HomeMy WebLinkAboutSunset Oaks Workforce Housing SWPPP - Charter Construction 05-12-20
Construction Stormwater
Pollution Prevention Plan
PREPARED FOR:
Renton Housing Authority
c/o Mr. Sean McCarty
2900 NE 10th St
Renton, WA 98056
PROJECT:
Sunset Oaks Workforce Housing
2650 NE 10th St
Renton, WA 98056
7227801315
PREPARED BY:
Jameson Griggs Project
Manager
REVIEWED BY:
Luke Hagler
Commercial Team Lead
DATE:
May 2020
Construction Stormwater Pollution Prevention Plan
Sunset Oaks Workforce Housing
7227801315
Table of Contents
Section Page
1.0 Introduction .................................................................................................................................... 1
2.0 Project Description ........................................................................................................................ 2
3.0 Existing Site Conditions ................................................................................................................ 2
4.0 Adjacent Areas and Drainage ....................................................................................................... 2
5.0 Critical Areas ..................................................................................................................................... 2
6.0 Soils .................................................................................................................................................... 2
7.0 Potential Erosion Problems .......................................................................................................... 2
8.0 Construction Stormwater Pollution Prevention Elements ......................................................... 3
8.1 Preserve Vegetation/Mark Clearing Limits ......................................................................... 3
8.2 Establish Construction Access ............................................................................................ 3
8.3 Control Flow Rates .............................................................................................................. 3
8.4 Install Sediment Controls .................................................................................................... 3
8.5 Stabilize Soils ...................................................................................................................... 3
8.6 Protect Slopes ..................................................................................................................... 4
8.7 Protect Drain Inlets .............................................................................................................. 4
8.8 Stabilize Channels and Outlets ........................................................................................... 4
8.9 Control Pollutants ................................................................................................................ 4
8.9.1 Required BMPs ........................................................................................................ 6
8.10 Control Dewatering ............................................................................................................. 6
8.11 Maintain BMPs .................................................................................................................... 7
8.12 Manage the Project ............................................................................................................. 8
8.13 Protect Low Impact Development BMPs ............................................................................ 9
9.0 Construction Sequence and Phasing ............................................................................................ 9
9.1 Construction Sequence ....................................................................................................... 9
9.2 Construction Phasing .......................................................................................................... 9
10.0 Construction Schedule .................................................................................................................. 9
11.0 Financial/Ownership Responsibilities ....................................................................................... 10
12.0 Certified Erosion and Sediment Control Lead (CESCL) .......................................................... 10
Construction Stormwater Pollution Prevention Plan
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Exhibits
Exhibit 1
Inspection Logs
Exhibit 2
Best Management Practices (BMPs)
BMP C120 ........Temporary and Permanent Seeding
BMP C123 ........Plastic Covering
BMP C140 ........Dust Control
BMP C151 ........Concrete Handling
BMP C152 ........Sawcutting and Surface Pollution Prevention
BMP C153 ........Material Delivery, Containment & Storage
BMP C160 ........Certified Erosion and Sediment Control Lead
BMP C162 ........Scheduling
BMP C200 ………Interceptor Dike and Swale
BMP C220 ........Storm Drain Inlet Protection
BMP C233 ........Silt Fence
BMP C240 ………Sediment Trap
Construction Stormwater Pollution Prevention Plan
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1.1 Introduction
In 1972, Congress passed the Federal Water Pollution Control Act (FWPCA), also known as the
Clean Water Act (CWA), to restore and maintain the quality of the nation's waterways. The
ultimate goal was to make sure that rivers and streams were fishable, swimmable, and drinkable.
In 1987, the Water Quality Act (WQA) added provisions to the CWA that allowed the
Environmental Protection Agency to govern stormwater discharges from construction sites. The
National Pollutant Discharge Elimination System (NPDES) General Permit includes provisions for
development of a Stormwater Pollution Prevention Plan (SWPPP) to maximize the potential
benefits of pollution prevention and sediment and erosion control measures at construction sites.
Development, implementation, and maintenance of the Construction SWPPP (CSWPPP) will
provide the selected General Contractor with the framework for reducing soil erosion and
minimizing pollutants in stormwater during construction of the proposed improvements.
This CSWPPP will:
· Define the characteristics of the site and the type of construction that will occur.
· Describe the existing site conditions, including existing land use, soil types at the site, and
the location of surface waters that are located on or next to the site.
· Identify the body or bodies of water that will receive runoff from the construction site,
including the ultimate body of water that receives the stormwater.
· Identify the drainage areas and potential stormwater contaminants.
· Describe the stormwater management controls and various Best Management Practices
(BMPs) necessary to reduce erosion, sediment, and pollutants in stormwater discharge.
· Create an implementation schedule to ensure that the practices described in this CSWPPP
are in fact implemented, and to evaluate the plan's effectiveness in reducing erosion,
sediment, and pollutant levels in stormwater discharged from the site.
· Identify the CSWPPP Coordinator with a description of this person's duties.
· Identify the Stormwater Pollution Prevention Team (SWPP Team) that will assist in
implementation of the CSWPPP during construction.
· Describe the facility monitoring plan and how controls will be coordinated with construction
activities.
· Describe the implementation schedule and provisions for amendment of the plan.
· Describe the final stabilization/termination design to minimize erosion and prevent
stormwater impacts after construction is complete.
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2.0 Project Description
The Sunset Oaks Workforce Housing project will include three new three story multi-family
buildings A, B & C, as well as a new 41-stall parking lot accessed from a new alley connecting
Glennwood Ave NE and Harrington Ave NE. In addition to these improvements, stormwater,
hardscape, and landscape improvements will also be a part of the proposed project. In this
report, the northwest building will be referred to as Building A, the south building will be referred
to as building B, while the northeast building will be referred to as Building C.
The project site is located at 2650 NE 10th St, Renton, Washington. The site is bordered to the
north by single-family residences, to the east by Harrington Ave NE, and to the South by Sunset
Lane NE, and to the West by Glennwood Ave NE. The site consists of one King County tax
parcel 7227801315, totaling slightly over 1 acre in size. Project improvements will occur
throughout the site and will disturb approximately 1.05 acres.
3.0 Existing Site Conditions
The project area is approximately 1.05 acres in size and is located at the northwest corner of the
intersection of Sunset Lane NE and Harrington. The site is accessed from Harrington Ave NE.
The project site was previously developed with single-family homes that were demolished.
4.0 Adjacent Areas and Drainage
The project site is bordered to the north by single-family residences, to the east by Harrington
Ave NE, and to the South by Sunset Lane NE, and to the West by Glennwood Ave NE.
Topographically, the site is relatively flat. The existing grades are such that offsite runoff should
be considered minimal. Existing storm structures around the site on Glennwood Ave NE,
Harrington Ave NE and Sunset Lane NE will have inlet protection inserts throughout the project
duration. A filter fabric fence with straw wattles will be installed at the perimeter of the site to
catch runoff. An interceptor swale and sediment trap will also be constructed onsite in the early
stage of grading to contain potential runoff.
5.0 Critical Areas
There are no known critical areas on the site or in the immediate vicinity of the project.
6.0 Soils
Zipper Geo Associates, LLC prepared a Geotechnical Engineering Study for the project site
(dated May 15, 2019), which indicates that soils generally consist of medium dense to dense
sand with variable silt and gravel contents, and very dense sand with variable silt and gravel
contents or glacial till. The upper 4 to 5 feet of soils observed in the subsurface exploration was
interpreted to be possibly undocumented fill associated with previous development of the site and
possibly demolition of the previously existing homes. Groundwater was not encountered at the
time of the exploration at any of the boring locations.
7.0 Potential Erosion Problems
There are no known areas that would create potential erosion problems on the site or in the
immediate vicinity of the project.
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8.1 Construction Stormwater Pollution Prevention Elements
The purpose of this section is to describe how each of the 13 Construction Stormwater Pollution
Prevention Elements has been addressed and to identify the type and location of BMPs used to
satisfy the required element. If an element is not applicable to the project, a reason is provided.
8.2 Preserve Vegetation/Mark Clearing Limits
Prior to beginning land-disturbing activities, clearing limits will be marked with high visibility silt
fence (BMP C233).
8.3 Establish Construction Access
The site was previously used for a temporary construction office and there is an existing
construction entrance on Harrington Ave NE. A new construction entrance will be installed at
the northeast corner of the site on Harrington Ave NE, and potentially a second on the
northwest side on Glennwood Ave NE as construction phasing of underground utilities allows.
8.4 Control Flow Rates
The new interceptor swale and sediment trap will provide an outlet structure that controls release
rates of runoff. This system will be used during site grading to control flow rates. In addition, straw
wattles (BMP C235) will be used to slow flow rates prior to entering the existing system,
minimizing the opportunity to become turbid.
8.5 Install Sediment Controls
Structural control measures will be used to reduce erosion and retain sediment on the
construction site. The control measures are selected to fit specific site and seasonal conditions.
The temporary erosion and sediment control (TESC) plans include the following structural
measures:
1. Filter fabric fencing (BMP C233) around the perimeter of the site to prevent sediment-
laden stormwater from being transported offsite, including fencing between
construction activities and critical areas.
2. Straw wattles (BMP C235) will be placed along flow paths of runoff to reduce flow velocities
and promote sheet flow.
3. Catch basin inlet protection to prevent sedimentation of stormwater conveyance systems.
4. Interceptor Swale and Sediment Trap (BMP C200 & BMP C240)
8.6 Stabilize Soils
Because source control is the most important form of erosion control, construction practices must
adhere to stringent cover requirements.
More specifically, during the period of May 1 through September 30, the Contractor will not be
allowed to leave soils unprotected for more than 15 days, and immediate seeding will be required
for areas brought to finish grade with no further work planned for the next 30 days. Areas to be
paved may be armored with crushed rock subbase in place of other stabilizing measures. The
area of clearing will be limited to the amount that can be stabilized by September 30 of that year.
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During the period of October 1 through April 30, all disturbed soil areas will be covered or
stabilized within 5 days or 24 hours when a major storm event is predicted. Cover measures may
include mulching, netting, plastic sheeting, erosion control blankets, or free draining material.
The extent of clearing shall be limited to the amount of land that can be covered or stabilized
within 24 hours.
Soil stockpiles shall be stabilized by plastic covering (BMP 123) or surrounded by filter fabric
fence (BMP C233). The stockpiles shall be a minimum of 50 feet from critical areas, including
wetland buffers and drainage swales.
Dust control (BMP C140) will be provided by sprinkling the site with water.
Permanent erosion control measures will include site paving and seeding of exposed soils.
8.7 Protect Slopes
Grading across the site will be minimal. If necessary, slopes across the site shall be stabilized
with temporary and permanent seeding (BMP C120) to prevent erosion. Runoff shall be directed
away from slopes by grading.
8.8 Protect Drain Inlets
Storm drain inlets shall be protected so that surface water runoff does not enter the conveyance
system without first being filtered. Inlets shall be inspected weekly, at a minimum, and daily
during storm events. Storm Drain Inlet Protection (BMP C220) will be provided.
8.9 Stabilize Channels and Outlets
The project will use the existing storm system throughout construction and in the final condition.
Existing channels and outlets will be maintained in their existing condition. No further BMPs are
expected to be required for this element.
8.10 Control Pollutants
The Contractor shall be responsible for controlling pollutants at the work site. Key elements, such
as centralized areas for equipment and concrete truck washing and temporary storage of debris
and other stockpiled materials, are the responsibility of the Contractor.
All pollutants, including waste materials and demolition debris, that occur onsite shall be handled
and disposed of in a manner that does not cause contamination of stormwater. Woody debris
may be chopped and spread onsite.
Cover, containment, and protection from vandalism shall be provided for all chemicals, liquid
products, petroleum products, and non-inert wastes present on the site (see Chapter 173-304
WAC for the definition of inert waste). Onsite fueling tanks shall include secondary containment.
Maintenance and repair of heavy equipment and vehicles involving oil changes, hydraulic system
drain down, solvent and de-greasing cleaning operations, fuel tank drain down and removal, and
other activities which may result in discharge or spillage of pollutants to the ground or into
stormwater runoff must be conducted using spill prevention measures, such as drip pans.
Contaminated surfaces shall be cleaned immediately following any discharge or spill incident.
Emergency repairs may be performed on-site using temporary plastic placed beneath and, if
raining, over the vehicle.
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Wheel wash or tire bath (if necessary) wastewater shall be discharged to a separate on-site
treatment system or to the sanitary sewer.
Application of agricultural chemicals, including fertilizers and pesticides, shall be conducted in a
manner and at application rates that will not result in loss of chemical to stormwater runoff.
Manufacturers’ recommendations for application rates and procedures shall be followed.
BMPs shall be used to prevent or treat contamination of stormwater runoff by pH modifying
sources. These sources include, but are not limited to, bulk cement, cement kiln dust, fly ash,
new concrete washing and curing waters, waste streams generated from concrete grinding and
sawing, exposed aggregate processes, and concrete pumping and mixer washout waters.
Stormwater discharges shall not cause or contribute to a violation of the water quality standard for
pH in the receiving water.
Construction sites with significant concrete work shall adjust the pH of stormwater if necessary to
prevent violations of water quality standards.
Table 1 below lists several pollutants that are commonly found on construction sites that have the
potential to contaminate storm runoff. These pollutants will be present, mainly in areas of building
and pavement construction. Charter Construction and the CSWPPP/TESC coordinator will be
responsible for identifying areas where these pollutants are being used and monitor runoff coming
from these areas. Pollutant sources will be covered with plastic if contaminated runoff is
observed from these areas. If contaminated runoff is found in the sediment trap or soils, the
Erosion Control Specialist will direct the Contractor to remove the polluted water/soil and dispose
of it in an approved area offsite.
Table 1 – Potential Construction Site Stormwater Pollutants
Trade Name Material Chemical/Physical
Description(1)
Stormwater Pollutants(1)
Pesticides (insecticides,
fungicides, herbicide,
rodenticides)
Various colored to colorless
liquid, powder, pellets, or grains
Chlorinated hydrocarbons,
organophosphates, carbamates,
arsenic
Fertilizer Liquid or solid grains Nitrogen, phosphorous
Plaster White granules or powder Calcium sulphate, calcium carbonate,
sulfuric acid
Cleaning solvents Colorless, blue, or yellow-green
liquid
Perchloroethylene, methylene
chloride, trichloroethylene, petroleum
distillates
Asphalt Black solid Oil, petroleum distillates
Concrete White solid Limestone, sand
Glue, adhesives White or yellow liquid Polymers, epoxies
Paints Various colored liquid Metal oxides, Stoddard solvent, talc,
calcium carbonate, arsenic
Curing compounds Creamy white liquid Naphtha
Wastewater from construction
equipment washing
Water Soil, oil & grease, solids
Wood preservatives Clear amber or dark brown
liquid
Stoddard solvent, petroleum
distillates, arsenic, copper, chromium
Hydraulic oil/fluids Brown oily petroleum
hydrocarbon
Mineral oil
Gasoline Colorless, pale brown or pink
petroleum hydrocarbon
Benzene, ethyl benzene, toluene,
xylene, MTBE
Diesel fuel Clear, blue-green to yellow
liquid
Petroleum distillate, oil & grease,
naphthalene, xylenes
Kerosene Pale yellow liquid petroleum
hydrocarbon
Coal oil, petroleum distillates
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Trade Name Material Chemical/Physical
Description(1)
Stormwater Pollutants(1)
Antifreeze/coolant Clear green/yellow liquid Ethylene glycol, propylene glycol,
heavy metals (copper, lead, zinc)
Erosion Solid Particles Soil, Sediment
(1) Data obtained from MSDS when available
8.9.1 Required BMPs
The following BMPs or equivalent measures are required of all businesses and agencies during
concrete pouring and asphalt application at temporary sites:
· Employees must be educated on the pollution hazards of concrete and asphalt application
and cutting.
· Loose aggregate chunks and dust must be swept or shoveled and collected (not hosed
down a storm drain) for recycling or proper disposal at the end of each work day, especially
at work sites such as streets, driveways, parking lots, sidewalks, curbs, and gutters where
rain can readily pick up the loose material and carry it to the nearest stormwater
conveyance. Small amounts of excess concrete, grout, and mortar can be disposed of in
the trash.
· Storm drain covers or similarly effective containment devices must be placed over all
nearby drains at the beginning of each day. Shovel or vacuum slurry and remove from the
site. All accumulated runoff and solids must be collected and properly disposed at the end
of each workday, or more often if necessary.
· Exposed aggregate washing, where the top layer of unhardened concrete is hosed or
scraped off to leave a rough finish, must be done with a mechanism for containment and
collection of the discarded concrete slurry (such as the storm drain covers mentioned
above). The easiest way to contain the wash water will be to direct the washings to a hole
in the ground where the water can percolate into the ground and the solids later covered
with soil.
· If directed to a drain, a catch basin filter insert must be used to remove the solids. This is
especially useful if the activity must proceed on rainy days.
· Cleaning of concrete application and mixing equipment or concrete vehicles on the work
site must be done in a designated area where the rinse water is controlled. The rinse water
must either be collected for proper disposal or put into a hole in the ground where the water
can percolate away and the solids later covered with soil or recovered and disposed or
recycled.
The use of any treatment BMP must not result in the violation of groundwater, surface water, or
drinking water quality standards.
8.11 Control Dewatering
Groundwater is not anticipated to be a factor in this project. Therefore, dewatering will not be
required.
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8.12 Maintain BMPs
In order for the ESC facilities to function properly, they must be maintained and sediment
removed on a regular basis. Inspection and sediment removal shall be performed on all ESC
facilities, as described in the following inspection schedule.
Erosion control facilities shall not be allowed to fall into disrepair. All ESC facilities shall be
inspected, at a minimum, according to the following schedule.
· Dry Season: Once a week.
· Wet Season: Daily and after every storm event that produces runoff.
Needed repairs shall be made within 24 hours or immediately, if possible.
The following inspection/maintenance schedules shall be utilized to ensure the ESC facilities are
functioning as designed:
Temporary and Permanent Seeding
· Seeding may be used throughout the project on disturbed areas. During the dry season,
areas that have reached final grade, or are not being actively worked, shall be seeding
within 15 days. Seeded areas shall be supplied with adequate moisture, but not watered to
the extent that it causes runoff.
· During the wet season, all disturbed areas not being actively worked shall be seeded or
stabilized with mulch or plastic sheeting.
· During the wet season, no more area shall be exposed than can be controlled and
effectively stabilized by the end of each working day.
· To prevent seed from being washed away, confirm that all other approved
erosion/sedimentation control facilities have been installed and are functioning properly.
· Any seeded areas that fail to establish 80 percent cover (100 percent cover for areas that
receive sheet or concentrated flows) shall be reseeded. If reseeding is ineffective, an
alternate method shall be used.
· Seeded areas shall be inspected after every rainfall event during the wet season. Any
areas that experience erosion shall be reseeded and protected by mulch. If the erosion
problem is drainage related, the problem shall be fixed and the eroded area reseeded and
protected by mulch.
· Seeding shall not be used in areas subject to heavy vehicular traffic.
Plastic Covering
· Plastic sheeting shall be inspected once a week during both the wet and dry season.
· Torn sheets must be replaced and open seams repaired.
· If the plastic begins to deteriorate due to ultraviolet radiation, it must be completely
removed and replaced.
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· When the plastic is no longer needed, it shall be completely removed.
· If tires are used to weight down the plastic sheeting, they must be disposed of properly.
Inlet Protection
· Catch basin filter inserts shall be inspected frequently, especially after storm events. If the
filter becomes clogged, it should be cleaned or replaced.
· Inserts shall be replaced when tears are detected.
Silt Fence
· Any damage shall be repaired immediately.
· If concentrated flows are evident uphill of the fence, they must be intercepted and
conveyed to a sediment pond.
· Check the uphill side of the fence for signs of the fence clogging and acting as a barrier to
flow and causing channelization of flows parallel to the fence. If this occurs, replace the
fence or remove the trapped sediment.
· Sediment deposits shall be removed when the deposit reaches approximately one-third the
height of the silt fence, or a second silt fence shall be installed.
· If the filter fabric (geotextile) has deteriorated due to ultraviolet breakdown, it shall be
replaced.
The maintenance inspection report will be made after each inspection. Copies of the report forms
to be completed by the CSWPPP coordinator are attached as Exhibit 1 of this CSWPPP.
Completed forms will be provided to the City Inspector and will also be maintained onsite during
the entire construction project. If construction activities or design modifications are made to the
site plan that could impact stormwater, or if Charter Construction determines that the measures
are not adequate to prevent erosion and the discharge of sediment from the site (based on
turbidity measurements), this CSWPPP will be amended appropriately. The amended CSWPPP
will have a description of the new activities that contribute to the increased pollutant loading and
the planned source control activities.
8.13 Manage the Project
The following practices will be required during construction to properly manage activities:
· Comply with seasonal work limitations.
· Inspect, maintain, and repair BMPs.
· Identify a Certified Erosion and Sediment Control Lead (CESCL).
· Maintain the CSWPPP onsite at all times, including narrative and plans.
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8.14 Protect Low Impact Development BMPs
This project does not contain low impact development BMPs. Therefore, this element does not
apply to this project.
9.1 Construction Sequence and Phasing
9.2 Construction Sequence
The construction sequence is described below:
1. Attend a pre-construction meeting with the City of Renton.
2. Stake/flag clearing and construction limits.
3. Construct all temporary erosion control BMPs according to the TESC plan. Install inlet
sediment protection in existing catch basins.
4. Pothole existing utilities where indicated on plans and as necessary.
5. Demolish existing site features indicated for removal.
6. Maintain erosion control measures in accordance with the Washington State Department of
Ecology 2014 Stormwater Management Manual for Western Washington (SMMWW)
recommendations.
7. Rough grade site. All grading shall be done in accordance with the grading plan.
8. Construct storm system and install inlet sediment protection to new catch basins.
9. Apply erosion control mulch and seeding, straw mulch or equal, to areas that will not be
brought to final grade or permanently vegetated within 7 days of exposure during the dry
season, and 2 days of exposure during the wet season (October 1 – April 30).
10. Relocate erosion control measures or install new measures so that, as the site conditions
change, the erosion and sediment control is always in accordance with the SWPPP
minimum requirements.
11. Final grade site and install surface treatments. Ensure that surface water is positively
directed toward proposed storm collection facilities and away from the building.
12. Remove remaining temporary erosion control items once site has been stabilized and upon
approval from the City of Renton.
9.3 Construction Phasing
The project is anticipated to be constructed in a single phase.
10.0 Construction Schedule
Construction is scheduled to begin in spring of 2020. Completion of the final project phase will be
based on market conditions, but mass grading activities will be primarily limited to the dry season.
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11.0 Financial/Ownership Responsibilities
The Renton Housing Authority is the party responsible for initiation of bonds and other financial
securities. The project must comply with City of Renton financial liability requirements.
12.1 Certified Erosion and Sediment Control Lead (CESCL)
The General Contractor shall be required to provide a CESCL prior to construction. Once this
individual is identified, the City Inspector will be notified.
The contractor will designate their CESCL here:
Name: Jeff Snowden
Address: 980 S Harney St, Seattle, WA 98108
Phone: 206-382-1900
Fax Number: N/A
The CESCL is required to meet Washington State Department of Ecology (DOE) certification
requirements. The City Inspector will be provided with CESCL information.
The duties of the CESCL include:
· Implement the CSWPPP/TESC plan with the aid of the SWPP Team.
· Oversee maintenance practices identified as BMPs in the CSWPPP.
· Conduct or provide for inspection and monitoring activities.
· Sample stormwater for turbidity using a turbidity meter.
· Identify other potential pollutant sources and make sure they are added to the plan.
· Identify any deficiencies in the CSWPPP and make sure they are corrected.
· Ensure that any changes in construction plans are addressed in the CSWPPP.
To aid in the implementation of the CSWPPP, the members of the SWPP Team include the
following: General Contractor, City of Renton Inspector, Owner, the geotechnical engineering
consultant, and Coterra.
Charter Construction will ensure that all housekeeping and monitoring procedures are
implemented, while the CESCL will ensure the integrity of the structural BMPs. The SWPP Team
will observe construction and erosion control practices and recommend revisions or additions to
the CSWPPP and drawings.
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This analysis is based on data and records either supplied to or obtained by Charter Construction. These
documents are referenced within the text of the analysis. The analysis has been prepared using
procedures and practices within the standard accepted practices of the industry.
Charter Construction.
Jameson Griggs
Project manager
May 2020
Construction Stormwater Pollution Prevention Plan
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Exhibit 1
Inspection Logs
Construction Stormwater Pollution Prevention Plan
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2180406.10
Exhibit 1 – 1
Sunset Oaks Workforce Housing
Stormwater Pollution Prevention Plan
Inspection and Maintenance Report Form
To be completed every 7 days and within 24 hours of a rainfall event of 0.5 inches or more
Inspector: Date:
Inspector's Qualifications:
Days since last rainfall: Amount of last rainfall: inches
Stabilization Measures
Drainage Area Date Since
Last
Disturbance
Date of Next
Disturbance
Stabilized
(yes/No)
Stabilized With Condition
Stabilization required:
To be performed by: On or before:
Construction Stormwater Pollution Prevention Plan
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2180406.10
Exhibit 1 – 2
Sunset Oaks Workforce Housing
Stormwater Pollution Prevention Plan
Inspection and Maintenance Report Form
Structural Controls:
Date:
Inlet Protection
Drainage Area
Perimeter
Has Silt Reached 1/3 of
holding capacity?
Is Inlet Protection
Properly Secured?
Is There Evidence of
tearing or Overtopping?
Maintenance required for inlet protection:
To be performed by: On or before:
Construction Stormwater Pollution Prevention Plan
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2180406.10
Exhibit 1 – 3
Sunset Oaks Workforce Housing
Stormwater Pollution Prevention Plan
Inspection and Maintenance Report Form
Changes required to the pollution prevention plan:
Reasons for changes:
I certify under penalty of law that this document and all attachments were prepared under my
direction or supervision in accordance with a system designed to assure that qualified personnel
properly gathered and evaluated the information submitted. Based on my inquiry of the person
or persons who manage the system, or those persons directly responsible for gathering the
information, the information submitted is, to the best of my knowledge and belief, true, accurate,
and complete. I am aware that there are significant penalties for submitting false information,
including the possibility of fine and imprisonment for knowing violations.
Signature: Date:
Construction Stormwater Pollution Prevention Plan
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Exhibit 2
Best Management Practices (BMPs)
BMP C120 .................................. Temporary and Permanent Seeding
BMP C123 .................................. Plastic Covering
BMP C140 .................................. Dust Control
BMP C151 .................................. Concrete Handling
BMP C152 .................................. Sawcutting and Surface Pollution Prevention
BMP C153 .................................. Material Delivery, Containment & Storage
BMP C160 .................................. Certified Erosion and Sediment Control Lead
BMP C162 .................................. Scheduling
BMP C200 ………………………………….Interceptor Dike and Swale
BMP C220 .................................. Storm Drain Inlet Protection
BMP C233 .................................. Silt Fence
BMP C240 ………………………………….Sediment Trap
2014 Stormwater Management Manual for Western Washington
Volume II - Chapter 4 - Page 278
l Storm drain inlets shall be protected to prevent sediment-laden water entering the
storm drain system (see BMP C220: Storm Drain Inlet Protection (p.357)).
Maintenance Standards
Inspect stabilized areas regularly, especially after large storm events.
Crushed rock, gravel base, etc., shall be added as required to maintain a stable driving
surface and to stabilize any areas that have eroded.
Following construction, these areas shall be restored to pre-construction condition or bet-
ter to prevent future erosion.
Perform street cleaning at the end of each day or more often if necessary.
BMP C120: Temporary and Permanent Seeding
Purpose
Seeding reduces erosion by stabilizing exposed soils. A well-established vegetative
cover is one of the most effective methods of reducing erosion.
Conditions of Use
Use seeding throughout the project on disturbed areas that have reached final grade or
that will remain unworked for more than 30 days.
The optimum seeding windows for western Washington are April 1 through June 30 and
September 1 through October 1.
Between July 1 and August 30 seeding requires irrigation until 75 percent grass cover is
established.
Between October 1 and March 30 seeding requires a cover of mulch with straw or an
erosion control blanket until 75 percent grass cover is established.
Review all disturbed areas in late August to early September and complete all seeding
by the end of September. Otherwise, vegetation will not establish itself enough to
provide more than average protection.
l Mulch is required at all times for seeding because it protects seeds from heat, mois-
ture loss, and transport due to runoff. Mulch can be applied on top of the seed or
simultaneously by hydroseeding. See BMP C121: Mulching (p.284) for spe-
cifications.
l Seed and mulch, all disturbed areas not otherwise vegetated at final site sta-
bilization. Final stabilization means the completion of all soil disturbing activities at
the site and the establishment of a permanent vegetative cover, or equivalent per-
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manent stabilization measures (such as pavement, riprap, gabions, or geotextiles)
which will prevent erosion.
Design and Installation Specifications
Seed retention/detention ponds as required.
Install channels intended for vegetation before starting major earthwork and hydroseed
with a Bonded Fiber Matrix. For vegetated channels that will have high flows, install
erosion control blankets over hydroseed. Before allowing water to flow in vegetated
channels, establish 75 percent vegetation cover. If vegetated channels cannot be estab-
lished by seed before water flow; install sod in the channel bottom—over hydromulch
and erosion control blankets.
l Confirm the installation of all required surface water control measures to prevent
seed from washing away.
l Hydroseed applications shall include a minimum of 1,500 pounds per acre of
mulch with 3 percent tackifier. See BMP C121: Mulching (p.284) for specifications.
l Areas that will have seeding only and not landscaping may need compost or meal-
based mulch included in the hydroseed in order to establish vegetation. Re-install
native topsoil on the disturbed soil surface before application.
l When installing seed via hydroseeding operations, only about 1/3 of the seed actu-
ally ends up in contact with the soil surface. This reduces the ability to establish a
good stand of grass quickly. To overcome this, consider increasing seed quantities
by up to 50 percent.
l Enhance vegetation establishment by dividing the hydromulch operation into two
phases:
1. Phase 1- Install all seed and fertilizer with 25-30 percent mulch and tackifier
onto soil in the first lift.
2. Phase 2- Install the rest of the mulch and tackifier over the first lift.
Or, enhance vegetation by:
1. Installing the mulch, seed, fertilizer, and tackifier in one lift.
2. Spread or blow straw over the top of the hydromulch at a rate of 800-1000
pounds per acre.
3. Hold straw in place with a standard tackifier.
Both of these approaches will increase cost moderately but will greatly improve
and enhance vegetative establishment. The increased cost may be offset by the
reduced need for:
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l Irrigation.
l Reapplication of mulch.
l Repair of failed slope surfaces.
This technique works with standard hydromulch (1,500 pounds per acre minimum)
and BFM/MBFMs (3,000 pounds per acre minimum).
l Seed may be installed by hand if:
l Temporary and covered by straw, mulch, or topsoil.
l Permanent in small areas (usually less than 1 acre) and covered with mulch,
topsoil, or erosion blankets.
l The seed mixes listed in the tables below include recommended mixes for
both temporary and permanent seeding.
l Apply these mixes, with the exception of the wetland mix, at a rate of 120
pounds per acre. This rate can be reduced if soil amendments or slow-
release fertilizers are used.
l Consult the local suppliers or the local conservation district for their recom-
mendations because the appropriate mix depends on a variety of factors,
including location, exposure, soil type, slope, and expected foot traffic. Altern-
ative seed mixes approved by the local authority may be used.
l Other mixes may be appropriate, depending on the soil type and hydrology of
the area.
l Table II-4.1.2 Temporary Erosion Control Seed Mix (p.280) lists the standard mix
for areas requiring a temporary vegetative cover.
Table II-4.1.2 Temporary Erosion Control Seed Mix
% Weight % Purity % Germination
Chewings or annual blue grass
Festuca rubra var. commutata or Poa anna
40
98
90
Perennial rye
Lolium perenne
50
98
90
Redtop or colonial bentgrass
Agrostis alba or Agrostis tenuis
5
92
85
White dutch clover
Trifolium repens
5
98
90
l Table II-4.1.3 Landscaping Seed Mix (p.281) lists a recommended mix for land-
scaping seed.
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Table II-4.1.3 Landscaping Seed Mix
% Weight % Purity % Germination
Perennial rye blend
Lolium perenne
70
98
90
Chewings and red fescue blend
Festuca rubra var. commutata or Festuca rubra
30
98
90
l Table II-4.1.4 Low-Growing Turf Seed Mix (p.281) lists a turf seed mix for dry situ-
ations where there is no need for watering. This mix requires very little main-
tenance.
Table II-4.1.4 Low-Growing Turf Seed Mix
% Weight % Purity % Germination
Dwarf tall fescue (several varieties)
Festuca arundinacea var.
45
98
90
Dwarf perennial rye (Barclay)
Lolium perenne var. barclay
30
98
90
Red fescue
Festuca rubra
20
98
90
Colonial bentgrass
Agrostis tenuis
5
98
90
l Table II-4.1.5 Bioswale Seed Mix* (p.281) lists a mix for bioswales and other inter-
mittently wet areas.
Table II-4.1.5 Bioswale Seed Mix*
% Weight % Purity % Germination
Tall or meadow fescue
Festuca arundinacea or Festuca ela-
tior
75-80
98
90
Seaside/Creeping bentgrass
Agrostis palustris
10-15
92
85
Redtop bentgrass
Agrostis alba or Agrostis gigantea
5-10
90
80
* Modified Briargreen, Inc. Hydroseeding Guide Wetlands Seed Mix
l Table II-4.1.6 Wet Area Seed Mix* (p.282) lists a low-growing, relatively non-invas-
ive seed mix appropriate for very wet areas that are not regulated wetlands. Apply
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this mixture at a rate of 60 pounds per acre. Consult Hydraulic Permit Authority
(HPA) for seed mixes if applicable.
Table II-4.1.6 Wet Area Seed Mix*
% Weight % Purity % Germination
Tall or meadow fescue
Festuca arundinacea or Festuca ela-
tior
60-70
98
90
Seaside/Creeping bentgrass
Agrostis palustris
10-15
98
85
Meadow foxtail
Alepocurus pratensis
10-15
90
80
Alsike clover
Trifolium hybridum
1-6
98
90
Redtop bentgrass
Agrostis alba
1-6
92
85
* Modified Briargreen, Inc. Hydroseeding Guide Wetlands Seed Mix
l Table II-4.1.7 Meadow Seed Mix (p.282) lists a recommended meadow seed mix
for infrequently maintained areas or non-maintained areas where colonization by
native plants is desirable. Likely applications include rural road and utility right-of-
way. Seeding should take place in September or very early October in order to
obtain adequate establishment prior to the winter months. Consider the appro-
priateness of clover, a fairly invasive species, in the mix. Amending the soil can
reduce the need for clover.
Table II-4.1.7 Meadow Seed Mix
% Weight % Purity % Germination
Redtop or Oregon bentgrass
Agrostis alba or Agrostis oregonensis
20
92
85
Red fescue
Festuca rubra
70
98
90
White dutch clover
Trifolium repens
10
98
90
l Roughening and Rototilling:
l The seedbed should be firm and rough. Roughen all soil no matter what the
slope. Track walk slopes before seeding if engineering purposes require
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compaction. Backblading or smoothing of slopes greater than 4H:1V is not
allowed if they are to be seeded.
l Restoration-based landscape practices require deeper incorporation than
that provided by a simple single-pass rototilling treatment. Wherever prac-
tical, initially rip the subgrade to improve long-term permeability, infiltration,
and water inflow qualities. At a minimum, permanent areas shall use soil
amendments to achieve organic matter and permeability performance
defined in engineered soil/landscape systems. For systems that are deeper
than 8 inches complete the rototilling process in multiple lifts, or prepare the
engineered soil system per specifications and place to achieve the specified
depth.
l Fertilizers:
l Conducting soil tests to determine the exact type and quantity of fertilizer is
recommended. This will prevent the over-application of fertilizer.
l Organic matter is the most appropriate form of fertilizer because it provides
nutrients (including nitrogen, phosphorus, and potassium) in the least water-
soluble form.
l In general, use 10-4-6 N-P-K (nitrogen-phosphorus-potassium) fertilizer at a
rate of 90 pounds per acre. Always use slow-release fertilizers because they
are more efficient and have fewer environmental impacts. Do not add fer-
tilizer to the hydromulch machine, or agitate, more than 20 minutes before
use. Too much agitation destroys the slow-release coating.
l There are numerous products available that take the place of chemical fer-
tilizers. These include several with seaweed extracts that are beneficial to
soil microbes and organisms. If 100 percent cottonseed meal is used as the
mulch in hydroseed, chemical fertilizer may not be necessary. Cottonseed
meal provides a good source of long-term, slow-release, available nitrogen.
l Bonded Fiber Matrix and Mechanically Bonded Fiber Matrix:
l On steep slopes use Bonded Fiber Matrix (BFM) or Mechanically Bonded
Fiber Matrix (MBFM) products. Apply BFM/MBFM products at a minimum rate
of 3,000 pounds per acre of mulch with approximately 10 percent tackifier.
Achieve a minimum of 95 percent soil coverage during application. Numer-
ous products are available commercially. Installed products per man-
ufacturer’s instructions. Most products require 24-36 hours to cure before
rainfall and cannot be installed on wet or saturated soils. Generally, products
come in 40-50 pound bags and include all necessary ingredients except for
seed and fertilizer.
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BMP C121: Mulching
Purpose
Mulching soils provides immediate temporary protection from erosion. Mulch also
enhances plant establishment by conserving moisture, holding fertilizer, seed, and top-
soil in place, and moderating soil temperatures. There is an enormous variety of
mulches that can be used. This section discusses only the most common types of mulch.
Conditions of Use
As a temporary cover measure, mulch should be used:
l BFMs and MBFMs provide good alternatives to blankets in most areas requir-
ing vegetation establishment. Advantages over blankets include:
l BFM and MBFMs do not require surface preparation.
l Helicopters can assist in installing BFM and MBFMs in remote areas.
l On slopes steeper than 2.5H:1V, blanket installers may require ropes
and harnesses for safety.
l Installing BFM and MBFMs can save at least $1,000 per acre com-
pared to blankets.
Maintenance Standards
Reseed any seeded areas that fail to establish at least 80 percent cover (100 percent
cover for areas that receive sheet or concentrated flows). If reseeding is ineffective, use
an alternate method such as sodding, mulching, or nets/blankets. If winter weather pre-
vents adequate grass growth, this time limit may be relaxed at the discretion of the local
authority when sensitive areas would otherwise be protected.
l Reseed and protect by mulch any areas that experience erosion after achieving
adequate cover. Reseed and protect by mulch any eroded area.
l Supply seeded areas with adequate moisture, but do not water to the extent that it
causes runoff.
Approved as Equivalent
Ecology has approved products as able to meet the requirements of BMP C120: Tem-
porary and Permanent Seeding. The products did not pass through the Technology
Assessment Protocol – Ecology (TAPE) process. Local jurisdictions may choose not to
accept this product approved as equivalent, or may require additional testing prior to con-
sideration for local use. The products are available for review on Ecology’s website at
http://www.ecy.wa.gov/programs/wq/stormwater/newtech/equivalent.html.
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BMP C123: Plastic Covering
Purpose
Plastic covering provides immediate, short-term erosion protection to slopes and dis-
turbed areas.
Conditions of Use
Plastic covering may be used on disturbed areas that require cover measures for less
than 30 days, except as stated below.
l Plastic is particularly useful for protecting cut and fill slopes and stockpiles. Note:
The relatively rapid breakdown of most polyethylene sheeting makes it unsuitable
for long-term (greater than six months) applications.
l Due to rapid runoff caused by plastic covering, do not use this method upslope of
areas that might be adversely impacted by concentrated runoff. Such areas include
steep and/or unstable slopes.
l Plastic sheeting may result in increased runoff volumes and velocities, requiring
additional on-site measures to counteract the increases. Creating a trough with
wattles or other material can convey clean water away from these areas.
l To prevent undercutting, trench and backfill rolled plastic covering products.
l While plastic is inexpensive to purchase, the added cost of installation, main-
tenance, removal, and disposal make this an expensive material, up to $1.50-2.00
per square yard.
l Whenever plastic is used to protect slopes install water collection measures at the
base of the slope. These measures include plastic-covered berms, channels, and
pipes used to covey clean rainwater away from bare soil and disturbed areas. Do
not mix clean runoff from a plastic covered slope with dirty runoff from a project.
l Other uses for plastic include:
1. Temporary ditch liner.
2. Pond liner in temporary sediment pond.
3. Liner for bermed temporary fuel storage area if plastic is not reactive to the
type of fuel being stored.
4. Emergency slope protection during heavy rains.
5. Temporary drainpipe (“elephant trunk”) used to direct water.
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Design and Installation Specifications
l Plastic slope cover must be installed as follows:
1. Run plastic up and down slope, not across slope.
2. Plastic may be installed perpendicular to a slope if the slope length is less
than 10 feet.
3. Minimum of 8-inch overlap at seams.
4. On long or wide slopes, or slopes subject to wind, tape all seams.
5. Place plastic into a small (12-inch wide by 6-inch deep) slot trench at the top
of the slope and backfill with soil to keep water from flowing underneath.
6. Place sand filled burlap or geotextile bags every 3 to 6 feet along seams and
tie them together with twine to hold them in place.
7. Inspect plastic for rips, tears, and open seams regularly and repair imme-
diately. This prevents high velocity runoff from contacting bare soil which
causes extreme erosion.
8. Sandbags may be lowered into place tied to ropes. However, all sandbags
must be staked in place.
l Plastic sheeting shall have a minimum thickness of 0.06 millimeters.
l If erosion at the toe of a slope is likely, a gravel berm, riprap, or other suitable pro-
tection shall be installed at the toe of the slope in order to reduce the velocity of run-
off.
Maintenance Standards
l Torn sheets must be replaced and open seams repaired.
l Completely remove and replace the plastic if it begins to deteriorate due to ultra-
violet radiation.
l Completely remove plastic when no longer needed.
l Dispose of old tires used to weight down plastic sheeting appropriately.
Approved as Equivalent
Ecology has approved products as able to meet the requirements of BMP C123: Plastic
Covering. The products did not pass through the Technology Assessment Protocol –
Ecology (TAPE) process. Local jurisdictions may choose not to accept this product
approved as equivalent, or may require additional testing prior to consideration for local
use. The products are available for review on Ecology’s website at
http://www.ecy.wa.gov/programs/wq/stormwater/newtech/equivalent.html
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BMP C140: Dust Control
Purpose
Dust control prevents wind transport of dust from disturbed soil surfaces onto roadways,
drainage ways, and surface waters.
Conditions of Use
l In areas (including roadways) subject to surface and air movement of dust where
on-site and off-site impacts to roadways, drainage ways, or surface waters are
likely.
Design and Installation Specifications
l Vegetate or mulch areas that will not receive vehicle traffic. In areas where plant-
ing, mulching, or paving is impractical, apply gravel or landscaping rock.
l Limit dust generation by clearing only those areas where immediate activity will
take place, leaving the remaining area(s) in the original condition. Maintain the ori-
ginal ground cover as long as practical.
l Construct natural or artificial windbreaks or windscreens. These may be designed
as enclosures for small dust sources.
l Sprinkle the site with water until surface is wet. Repeat as needed. To prevent
carryout of mud onto street, refer to BMP C105: Stabilized Construction Entrance /
Exit (p.270).
l Irrigation water can be used for dust control. Irrigation systems should be installed
as a first step on sites where dust control is a concern.
l Spray exposed soil areas with a dust palliative, following the manufacturer’s
instructions and cautions regarding handling and application. Used oil is pro-
hibited from use as a dust suppressant. Local governments may approve other
dust palliatives such as calcium chloride or PAM.
l PAM (BMP C126: Polyacrylamide (PAM) for Soil Erosion Protection (p.300))
added to water at a rate of 0.5 lbs. per 1,000 gallons of water per acre and applied
from a water truck is more effective than water alone. This is due to increased infilt-
ration of water into the soil and reduced evaporation. In addition, small soil
particles are bonded together and are not as easily transported by wind. Adding
PAM may actually reduce the quantity of water needed for dust control. Use of
PAM could be a cost-effective dust control method.
Techniques that can be used for unpaved roads and lots include:
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BMP C150: Materials on Hand
Purpose
Keep quantities of erosion prevention and sediment control materials on the project site
at all times to be used for regular maintenance and emergency situations such as unex-
pected heavy summer rains. Having these materials on-site reduces the time needed to
implement BMPs when inspections indicate that existing BMPs are not meeting the Con-
struction SWPPP requirements. In addition, contractors can save money by buying some
materials in bulk and storing them at their office or yard.
l Lower speed limits. High vehicle speed increases the amount of dust stirred up
from unpaved roads and lots.
l Upgrade the road surface strength by improving particle size, shape, and mineral
types that make up the surface and base materials.
l Add surface gravel to reduce the source of dust emission. Limit the amount of fine
particles (those smaller than .075 mm) to 10 to 20 percent.
l Use geotextile fabrics to increase the strength of new roads or roads undergoing
reconstruction.
l Encourage the use of alternate, paved routes, if available.
l Restrict use of paved roadways by tracked vehicles and heavy trucks to prevent
damage to road surface and base.
l Apply chemical dust suppressants using the admix method, blending the product
with the top few inches of surface material. Suppressants may also be applied as
surface treatments.
l Pave unpaved permanent roads and other trafficked areas.
l Use vacuum street sweepers.
l Remove mud and other dirt promptly so it does not dry and then turn into dust.
l Limit dust-causing work on windy days.
l Contact your local Air Pollution Control Authority for guidance and training on other
dust control measures. Compliance with the local Air Pollution Control Authority
constitutes compliance with this BMP.
Maintenance Standards
Respray area as necessary to keep dust to a minimum.
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BMP C151: Concrete Handling
Purpose
Concrete work can generate process water and slurry that contain fine particles and high
pH, both of which can violate water quality standards in the receiving water. Concrete
spillage or concrete discharge to surface waters of the State is prohibited. Use this BMP
to minimize and eliminate concrete, concrete process water, and concrete slurry from
entering waters of the state.
Conditions of Use
Any time concrete is used, utilize these management practices. Concrete construction
projects include, but are not limited to, the following:
l Curbs
l Sidewalks
l Roads
l Bridges
l Foundations
l Floors
l Runways
Design and Installation Specifications
l Assure that washout of concrete trucks, chutes, pumps, and internals is performed
at an approved off-site location or in designated concrete washout areas. Do not
wash out concrete trucks onto the ground, or into storm drains, open ditches,
streets, or streams. Refer to BMP C154: Concrete Washout Area (p.317) for inform-
ation on concrete washout areas.
l Return unused concrete remaining in the truck and pump to the originating batch
plant for recycling. Do not dump excess concrete on site, except in designated con-
crete washout areas.
l Wash off hand tools including, but not limited to, screeds, shovels, rakes, floats,
and trowels into formed areas only.
l Wash equipment difficult to move, such as concrete pavers in areas that do not dir-
ectly drain to natural or constructed stormwater conveyances.
l Do not allow washdown from areas, such as concrete aggregate driveways, to
drain directly to natural or constructed stormwater conveyances.
l Contain washwater and leftover product in a lined container when no formed areas
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are available. Dispose of contained concrete in a manner that does not violate
ground water or surface water quality standards.
l Always use forms or solid barriers for concrete pours, such as pilings, within 15-
feet of surface waters.
l Refer to BMP C252: High pH Neutralization Using CO2 (p.409) and BMP C253:
pH Control for High pH Water (p.412) for pH adjustment requirements.
l Refer to the Construction Stormwater General Permit for pH monitoring require-
ments if the project involves one of the following activities:
l Significant concrete work (greater than 1,000 cubic yards poured concrete or
recycled concrete used over the life of a project).
l The use of engineered soils amended with (but not limited to) Portland
cement-treated base, cement kiln dust or fly ash.
l Discharging stormwater to segments of water bodies on the 303(d) list (Cat-
egory 5) for high pH.
Maintenance Standards
Check containers for holes in the liner daily during concrete pours and repair the same
day.
BMP C152: Sawcutting and Surfacing Pollution Prevention
Purpose
Sawcutting and surfacing operations generate slurry and process water that contains
fine particles and high pH (concrete cutting), both of which can violate the water quality
standards in the receiving water. Concrete spillage or concrete discharge to surface
waters of the State is prohibited. Use this BMP to minimize and eliminate process water
and slurry created through sawcutting or surfacing from entering waters of the State.
Conditions of Use
Utilize these management practices anytime sawcutting or surfacing operations take
place. Sawcutting and surfacing operations include, but are not limited to, the following:
l Sawing
l Coring
l Grinding
l Roughening
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l Hydro-demolition
l Bridge and road surfacing
Design and Installation Specifications
l Vacuum slurry and cuttings during cutting and surfacing operations.
l Slurry and cuttings shall not remain on permanent concrete or asphalt pavement
overnight.
l Slurry and cuttings shall not drain to any natural or constructed drainage con-
veyance including stormwater systems. This may require temporarily blocking
catch basins.
l Dispose of collected slurry and cuttings in a manner that does not violate ground
water or surface water quality standards.
l Do not allow process water generated during hydro-demolition, surface rough-
ening or similar operations to drain to any natural or constructed drainage con-
veyance including stormwater systems. Dispose process water in a manner that
does not violate ground water or surface water quality standards.
l Handle and dispose cleaning waste material and demolition debris in a manner
that does not cause contamination of water. Dispose of sweeping material from a
pick-up sweeper at an appropriate disposal site.
Maintenance Standards
Continually monitor operations to determine whether slurry, cuttings, or process water
could enter waters of the state. If inspections show that a violation of water quality stand-
ards could occur, stop operations and immediately implement preventive measures such
as berms, barriers, secondary containment, and vacuum trucks.
BMP C153: Material Delivery, Storage and Containment
Purpose
Prevent, reduce, or eliminate the discharge of pollutants to the stormwater system or
watercourses from material delivery and storage. Minimize the storage of hazardous
materials on-site, store materials in a designated area, and install secondary con-
tainment.
Conditions of Use
These procedures are suitable for use at all construction sites with delivery and
storage of the following materials:
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l Petroleum products such as fuel, oil and grease
l Soil stabilizers and binders (e.g., Polyacrylamide)
l Fertilizers, pesticides and herbicides
l Detergents
l Asphalt and concrete compounds
l Hazardous chemicals such as acids, lime, adhesives, paints, solvents, and curing
compounds
l Any other material that may be detrimental if released to the environment
Design and Installation Specifications
The following steps should be taken to minimize risk:
l Temporary storage area should be located away from vehicular traffic, near the con-
struction entrance(s), and away from waterways or storm drains.
l Material Safety Data Sheets (MSDS) should be supplied for all materials stored.
Chemicals should be kept in their original labeled containers.
l Hazardous material storage on-site should be minimized.
l Hazardous materials should be handled as infrequently as possible.
l During the wet weather season (Oct 1 – April 30), consider storing materials in a
covered area.
l Materials should be stored in secondary containments, such as earthen dike, horse
trough, or even a children’s wading pool for non-reactive materials such as deter-
gents, oil, grease, and paints. Small amounts of material may be secondarily con-
tained in “bus boy” trays or concrete mixing trays.
l Do not store chemicals, drums, or bagged materials directly on the ground. Place
these items on a pallet and, when possible, and within secondary containment.
l If drums must be kept uncovered, store them at a slight angle to reduce ponding of
rainwater on the lids to reduce corrosion. Domed plastic covers are inexpensive
and snap to the top of drums, preventing water from collecting.
Material Storage Areas and Secondary Containment Practices:
l Liquids, petroleum products, and substances listed in 40 CFR Parts 110, 117, or
302 shall be stored in approved containers and drums and shall not be overfilled.
Containers and drums shall be stored in temporary secondary containment facil-
ities.
l Temporary secondary containment facilities shall provide for a spill containment
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BMP C154: Concrete Washout Area
Purpose
Prevent or reduce the discharge of pollutants to stormwater from concrete waste by con-
ducting washout off-site, or performing on-site washout in a designated area to prevent
pollutants from entering surface waters or ground water.
Conditions of Use
Concrete washout area best management practices are implemented on construction
projects where:
volume able to contain 10% of the total enclosed container volume of all con-
tainers, or 110% of the capacity of the largest container within its boundary,
whichever is greater.
l Secondary containment facilities shall be impervious to the materials stored
therein for a minimum contact time of 72 hours.
l Secondary containment facilities shall be maintained free of accumulated rain-
water and spills. In the event of spills or leaks, accumulated rainwater and spills
shall be collected and placed into drums. These liquids shall be handled as haz-
ardous waste unless testing determines them to be non-hazardous.
l Sufficient separation should be provided between stored containers to allow for
spill cleanup and emergency response access.
l During the wet weather season (Oct 1 – April 30), each secondary containment
facility shall be covered during non-working days, prior to and during rain events.
l Keep material storage areas clean, organized and equipped with an ample supply
of appropriate spill clean-up material (spill kit).
l The spill kit should include, at a minimum:
o 1-Water Resistant Nylon Bag
o 3-Oil Absorbent Socks 3”x 4’
o 2-Oil Absorbent Socks 3”x 10’
o 12-Oil Absorbent Pads 17”x19”
o 1-Pair Splash Resistant Goggles
o 3-Pair Nitrile Gloves
o 10-Disposable Bags with Ties
o Instructions
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BMP C160: Certified Erosion and Sediment Control Lead
Purpose
The project proponent designates at least one person as the responsible representative
in charge of erosion and sediment control (ESC), and water quality protection. The des-
ignated person shall be the Certified Erosion and Sediment Control Lead (CESCL) who
is responsible for ensuring compliance with all local, state, and federal erosion and sed-
iment control and water quality requirements.
Conditions of Use
A CESCL shall be made available on projects one acre or larger that discharge storm-
water to surface waters of the state. Sites less than one acre may have a person without
CESCL certification conduct inspections; sampling is not required on sites that disturb
less than an acre.
l The CESCL shall:
l Have a current certificate proving attendance in an erosion and sediment con-
trol training course that meets the minimum ESC training and certification
requirements established by Ecology (see details below).
Ecology will maintain a list of ESC training and certification providers at:
http://www.ecy.wa.gov/programs/wq/stormwater/cescl.html
OR
l Be a Certified Professional in Erosion and Sediment Control (CPESC); for
additional information go to: http://www.envirocertintl.org/cpesc/
Specifications
l Certification shall remain valid for three years.
l The CESCL shall have authority to act on behalf of the contractor or developer and
shall be available, or on-call, 24 hours per day throughout the period of con-
struction.
l The Construction SWPPP shall include the name, telephone number, fax number,
and address of the designated CESCL.
l A CESCL may provide inspection and compliance services for multiple con-
struction projects in the same geographic region.
Duties and responsibilities of the CESCL shall include, but are not limited to the fol-
lowing:
2014 Stormwater Management Manual for Western Washington
Volume II - Chapter 4 - Page 326
l Maintaining permit file on site at all times which includes the Construction SWPPP
and any associated permits and plans.
l Directing BMP installation, inspection, maintenance, modification, and removal.
l Updating all project drawings and the Construction SWPPP with changes made.
l Completing any sampling requirements including reporting results using
WebDMR.
l Keeping daily logs, and inspection reports. Inspection reports should include:
l Inspection date/time.
l Weather information; general conditions during inspection and approximate
amount of precipitation since the last inspection.
l A summary or list of all BMPs implemented, including observations of all
erosion/sediment control structures or practices. The following shall be
noted:
1. Locations of BMPs inspected.
2. Locations of BMPs that need maintenance.
3. Locations of BMPs that failed to operate as designed or intended.
4. Locations of where additional or different BMPs are required.
l Visual monitoring results, including a description of discharged stormwater.
The presence of suspended sediment, turbid water, discoloration, and oil
sheen shall be noted, as applicable.
l Any water quality monitoring performed during inspection.
l General comments and notes, including a brief description of any BMP
repairs, maintenance or installations made as a result of the inspection.
l Facilitate, participate in, and take corrective actions resulting from inspections per-
formed by outside agencies or the owner.
BMP C162: Scheduling
Purpose
Sequencing a construction project reduces the amount and duration of soil exposed to
erosion by wind, rain, runoff, and vehicle tracking.
Conditions of Use
The construction sequence schedule is an orderly listing of all major land-disturbing
activities together with the necessary erosion and sedimentation control measures
2014 Stormwater Management Manual for Western Washington
Volume II - Chapter 4 - Page 327
II-4.2 Runoff Conveyance and Treatment BMPs
This section contains the standards and specifications for Runoff Conveyance and Treat-
ment BMPs. Table II-4.2.1 Runoff Conveyance and Treatment BMPs by SWPPP Ele-
ment (p.327), below, shows the relationship of the BMPs in II-4.2 Runoff Conveyance
and Treatment BMPs to the Construction Stormwater Pollution Prevention Plan
(SWPPP) Elements described in II-3.3.3 Step 3 - Construction SWPPP Development
and Implementation (p.236).
Table II-4.2.1 Runoff Conveyance and Treatment BMPs by SWPPP
Element
Ele- Element Ele- Element Ele-
ment #4 Ele- ment #8 Stab- Element ment Element
BMP or Ele- #3 Install ment #7 Pro- ilize #9 Con- #10 #13 Protect
ment Name Con- Sed- #6 Pro- tect Chan- trol Pol- Control Low Impact
trol iment tect Drain nels lutants De- Devel- Flow
Con- Slopes Inlets and Out- Water- opment Rates trols
lets ing
BMP C200:
Interceptor
Dike and ü ü
Swale
(p.331)
planned for the project. This type of schedule guides the contractor on work to be done
before other work is started so that serious erosion and sedimentation problems can be
avoided.
Following a specified work schedule that coordinates the timing of land-disturbing activ-
ities and the installation of control measures is perhaps the most cost-effective way of
controlling erosion during construction. The removal of surface ground cover leaves a
site vulnerable to accelerated erosion. Construction procedures that limit land clearing
provide timely installation of erosion and sedimentation controls, and restore protective
cover quickly can significantly reduce the erosion potential of a site.
Design Considerations
l Minimize construction during rainy periods.
l Schedule projects to disturb only small portions of the site at any one time. Com-
plete grading as soon as possible. Immediately stabilize the disturbed portion
before grading the next portion. Practice staged seeding in order to revegetate cut
and fill slopes as the work progresses.
2014 Stormwater Management Manual for Western Washington
Volume II - Chapter 4 - Page 331
BMP C200: Interceptor Dike and Swale
Purpose
Provide a ridge of compacted soil, or a ridge with an upslope swale, at the top or base of a
disturbed slope or along the perimeter of a disturbed construction area to convey storm-
water. Use the dike and/or swale to intercept the runoff from unprotected areas and direct it to
areas where erosion can be controlled. This can prevent storm runoff from entering the work
area or sediment-laden runoff from leaving the construction site.
Conditions of Use
Where the runoff from an exposed site or disturbed slope must be conveyed to an
erosion control facility which can safely convey the stormwater.
l Locate upslope of a construction site to prevent runoff from entering disturbed area.
l When placed horizontally across a disturbed slope, it reduces the amount and velo- city
of runoff flowing down the slope.
l Locate downslope to collect runoff from a disturbed area and direct water to a sed- iment
basin.
Design and Installation Specifications
l Dike and/or swale and channel must be stabilized with temporary or permanent
vegetation or other channel protection during construction.
l Channel requires a positive grade for drainage; steeper grades require channel
protection and check dams.
l Review construction for areas where overtopping may occur.
l Can be used at top of new fill before vegetation is established.
2014 Stormwater Management Manual for Western Washington
Volume II - Chapter 4 - Page 332
l May be used as a permanent diversion channel to carry the runoff.
l Sub-basin tributary area should be one acre or less.
l Design capacity for the peak volumetric flow rate calculated using a 10-minute time step
from a 10-year, 24-hour storm, assuming a Type 1A rainfall distribution, for temporary
facilities. Alternatively, use 1.6 times the 10-year, 1-hour flow indicated by an approved
continuous runoff model. For facilities that will also serve on a per- manent basis, consult
the local government’s drainage requirements.
Interceptor dikes shall meet the following criteria:
l Top Width: 2 feet minimum.
l Height: 1.5 feet minimum on berm.
l Side Slope: 2H:1V or flatter.
l Grade: Depends on topography, however, dike system minimum is 0.5%, and max-
imum is 1%.
l Compaction: Minimum of 90 percent ASTM D698 standard proctor.
l Horizontal Spacing of Interceptor Dikes:
Average Slope Slope Percent Flowpath Length
20H:1V or less 3-5% 300 feet
(10 to 20)H:1V 5-10% 200 feet
(4 to 10)H:1V 10-25% 100 feet
(2 to 4)H:1V 25-50% 50 feet
l Stabilization: depends on velocity and reach
l Slopes <5%: Seed and mulch applied within 5 days of dike construction (see BMP C121:
Mulching (p.284)).
l Slopes 5 - 40%: Dependent on runoff velocities and dike materials. Stabilization should
be done immediately using either sod or riprap or other measures to avoid erosion.
l The upslope side of the dike shall provide positive drainage to the dike outlet. No
erosion shall occur at the outlet. Provide energy dissipation measures as neces- sary.
Sediment-laden runoff must be released through a sediment trapping facility.
l Minimize construction traffic over temporary dikes. Use temporary cross culverts for
channel crossing.
Interceptor swales shall meet the following criteria:
l Bottom Width: 2 feet minimum; the cross-section bottom shall be level.
l Depth: 1-foot minimum.
2014 Stormwater Management Manual for Western Washington
Volume II - Chapter 4 - Page 333
l Side Slope: 2H:1V or flatter.
l Grade: Maximum 5 percent, with positive drainage to a suitable outlet (such as a
sediment pond).
l Stabilization: Seed as per BMP C120: Temporary and Permanent Seeding (p.278), or
BMP C202: Channel Lining (p.338), 12 inches thick riprap pressed into the bank and
extending at least 8 inches vertical from the bottom.
Inspect diversion dikes and interceptor swales once a week and after every rainfall.
Immediately remove sediment from the flow area.
Damage caused by construction traffic or other activity must be repaired before the end
of each working day.
Check outlets and make timely repairs as needed to avoid gully formation. When the
area below the temporary diversion dike is permanently stabilized, remove the dike
and fill and stabilize the channel to blend with the natural surface.
2014 Stormwater Management Manual for Western Washington
Volume II - Chapter 4 - Page 357
1
BMP C220: Storm Drain Inlet Protection
Purpose
Storm drain inlet protection prevents coarse sediment from entering drainage systems
prior to permanent stabilization of the disturbed area.
Conditions of Use
Use storm drain inlet protection at inlets that are operational before permanent sta-
bilization of the disturbed drainage area. Provide protection for all storm drain inlets
downslope and within 500 feet of a disturbed or construction area, unless conveying run-
off entering catch basins to a sediment pond or trap.
Also consider inlet protection for lawn and yard drains on new home construction. These
small and numerous drains coupled with lack of gutters in new home construction can
add significant amounts of sediment into the roof drain system. If possible delay
installing lawn and yard drains until just before landscaping or cap these drains to pre-
2014 Stormwater Management Manual for Western Washington
Volume II - Chapter 4 - Page 358
vent sediment from entering the system until completion of landscaping. Provide 18-
inches of sod around each finished lawn and yard drain.
Table II-4.2.2 Storm Drain Inlet Protection (p.358) lists several options for inlet protection.
All of the methods for storm drain inlet protection tend to plug and require a high fre-
quency of maintenance. Limit drainage areas to one acre or less. Possibly provide emer-
gency overflows with additional end-of-pipe treatment where stormwater ponding would
cause a hazard.
Table II-4.2.2 Storm Drain Inlet Protection
Type of Inlet
Protection
Emergency
Overflow
Applicable for
Paved/ Earthen
Surfaces
Conditions of Use
Drop Inlet Protection
Excavated drop
inlet protection
Yes, tem-
porary flood-
ing will occur
Earthen
Applicable for heavy flows. Easy
to maintain. Large area Require-
ment: 30'x30'/acre
Block and
gravel drop inlet
protection
Yes
Paved or Earthen Applicable for heavy concentrated
flows. Will not pond.
Gravel and wire
drop inlet pro-
tection
No
Applicable for heavy concentrated
flows. Will pond. Can withstand
traffic.
Catch basin fil-
ters Yes Paved or Earthen Frequent Maintenance required.
Curb Inlet Protection
Curb inlet pro-
tection with
wooden weir
Small capacity
overflow
Paved Used for sturdy, more compact
installation.
Block and
gravel curb inlet
protection
Yes
Paved
Sturdy, but limited filtration.
Culvert Inlet Protection
Culvert inlet Sed
iment trap
- 18 month expected life.
Design and Installation Specifications
Excavated Drop Inlet Protection - An excavated impoundment around the storm drain.
Sediment settles out of the stormwater prior to entering the storm drain.
2014 Stormwater Management Manual for Western Washington
Volume II - Chapter 4 - Page 359
l Provide a depth of 1-2 ft as measured from the crest of the inlet structure.
l Slope sides of excavation no steeper than 2H:1V.
l Minimum volume of excavation 35 cubic yards.
l Shape basin to fit site with longest dimension oriented toward the longest inflow
area.
l Install provisions for draining to prevent standing water problems.
l Clear the area of all debris.
l Grade the approach to the inlet uniformly.
l Drill weep holes into the side of the inlet.
l Protect weep holes with screen wire and washed aggregate.
l Seal weep holes when removing structure and stabilizing area.
l Build a temporary dike, if necessary, to the down slope side of the structure to pre-
vent bypass flow.
Block and Gravel Filter - A barrier formed around the storm drain inlet with standard con-
crete blocks and gravel. See Figure II-4.2.8 Block and Gravel Filter (p.360).
l Provide a height of 1 to 2 feet above inlet.
l Recess the first row 2-inches into the ground for stability.
l Support subsequent courses by placing a 2x4 through the block opening.
l Do not use mortar.
l Lay some blocks in the bottom row on their side for dewatering the pool.
l Place hardware cloth or comparable wire mesh with ½-inch openings over all
block openings.
l Place gravel just below the top of blocks on slopes of 2H:1V or flatter.
l An alternative design is a gravel donut.
l Provide an inlet slope of 3H:1V.
l Provide an outlet slope of 2H:1V.
l Provide a1-foot wide level stone area between the structure and the inlet.
l Use inlet slope stones 3 inches in diameter or larger.
l Use gravel ½- to ¾-inch at a minimum thickness of 1-foot for the outlet slope.
2014 Stormwater Management Manual for Western Washington
Volume II - Chapter 4 - Page 360
Figure II-4.2.8 Block and Gravel Filter
A
Drain grate
s3
4Q n
Og4£jo o Concrete block
S3 ?P>’o
Gravel backfill
o
Cu ^p Oa-
^2Bb nsefii
PY> se Q5->D 0
A
Plan View
Concrete block Wire screen or
filter fabric
Gravel backfill Overflow
water Ponding height
Water —
RSaSS3Sg8^r
Drop inlet
Section A-A
Notes:
1. Drop inlet sediment barriers are to be used for small, nearly level drainage areas. (less
than 5%)
2. Excavate a basin of sufficient size adjacent to the drop inlet.
3. The top of the structure (ponding height) must be well below the ground elevation
downslope to prevent runoff from bypassing the inlet. A temporary dike may be
necessary on the downslope side of the structure.
NOT TO SCALE
D E P A R T M E N T O F
ECOLOGY
State of Washington
Figure II-4.2.8
Block and Gravel Filter
Revised August 2015
Please see http://www.ecy.wa.gov/copyright.html for copyright notice including permissions,
limitation of liability, and disclaimer.
2014 Stormwater Management Manual for Western Washington
Volume II - Chapter 4 - Page 361
Gravel and Wire Mesh Filter - A gravel barrier placed over the top of the inlet. This struc-
ture does not provide an overflow.
l Use a hardware cloth or comparable wire mesh with ½-inch openings.
l Use coarse aggregate.
l Provide a height 1-foot or more, 18-inches wider than inlet on all sides.
l Place wire mesh over the drop inlet so that the wire extends a minimum of 1-foot
beyond each side of the inlet structure.
l Overlap the strips if more than one strip of mesh is necessary.
l Place coarse aggregate over the wire mesh.
l Provide at least a 12-inch depth of gravel over the entire inlet opening and extend
at least 18-inches on all sides.
Catchbasin Filters – Use inserts designed by manufacturers for construction sites. The
limited sediment storage capacity increases the amount of inspection and maintenance
required, which may be daily for heavy sediment loads. To reduce maintenance require-
ments combine a catchbasin filter with another type of inlet protection. This type of inlet
protection provides flow bypass without overflow and therefore may be a better method
for inlets located along active rights-of-way.
l Provides 5 cubic feet of storage.
l Requires dewatering provisions.
l Provides a high-flow bypass that will not clog under normal use at a construction
site.
l Insert the catchbasin filter in the catchbasin just below the grating.
Curb Inlet Protection with Wooden Weir – Barrier formed around a curb inlet with a
wooden frame and gravel.
l Use wire mesh with ½-inch openings.
l Use extra strength filter cloth.
l Construct a frame.
l Attach the wire and filter fabric to the frame.
l Pile coarse washed aggregate against wire/fabric.
l Place weight on frame anchors.
Block and Gravel Curb Inlet Protection – Barrier formed around a curb inlet with concrete
blocks and gravel. See Figure II-4.2.9 Block and Gravel Curb Inlet Protection (p.363).
2014 Stormwater Management Manual for Western Washington
Volume II - Chapter 4 - Page 362
l Use wire mesh with ½-inch openings.
l Place two concrete blocks on their sides abutting the curb at either side of the inlet
opening. These are spacer blocks.
l Place a 2x4 stud through the outer holes of each spacer block to align the front
blocks.
l Place blocks on their sides across the front of the inlet and abutting the spacer
blocks.
l Place wire mesh over the outside vertical face.
l Pile coarse aggregate against the wire to the top of the barrier.
Curb and Gutter Sediment Barrier – Sandbag or rock berm (riprap and aggregate) 3 feet
high and 3 feet wide in a horseshoe shape. See Figure II-4.2.10 Curb and Gutter Barrier
(p.364).
l Construct a horseshoe shaped berm, faced with coarse aggregate if using riprap, 3
feet high and 3 feet wide, at least 2 feet from the inlet.
l Construct a horseshoe shaped sedimentation trap on the outside of the berm sized
to sediment trap standards for protecting a culvert inlet.
Maintenance Standards
l Inspect catch basin filters frequently, especially after storm events. Clean and
replace clogged inserts. For systems with clogged stone filters: pull away the
stones from the inlet and clean or replace. An alternative approach would be to use
the clogged stone as fill and put fresh stone around the inlet.
l Do not wash sediment into storm drains while cleaning. Spread all excavated
material evenly over the surrounding land area or stockpile and stabilize as appro-
priate.
Approved as Equivalent
Ecology has approved products as able to meet the requirements of BMP C220: Storm
Drain Inlet Protection. The products did not pass through the Technology Assessment
Protocol – Ecology (TAPE) process. Local jurisdictions may choose not to accept this
product approved as equivalent, or may require additional testing prior to consideration
for local use. The products are available for review on Ecology’s website at
http://www.ecy.wa.gov/programs/wq/stormwater/newtech/equivalent.html
2014 Stormwater Management Manual for Western Washington
Volume II - Chapter 4 - Page 363
Figure II-4.2.9 Block and Gravel Curb Inlet Protection
A
Catch basin
Back of sidewalk
2x4 Wood stud
Back of curb Curb inlet Concrete block
Wire screen or m
filter fabric /me
3 A Concrete block
4 inch (20 mm)
Drain gravel Plan View
Ponding height
3/4 inch (20 mm)
Drain gravel
a Curb inlet
I<xk Wire screen or
filter fabric 2x4 Wood stud
(100x50 Timber stud) Catch basin
Concrete block &
Section A-A
Notes:
1. Use block and gravel type sediment barrier when curb inlet is located in gently sloping street
segment, where water can pond and allow sediment to separate from runoff.
2. Barrier shall allow for overflow from severe storm event.
3. Inspect barriers and remove sediment after each storm event. Sediment and gravel must be
removed from the traveled way immediately. NOT TO SCALE
D E P A R T M E N T O F
ECOLOGY
State of Washington
Figure II-4.2.9
Block and Gravel Curb Inlet Protection
Revised August 2015
Please see http://www.ecy.wa.gov/copyright.html for copyright notice including permissions,
limitation of liability, and disclaimer.
2014 Stormwater Management Manual for Western Washington
Volume II - Chapter 4 - Page 364
Figure II-4.2.10 Curb and Gutter Barrier
ECOLOGY
Revised September 2015
Please see http://www.ecy.wa.gov/copyright.html for copyright notice including permissions,
limitation of liability, and disclaimer.
Back of sidewalk
Burlap sacks to
overlap onto curb Back of curb
Curb inlet
A
Catch basin
Gravel filled sandbags
stacked tightly
Notes:
Place curb type sediment barriers on gently sloping street segments, where water can
pond and allow sediment to separate from runoff.
Sandbags of either burlap or woven 'geotextile' fabric, are filled with gravel, layered
and packed tightly.
Leave a one sandbag gap in the top row to provide a spillway for overflow.
Inspect barriers and remove sediment after each storm event. Sediment and gravel
must be removed from the traveled way immediately. NOT TO SCALE
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Volume II - Chapter 4 - Page 365
BMP C233: Silt Fence
Purpose
Use of a silt fence reduces the transport of coarse sediment from a construction site
by providing a temporary physical barrier to sediment and reducing the runoff
velocities of overland flow. See Figure II-4.2.12 Silt Fence (p.369) for details on silt
fence con- struction.
Conditions of Use
Silt fence may be used downslope of all disturbed areas.
l Silt fence shall prevent soil carried by runoff water from going beneath, through, or
over the top of the silt fence, but shall allow the water to pass through the fence.
l Silt fence is not intended to treat concentrated flows, nor is it intended to treat sub-
stantial amounts of overland flow. Convey any concentrated flows through the
drainage system to a sediment pond.
l Do not construct silt fences in streams or use in V-shaped ditches. Silt fences do
not provide an adequate method of silt control for anything deeper than sheet or
overland flow.
2014 Stormwater Management Manual for Western Washington
Volume II - Chapter 4 - Page 366
Figure II-4.2.12 Silt Fence
Joints in filter fabric shall be spliced
at posts. Use staples, wire rings or
equivalent to attach fabric to posts
2"x2" by 14 Ga. wire or equivalent,
if standard strength fabric used
rr ri-
Minimum 6' max
4"x4" trench
Post spacing may be increased
to 8' if wire backing is used 2"x2" wood posts, steel
fence posts, or equivalent
2"x2" by 14 Ga. wire or equivalent,
if standard strength fabric used
Filter fabric
2' min
Backfill trench with
native soil or 3 4" - " ; r -
1.5" washed gravel 12" min
Minimum
4"x4" trench
2"x2" wood posts, steel
fence posts, or equivalent NOT TO SCALE
D E P A R T M E N T O F
ECOLOGY
State of Washington
Figure II-4.2.12
Silt Fence
Revised October 2014
Please see http://www.ecy.wa.gov/copyright.html for copyright notice including permissions,
limitation of liability, and disclaimer.
2014 Stormwater Management Manual for Western Washington
Volume II - Chapter 4 - Page 370
Design and Installation Specifications
l Use in combination with sediment basins or other BMPs.
l Maximum slope steepness (normal (perpendicular) to fence line) 1H:1V.
l Maximum sheet or overland flow path length to the fence of 100 feet.
l Do not allow flows greater than 0.5 cfs.
l The geotextile used shall meet the following standards. All geotextile properties lis-
ted below are minimum average roll values (i.e., the test result for any sampled roll
in a lot shall meet or exceed the values shown in Table II-4.2.3 Geotextile Stand-
ards (p.370)):
Table II-4.2.3 Geotextile Standards
Polymeric Mesh AOS
(ASTM D4751)
0.60 mm maximum for slit film woven (#30 sieve).
0.30 mm maximum for all other geotextile types (#50 sieve).
0.15 mm minimum for all fabric types (#100 sieve).
Water Permittivity
(ASTM D4491)
0.02 sec-1 minimum
Grab Tensile Strength
(ASTM D4632)
180 lbs. Minimum for extra strength fabric.
100 lbs minimum for standard strength fabric.
Grab Tensile Strength
(ASTM D4632)
30% maximum
Ultraviolet Resistance
(ASTM D4355)
70% minimum
l Support standard strength fabrics with wire mesh, chicken wire, 2-inch x 2-inch
wire, safety fence, or jute mesh to increase the strength of the fabric. Silt fence
materials are available that have synthetic mesh backing attached.
l Filter fabric material shall contain ultraviolet ray inhibitors and stabilizers to provide
a minimum of six months of expected usable construction life at a temperature
range of 0°F. to 120°F.
l One-hundred percent biodegradable silt fence is available that is strong, long last-
ing, and can be left in place after the project is completed, if permitted by local reg-
ulations.
l Refer to Figure II-4.2.12 Silt Fence (p.369) for standard silt fence details. Include
the following standard Notes for silt fence on construction plans and specifications:
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Volume II - Chapter 4 - Page 371
1. The contractor shall install and maintain temporary silt fences at the locations
shown in the Plans.
2. Construct silt fences in areas of clearing, grading, or drainage prior to starting
those activities.
3. The silt fence shall have a 2-feet min. and a 2½-feet max. height above the
original ground surface.
4. The filter fabric shall be sewn together at the point of manufacture to form fil-
ter fabric lengths as required. Locate all sewn seams at support posts. Altern-
atively, two sections of silt fence can be overlapped, provided the Contractor
can demonstrate, to the satisfaction of the Engineer, that the overlap is long
enough and that the adjacent fence sections are close enough together to
prevent silt laden water from escaping through the fence at the overlap.
5. Attach the filter fabric on the up-slope side of the posts and secure with
staples, wire, or in accordance with the manufacturer's recommendations.
Attach the filter fabric to the posts in a manner that reduces the potential for
tearing.
6. Support the filter fabric with wire or plastic mesh, dependent on the properties
of the geotextile selected for use. If wire or plastic mesh is used, fasten the
mesh securely to the up-slope side of the posts with the filter fabric up-slope
of the mesh.
7. Mesh support, if used, shall consist of steel wire with a maximum mesh spa-
cing of 2-inches, or a prefabricated polymeric mesh. The strength of the wire
or polymeric mesh shall be equivalent to or greater than 180 lbs. grab tensile
strength. The polymeric mesh must be as resistant to the same level of ultra-
violet radiation as the filter fabric it supports.
8. Bury the bottom of the filter fabric 4-inches min. below the ground surface.
Backfill and tamp soil in place over the buried portion of the filter fabric, so
that no flow can pass beneath the fence and scouring cannot occur. When
wire or polymeric back-up support mesh is used, the wire or polymeric mesh
shall extend into the ground 3-inches min.
9. Drive or place the fence posts into the ground 18-inches min. A 12–inch min.
depth is allowed if topsoil or other soft subgrade soil is not present and 18-
inches cannot be reached. Increase fence post min. depths by 6 inches if the
fence is located on slopes of 3H:1V or steeper and the slope is perpendicular
to the fence. If required post depths cannot be obtained, the posts shall be
adequately secured by bracing or guying to prevent overturning of the fence
due to sediment loading.
10. Use wood, steel or equivalent posts. The spacing of the support posts shall
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Volume II - Chapter 4 - Page 372
be a maximum of 6-feet. Posts shall consist of either:
l Wood with dimensions of 2-inches by 2-inches wide min. and a 3-feet
min. length. Wood posts shall be free of defects such as knots, splits, or
gouges.
l No. 6 steel rebar or larger.
l ASTM A 120 steel pipe with a minimum diameter of 1-inch.
l U, T, L, or C shape steel posts with a minimum weight of 1.35 lbs./ft.
l Other steel posts having equivalent strength and bending resistance to
the post sizes listed above.
11. Locate silt fences on contour as much as possible, except at the ends of the
fence, where the fence shall be turned uphill such that the silt fence captures
the runoff water and prevents water from flowing around the end of the fence.
12. If the fence must cross contours, with the exception of the ends of the fence,
place gravel check dams perpendicular to the back of the fence to minimize
concentrated flow and erosion. The slope of the fence line where contours
must be crossed shall not be steeper than 3H:1V.
l Gravel check dams shall be approximately 1-foot deep at the back of
the fence. Gravel check dams shall be continued perpendicular to the
fence at the same elevation until the top of the check dam intercepts the
ground surface behind the fence.
l Gravel check dams shall consist of crushed surfacing base course,
gravel backfill for walls, or shoulder ballast. Gravel check dams shall be
located every 10 feet along the fence where the fence must cross con-
tours.
l Refer to Figure II-4.2.13 Silt Fence Installation by Slicing Method (p.374) for slicing
method details. Silt fence installation using the slicing method specifications:
1. The base of both end posts must be at least 2- to 4-inches above the top of
the filter fabric on the middle posts for ditch checks to drain properly. Use a
hand level or string level, if necessary, to mark base points before install-
ation.
2. Install posts 3- to 4-feet apart in critical retention areas and 6- to 7-feet apart
in standard applications.
3. Install posts 24-inches deep on the downstream side of the silt fence, and as
close as possible to the filter fabric, enabling posts to support the filter fabric
from upstream water pressure.
4. Install posts with the nipples facing away from the filter fabric.
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5. Attach the filter fabric to each post with three ties, all spaced within the top 8-
inches of the filter fabric. Attach each tie diagonally 45 degrees through the fil-
ter fabric, with each puncture at least 1-inch vertically apart. Each tie should
be positioned to hang on a post nipple when tightening to prevent sagging.
6. Wrap approximately 6-inches of fabric around the end posts and secure with
3 ties.
7. No more than 24-inches of a 36-inch filter fabric is allowed above ground
level.
Compact the soil immediately next to the filter fabric with the front wheel of
the tractor, skid steer, or roller exerting at least 60 pounds per square inch.
Compact the upstream side first and then each side twice for a total of four
trips. Check and correct the silt fence installation for any deviation before
compaction. Use a flat-bladed shovel to tuck fabric deeper into the ground if
necessary.
2014 Stormwater Management Manual for Western Washington
Volume II - Chapter 4 - Page 374
Steel support post Figure II-4.2.13 Silt Fence Installation by Slicing Method
POST SPACING: ■ 3 i
Ponding height max. 24"
7' max. on open runs
Attach fabric to 4' max. on pooling areas Top of Fabric
upstream side of post ' / / / / / / Belt T
silt fence 2 to 4 times as fabric above ground i FLOW POST DEPTH: > K top 8"
Drive over each side of As much below ground
\ 1
with device exerting 60
p.s.i. or greater
Diagonal attachment 100% compaction 100% compaction doubles strength
■
Attachment Details:
Ï Gather fabric at posts, if needed.
Ï Utilize three ties per post, all within top 8"
of fabric.
Ï Position each tie diagonally, puncturing
holes vertically a minimum of 1" apart.
Ï Hang each tie on a post nipple and tighten
No more than 24" of a 36" securely. Use cable ties (50 lbs) or soft
fabric is allowed above ground wire.
Roll of silt fence Operation
Post
installed
Fabric after
above compaction ground
D Silt Fence
\
Ji= or V 300mm '^1 200 -
Horizontal chisel point Slicing blade
(76 mm width) (18 mm width)
Completed Installation
Vibratory plow is not acceptable because of horizontal compaction NOT TO SCALE
D E P A R T M E N T O F
ECOLOGY
State of Washington
Figure II-4.2.13
Silt Fence Installation by Slicing Method
Revised November 2015
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limitation of liability, and disclaimer.
2014 Stormwater Management Manual for Western Washington
Volume II - Chapter 4 - Page 375
BMP C234: Vegetated Strip
Purpose
Vegetated strips reduce the transport of coarse sediment from a construction site by
providing a temporary physical barrier to sediment and reducing the runoff velocities of
overland flow.
Conditions of Use
l Vegetated strips may be used downslope of all disturbed areas.
l Vegetated strips are not intended to treat concentrated flows, nor are they intended
to treat substantial amounts of overland flow. Any concentrated flows must be con-
veyed through the drainage system to a sediment pond. The only circumstance in
which overland flow can be treated solely by a strip, rather than by a sediment
pond, is when the following criteria are met (see Table II-4.2.4 Contributing Drain-
age Area for Vegetated Strips (p.375)):
Table II-4.2.4 Contributing Drainage Area for Vegetated Strips
Average Contributing Average Contributing Area Max Contributing area
Area Slope Percent Slope Flowpath Length
1.5H : 1V or flatter 67% or flatter 100 feet
2H : 1V or flatter 50% or flatter 115 feet
4H : 1V or flatter 25% or flatter 150 feet
6H : 1V or flatter 16.7% or flatter 200 feet
10H : 1V or flatter 10% or flatter 250 feet
Maintenance Standards
l Repair any damage immediately.
l Intercept and convey all evident concentrated flows uphill of the silt fence to a sed-
iment pond.
l 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.
l Remove sediment deposits when the deposit reaches approximately one-third the
height of the silt fence, or install a second silt fence.
l Replace filter fabric that has deteriorated due to ultraviolet breakdown.
2014 Stormwater Management Manual for Western Washington
Volume II - Chapter 4 - Page 383
BMP C240: Sediment Trap
Purpose
A sediment trap is a small temporary ponding area with a gravel outlet used to collect
and store sediment from sites cleared and/or graded during construction. Sediment
traps, along with other perimeter controls, shall be installed before any land
disturbance takes place in the drainage area.
Conditions of Use
Prior to leaving a construction site, stormwater runoff must pass through a sediment
pond or trap or other appropriate sediment removal best management practice. Non-
engineered sediment traps may be used on-site prior to an engineered sediment trap
or sediment pond to provide additional sediment removal capacity.
It is intended for use on sites where the tributary drainage area is less than 3 acres,
with no unusual drainage features, and a projected build-out time of six months or
less. The sediment trap is a temporary measure (with a design life of approximately 6
months) and shall be maintained until the site area is permanently protected against
erosion by veget- ation and/or structures.
Sediment traps and ponds are only effective in removing sediment down to about the
medium silt size fraction. Runoff with sediment of finer grades (fine silt and clay) will
pass through untreated, emphasizing the need to control erosion to the maximum
extent first.
Whenever possible, sediment-laden water shall be discharged into on-site, relatively
level, vegetated areas (see BMP C234: Vegetated Strip (p.375)). This is the only way
to effectively remove fine particles from runoff unless chemical treatment or filtration is
used. This can be particularly useful after initial treatment in a sediment trap or pond.
The areas of release must be evaluated on a site-by-site basis in order to determine
appropriate locations for and methods of releasing runoff. Vegetated wetlands shall
not be used for this purpose. Frequently, it may be possible to pump water from the
col- lection point at the downhill end of the site to an upslope vegetated area.
Pumping shall only augment the treatment system, not replace it, because of the
possibility of pump fail- ure or runoff volume in excess of pump capacity.
All projects that are constructing permanent facilities for runoff quantity control
should use the rough-graded or final-graded permanent facilities for traps and ponds.
This includes combined facilities and infiltration facilities. When permanent facilities
are used as temporary sedimentation facilities, the surface area requirement of a
sediment trap or pond must be met. If the surface area requirements are larger than
the surface area of the permanent facility, then the trap or pond shall be enlarged to
comply with the surface
2014 Stormwater Management Manual for Western Washington
Volume II - Chapter 4 - Page 384
area requirement. The permanent 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
BMP C241: Temporary Sediment Pond (p.388)) can be used. If a permanent control
structure is used, it may be advisable to partially restrict the lower orifice with gravel to
increase residence time while still allowing dewatering of the pond. A shut-off valve
may be added to the control structure to allow complete retention of stormwater in
emergency situations. In this case, an emergency overflow weir must be added.
A skimmer may be used for the sediment trap outlet if approved by the Local
Permitting Authority.
Design and Installation Specifications
l See Figure II-4.2.16 Cross Section of Sediment Trap (p.386) and Figure II-4.2.17
Sediment Trap Outlet (p.387) for details.
l If permanent runoff control facilities are part of the project, they should be used for
sediment retention.
l To determine the sediment trap geometry, first calculate the design surface area (SA)
of the trap, measured at the invert of the weir. Use the following equation:
SA = FS(Q2/Vs)
where
Q2 = Design inflow based on the peak discharge from the developed 2-year runoff
event from the contributing drainage area as computed in the hydrologic analysis. The
10-year peak flow shall be used if the project size, expected timing and duration of
construction, or downstream conditions warrant a higher level of protection. If no
hydrologic analysis is required, the Rational Method may be used.
Vs = The settling velocity of the soil particle of interest. The 0.02 mm (medium silt)
particle with an assumed density of 2.65 g/cm3 has been selected as the particle of
interest and has a settling velocity (Vs) of 0.00096 ft/sec.
FS = A safety factor of 2 to account for non-ideal settling.
Therefore, the equation for computing surface area becomes:
SA = 2 x Q2/0.00096
or
2080 square feet per cfs of inflow
2014 Stormwater Management Manual for Western Washington
Volume II - Chapter 4 - Page 385
Note: Even if permanent facilities are used, they must still have a surface area that is at least
as large as that derived from the above formula. If they do not, the pond must be enlarged.
l To aid in determining sediment depth, all sediment traps shall have a staff gauge with a
prominent mark 1-foot above the bottom of the trap.
l Sediment traps may not be feasible on utility projects due to the limited work space or
the short-term nature of the work. Portable tanks may be used in place of sed- iment
traps for utility projects.
Maintenance Standards
l Sediment shall be removed from the trap when it reaches 1-foot in depth.
l Any damage to the pond embankments or slopes shall be repaired.
2014 Stormwater Management Manual for Western Washington
Volume II - Chapter 4 - Page 386
Figure II-4.2.16 Cross Section of Sediment Trap
Surface area determined 4' Min. at top of weir
1' Min. Overflow
1' Min.
1' Min.
3.5' - 5'
1.5' Min. Flat Bottom
3
4" - 1.5"
Washed gravel Discharge to
Note: Trap may be formed by berm or by Geotextile stabilized
conveyance,
partial or complete excavation. 2" - 4" Rock outlet, or level
spreader
Rip Rap
NOT TO SCALE
D E P A R T M E N T O F
ECOLOGY
State of Washington
Figure II-4.2.16
Cross Section of Sediment Trap
Revised November 2015
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limitation of liability, and disclaimer.
2014 Stormwater Management Manual for Western Washington
Volume II - Chapter 4 - Page 387
Figure II-4.2.17 Sediment Trap Outlet
6' Min.
1' Min. depth overflow spillway
Min. 1' depth 2" - 4" rock
Native soil or Min. 1' depth 3 4" - 1.5"
compacted backfill washed gravel
Geotextile
NOT TO SCALE
D E P A R T M E N T O F
ECOLOGY
State of Washington
Figure II-4.2.17
Sediment Trap Outlet
Revised November 2015
Please see http://www.ecy.wa.gov/copyright.html for copyright notice including permissions,
limitation of liability, and disclaimer.