generally requires
coarse material or 2-3 tons per acre greater thickness than blown straw. Straw should be
crimped to avoid wind blow. The thickness of straw
may be reduced by half when used in conjunction
with seeding.
Wood Fiber No growth inhibiting Approx. 25-30 Ibs Shall be applied with hydromulcher. Shall not be
Cellulose factors per 1000 sf or used without seed and tackifier unless the application
1000-1500 Ibs per rate is at least doubled. Some wood fiber with very
acre long fibers can be effective at lower application rates
and without seed or tackifier.
Compost No visible water or 2"thick min.; More effective control can be obtained by increasing
dust during handling. approx. 100 tons thickness to 3". Excellent mulch for protecting final
Must be purchased per acre (approx. grades until landscaping because it can be directly
from supplier with 800 Ibs per cubic seeded or tilled into soil as an amendment. Sources
Solid Waste Handling yard) for compost are available from the King County
Permit. Commission for Marketing Recyclable Materials at
(206)296-4439. Compost may not be used in
Sensitive Lake'basins unless analysis of the
compost shows no phosphorous release.
Hydraulic This mulch category Apply at rates from The BFM shall not be applied immediately before,
Matrices includes hydraulic 3,000 Ibs per acre during or immediately after rainfall so that the matrix
(Bonded slurries composed of to 4,000 Ibs per will have an opportunity to dry for 24 hours after
Fiber Matrix) wood fiber, paper fiber acre and based on installation.Application rates beyond 2,500 pounds
or a combination of manufacturers may interfere with germination and are not usually
the two held together recommendations recommended for turF establishment. BFM is
by a binding system. generally a matrix where all fiber and binders are in
The BFM shall be a one bag, rather than having to mix components from
mixture of long wood various manufacturers to create a matrix. BFMs can
fibers and various be installed via helicopter in remote areas. They are
bonding agents. approximately$1,000 per acre cheaper to install.
Chipped Site Average size shall be 2" minimum This is a cost-effective way to dispose of debris from
Vegetation several inches. thickness 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.
' Sensitrve lake means a lake that has proved to be particularly prone to eutrophication;the County gives this designation when
an active input plan has been adopted to limit the amount of phosphorous entering the lake. I
1/9/2009 2009 Surface Water Design Manual—Appendix D
D-14
D.�? CO\'ER �1E:�SL'RES
D.3.2.4 PLASTIC CO�'ERING
� ►
Code: PC Svmbol: ___
Purpose
Plastic covering provides immediate, short-tenn erosion protection to slopes and di�turbed areas.
Conditions of Use
1. Plastic covering may be used on disturbed areas t11at require cover measures for les�than �0 days.
2. Plastic is particularly useful for protecting cut and fill slopes and stockpiles. .�'ote: The r-elatii ell
rapid breakdown of most polyethyler�e sheeting makes i1 unsuitable for long-te�-m applicatrons.
3. Clear plastic sheeting may be used over newly-seeded areas to create a greenhouse effect and
encourage grass growth. Clear plastic should not be used for this purpose during the summer months
because the resulting high temperatures can kill the grass.
4. Due to rapid runoff caused by plastic sheeting,this method shall not be used upslope of areas that
might be adversely impacted by concentrated runoff. Such areas include steep and;'or unstable slopes.
.'�'ote: There have been many problems with plastic, usually attributable to poor installation and
rnaintenance. However, the material itseljcan cause problems, e��en when correctly installed m�d
maintained, because it generates high-velocity runoff and breaks down quickly due to ultraviolet
r�adiation. In addition, if the plastic is not completely removed, it carr clog drainage s��stem irrlets and
outlets. It is highly recommertded that alter-nati��es to plastic sheeting be used wheneve�•possible ai�d that
its use be limited.
Design and Installation Specifications
1. See Figure D.3.2.D for details.
2. Plastic sheeting shall have a miniinum thickness of 0.06 inilliineters.
�. 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.
FIGtiRE D.3.2.D PLASTIC COVERING
� '0 N.Ax. � � TIRES, S�NDBAGS, OR EOJIVALEN'T
� �� � �_ MI�Y BE USE� `C WEIGHT PLkSTI�
—�-- � __——— � SEAMS BETWEEN SHEETS MUST
— I — T— _------ \ OVERLAP A I�INIM�M OF '2" 4N�
I'— — — --
_.. I_ _ — — — I FT R TnP
i,
BE WE G EC G ED
—I I I—I �
-_ - � �I I I�'I'I�.I I ' ;
�,�-� T I-''I I- : ''
`���-1 I I-1I I- �`��--� ;
- !�- �'� , ,
-CE Iv SdEETRd� iN — �I�_�,I 10' �MAX. j
41VIMJM 4"X4'� ?�ENCH� ���
,—�_���.,_.
� �—I I I— � '',
��—��� ���� �� ., �.
PROViDE ENERGY DISS�PATI�N I—I I `
A' TOE WHEN N�ED_D — _ �
-' II1.—
;�`
2009 Surface Water Design Manual—Appendix D 1!9r'2009 '
D-17
SECTION D.3 ESC'v1EASURES
Maintenance Standards for Plastic Covering
1. Torn sheets must be replaced and open seams repaired.
2. If the plastic begins to deteriorate due to ultraviolet radiation,it must be completely removed and
replaced.
3. When the plastic is no longer needed, it shall be completely remo��ed.
D.3.2.5 STRAW WATTLES
Code: SVJ Symbol: "
Purpose
Wattles are erosion and sediment control barriers consisting of straw wrapped in biodegradable tubular
plastic or similar encasing material. Vl�attles may reduce the velocity and can spread the flow of rill and
sheet runoff, and can capture and retain sediment. Straw wattles are typically 8 to 10 inches in diameter
and 25 to 30 feet in length. The wattles are placed in shallow trenches and staked along the contour of
disturbed or new�ly constructed slopes.
Conditions of Use
1. Install on disturbed areas that require immediate erosion protection.
2. Use on slopes requiring stabilization until permanent vegetation can be established.
3. Can be used along the perimeter of a project,as a check dam in unlined ditches and around temporary
stockpiles
4. Wattles can be staked to the ground using willow cuttings for added revegetation.
5. Rilling can occur beneath and between wattles if not properly entrenched,allowing water to pass
below and between wattles
Design and Installation Specifications
1. It is critical that wattles are installed perpendicular to the flow direction and parallel to the slope
contour.
2. 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 during high rainfall events,the
trenches should be dug to a depth of 5 to 7 incbes, or'/z to 2/3 of the thickness of the wattle.
3. Start construction of trenches and installing wattles from the base of the slope and work uphill.
Excavated material should be spread evenly along the uphill slope and compacted using hand tamping
or other method. Construct trenches at contour intervals of 3 to 30 feet apart depending on the
steepness of the slope,soil type,and rainfall. The steeper the slope the closer together the trenches
should be constructed.
4. Install the wattles snugly into the trenches and abut tightly end to end. Do not overlap the ends. I'
5. Install stakes at each end of the wattle, and at 4 foot centers along the entire length of the wattle.
6. If required,install pilot holes for the stakes using a straight bar to drive holes through the wattle and
into the soil.
7. At a minimum,wooden stakes should be approximately 'i x �-� x 24 inches. �'��illow cuttings or 3!8
inch rebar can also be used for stakes.
1!9r'2009 2009 Surface l'��ater Design M1�lanua]—Ap��endix D
D-18
D.�.2 COVER �tEASLRES
D.3.2.6 TEMPORARY AND PERMANENT SEEDING
�.
� - - --�-
Code: SE Svmbol: __
Purpose
Seeding is intended to reduce erosion bv stabilizing exposed soils. A���ell-established vegetati�c co�er is
one of the most effecti��e methods of reducin� erosion.
Conditions of Use
1. Seeding shall be used tl�roughout the project on disturbed areas that ha�e reached final tn�ade or that
will remain unworked for inore than 30 days.
2. Vegetation-lined channels shall be seeded. Channels that wil] be �egetated should be installed
before major earth���ork and hydroseeded or covered with a Bonded Fiber Matris (BFM).
3. Retention/detention ponds shall be seeded as required.
4. At the County's discretion,seeding without mulch during the dr�� season is allo«�ed e�en thou�h it
will take more than seven days to develop an effective cover. Mulch is,however,recommended at all
times because it protects seeds from heat,moisture loss,and transport due to runoff.
5. At the beginning of the wet season,all disturbed areas shall be reviewed to identify���l�ich ones can
be seeded in preparation for the winter rains(see Section D.5.2). Disturbed areas shall be seeded
within one week of the beginning of the wet season. A sketch map of those areas to be seeded and
those areas to remain uncovered shall be submitted to the DDES inspector. The DDES inspector ma�
require seeding of additional areas in order to protect surface «-aters, adjacent properties, or draina�e
facilities.
6. At final site stabilization, all disturbed area�not other�vise vegetated or stabilized shal] be seeded and
mulched (see Section D.5.5).
Design and Installation Specifications
1. The best time to seed is April l through June 30,and September 1 through October 15. Areas may be
seeded between July 1 and August 31,but irrigation may be required in order to grow adequate cover.
Areas may also be seeded during the�vinter months,but it may take several months to develop a
dense groundcover due to cold temperatures. The application and maintenance of mulch is critical for
winter seeding.
2. To prevent seed from being w ashed a�vay, confinn that all required surface��ater control measures
have been installed.
3. The seedbed should be firm but not compacted because soils that are«-e11 compacted���ill not
vegetate as quickly or thoroughly. Slopes steeper than 3H:1 V shall be surface roughened.
Roughening can be accomplished in a variety of ways,but the typical method is track walking, or
driving a crawling tractor up and down the slope,leaving cleat imprints parallel to the slope contours.
4. In general, 10-20-20 N-P-K(nitrogen-phosphorus-potassium)fertilizer may be used at a rate of 90
pounds per acre. Slow-release fertilizers are preferred because they are more efficient and have fe��-er
environmental impacts. It is recommended that areas being seeded for final landscaping conduct soil
tests to detennine the exact type and quantity of fertilizer needed. This will prevent the over-
application of fertilizer. Disturbed areas within 200 feet of water bodies and «etlands must use slo��-
release low-phosphorus fertilizer(typical proportions 3-1-2 N-P-K).
5. The following requirements apply to mulching:
a) Mulch is always required for seeding slopes greater than 3H:1 V (see Section D.4.2.1).
2009 Surface\�v'ater Desien h7anual—Appendix D 1 9�009
D-21
SECTION D.� ESC '�9E.ASURES
b) If seeding during the wet season,mulch is required. �
c) The use of mulch may be required during the dry season at the County's discretion if grass growth
is expected to be slow,the soils are highly erodible due to soil type or gradient,there is a water
body close to the disturbed area, or significant precipitation(see Section D.5.2)is anticipated
before the grass��ill provide effective cover.
dl Mulch may be applied on top of the seed or simultaneously by hydroseeding.
6. Hydroseeding is allowed as long as tackifier is included. Hydroseeding with wood fiber mulch is
adequate during the dry season. During the wet season,the application rate shall be doubled because
the mulch and tackifier used in hydroseeding break down fairly rapidly. It may be necessary in some
applications to include straw��ith the wood fiber,but this can be detrimental to germination.
�. Areas to be pennanently landscaped shall use soil amendments. Good quality topsoil shall be tilled
into the top six inches to reduce the need for fertilizer and improve the overall soil quality. Most
native soils will require the addition of four inches of well-rotted compost to be tilled into the soil to
provide a good quality topsoil. Compost used should meet Ecology publication 98-38 specifications
for Grade A quality compost.
C. The seed mixes listed below include recommended mixes for both temporary and pennanent seeding.
These mixes,with the exception of the wetland inix, shall be applied at a rate of 120 pounds per acre.
This rate may be reduced if soil amendments or slow-release fertilizers are used. Local suppliers
should be consulted for their recommendations because the appropriate mix depends on a variety of
factors, including exposure, soil type, slope, and expected foot traffic. Alternative seed mixes
approved by the County may be used.
Table D.3.2.B presents the standard mix for those areas�vhere just a temporary vegetative cover is
required.
TABLE D.3.2.BTE'.VIPOR.ARY EROSION CONTROL SEED;VII�
%Weight % Purity % Germination
Chewings or red fescue 40 98 90
Festuca rubra var. commutata or
Festuca rubra
Annual or perennial rye 40 98 90
Lolium multiflorum or Lolium perenne
Redtop or colonial bentgrass 10 92 85
Agrostis alba or Agrostis tenuis
White dutch clover 10 98 90
Trifolium repens
I;9i2009 ?009 Surface Watcr Design h�lanual—Appendix D
D-22
D._? CO�'ER �1E.�S�RES
Table D.3.2.0 provides just one recommended possibility for landscaping seed.
TABLE D.3.2.0 LAI�'DSCAPING SEED 111IX
%Weight % Purity %Germination
Perennial rye blend 70 98 90
Lolium perenne
Chewings and red fescue blend 30 98 90
Festuca rubra var. commutata or
Festuca rubra
This turf seed mix in Table D.3.2.D is for dry situations where there is no need for much water. The I�
ad�-antage is that this mix requires very little maintenance.
TABLE D.3Z.D LOW-GROWING TURF SEED MIX
%Weight % Purity %Germination
Dwarf tall fescue(several varieties) 45 98 90
Festuca arundinacea var.
Dwarf perennial rye(Barclay) 30 98 90 I�
Lo/ium perenne var. barclay 'I
Redfescue 20 98 90
Festuca rubra
Colonial bentgrass 5 98 90
Agrostis tenurs
Table D.3.2.E presents a mix reconunended for bioswales and other intennittently «�et areas. Sod shall
��enerally not be used for bioswales because the seed mix is inappropriate for this application. Sod may be
used for lining ditches to prevent erosion,but it will provide little water quality benefit during the wet
season.
TABLE D.3.2.E BIOSWALE SEED MIX*
%Weight °/a Purity °/a Germination
Tall or meadow fescue 75-80 98 90
Festuca arundinacea or
Festuca elatior
Seaside/Creeping bentgrass 10-15 92 85
Agrostis palustris
Redtop bentgrass 5-10 90 80
Agrostis alba or Agrostis gigantea
' Modified Briargreen, Inc. Hydroseeding Guide Wetlands Seed Mix
2009 Surface V4'ater Desien Manual—Appendis D 1;9'20Q9
D-23
SECTIOT� D.3 ESC �1EASURES
The seed mix shown in Table D.3.2.F is a reconimended low-growing,relatively non-invasive seed mix
appropriate for very wet areas that are not regulated wetlands(if planting in wedand areas,see Section
6.3.1 of the Strr/�ace 1�''ater Design Manual). Other mixes may be appropriate,depending on the soil type
and hydrology of the area. Apply this mixture at a rate of 60 pounds per acre.
TABLE D.3.2.F WET AREA SEED NITX*
%Weight % Purity %Germination
Tall or meadow fescue 60-70 98 90
Festuca arundinacea or
Festuca elatior
Seaside/Creeping bentgrass 10-15 98 85
Agrosfis palustris
Meadow foxtail 10-15 90 80
Alepocurus pratensis
Alsike clover 1-6 98 90
Trifolium hybridum
Redtop bentgrass 1-6 92 85
Agrostis alba
*Modified Briargreen, Inc. Hydroseeding Guide Wetlands Seed Mix
The meadov� seed mix in Table D.3.2.G is recommended for areas that will be maintained infrequently or
Inot at all and 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 establishinent prior to the winter months. The appropriateness of clover in the mix may need to
be considered as this can be a fairly invasive species. If the soil is amended, the addition of clo�er mav
not be necessar�.
TABLE D.3.2.G MEADOVV SEED MIX
%Weight % Purity % Germination
Redtop or Oregon bentgrass 40 92 85
Agrostis alba or Agrostis oregonensis
Red fescue 40 98 90 ,
Festuca rubra I
White dutch clover 20 98 90
Trifolium repens
Maintenance Standards for Temporary and Permanent Seeding
1. Any seeded areas that fail to establish at least 80 percent cover within one month shall be reseeded. If
reseeding is ineffective,an alternate method, such as sodding or nets/blankets,shall be used. If winter
weather prevents adequate grass growth,this time limit may be relaxed at the discretion of the County I
when critical areas���ould otherwise be protected. �
1i9�2009 2009 Surface Vvater Design Manual—.Appendix D
D-24
D.3.2 COVER'v1EASURES I�
2. After adequate cover is achieved, any areas that experience erosion shall be re-seeded and protected
by mulch. If the erosion problem is drainage related,the problem shall be fixed and the eroded area '
re-seeded and protected by mulch.
3. Seeded areas shall be supplied with adequate moisture,but not watered to the extent that it causes
runoff.
D.3.2.7 SODDING
�.
�---�� —
Code: SO Symbol: �
Purpose
The purpose of sodding is to establish permanent turf for immediate erosion protection and to stabitize
drainage ways where concentrated overland flow will occur.
Conditions of Use
Sodding may be used in the following areas:
1. Disturbed areas that require short-term or long-term cover
2. Disturbed areas that require immediate vegetative cover
3. All waterways that require vegetative lining(except biofiltration swales—the seed mix used in most
sod is not appropriate for biofiltration swales). Waterways may also be seeded rather than sodded,
and protected with a net or blanket(see Section D.3.2.3).
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:
1. Shape and smooth the surface to fina] grade in accordance with the approved grading plan. '
2. Amend two inches(minimum)of well-rotted compost into the top six inches of the soil if the organic ,
content of the soil is less than ten percent. Compost used should meet Ecology publication 98-38
specifications for Grade A quality compost.
3. Fertilize according to the supplier's recommendations. Disturbed areas within 200 feet of water
bodies and wetlands must use non-phosphorus fertilizer.
4. 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:1 V.
6. Roll the sodded area and irrigate.
7. 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 detennined and appropriate action taken to reestablish a
healthy groundcover. lf it is impossible to establish a healthy groundcover due to frequent saturation,
instability,or some other cause,the sod shal]be removed,the area seeded with an appropriate mix, and
protected with a net or blanket.
2009 Surface Water Design Manual—Appendix D 1!9,-2009
D-25
SECTION D.3 ESC 1�9E.4Sl,RES
D.3.3 PERIMETER PROTECTION '
Perimeter protection to filter sediment from sheet�vash shall be located downslope of all disturbed areas
and shall be installed prior to upslope grading. Perimeter protection includes the use of vegetated strips as
��ell as,constructed measures, such as silt fences, fiber rolls, sand,�gravel bamers,brush or rock filters,
triangular silt dikes and other methods. During the wet season,SO linear feet of silt fence(and the
necessary stakes)per acre of disturbed area must be stockpiled on site.
Purpose: The purpose of penmeter protection is to reduce the amount of sediment transported beyond the
disturbed areas of the construction site. Perimeter protection is primarily a backup means of sediment
control. Most, if not all, sediment-laden water is to be treated in a sediment trap or pond. T'he only
circumstances in�;�hich perimeter control is to be used as a primary means of sediment removal is when
the catclunent is very small (see below).
��'hen to Install: Perimeter protection is to be installed prior to any upslope clearing and grading.
:�leasures to Use: The above measures may be used interchangeably and are not the only perimeter
pratection measures available. If surface water is collected by an interceptor dike or swale and routed to a
sediinent pond or trap,there may be no need for the perimeter protection measures specified in this
section.
Criteria for Use as Primar� Treatment: At the boundary of a site,perimeter protection may be used as
the sole form of treatment«lhen the flowpath meets the criteria listed below. If these criteria are not met,
perimeter protection shall only be used as a backup to a sediment trap or pond.
Average Slope Slope Percent Flowpath Length
1.SH:I V or less 67%or less 100 feet
2H:1 V or less 50%or less 115 feet
4H:1 V or less 25%or less 150 feet
6H:1 V or less 16.7%or less 200 feet
l OH:l V or less 10%or less 250 feet
D.3.3.1 SILT FENCE
Code: SF Svmbol: -�E
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.
Conditions of Use
l. Silt fence may be used do���nslope of all disturbed areas.
2. Silt fence is not intended to treat concentrated flows,nor is it intended to treat substantial amounts of
overland flow. Any concentrated flows must be conveyed through the drainage system to a sediment
trap or pond. The only circumstance in which overland flow may be treated solely by a silt fence,
rather than by a sediment trap or pond,is when the area draining to the fence is small (see"Criteria
for Use as Primary Treatment"on page D-30).
Design and Installation Specifications
1. See Fiaure D.�.3.� and Fi��ure D.3.3.B for details.
I i9:2009 2009 Surface 4Vater Design R4anual—Appendix D
D-30
D.�.3 PERIMETER PROTECTIOT�'
2. The geotextile used must meet the standards listed belo���. A copy of the manufacturer's fabric
specifications must be available on site.
AOS (ASTM D4751) 30-100 sieve size (0.60-0.15 mm)for slit film
' 50-100 sieve size (0.30-0.15 mm)for other fabrics
Water Permittivity(ASTM D4491) 0.02 sec-� minimum
Grab Tensile Strength (ASTM D4632) 180 Ibs. min, for extra strength fabric
100 Ibs. min. for standard strength fabric
Grab Tensile Elongation (ASTM D4632) 30% max.
Ultraviolet Resistance(ASTM D4355) 70% min.
3. Standard strength fabric reyuires wire backing to increase the strength of the fence. Vdire backing or
closer post spacing may be required for extra strength fabric if field perfonnance warrants a stronger
fence.
4. Where the fence is installed,the slope shall be no steeper than 2H:1 V.
�. If a typical silt fence(per Figure D.3.3.A)is used,the standard 4 x 4 trench may not be reduced as
]ong as the bottom 8 inches of the silt fence is well buried and secured in a trench that stabilizes the
fence and does not allow water to bypass or undermine the silt fence.
Maintenance Standards
1. Any damage shall be repaired immediately.
2. If concentrated flows are evident uphill of the fence,they must be intercepted and conveyed to a
sediment trap or pond.
�. It is important to 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.
4. Sediment must be removed when the sediment is 6 inches high.
5. If the filter fabric (geotextile)has deteriorated due to ultraviolet breakdo�m, it shall be replaced.
FIGURE D.3.3.A SILT FENCE
��T� r��TE- _ ��R c �N��.�_ eE �P_c_�
- -os-s. �sE �T�F��E�, �s��P- �r�..cs, �-�
_..JPJALENT TO i;-.'�,��H =a.=RP� TC '�O�TS. 2"x2'' BY 1� �a. N.'RE �:'t
EQUI`JALEN7, IF S-4N;'�A�D
STRENGTF FAcP.'C USE�
�' � � F LTER -P?:R C —
I I I
I I I �
I I I C�
I 1 �� I I I�- � I II ,��— --
������ � ��C_, I.-1 I 1-I I CI I�-)I I-I I I-�I�_I I�I� I I�_���C .i-i� � -�_
'- C�I 1-1 I I-1 I i I I i-"
_��� Z
i �- — — — — —� �� � � ��I�IiI ', �
E' '��PX. M:N�M�A� �°z4" 7REN�H
% �
IJ � 3P.CKFILL TwENCd 'NTri� �.�
NAT'✓E SOIL OR 3!�"-'.�" /
F���l SPACING Ad.�,Y aE iNCR=k�EG I� WASHED GRAVEL J"
-G 3' Ir W'�RE BAC�ING IS '.;SED �
2"xa" ta�OGD F�STS, STEEL �Er..;E
aOTE: �ILTER FABR�C FENC�S SHALL BE "��7= �EB<R, ^r^. EGi,P.;�:_E'.-
rJ�TA.�_LED P-LONG CGNTDUR �.a'�-EN�VER POSS'2L=
2009 Surface�'�'ater Design Manual—Appendix D 1l9,�2009 '
p-31 I
D.�.� TRaFFIC �R[.-� STaBILl7:\TIO�
D.3.4.1 STABILIZED CONSTRUCTIOI�' ENTR�I�CE
,�_::
-�
Code: CE Svmhol:
Purpose
Construction entrances are stabilized to reduce the amount o1�sediiuent trancp�rted onto pa��ed roads b�°
motor vehicles or runoff b.� constructing a stabilized pad of quam- spalls at entrances to cc�nstruction sites.
Conditions of Use
Construction entrances shall be stabilized wherever traffic will be ]eaving a construction site and traveling
on paved roads or other paved areas within 1,000 feet of the site. Access and exits shall be limited to one
route if possible,or two for linear projects such as road���ay where more than one accessiexit is necessary
for maneuvering large equipment.
Design and Installation Specifications
1. See Figure D.3.4.A for details.
2. A separation geotextile shall be placed under the spalls to pre��ent 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)
3. Hog fuel (wood based mulch)may be substituted for or combined with quarry spalls in areas that«�il]
not be used for pennanent roads. The effectiveness of hog fuel is highly variable,but it has been used
successfully on many sites. It generally reyuires more maintenance than quarry spalls. Hog fuel is
not recommended for entrance stabilization in urban areas. The inspector may at any time require the
use of quarry spalls if the hog fuel is not preventing sediment from being tracked onto pavement or if
the hog fuel is being carried onto pavement. Hog fuel is prohibited in permanent roadbeds because
organics in the subgrade soils cause difficulties with compaction.
4. Fencing (see Section D.3.1) shall be installed as necessary to restrict traffic to the construction
entrance.
5. Whenever possible, the entrance shall be construcred on a firn�, compacted subgrade. This can
substantially increase the effectiveness of the pad and reduce the need for maintenance.
Maintenance Standards
1. Quarry spalls(or hog fuel) shall be added if the pad is no longer in accordance with the specifications.
2. If the entrance is not preventing sediment from being tracked onto pavement,then alternative
measures to keep the streets free of sediment shal]be used. This may include street sweeping, an
increase in the dimensions of the entrance,or the installation of a wheel wash. If washing is used, it
shall be done on an area covered with crushed rock, and wash water shall drain to a sediment trap or
pond.
2009 Surface�ti'ater Design'�9anual—Appendis D 1-9,-2009
D-39
SECTION D3 ESC MEASL'RES
3. Any sediinent that is tracked onto pavement shal]be removed immediately by sweeping. The
sediment collected by sweeping shall be removed or stabilized on site. The pavement shall not be
cleaned by���ashing do�un the street,except when sweeping is ineffective and there is a threat to
public safety. If it is necessary to wash the streets,a small sump must be constructed. The sediment
would then be���ashed into the sump�;�here it can be controlled. Wash water must be pumped back
onto the site and can not discharge to systems tributary to surface waters.
4. Any quarry spalls that are loosened from the pad and end up on the roadway shall be removed
immediately.
5. If vehicles are entering or exiting the site at points other than the construction entrance(s), fencing
(see Section D.3.1)shall be installed to control traffic.
FIGURE D.3.4.A STABILIZED CO'vSTRUCTION E1�TRANCE
AS PER KING COUNTY ROAD STANDARDS,
DRIVEWAYS SHALL BE PAVED TO THE EDGE
ROP� OF R—O—W PRIOR TC INSTALLATION OF THE
�X�51\N� CONSTRUCTION ENTRANCE TO AVOID
/ DAMAGING OF THE ROADWAY
� IT IS RECOMMENDED THAT THE
R = 25' MIN�j `� ENTRANCE BE CROWNED SO THAT
\ RUNOFF DRAINS OFF THE PAD
.�
�D.
� �� �y
� j �\
� INSTAL_ DR'J=WAY CULVERT IF THERE �'
IS A ROADSIDE DITCH PRESENT, AS �/
PER KING COUNTY ROAD STANDARDS /I
i"
4"-8" QUARRY SPALLS �
GEOTEXTILE
. ��� ',
� , �h
1 2" MIN. THICKNESS�`, ; PROVIDE FULL WI�'H OF
INGRESS/EGRESS AREA
I�9,�2009 2009 Surface Water Design Manual—Appendix D
D-40
D.3.� TR.AFFIC.AREA ST.ABILIZATION
D.3.4.2 CONSTRUCTION ROAD/PARHING AREA STABILIZATION
�
r��
Code: CRS Svmbol: —�
Purpose
Stabilizing subdivision roads,parking areas,and other onsite vehicle transportation routes immediately
after grading reduces erosion caused by construction traffic or runoff.
Conditions of Use
1. Roads or parking areas shall be stabilized wherever they are constructed, v�jhether permanent or
temporary, for use by construction traffic.
?. Fencing(see Section D.3.1)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
1. 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 the area will not be used for pennanent roads,
parking areas,or sh-uctures, 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
finn,compacted subgrade. ,'�'ote:If the area will be used,for perrnanent road or parking installation
later in the project, the subgrade will be subject to inspection.
?. Temporary road gradients shall not exceed l5 percent. Roadways shall be carefully graded to drain
transversely. 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 designed in
� accordance with the standards given in Section D.3.6.3 (p. D-60) and directed to a sediment pond or
trap.
3. 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,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 vegetated wetlands. If
runoff is allowed to sheet flow through adjacent vegetated areas, it is vital to design the roadways and
parking areas so that no concentrated runoff is created.
4. In order to control construction traffic,the County may require that signs be erected on site informing
construction personnel that vehicles,other than those performing clearing and grading,are restricted
to stabilized areas.
5. If construction roads do not adequately reduce trackout to adjacent property or roadways,a wheel
wash system will be required.
Maintenance Standards
Crushed rock,gravel base,hog fuel,etc. shall be added as reyuired to maintain a stable driving surface
and to stabilize any areas that have eroded.
2009 Surtace\��ater Design Vlanual—Appendix D ll9/2009
D-41
SECTION D.3 ESC MEASL'RES
D.3.5 SEDIMENT RETENTION
Surface«�ater collected froin disturbed areas of the site shall be routed through a sediment pond or trap
prior to release from the site. An exception is for areas at the perimeter of the site with drainage areas
srnall enough to be treated solely with perimeter protection (see Section D.3.3,p. D-30). Also, if the soils
and topography are such that no offsite discharge of surface water is anticipated up to and including the
developed 2-year runoff event,sediment ponds and traps are not required. A ]0-year peak flow using
KCRTS with 15-minute time steps shall be used for sediment pond./trap sizing if the project size,expected
timing and duration of construction,or downstream conditions warrant a higher level of protection (see
below). At the County's discretion,sites may be worked during the dry season without sediment ponds
and traps if there is some othcr form of protection of surface waters, such as a 100-foot forested buffer
between the disturbed areas and adjacent surface waters. For small sites;use the criteria defined in
Section D.3.3,Perimeter Protection to determine minimum flow path length. If the site�;-ork has to be
extended into the wet season, a back-up plan must be identified in the CSVdPPP and implemented.
Protection of catch basins is required for inlets that are likely to be impacted by sediment generated by the
project and that do not drain to an onsite sediment pond or trap. Sediment retention facilities shall be
installed prior to grading of any contributing area and shall be located so as to avoid interference with the
movement of juvenile salmonids attempting to enter off-channel areas or drainages.
Purpose: The purpose of sediment retention facilities is to remove sediment from runoff generated from
disturbed areas.
«'hen to Install: The facilities shall be constructed as the first step in the clearing and erading of the site.
The surface water conveyances may then be connected to the facilities as site development proceeds.
Measures to Use: There are three sediment retention measures in this section. The first two.sediment
traps and ponds, serve the same function but for different size catchments. All runoff from disturbed areas
must be routed through a trap or pond except for very small areas at the perimeter of the site small enough
to be treated solely with perimeter protection(see Section D.3.3,p. D-30). The third measure is for catch
basin protection. It is only to be used in limited circumstances and is not a primary sediment treatment
facility. It is only intended as a backup in the event of failure of other onsite systems.
Use of Permanent Drainage Facilities: All projects that are constructing permanent facilities for runoff
quantity control are strongly encouraged to use the rough-graded or final-graded permanent facilities for
ponds and traps. This includes combined facilities and infiltration facilities. When permanent facilities
are used as temporary sedimentation facilities,the surface area requirements of sediment traps (for
drainages less than 3 acres) or sediment ponds(more than 3 acres)must be met. If the surface area
requireinents are larger than the surface area of the pennanent facility,then the pond shall be enlarged to
comply with the surface area reyuirement. The pennanent pond shall also be divided into two cells as
required for sediment ponds. Either a permanent control structure or the temporary control structure
described in Section D.3.5.2 may be used. If a pennanent 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.
If infiltration facilities are to be used,the sides and bottom of the facility must only be rough excavated to
a minimum of three feet above final grade. Excavation should be done with a backhoe working at"arms
length" to minimize disturbance and compaction of the infiltration surface. Additionally, any required
pretreannent facilities shall be fully constructed prior to any release of sediment-laden water to the
facility. Pretreatment and shallow excavation are intended to prevent the clogging of soil with fines.
Fina] grading of the infiltration facility shall occur only when all contributing drainage areas are fully
stabilized(see Section D.5.5,p. D-76).
Selecrion of the Design Storm: In most circumstances,the developed condition 2-year peak flow using
KCRTS with 15-minute time steps is sufficient for calculating surface area for ponds and traps and for
determining exemptions from the sediment retention and surface water collection requirements (Sections
li9r'2009 2009 Surface V4'ater Design Manual—Appendix D
D-44
ID.3.5 SEDIMENT RETEI�TION
D.3.5 and D.3.6,respectively). In some circumstances,however,the 10-year KCRTS 15aninute peak
flow should be used. Examples of such circumstances include the following:
• Sites that are within '/ mile of salmonid streams,wetlands, and designated sensitive lakes such as
Lake Sammamish
• Sites where significant clearing and grading is ]ikely to occur during the wet season
• Sites with downstream erosion or sedimentation problems.
Tatural Vegetation: Whenever possible, sediment-laden water shall be discharged into onsite,relatively
level,vegetated areas. This is the only way to effectively remove fine particles from runoff. This can be
particularly useful after initial treatment in a sediment retention facility. The areas of release must be
evaluated on a site-by-site basis in order to detennine appropriate locations for and methods of releasing
runoff. Vegetated�vetlands 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 au�nent the treatment system,not replace it because of the possibility of pump failure or runoff
volume in excess of pump capacity.
D.3.5.1 SEDIMENT TRAP
Code: ST Svmbol: �
Purpose
Sediment traps remove sediment from runoff originating from disturbed areas of the site. Sediment traps
are typically designed to only remove sediment as small as medium silt(0.02 mm). As a consequence,
they usually only result in a small reduction in turbidity.
Conditions of Use
A sediment trap shall be used where the contributing drainage area is 3 acres or less.
Design and Installation Specifications
1. See Figure D.3.S.A for details.
2. If permanent runoff control facilities are part of the project,they should be used for sediment retention
(see"Use of Pennanent Drainage Facilities"on page D-44).
3. To determine the tiap geometry,first calculate the design surface area(SA)of the trap,measured at
the invert of the weir. Use the following equation:
SA = FS(Q�,'i's) I
where Q� = Design inflow (cfs)from the contributing drainage area based on the developed
condition 2-year peak discharge using KCRTS with 15-minute time steps as
computed in the hydrologic analysis. The 10-year KCRTS 15-minute peak flow ,
shall be used if the project size,expected timing and duration of construction,ar '
downstream conditions wanant a higher level of protection. If no hydrologic
analysis is required,the Rational Method may be used(Section 32.1 of the Surrace
T�Y'ater Design Manua�.
VS = The settling velocity(ft/sec)of the soil particle of interest. The 0.02 mm(inedium
silt)particle with an assumed density of 2.65 g/cm�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.
2009 Surface Water Design Manual—Appendix D I i9.2009
D-45
D.3.5 SEDI'�7E�'T RETENTION ��I
D.3.5.2 SEDI11'IENT POND �
Code: SP SymboL• '
' Purpose
Sediment ponds remove sediment from runoff originating from disturbed areas of the site. Sediment
ponds are typically designed to only remoti=e sediinent as small as inedium silt (0.02 mm). As a
consequence,they usually reduce turbidity only slightly.
Conditions of Use
A sediment pond shall be used where the contributing drainage area is 3 acres or more.
Design and Installation Specifications
1. See Figure D.3.S.B,Figure D.3.S.C,and Figure D.3.S.D for details.
2. If permanent runoff control facilities are part of the project,they should be used for sediment retention
(see "Use of Permanent Drainage Facilities"on page D-44).
Determining Pond Geometry
1. Obtain the discharge from the hydrologic calculations for the 2-year peak flow using KCRTS with 15-
ininute time steps (Qz). The 10-year KCRTS 15-minute 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(Section 3.2.1 of
the Su�face Water Design Manuan.
2. Detennine the required surface area at the top of the riser pipe with the equation:
SA = 2 x Qz!0.00096 or 2080 square feet per cfs of inflow
See Section D.3.5.1 (p. D-45) for more information on the derivation of the surface area calculation.
3. 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 3:1 interior side slopes and maximum 2:1 exterior slopes. The interior slopes may be
increased to a maximum of 2:1 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 one foot deep spillway
• Length-to-width ratio between 3:1 and 6:1.
Sizing of Discharge Mechanisms
Principal Spilhvay: Detennine the required diameter for the principal spillway(riser pipe). The diameter
shall be the minimum necessary•to pass the developed condition 10-year peak flow using KCRTS with 15-
minute time steps(Q�o). Use Figure 5.3.4.H(SWDM Chapter 5)to determine this diameter(h=one foot).
Note:A permanent cont�-ol structure may be used instead of a temporary riser.
2009 Surface W'ater Design Manual—Appendix D lr9!2009
D-47
SECTIO.\ D.� ESC '�9E.AS�RF�
Emergency Overflo�i� Spilh��a��: Detennine the required size and design of the emergency overilo��
spillway for the developed condition ]00-year KCRTS 15-minute peak flow using the procedure i�i
Section 5.3.1 ("Emergency Overflow Spillway" subsection) of the Surface {�'ater Design Alanuul.
De���atering Orifice: Detennine the size of the dewatering orifice(s) (minimum 1-inch diameter)usin<� a
modified�-ersion of the discharge equation for a vertical orifice and a basic equation for the area of a
circular orifice.
I. Determine the required area of the orifice���ith the follo��ing equation:
�I t
A� _ As�2h) ��< = 4.�1(10-„�.-1�v'1�
0.6x 3600 Tt
where Ao = orifice area(square feetj
AS = pond surface area(square feet)
h = head of water above orifice(tieight of riser in feet)
T = de���atering time(24 hours)
g = acceleration of gravity(32.2 feet,'second')
2. Convert the required surface area to the required diameter D(inchesj of the orifice:
D=24x `�° = 13.54x�
;�
3. The vertical,perforated tubing connected to the de���atering orifice inust be at least 2 inches larger in
diaineter 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 flo«� rate should be
controlled bv the orifice.
Additional Design Specifications
• The pond shall be divided into two roughl� equal volwne cells by a penneable di�-ider 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(see Section D.3.3.1) supported by treated 4"x4"s may 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 embanlcment
is one acceptable method of 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 pre�-ent
erosion under or around the barrier.
• To aid in detennining sediment depth,one-foot inten�als shall be prominently marked on the riser.
• If an embankment of more than 6 feet is proposed,the pond must comply���ith the criteria under
"Embankments"in Section 5.3.1 of the Su�.face j�ater Design,'l�Ianual.
Maintenance Standards
1. Sediment shall be removed from the pond���hen it reaches 1 foot in depth.
2. Any damage to the pond embankments or slopes shall be repaired.
1'9�2009 2009 Surface 11�ater Design M19anual—Appendix D
D-48
D.�.� SEDI\1E\l REl E�TIO.\
FIGURE D.3.S.B SEDIMENT POND PLA?� �'IEV1'
__
NEY D'�VI�ER IVTO SLOPE
'0 PREYEYT F_OW -.� ......
RRDJN7 S DES j ��
THE POVD LENGTr SHnLL BE 3"0 E
. TIAIES-HE NRX�M.iI! =OND N9DTH �
�,
�
1,
� c: .
1
,'\ , o�o�,�� �'
� � ���`��`� � '1 /',_
, ��, o��y
1 1
, 11 1 � 1 �:�
11
PONJ �EN�T'n F � � � \C-=..:_
�_-��.'— ��Q� � . 'C.�_
RISER P PE� �—
SiU FENCE OR�p �
EpUIVA:EM DIV:DER i p15CHARGE 7C °---- -_�
CO'.�hvANC�. c��.�-
, I FYEI SPp_c'fr.
I
I � I 1
I
I
I I
� �
'
NOTE: PONC MAY BE FORMED 6Y 9ERN �R /
� . PY PARTWL OR �CInP��ETE EXCAVa'ION ., j�
1� /�,
FIGURE D.3.S.0 SEDI:�'IE1�T POnD CROSS SECTION
—.,._ �a,:. , -�,�=R�_h�:' __�__�',;.. - . ,�_ -
�=E'� AT iCP wITH
. TRASN RACK
�_�f=I=�i PER FIG. 5 3 1.0 �._ ��IV. _MBA �M . _ ,__`.
����I I I I�I ' �ERVIOJ� r i h �_
I � CEWATERING DEV�CE TT� ---- � / ;aAV L � -, c.+;,
,I I I �5 :SEE RiSER DETAI'�)�- � } -—- ---� ' � '
=I I I ` - : � ��"--"_-= F �
'�=il,f = �=-======--=--==--=`�
T=I - �---=-==-==-----====_--
-1 I_�-I I � --- -- ---------=------------------==-- -
,.s ;_ _,
;
I I 1=�I I—I I 1=1 I 1=I I-1 i I ��'�
I'l ll l I I �I I i l I�I I I I�'I'�I'I— 1=11 I�"'—���_��_�'�=1 I I— _ �
=1 I -1 I I i I�— I ,I I 1=1 I I I I I I�I I —I I I—I I I-1 I I
-1 I I_I i I-1 I-1 I 1=I!�_i I I�I_I I I_:I I_
i DISCHARGE iC �->=_<--
iVIRE-BACKEC SILT FENCE. DEWA"E�'�.NG CONCRET= 9ASE CONVE"ANCE �� - _- __
_TtuEC HA = .-c V.'= =FE� f`a-�� iSFE <�S-tz ,r-A_. i_E'.". c=pE�_--
r:�- - - - -.—- -,_ .
?009 Surface A�'ater Desien ti7anual—Appendix D 1�912009
D-49
SECTf01�D.3 ESC MEASURES
FIGURE D.3.S.D SEDIAZENT POND RISER DETAIL
-__-_,N���E�,�E c.:F ���_�v�,.�� a_,=c��a-_
�� _."..::-F'i._
- / �
� PER=0R4TEG PC'_"=THYLEv_
� DRA!�AGE TL5 V�. CIkA4ETEF. � "ORRUGATE� .
�. M�.N_ 2'� LFR�ER -�-AN �_� NETP.L RIScR ',.
� DEW'A ERING CR.^ICE. � ��.
iLB'V� SHAIL CONFLY �
WITH ASTM F66; ANC -j 3.5' IdiN.
AhSH7C M25�. -�
� .: �= Y�ATERTI�ri '�, �=N'A1�RING ORiFICE, SCHEDULE
�. �_ CCI:=�ING 7FCK N'=LD 40 STEEL STU7 '.11N.
��� rC �AMET�R AS FER C.4LCULATIONS
I� �
�� :. 'I ',. �
I �i E" '.t I�._ ,-___
i L___ __J
I I j_
` '���� I I � ALiERNATIVELY, N�TAL STAKES
AND W"RE MAY 3E JSED �0
�ONCRETE BAS� �R=dEN7 �LOTA�ICN
�
��. . . �2X RISER DIP.. M��V.�
I i
i �
II
II
1'9i2009 2009 Surface VVater Design Manual—Appendix D
D-50
SECT10\ D.� ESC �9 EASI RES
D.3.6 SURFACE WATER COLLECTION I'�
All surface water from disturbed areas shall be intercepted, con�eyed to a sediment pond or trap, and
discharged do�rnslope of any disturbed areas. An exception is for areas at the perimeter of the site with I
drainage areas small enough to be treated solely with perimeter protection (see Section D.3.3). Also,if I
the soils and topography are such that no offsite discharge of surface water is anticipated up to and '
including the developed 2-year runoff event, surface water controls are not required. A ]0-year KCRTS I
15-minute peak flow shall be used for sizing surface water controls if the project size,expected timing and �,
duration of construction,or downstream conditions warrant a higher level of protection (see the I
introduction to Section D.3.5). At the County's discretion, sites may be v�rorked during the dry season !
without surface water controls,if there is some other forni of protection of surface waters, such as a 100- �I
foot forested buffer between the disturbed areas and adjacent surface���aters. Significant sources of 'i
upslope surface water that drain onto disturbed areas shall be intercepted and conveyed to a stabilized '
discharge point downslope of the disturbed areas. Surface water controls shall be installed concurrently
with rough grading.
Purpose: The purpose of surface water control is to collect and convey surface water so that erosion is
ininimized, and runoff from disturbed areas is treated by a sediment pond or trap. Surface water control
essentially consists of three elements:
1. Interception of runoff on and above slopes
?. Conveyance of the runoff to a sediment pond or trap (if the runoff was collected from a disturbed
area)
3. Release of the runoff downslope of any disturbed areas. ,
�'�'hen to Install: Surface water controls shall be constructed during the initial grading of an area and must ,
be in place before there is any opportunity for storm runoff to cause erosion.
Measures to Install: Interceptor dikes/swales intercept runoff,ditches and pipe slope drains convey the
runoff,and riprap or level spreaders help release the runoff in a non-erosive manner. Each measure is to '
be used under different circumstances so there is very little overlap. However,the two options far
releasing��ater in a non-erosive manner,outlet protection and level spreaders,can be somewhat
interchangeable. See Figure D.3.6.A for a schematic dra�vine demonstrating the use of these measures.
'
Ir9i2009 2009 Surface 1�-ater Design Manual—Appendix D
D-56
D.�.6 SL:RFACE�'��.aTER COLLECTIO'�
FIGURE D.3.6.A SKETCH PLAI�OF SURFACE R'ATER CONTROLS
�c;;
� �I
t �
��'= =�F� s�oaE �Fa�n
. ��\I INTEFC'P"':;R .,,+:E
V� —.—_ i�l 'lIF Q� S_' .
x JF: .. LET �qC'E�T10� —.—
� —_.. � .- _._._-.
": �
�(
C �ti
'i
� �.
� � �
� ;�F; �
ISEG'dE�- FGNC
�� c_- F_�,��_ .�.
., ., �� .., , . . .
.�c---�. �� .
��
D.3.6.1 INTERCEPTOR DIKE AND S��'ALE
Code: ID or IS Svmhol: �—=�—f or —�;�� ►
' Purpose
Interceptor dikes and sn ales �ntei-cept stornl runoff from draina`�e areas on or above disturbed slopes and
convey it to a sediment pond or trap. They may also be used to intercept runoff from undisturbed areas
and convey the runoff to a point below any exposed soils. Interception of surface water reduces the
possibility of slope erosion. Interceptor dikes and swales differ from ditches(see Section D.3.6.3)in that
they are intended to convey smaller flows along low-gradient drainage ways to larger conveyance s�-stems
such as ditches or pipe slope drains.
Conditions of Use
Interceptor dikes and swales are required in the following situations:
1. At the top of all slopes in excess of 3H:1 V and with more than 20 feet of vertical relief.
2. At intervals on any slope that exceeds the dimensions specified in this section for the horizontal
spacing of dikes and swales.
Design and Installation Specifications
]. See Figure D3.6.B for details of an interceptor dike and Figure D.3.6.0 for an interceptor s���ale.
2009 Surface�4�ater Design Manual–.Appendix D 1�9i2009
D-57
SECTl01� D.� ESC 1�1EASLRES
2. Interceptor dikes and s�vales shall be spaced horizontally as follo��-s:
Average Slope Slope Percent Flowpath Length
20H:1 V or less 3-5% 300 feet
(10 to 20)H:1V 5-10% 200 feet
(4 to 10)H:1 V 10-25% ]00 feet
(2 to 4)H:l V 25-50% 50 feet
3. For slopes steeper than 2H:1 V with more than 10 feet of��enica] relief, benches ma��be constructed
or closer spaced interceptor dikes or swales may be used. VVhiche�-er measure is chosen, the spacing
and capacity of the measures must be designed by the engineer and the design must include provision�
far effectively intercepting the high velocity runoffassociated with steep slopes.
4. If the dike or s���ale intercepts runoff from disturbed areas,it shall discharge to a stable conveyance
system that routes the runoff to a sediment pond or trap(see Section D.3.5). If the dike or swale
intercepts runoffthat originates from undisturbed areas, it shall discharge to a stable com�eyance
system that routes the runoff do���nslope of any disturbed areas and releases the n�atet-at a stahilized
outlet.
5. Construction traffic o�er temporary dikes and s���ales shall be minimized.
Maintenance Standards
]. Damage resulting from runoff or construction activity shall be repaired immediately.
2. If the facilities do not re�aularlv retain stonn runoff, the capacit}�and'ar frequenc� of the dikes s��ales
shall be increased.
FIGURE D.3.6.B INTERCEPTOR DIKE
2:1 MAX. S��_�AE
DIKE MATERIAL COMPACTED
90% MODIFIED PROCTOR
�2' MIN.
r–18" MIN. — I -
�
— —I�I—I
' I—I I�— —I I I—i
' � DIdE SFACIVG DEPENDS ON SLCa� GP.ADIEN"�
FIGURE D.3.6.0 INTERCEPTOR SWALE
2:1 MAX. SLO'E
LEVEL BOTTOM r��- iI,
1' MIN.- / - - - -! -III�!II=i'' - -
/ - - �'_ -���- -
- � �` ��-�,I I I-1 I�_ �i i
_ _�,I I I- �
=lii
- I
'�'z� M,N
�� ---- —
SWALE SPACING DEPENDS ON SLOPE GRADIENT
1%'912009 2009 Surface Water Design Manual—.4ppendix D
D-58
D.3.6 SURFACE��I-ATER COLLECTION
a) Relief drains are used either to lower the���ater table in large,relatively flat areas, improve the
growth of vegetation, or to remove surface water. They are installed along a slope and drain in
the direction of the slope. They may be installed in a grid pattern,a hemngbone pattern,or a
random pattern.
b) Interceptor drains are used to reinove excess groundwater from a slope, stabilize steep slopes,
and lower the���ater table below a slope to prevent the soil from becoming saturated. They are
installed perpendicular to a slope and drain to the side of the slope. They usually consist of a
single pipe or single pipes instead of a patterned layout.
2. Size of Drains– Size subsurface drains to carry the required capacity without pressurized flo��.
Minimum diameter for a subsurface drain is 4 inches.
3. Outlet–Ensure that the outlet of a drain empties into a channel or other watercourse above the
norma] water level.
Maintenance Standards
1. Subsurface drains shall be checked periodically to ensure that they are free flo���ing and not clogged
with sediment or roots.
2. The outlet shall be kept clear and free of debris.
3. Surface inlets shall be kept open and free of sediment and other debris.
4. Trees located too close to a subsurface drain ofren clog the system with roots. If a drain becomes
clogged,relocate the drain oi-remove the trees as a last resart. Drain placement should be planned to
minimize this problem.
5. Where drains are crossed b� hea�� equipment, the line shall be checked to ensure that it is not
crushed and ha�e adequate co�er protection.
D.3.6.4 DITCHES
Code: D] S��mboi: �—�.�—
Purpose
Ditches convey intercepted runoff from disturbed areas to and from sediment ponds or traps. They also
convey runoff intercepted from undisturbed areas around the site to a non-erosive discharQe point.
Conditions of Use
Ditches may be used any���here that concentrated runoff is to be conveyed on or around the construction
site. Temporary pipe systems may also be used to con�ey runoff.
Design and Installation Specifications
l. Channels and ditches shall be sized to accommodate the developed condition ]0-year KCRTS 1�-
minute peak flow with 0.5 feet of freeboard. If no hydrologic analysis is required for the site, the
Rational Method mav be used [see Section 3.2.1 of the Surface T�Vater Design Manual(Si�i'DAl)].
2. See SWDM Section 4.4.1 for open-channel design requirements.
3. The only exception to the requirements of SbVDM Section 4.4.1 is the use of check dams,rather than
grass lining, for channels in which the design flow velocity does not exceed 5 fps. See Figure D.3.6.E
for details on check dam installation.
2009 Surf�ace�'�'ater Design '�1anual—Appendix D 1!9;2009
D-61
SECT10\ D.= ESC �1E.ASl RES I
Maintenance Standards
]. Am-sediment deposition of more than 0.5 feet shall be removed so that the channel is restored to its
design capacity.
2. If the channel capacity is insufficient far the design flow,it must be detennined whether the problem
is local (e.g., a constriction or bend)or the channel is under-designed. If the problem is 1oca1,the
channel capacity must be increased through construction of a berm(s)or by excavation. If the !
problem is under-design,the design engineer shall be notified and the channel redesigned to a more
conservative standard to be approved by King County.
3. The channel shall be examined for signs of scouring and erosion of the bed and banks. lf scouring or
erosion has occurred, affected areas shall be protected by riprap or an erosion control blanket or net.
FIGtiRE D.3.6.E CHECK DAMS
ROCK MUST CCMPLETELY COVER THE
�' BOTTOM AND SIDES OF 'HE DITCH
i�� CC� �
:� ��\ 6" MIN.
„'%�:���.�-iL>"��D�C�f����(✓ 24" MIN.
� �=,' �� 'C�'1� '� �- —�-
CROSS SECTION
2:1 SLOPES
/`,
C�������i 2"-4" ROCK
�� � � /
I— �' A B
-- ' -- ' � �
— - �-���-- � — "�' �1�C�^
,—�' —I I�-�I —
_ ,,_� �=r��
_I I-1 I— � — �—
_ _ 'hE �STANCE SUCH THAT POINTS ��� �—I I—I�I=I�� -
a CN� B F.RE 0= EOUA_ ELEVATION —' �I
CHECK DAM SPACING
],9,2009 2009 Surface V4'ater Design'vlanual—Appendix D
D-62
D.=.� DE�1.�,TERI�G CO'�TROL
D.3.7 DEWATERING CONTROL i
Any runoff generated by dewatering shall be treated through construction of a sediment trap(Section '�
D.3.5.1)when there is sufficient space or by releasing the water to a well vegetated,gently sloping area. 'i
Since pumps are used for dewatering, it may be possible to pump the sediment-laden water���ell away '
from the surface���ater so that vegetation can be more effectively utilized for treatment. Discharge of II
sediment-laden���ater from dewatering activities to surface and storm �y�aters is prohibited. If dewatering
occurs from areas where the water has come in contact with new concrete, such as tanks,vaults, or
foundations, the pH of the���ater must be monitored and must be neutralized prior to discharge. Clean �I
non-turbid de�-atering water,such as«�ell point ground water can be discharged to systems tributarv to,or
directly to surface waters pro��ided the flows are controlled so no erosion or flooding occurs. Clean water
must not be routed through a stonnwater sediment pond. Highly turbid or contaminated dewatering water
must be handled separately from stonnwater.
Purpose: To pre�-ent the untreated discharge of sediment-laden water from dewatering of utilities,
excavated areas, foundations, etc. ',
�'�'hen to Install: Dewatering contro]�neasures shall be used whenever there is a potential for runoff from �
dewatering of utilities,excavations, foundations,etc.
'�leasures to install:
1. Foundation,vault,excavation, and trench dewatering water that has similar characteristics to
stonnwater runoff at the site shall be discharged into a controlled conveyance system prior to
discharge to a sediment trap or sediment pond. Foundation and trench dewatering water,which has '
similar characteristics to stormwater runoff at the site,must be disposed of through one of the
following options depending on site constraints:
I a) Infiltration,
b) Transport offsite in a vehicle,such as a vacuum flush truck, for legal disposal in a manner that
does not pollute surface waters,
c) Discharge to the sanitary sewer discharge���ith local sewer district approval if there is no other
option, or
d) Use of a sedimentation bag with outfall to a ditch or swale for small volwnes of localized
dewatering.
2. Clean,non-turbid dewatering water,such as well-point ground water,may be discharged via stable
comreyance to systems Mbutary to surface waters,provided the dewatering flow does not cause
erosion or flooding of receiving waters.
3. Highly turbid or contaminated de�vatering�;�ater shall be handled separately from stonnwater.
2009 Surface��'ater Design 'vlanual—Appendix D 1!9/2009
D-6�
KItiG COII\T1 . \�1'.ASHI\GTO'�J, Sl!RFACE 1�'ATER DESIG\' !�1A\�AL
D.4 ESC PERFORMANCE AND COMPLIANCE PROVISIONS
The changing conditions typical of construction sites call for frequent field adjustments of existin�� ESC
measures or additional ESC ineasures in order to meet required performance. In some cases,strict
adherence to specified measures may not be necessary or practicable based on site conditions or project
type. In other cases,immediate action may be needed to avoid severe impacts. Therefore,careful
attention must be paid to ESC perfonnance and compliance in accordance with the provisions contained in '
tl�is section.
D.4.1 ESC SUPER�'ISOR
For projects in Targeted, Full,or Large Project Drainage Review, the applicant must designate an ESC
supervisor who shall be responsible for the performance,maintenance, and review of ESC measures and '
for compliance with all permit conditions relating to ESC as described in the ESC Standards. The
applicant's selection of an ESC supervisor must be approved by King County. For projects that disturb II
one acre or more of land, the ESC supervisor must be a Certi�ed Professional in Erosion and Sediment i
Control(see www.cpesc.net for more information)or a Certified Erosion and Sediment Control Lead '�,
whose certification is recognized by King County.8 King County may also require a certified ESC ��'
supervisor for sites smaller than one acre of disturbance if DDES determines that onsite ESC measures are '
inadequately installed, located,or maintained.
For larger,more sensitive sites, King County may require a certified ESC supervisor with several years i
of experience in construction supervision/inspection and a background in geology,soil science,or '
agronomy. Typically, if a geotechnical consultant is already working on the project,the consultant may
also be the designated ESC supervisor. The design engineer may also be qualified for this position. This
requirement shall only be used for sensitive sites that pose an unusually high risk of impact to surface
waters as determined by DDES. At a minimum,the project site must meet all of the following conditions
in order to require the applicant to designate a certified ESC supervisor with such expertise:
• Aldervvood soils or other soils of Hydrologic Group C or D
• Five acres of disturbance
• Large areas (i.e.,two or more acres)with slopes in excess of 10 percent.
Proximity to streams or wetlands or phosphorus-sensitive lakes,such as Lake Sammamish, shall also be a
factor in detennining if such expertise in the ESC supervisor is warranted. However,proximity alone
shall not be a determining factor because even projects that are a considerable distance from surface
��-aters can result in significant impacts if there is a natural or constructed drainage system with direct
connections to surface waters.
The name,address, and phone number of the ESC supervisor shall be supplied to the County prior to the
start of construction. A sign shall be posted at all primary entrances to the site identifying the ESC
supervisor and his/her phone number. The requirement for an ESC supervisor does not relieve the
applicant of ultimate responsibility for the project and compliance���ith King County Code.
s King County recognition of certification means that the individual has taken a King County-approved third party training
program and has passed the King County-approved test for that training program.
2009 Surface Water Design Manual—Appendix D 1i9;2009
D-69
� CHAQ �4Rf�fC�l�R, LL� 6500126`hAvenueS.E.
Bellevue,Washington 98006-3941
(425)641-9743 Office (425)643-3499 Fax
chad@chadarmour.com
November 18, 2010 CITY OF RENTON
Job No. 10-007 ���E��,�!��
F
Mr. Michael Gladstein DF(' 0 � ?U10 $
American Classic Homes w
2821 Northup Way, Suite 100 PLA� REVI�VII `
Bellevue, Washington 98004
Subject: Wetland Hydrology Report - Revised
Rosewood Highlands Project
Renton, Washington
Dear Mr. Gladstein:
We are pleased to present the results of our revised wetland hydrology assessment for
the above-referenced property located in Renton, Washington. The work was
accomplished in accordance with our proposal (No. 388) dated October 25, 2010.
BACKGROUND INFORMATION
We understand that in their May 12, 2008 plan review letter, the City of Renton (City)
asked for additional stormwater management information. Among other things, they
asked that you address potential impacts to wetlands as a result of the proposed project.
Specifically, they requested that the analyses address both existing and development
wetland hydrological conditions and follows Guide Sheet 26 Wetland HvdroloQv
Protection Guideline in the reference section found in the 2005 King County Design
Manual. Our analysis utilized information gleaned from our February 26, 2007 critical
areas assessment and delineation report as well as reports and drawings provided by
ESM Consulting Engineers (ESM).
After reviewing our October 26'h letter, the City asked us to revise our analysis to
address potential short-term impacts to the on-site wetland. Specifically they asked us
to conduct a hydrological assessment using existing conditions for the 2-year storm
event. Previously we evaluated the potential hydrological impact to the wetland
assuming forested conditions for the 2-, 10-, and 100-year storm events.
Wetland and Buffer
The on-site wetland is a part of a larger wetland located off of the site to the north
(Attachment A— Figure 4). The on-site portion of the wetland covers 1,543 square feet
(sf). Although we did not survey the entire wetland, based on the information provided
by ESM and found on the King County iMap for Parcel No.518210-0022 (the parcel that
contains the wetland), it appears the wetland covers an estimated 50,000 sf.
The buffer subject to this analysis is composed of approximately 25% forest and 75%
pasture.
C:/ESMlRose/Wetland Hydrology Report(rev).doc 1 11i18/10
Chad Armour, LLC
� Revised Wetland Hydrology Report Rosewood Highlands Project
Renton, Washington
Hydrology
The site is located at the upper reaches of west branch of Maplewood Creek, which
flows south along the eastern portion of the site. The drainage basin upgradient of the
site drains a small area bounded by NE 4'h Street(north), Union Street (east), and the
Post Office (west). This basin includes two smaller on-site sub-basins, both of which
discharge to Maplewood Creek (Figure 9). Most of the site (->90%) drains to
Maplewood Creek and the remaining about <10% of the site drains to the wetland which
in-turn drains to Maplewood Creek.
Portions of future Lots 20 through 23 are located in the sub-basin that currently drains to
the wetland. We understand that with the exception of Lots 23 through 27, all of the
precipitation that falls on impervious surfaces will be directed to the stormwater vault.
Precipitation that falls on the roofs and rear yards of Lots 24 through 27 will bypass the
stormwater management system and be directed to the stream. Precipitation that falls
on the roof and rear yard of Lot 23 will be directed to the wetland (Figure 11).
Soils
The King County soil survey indicates that the site supports one soil type, Alderwood
gravelly sandy loam. Alderwood soils are made up of moderately well drained soils
underlain by a dense till layer typically two to 3.5 feet(ft) below the surface. The
geotechnical engineering report confirmed that glacial till underlies the site, but to a
depth ranging from 5 to more than 10 ft below the ground surface. The same report
indicates that the north and eastern portions of the site have been filled with 3.5 to 9.5 ft
of fill, including all or part of Lots 17 through 27.
Analysis
Using the King County Runoff Time Series (KCRTS) method for estimating runoff and
volume, the City will require 44,286 cubic feet (cf) of storage to detain the runoff from the
developed site. An underground water quality/detention vault will be constructed in the
southeast corner of the site.
The developed estimated runoff an 30-da � �lume for the portion of the site draining to
the wet ,project pre-development or e 2-year event for Lots 20 through 23 is 0.003
cfs an 417 ef for a 30-day storm. Post-development runoff for Lot 23 will be 0.014 cfs
and 1,4 cf:
Estimated runoff from the Rosewood Heights pro�ect
Condition 2-Year Storm Intensit a
Flow Volume°
Pre-Developmentb 0.003 cfs 417 cf
Post-Develo ment` 0.014 cfs 1431 cf
a data provided by ESM Consulting Engineers
b Lots 20 through 23
� Lot 23 only
d 30-day storm
C:/ESMlRose/Wetland Hydrology Report(rev).doc 2 11/18/10
Chad Armour, LLC
' Revised Wetland Hydrology Report Rosewood Highlands Project
Renton, Washington
Conclusions �,
We understand that the City requires discharge runoff from the site post-development to
be roughly equivalent to pre-development conditions. As indicated on the previous table '�,
runoff to the wetland will slightly increase after the site is developed. From an ecological '
perspective this increase should have a negligible effect on the wetland, particularly
because the wetland is connected to Maplewood Creek. The additional water will flow
through the wetland and as such site development should have no detrimental
hydrological effect on the wetland.
Because there will be little if any effect on wetland hydrology from the site post-
development, the development should have no cumulative hydrological effect on the
wetland. Similarly, because the stormwater captured on the site, detained in a
stormwater vault, and released per the requirements of the stormwater design manual,
we anticipate no cumulative hydrological effect on the watershed.
LIMITATIONS
Work for this project was perFormed, and this letter report prepared, in accordance with
generally accepted professional practices for the nature and conditions of the work
completed in the same or similar localities, at the time the work was performed. It is
intended for the exclusive use of American Classic H�mes and their assigns for specific
application to the referenced property. This report is not meant to represent a legal
opinion. No other warranty, express or implied, is made.
It should be noted that Chad Armour relied on information provided by others indicated
previously. Chad Armour can only relay this information and cannot be responsible for
its accuracy or completeness. Also note that assessing wetland hydrology is an inexact
science. Biological professionals may disagree on the mechanics of this function.
Accordingly, the wetland hydrology assessment performed for this study, as well as the
conclusions drawn in this report, should be reviewed by the appropriate permitting
authority prior to committing to detailed planning and design activities.
Any questions regarding our work and this report, the presentation of the information,
and the interpretation of the data are welcome and should be referred to the
undersigned.
Sincerely,
Chad Armour, LLC
Chad Armour
Principal
Attachments:
References
Attachment A— Figure 4
— Figure 9
— Figure 11
C:lESM/RoselWetland Hydrology Report(rev).doc 3 11/18/10
Chad Armour, LI.0
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