2402-SWPPP
Yelm Short Plat
16418 Middle Road SE, Yelm, WA
Parcel No 64303500505, 64303500501
Nw ¼ of the SE ¼, S19, T17 N, R02E, WM, Thurston County, WA
Construction Stormwater Pollution Prevention
Plan (SWPPP)
February 2025
JKA Civil Engineering Inc.
950 Broadway, Suite 305
Tacoma, WA 98402
Ph: (253) 539-1400
E-mail: jkawills@gmail.com
Yelm Short Plat
Prepared for: ABN CONTRACTORS
PO BOX 7528
Tacoma, WA 98417
(253) 686-2867
Attn: Adam Norbjerg
Adam@abncontractors.com
Prepared by: JKA Civil Engineering Inc.
950 Broadway Suite 305
Tacoma, WA 98402
(253) 539-1400
jkawills@gmail.com
JKA Project No.: 2402
2-4-2025
Project Engineer’s Certification:
I hereby state that this SWPPP Report for Yelm Short Plat has been prepared by me or under
my supervision and meets the minimum standard of care and expertise which is usual and
customary in this community for professional engineers. I understand that the City of Yelm
does not and will not assume liability for the sufficiency, suitability, or performance of drainage
facilities prepared by me.
i
Table of Contents
SWPPP Report Page
SECTION 1 – CONSTRUCTION SWPPP NARRATIVE. . . . . . . .. . . . . . . . . . . . . . .1
SECTION 2 – EROSION AND SEDIMENT CONTROL PLANS . . . . . . . . . . . . . . . . . 18
Appendices
I - Erosion and Sediment Control Plans
II - Best Management Practices
ii
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SWPPP REPORT
(Note: This report has been prepared in accordance with the 2024 Washington State DOE SWMM)
SECTION I – CONSTRUCTION SWPPP NARRATIVE
1. PROJECT DESCRIPTION
The project proponent is applying for residential building permits with related site development,
minor driveway approaches, stormwater improvements, septic tank effluent pump (STEP)
tanks, and public water permitting for the property at 16418 Middle Road SE, Parcel No’s
64303500505, 64303500501. The project will include 23 new single-family residences. Minor
improvements are proposed for Middle Road SE public right-of-way (primarily new ADA curb
ramps, sidewalk, curb and gutter). Onsite improvements include a paved minor local road and
cul-de-sac with cement concrete rolled curb and gutter, sidewalk, closed drainage, stormwater
collection/conveyance/infiltration system and park/open spaces. Existing uninhabitable home,
structures, debris, abandoned vehicles, and equipment will be demolished/removed as part of
site development.
The project is currently served by the City of Yelm. Construction will include domestic and fire
supply water from a new water main extension; the point of connection will be at Middle Rd SE.
All homes shall be served with a water service line and meter.
The goal project will request City of Yelm site development approvals to allow construction of
onsite private site and public improvements as well as minor public improvements along the
Middle Road SE frontage. The proponent will also obtain approvals for public sewer extension
into the site and for public water service.
Proposed Stormwater System - (refer to JKA construction plan “C” sheets.)
Refer to the basin map contained in Appendix III of the SSP report and the C Sheets of the JKA
Construction Plan set.
The storm drainage mitigation objectives for this residential development are to control runoff of
the development area by virtue of:
• All new roof areas will be directed to individual downspout infiltration trenches
located on each lot.
• Rear portion of the existing home and garage roof areas (Lot 2) will have dowspouts
tightlined to a downspout infiltration trench to be installed in the rear of the lot.
• Individual driveways, front yard landscaping areas, roadway pavement and sidewalk
areas will drain to a roadside storm drainage system to convey stormwater to a
bioretention area.
• Curb/gutter and sidewalk road improvements areas along the frontage of Middle Rd
will have drainage collected and conveyed to the onsite bioretention cell.
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• All remaining areas of the site that will be disturbed, but not covered with roof or
other hard surfacing, will have soil amended and/or well-draining topsoil placed to
promote infiltration/evaporation of precipitation on individual lots. The project site is
very flat and with such well draining soils, the rear yard areas will infiltrate and thus
are not counted as contributing to the onsite storm drainage system.
2. Existing Site Conditions
The 4.35-acre site consists of one unoccupied rectangular 3.44 acre parcel and one irregular
shaped 0.91-acre parcel with an existing home and garage. Topography is generally flat with a
general elevation of 343’. Vegetation consists mostly of field grasses on the larger rectangular
parcel and landscaping on the smaller parcel. The project site is bounded by residential
property on all sides.
Current access is off Middle Rd SE via a gravel driveway.
3. ADJACENT AREAS and DRAINAGE
The site and surrounding area is generally level. The site is bound by residential properties to
the east, south, west and north. Middle Rd SE is to the southwest.
There is virtually no potential for offsite surface water tributary to the site other than from the
southwest via a conveyance system to be installed in Middle Road and connected to the site
storm system. The area of Middle Rd tributary to the site is accounted for in the sizing
calculations for the drainage system.
It is the contractor’s and owner’s responsibility to ensure that no silt-laden or other pollutant-
laden runoff leaves the site. This includes a prohibition on tracking any sediment from the
construction site on to Middle Road.
4. CRITICAL AREAS
No critical areas exist on or in the immediate vicinity of the project site.
5. SOILS
The USDA Natural Resource Conservation Service (NRCS) Web Soil Survey indicates that the
site is underlain by Spanaway gravelly sandy loam (110) and Spanaway stony sandy loam
(112) soils. Spanaway soils are derived from volcanic ash over gravelly outwash. These soils
have are generally excessively well drained and are included in hydrologic soils group A.
On February 16, 2024, Bill Parnell, P.E. visited the site and monitored the excavation of
five test pits. He found the soils to be Spanaway series as mapped. Test pits were excavated
to a maximum depth of 144” below existing grade. Grain size analysis was used to determine
design infiltration rates of 20 in/hr.
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6. POTENTIAL EROSION PROBLEM AREAS
There are no known or predicted erosion problem areas on or immediately adjacent to this site.
Appropriate erosion control and construction period BMPs have been selected for this project
and are described herein and depicted on the civil plans.
7. CONSTRUCTION STORMWATER POLLUTION PREVENTION ELEMENTS
Element #1: Mark Clearing Limits –
Clearing limits will be marked in the field by the owner’s surveyor and contractor prior to
beginning land disturbing activities, including clearing and grading, clearly mark all
clearing limits. These limits are generally around the perimeter of the project site as
shown on the construction SWPPP sheet.
These limits shall be clearly marked to prevent damage and offsite impacts. Plastic,
metal, or stake wire fence may be used to mark the clearing limits.
The duff layer, native top soil, and natural vegetation shall be retained in an undisturbed
state to the maximum extent practicable. If it is not practicable to retain the duff layer in
place, it should be stockpiled onsite, covered to prevent erosion, and replaced
immediately upon completion of the ground disturbing activities.
The perimeter of infiltration facility areas shall be enveloped by High Visibility
Plastic or Metal Fencing prior to any clearing/grading operations.
Successful construction starts from the ground up – literally. Care must be taken
to not compact INFILTRATION FACILITY area subgrade during excavation and
construction, as excessive compaction would reduce infiltration. Using backhoes
and positioning the equipment alongside the recharge bed is one technique that
can be used.
Where this is not feasible, excavate using equipment with tracks or over-sized
tires. Narrow rubber tires should be avoided. The infiltration facility area shall
also be protected from other heavy equipment running on the subgrade.
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It is critical to protect the INFILTRATION FACILITY areas during and after
construction from sediment-laden water and construction debris that may clog it.
Temporary stormwater controls need to remain in place until the site is stabilized
so that soil-laden stormwater does not wash onto INFILTRATION FACILITY areas,
clogging surfaces.
• Suggested BMPs
BMP C103: High Visibility Plastic or Metal Fence
Purpose Fencing is intended to: (1) restrict clearing to approved limits; (2)
prevent disturbance of sensitive areas, their buffers, and other areas required to
be left undisturbed; (3) limit construction traffic to designated construction
entrances or roads; and, (4) protect areas where marking with survey tape may
not provide adequate protection.
Conditions of Use To establish clearing limits, plastic or metal fence may be
used:
• At the boundary of sensitive areas, their buffers, and other areas required to be
left uncleared.
• As necessary to control vehicle access to and on the site.
Design and Installation Specifications
• High visibility plastic fence shall be composed of a high-density polyethylene
material and shall be at least four feet in height. Posts for the fencing shall be
steel or wood and placed every 6 feet on center (maximum) or as needed to
ensure rigidity. The fencing shall be fastened to the post every six inches with a
polyethylene tie. On long continuous lengths of fencing, a tension wire or rope
shall be used as a top stringer to prevent sagging between posts. The fence
color shall be high visibility orange. The fence tensile strength shall be 360
lbs./ft. using the ASTM D4595 testing method.
• Metal fences shall be designed and installed according to the manufacturer's
specifications.
• Metal fences shall be at least 3 feet high and must be highly visible.
• Fences shall not be wired or stapled to trees.
Maintenance Standards
• If the fence has been damaged or visibility reduced, it shall be repaired or
replaced immediately and visibility restored.
Element #2: Establish Construction Access –
Construction access will be established pursuant to the erosion control plans. The
construction access will be off the existing approach access at Middle Rd. The
contractor is required to minimize the tracking of sediment from the site to the adjacent
paved surface. Temporary rock construction entrances will be installed pursuant to City
standard plans
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Construction vehicle access and exit shall be limited to routes as described above and
shown on the construction plans.
If sediment is tracked off site, public roads shall be cleaned thoroughly at the end of
each day, or more frequently during wet weather, if necessary to prevent sediment from
entering waters of the state. Contractor shall reference the city-approved traffic control
plan and conditions of City right-of-way permit; said traffic control plan and R/W permit
submittal shall be done by contractor.
Sediment shall be removed from existing roads by shoveling or pickup sweeping and
shall be transported to a controlled sediment disposal area. Street washing will be
allowed only after sediment is removed in this manner.
Street wash wastewater shall be prevented from discharging into systems tributary to
state surface waters.
Suggested BMPs
BMP C105: Stabilized Construction Entrance
Purpose Construction entrances are stabilized to reduce the amount of
sediment transported onto paved roads by vehicles or equipment by constructing
a stabilized pad of quarry spalls at entrances to construction sites.
Conditions of Use Construction entrances shall be stabilized wherever traffic
will be leaving a construction site and traveling on paved roads or other paved
areas within 1,000 feet of the site.
Design and Installation Specifications
• See Construction SWPPP for details.
• A separation geotextile shall be placed under the spalls to prevent fine
sediment from pumping up into the rock pad. The geotextile shall meet the
following standards:
• Fencing (see BMPs C103 and C104) shall be installed as necessary to restrict
traffic to the construction entrance.
• Whenever possible, the entrance shall be constructed on a firm, compacted
subgrade. This can substantially increase the effectiveness of the pad and
reduce the need for maintenance.
Maintenance Standards
• Quarry spalls shall be added if the pad is no longer in accordance with the
specifications.
• If the entrance is not preventing sediment from being tracked onto pavement,
then alternative measures to keep the streets free of sediment shall be used.
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This may include street sweeping, an increase in the dimensions of the entrance,
or the installation of a wheel wash.
• Any sediment that is tracked onto pavement shall be removed by shoveling or
street sweeping. The sediment collected by sweeping shall be removed or
stabilized on site. The pavement shall not be cleaned by washing down the
street, except when sweeping is ineffective and there is a threat to public safety.
If it is necessary to wash the streets, the construction of a small sump shall be
considered.
The sediment would then be washed into the sump where it can be controlled.
• Any quarry spalls that are loosened from the pad, which end up on the roadway
shall be removed immediately.
• If vehicles are entering or exiting the site at points other than the construction
entrance(s), fencing (see BMPs C103 and C104) shall be installed to control
traffic.
• Upon project completion and site stabilization, all construction accesses
intended as permanent access for maintenance shall be permanently stabilized.
The roads shall be swept daily should sediment collect on them.
Element #3: Control Flow Rates –
This project relies on infiltration of precipitation and runoff. Sediment laden water will be
trapped in the bioretention cell during construction. To protect the native soils of the
bioretention cell, it will be excavated down to two feet above the proposed bottom
elevation of gravel under the bioretention cell.
Properties and receiving systems downstream from the site will be protected from
erosion due to increases in the volume, velocity, and peak flow rate of stormwater runoff
from the project site with proper implementation of the approved erosion control design
as indicated on the JKA civil plans.
Element #4: Install Sediment Controls –
Prior to leaving a construction site, stormwater runoff from disturbed areas shall pass
through a sediment removal BMP.
Silt Fence is proposed along the site perimeter in strategic locations to inhibit sediment
from leaving the site via sheetflow as shown on the JKA “temporary erosion control”
plans.
Runoff from fully stabilized areas may be discharged without a sediment removal BMP,
but must meet the flow control performance standard of Element #3. Full stabilization
means concrete or asphalt paving; quarry spalls used as ditch lining; or the use of rolled
erosion products, a bonded fiber matrix product, or vegetative cover in a manner that
will fully prevent soil erosion. The Local Permitting Authority shall inspect and approve
areas fully stabilized by means other than pavement or quarry spalls.
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BMPs intended to trap sediment on site shall be constructed as one of the first steps in
grading. These BMPs shall be functional before other land disturbing activities take
place.
Disturbed areas shall be seeded and mulched according to the timing indicated in
Element #5.
Suggested BMPs:
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.
Conditions of Use Silt fence may be used down slope of all disturbed areas.
• Silt fence is not intended to treat concentrated flows, nor is it intended to treat
substantial amounts of overland flow. Any concentrated flows must be conveyed
through the drainage system to a sediment pond.
The only circumstance in which overland flow can be treated solely by a silt
fence, rather than by a sediment pond, is when the area draining to the fence is
one acre or less and flow rates are less than 0.5 cfs.
• Silt fences should not be constructed in streams or used in V-shaped ditches.
They are not an adequate method of silt control for anything deeper than sheet
or overland flow.
• Standard strength fabrics shall be supported 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.
• 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.
• 100 percent biodegradable silt fence is available that is strong, long lasting, and
can be left in place after the project is completed, if permitted by local
regulations.
Maintenance Standards
• 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.
• It is important to check the uphill side of the fence for signs of the fence
clogging and acting as a barrier to flow and then causing channelization of flows
parallel to the fence. If this occurs, replace the fence or remove the trapped
sediment.
• Sediment deposits shall either 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.
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Alternate sediment control BMPs are included in SWPPP Appendix “II“ as a
reference for the onsite inspector in the event the BMP(s) listed above are
deemed ineffective or inappropriate during construction. To avoid potential
erosion and sediment control issues, the project inspector will promptly initiate
the implementation of one or more of the alternative BMPs after the first sign that
existing BMPs are ineffective or failing.
The alternative BMP’s are: BMP C232: Gravel Filter Berm, BMP C235: Straw Wattles
Element #5: Stabilize Soils –
Due to the low topographic relief on-site, temporary stabilizing of soils will be
accomplished primarily by straw and/or mulch. The contractor shall minimize
disturbance of duff and native topsoil areas. Before reseeding any disturbed soil area for
permanent lawn and/or landscaping, contractor shall amend soils with compost
wherever topsoil has been removed.
All exposed and unworked soils shall be stabilized by application of effective BMPs that
protect the soil from the erosive forces of raindrop impact, flowing water, and wind.
From October 1 through April 30, no soils shall remain exposed and unworked for more
than 2 days. From May 1 to September 30, no soils shall remain exposed and unworked
for more than 7 days. This condition applies to all soils on site, whether at final grade or
not.
Soils shall be stabilized at the end of the shift before a holiday or weekend if needed
based on the weather forecast.
Applicable practices include, but are not limited to, temporary and permanent seeding,
sodding, mulching, plastic covering, erosion control fabrics and matting, soil application
of polyacrylamide (PAM), the early application of gravel base on areas to be paved, and
dust control.
Soil stabilization measures should be appropriate for the time of year, site conditions,
estimated duration of use, and potential water quality impacts that stabilization agents
may have on downstream waters or ground water.
Soil stockpiles must be stabilized from erosion, protected with sediment trapping
measures, and when possible, be located away from storm drain inlets, waterways and
drainage channels.
Linear construction activities, including right-of-way and easement clearing, roadway
development, pipelines, and trenching for utilities, shall be conducted to meet the soil
stabilization requirement.
Contractors shall install the bedding materials, roadbeds, structures, pipelines, or
utilities and re-stabilize the disturbed soils so that:
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− from October 1 through April 30 no soils shall remain exposed and unworked for more
than 2 days and
− from May 1 to September 30, no soils shall remain exposed and unworked for more
than 7 days.
• Suggested BMPs
BMP C120: Temporary and Permanent Seeding
BMP C121: Mulching
BMP C123: Plastic Covering
Alternate sediment control BMPs are included in SWPPP Appendix “II“as a reference for
the onsite inspector in the event the BMP(s) listed above are deemed ineffective or
inappropriate during construction. To avoid potential erosion and sediment control
issues, the project inspector will promptly initiate the implementation of one or more of
the alternative BMPs after the first sign that existing BMPs are ineffective or failing.
The alternative BMP’s are: BMP C122: Nets and Blankets, BMP C124: Sodding, BMP
C125: Topsoiling, BMP C126: Polyacrylamide for Soil Erosion Protection, BMP C140:
Dust Control, BMP C180: Small Project Construction Stormwater Pollution Prevention
Element #6: Protect Slopes –
Due to the low topographic relief of the site, temporary stabilizing of soils will be limited
to straw and/or mulch. There are no plans for cut or fill slopes exceeding 2:1.
Element #7: Protect Drain Inlets –
All new and existing catch basins will be protected from sediment by installation of
Storm Drain Inlet Protection per the City Standards as shown on the construction plans.
All storm drain inlets made operable during construction shall be protected so that
stormwater runoff does not enter the conveyance system without first being filtered or
treated to remove sediment.
All approach roads shall be kept clean. Sediment and street wash water shall not be
allowed to enter storm drains without prior and adequate treatment unless treatment is
provided before the storm drain discharges to waters of the state.
Inlets should be inspected weekly at a minimum and daily during storm events. Inlet
protection devices should be cleaned or removed and replaced when sediment has filled
one-third of the available storage (unless a different standard is specified by the product
manufacturer).
• Suggested BMPs
BMP C220: Storm Drain Inlet Protection
Purpose
To prevent coarse sediment from entering drainage systems prior to permanent
stabilization of the disturbed area.
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Conditions of Use Where storm drain inlets are to be made operational before
permanent stabilization of the disturbed drainage area. Protection should be
provided for all storm drain inlets downslope and within 500 feet of a disturbed or
construction area, unless the runoff that enters the catch basin will be conveyed
to a sediment pond or trap. Inlet protection may be used anywhere to protect the
drainage system. It is likely that the drainage system will still require cleaning.
Block and Gravel Filter - A barrier formed around the storm drain inlet with
standard concrete blocks and gravel.
• Height 1 to 2 feet above inlet.
• Recess the first row 2 inches into the ground for stability.
• Support subsequent courses by placing a 2x4 through the block opening.
• Do not use mortar.
• Lay some blocks in the bottom row on their side for dewatering the pool.
• Place hardware cloth or comparable wire mesh with ½-inch openings over all
block openings.
• Place gravel just below the top of blocks on slopes of 2:1 or flatter.
• An alternative design is a gravel donut.
• Inlet slope of 3:1.
• Outlet slope of 2:1.
• 1-foot wide level stone area between the structure and the inlet.
• Inlet slope stones 3 inches in diameter or larger.
• Outlet slope use gravel ½- to ¾-inch at a minimum thickness of 1-foot.
Maintenance Standards
• Catch basin filters should be inspected frequently, especially after storm
events. If the insert becomes clogged, it should be cleaned or replaced.
• For systems using stone filters: If the stone filter becomes clogged with
sediment, the stones must be pulled away from the inlet and cleaned or
replaced. Since cleaning of gravel at a construction site may be difficult, an
alternative approach would be to use the clogged stone as fill and put fresh
stone around the inlet.
• Do not wash sediment into storm drains while cleaning. Spread all excavated
material evenly over the surrounding land area or stockpile and stabilize as
appropriate.
Element #8: Stabilize Channels and Outlets –
Not applicable to this project. Channels will not be created. Most construction-period
stormwater will be controlled by filter fabric fencing and the detention pond (with
restricted outlet standpipe/orifices).
Element #9: Control Pollutants –
Project plans and this SWPPP include instructions to the contractor regarding control of
construction period pollutants such as heavy equipment and vehicle oil, hydraulic
system fluids, etc. The contractor is required to control such pollutants during
construction with the use of drip pans, proper vehicle maintenance, and other normal
operational methods.
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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 on site.
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). On-site 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.
Wheel wash or tire bath wastewater shall be discharged to the sanitary sewer (with prior
County approval).
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.
• Suggested BMPs
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. This BMP is intended to minimize and eliminate concrete
process water and slurry from entering waters of the state.
Conditions of Use Any time concrete is used, these management practices
shall be utilized.
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Design and Installation Specifications
• Concrete truck chutes, pumps, and internals shall be washed out only into
formed areas awaiting installation of concrete or asphalt.
• Unused concrete remaining in the truck and pump shall be returned to the
originating batch plant for recycling.
• Hand tools including, but not limited to, screeds, shovels, rakes, floats, and
trowels shall be washed off only into formed areas awaiting installation of
concrete or asphalt.
• Equipment that cannot be easily moved, such as concrete pavers, shall only be
washed in areas that do not directly drain to natural or constructed stormwater
conveyances.
• Washdown from areas such as concrete aggregate driveways shall not drain
directly to natural or constructed stormwater conveyances.
• When no formed areas are available, washwater and leftover product shall be
contained in a lined container. Contained concrete shall be disposed of in a
manner that does not violate groundwater or surface water quality standards.
Maintenance
Standards
Containers shall be checked for holes in the liner daily during concrete pours and
repaired the same day.
If the BMP options listed are deemed ineffective or inappropriate during
construction to satisfy the requirements set forth in the County permit, or if no
BMPs are listed above but deemed necessary during construction, the project
contractor shall implement one or more of alternative BMP’s listed in SWPPP
Appendix “II”.
Alternate BMP: C106 Wheel Wash
Element #10: Control Dewatering –
Dewatering of groundwater during trenching operations is not likely due to shallow
trenching and construction during late spring and summer.
If dewatering is necessary, clean, non-turbid de-watering water, such as well-point
groundwater, can be discharged to systems tributary to state surface waters, as
specified in Element #8, provided the de-watering flow does not cause erosion or
flooding of receiving waters.
These clean waters should not be routed through stormwater sediment controls.
Highly turbid or contaminated dewatering water from construction equipment operation,
clamshell digging, concrete tremie pour, or work inside a cofferdam, shall be handled
separately from stormwater.
Other disposal options, depending on site constraints, may include:
• Transport offsite in a vehicle, such as a vacuum flush truck, for legal disposal in
a manner that does not pollute state waters
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• Ecology-approved on-site chemical treatment or other suitable treatment
technologies
• Sanitary sewer discharge with Public Works source control approval, if there is
no other option
Element #11: Maintain BMPs –
All temporary and permanent erosion and sediment control BMPs shall be maintained
and repaired as needed to assure continued performance of their intended function.
Maintenance and repair shall be conducted in accordance with each particular BMP's
specifications.
Visual monitoring of the BMPs will be conducted at least once every calendar week and
within 24 hours of any rainfall event that causes a discharge from the site. If the site
becomes inactive, and is temporarily stabilized, the inspection frequency will be reduced
to once every month.
Maintenance and monitoring is the responsibility of the site general contractor.
All temporary erosion and sediment control BMPs shall be removed within 30 days after
the final site stabilization is achieved or after the temporary BMPs are no longer needed.
Trapped sediment shall be removed or stabilized on site. Disturbed soil resulting from
removal of BMPs or vegetation shall be permanently stabilized.
The contractor may elect to use other methods in addition to the BMPs that are dictated
(Silt Fence, Inlet Protection, and Amended Soils).
Element #12: Manage the Project –
The contractor is instructed to phase activities in order to prevent soil erosion and, to the
maximum extent practicable, the transport of sediment from the site during construction.
Clearing and grading activities will be permitted only per the approved construction
plans. All wetland buffers will be marked to ensure they are not disturbed by
construction activities.
Seasonal Work Limitations
From October 1 through April 30, clearing, grading, and other soil disturbing activities
shall only be permitted if shown to the satisfaction of the local permitting authority that
silt-laden runoff will be prevented from leaving the site through a combination of the
following:
1. Site conditions including existing vegetative coverage, slope, soil type, and proximity
to receiving waters; and
2. Limitations on activities and the extent of disturbed areas; and
3. Proposed erosion and sediment control measures.
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Based on the information provided and/or local weather conditions, the local permitting
authority may expand or restrict the seasonal limitation on site disturbance. The local
permitting authority shall take enforcement action - such as a notice of violation,
administrative order, penalty, or stop-work order under the following circumstances:
• If, during the course of any construction activity or soil disturbance during the
seasonal limitation period, sediment leaves the construction site causing a
violation of the surface water quality standard; or
• If clearing and grading limits or erosion and sediment control measures shown in
the approved plan are not maintained.
The following activities are exempt from the seasonal clearing and grading limitations:
1. Routine maintenance and necessary repair of erosion and sediment control BMPs;
2. Routine maintenance of public facilities or existing utility structures that do not expose
the soil or result in the removal of the vegetative cover to soil; and
3. Activities where there is one hundred percent infiltration of surface water runoff within
the site in approved and installed erosion and sediment control facilities.
Inspection and Monitoring
All BMPs shall be inspected, maintained, and repaired as needed to assure continued
performance of their intended function. Site inspections shall be conducted by a person
who is knowledgeable in the principles and practices of erosion and sediment control.
The person must have the skills to 1) assess the site conditions and construction
activities that could impact the quality of stormwater, and 2) assess the effectiveness of
erosion and sediment control measures used to control the quality of stormwater
discharges.
This project does require a CESL (Certified Erosion and Sediment Control Specialist)
because the project exceeds the 1 AC threshold set for construction sites [one acre or
larger that discharge stormwater to surface waters of the state]. The owner
understands that the CESCL must be selected and his contact information submitted to
the County prior to issuance of construction permits.
Whenever inspection and/or monitoring reveals that the BMPs identified in the
Construction SWPPP are inadequate, due to the actual discharge of or potential to
discharge a significant amount of any pollutant, appropriate BMPs or design changes
shall be implemented as soon as possible.
The Construction SWPPP shall be retained on-site or within reasonable access to the
site. The SWPPP shall be modified if, during inspections or investigations conducted by
the engineer, owner/operator, or the applicable local or state regulatory authority, it is
determined that the SWPPP is ineffective in eliminating or significantly minimizing
pollutants in stormwater discharges from the site. The SWPPP shall be modified as
necessary to include additional or modified BMPs designed to correct problems
identified. Revisions to the SWPPP shall be completed within seven (7) days following
the inspection.
Yelm Short Plat - SWPPP
JKA Civil Engineering Page 15
February 2025
Element #13: Protect Permanent Stormwater BMPs -
Restore the BMPs to their fully functioning condition if they accumulate sediment during
construction. Restoring the BMP must include removal of sediment from bioretention
cell, piping, catch basin sumps, and areas of amendment for lawns and landscaping.
Protect completed lawn and landscaped areas from compaction due to construction
equipment by using construction notes on the plans warning contractor against running
construction equipment on said areas. Control erosion and avoid introducing sediment
from surrounding land uses onto paved areas. Do not allow muddy construction
equipment on the base material or pavement. Do not allow sediment-laden runoff onto
permeable pavements.
See notes on JKA construction plans.
8. CONSTRUCTION PHASING
Project design includes site grading and erosion control measures to contain silt and soil within
the project boundaries during construction until permanent erosion control is in place in the
form of landscaping, hydroseeding, and hard surfaces. Erosion/sediment control shall be
achieved by a combination of structural and vegetation cover measures and construction
practices tailored to fit the site. Best management practices (BMPs) will be employed to
properly clear and grade the site and to schedule construction activities. Before any
construction begins on-site, appropriate erosion control shall first be installed. The planned
construction sequence is presented on JKA construction plans.
9. CONSTRUCTION SCHEDULE
The owner intends to commence site work as early as possible, early summer 2025 and
complete project by end of 2025.
10. FINANCIAL/OWNERSHIP RESPONSIBILITIES
The property owner will be responsible for ensuring proper erosion and sediment control; owner
will also be responsible for financial guarantees, either by bond or Assignment of Funds.
A right of entry form can be signed by the property owner to give right to the City to enter onto
the property.
A reclamation guarantee can be provided by the owner to the city to ensure that adequate
erosion control measures are employed during the course of construction and that permanent
stabilization is achieved at the conclusion of significant activity.
11. ENGINEERING CALCULATIONS
Engineering calculations associated with the stormwater flow control design have been
prepared by JKA and are included in the SSP report.
Yelm Short Plat - SWPPP
JKA Civil Engineering Page 16
February 2025
SECTION 2 – EROSION AND SEDIMENT CONTROL PLANS
GENERAL
A vicinity map for the project site is depicted on Sheet C1 of the civil plans. Erosion and
sediment control notes are depicted on the civil plans.
SITE PLAN
Refer to the civil plan sheets for plan view and details on the project.
CONVEYANCE SYSTEMS
Refer to Civil Plan Sheets for information regarding erosion and stormwater BMPs, existing and
finish grades, clearing limits, etc.
EROSION AND SEDIMENT CONTROL FACILITIES
Refer to civil plans for detailed discussion and specifications for all erosion and sediment
control facilities.
The on-site soils belong primarily to the Spanaway series. The soils have a potential for
erosion. Filtered fabric fencing shall be installed as needed to control erosion. The construction
documents depict the location and provide details for said silt fencing. If silt build-up exceeds 4”
in depth behind the fence, then silt shall be removed down to the original grade. When site
construction is stabilized and no longer subject to erosion, the contractor shall remove the filter
fabric fencing and hydroseed any disturbed area in the location of the fence. The contractor
shall recycle fencing materials.
A stabilized construction entrance will be installed to prevent vehicles from tracking soil from the
site to the adjacent paved roadway of Middle Rd. If sediment is tracked off-site, sediment shall
be swept or shoveled from the public roadway on a daily basis. Washing down pavement is not
allowed to remove sediment.
INSPECTION SEQUENCE
In addition to City inspections for grading and erosion control, the contractor must notify the
engineer (JKA) to observe facilities related to clearing, grading, and drainage improvements. At
a minimum, the following items should be observed at the time specified:
1. Erosion control measures installed by the contractor and inspected by the City before
the start of clearing and grading:
a. Construction Entrance
b. Filter fabric fencing
c. Clearing limit delineation/demarcation with fencing
d. Construction of bioretention cell to serve as temporary sediment trap.
Bioretention cell will not be completed and excavated down below the bottom cell
surface until sediment laden water ceases.
2. The contractor must notify the project engineer (JKA) to observe construction of project
drainage facilities to ensure the following are in working order:
a. Inlet protection devices.
Yelm Short Plat - SWPPP
JKA Civil Engineering Page 17
February 2025
b. Temporary sediment trap
c. Bioretention cell.
It is the responsibility of the contractor to inform the engineer (JKA) of the timing of the
above construction phases. A final site visit will be performed to verify grades, drainage
construction, and all of the necessary information to complete a project engineer’s final
certification. The owner is responsible for advising the contractor of his responsibility to
notify the engineer regarding construction progress and inspection timing.
CONTROLLED POLLUTANTS OTHER THAN SEDIMENTS
Wash out from concrete trucks shall not be dumped onsite. Excess concrete and any washout
water shall be returned to the concrete plant.
DETAILED DRAWINGS
Details for BMPs and improvements are illustrated on civil plan sheets.
CERTIFIED EROSION CONTROL SPECIALIST
A CESCL will be required for this > 1 AC project; CESCL must be registered in the State of
Washington.
Appendix I
Erosion and Sediment Control Plans
YELM PLAT — CIVIL PLANS
A PORTION OF THE NW 1 /4 OF THE SE 1 /4 OF SECTION 19, TOWNSHIP 17 NORTH, RANGE 02 E, W.M.,
CITY OF YELM, THURSTON COUNTY, WASHINGTON
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ACCESS & UTILITY EASEMENT
TO BE RELINQUISHED UPON
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FOR FUTURE DEVELOPMENT.
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CONSTRUCTION LEGEND
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ENTRANCE 100' LONG X 15' WIDE. C5.0
X X FF INSTALL TEMPORARY FILTER FABRIC FENCE
2
AS SHOWN HEREON C5.0
CLEARING LIMITS (LIMIT DEPICTED IS
CL APPROX AREA TO BE CLEARED FOR
HOME/DRIVEWAY/UTILITIES CONSTRUCTION
AND YARD/LANDSCAPING) 4.4 ACRES)
DESIGNATED CONCRETE TRUCK WASHOUT
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INSTALL CATCH BASIN INLET PROTECTION
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AS REQUIRED - 10Y (FT) MIN-, EXCEPT
MAY BE REDUCED TO 50' (FT) MIN FOR
SITES WITH LESS THAN ONE ACRE
OF EXPOSED SOIL
000
tac
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1' (FT.) MIN.
DEPTH (TYP,)
PLACE CONSTRUCTION OEOTEXTILE FOR SOIL
STABILIZATION FROM THE EDGE OF THE EXISTING
ROADWAY TO THE CONSTRUCTION ENTRANCE,
OR AS DIRECTED BY THE ENGINEER
YELM PLAT - CIVIL PLANS
A PORTION OF THE NW 1 /4 OF THE SE 1 /4 OF SECTION 19, TOWNSHIP 17 NORTH, RANGE 02 E, W.M.,
CITY OF YELM, THURSTON COUNTY, WASHINGTON
POST - SEE am.
SPEC. i-01AVA
f f / 30' MIN. 9VP-) FASTEN GIEOTE7XTILE TO
- / POST EVERY V' (IN) ID.0
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PERMEABLE BALLAST (TYP.) SEE
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�•�`` SECTION 9 03,9(2) Et ��'' - 1200 MIN. TENSILE STRENGTH. UV STABILIZED
PROVIDE FULL VVICTH OF
INGRESS ! EGRESS AREA
19 (FT} MINIMUM
ISOMETRIC VIEW
STABILIZED CONSTRUCTION ENTRANCE
STABILIZED CONSTRLICTIOIN ENTRANCE SHALL M=ET THE REQUIREMENTS
OF STANDARD SPECIFICATION SECTION S-D1.3(7).
STATE OF
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MISCELLANEOUS
EROSION CONTROL DETAILS
STANDARD PLAN 1-80.10-02
SHEET 1 OF 1 SHEET
APPROVED FOR PUBLICATION
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STABILIZED CONSTRUCTION ENTRANCE
NTS
NOTES:
1. FILTER SHALL BE REMOVED AND CLEANED
OR REPLACED AFTER EACH STORM EVENT.
GOETEXTILE FABRIC
1yAl011iEi0-�M1,1
SEDIMENT ACCUMULATION
RETRIEVAL STRAPS
ADAPTER SKIRT
OVERFLOW (TO BYPASS
PEAK STORM VOLUMES)
#3003 SEDIMENT ONLY
PROVIDE CATCH BASIN SEDIMENT
PROTECTION WITH STREAMGUARD
BASIN INSERT #3003
MAINTENANCE STANDARDS:
1. ANY ACCUMULATED SEDIMENT ON OR AROUND THE FILTER FABRIC PROTECTION SHALL BE REMOVED
IMMEDIATELY. SEDIMENT SHALL NOT BE REMOVED WITH WATER AND ALL SEDIMENT MUST BE
DISPOSED OF AS FILL ON —SITE OR HAULED OFF —SITE.
2. ANY SEDIMENT IN THE CATCH BASIN INSERT MUST BE REMOVED WITH THE SEDIMENT HAS FILLED
ONE—THIRD OF THE AVAILABLE STORAGE. THE FILTER MEDIA FOR THE INSERT SHALL BE CLEANED
OR REPLACED AT LEAST MONTHLY.
3. REGULAR MAINTENANCE IS CRITICAL FOR BOTH FORMS OF THE CATCH BASIN PROTECTION. UNLIKE
MANY FORMS OF PROTECTION THAT FAIL GRADUALLY. CATCH BASIN PROTECTION WILL FAIL
SUDDENLY AND COMPLETELY IF NOT MAINTAINED PROPERLY.
INLET PROTECTION
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NOTE
DURING EXCAVATION, MINIMIZE d1STURBING T}IE GROUND
AROUND TRENCH AS MUCH AS is FEASIBLE- ANU SMOOTH rr
SURFACE FOLLOWING EXCAVATION 70 AVOID CONCf NT-
RATING FLOWS. COMPACTION MUST BE ADEQUATE TO�� f`
PREVENT UNDERCUTTING FLOWS
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TYPICAL INSTALLATION DETAIL frrF'rr•`rP
(STEEL POSTS SHOWN)
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TYPICAL SILT FENCE
SEE NOTE 1 -' WYITHOUT BACKUP SUPPORT
ISOMETRIC
ISTEEL POSTS SHGWM
NOTES
1 Install the ends of the silt fence to polni slightly upslope to prevent
sediment from flowing around the ends of the fence
2. Perform maintenance in accordance with Standard Specifications
B-01.3(9)A and 8-01.3 i5j.
3. Splices shall never be placed in low spots or Sump locations. If
splices are located in low or sump areas, the fence may need to be
reinstalled unless the Project Engineer approves the Installativfi
4. Install sit fencing parallel to mapped contour limes
r' SEE NOTE 1
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SPECIFICATION SECTION
9-33.2 (1), TABLE 6
SILT FENCE
NTS
POST
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(T1rPICALI
FASTEN TG POST
EVERY 6' O C
FABRIC (GEOTEXTILE)
(TYPICAL)
SPLICED FFNCG SCCTIONS SHALL BE CLOSE ENOUGH
TOGETHER TO PREVENT SILT LADEN WATER FROM
ESCAPING THROUGH THE FENCE AT THE OVERLAID
SPLICE DETAIL
fVV000 POSTS SmoomH
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Appendix II
Best Management Practices
BMP C103: High -Visibility Fence
Purpose
High -visibility fencing is intended to:
• Restrict clearing to approved limits.
• Prevent disturbance of sensitive areas, their buffers, and other areas required to be left
undisturbed.
• Limit construction traffic to designated construction entrances, exits, or internal roads.
• Protect areas where marking with survey tape may not provide adequate protection.
2024 Stormwater Management Manual for Western Washington
Volume 11 - Chapter 4 - Page 315
Conditions of Use
To establish clearing limits, plastic, fabric, or metal fence may be used:
• At the boundary of sensitive areas, their buffers, and other areas required to be left
uncleared.
• As necessary to control vehicle access to and on the site.
Design and Installation Specifications
High -visibility plastic fence shall be composed of a high -density polyethylene (HDPE) material
and shall be at least four feet in height. Posts for the fencing shall be steel or wood and placed
every 6 feet on center (maximum) or as needed to ensure rigidity. The fencing shall be fastened to
the post every six inches with a polyethylene tie. On long continuous lengths of fencing, a tension
wire or rope shall be used as a top stringer to prevent sagging between posts. The fence color
shall be high -visibility orange. The fence tensile strength shall be 360 Ibs/ft using the ASTM
D4595 testing method.
If appropriate, install fabric silt fence in accordance with BMP C233: Silt Fence to act as high -vis-
ibility fence. Silt fence shall be at least 3 feet high and must be highly visible to meet the require-
ments of this BMP.
Metal fences shall be designed and installed according to the manufacturer's specifications.
Metal fences shall be at least 3 feet high and must be highly visible.
Fences shall not be wired or stapled to trees.
Maintenance Standards
If the fence has been damaged or visibility reduced, it shall be repaired or replaced immediately
and visibility restored.
BMP C105: Stabilized Construction Access
Purpose
Stabilized construction accesses are established to reduce the amount of sediment transported
onto paved roads outside the project site by vehicles or equipment. This is done by constructing a
stabilized pad of quarry spalls at entrances and exits for project sites.
Conditions of Use
Construction accesses shall be stabilized wherever traffic will be entering or leaving a con-
struction site if paved roads or other paved areas are within 1,000 feet of the site.
For residential subdivision construction sites, provide a stabilized construction access for each
residence, rather than only at the main subdivision entrance. Stabilized surfaces shall be of suf-
ficient length/width to provide vehicle access/parking, based on lot size and configuration.
2024 Stormwater Management Manual for Western Washington
Volume 11 - Chapter 4 - Page 316
On large commercial, highway, and road projects, the designer should include enough extra
materials in the contract to allow for additional stabilized accesses not shown in the initial Con-
struction SWPPP. It is difficult to determine exactly where access to these projects will take place;
additional materials will enable the contractor to install them where needed.
Design and Installation Specifications
• See Figure 11-4.1: Stabilized Construction Access for details. Note: the 100' minimum length
of the access shall be reduced to the maximum practicable size when the size or con-
figuration of the site does not allow the full length (100').
Construct stabilized construction accesses with a 12-inch thick pad of 4-inch to 8-inch
quarry spalls, a 4-inch course of asphalt treated base (ATB), or use existing pavement. Do
not use crushed concrete, cement, or calcium chloride for construction access stabilization
because these products raise pH levels in stormwater and concrete discharge to waters of
the State is prohibited.
A separation geotextile shall be placed under the spalls to prevent fine sediment from pump-
ing up into the rock pad. The geotextile shall meet the standards listed in Table 11-4.2: Stab-
ilized Construction Access Geotextile Standards.
Table II-4.2: Stabilized Construction Access Geotextile
Standards
Geotextile Property
Required Value
Grab Tensile Strength (ASTM D4751)
200 psi min.
Grab Tensile Elongation (ASTM D4632)
30% max.
Mullen Burst Strength (ASTM D3786-80a)
400 psi min.
AOS (ASTM D4751)
No. 20 to No. 45 (U.S. standard sieve size)
• Consider early installation of the first lift of asphalt in areas that will be paved; this can be
used as a stabilized access. Also consider the installation of excess concrete as a sta-
bilized access. During large concrete pours, excess concrete is often available for this pur-
pose.
• Fencing (see BMP C103: High -Visibility Fence) shall be installed as necessary to restrict
traffic to the construction access.
• Whenever possible, the access shall be constructed on a firm, compacted subgrade. This
can substantially increase the effectiveness of the pad and reduce the need for main-
tenance.
• Construction accesses should avoid crossing existing sidewalks and back of walk drains if
at all possible. If a construction access must cross a sidewalk or back of walk drain, the full
length of the sidewalk and back of walk drain must be covered and protected from sediment
leaving the site.
Alternative Material Specification
2024 Stormwater Management Manual for Western Washington
Volume 11 - Chapter 4 - Page 317
WSDOT has raised safety concerns about the quarry spall rock specified above. WSDOT
observes that the 4-inch to 8-inch rock sizes can become trapped between dually truck tires, and
then released off -site at highway speeds. WSDOT has chosen to use a modified specification for
the rock while continuously verifying that the stabilized construction access remains effective. To
remain effective, the BMP must prevent sediment from migrating off site. To date, there has been
no performance testing to verify operation of this new specification. Local jurisdictions may use
the alternative specification, but must perform increased off -site inspection if they use, or allow
others to use, it.
Stabilized construction accesses may use material that meets the requirements of WSDOT's
Standard Specifications for Road, Bridge, and Municipal Construction Section 9-03.9(1)
(WSDOT, 2016) for ballast except for the following special requirements.
The grading and quality requirements are listed in Table II-4.3: Stabilized Construction Access
Alternative Material Requirements.
Table II-4.3: Stabilized Construction
Access Alternative Material
Requirements
Sieve Size
Percent Passing
21/"
99 to 100
2"
65 to 100
3/4"
40 to 80
No. 4
5 max.
No. 100
0 to 2
% Fracture
75 min.
Notes:
1. All percentages are by weight.
2. The sand equivalent value and dust ratio require-
ments do not apply.
3. The fracture requirement shall be at least one
fractured face and will apply the combined
aggregate retained on the No. 4 sieve in accord-
ance with FOP for AASHTO T 335.
Maintenance Standards
Quarry spalls shall be added if the pad is no longer in accordance with the specifications.
• If the access is not preventing sediment from being tracked onto pavement, then alternative
measures to keep the streets free of sediment shall be used. This may include replace-
ment/cleaning of the existing quarry spalls, street sweeping, an increase in the dimensions
2024 Stormwater Management Manual for Western Washington
Volume 11 - Chapter 4 - Page 318
of the access, or the installation of BMP C106: Wheel Wash.
• Any sediment that is tracked onto pavement shall be removed by shoveling or street sweep-
ing. The sediment collected by sweeping shall be removed or stabilized on site. The pave-
ment shall not be cleaned by washing down the street, except when sweeping is ineffective
and there is a threat to public safety. If it is necessary to wash the streets, the construction
of a small sump to contain the wash water shall be considered. The sediment would then be
washed into the sump where it can be controlled.
• Perform street sweeping by hand or with a high efficiency sweeper. Do not use a non -high
efficiency mechanical sweeper because this creates dust and throws soils into storm sys-
tems or conveyance ditches.
• Any quarry spalls that are loosened from the pad, which end up on the roadway shall be
removed immediately.
• If vehicles are entering or exiting the site at points other than the construction access(es),
BMP C103: High -Visibility Fence shall be installed to control traffic.
• Upon project completion and site stabilization, all construction accesses intended as per-
manent access for maintenance shall be permanently stabilized.
2024 Stormwater Management Manual for Western Washington
Volume 11 - Chapter 4 - Page 319
Figure 11-4.1: Stabilized Construction Access
cu
roadsi
Notes:
1. Driveway shall meet
the requirements of the
permitting agency.
2. It is recommended that
the access be crowned
so that runoff drains off
the pad.
06r�
77=—
DEPARTMENT OF
ECOLOGY
State of Washington
12" minimum thickness
NOT TO SCALE
n.
/15' min.
\i
Provide full width
of ingress/egress
area
Stabilized Construction Access
Revised June 2018
2024 Stormwater Management Manual for Western Washington
Volume 11 - Chapter 4 - Page 320
Approved as Functionally Equivalent
Ecology has approved products as able to meet the requirements of this BMP. The products did
not pass through the Technology Assessment Protocol — Ecology (TAPE) process. Local jur-
isdictions may choose not to accept these products, or may require additional testing prior to con-
sideration for local use. Products that Ecology has approved as functionally equivalent are
available for review on Ecology's website at:
https://ecology.wa.gov/Regulations-Permits/Guidance-tech nical-assistance/Stormwater-per-
mittee-auidance-resources/Emeraina-stormwater-treatment-technoloaies
BMP C106: Wheel Wash
Purpose
Wheel washes reduce the amount of sediment transported onto paved roads by washing dirt from
the wheels of motor vehicles prior to the motor vehicles leaving the construction site.
Conditions of Use
• Use a wheel wash when BMP C105: Stabilized Construction Access is not preventing sed-
iment from being tracked off site.
• Wheel washing is generally an effective BMP when installed with careful attention to topo-
graphy. For example, a wheel wash can be detrimental if installed at the top of a slope abut-
ting a right-of-way where the water from the dripping truck can run unimpeded into the
street.
• Pressure washing combined with an adequately sized and surfaced pad with direct drain-
age to a large 10-foot x 10-foot sump can be very effective.
• Wheel wash wastewater is not stormwater. It is commonly called process water, and must
be discharged to a separate on -site treatment system that prevents discharge to waters of
the State, or to the sanitary sewer with local sewer district approval.
• Wheel washes may use closed -loop recirculation systems to conserve water use.
• Wheel wash wastewater shall not include wastewater from concrete washout areas.
• When practical, the wheel wash should be placed in sequence with BMP C105: Stabilized
Construction Access. Locate the wheel wash such that vehicles exiting the wheel wash will
enter directly onto BMP C105: Stabilized Construction Access. In order to achieve this,
BMP C105: Stabilized Construction Access may need to be extended beyond the standard
installation to meet the exit of the wheel wash.
Design and Installation Specifications
Suggested details are shown in Figure II-4.2: Wheel Wash. The local permitting authority may
allow other designs. A minimum of 6 inches of asphalt treated base (ATB) over crushed base
2024 Stormwater Management Manual for Western Washington
Volume 11 - Chapter 4 - Page 321
material or 8 inches over a good subgrade is recommended to pave the wheel wash.
Use a low clearance truck to test the wheel wash before paving. Either a belly dump or lowboy will
work well to test clearance.
Keep the water level from 12 to 14 inches deep to avoid damage to truck hubs and filling the truck
tongues with water.
Midpoint spray nozzles are only needed in extremely muddy conditions.
Wheel wash systems should be designed with a small grade change, 6- to 12-inches for a 10-foot-
wide pond, to allow sediment to flow to the low side of pond to help prevent re -suspension of sed-
iment. A drainpipe with a 2- to 3-foot riser should be installed on the low side of the pond to allow
for easy cleaning and refilling. Polymers may be used to promote coagulation and flocculation in a
closed -loop system. Polyacrylamide (PAM) added to the wheel wash water at a rate of 0.25 to 0.5
pounds per 1,000 gallons of water increases effectiveness and reduces cleanup time. If PAM is
already being used for dust or erosion control and is being applied by a water truck, the same
truck can be used to change the wash water. PAM use shall be reviewed and approved by the
local permitting authority. Discharge of PAM may be a basis for penalties per RCW 90.48.080.
Maintenance Standards
The wheel wash should start out each day with fresh water.
The wheel wash water should be changed a minimum of once per day. On large earthwork jobs
where more than 10 to 20 trucks per hour are expected, the wheel wash water will need to be
changed more often.
Approved as Functionally Equivalent
Ecology has approved products as able to meet the requirements of this BMP. The products did
not pass through the Technology Assessment Protocol — Ecology (TAPE) process. Local jur-
isdictions may choose not to accept these products, or may require additional testing prior to con-
sideration for local use. Products that Ecology has approved as functionally equivalent are
available for review on Ecology's website at:
https://ecology.wa.gov/Regulations-Permits/Guidance-technical-assistance/Stormwater-per-
mittee-guidance-resources/Emerging-stormwater-treatment-technologies
2024 Stormwater Management Manual for Western Washington
Volume // - Chapter 4 - Page 322
Figure II-4.2: Wheel Wash
3" trash pump with
6" sewer pipe with A floats on suction hose
butterfly valves 2" schedule 40
8' x 8' sump with 5' of catch 1 %2 " schedule 40 for sprayers
—/
midpoint spray nozzles, if needed
2% slope 5:1 slope 5:1 slope
2% slope
I I
I I
1:1 slope y
15' ATB apron to protect 6" ATB construction entrance
ground from splashing water A Ball valves Asphalt curb on the low road
side to direct water back to pond
Plan \/iAW 6" sleeve under road
15' 15, 20' 15' 50'
-
1=i Curb
6" sleeve
Elevation View
Locate invert of top pipe 1'
above bottom of wheel wash
8' x 8' sump 18'
Water level
3'
5 ra� 12'
Drain pipe I 1:1 slope
Section A -A
Notes:
1. Build 8' x 8' sump to accomodate
cleaning by trackhoe. NOT TO SCALE
Wheel Wash
77=—
DEPARTMENT OF
ECOLOGY
State of Washington Revised June 2016
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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. See II-2.5 Element 5: Stabilize Soils for spe-
cific timelines for stabilizing exposed soils.
• See Table II-4.4: Seeding Windows in Western Washington (continued) for appropriate
seeding windows.
• Review all disturbed areas in late August to early September and complete all seeding by
the end of September. Otherwise, vegetation will not establish itself enough to provide
more than average protection.
• Mulch is required at all times for seeding because it protects seeds from heat, moisture
loss, and transport due to runoff. Mulch can be applied on top of the seed or simultaneously
by hydroseeding. See BMP C121: Mulching for specifications.
• Seed and mulch all disturbed areas not otherwise vegetated at final site stabilization. Final
stabilization means the completion of all soil disturbing activities at the site and the estab-
lishment of a permanent vegetative cover, or equivalent permanent stabilization measures
(such as pavement, riprap, gabions, or geotextiles) which will prevent erosion. See BMP
T5.13: Post -Construction Soil Qualitv and Depth.
Table II-4.4: Seeding Windows in Western Washington
Month Seeding Recommendations
January
February Seeding requires a cover of mulch or an erosion control blanket until 75% grass
cover is established
March
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Table II-4.4: Seeding Windows in Western Washington (continued)
Month
Seeding Recommendations
April
Optimum seeding window
May
June
July
Seeding requires irrigation until 75% grass cover is established
August
September
Optimum seeding window
October
Seeding requires a cover of mulch or an erosion control blanket until 75 percent
grass cover is established
November
December
Design and Installation Specifications
General
Install channels intended for vegetation before starting major earthwork and hydroseed with
a Bonded Fiber Matrix (BFM). For vegetated channels that will have high flows, install
erosion control blankets over the top of hydroseed. Before allowing water to flow in veget-
ated channels, establish a 75% vegetation cover. If vegetated channels cannot be estab-
lished by seed before water flow, install sod or prevegetated mats in the channel bottom
overtop of hydromulch and erosion control blankets.
• Confirm the installation of all required stormwater control measures to prevent seed from
washing away.
• Hydroseed applications shall include a minimum of 1,500 pounds per acre (lb/acre) of
mulch with 3% tackifier. See BMP C121: Mulching for specifications.
• Areas that will have seeding only, and not landscaping, may need compost or meal -based
mulch included in the hydroseed in order to establish vegetation. Re -install native topsoil on
the disturbed soil surface before application. See BMP T5.13: Post -Construction Soil Qual-
ity and Depth.
• When installing seed via hydroseeding operations, only about 1 /3 of the seed actually ends
up in contact with the soil surface. This reduces the ability to establish a good stand of grass
quickly. To overcome this, consider increasing seed quantities by up to 50 percent.
• Vegetation establishment can be enhanced by one of the following two approaches:
Approach 1: Enhance vegetation establishment by dividing the hydromulch operation
into two phases:
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■ Phase 1 — Install all seed and fertilizer with 25% to 30% mulch and tackifier
onto the soil in the first lift.
■ Phase 2 — Install the remaining mulch and tackifier over the first lift.
Approach 2: Vegetation can also be enhanced by:
■ Installing the mulch, seed, fertilizer, and tackifier in one lift;
■ Spreading or blowing straw over the top of the hydromulch at a rate of about
800 to 1,000 lb/acre; or
■ Holding straw in place with a standard tackifier.
Both of these approaches (Approach 1 and Approach 2) will increase cost moderately but
will greatly improve and enhance vegetative establishment. The increased cost may be off-
set by the reduced need for:
o Irrigation,
o Reapplication of mulch, and
o Repair of failed slope surfaces.
Either of these approaches can use standard hydromulch (1,500 lb/acre minimum) and
BFM/mechanically bonded fiber matrix (MBFM) (3,000 lb/acre minimum).
• Seed may be installed by hand if it is:
o Temporary and covered by straw, mulch, or topsoil; or
Permanent in small areas (usually less than 1 acre) and covered with mulch, topsoil,
or erosion blankets.
• Consult the local suppliers and/or the local conservation district for their recommendations
for appropriate seed mixes and application rates. The appropriate mix depends on a variety
of factors, including location, exposure, soil type, slope, and expected foot traffic.
• In addition to meeting erosion control functions and not hindering maintenance operations,
selection of long-lived, successional growth native vegetation that can compete against or
exclude weeds and grow with minimal maintenance after plant establishment is preferred.
Provide diversity to the greatest extent possible and plan for a succession of flowering
times to improve pollinator habitat.
• The seed mixes listed in Table II-4.5: Temporary and Permanent Seed Mixes for Western
Washington (continued) include recommended mixes for both temporary and permanent
seeding. Alternative seed mixes approved by the local jurisdiction may also be used.
• Apply the mixes in Table 11-4.5: Temporary and Permanent Seed Mixes for Western Wash-
ington (continued), with the exception of the wet area seed mix, at a rate of 120 pounds per
acre. This rate can be reduced if soil amendments or slow -release fertilizers are used.
Apply the wet area seed mix at a rate of 60 pounds per acre.
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Table II-4.5: Temporary and Permanent Seed Mixes for Western
Washington
Common Name
Latin Name
% Weight
% Purity
% Germination
Temporary Erosion Control Seed Mix
A standard mix for areas requiring a temporary vegetative cover.
Chewings or annual
Festuca rubra var.
blue grass
commutata or
40
98
90
Poa anna
Perennial rye
Lolium perenne
50
98
90
Redtop or colonial
Agrostis alba or
5
92
85
bentgrass
Agrostis tenuis
White dutch clover
Trifolium repens
5
98
90
Landscaping Seed Mix
A recommended mix for landscaping seed.
Perennial rye blend
Lolium perenne
70
98
90
Chewings and red
Festuca rubra var.
fescue blend
commutata or Fes-
30
98
90
tuca rubra
Low -Growing Turf Seed Mix
A turf seed mix for dry situations where there is no need for watering. This mix requires very little main-
tenance.
Dwarf tall fescue
Festuca arundin-
45
98
90
(several varieties)
acea var.
Dwarf perennial rye
Lolium perenne
30
98
90
(Barclay)
var. barclay
Red fescue
Festuca rubra
20
98
90
Colonial bentgrass
Agrostis tenuis
5
98
90
Bioswale Seed Mix
A seed mix for bioswales and other intermittently wet areas.
Tall or meadow fes-
Festuca arundin-
acea or Festuca
75-80
98
90
cue
elatior
Seaside/Creeping
Agrostis pa/ustris
10-15
92
85
bentgrass
Redtop bentgrass
Agrostis alba or
5-10
90
80
Agrostis gigantea
Wet Area Seed Mix
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Table II-4.5: Temporary and Permanent Seed Mixes for Western
Washington (continued)
Common Name
Latin Name
% Weight
% Purity
% Germination
A low -growing, relatively non-invasive seed mix appropriate for very wet areas that are not regulated wet-
lands. Consult Hydraulic Permit Authority (HPA) for seed mixes if applicable.
Tall or meadow fes-
Festuca arundin-
acea or Festuca
60-70
98
90
cue
elatior
Seaside/Creeping
Agrostis pa/ustris
10-15
98
85
bentgrass
Meadow foxtail
Alepocurus
10-15
90
80
pratensis
Alsike clover
Trifolium
1-6
98
90
hybridum
Redtop bentgrass
Agrostis alba
1-6
92
85
Meadow Seed Mix
A recommended meadow seed mix for infrequently maintained areas or non -maintained areas where
colonization by native plants is desirable. Likely applications include rural road and utility right-of-way.
Seeding should take place in September or very early October in order to obtain adequate establishment
prior to the winter months. Consider the appropriateness of clover, a fairly invasive species, in the mix.
Amending the soil can reduce the need for clover.
Redtop or Oregon
Agrostis alba or
bentgrass
Agrostis ore-
20
92
85
gonensis
Red fescue
Festuca rubra
70
98
90
White dutch clover
Trifolium repens
10
98
90
Roughening and Rototilling
The seedbed should be firm and rough. Roughen all soil no matter what the slope. Track
walk slopes before seeding if engineering purposes require compaction. Backblading or
smoothing of slopes greater than 4HA V is not allowed if they are to be seeded.
Restoration -based landscape practices require deeper incorporation than that provided by
a simple, single -pass rototilling treatment. Wherever practical, initially rip the subgrade to
improve long-term permeability, infiltration, and water inflow qualities. At a minimum, per-
manent areas shall receive 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 soil amend-
ments per the specifications and place to achieve the specified depth.
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Fertilizers
• Conducting soil tests to determine the exact type and quantity of fertilizer needed is recom-
mended. This will prevent the overapplication of fertilizer.
• Organic matter is the most appropriate form of fertilizer because it provides nutrients (includ-
ing nitrogen, phosphorus, and potassium) in the least water-soluble form.
• In general, use 10-4-6 N-P-K (nitrogen -phosphorus -potassium) fertilizer at a rate of 90
pounds per acre.
• Always use slow -release fertilizers because they are more efficient and have fewer envir-
onmental impacts. Do not add fertilizer to the hydromulch machine, or agitate, more than 20
minutes before use. Too much agitation destroys the slow -release coating.
• There are numerous products available to take the place of chemical fertilizers, including
several with seaweed extracts that are beneficial to soil microbes and organisms. If 100%
cottonseed meal is used as the mulch in hydroseed, chemical fertilizer may not be neces-
sary. Cottonseed meal provides a good source of long-term, slow -release, available nitro-
gen.
Bonded Fiber Matrix and Mechanically Bonded Fiber Matrix
• On steep slopes, use Bonded Fiber Matrix (BFM) or Mechanically Bonded Fiber Matrix
(MBFM) products. Apply BFM/MBFM products at a minimum rate of 3,000 pounds per acre
with approximately 10% tackifier. Achieve a minimum of 95% soil coverage during applic-
ation. Numerous products are available commercially. 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 fer-
tilizer.
• Install products per manufacturer's instructions.
• BFMs and MBFMs provide good alternatives to blankets in most areas requiring vegetation
establishment. Advantages over blankets include the following:
• BFM and MBFMs do not require surface preparation.
• Helicopters can assist in installing BFM and MBFMs in remote areas.
• On slopes steeper than 2.5H:1 V, blanket installers may require ropes and harnesses
for safety.
• Installing BFM and MBFMs can save at least $1,000 per acre compared to blankets.
Maintenance Standards
Reseed any seeded areas that fail to establish at least 75% cover (100% cover for areas
that receive sheet or concentrated flows) of all seeded areas after 3 months of active
growth following germination during the growing season. If reseeding is ineffective, use an
alternate method, such as sodding, mulching, or nets/blankets. If winter weather prevents
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Volume 11 - Chapter 4 - Page 330
adequate grass growth, this time limit may be relaxed at the discretion of the local authority
when sensitive areas would otherwise be protected.
• Reseed and protect by mulch any areas that experience erosion after achieving adequate
cover. If the erosion problem is drainage related, the problem shall be fixed and the eroded
area reseeded and protected by mulch.
• Supply seeded areas with adequate moisture, but do not water to the extent that it causes
runoff.
Approved as Functionally Equivalent
Ecology has approved products as able to meet the requirements of this BMP. The products did
not pass through the Technology Assessment Protocol — Ecology (TAPE) process. Local jur-
isdictions may choose not to accept these products, or may require additional testing prior to con-
sideration for local use. Products that Ecology has approved as functionally equivalent are
available for review on Ecology's website at:
https://ecology.wa.gov/Regulations-Permits/Guidance-technical-assistance/Stormwater-per-
mittee-guidance-resources/Emerging-stormwater-treatment-technologies
BMP C121: Mulching
Purpose
Mulching soils provides immediate temporary protection from erosion. Mulch also enhances plant
establishment by conserving moisture, holding fertilizer, seed, and topsoil in place, and mod-
erating soil temperatures. There are a variety of mulches that can be used. This section discusses
only the most common types of mulch.
Conditions of Use
As a temporary cover measure, mulch should be used:
• For less than 30 days on disturbed areas that require cover.
At all times for seeded areas, especially during the wet season and during the hot summer
months.
During the wet season on slopes steeper than 3H:1 V with more than 10 feet of vertical
relief.
Mulch may be applied at any time of the year and must be refreshed periodically.
For seeded areas, mulch may be made up of 100 percent:
• Cottonseed meal;
• Fibers made of wood, recycled cellulose, hemp, or kenaf;
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• Compost;
• Or blends of these.
Tackifier shall be plant -based, such as guar or alpha plantago, or chemical -based such as poly-
acrylamide or polymers.
Generally, mulches come in 40-50 pound bags. Seed and fertilizer are added at time of applic-
ation.
Recycled cellulose may contain polychlorinated biphenyl (PCBs). Ecology recommends that
products should be evaluated for PCBs prior to use.
Refer to BMP C126: Polyacrylamide (PAM) for Soil Erosion Protection for conditions of use. PAM
shall not be directly applied to water or allowed to enter a water body.
Any mulch or tackifier product used shall be installed per the manufacturer's instructions.
Design and Installation Specifications
For mulch materials, application rates, and specifications, see Table 11-4.7: Mulch Standards and
Guidelines (continued). Consult with the local supplier or the local conservation district for their
recommendations. Increase the application rate until the ground is 95% covered (i.e. not visible
under the mulch layer). Note: Thickness may be increased for disturbed areas in or near sensitive
areas or other areas highly susceptible to erosion.
Where the option of "Compost" is selected, it should be a coarse compost that meets the size grad-
ations listed in Table 11-4.6: Size Gradations of Compost as Mulch Material when tested in accord-
ance with Test Method 02.02-B found in Test Methods for the Examination of Composting and
Compost (Thompson, 2001).
Mulch used within the ordinary high-water mark of surface waters should be selected to minimize
potential flotation of organic matter. Composted organic materials have higher specific gravities
(densities) than straw, wood, or chipped material. Consult the Hydraulic Permit Authority (HPA)
for mulch mixes if applicable.
Table II-4.6: Size Gradations of Compost as Mulch Material
Sieve Size
Percent Passing
3"
100%
1"
90%- 100%
3/4"
70% - 100%
1/4"
40%- 100%
Table II-4.7: Mulch Standards and Guidelines
Mulch Mater-
Guideline
Description
ial
Straw
Quality Stand-
Air-dried; free from undesirable seed and coarse material.
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Table II-4.7: Mulch Standards and Guidelines (continued)
Mulch Mater-
Guideline
Description
ial
ards
Application
2" to 3" thick; 5 bales per 1,000 sf or 2 to 3 tons per acre
Rates
Cost-effective protection when applied with adequate thickness.
Hand -application generally requires greater thickness than blown
straw. The thickness of straw may be reduced by half when used in
conjunction with seeding. In windy areas, straw must be held in
place by crimping, using a tackifier, or covering with netting. Blown
straw always has to be held in place with a tackifier because even
Remarks
light winds will blow it away. Straw, however, has several defi-
ciencies that should be considered when selecting mulch materials.
It often introduces and/or encourages the propagation of weed spe-
cies, and it has no significant long-term benefits. Straw should only
be used if mulches with long-term benefits are unavailable locally. It
should also not be used within the ordinary high-water elevation of
surface waters (due to flotation).
Quality Stand-
No growth inhibiting factors.
ards
Application
Approx. 35-45 Ibs per 1,000 sf or 1,500 - 2,000 Ibs per acre
Hydromulch
Rates
Shall be applied with hydromulcher. Shall not be used without seed
Remarks
and tackifier unless the application rate is at least doubled. Fibers
longer than about 3/4 - 1 inch clog hydromulch equipment. Fibers
should be kept to less than 3/4 inch.
Quality Stand-
No visible water or dust during handling. Must be produced per WAC
ards
173-350, Solid Waste Handling Standards, but may have up to 35 /o
biosolids.
Application
2" thick minimum; approximately 100 tons per acre (approximately
Rates
750 Ibs per cubic yard)
More effective control can be obtained by increasing thickness to 3".
Compost
Compost makes an excellent mulch for protecting final grades until
landscaping because it can be directly seeded or tilled into soil as an
amendment. Compost used for mulch has a coarser size gradation
Remarks
than compost used for BMP C125: Topsoiling / Composting or BMP
T5.13: Post -Construction Soil Quality and Depth. It is more stable
and practical to use in wet areas and during rainy weather con-
ditions. Do not use compost near wetlands if biosolids are included.
Do not use compost near phosphorous impaired water bodies.
Chipped Site
Quality Stand-
Gradations from fines to 6 inches in length for texture, variation, and
Vegetation
ards
interlocking properties. Include a mix of various sizes so that the
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Volume 11 - Chapter 4 - Page 333
Table II-4.7: Mulch Standards and Guidelines (continued)
Mulch Mater-
Guideline
Description
ial
average size is between 2 and 4 inches.
Application
2" thick minimum.
Rates
This is a cost-effective way to dispose of debris from clearing and
grubbing, and it eliminates the problems associated with burning.
Generally, it should not be used on slopes above approximately 10%
because of its tendency to be transported by runoff. It is not recom-
mended within 200 feet of surface waters. If permanent seeding or
Remarks
planting is expected shortly after mulch, the decomposition of the
chipped vegetation may tie up nutrients important to grass estab-
lishment.
Note: Thick application of this material over existing grass, herb-
aceous species, and some groundcovers could smother and kill
vegetation.
Quality Stand-
No visible water or dust during handling. Must be purchased from a
ards
supplier with a Solid Waste Handling Permit or one exempt from
solid waste regulations.
Application
2" thick minimum; approximately 100 tons per acre (approximately
Rates
750 lbs. per cubic yard).
Wood -Based
This material is often called "wood straw" or "hog fuel". The use of
Mulch
mulch ultimately improves the organic matter in the soil. Special cau-
tion is advised regarding the source and composition of wood -based
Remarks
mulches. Its preparation typically does not provide any weed seed
control, so evidence of residual vegetation in its composition or
known inclusion of weed plants or seeds should be monitored and
prevented (or minimized).
Quality Stand-
A blend of loose, long, thin wood pieces derived from native conifer
ards
or deciduous trees with high length -to -width ratio.
Application
2" thick minimum.
Rates
Wood Strand
Cost-effective protection when applied with adequate thickness. A
Mulch
minimum of 95% of the wood strand shall have lengths between 2
and 10 inches, with a width and thickness between 1/16 and 0.5
Remarks
inches. The mulch shall not contain resin, tannin, or other com-
pounds in quantities that would be detrimental to plant life. Sawdust
or wood shavings shall not be used as mulch. See specification 9-
14.4(4) from the Standard Specifications for Road, Bridge, and Muni-
cipal Construction (WSDOT, 2016)
Maintenance Standards
The thickness of the mulch cover must be maintained.
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Any areas that experience erosion shall be remulched and/or protected with a net or blanket. If the
erosion problem is drainage related, then the problem shall be fixed and the eroded area rem-
ulched.
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BMP C123: Plastic Covering
Purpose
Plastic covering provides immediate, short-term erosion protection to slopes and disturbed areas.
Conditions of Use
Plastic covering may be used on disturbed areas that require cover measures for less than 30
days, except as stated below.
• Plastic is particularly useful for protecting cut and fill slopes and stockpiles. However, the rel-
atively rapid breakdown of most polyethylene sheeting makes it unsuitable for applications
greater than six months.
• Due to rapid runoff caused by plastic covering, do not use this method upslope of areas that
might be adversely impacted by concentrated runoff. Such areas include steep and/or
unstable slopes.
• Plastic sheeting may result in increased runoff volumes and velocities, requiring additional
on -site measures to counteract the increases. Creating a trough with wattles or other mater-
ial can convey clean water away from these areas.
• To prevent undercutting, trench and backfill rolled plastic covering products.
• Although the plastic material is inexpensive to purchase, the cost of installation, main-
tenance, removal, and disposal add to the total costs of this BMP.
• 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 con-
vey clean rainwater away from bare soil and disturbed areas. Do not mix clean runoff from a
plastic covered slope with dirty runoff from a project.
• Other uses for plastic include:
• Temporary ditch liner.
• Pond liner in temporary sediment pond.
• Liner for bermed temporary fuel storage area if plastic is not reactive to the type of
fuel being stored.
• Emergency slope protection during heavy rains.
• Temporary drainpipe ("elephant trunk") used to direct water.
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Design and Installation Specifications
• Plastic slope cover must be installed as follows:
1. Run plastic up and down the slope, not across the slope.
2. Plastic may be installed perpendicular to a slope if the slope length is less than 10
feet.
3. Provide a minimum of 8-inch overlap at the 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 immediately. This
prevents high velocity runoff from contacting bare soil, which causes extreme
erosion.
8. Sandbags may be lowered into place tied to ropes. However, all sandbags must be
staked in place.
• Plastic sheeting shall have a minimum thickness of 6 mil.
• If erosion at the toe of a slope is likely, a gravel berm, riprap, or other suitable protection
shall be installed at the toe of the slope in order to reduce the velocity of runoff.
Maintenance Standards
• Torn sheets must be replaced and open seams repaired.
• Completely remove and replace the plastic if it begins to deteriorate due to ultraviolet radi-
ation.
• Completely remove plastic when no longer needed.
• Dispose of old tires used to weight down plastic sheeting appropriately.
Approved as Functionally Equivalent
Ecology has approved products as able to meet the requirements of this BMP. The products did
not pass through the Technology Assessment Protocol — Ecology (TAPE) process. Local jur-
isdictions may choose not to accept these products, or may require additional testing prior to con-
sideration for local use. Products that Ecology has approved as functionally equivalent are
available for review on Ecology's website at:
https://ecology.wa.gov/Regulations-Permits/Guidance-technical-assistance/Stormwater-per-
mittee-guidance-resources/Emerging-stormwater-treatment-technologies
2024 Stormwater Management Manual for Western Washington
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BMP C124: Sodding
Purpose
The purpose of sodding is to establish turffor immediate erosion protection and to stabilize drain-
age paths where concentrated overland flow will occur.
Conditions of Use
Sodding may be used in the following areas:
• Disturbed areas that require short-term or long-term cover.
• Disturbed areas that require immediate vegetative cover.
• All waterways that require vegetative lining. Waterways may also be seeded rather than
sodded, and protected with a net or blanket.
Design and Installation Specifications
Sod shall be free of weeds, have a uniform thickness (approximately 1-inch thick), and have a
dense root mat for mechanical strength.
The following steps are recommended for sod installation:
1. Shape and smooth the surface to final grade in accordance with the approved grading plan.
Consider any areas (such as swales) that need to be overexcavated below design elevation
to allow room for placing soil amendment and sod.
2. Amend 4 inches (minimum) of compost into the top 8 inches of the soil if the organic content
of the soil is less than ten percent or the permeability is less than 0.6 inches per hour. See
Ecology's Compost web page for further information:
https://ecology.wa.gov/Waste-Toxics/Reducing-recycling-waste/Organic-mater-
ials/Managing-organics-compost
3. Fertilize according to the sod supplier's recommendations.
4. Work lime and fertilizer 1 to 2 inches into the soil, and smooth the surface.
5. Lay strips of sod beginning at the lowest area to be sodded and perpendicular to the dir-
ection of water flow. Wedge strips securely into place. Square the ends of each strip to
provide for a close, tight fit. Stagger joints at least 12 inches. Staple on slopes steeper than
3H:1 V. Staple the upstream edge of each sod strip.
6. Roll the sodded area and irrigate.
7. When sodding is carried out in alternating strips or other patterns, seed the areas between
the sod immediately after sodding.
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Maintenance Standards
If the grass is unhealthy, the cause shall be determined and appropriate action taken to rees-
tablish a healthy ground cover. If it is impossible to establish a healthy ground cover due to fre-
quent saturation, instability, or some other cause, the sod shall be removed, the area seeded with
an appropriate mix, and protected with a net or blanket (BMP C122: Nets and Blankets).
BMP C125: Topsoiling / Composting
Purpose
Topsoiling and composting provide a suitable growth medium for final site stabilization with veget-
ation. While not a permanent cover practice in itself, topsoiling and composting are an integral
component of providing permanent cover in those areas where there is an unsuitable soil surface
for plant growth. Use this BMP in conjunction with other BMPs such as BMP C120: Temporary
and Permanent Seeding, BMP C121: Mulching, or BMP C124: Sodding.
Implementation of this BMP may meet the post -construction requirements of BMP T5.13: Post -
Construction Soil Quality and Depth.
Native soils and disturbed soils that have been organically amended not only retain much more
stormwater, but also serve as effective biofilters for urban pollutants and, by supporting more vig-
orous plant growth, reduce the water, fertilizer, and/or pesticides needed to support installed land-
scapes. Topsoil does not include any subsoils but only the material from the top several inches
including organic debris.
Conditions of Use
• Permanent landscaped areas shall contain healthy topsoil that reduces the need for fer-
tilizers, improves overall topsoil quality, provides for better vegetative health and vitality,
improves hydrologic characteristics, and reduces the need for irrigation.
• Leave native soils and the duff layer undisturbed to the maximum extent practicable. Strip-
ping of existing, properly functioning soil system and vegetation for the purpose of top -
soiling during construction is not acceptable. Preserve existing soil systems in undisturbed
and uncompacted conditions if functioning properly.
• Areas that already have good topsoil, such as undisturbed areas, do not require soil amend-
ments.
• Restore, to the maximum extent practical, native soils disturbed during clearing and grading
to a condition equal to or better than the original site condition's moisture -holding capacity.
Use on -site native topsoil, incorporate amendments into on -site soil, or import blended top-
soil to meet this requirement.
• Topsoiling is a required procedure when establishing vegetation on shallow soils, and soils
of critically low pH (high acid) levels.
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Beware of where the topsoil comes from, and what vegetation was on site before dis-
turbance. Invasive plant seeds may be included and could cause problems for establishing
native plants, landscaped areas, or grasses.
Topsoil from the site will contain mycorrhizal bacteria that are necessary for healthy root
growth and nutrient transfer. These native mycorrhizae are acclimated to the site and will
provide optimum conditions for establishing grasses. Use commercially available mycor-
rhizae products when using off -site topsoil.
Design and Installation Specifications
Meet the following requirements for disturbed areas where topsoil will be applied (e.g. for dis-
turbed areas that will be developed as lawn or other landscape):
• Maximize the depth of the topsoil wherever possible to provide the maximum possible infilt-
ration capacity and beneficial growth medium. Topsoil shall have:
A minimum depth of 8 inches. Scarify subsoils below the topsoil layer at least 4
inches with some incorporation of the upper material to avoid stratified layers, where
feasible. Ripping or re -structuring the subgrade may also provide additional benefits
regarding the overall infiltration and interflow dynamics of the soil system. The
decision to either layer topsoil over a subgrade or incorporate topsoil into the under-
lying layer may vary depending on the planting specified.
• A minimum organic content of 10% dry weight in planting beds, and 5% organic mat-
ter content in turf areas. Incorporate organic amendments to a minimum 8 inch depth
except where tree roots or other natural features limit the depth of incorporation.
• A pH between 6.0 and 8.0 or matching the pH of the undisturbed soil.
• If blended topsoil is imported, then fines should be limited to 25% passing through a
200 sieve.
• Mulch planting beds with 2 inches of organic material
• Accomplish the required organic content, depth, and pH by returning native topsoil to the
site, importing topsoil of sufficient organic content, and/or incorporating organic amend-
ments. When using the option of incorporating amendments to meet the organic content
requirement, use compost that meets the compost specification for Bioretention (See BMP
T7.30: Bioretention), with the exception that the compost may have up to 35% biosolids or
manure.
The final composition and construction of the soil system will result in a natural selection or
favoring of certain plant species over time. For example, incorporation of topsoil may favor
grasses, while layering with mildly acidic, high -carbon amendments may favor more woody
vegetation.
Allow sufficient time in scheduling for topsoil spreading prior to seeding, sodding, or plant-
ing.
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• Take care when applying topsoil to subsoils with contrasting textures. Sandy topsoil over
clayey subsoil is a particularly poor combination, as water creeps along the junction
between the soil layers and causes the topsoil to slough. If topsoil and subsoil are not prop-
erly bonded, water will not infiltrate the soil profile evenly and it will be difficult to establish
vegetation. The best method to promote bonding is to actually work the topsoil into the layer
below for a depth of at least 6 inches.
• Field exploration of the site shall be made to determine if there is surface soil of sufficient
quantity and quality to justify stripping. Topsoil shall be friable and loamy (loam, sandy
loam, silt loam, sandy clay loam, and/or clay loam). Avoid areas of natural groundwater
recharge.
• Stripping shall be confined to the immediate construction area. A 4 to 6 inch stripping depth
is common, but depth may vary depending on the particular soil. All surface runoff control
structures shall be in place prior to stripping.
• Do not place topsoil while in a frozen or muddy condition, when the subgrade is excessively
wet, or when conditions exist that may otherwise be detrimental to proper grading or pro-
posed sodding or seeding.
• In any areas requiring grading, remove and stockpile the duff layer and topsoil on site in a
designated, controlled area, not adjacent to public resources and critical areas. Reapply
stockpiled topsoil to other portions of the site where feasible.
• Locate the topsoil stockpile so that it meets specifications and does not interfere with work
on the site. It may be possible to locate more than one pile in proximity to areas where top-
soil will be used.
• Stockpiling of topsoil shall occur in the following manner:
• Side slopes of the stockpile shall not exceed 2H:1 V.
• Between October 1 and April 30:
■ An interceptor dike with gravel outlet and silt fence shall surround all topsoil
stockpiles.
■ Within 2 days complete erosion control seeding, or covering stockpiles with
clear plastic, or other mulching materials.
• Between May 1 and September 30:
■ An interceptor dike with gravel outlet and silt fence shall surround all topsoil
stockpiles if the stockpile will remain in place for a longer period of time than
active construction grading.
■ Within 7 days complete erosion control seeding, or covering stockpiles with
clear plastic, or other mulching materials.
• When native topsoil is to be stockpiled and reused, the following should apply to ensure that
the mycorrhizal bacteria, earthworms, and other beneficial organisms will not be destroyed:
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o Reinstall topsoil within 4 to 6 weeks.
o Do not allow the saturation of topsoil with water.
o Do not use plastic covering.
Maintenance Standards
• Inspect stockpiles regularly, especially after large storm events. Stabilize any areas that
have eroded.
• Establish soil quality and depth toward the end of construction and once established, pro-
tect from compaction, such as from large machinery use, and from erosion.
• Plant and mulch soil after installation.
• Leave plant debris or its equivalent on the soil surface to replenish organic matter.
• Reduce and adjust, where possible, the use of irrigation, fertilizers, herbicides and pesti-
cides, rather than continuing to implement formerly established practices.
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BMP C130: Surface Roughening
Purpose
Surface roughening aids in the establishment of vegetative cover, reduces runoff velocity,
increases infiltration, and provides for sediment trapping through the provision of a rough soil sur-
face. Horizontal depressions are created by operating a tiller or other suitable equipment on the
contour or by leaving slopes in a roughened condition by not fine grading them.
Use this BMP in conjunction with other BMPs such as BMP C120: Temporary and Permanent
Seeding, BMP C121: Mulching, or BMP C124: Sodding.
Conditions for Use
• All slopes steeper than 3HA V and greater than 5 vertical feet require surface roughening to
a depth of 2 to 4 inches prior to seeding.
• Areas that will not be stabilized immediately may be roughened to reduce runoff velocity
until seeding takes place.
• Slopes with a stable rock face do not require roughening.
• Slopes where mowing is planned should not be excessively roughened.
Design and Installation Specifications
There are different methods for achieving a roughened soil surface on a slope, and the selection
of an appropriate method depends on the type of slope. Roughening methods include stair -step
grading, grooving, contour furrows, and tracking. See Figure 11-4.5: Surface Roughening by Track-
ing and Contour Furrows. Factors to be considered in choosing a roughening method are slope
steepness, mowing requirements, and whether the slope is formed by cutting or filling.
• Disturbed areas that will not require mowing may be stair -step graded, grooved, or left
rough after filling.
• Stair -step grading is particularly appropriate in soils containing large amounts of soft rock.
Each "step" catches material that sloughs from above, and provides a level site where
vegetation can become established. Stairs should be wide enough to work with standard
earth moving equipment. Stair steps must be on contour or gullies will form on the slope.
• Areas that will be mowed (these areas should have slopes less steep than 3H:1 V) may
have small furrows left by disking, harrowing, raking, or seed -planting machinery operated
on the contour.
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Graded areas with slopes steeper than 3H:1 V but less than 2H:1 V should be roughened
before seeding. This can be accomplished in a variety of ways, including "track walking", or
driving a crawler tractor up and down the slope, leaving a pattern of cleat imprints parallel to
slope contours.
• Tracking is done by operating equipment up and down the slope to leave horizontal depres-
sions in the soil.
Maintenance Standards
• Areas that are surface roughened should be seeded as quickly as possible.
Regular inspections should be made of the area. If rills appear, they should be re -
roughened and re -seeded immediately.
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Figure 11-4.5: Surface Roughening by Tracking and Contour Furrows
Tracking with machinery up and down
the slope provides grooves that will
catch seed, rainfall, and reduce runoff.
Gn
mu
00r�
77=—
DEPARTMENT OF
ECOLOGY
State of Washington
\ems g
8-
8
e-�-
Tracking
O SCALE
Surface Roughening by Tracking
and Contour Furrows
Revised June 2016
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BMP C140: Dust Control
Purpose
Dust control prevents wind transport of dust from disturbed soil surfaces onto roadways, into drain-
age systems, and into surface waters.
Conditions of Use
Use dust control in areas (including roadways) subject to surface and air movement of dust where
on -site or off -site impacts to roadways, drainage systems, or surface waters are likely.
Design and Installation Specifications
• Vegetate or mulch areas that will not receive vehicle traffic. In areas where planting, mulch-
ing, or paving is impractical, apply gravel or landscaping rock.
• Limit dust generation by clearing only those areas where immediate activity will take place,
leaving the remaining area(s) in the original condition. Maintain the original ground cover as
long as practical.
• Construct natural or artificial windbreaks or windscreens. These may be designed as
enclosures for small dust sources.
• Sprinkle the site with water until the surface is wet. Repeat as needed. To prevent carryout
of mud onto the street, refer to BMP C105: Stabilized Construction Access and BMP C106:
Wheel Wash.
• Irrigation water can be used for dust control. Irrigation systems should be installed as a first
step on sites where dust control is a concern.
• Spray exposed soil areas with a dust palliative, following the manufacturer's instructions
and cautions regarding handling and application. Used oil is prohibited from use as a dust
suppressant. Local jurisdictions may approve other dust palliatives such as calcium chlor-
ide or PAM.
• PAM (BMP C126: Polyacrylamide (PAM) for Soil Erosion Protection) added to water at a
rate of 0.5 pounds per 1,000 gallons of water per acre and applied from a water truck is
more effective than water alone. This is due to the increased infiltration of water into the soil
and reduced evaporation. In addition, small soil particles are bonded together and are not
as easily transported by wind. Adding PAM may reduce the quantity of water needed for
dust control.
Note that the application rate specified here applies to this BMP, and is not the same applic-
ation rate that is specified in BMP C126: Polyacrylamide (PAM) for Soil Erosion Protection,
but the downstream protections still apply.
Refer to BMP C126: Polyacrylamide (PAM) for Soil Erosion Protection for conditions of use.
PAM shall not be directly applied to water or allowed to enter a water body. PAM use shall
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be reviewed and approved by the local permitting authority and discharge of PAM may be a
basis for penalties per RCW 90.48.080.
• 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 com-
pliance with this BMP. See the following website for more information:
https://ecology.wa.gov/About-us/Our-role-in-the-community/Partnerships-com-
mittees/Clean-air-agencies
• Use vacuum street sweepers.
• Remove mud and other dirt promptly so it does not dry and then turn into dust.
• Techniques that can be used for unpaved roads and lots include:
• Lower speed limits. High vehicle speed increases the amount of dust stirred up from
unpaved roads and lots.
• Upgrade the road surface strength by improving particle size, shape, and mineral
types that make up the surface and base materials.
• Add surface gravel to reduce the source of dust emission. Limit the amount of fine
particles (those smaller than .075 mm) to 10 to 20 percent.
• Use geotextile fabrics to increase the strength of new roads or roads undergoing
reconstruction.
• Encourage the use of alternate, paved routes, if available.
• 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.
• Limit dust -generating work on windy days.
• Pave unpaved permanent roads and other trafficked areas.
Maintenance Standards
Respray area as necessary to keep dust to a minimum.
BMP C150: Materials on Hand
Purpose
Keep quantities of erosion prevention and sediment control materials on the project site at all
times to be used for regular maintenance and emergency situations such as unexpected heavy
rains. Having these materials on -site reduces the time needed to replace existing or implement
new BMPs when inspections indicate that existing BMPs are not meeting the Construction
SWPPP requirements. In addition, contractors can save money by buying some materials in bulk
and storing them at their office or yard.
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Conditions of Use
• Construction projects of any size or type can benefit from having materials on hand. A small
commercial development project could have a roll of plastic and some gravel available for
immediate protection of bare soil and temporary berm construction. A large earthwork pro-
ject, such as highway construction, might have several tons of straw, several rolls of plastic,
flexible pipe, sandbags, geotextile fabric and steel "T" posts.
• Materials should be stockpiled and readily available before any site clearing, grubbing, or
earthwork begins. A large contractor or project proponent could keep a stockpile of mater-
ials that are available for use on several projects.
• If storage space at the project site is at a premium, the contractor could maintain the mater-
ials at their office or yard. The office or yard must be less than an hour from the project site.
Design and Installation Specifications
Depending on project type, size, complexity, and length, materials and quantities will vary. A good
minimum list of items that will cover numerous situations includes:
• Clear plastic, 6 mil
• Drainpipe, 6 or 8 inch diameter
• Sandbags, filled
• Straw bales for mulching
• Quarry spalls
• Washed gravel
• Geotextile fabric
• Catch basin inserts
• Steel "T" posts
• Silt fence material
• Straw wattles
Maintenance Standards
• All materials with the exception of the quarry spalls, steel "T" posts, and gravel should be
kept covered and out of both sun and rain.
• Re -stock materials as needed.
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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 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 project
components include, but are not limited to:
• Curbs
• Sidewalks
• Roads
• Bridges
• Foundations
• Floors
• Runways
Disposal options for concrete, in order of preference are:
1. Off -site disposal
2. Concrete wash -out areas (see BMP C154: Concrete Washout Area)
3. De minimus washout to formed areas awaiting concrete
Design and Installation Specifications
• Wash concrete truck drums at an approved off -site location or in designated concrete
washout areas only. Do not wash out concrete trucks onto the ground (including formed
areas awaiting concrete), or into storm drains, open ditches, streets, or streams. Refer to
BMP C154: Concrete Washout Area for information on concrete washout areas.
Return unused concrete remaining in the truck and pump to the originating batch
plant for recycling. Do not dump excess concrete on site, except in designated con-
crete washout areas as allowed in BMP C154: Concrete Washout Area.
Wash small concrete handling equipment (e.g. hand tools, screeds, shovels, rakes, floats,
trowels, and wheelbarrows) into designated concrete washout areas or into formed areas
awaiting concrete pour.
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• At no time shall concrete be washed off into the footprint of an area where an infiltration fea-
ture will be installed.
• Wash equipment difficult to move, such as concrete paving machines, in areas that do not
directly drain to natural or constructed stormwater conveyance or potential infiltration areas.
• Do not allow washwater from areas, such as concrete aggregate driveways, to drain directly
(without detention or treatment) to natural or constructed stormwater conveyances.
• Contain washwater and leftover product in a lined container when no designated concrete
washout areas (or formed areas, allowed as described above) are available. Dispose of con-
tained concrete and concrete washwater (process water) properly.
• Always use forms or solid barriers for concrete pours, such as pilings, within 15-feet of sur-
face waters.
• Refer to BMP C252: Treating and Disposing of High pH Water for pH adjustment require-
ments.
• Refer to the Construction Stormwater General Permit (CSWGP) for pH monitoring require-
ments if the project involves one of the following activities:
• Significant concrete work (as defined in the CSWGP).
• The use of soils amended with (but not limited to) Portland cement -treated base,
cement kiln dust or fly ash.
• Discharging stormwater to segments of water bodies on the 303(d) list (Category 5)
for high pH.
Maintenance Standards
Check containers for holes in the liner daily during concrete pours and repair the same day.
BMP C152: Sawcutting and Surfacing Pollution
Prevention
Purpose
Sawcutting and surfacing operations generate slurry and process water that contain fine particles
and have a high pH (concrete cutting), both of which can violate the water quality standards in the
receiving water. Concrete spillage or concrete discharge to waters of the State is prohibited. Use
this BMP to minimize and eliminate process water and slurry created by sawcutting or surfacing
from entering waters of the State.
Conditions of Use
Utilize these management practices anytime sawcutting or surfacing operations take place. Saw -
cutting and surfacing operations include, but are not limited to:
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• Sawing
• Coring
• Grinding
• Roughening
• Hydro -demolition
• Bridge and road surfacing
Design and Installation Specifications
• Vacuum slurry and cuttings during cutting and surfacing operations.
• Slurry and cuttings shall not remain on permanent concrete or asphalt pavement overnight.
• Slurry and cuttings shall not drain to any natural or constructed drainage conveyance includ-
ing stormwater systems. This may require temporarily blocking catch basins.
• Dispose of collected slurry and cuttings in a manner that does not violate groundwater or
surface water quality standards.
• Do not allow process water generated during hydro -demolition, surface roughening, or sim-
ilar operations to drain to any natural or constructed drainage conveyance including storm -
water systems. Dispose of process water in a manner that does not violate groundwater or
surface water quality standards.
• Handle and dispose of cleaning waste material and demolition debris in a manner that does
not cause contamination of water. Dispose of sweeping material from a pick-up sweeper at
an appropriate disposal site.
Maintenance Standards
Continually monitor operations to determine whether slurry, cuttings, or process water could enter
waters of the state. If inspections show that a violation of water quality standards could occur, stop
operations and immediately implement preventive measures such as berms, barriers, secondary
containment, and/or vacuum trucks.
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BMP C154: Concrete Washout Area
Purpose
Prevent or reduce the discharge of pollutants from concrete waste to stormwater by conducting
washout off -site, or performing on -site washout in a designated area.
Conditions of Use
Concrete washout areas are implemented on construction projects where:
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• Concrete is used as a construction material
• It is not possible to dispose of all concrete wastewater and washout off -site (ready mix
plant, etc.).
• Concrete truck drums are washed on -site.
Note that auxiliary concrete truck components (e.g. chutes and hoses) and small concrete
handling equipment (e.g. hand tools, screeds, shovels, rakes, floats, trowels, and wheel-
barrows) may be washed into formed areas awaiting concrete pour.
At no time shall concrete be washed off into the footprint of an area where an infiltration feature
will be installed.
Design and Installation Specifications
Implementation
• Perform washout of concrete truck drums at an approved off -site location or in designated
concrete washout areas only.
• Do not wash out concrete onto non -formed areas, or into storm drains, open ditches,
streets, or streams.
• Wash equipment difficult to move, such as concrete paving machines, in areas that do not
directly drain to natural or constructed stormwater conveyance or potential infiltration areas.
• Do not allow excess concrete to be dumped on -site, except in designated concrete washout
areas as allowed above.
• Concrete washout areas may be prefabricated concrete washout containers, or self -
installed structures (above -grade or below -grade).
• Prefabricated containers are most resistant to damage and protect against spills and leaks.
Companies may offer delivery service and provide regular maintenance and disposal of
solid and liquid waste.
• If self -installed concrete washout areas are used, below -grade structures are preferred
over above -grade structures because they are less prone to spills and leaks.
• Self -installed above -grade structures should only be used if excavation is not practical.
• Concrete washout areas shall be constructed and maintained in sufficient quantity and size
to contain all liquid and concrete waste generated by washout operations.
Education
• Discuss the concrete management techniques described in this BMP with the ready -mix
concrete supplier before any deliveries are made.
• Educate employees and subcontractors on the concrete waste management techniques
described in this BMP.
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• Arrange for the contractor's superintendent or Certified Erosion and Sediment Control Lead
(CESCL) to oversee and enforce concrete waste management procedures.
• A sign should be installed adjacent to each concrete washout area to inform concrete equip-
ment operators to utilize the proper facilities.
Contracts
Incorporate requirements for concrete waste management into concrete supplier and sub-
contractor agreements.
Location and Placement
• Locate concrete washout areas at least 50 feet from sensitive areas such as storm drains,
open ditches, water bodies, or wetlands.
• Allow convenient access to the concrete washout area for concrete trucks, preferably near
the area where the concrete is being poured.
• If trucks need to leave a paved area to access the concrete washout area, prevent track -out
with a pad of rock or quarry spalls (see BMP C105: Stabilized Construction Access). These
areas should be far enough away from other construction traffic to reduce the likelihood of
accidental damage and spills.
• The number of concrete washout areas you install should depend on the expected demand
for storage capacity.
• On large sites with extensive concrete work, concrete washout areas should be placed in
multiple locations for ease of use by concrete truck drivers.
Concrete Truck Washout Procedures
• Washout of concrete truck drums shall be performed in designated concrete washout areas
only.
• Concrete washout from concrete pumper bins can be washed into concrete pumper trucks
and discharged into designated concrete washout areas or properly disposed of off -site.
Concrete Washout Area Installation
• Concrete washout areas should be constructed as shown in the figures below, with a recom-
mended minimum length and minimum width of 10 ft, but with sufficient quantity and volume
to contain all liquid and concrete waste generated by washout operations.
• Plastic lining material should be a minimum of 10 mil polyethylene sheeting and should be
free of holes, tears, or other defects that compromise the impermeability of the material.
• Lath and flagging should be commercial type.
• Liner seams shall be installed in accordance with manufacturers' recommendations.
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• Soil base shall be prepared free of rocks or other debris that may cause tears or holes in the
plastic lining material.
Maintenance Standards
Inspection and Maintenance
• Inspect and verify that concrete washout areas are in place prior to the commencement of
concrete work.
• Once concrete wastes are washed into the designated washout area and allowed to
harden, the concrete should be broken up, removed, and disposed of per applicable solid
waste regulations. Dispose of hardened concrete on a regular basis.
• During periods of concrete work, inspect the concrete washout areas daily to verify con-
tinued performance.
• Check overall condition and performance.
• Check remaining capacity (% full).
• If using self -installed concrete washout areas, verify plastic liners are intact and side -
walls are not damaged.
• If using prefabricated containers, check for leaks.
Maintain the concrete washout areas to provide adequate holding capacity with a minimum
freeboard of 12 inches.
Concrete washout areas must be cleaned, or new concrete washout areas must be con-
structed and ready for use once the concrete washout area is 75% full.
If the concrete washout area is nearing capacity, vacuum and dispose of the waste material
in an approved manner.
• Do not discharge liquid or slurry to waterways, storm drains or directly onto ground.
• Do not discharge to the sanitary sewer without local approval.
• Place a secure, non -collapsing, non -water collecting cover over the concrete
washout area prior to predicted wet weather to prevent accumulation and overflow of
precipitation.
• Remove and dispose of hardened concrete and return the structure to a functional
condition. Concrete may be reused on -site or hauled away for disposal or recycling.
When you remove materials from a self -installed concrete washout area, build a new struc-
ture; or, if the previous structure is still intact, inspect for signs of weakening or damage, and
make any necessary repairs. Re -line the structure with new plastic after each cleaning.
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Removal of Concrete Washout Areas
• When concrete washout areas are no longer required for the work, the hardened concrete,
slurries and liquids shall be removed and properly disposed of.
• Materials used to construct concrete washout areas shall be removed from the site of the
work and disposed of or recycled.
• Holes, depressions or other ground disturbance caused by the removal of the concrete
washout areas shall be backfilled, repaired, and stabilized to prevent erosion.
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Figure II-4.7: Concrete Washout Area with Wood Planks
77,
Type "Be
C
Lath and flagging
on 3 sides
Sandbag
3erm
10 mil plastic lining
A
1m /
f" /1 11 /1 Berm
Section A -A
,,.., ,..,.,,— lining
Notes:
1. Actual layout
determined in the field.
low Grade" 2. A concrete washout
sign shall be installed
within 10 m of the
temporary concrete
washout facility.
Sandbag
Stake (typ.)
iil plastic lining
Wood frame
securely fastened
around entire
perimeter with two
stakes
10 mil
plastic lining
2x12 rough Plan
wood frame
Type "Above Grade" with Wood Planks
NOT TO SCALE
00r�
Concrete Washout Area with Wood Planks
DEPARTMENT OF
ECOLOGY
State of Washington Revised June 2016
2024 Stormwater Management Manual for Western Washington
Volume 11 - Chapter 4 - Page 368
Figure II-4.8: Concrete Washout Area with Straw Bales
Straw bale
10 mil plastic lining
Binding wire
Staples
Native material
(2 per bale)
(optional)
Wood or
Plywood
metal stakes
1200 mm x 610 mm
Wood post
(2 per bale)
painted white
(89 mm x 89 mm
Lag screws
x 2.4 m)
Section B-B
(12.5 mm)� I :CONCRETE!�i
Black letters
WASHOUT
150 mm height
915 mm
3m Minimum
Stake (typ)
B1L Varies
Straw bale J
(typ•)
DEPARTMENT OF
ECOLOGY
State of Washington
Plan
u
u 915 mm
F
Concrete Washout Sign
Detail
(or equivalent)
�B
1 — -4 50 mm
200 mm (1�� 3.05 mm dia.
fsteel wire
Staple Detail
10 mil plastic lining
Notes:
1. Actual layout
determined in the field.
2. The concrete washout
sign shall be installed
within 10 m of the
temporary concrete
washout facility.
Type "Above Grade" with Straw Bales
NOT TO SCALE
Concrete Washout Area with Straw Bales
Revised June 2016
2024 Stormwater Management Manual for Western Washington
Volume 11 - Chapter 4 - Page 369
Figure II-4.9: Prefabricated Concrete Washout Container with Ramp
77=-
DEPARTMENT OF
ECOLOGY
State of Washington
NOT TO SCALE
Prefabricated Concrete Washout Container
with Ramp
Revised June 2016
2024 Stormwater Management Manual for Western Washington
Volume 11 - Chapter 4 - Page 370
BMP C160: Certified Erosion and Sediment Control
Lead
Purpose
The project proponent designates at least one person as the responsible representative in charge
of erosion and sediment control (ESC) and water quality protection. The designated person shall
be responsible for ensuring compliance with all local, state, and federal erosion and sediment con-
trol and water quality requirements. Construction sites one acre or larger that discharge to waters
of the State must designate a Certified Erosion and Sediment Control Lead (CESCL) as the
responsible representative.
Conditions of Use
A CESCL shall be made available on projects one acre or larger that discharge stormwater to sur-
face waters of the state. Sites less than one acre may have a person without CESCL certification
conduct inspections.
The CESCL shall:
• Have a current certificate proving attendance in an ESC training course that meets the min-
imum ESC training and certification requirements established by Ecology.
Ecology has provided the minimum requirements for CESCL course training, as well as a
list of ESC training and certification providers at:
https://ecology.wa.gov/Regulations-Permits/Permits-certifications/Certified-erosion-sed-
iment-cnntmi
OR
• Be a Certified Professional in Erosion and Sediment Control (CPESC). For additional
information go to:
http://www.envirocertintl.org/cpesc/
Specifications
• CESCL certification shall remain valid for three years.
• The CESCL shall have authority to act on behalf of the contractor or project proponent and
shall be available, or on -call, 24 hours per day throughout the period of construction.
• The Construction SWPPP shall include the name, telephone number, fax number, and
address of the designated CESCL. See II-3 Construction Stormwater Pollution Prevention
Plans (Construction SWPPPs).
• A CESCL may provide inspection and compliance services for multiple construction pro-
jects in the same geographic region, but must be on site whenever earthwork activities are
occurring that could generate release of turbid water.
2024 Stormwater Management Manual for Western Washington
Volume // - Chapter 4 - Page 371
• Duties and responsibilities of the CESCL shall include, but are not limited to, the following:
• Maintaining a permit file on site at all times which includes the Construction SWPPP
and any associated permits and plans.
• Directing BMP installation, inspection, maintenance, modification, and removal.
• Updating all project drawings and the Construction SWPPP with changes made.
• Completing any sampling requirements including reporting results using electronic
Discharge Monitoring Reports (WebDMR).
• Facilitating, participating in, and taking corrective actions resulting from inspections
performed by outside agencies or the owner.
• Keeping daily logs and inspection reports. Inspection reports should include:
■ Inspection date/time.
■ Weather information; general conditions during inspection and approximate
amount of precipitation since the last inspection.
■ Visual monitoring results, including a description of discharged stormwater.
The presence of suspended sediment, turbid water, discoloration, and oil
sheen shall be noted, as applicable.
■ Any water quality monitoring performed during inspection.
■ General comments and notes, including a brief description of any BMP repairs,
maintenance or installations made as a result of the inspection.
■ A summary or list of all BMPs implemented, including observations of all ESC
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.
BMP C162: Scheduling
Purpose
Sequencing a construction project can reduce 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 sediment control (ESC) measures planned for the
2024 Stormwater Management Manual for Western Washington
Volume 11 - Chapter 4 - Page 372
project. This type of schedule guides the contractor on work to be done before other work is star-
ted so that serious erosion and sedimentation problems can be avoided.
Following a specified work schedule that coordinates the timing of land -disturbing activities and
the installation of control measures is perhaps the most cost-effective way of controlling erosion
during construction. The removal of ground cover leaves a site vulnerable to erosion. Con-
struction sequencing that limits land clearing, provides timely installation of ESC BMPs, and
restores protective cover quickly can significantly reduce the erosion potential of a site.
Design Considerations
• Minimize construction during rainy periods.
• Schedule projects to disturb only small portions of the site at any one time. Complete grad-
ing 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 pro-
gresses.
2024 Stormwater Management Manual for Western Washington
Volume 11 - Chapter 4 - Page 373
BMP C208: Triangular Silt Dike (TSD)
Purpose
Triangular silt dikes (TSDs) may be used as check dams, for perimeter protection, for temporary
soil stockpile protection, for drop inlet protection, or as a temporary interceptor dike.
Conditions of Use
• TSDs maybe used on soil or pavement with adhesive or staples.
• TSDs have been used to build the following temporary BMPs:
• BMP C241: Sediment Pond (Temporary);
• BMP C200: Interceptor Dike and Swale;
• BMP C154: Concrete Washout Area;
• BMP C203: Water Bars;
• BMP C206: Level Spreader;
• BMP C220: Inlet Protection;
o RRAID (`)()7• (`hnf le rinmc
curbing; and
berms.
Design and Installation Specifications
• TSDs are made of urethane foam sewn into a woven geosynthetic fabric.
• TSDs are triangular, 10 to 14 inches high in the center, with a 20 to 28 inch base. A 2 foot
apron extends beyond both sides of the triangle along its standard section of 7 feet. A
sleeve at one end allows attachment of additional sections as needed.
• Install with ends curved up to prevent water from flowing around the ends.
• The fabric flaps and check dam units are attached to the ground with wire staples. Wire
staples should be No. 11 gauge wire and 200 to 300 mm in length.
• When multiple units are installed, the sleeve of fabric at the end of the unit shall overlap the
abutting unit and be stapled.
• When TSDs are used as check dams, the following guidelines apply:
TSDs should be located and installed as soon as construction will allow.
TSDs should be placed perpendicular to the flow of water.
2024 Stormwater Management Manual for Western Washington
Volume 11 - Chapter 4 - Page 398
The leading edge of the TSD must be secured with rocks, sandbags, or a small key
slot and staples.
In the case of grass -lined ditches and swales, check dams and accumulated sed-
iment shall be removed when the grass has matured sufficiently to protect the ditch or
swale unless the slope of the swale is greater than 4%. The area beneath the check
dams shall be seeded and mulched immediately after dam removal.
Maintenance Standards
• Inspect TSDs for performance and sediment accumulation during and after each rainfall
that produces runoff. Remove sediment when it reaches one half the height of the TSD.
• Anticipate submergence and deposition above the TSD and erosion from high flows around
the edges of the TSD. Immediately repair any damage or any undercutting of the TSD.
BMP C209: Outlet Protection
Purpose
Outlet protection prevents scour at conveyance outlets and minimizes the potential for down-
stream erosion by reducing the velocity of concentrated stormwater flows.
Conditions of Use
Use outlet protection at the outlets of all ponds, pipes, ditches, or other conveyances that dis-
charge to a natural or constructed drainage feature such as a stream, wetland, lake, or ditch.
Design and Installation Specifications
• The receiving channel at the outlet of a pipe shall be protected from erosion by lining a min-
imum of 6 feet downstream and extending up the channel sides a minimum of 1 foot above
the maximum tailwater elevation, or 1 foot above the crown, whichever is higher. For pipes
larger than 18 inches in diameter, the outlet protection lining of the channel shall be four
times the diameter of the outlet pipe.
• Standard wingwalls, tapered outlets, and paved channels should also be considered when
appropriate for permanent culvert outlet protection (WSDOT, 2015).
• BMP C122: Nets and Blankets or BMP C202: Riprap Channel Lining provide suitable
options for lining materials.
• With low flows, BMP C201: Grass -Lined Channels can be an effective alternative for lining
material.
• The following guidelines shall be used for outlet protection with riprap:
O If the discharge velocity at the outlet is less than 5 fps, use 2-inch to 8-inch riprap. Min-
imum thickness is 1 foot.
2024 Stormwater Management Manual for Western Washington
Volume 11 - Chapter 4 - Page 399
o For a 5 to 10 fps discharge velocity at the outlet, use 24-inch to 48-inch riprap. Min-
imum thickness is 2 feet.
o For outlets at the base of steep slope pipes (pipe slope greater than 10 percent), use
an engineered energy dissipator.
Filter fabric or erosion control blankets should always be used under riprap to prevent
scour and channel erosion. See BMP C122: Nets and Blankets.
• Bank stabilization, bioengineering, and habitat features maybe required for disturbed
areas. This work may require a Hydraulic Project Approval (HPA) from the Washington
State Department of Fish and Wildlife. See 1-2.14 Hydraulic Project Approvals.
Maintenance Standards
• Inspect and repair as needed.
• Add rock as needed to maintain the intended function.
• Clean energy dissipator if sediment builds up.
BMP C220: Inlet Protection
Purpose
Inlet protection prevents coarse sediment from entering drainage systems prior to permanent sta-
bilization of the disturbed area.
Conditions of Use
Use inlet protection at inlets that are operational before permanent stabilization of the disturbed
areas that contribute runoff to the inlet. Provide protection for all storm drain inlets downslope and
within 500 feet of a disturbed or construction area, unless those inlets are preceded by a sediment
trapping BMP.
Also consider inlet protection for lawn and yard drains on new home construction. These small
and numerous drains coupled with lack of gutters can add significant amounts of sediment into the
roof drain system. If possible, delay installing lawn and yard drains until just before landscaping,
or cap these drains to prevent sediment from entering the system until completion of landscaping.
Provide 18-inches of sod around each finished lawn and yard drain.
Table II-4.11: Storm Drain Inlet Protection lists several options for inlet protection. All of the meth-
ods for inlet protection tend to plug and require a high frequency of maintenance. Limit con-
tributing drainage areas for an individual inlet to one acre or less. If possible, provide emergency
overflows with additional end -of -pipe treatment where stormwater ponding would cause a hazard.
2024 Stormwater Management Manual for Western Washington
Volume 11 - Chapter 4 - Page 400
Table II-4.11: Storm Drain Inlet Protection
Type of Inlet Pro-
Emergency
Applicable for
tection
Overflow
Paved / Earthen
Conditions of Use
Surfaces
Drop Inlet Protection
Excavated drop
Yes, temporary
Applicable for heavy flows. Easy
inlet protection
flooding may
Earthen
to maintain. Large area requirement:
occur
30'x30'/acre
Block and gravel
Applicable for heavy concentrated flows.
drop inlet pro-
Yes
Paved or Earthen
Will not pond.
tection
Gravel and wire
Applicable for heavy concentrated flows.
drop inlet pro-
No
Paved or Earthen
Will pond. Can withstand traffic.
tection
Catch basin filters
Yes
Paved or Earthen
Frequent maintenance required.
Curb Inlet Protection
Curb inlet pro-
Small capacity
Used for sturdy, more compact install-
tection with
overflow
Paved
ation.
wooden weir
Block and gravel
curb inlet pro-
Yes
Paved
Sturdy, but limited filtration.
tection
Culvert Inlet Protection
Culvert inlet sed-
N/A
N/A
18 month expected life.
iment trap
Design and Installation Specifications
Excavated Drop Inlet Protection
Excavated drop inlet protection consists of an excavated impoundment around the storm drain
inlet. Sediment settles out of the stormwater prior to entering the storm drain. Design and install-
ation specifications for excavated drop inlet protection include:
• Provide a depth of 1 to 2 feet as measured from the crest of the inlet structure.
• Side slopes of excavation should be no steeper than 2HAV.
• Minimum volume of excavation is 35 cubic yards.
• Shape the excavation to fit the site, with the longest dimension oriented toward the longest
inflow area.
• Install provisions for draining to prevent standing water.
• Clear the area of all debris.
2024 Stormwater Management Manual for Western Washington
Volume // - Chapter 4 - Page 401
• Grade the approach to the inlet uniformly.
• Drill weep holes into the side of the inlet.
• Protect weep holes with screen wire and washed aggregate.
• Seal weep holes when removing structure and stabilizing area.
• Build a temporary dike, if necessary, to the down slope side of the structure to prevent
bypass flow.
Block and Gravel Filter
A block and gravel filter is a barrier formed around the inlet with standard concrete blocks and
gravel. See Figure II-4.17: Block and Gravel Filter. Design and installation specifications for block
and gravel filters include:
• Provide a height of 1 to 2 feet above the inlet.
• Recess the first row of blocks 2-inches into the ground for stability.
• Support subsequent courses by placing a pressure treated wood (2x4) through the block
opening.
• Do not use mortar.
• Lay some blocks in the bottom row on their side to allow for dewatering the pool.
• Place hardware cloth or comparable wire mesh with 0.5-inch openings over all block open-
ings.
• Place gravel to just below the top of blocks on slopes of 2HA V or flatter.
• An alternative design is a gravel berm surrounding the inlet, as follows:
• Provide a slope of 3H:1 V on the upstream side of the berm.
• Provide a slope of 2H:1 V on the downstream side of the berm.
• Provide a 1-foot wide level rock area between the gravel berm and the inlet.
• Use rocks 3 inches in diameter or larger on the upstream slope of the berm.
• Use gravel 0.5 to 0.75 inch at a minimum thickness of 1-foot on the downstream
slope of the berm.
2024 Stormwater Management Manual for Western Washington
Volume 11 - Chapter 4 - Page 402
Figure II-4.17: Block and Gravel Filter
A
Drain grate <_� °
o �o •��o� o0 a °�� � od4. o Concrete block
.01
0 00 0.0
0 00 O
C�r���°D1eo O4 :Q 0��p�0
dCN: °O ° o . Q o 0 °
Q�.°oa.00
vo0 oQ° °oo�a Gravel backfill
Q W.
CJ .0 °
°
Q°oo�o .o oo�a
d Qo�p°oo dOo°a° 10
o4�a°��de�
o
a� Qog "IC)04QQ odq o -°d oo�o
•v moo° °a
ey0 5�0� `�'• o°oo� °o0.Oo 000•
A
Plan View
Concrete block
Wire screen or
filter fabric
Gravel backfill _ Overflow
o.o water o Ponding height
0 . . ~ Water
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
00r�
Block and Gravel Filter
77�—_ Revised June 2016
DEPARTMENT OF
ECOLOGY
State of Washington
2024 Stormwater Management Manual for Western Washington
Volume 11 -Chapter 4 -Page 403
Gravel and Wire Mesh Filter
Gravel and wire mesh filters are gravel barriers placed over the top of the inlet. This method does
not provide an overflow. Design and installation specifications for gravel and wire mesh filters
include:
• Use a hardware cloth or comparable wire mesh with 0.5 inch openings.
• Place wire mesh over the drop inlet so that the wire extends a minimum of 1-foot bey-
ond each side of the inlet structure.
• Overlap the strips if more than one strip of mesh is necessary.
• Place coarse aggregate over the wire mesh.
o Provide at least a 12-inch depth of aggregate over the entire inlet opening and extend
at least 18-inches on all sides.
Catch Basin Filters
Catch basin filters are designed by manufacturers for construction sites. The limited sediment stor-
age capacity increases the amount of inspection and maintenance required, which may be daily
for heavy sediment loads. To reduce maintenance requirements, combine a catch basin 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. Design and
installation specifications for catch basin filters include:
• Provides 5 cubic feet of storage.
• Requires dewatering provisions.
• Provides a high -flow bypass that will not clog under normal use at a construction site.
• Insert the catch basin filter in the catch basin just below the grating.
Curb Inlet Protection with Wooden Weir
Curb inlet protection with wooden weir is an option that consists of a barrier formed around a curb
inlet with a wooden frame and gravel. Design and installation specifications for curb inlet pro-
tection with wooden weirs include:
• Use wire mesh with 0.5 inch openings.
• Use extra strength filter cloth.
• Construct a frame.
• Attach the wire and filter fabric to the frame.
• Pile coarse washed aggregate against the wire and fabric.
• Place weight on the frame anchors.
2024 Stormwater Management Manual for Western Washington
Volume 11 - Chapter 4 - Page 404
Block and Gravel Curb Inlet Protection
Block and gravel curb inlet protection is a barrier formed around a curb inlet with concrete blocks
and gravel. See Figure II-4.18: Block and Gravel Curb Inlet Protection. Design and installation spe-
cifications for block and gravel curb inlet protection include:
• Use wire mesh with 0.5 inch openings.
• Place two concrete blocks on their sides abutting the curb at either side of the inlet opening.
These are spacer blocks.
• Place a 2x4 stud through the outer holes of each spacer block to align the front blocks.
• Place blocks on their sides across the front of the inlet and abutting the spacer blocks.
• Place wire mesh over the outside vertical face.
• Pile coarse aggregate against the wire to the top of the barrier.
2024 Stormwater Management Manual for Western Washington
Volume 11 - Chapter 4 - Page 405
Figure II-4.18: Block and Gravel Curb Inlet Protection
n
Back of sidewalk
Back of curb
Wire scre
filter
3/.
Drain gravel Plan View
:ud
a block
Ponding height
Y4 inch (20 mm)
Drain gravel
— — — Overflow
Wire screen or
filter fabric 2x4 Wood
(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
80r�
Block and Gravel Curb Inlet Protection
DEPARTMENT OF
ECOLOGY
State of Washington Revised June 2016
2024 Stormwater Management Manual for Western Washington
Volume 11 - Chapter 4 - Page 406
Curb and Gutter Sediment Barrier
A curb and gutter sediment barrier is a sandbag or rock berm (riprap and aggregate) 3 feet high
and 3 feet wide in a horseshoe shape. See Figure II-4.19: Curb and Gutter Barrier. Design and
installation specifications for curb and gutter sediment barriers include:
Construct a horseshoe shaped berm, faced with coarse aggregate if using riprap, 3 feet
high and 3 feet wide, at least 2 feet from the inlet.
• Construct a horseshoe shaped sedimentation trap on the upstream side of the berm. Size
the trap to sediment trap standards for protecting a culvert inlet.
2024 Stormwater Management Manual for Western Washington
Volume 11 - Chapter 4 - Page 407
Figure II-4.19: Curb and Gutter Barrier
Back of sidewalk
Burlap sacks to
overlap onto curb Back of curb
Runoff Curb inlet
Runoff Spillway
Catch basin
Plan View
Gravel filled sandbags
stacked tightly
Notes:
1. Place curb type sediment barriers on gently sloping street segments, where water can
pond and allow sediment to separate from runoff.
2. Sandbags of either burlap or woven 'geotextile' fabric, are filled with gravel, layered
and packed tightly.
3. Leave a one sandbag gap in the top row to provide a spillway for overflow.
4. Inspect barriers and remove sediment after each storm event. Sediment and gravel
must be removed from the traveled way immediately. NOT TO SCALE
Curb and Gutter Barrier
77=-
DEPARTMENT OF
ECOLOGY
State of Washington
Revised June 2016
2024 Stormwater Management Manual for Western Washington
Volume 11 - Chapter 4 - Page 408
Maintenance Standards
Inspect all forms of inlet protection frequently, especially after storm events. Clean and
replace clogged catch basin filters. For rock and gravel filters, pull away the rocks from the
inlet and clean or replace. An alternative approach would be to use the clogged rock as fill
and put fresh rock around the inlet.
Do not wash sediment into storm drains while cleaning. Spread all excavated material
evenly over the surrounding land area or stockpile and stabilize as appropriate.
Approved as Functionally Equivalent
Ecology has approved products as able to meet the requirements of this BMP. The products did
not pass through the Technology Assessment Protocol — Ecology (TAPE) process. Local jur-
isdictions may choose not to accept these products, or may require additional testing prior to con-
sideration for local use. Products that Ecology has approved as functionally equivalent are
available for review on Ecology's website at:
https://ecology.wa.gov/Regulations-Permits/Guidance-technical-assistance/Stormwater-per-
mittee-guidance-resources/Emerging-stormwater-treatment-technologies
2024 Stormwater Management Manual for Western Washington
Volume 11 - Chapter 4 - Page 409
BMP C232: Gravel Filter Berm
Purpose
A gravel filter berm retains sediment by filtering runoff through a berm of gravel or crushed rock.
Conditions of Use
Use a gravel filter berm where a temporary measure is needed to retain sediment from con-
struction sites.
Do not place gravel filter berms in traffic areas; gravel filter berms are not intended to be driven
over.
Place gravel filter berms perpendicular to the flow of runoff, such that the runoff will filter through
the berm prior to leaving the site.
Design and Installation Specifications
• Berm material shall be 0.75 to 3 inches in size, washed well -graded gravel or crushed rock
with less than 5% fines. Do not use crushed concrete.
• Spacing of berms:
o Every 300 feet on slopes less than 5%
o Every 200 feet on slopes between 5% and 10%
o Every 100 feet on slopes greater than 10%
• Berm dimensions:
1 foot high with 3H:1 V side slopes
o 8 linear feet per 1 cfs runoff based on the 10-year, 24-hour design storm
• See Figure 11-4.21: Gravel Filter Berm for a photo of a gravel filter berm application.
Maintenance Standards
Regular inspection is required. Sediment shall be removed and filter material replaced as needed.
2024 Stormwater Management Manual for Western Washington
Volume 11 - Chapter 4 - Page 412
Figure II-4.21: Gravel Filter Berm
Gravel Filter Berm
DEPARTMENT OF
ECOLOGY
State of Washington
Revised July 2017
2024 Stormwater Management Manual for Western Washington
Volume 11 - Chapter 4 - Page 413
BMP C233: Silt Fence
Purpose
Silt fence reduces the transport of coarse sediment from a construction site by providing a tem-
porary physical barrier to sediment and reducing the runoff velocities of overland flow.
Conditions of Use
Silt fence may be used downslope of all disturbed areas.
• Silt fence shall prevent sediment carried by runoff from going beneath, through, or over the
top of the silt fence, but shall allow the water to pass through the fence.
Silt fence is not intended to treat concentrated flows, nor is it intended to treat substantial
amounts of overland flow. Convey any concentrated flows through the drainage system to a
sediment trapping BMP.
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.
2024 Stormwater Management Manual for Western Washington
Volume 11 - Chapter 4 - Page 414
Figure II-4.22: Silt Fence
Joints in geotextile 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
Minimum I I 6' max I
4"x4" trench I � I
u
Post spacing may be increased 2"x2" wood posts, steel
to 8' if wire backing is used fence posts, or equivalent
2"x2" by 14 Ga. wire or equivalent,
if standard strength fabric used
\�\\ Geotextile fabric
2' min
Backfill trench with
native soil or 3/4'
1.5" washed gravel min
Minimum
4"x4" trench
2"x2" wood posts, steel
fence posts, or equivalent NOT TO SCALE
Silt Fence
77�—
DEPARTMENT OF
ECOLOGY
State of Washington Revised July2017
2024 Stormwater Management Manual for Western Washington
Volume 11 - Chapter 4 - Page 415
Design and Installation Specifications
• Use in combination with other construction stormwater BMPs.
• Maximum slope steepness (perpendicular to the silt fence line)1 H:1 V.
• Maximum sheet or overland flow path length to the silt fence of 100 feet.
• Do not allow flows greater than 0.5 cfs.
• Use geotextile fabric that meets the following standards. All geotextile properties listed
below are minimum average roll values (i.e. the test result for any sampled roll in a lot shall
meet or exceed the values shown in Table II-4.12: Geotextile Fabric Standards for Silt
Fence):
Table II-4.12: Geotextile Fabric Standards for Silt Fence
Geotextile Property
Minimum Average Roll Value
0.60 mm maximum for slit film woven (#30 sieve).
Polymeric Mesh AOS
0.30 mm maximum for all other geotextile types (#50 sieve).
(ASTM D4751)
0.15 mm minimum for all fabric types (#100 sieve).
Water Permittivity
0.02 sec-1 minimum
(ASTM D4491)
Grab Tensile Strength
180 Ibs minimum for extra strength fabric.
(ASTM D4632)
100 Ibs minimum for standard strength fabric.
Grab Tensile Strength
30%maximum
(ASTM D4632)
Ultraviolet Resistance
70% minimum
(ASTM D4355)
• Support standard strength geotextiles with wire mesh, chicken wire, 2-inch x 2-inch wire,
safety fence, orjute mesh to increase the strength of the geotextile. Silt fence materials are
available that have synthetic mesh backing attached.
• Silt fence material shall contain ultraviolet ray inhibitors and stabilizers to provide a min-
imum of 6 months of expected usable construction life at a temperature range of 0°F to
120°F.
• 100% biodegradable silt fence is available that is strong, long lasting, and can be left in
place after the project is completed, if permitted by the local jurisdiction.
• Refer to Figure 11-4.22: Silt Fence for standard silt fence details. Include the following Stand-
ard Notes for silt fence on construction plans and specifications:
The Contractor shall install and maintain temporary silt fences at the locations shown
in the Plans.
2024 Stormwater Management Manual for Western Washington
Volume 11 - Chapter 4 - Page 416
2. Construct silt fences in areas of clearing, grading, or drainage prior to starting those
activities.
3. The silt fence shall have a 2-foot min. and a 2.5-feet max. height above the original
ground surface.
4. The geotextile fabric shall be sewn together at the point of manufacture to form fabric
lengths as required. Locate all sewn seams at support posts. Alternatively, two sec-
tions of silt fence can be overlapped, provided that the overlap is long enough and
that the adjacent silt fence sections are close enough together to prevent silt laden
water from escaping through the fence at the overlap.
5. Attach the geotextile fabric on the up -slope side of the posts and secure with staples,
wire, or in accordance with the manufacturer's recommendations. Attach the geo-
textile fabric to the posts in a manner that reduces the potential for tearing.
6. Support the geotextile 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 geotextile fabric up -slope of the
mesh.
Mesh support, if used, shall consist of steel wire with a maximum mesh spacing of 2-
inches, or a prefabricated polymeric mesh. The strength of the wire or polymeric
mesh shall be equivalent to or greater than 180 Ibs grab tensile strength. The poly-
meric mesh must be as resistant to the same level of ultraviolet radiation as the geo-
textile fabric it supports.
8. Bury the bottom of the geotextile fabric 4-inches min. below the ground surface. Back -
fill and tamp soil in place over the buried portion of the geotextile fabric, so that no
flow can pass beneath the silt fence and scouring cannot occur. When wire or poly-
meric back-up support mesh is used, the wire or polymeric mesh shall extend into the
ground 3-inches min.
9. Drive or place the silt 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 can-
not be reached. Increase fence post min. depths by 6 inches if the fence is located on
slopes of 3H:1 V or steeper and the slope is perpendicular to the fence. If required
post depths cannot be obtained, the posts shall be adequately secured by bracing or
guying to prevent overturning of the fence due to sediment loading.
10. Use wood, steel or equivalent posts. The spacing of the support posts shall be a max-
imum of 6 feet. Posts shall consist of one of the following:
• Wood with minimum dimensions of 2 inches by 2 inches by 3 feet. Wood shall
be free of defects such as knots, splits, or gouges.
• No. 6 steel rebar or larger.
• ASTM A 120 steel pipe with a minimum diameter of 1-inch.
• U, T, L, or C shape steel posts with a minimum weight of 1.35 Ibs./ft.
2024 Stormwater Management Manual for Western Washington
Volume 11 - Chapter 4 - Page 417
• 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
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:1 V.
• Check dams shall be approximately 1 foot deep at the back of the fence. 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.
• Check dams shall consist of crushed surfacing base course, gravel backfill for
walls, or shoulder ballast. Check dams shall be located every 10 feet along the
fence where the fence must cross contours.
• Refer to Figure II-4.23: Silt Fence Installation by Slicing Method for slicing method details.
The following are specifications for silt fence installation using the slicing method:
1. The base of both end posts must be at least 2 to 4 inches above the top of the geo-
textile fabric on the middle posts for ditch checks to drain properly. Use a hand level
or string level, if necessary, to mark base points before installation.
2. Install posts 3 to 4 feet apart in critical retention areas and 6 to 7 feet apart in stand-
ard applications.
3. Install posts 24 inches deep on the downstream side of the silt fence, and as close as
possible to the geotextile fabric, enabling posts to support the geotextile fabric from
upstream water pressure.
4. Install posts with the nipples facing away from the geotextile fabric.
5. Attach the geotextile fabric to each post with three ties, all spaced within the top 8
inches of the fabric. Attach each tie diagonally 45 degrees through the 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 the geotextile fabric around the end posts and
secure with 3 ties.
7. No more than 24 inches of a 36 inch geotextile fabric is allowed above ground level.
8. Compact the soil immediately next to the geotextile 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 the fabric deeper into the ground if necessary.
2024 Stormwater Management Manual for Western Washington
Volume 11 - Chapter 4 - Page 418
Figure II-4.23: Silt Fence Installation by Slicing Method
Ponding height max. 24"
Attach fabric to
upstream side of post
FLOW -
Drive over each side of
silt fence 2 to 4 times
with device exerting 60
p.s.i. or greater
100%
POST SPACING:
7' max. on open runs
4' max. on pooling areas
POST DEPTH:
As much below ground
as fabric above ground
100%
U)
No more than 24" of a 36"
fabric is allowed above ground
f Operation
Horizontal chisel point
(76 mm width)
Top of Fabric
Belt
top 8"
i
Diagonal attachment
doubles strength
Attachment Details:
• Gather fabric at posts, if needed.
• Utilize three ties per post, all within top 8"
of fabric.
• Position each tie diagonally, puncturing
holes vertically a minimum of 1" apart.
• Hang each tie on a post nipple and tighten
securely. Use cable ties (50 Ibs) or soft
wire.
Roll of silt fence
Slicing blade
(18 mm width)
Vibratory plow is not acceptable because of horizontal compaction
77=-
DEPARTMENT OF
ECOLOGY
State of Washington
Fabric
above
ground
200 -
300mm
F
Post
installed
after
compaction
Silt Fence
Completed Installation
NOT TO SCALE
Silt Fence Installation by Slicing Method
Revised June 2016
2024 Stormwater Management Manual for Western Washington
Volume 11 - Chapter 4 - Page 419
Maintenance Standards
• Repair any damage immediately.
• Intercept and convey all evident concentrated flows uphill of the silt fence to a sediment trap-
ping BMP.
• Check the uphill side of the silt 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 and remove the trapped sediment.
• Remove sediment deposits when the deposit reaches approximately one-third the height of
the silt fence, or install a second silt fence.
• Replace geotextile fabric that has deteriorated due to ultraviolet breakdown.
BMP C234: Vegetated Strip
Purpose
Vegetated strips reduce the transport of coarse sediment from a construction site by providing a
physical barrier to sediment and reducing the runoff velocities of overland flow.
Conditions of Use
• Vegetated strips may be used downslope of all disturbed areas.
Vegetated strips are not intended to treat concentrated flows, nor are they intended to treat
substantial amounts of overland flow. Any concentrated flows must be conveyed through
the drainage system to BMP C241: Sediment Pond (Temporary) or other sediment trapping
BMP. The only circumstance in which overland flow can be treated solely by a vegetated
strip, rather than by a sediment trapping BMP, is when the following criteria are met (see
Table I I-4.13: Contributing Drainage Area for Vegetated Strips):
Table II-4.13: Contributing Drainage Area for Vegetated Strips
Average Contributing
Area Slope
Average Contributing Area Per-
cent Slope
Maximum Contributing Area
Flowpath Length
1.5H : 1 V or flatter
67% or flatter
100 feet
2H : 1 V or flatter
50% or flatter
115 feet
4H : 1 V or flatter
25% or flatter
150 feet
6H : 1 V or flatter
16.7% or flatter
200 feet
1 OH : 1 V or flatter
10% or flatter
250 feet
2024 Stormwater Management Manual for Western Washington
Volume 11 - Chapter 4 - Page 420
Design and Installation Specifications
The vegetated strip shall consist of a continuous strip of dense vegetation with topsoil for a
minimum length of 25 feet along the flow path. Grass -covered, landscaped areas are gen-
erally not adequate because the volume of sediment overwhelms the grass. Ideally, veget-
ated strips shall consist of undisturbed native growth with a well -developed soil that allows
for infiltration of runoff.
• The slope within the vegetated strip shall not exceed 4H:1 V.
• The uphill boundary of the vegetated strip shall be delineated with clearing limits.
Maintenance Standards
• Any areas damaged by erosion or construction activity shall be seeded immediately and
protected by mulch.
• If more than 5 feet of the original vegetated strip width has had vegetation removed or is
being eroded, sod must be installed.
If there are indications that concentrated flows are traveling across the vegetated strip,
stormwater runoff controls must be installed to reduce the flows entering the vegetated
strip, or additional perimeter protection must be installed.
BMP C235: Wattles
Purpose
Wattles are temporary erosion and sediment control barriers consisting of straw, compost, or
other material that is wrapped in netting made of natural plant fiber or similar encasing material.
They reduce the velocity and can spread the flow of rill and sheet runoff, and can capture and
retain sediment.
Conditions of Use
• Use wattles:
o In disturbed areas that require immediate erosion protection.
On exposed soils during the period of short construction delays, or over winter
months.
o On slopes requiring stabilization until permanent vegetation can be established.
The material used dictates the effectiveness period of the wattle. Generally, wattles are
effective for one to two seasons.
• Prevent rilling beneath wattles by entrenching and overlapping wattles to prevent water
from passing between them.
2024 Stormwater Management Manual for Western Washington
Volume 11 - Chapter 4 - Page 421
Design Criteria
• Wattles shall consist of cylinders of plant material such as weed -free straw, coir, wood
chips, excelsior, or wood fiber or shavings encased within netting made of natural plant
fibers unaltered by synthetic materials.
• See Figure 11-4.24: Wattles for typical construction details.
• Wattles are typically 8 to 10 inches in diameter and 25 to 30 feet in length.
• Install wattles perpendicular to the flow direction and parallel to the slope contour.
• Place wattles in shallow trenches, staked along the contour of disturbed or newly con-
structed slopes. Dig narrow trenches across the slope (on contour) to a depth of 3 to 5
inches on clay soils and soils with gradual slopes. On loose soils, steep slopes, and areas
with high rainfall, the trenches should be dug to a depth of 5 to 7 inches, or 1/2 to 2/3 of the
thickness of the wattle.
• Start building trenches and installing wattles from the base of the slope and work up.
Spread excavated material evenly along the uphill slope and compact it using hand tamping
or other methods.
• Construct trenches at intervals of 10 to 25 feet depending on the steepness of the slope,
soil type, and rainfall. The steeper the slope the closer together the trenches.
• Install the wattles snugly into the trenches and overlap the ends of adjacent wattles 12
inches behind one another.
• Install stakes at each end of the wattle, and at 4 foot centers along entire length of wattle.
• If required, install pilot holes for the stakes using a straight bar to drive holes through the
wattle and into the soil.
• Wooden stakes should be approximately 0.75 x 0.75 x 24 inches minimum. Willow cuttings
or 3/8 inch rebar can also be used for stakes.
• Stakes should be driven through the middle of the wattle, leaving 2 to 3 inches of the stake
protruding above the wattle.
2024 Stormwater Management Manual for Western Washington
Volume 11 - Chapter 4 - Page 422
Figure 11-4.24: Wattles
Straw rolls must be
placed along slope
contours
10' - 25' (3-8m)
Spacing depends
on soil type and
slope steepness
Liv
3'- 4'
Overlap adjacent
\ rolls 1 behind
\ one another
d4
Sediment, organic matter,
and native seeds are
captured behind the rolls.
3" - 5" (75-125mm)
8" - 10" Dia.
(200-250mm)
1" x 1" Stake
l/ (25 x 25mm)
NOTE:
1. Straw roll installation requires the placement and secure staking
i of the roll in a trench, 3" - 5" (75-125mm) deep, dug on contour.
Runoff must not be allowed to run under or around roll. NOT TO SCALE
Wattles
77=-
DEPARTMENT OF
ECOLOGY
State of Washington
Revised December 2016
2024 Stormwater Management Manual for Western Washington
Volume 11 - Chapter 4 - Page 423
Maintenance Standards
• Wattles may require maintenance to ensure they are in contact with soil and thoroughly
entrenched, especially after significant rainfall on steep sandy soils.
Inspect the slope after significant storms and repair any areas where wattles are not tightly
abutted or water has scoured beneath the wattles.
Approved as Functionally Equivalent
Ecology has approved products as able to meet the requirements of this BMP. The products did
not pass through the Technology Assessment Protocol — Ecology (TAPE) process. Local jur-
isdictions may choose not to accept these products, or may require additional testing prior to con-
sideration for local use. Products that Ecology has approved as functionally equivalent are
available for review on Ecology's website at:
https://ecology.wa.gov/Regulations-Permits/Guidance-technical-assistance/Stormwater-per-
mittee-guidance-resources/Emerging-stormwater-treatment-technologies
BMP C236: Vegetative Filtration
Purpose
Vegetative filtration as a BMP is used in conjunction with detention storage in the form of portable
tanks or BMP C241: Sediment Pond (Temporary), BMP C206: Level Spreader, and a pumping
system with surface intake. Vegetative filtration improves turbidity levels of stormwater discharges
by filtering runoff through existing vegetation where undisturbed forest floor duff layer or estab-
lished lawn with thatch layer are present. Vegetative filtration can also be used to infiltrate dewa-
tering waste from foundations, vaults, and trenches as long as runoff does not occur.
Conditions of Use
• For every 5 acres of disturbed soil, use 1 acre of grass field, farm pasture, or wooded area.
Reduce or increase this area depending on project size, groundwater table height, and
other site conditions.
• Wetlands shall not be used for vegetative filtration.
• Do not use this BMP in areas with a high groundwater table, or in areas that will have a high
seasonal groundwater table during the use of this BMP.
• This BMP may be less effective on soils that prevent the infiltration of the water, such as
hard till.
• Using other effective source control measures throughout a construction site will prevent
the generation of additional highly turbid water and may reduce the time period or area
need for this BMP.
• Stop distributing water into the vegetated filtration area if standing water or erosion results.
2024 Stormwater Management Manual for Western Washington
Volume 11 - Chapter 4 - Page 424
• On large projects that phase the clearing of the site, areas retained with native vegetation
may be used as a temporary vegetative filtration area.
Design Criteria
• Find land adjacent to the project site that has a vegetated field, preferably a farm field or
wooded area.
• If the site does not contain enough vegetated field area consider obtaining permission from
adjacent landowners (especially for farm fields).
• Install a pump and downstream distribution manifold depending on the project size. Gen-
erally, the main distribution line should reach 100 to 200 feet long. Large projects, or pro-
jects on tight soil, will require systems that reach several thousand feet long with numerous
branch lines off of the main distribution line.
• The manifold should have several valves, allowing for control over the distribution area in
the field.
• Install several branches of 4 inch diameter schedule 20 polyvinyl chloride (PVC), swaged -fit
common septic tight -lined sewer line, or 6 inch diameter fire hose, which can convey the tur-
bid water out to various sections of the field. See Figure II-4.25: Manifold and Branches in a
Wooded, Vegetated Spray Field.
• Determine the branch length based on the field area geography and number of branches.
Typically, branches stretch from 200 feet to several thousand feet. Lay the branches on con-
tour with the slope.
• On uneven ground, sprinklers perform well. Space sprinkler heads so that spray patterns
do not overlap.
• On relatively even surfaces, a level spreader using 4 inch diameter perforated pipe may be
used as an alternative option to the sprinkler head setup. Install drain pipe at the highest
point on the field and at various lower elevations to ensure full coverage of the filtration
area. Place the pipe with the holes up to allow for gentle weeping evenly out all holes. Lev-
eling the pipe by staking and using sandbags may be required.
• To prevent over saturating of the vegetative filtration area, rotate the use of branches or
spray heads. Repeat as needed based on monitoring of the spray field.
Table II-4.14: Flowpath Guidelines for Vegetative
Filtration
Average Slope
Average Area % Slope
Estimated Flowpath Length (ft)
1.5H:1 V
67%
250
2H:1 V
50%
200
4H:1 V
25%
150
6H:1 V
16.7%
115
10H:1 V
10%
100
2024 Stormwater Management Manual for Western Washington
Volume 11 - Chapter 4 - Page 425
Figure II-4.25: Manifold and Branches in a Wooded, Vegetated Spray
Field
WWI
DEPARTMENT OF
ECOLOGY
State of Washington
NOT TO SCALE
Manifold and Branches in a Wooded,
Vegetated Spray Field
Revised June 2016
2024 Stormwater Management Manual for Western Washington
Volume 11 - Chapter 4 - Page 426
Maintenance Standards
• Monitor the spray field on a daily basis to ensure that over saturation of any portion of the
field does not occur at any time. The presence of standing puddles of water or creation of
concentrated flows visually signify that over saturation of the field has occurred.
• Monitor the vegetated spray field all the way down to the nearest surface water, or farthest
spray area, to ensure that the water has not caused overland or concentrated flows, and
has not created erosion around the spray nozzle(s).
• Do not exceed water quality standards for turbidity.
• Ecology recommends that a separate inspection log be developed, maintained, and kept
with the existing site logbook to aid the operator conducting inspections. This separate
"Field Filtration Logbook" can also aid in demonstrating compliance with permit conditions.
• Inspect the spray nozzles daily, at a minimum, for leaks and plugging from sediment
particles.
• If erosion, concentrated flows, or over saturation of the field occurs, rotate the use of
branches or spray heads or move the branches to a new field location.
• Check all branches and the manifold for unintended leaks.
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 during construction. Sediment traps, along with other perimeter controls, shall
be installed before any land disturbance takes place in the contributing drainage area.
Conditions of Use
Sediment traps are intended for use on sites where the contributing drainage area is less
than 3 acres, with no unusual drainage features, and a projected build -out time of 6 months
or less. The sediment trap is a temporary measure (with a design life of approximately 6
months) and shall be maintained until the contributing drainage area is permanently pro-
tected against erosion by vegetation and/or structures.
Sediment traps 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.
Projects that are constructing permanent Flow Control BMPs, or permanent Runoff Treat-
ment BMPs that use ponding for treatment, may use the rough -graded or final -graded per-
manent BMP footprint for the temporary sediment trap. When permanent BMP footprints
are used as temporary sediment traps, the surface area requirement of the sediment trap
must be met. If the surface area requirement of the sediment trap is larger than the surface
area of the permanent BMP, then the sediment trap shall be enlarged beyond the
2024 Stormwater Management Manual for Western Washington
Volume 11 - Chapter 4 - Page 427
permanent BMP footprint to comply with the surface area requirement.
A floating pond skimmer may be used for the sediment trap outlet if approved by the Local
Permitting Authority.
• Sediment traps may not be feasible on utility projects due to the limited work space or the
short-term nature of the work. Portable tanks may be used in place of sediment traps for util-
ity projects.
Design and Installation Specifications
• See Figure II-4.26: Cross Section of Sediment Trap and Figure II-4.27: Sediment Trap Out-
let for details.
• 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:
SA = Design surface area of the trap (square feet)
FS = A safety factor of 2 to account for non -ideal settling.
Q2 = The peak volumetric flow rate (cubic feet per second), calculated using one of the fol-
lowing options:
o Option 1 - Single Event Hydrograph Method
The peak volumetric flow rate calculated using a 10-minute time step from a Type 1A,
2-year, 24-hour frequency storm for the developed condition. The 10-year peak volu-
metric flow rate shall be used if the project size, expected timing and duration of con-
struction, or downstream conditions warrant a higher level of protection.
on 2 - The Rational Method
For construction sites that are less than 1 acre, the peak volumetric flow rate cal-
culated using the Rational Method.
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.
Therefore, the equation for computing sediment trap surface area becomes:
SA = 2 x Q2/0.00096
or
2080 square feet per cfs of inflow
2024 Stormwater Management Manual for Western Washington
Volume 11 - Chapter 4 - Page 428
Sediment trap depth shall be 3.5 feet minimum from the bottom of the trap to the top of the
overflow weir.
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.
• Design the discharge from the sediment trap by using the guidance for discharge from tem-
porary sediment ponds in BMP C241: Sediment Pond (Temporary).
Maintenance Standards
• Sediment shall be removed from the trap when it reaches 1 foot in depth.
• Any damage to the trap embankments or slopes shall be repaired.
2024 Stormwater Management Manual for Western Washington
Volume 11 - Chapter 4 - Page 429
Figure 11-4.26: Cross Section of Sediment Trap
Surface area determined
at top of weir
II'Min.
3.5' - 5'
Flat Bottom
Note: Trap may be formed by berm or by
partial or complete excavation.
000�
DEPARTMENT OF
ECOLOGY
State of Washington
1.5' Min.
a 4'Min.
Overflow
I'Min.
I'Min.
`� f
3/,, , -
Washed l gravel
Geotextile
2" - 4" Rock
Rip Rap
Cross Section of Sediment Trap
Discharge to
stabilized
conveyance,
outlet, or level
spreader
NOT TO SCALE
Revised June 2016
2024 Stormwater Management Manual for Western Washington
Volume 11 - Chapter 4 - Page 430