2021.0053 21-120 RPT-SWPPP 2021-09-23
STORMWATER POLLUTION PREVENTION PLAN (SWPPP)
(REQUIREMENT #2) REPORT
of
Farrelli’s Yelm
813 W Yelm Avenue
Yelm, Washington 98597
for
Blackrock Industries
1106 39th Ave SE
Puyallup, WA 98374
by
THE LAND DEVELOPER’S
ENGINEERED SOLUTION
A Division of THE LAND DEVELOPER, LLC
Erik B. Ainsworth, PE
PO Box 4420
Tumwater, WA 98501
(360) 250-3973
September 23, 2021
Farrelli’s Yelm September 23, 2021 PAGE 2
TABLE OF CONTENTS
I. SWPPP (REQUIREMENT 2) CONSTRUCTION STORMWATER
POLLUTION PREVENTION PLAN (SWPPP) ............................................ 3
Element 1: Preserve vegetation/Mark Clearing Limits ............................................. 3
Element 2: Establish Construction Access .............................................................. 3
Element 3: Control Flow Rates (Not required this project, threshold not met) ........ 4
Element 4: Install Sediment Controls ....................................................................... 4
Element 5: Stabilize Soils ........................................................................................ 4
Element 6: Protect Slopes ....................................................................................... 5
Element 7: Protect Drain Inlets ................................................................................ 6
Element 8: Stabilize Channels and Outlets (Not applicable) ................................... 6
Element 9: Control Pollutants .................................................................................. 7
Element 10: Control Dewatering (Not applicable) ................................................... 7
Element 11: Maintain BMPs .................................................................................... 8
Element 12: Manage the Project ............................................................................. 8
Element 13: Protect Low Impact Development BMP’s .......................................... 10
II. CONSTRUCTION PHASING AND BMP IMPLEMENTATION ................. 11
III. SITE INSPECTION AND MONITORING .................................................. 12
VIII. APPENDICES
Appendix A Erosion Control Best Management Practices (BMP)
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I. SWPPP (REQUIREMENT 2) CONSTRUCTION
STORMWATER POLLUTION PREVENTION PLAN
(SWPPP)
Please reference Appendix A for construction plan sheets and Appendix B for applicable Erosion
and Sediment Control Best Management Practices (BMP).
Element 1: Preserve vegetation/Mark Clearing Limits
• Prior to beginning land disturbing activities, including clearing and grading, clearly mark all
clearing limits, sensitive areas and their buffers, and trees that are to be preserved within the
construction area. These shall be clearly marked, both in the field and on the plans, 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 on site, covered to prevent erosion, and replaced immediately upon completion of the
ground disturbing activities.
• Suggested BMPs:
• BMP C101: Preserving Natural Vegetation
• BMP C102: Buffer Zones
• BMP C103: High Visibility Plastic Fence.
Element 2: Establish Construction Access
• Construction vehicle access and exit shall be limited to one route, if possible, or two for linear
projects such as roadways where more than one access is necessary for large equipment
maneuvering.
• Access points shall be stabilized with a pad of quarry spalls, crushed rock, or equivalent BMP
prior to traffic leaving the construction site to minimize the tracking of sediment onto all roads and
accesses.
• Wheel wash or tire baths should be located on site, if the stabilized constructions entrance is not
effective in preventing sediment from being tracked onto roads/accesses.
• If sediment is tracked off site, roads/accesses 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. Sediment shall be removed from 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 controlled by pumping back on site to an approved infiltration
facility, or otherwise must be prevented from discharging into systems tributary to state surface
waters. Options include discharge to the sanitary sewer, or discharge to an approved offsite
Farrelli’s Yelm September 23, 2021 PAGE 4
treatment system. For discharges to the sanitary sewer, permits must be obtained from the County
Industrial Pretreatment Program at (253) 798-3013.
• Suggested BMPs:
• BMP C105: Stabilized Construction Entrance
• BMP C107: Construction Road/Parking Area Stabilization.
Element 3: Control Flow Rates (Not required this project, threshold not met)
Element 4: Install Sediment Controls
• Prior to leaving a construction site or prior to discharge to an infiltration facility, stormwater runoff
from disturbed areas shall pass through a sediment pond or other appropriate sediment removal
BMP. Runoff from fully stabilized areas (see Element #5 second bullet item) may be discharged
without a sediment removal BMP, but must meet the flow control performance standard of Element
#3 (first bullet item).
• Sediment ponds, vegetated buffer strips, sediment barriers or filters, dikes, and other 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.
• Earthen structures such as dams, dikes, and diversions shall be seeded and mulched according
to the timing indicated in Element #5.
• BMPs intended to trap sediment on site must be located in a manner to avoid interference with
the movement of juvenile salmonids attempting to enter off-channel areas or drainages, often
during non-storm events, in response to rain event changes in stream elevation or wetted area.
• Suggested BMPs:
• BMP C233: Silt Fence
• BMP C234: Vegetated Strip
Element 5: Stabilize Soils
• 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.
• Full stabilization means all soil disturbing activities at the site have been completed and areas
where the soil or natural vegetative cover has been disturbed have been properly covered and
accepted to meet permanent erosion control. Permanent erosion control can
include concrete or asphalt paving; quarry spalls used as ditch lining; application of thick layers of
gravel or mulch; or vegetative cover in a manner that will fully prevent soil erosion. Where the term
"fully established" is used to describe vegetative cover or plantings, it shall be understood to mean
that healthy vegetation covers 90 percent of exposed bare soil. The application of hydroseeding,
even in conjunction with a bonded fiber matrix (BFM) or rolled erosion product, will not be accepted
as fully established permanent erosion control before the necessary development and ground
cover requirements of the plantings are met. The strong root structures of well established
vegetation are an essential mechanism in controlling soil erosion. The county will inspect and must
approve all areas as fully stabilized before the release of financial guarantees.
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• Temporary erosion control measures shall remain in place until permanent measures are
established.
• 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 groundwater.
• 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 restabilize the disturbed soils so that:
• 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.
• Permanent site stability will be achieved by hydroseeding, mulch and placing beauty bark on
disturbed areas. Coordinate with owner for location of each permanent BMP.
Suggested BMPs:
• BMP C120: Temporary and Permanent Seeding
• BMP C121: Mulching
• BMP C123: Plastic Covering
• BMP C124: Sodding
• BMP C125: Topsoiling
• BMP C140: Dust Control.
Element 6: Protect Slopes
• Design and construct cut and fill slopes in a manner that will minimize erosion. Cover slopes with
plastic covering BMP C123 as necessary to minimize erosion.
• Consider soil type and its potential for erosion.
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• Reduce slope runoff velocities by reducing continuous length of slope with terracing and
diversions, reduce slope steepness, and roughen slope surface.
• Offsite stormwater (run-on) shall be diverted away from slopes and disturbed areas with
interceptor dikes and/or swales. Offsite stormwater must be managed separately from stormwater
generated on the site.
• At the top of slopes, collect drainage in pipe slope drains or protected channels to prevent
erosion. Temporary pipe slope drains shall handle the peak flow from a 10-year, 24-hour event
assuming a Type 1A rainfall distribution. Alternatively, the 10-year, 1-hour time step flow rates
indicated by an approved continuous runoff model, increased by a factor of 1.6, may be used. If a
15-minute (or less) time step is used, no correction factor is required. The hydrologic analysis shall
use the existing land cover condition for predicting flow rates from tributary areas outside the
project limits. For tributary areas on the project site, the analysis shall use the temporary or
permanent project land cover condition, whichever will produce the highest flow rates.
• Permanent pipe slope drains shall be sized for the 100-year, 24-hour event.
• Provide drainage to remove groundwater intersecting the slope surface of exposed soil areas.
• Excavated material shall be placed on the uphill side of trenches, consistent with safety and
space considerations.
• Check dams shall be placed at regular intervals within channels that are cut down a slope.
• Stabilize soils on slopes, as specified in Element #5.
• Suggested BMPs:
• BMP C120: Temporary and Permanent Seeding
Element 7: Protect Drain Inlets
• 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 wastewater shall be controlled
as specified above in Element #2.
• 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.
Element 8: Stabilize Channels and Outlets (Not applicable)
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Element 9: Control Pollutants
• All pollutants, including waste materials and demolition debris, that occur onsite shall be handled
and disposed of in a manner that does not cause contamination of stormwater. 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 other materials that have the potential to pose a threat to human
health or the environment. Onsite fueling tanks shall include secondary containment.
• Maintenance and repair of heavy equipment and vehicles involving oil changes, hydraulic system
drain down, solvent and de-greasing cleaning operations, fuel tank drain down and removal, and
other activities which may result in discharge or spillage of pollutants to the ground or into
stormwater runoff must be conducted using spill prevention measures, such as drip pans.
Contaminated surfaces shall be cleaned immediately following any discharge or spill incident.
Emergency repairs may be performed on site using temporary plastic placed beneath and, if
raining, over the vehicle.
• Wheel wash or tire bath wastewater shall be discharged to a separate onsite treatment system or
to the sanitary sewer. • Application of agricultural chemicals, including fertilizers and pesticides,
shall be conducted in a manner and at application rates that will not result in loss of chemical to
stormwater runoff. Manufacturers’ recommendations for application rates and procedures shall be
followed.
• BMPs shall be used to prevent or treat contamination of stormwater runoff by pH modifying
sources. These sources include, but are not limited to, bulk cement, cement kiln dust, fly ash, new
concrete washing and curing waters, waste streams generated from concrete grinding and sawing,
exposed aggregate processes, and concrete pumping and mixer washout waters. Stormwater
discharges shall not cause or contribute to a violation of the water quality standard for pH in the
receiving water.
• Construction sites shall adjust the pH of stormwater if necessary to prevent violations of water
quality standards. Projects must obtain written approval from the Department of Ecology prior to
using chemical treatment other than CO2 or dry ice to adjust pH.
• Suggested BMPs:
• BMP C151: Concrete Handling
• BMP C152: Sawcutting and Surfacing Pollution Prevention
• See Volume IV – Source Control BMPs.
Element 10: Control Dewatering (Not applicable)
• Foundation, vault, and trench dewatering water, which have similar characteristics to stormwater
runoff at the site, shall be discharged into a controlled conveyance system prior to discharge to a
sediment trap or sediment pond. Channels must be stabilized, as specified in Element #8.
• Clean, non-turbid dewatering water, such as well-point groundwater, can be discharged to
systems tributary to state surface waters, as specified in Element #8, provided the dewatering flow
does not cause erosion or flooding of receiving waters. These clean waters should not be routed
through stormwater sediment ponds.
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• 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:
• Infiltration
• Transport offsite in a vehicle, such as a vacuum flush truck, for legal disposal in a manner
that does not pollute state waters
• Ecology-approved onsite chemical treatment or other suitable treatment technologies
• Sanitary sewer discharge with local sewer district approval, if there is no other option
• Use of a sedimentation bag with outfall to a ditch or swale for small volumes of localized
dewatering.
Element 11: Maintain BMPs
• All temporary and permanent ESC 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 BMP specifications.
• All temporary ESC BMPs shall be removed within 30 days after final site stabilization is achieved
or after the temporary BMPs are no longer needed. Trapped sediment shall be removed or
stabilized on site. Disturbed soil resulting from removal of BMPs
or vegetation shall be permanently stabilized.
Element 12: Manage the Project
Phasing of Construction
• Development projects shall be phased where feasible in order to prevent soil erosion and, to the
maximum extent practicable, the transport of sediment from the site during construction.
Revegetation of exposed areas and maintenance of that vegetation shall be an integral part of the
clearing activities for any phase.
• Clearing and grading activities for developments shall be permitted only if conducted pursuant to
an approved site development plan (e.g., subdivision approval) that establishes permitted areas of
clearing, grading, cutting, and filling. When establishing these permitted clearing and grading
areas, consideration should be given to minimizing removal of existing trees and minimizing
disturbance/compaction of native soils except as needed for building purposes. These permitted
clearing and grading areas and any other areas required to preserve critical or sensitive areas,
buffers, native growth protection easements, or tree retention areas as may be required by local
jurisdictions, shall be delineated on the site plans and the development site.
• 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 county that silt-laden runoff will be prevented from
leaving the site through a combination of the following:
• Site conditions including existing vegetative coverage, slope, soil type, and proximity to
receiving waters
• Limitations on activities and the extent of disturbed areas
• Proposed ESC measures.
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• Based on the information provided and/or local weather conditions, the county may expand or
restrict the seasonal limitation on site disturbance. The county 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
• If clearing and grading limits or ESC measures shown in the approved plan are not
maintained.
• The following activities are exempt from the seasonal clearing and grading limitations:
• Routine maintenance and necessary repair of ESC BMPs
• 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
• Activities where there is 100 percent infiltration of surface water runoff within the site in
approved and installed ESC facilities.
Coordination with Utilities and Other Contractors
• The primary project applicant shall evaluate, with input from utilities and other contractors, the
stormwater management requirements for the entire project, including the utilities, when preparing
the Construction SWPPP.
• 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 ESC. 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 ESC measures used to control the
quality of stormwater discharges.
• For construction sites that will disturb 1 acre or more and that discharge stormwater to
surface waters of the state, a Certified Erosion and Sediment Control Lead (CESCL) shall
be identified in the Construction SWPPP and shall be on site or on-call at all times.
Certification may be obtained through an approved training program that meets the ESC
training standards established by Ecology.
• 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.
• Maintaining an updated Construction SWPPP:
• The Construction SWPPP shall be retained on site or within reasonable access to the site.
• The SWPPP shall be modified whenever there is a change in the design, construction,
operation, or maintenance at the construction site that has, or could have, a significant
effect on the discharge of pollutants to waters of the state.
• The SWPPP shall be modified if, during inspections or investigations conducted by the
owner/operator, or the applicable local or state regulatory authority, it is determined that
the SWPPP is ineffective in eliminating or significantly minimizing pollutants in stormwater
discharges from the site. The SWPPP shall be m odified as necessary to include additional
or modified BMPs designed to correct problems identified. Revisions to the SWPPP shall
be completed within 7 days following the inspection.
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Element 13: Protect Low Impact Development BMP’s
Phasing of Construction
• Protect all Bioretention and Rain Garden BMPs from sedimentation through
installation and maintenance of Construction SWPPP BMPs on portions of the
site that drain into the Bioretention and/or Rain Garden BMPs. Restore the BMPs
to their fully functioning condition if they accumulate sediment during
construction. Restoring the BMP must include removal of sediment and any
sediment-laden Bioretention/Rain Garden soils, and replacing the removed soils
with soils meeting the design specification.
• Prevent compacting Bioretention and Rain Garden BMPs by excluding
construction equipment and foot traffic. Protect completed lawn and
landscaped areas from compaction due to construction equipment.
• Control erosion and avoid introducing sediment from surrounding land uses onto permeable pavements. Do not allow muddy construction equipment on the base material or pavement. Do not allow sediment-laden runoff onto permeable pavements, including permeable pavement subgrade, reservoir course, or wearing course.
• Pavements fouled with sediments or no longer passing an initial infiltration test
must be cleaned using procedures shown in Volume III of this manual or the
manufacturer’s procedures.
• Keep all heavy equipment off existing soils under LID facilities that have
been excavated to final grade to retain the infiltration rate of the soils.
• See Section 3.3 for more details on protecting LID BMPs.
• Suggested BMPs:
• BMP C102: Buffer Zone
• BMP C103: High Visibility Fence
Farrelli’s Yelm September 23, 2021 PAGE 11
• BMP C233: Silt Fence
• BMP C234: Vegetated Strip
• BMP C235: Straw Wattles
II. CONSTRUCTION PHASING AND BMP
IMPLEMENTATION
The BMP implementation schedule will be driven by the construction schedule. The following
provides a sequential list of the proposed construction schedule milestones and the corresponding
BMP implementation schedule. The list contains key milestones such as wet season construction.
The BMP implementation schedule listed below is keyed to proposed phases of construction
project, and reflects differences in BMP installations and inspections that relate to wet season
construction. The project site is located west of the Cascade Mountain Crest. As such, the dry
season is considered to be from May 1 to September 30 and the wet season is considered to be
from October 1 to April 30.
Contractor will verify dates below.
Estimated construction start date (during wet season):
Estimated construction end date:
Mobilize equipment on-site:
Mobilize and store all ESC and soil stabilization products
Install ESC measures:
Install stabilized construction entrance:
Begin clearing and grading:
Begin site grading:
Site inspections and monitoring conducted weekly and for
applicable rain events:
Implement Element #12 BMP’s and manage site to minimize
soil disturbance during the wet season:
Final landscaping and planting begins:
Permanent erosion control measures:
Farrelli’s Yelm September 23, 2021 PAGE 12
III. SITE INSPECTION AND MONITORING
Monitoring includes visual inspection and monitoring for water quality parameters of concern, and
documentation of the inspection and monitoring findings in a site log book. A site log book shall be
maintained for all on-site construction activities and shall include:
1. A record of the implementation of the erosion control plan BMP’s.
2. Site Inspections.
SITE INSPECTION
All BMP’s shall be inspected, maintained, and repaired as needed to assure continued
performance of their intended function.
Site inspection shall occur in all areas disturbed by construction activities and at all stormwater
discharge points. The site inspection shall evaluate and document the effectiveness of the
installed BMP’s and determine if it is necessary to repair or replace any of the BMP’s to improve
the quality of stormwater discharges. All maintenance and repairs shall be documented in the site
log book or forms provided in this document. All new BMP’s or design changes shall be
documented as soon as possible.
SITE INSPECTION FREQUENCY
Site inspections shall be conducted at least once a week and within 24 hours following any rainfall
event which causes a discharge of stormwater from the site. For sites with temporary stabilization
measures, the site inspection frequency can be reduce to once every month.
Farrelli’s Yelm September 23, 2021
APPENDIX B – EROSION CONTROL BMP’S
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BMP C101: Preserving Natural Vegetation
Purpose The purpose of preserving natural vegetation is to reduce erosion wherever
practicable. Limiting site disturbance is the single most effective method
for reducing erosion. For example, conifers can hold up to about 50
percent of all rain that falls during a storm. Up to 20-30 percent of this rain
may never reach the ground but is taken up by the tree or evaporates.
Another benefit is that the rain held in the tree can be released slowly to
the ground after the storm.
Conditions of Use Natural vegetation should be preserved on steep slopes, near perennial
and intermittent watercourses or swales, and on building sites in wooded
areas.
• As required by local governments.
• Phase construction to preserve natural vegetation on the project site for
as long as possible during the construction period.
Design and
Installation
Specifications
Natural vegetation can be preserved in natural clumps or as individual
trees, shrubs and vines.
The preservation of individual plants is more difficult because heavy
equipment is generally used to remove unwanted vegetation. The points
to remember when attempting to save individual plants are:
• Is the plant worth saving? Consider the location, species, size, age, vigor,
and the work involved. Local governments may also have ordinances to
save natural vegetation and trees.
• Fence or clearly mark areas around trees that are to be saved. It is
preferable to keep ground disturbance away from the trees at least as
far out as the dripline.
Plants need protection from three kinds of injuries:
• Construction Equipment - This injury can be above or below the
ground level. Damage results from scarring, cutting of roots, and
compaction of the soil. Placing a fenced buffer zone around plants to
be saved prior to construction can prevent construction equipment
injuries.
• Grade Changes - Changing the natural ground level will alter grades,
which affects the plant's ability to obtain the necessary air, water, and
minerals. Minor fills usually do not cause problems although
sensitivity between species does vary and should be checked. Trees
can typically tolerate fill of 6 inches or less. For shrubs and other
plants, the fill should be less.
When there are major changes in grade, it may become necessary to
supply air to the roots of plants. This can be done by placing a layer of
gravel and a tile system over the roots before the fill is made. A tile
system protects a tree from a raised grade. The tile system should be
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laid out on the original grade leading from a dry well around the tree
trunk. The system should then be covered with small stones to allow
air to circulate over the root area.
Lowering the natural ground level can seriously damage trees and
shrubs. The highest percentage of the plant roots are in the upper 12
inches of the soil and cuts of only 2-3 inches can cause serious injury.
To protect the roots it may be necessary to terrace the immediate area
around the plants to be saved. If roots are exposed, construction of
retaining walls may be needed to keep the soil in place. Plants can also
be preserved by leaving them on an undisturbed, gently sloping
mound. To increase the chances for survival, it is best to limit grade
changes and other soil disturbances to areas outside the dripline of the
plant.
• Excavations - Protect trees and other plants when excavating for
drainfields, power, water, and sewer lines. Where possible, the
trenches should be routed around trees and large shrubs. When this is
not possible, it is best to tunnel under them. This can be done with
hand tools or with power augers. If it is not possible to route the trench
around plants to be saved, then the following should be observed:
Cut as few roots as possible. When you have to cut, cut clean. Paint
cut root ends with a wood dressing like asphalt base paint if roots will
be exposed for more than 24-hours.
Backfill the trench as soon as possible.
Tunnel beneath root systems as close to the center of the main trunk to
preserve most of the important feeder roots.
Some problems that can be encountered with a few specific trees are:
• Maple, Dogwood, Red alder, Western hemlock, Western red cedar,
and Douglas fir do not readily adjust to changes in environment and
special care should be taken to protect these trees.
• The windthrow hazard of Pacific silver fir and madrona is high, while
that of Western hemlock is moderate. The danger of windthrow
increases where dense stands have been thinned. Other species (unless
they are on shallow, wet soils less than 20 inches deep) have a low
windthrow hazard.
• Cottonwoods, maples, and willows have water-seeking roots. These
can cause trouble in sewer lines and infiltration fields. On the other
hand, they thrive in high moisture conditions that other trees would
not.
• Thinning operations in pure or mixed stands of Grand fir, Pacific silver
fir, Noble fir, Sitka spruce, Western red cedar, Western hemlock,
Pacific dogwood, and Red alder can cause serious disease problems.
Disease can become established through damaged limbs, trunks, roots,
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and freshly cut stumps. Diseased and weakened trees are also
susceptible to insect attack.
Maintenance
Standards
Inspect flagged and/or fenced areas regularly to make sure flagging or
fencing has not been removed or damaged. If the flagging or fencing
has been damaged or visibility reduced, it shall be repaired or
replaced immediately and visibility restored.
• If tree roots have been exposed or injured, “prune” cleanly with an
appropriate pruning saw or lopers directly above the damaged roots
and recover with native soils. Treatment of sap flowing trees (fir,
hemlock, pine, soft maples) is not advised as sap forms a natural
healing barrier.
BMP C102: Buffer Zones
Purpose Creation of an undisturbed area or strip of natural vegetation or an
established suitable planting that will provide a living filter to reduce soil
erosion and runoff velocities.
Conditions of Use Natural buffer zones are used along streams, wetlands and other bodies of
water that need protection from erosion and sedimentation. Vegetative
buffer zones can be used to protect natural swales and can be incorporated
into the natural landscaping of an area.
Critical-areas buffer zones should not be used as sediment treatment areas.
These areas shall remain completely undisturbed. The local permitting
authority may expand the buffer widths temporarily to allow the use of the
expanded area for removal of sediment.
Design and
Installation
Specifications
• Preserving natural vegetation or plantings in clumps, blocks, or strips
is generally the easiest and most successful method.
• Leave all unstable steep slopes in natural vegetation.
• Mark clearing limits and keep all equipment and construction debris
out of the natural areas and buffer zones. Steel construction fencing is
the most effective method in protecting sensitive areas and buffers.
Alternatively, wire-backed silt fence on steel posts is marginally
effective. Flagging alone is typically not effective.
• Keep all excavations outside the dripline of trees and shrubs.
• Do not push debris or extra soil into the buffer zone area because it
will cause damage from burying and smothering.
• Vegetative buffer zones for streams, lakes or other waterways shall be
established by the local permitting authority or other state or federal
permits or approvals.
Maintenance
Standards
Inspect the area frequently to make sure flagging remains in place and the
area remains undisturbed. Replace all damaged flagging immediately.
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BMP C103: High Visibility Fence
Purpose Fencing is intended to:
1. Restrict clearing to approved limits.
2. Prevent disturbance of sensitive areas, their buffers, and other areas
required to be left undisturbed.
3. Limit construction traffic to designated construction entrances, exits,
or internal roads.
4. Protect areas where marking with survey tape may not provide
adequate protection.
Conditions of Use To establish clearing limits plastic, fabric, or metal fence may be used:
• At the boundary of sensitive areas, their buffers, and other areas
required to be left uncleared.
• As necessary to control vehicle access to and on the site.
Design and
Installation
Specifications
High visibility plastic fence shall be composed of a high-density
polyethylene material and shall be at least four feet in height. Posts for
the fencing shall be steel or wood and placed every 6 feet on center
(maximum) or as needed to ensure rigidity. The fencing shall be fastened
to the post every six inches with a polyethylene tie. On long continuous
lengths of fencing, a tension wire or rope shall be used as a top stringer to
prevent sagging between posts. The fence color shall be high visibility
orange. The fence tensile strength shall be 360 lbs./ft. using the ASTM
D4595 testing method.
If appropriate install fabric silt fence in accordance with BMP C233 to
act as high visibility fence. Silt fence shall be at least 3 feet high and
must be highly visible to meet the requirements of this BMP.
Metal fences shall be designed and installed according to the
manufacturer's specifications.
Metal fences shall be at least 3 feet high and must be highly visible.
Fences shall not be wired or stapled to trees.
Maintenance
Standards
If the fence has been damaged or visibility reduced, it shall be repaired or
replaced immediately and visibility restored.
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BMP C105: Stabilized Construction Entrance / Exit
Purpose Stabilized Construction entrances are established to reduce the amount of
sediment transported onto paved roads by vehicles or equipment. This is
done by constructing a stabilized pad of quarry spalls at entrances and
exits for construction sites.
Conditions of Use Construction entrances shall be stabilized wherever traffic will be entering
or leaving a construction site if paved roads or other paved areas are
within 1,000 feet of the site.
For residential construction provide stabilized construction entrances for
each residence, rather than only at the main subdivision entrance.
Stabilized surfaces shall be of sufficient length/width to provide vehicle
access/parking, based on lot size/configuration.
On large commercial, highway, and road projects, the designer should
include enough extra materials in the contract to allow for additional
stabilized entrances not shown in the initial Construction SWPPP. It is
difficult to determine exactly where access to these projects will take
place; additional materials will enable the contractor to install them where
needed.
Design and
Installation
Specifications
See Figure 4.1.1 for details. Note: the 100’ minimum length of the
entrance shall be reduced to the maximum practicable size when the size
or configuration of the site does not allow the full length (100’).
Construct stabilized construction entrances with a 12-inch thick pad of 4-
inch to 8-inch quarry spalls, a 4-inch course of asphalt treated base
(ATB), or use existing pavement. Do not use crushed concrete, cement,
or calcium chloride for construction entrance stabilization because these
products raise pH levels in stormwater and concrete discharge to surface
waters of the State is prohibited.
A separation geotextile shall be placed under the spalls to prevent fine
sediment from pumping up into the rock pad. The geotextile shall meet
the following standards:
Grab Tensile Strength (ASTM D4751) 200 psi min.
Grab Tensile Elongation (ASTM D4632) 30% max.
Mullen Burst Strength (ASTM D3786-80a) 400 psi min.
AOS (ASTM D4751) 20-45 (U.S. standard sieve size)
• Consider early installation of the first lift of asphalt in areas that will
paved; this can be used as a stabilized entrance. Also consider the
installation of excess concrete as a stabilized entrance. During large
concrete pours, excess concrete is often available for this purpose.
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• Fencing (see BMP C103) shall be installed as necessary to restrict
traffic to the construction entrance.
• Whenever possible, the entrance shall be constructed on a firm,
compacted subgrade. This can substantially increase the effectiveness
of the pad and reduce the need for maintenance.
• Construction entrances should avoid crossing existing sidewalks and
back of walk drains if at all possible. If a construction entrance must
cross a sidewalk or back of walk drain, the full length of the sidewalk
and back of walk drain must be covered and protected from sediment
leaving the site.
Maintenance
Standards
Quarry spalls shall be added if the pad is no longer in accordance with
the specifications.
• If the entrance is not preventing sediment from being tracked onto
pavement, then alternative measures to keep the streets free of
sediment shall be used. This may include replacement/cleaning of the
existing quarry spalls, street sweeping, an increase in the dimensions
of the entrance, or the installation of a wheel wash.
• Any sediment that is tracked onto pavement shall be removed by
shoveling or street sweeping. The sediment collected by sweeping
shall be removed or stabilized on site. The pavement shall not be
cleaned by washing down the street, except when high efficiency
sweeping is ineffective and there is a threat to public safety. If it is
necessary to wash the streets, the construction of a small sump to
contain the wash water shall be considered. The sediment would then
be washed into the sump where it can be controlled.
• Perform street sweeping by hand or with a high efficiency sweeper. Do
not use a non-high efficiency mechanical sweeper because this creates
dust and throws soils into storm systems or conveyance ditches.
• Any quarry spalls that are loosened from the pad, which end up on the
roadway shall be removed immediately.
• If vehicles are entering or exiting the site at points other than the
construction entrance(s), fencing (see BMP C103) shall be installed to
control traffic.
• Upon project completion and site stabilization, all construction
accesses intended as permanent access for maintenance shall be
permanently stabilized.
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Figure 4.1.1 – Stabilized Construction Entrance
Approved as
Equivalent
Ecology has approved products as able to meet the requirements of BMP
C105. The products did not pass through the Technology Assessment
Protocol – Ecology (TAPE) process. Local jurisdictions may choose not
to accept this product approved as equivalent, or may require additional
testing prior to consideration for local use. The products are available for
review on Ecology’s website at
http://www.ecy.wa.gov/programs/wq/stormwater/newtech/equivalent.html
BMP C106: Wheel Wash
Purpose Wheel washes reduce the amount of sediment transported onto paved
roads by motor vehicles.
Conditions of Use When a stabilized construction entrance (see BMP C105) is not preventing
sediment from being tracked onto pavement.
• Wheel washing is generally an effective BMP when installed with
careful attention to topography. For example, a wheel wash can be
detrimental if installed at the top of a slope abutting a right-of-way
where the water from the dripping truck can run unimpeded into the
street.
Driveway shall meet the
requirements of the
permitting agency
It is recommended that the
entrance be crowned so that runoff drains off the pad
Provide full width of
ingress/egress area
12” min. thickness
Geotextile
4’ – 8” quarry spalls
Install driveway culvert if there
is a roadside ditch present
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stable driving surface and to stabilize any areas that have eroded.
Following construction, these areas shall be restored to pre-construction
condition or better to prevent future erosion.
Perform street cleaning at the end of each day or more often if necessary.
BMP C120: Temporary and Permanent Seeding
Purpose Seeding reduces erosion by stabilizing exposed soils. A well-established
vegetative cover is one of the most effective methods of reducing erosion.
Conditions of Use Use seeding throughout the project on disturbed areas that have reached
final grade or that will remain unworked for more than 30 days.
The optimum seeding windows for western Washington are April 1
through June 30 and September 1 through October 1.
Between July 1 and August 30 seeding requires irrigation until 75 percent
grass cover is established.
Between October 1 and March 30 seeding requires a cover of mulch with
straw or an erosion control blanket until 75 percent grass cover is
established.
Review all disturbed areas in late August to early September and complete
all seeding by the end of September. Otherwise, vegetation will not
establish itself enough to provide more than average protection.
• Mulch is required at all times for seeding because it protects seeds
from heat, moisture loss, and transport due to runoff. Mulch can be
applied on top of the seed or simultaneously by hydroseeding. See
BMP C121: Mulching for specifications.
• Seed and mulch, all disturbed areas not otherwise vegetated at final
site stabilization. Final stabilization means the completion of all soil
disturbing activities at the site and the establishment of a permanent
vegetative cover, or equivalent permanent stabilization measures (such
as pavement, riprap, gabions or geotextiles) which will prevent
erosion.
Design and
Installation
Specifications
Seed retention/detention ponds as required.
Install channels intended for vegetation before starting major
earthwork and hydroseed with a Bonded Fiber Matrix. For vegetated
channels that will have high flows, install erosion control blankets
over hydroseed. Before allowing water to flow in vegetated
channels, establish 75 percent vegetation cover. If vegetated
channels cannot be established by seed before water flow; install sod
in the channel bottom—over hydromulch and erosion control
blankets.
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• Confirm the installation of all required surface water control measures
to prevent seed from washing away.
• Hydroseed applications shall include a minimum of 1,500 pounds per
acre of mulch with 3 percent tackifier. See BMP C121: Mulching for
specifications.
• Areas that will have seeding only and not landscaping may need
compost or meal-based mulch included in the hydroseed in order to
establish vegetation. Re-install native topsoil on the disturbed soil
surface before application.
• When installing seed via hydroseeding operations, only about 1/3 of
the seed actually ends up in contact with the soil surface. This reduces
the ability to establish a good stand of grass quickly. To overcome this,
consider increasing seed quantities by up to 50 percent.
• Enhance vegetation establishment by dividing the hydromulch
operation into two phases:
1. Phase 1- Install all seed and fertilizer with 25-30 percent mulch
and tackifier onto soil in the first lift.
2. Phase 2- Install the rest of the mulch and tackifier over the first lift.
Or, enhance vegetation by:
1. Installing the mulch, seed, fertilizer, and tackifier in one lift.
2. Spread or blow straw over the top of the hydromulch at a rate of
800-1000 pounds per acre.
3. Hold straw in place with a standard tackifier.
Both of these approaches will increase cost moderately but will greatly
improve and enhance vegetative establishment. The increased cost
may be offset by the reduced need for:
• Irrigation.
• Reapplication of mulch.
• Repair of failed slope surfaces.
This technique works with standard hydromulch (1,500 pounds per
acre minimum) and BFM/MBFMs (3,000 pounds per acre minimum).
• Seed may be installed by hand if:
• Temporary and covered by straw, mulch, or topsoil.
• Permanent in small areas (usually less than 1 acre) and covered
with mulch, topsoil, or erosion blankets.
• The seed mixes listed in the tables below include recommended mixes
for both temporary and permanent seeding.
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• Apply these mixes, with the exception of the wetland mix, at a rate
of 120 pounds per acre. This rate can be reduced if soil
amendments or slow-release fertilizers are used.
• Consult the local suppliers or the local conservation district for
their recommendations because the appropriate mix depends on a
variety of factors, including location, exposure, soil type, slope,
and expected foot traffic. Alternative seed mixes approved by the
local authority may be used.
• Other mixes may be appropriate, depending on the soil type and
hydrology of the area.
• Table 4.1.2 lists the standard mix for areas requiring a temporary
vegetative cover.
Table 4.1.2
Temporary Erosion Control Seed Mix
% Weight % Purity % Germination
Chewings or annual blue grass
Festuca rubra var. commutata or
Poa anna
40 98 90
Perennial rye -
Lolium perenne
50 98 90
Redtop or colonial bentgrass
Agrostis alba or Agrostis tenuis
5 92 85
White dutch clover
Trifolium repens
5 98 90
• Table 4.1.3 lists a recommended mix for landscaping seed.
Table 4.1.3
Landscaping Seed Mix
% Weight % Purity % Germination
Perennial rye blend
Lolium perenne
70 98 90
Chewings and red fescue blend
Festuca rubra var. commutata
or Festuca rubra
30 98 90
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• Table 4.1.4 lists a turf seed mix for dry situations where there is no
need for watering. This mix requires very little maintenance.
Table 4.1.4
Low -Growing Turf Seed Mix
% Weight % Purity % Germination
Dwarf tall fescue (several varieties)
Festuca arundinacea var.
45 98 90
Dwarf perennial rye (Barclay)
Lolium perenne var. barclay
30 98 90
Red fescue
Festuca rubra
20 98 90
Colonial bentgrass
Agrostis tenuis
5 98 90
• Table 4.1.5 lists a mix for bioswales and other intermittently wet areas.
Table 4.1.5
Bioswale Seed Mix*
% Weight % Purity % Germination
Tall or meadow fescue
Festuca arundinacea or Festuca
elatior
75-80 98 90
Seaside/Creeping bentgrass
Agrostis palustris
10-15 92 85
Redtop bentgrass
Agrostis alba or Agrostis gigantea
5-10 90 80
* Modified Briargreen, Inc. Hydroseeding Guide Wetlands Seed Mix
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• Table 4.1.6 lists a low-growing, relatively non-invasive seed mix
appropriate for very wet areas that are not regulated wetlands. Apply
this mixture at a rate of 60 pounds per acre. Consult Hydraulic Permit
Authority (HPA) for seed mixes if applicable.
Table 4.1.6
Wet Area Seed Mix*
% Weight % Purity % Germination
Tall or meadow fescue
Festuca arundinacea or
Festuca elatior
60-70 98 90
Seaside/Creeping bentgrass
Agrostis palustris
10-15 98 85
Meadow foxtail
Alepocurus pratensis
10-15 90 80
Alsike clover
Trifolium hybridum
1-6 98 90
Redtop bentgrass
Agrostis alba
1-6 92 85
* Modified Briargreen, Inc. Hydroseeding Guide Wetlands Seed Mix
• Table 4.1.7 lists a recommended meadow seed mix for infrequently
maintained areas or non-maintained areas where colonization by native
plants is desirable. Likely applications include rural road and utility
right-of-way. Seeding should take place in September or very early
October in order to obtain adequate establishment prior to the winter
months. Consider the appropriateness of clover, a fairly invasive
species, in the mix. Amending the soil can reduce the need for clover.
Table 4.1.7
Meadow Seed Mix
% Weight % Purity % Germination
Redtop or Oregon bentgrass
Agrostis alba or Agrostis
oregonensis
20 92 85
Red fescue
Festuca rubra
70 98 90
White dutch clover
Trifolium repens
10 98 90
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• Roughening and Rototilling:
• The seedbed should be firm and rough. Roughen all soil no matter
what the slope. Track walk slopes before seeding if engineering
purposes require compaction. Backblading or smoothing of slopes
greater than 4H:1V is not allowed if they are to be seeded.
• Restoration-based landscape practices require deeper incorporation
than that provided by a simple single-pass rototilling treatment.
Wherever practical, initially rip the subgrade to improve long-term
permeability, infiltration, and water inflow qualities. At a
minimum, permanent areas shall use soil amendments to achieve
organic matter and permeability performance defined in
engineered soil/landscape systems. For systems that are deeper
than 8 inches complete the rototilling process in multiple lifts, or
prepare the engineered soil system per specifications and place to
achieve the specified depth.
• Fertilizers:
• Conducting soil tests to determine the exact type and quantity of
fertilizer is recommended. This will prevent the over-application
of fertilizer.
• Organic matter is the most appropriate form of fertilizer because it
provides nutrients (including nitrogen, phosphorus, and potassium)
in the least water-soluble form.
• In general, use 10-4-6 N-P-K (nitrogen-phosphorus-potassium)
fertilizer at a rate of 90 pounds per acre. Always use slow-release
fertilizers because they are more efficient and have fewer
environmental impacts. Do not add fertilizer to the hydromulch
machine, or agitate, more than 20 minutes before use. Too much
agitation destroys the slow-release coating.
• There are numerous products available that take the place of
chemical fertilizers. These include several with seaweed extracts
that are beneficial to soil microbes and organisms. If 100 percent
cottonseed meal is used as the mulch in hydroseed, chemical
fertilizer may not be necessary. Cottonseed meal provides a good
source of long-term, slow-release, available nitrogen.
• Bonded Fiber Matrix and Mechanically Bonded Fiber Matrix:
• On steep slopes use Bonded Fiber Matrix (BFM) or Mechanically
Bonded Fiber Matrix (MBFM) products. Apply BFM/MBFM
products at a minimum rate of 3,000 pounds per acre of mulch
with approximately 10 percent tackifier. Achieve a minimum of 95
percent soil coverage during application. Numerous products are
available commercially. Installed products per manufacturer’s
instructions. Most products require 24-36 hours to cure before
rainfall and cannot be installed on wet or saturated soils.
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Generally, products come in 40-50 pound bags and include all
necessary ingredients except for seed and fertilizer.
• BFMs and MBFMs provide good alternatives to blankets in most
areas requiring vegetation establishment. Advantages over
blankets include:
• BFM and MBFMs do not require surface preparation.
• Helicopters can assist in installing BFM and MBFMs in remote
areas.
• On slopes steeper than 2.5H:1V, blanket installers may require
ropes and harnesses for safety.
• Installing BFM and MBFMs can save at least $1,000 per acre
compared to blankets.
Maintenance
Standards
Reseed any seeded areas that fail to establish at least 80 percent cover
(100 percent cover for areas that receive sheet or concentrated flows). If
reseeding is ineffective, use an alternate method such as sodding,
mulching, or nets/blankets. If winter weather prevents adequate grass
growth, this time limit may be relaxed at the discretion of the local
authority when sensitive areas would otherwise be protected.
• Reseed and protect by mulch any areas that experience erosion after
achieving adequate cover. Reseed and protect by mulch any eroded
area.
• Supply seeded areas with adequate moisture, but do not water to the
extent that it causes runoff.
Approved as
Equivalent
Ecology has approved products as able to meet the requirements of BMP
C120. The products did not pass through the Technology Assessment
Protocol – Ecology (TAPE) process. Local jurisdictions may choose not to
accept this product approved as equivalent, or may require additional testing
prior to consideration for local use. The products are available for review on
Ecology’s website at
http://www.ecy.wa.gov/programs/wq/stormwater/newtech/equivalent.html
BMP C121: Mulching
Purpose Mulching soils provides immediate temporary protection from erosion.
Mulch also enhances plant establishment by conserving moisture, holding
fertilizer, seed, and topsoil in place, and moderating soil temperatures.
There is an enormous variety of mulches that can be used. This section
discusses only the most common types of mulch.
Conditions of Use As a temporary cover measure, mulch should be used:
• For less than 30 days on disturbed areas that require cover.
• At all times for seeded areas, especially during the wet season and
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during the hot summer months.
• During the wet season on slopes steeper than 3H:1V with more than
10 feet of vertical relief.
Mulch may be applied at any time of the year and must be refreshed
periodically.
• For seeded areas mulch may be made up of 100 percent: cottonseed
meal; fibers made of wood, recycled cellulose, hemp, kenaf; compost;
or blends of these. Tackifier shall be plant-based, such as guar or alpha
plantago, or chemical-based such as polyacrylamide or polymers. Any
mulch or tackifier product used shall be installed per manufacturer’s
instructions. Generally, mulches come in 40-50 pound bags. Seed and
fertilizer are added at time of application.
Design and
Installation
Specifications
For mulch materials, application rates, and specifications, see Table 4.1.8.
Always use a 2-inch minimum mulch thickness; increase the thickness
until the ground is 95% covered (i.e. not visible under the mulch layer).
Note: Thickness may be increased for disturbed areas in or near sensitive
areas or other areas highly susceptible to erosion.
Mulch used within the ordinary high-water mark of surface waters should
be selected to minimize potential flotation of organic matter. Composted
organic materials have higher specific gravities (densities) than straw,
wood, or chipped material. Consult Hydraulic Permit Authority (HPA) for
mulch mixes if applicable.
Maintenance
Standards
• The thickness of the cover must be maintained.
• Any areas that experience erosion shall be remulched and/or protected
with a net or blanket. If the erosion problem is drainage related, then
the problem shall be fixed and the eroded area remulched.
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Table 4.1.8
Mulch Standards and Guidelines
Mulch Material Quality Standards
Application
Rates Remarks
Straw Air-dried; free from
undesirable seed and
coarse material.
2"-3" thick; 5
bales per 1,000
sf or 2-3 tons per
acre
Cost-effective protection when applied with adequate thickness.
Hand-application generally requires greater thickness than
blown straw. The thickness of straw may be reduced by half
when used in conjunction with seeding. In windy areas straw
must be held in place by crimping, using a tackifier, or covering
with netting. Blown straw always has to be held in place with a
tackifier as even light winds will blow it away. Straw, however,
has several deficiencies that should be considered when
selecting mulch materials. It often introduces and/or encourages
the propagation of weed species and it has no significant long-
term benefits. It should also not be used within the ordinary
high-water elevation of surface waters (due to flotation).
Hydromulch No growth
inhibiting factors.
Approx. 25-30
lbs per 1,000 sf
or 1,500 - 2,000
lbs per acre
Shall be applied with hydromulcher. Shall not be used without
seed and tackifier unless the application rate is at least doubled.
Fibers longer than about ¾-1 inch clog hydromulch equipment.
Fibers should be kept to less than ¾ inch.
Composted
Mulch and
Compost
No visible water or
dust during
handling. Must be
produced in
accordance with
WAC 173-350,
Solid Waste
Handling Standards.
.
2" thick min.;
approx. 100 tons
per acre (approx.
800 lbs per yard)
More effective control can be obtained by increasing thickness
to 3". Excellent mulch for protecting final grades until
landscaping because it can be directly seeded or tilled into soil
as an amendment. Composted mulch has a coarser size
gradation than compost. It is more stable and practical to use in
wet areas and during rainy weather conditions. Do not use
composted mulch near wetlands or near phosphorous impaired
water bodies.
Chipped Site
Vegetation
Average size shall
be several inches.
Gradations from
fines to 6 inches in
length for texture,
variation, and
interlocking
properties.
2" thick min.; This is a cost-effective way to dispose of debris from clearing
and grubbing, and it eliminates the problems associated with
burning. Generally, it should not be used on slopes above
approx. 10% because of its tendency to be transported by
runoff. It is not recommended within 200 feet of surface waters.
If seeding is expected shortly after mulch, the decomposition of
the chipped vegetation may tie up nutrients important to grass
establishment.
Wood-based
Mulch or Wood
Straw
No visible water or
dust during
handling. Must be
purchased from a
supplier with a Solid
Waste Handling
Permit or one
exempt from solid
waste regulations.
2” thick min.;
approx. 100 tons
per acre (approx.
800 lbs. per
cubic yard)
This material is often called “hog or hogged fuel.” The use of
mulch ultimately improves the organic matter in the soil.
Special caution is advised regarding the source and composition
of wood-based mulches. Its preparation typically does not
provide any weed seed control, so evidence of residual
vegetation in its composition or known inclusion of weed plants
or seeds should be monitored and prevented (or minimized).
Wood Strand
Mulch
A blend of loose,
long, thin wood
pieces derived from
native conifer or
deciduous trees with
high length-to-width
ratio.
2” thick min. Cost-effective protection when applied with adequate thickness.
A minimum of 95-percent of the wood strand shall have lengths
between 2 and 10-inches, with a width and thickness between
1/16 and ⅜-inches. The mulch shall not contain resin, tannin, or
other compounds in quantities that would be detrimental to plant
life. Sawdust or wood shavings shall not be used as mulch.
(WSDOT specification (9-14.4(4))
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BMP C122: Nets and Blankets
Purpose Erosion control nets and blankets are intended to prevent erosion and hold
seed and mulch in place on steep slopes and in channels so that vegetation
can become well established. In addition, some nets and blankets can be
used to permanently reinforce turf to protect drainage ways during high
flows. Nets (commonly called matting) are strands of material woven into
an open, but high-tensile strength net (for example, coconut fiber matting).
Blankets are strands of material that are not tightly woven, but instead
form a layer of interlocking fibers, typically held together by a
biodegradable or photodegradable netting (for example, excelsior or straw
blankets). They generally have lower tensile strength than nets, but cover
the ground more completely. Coir (coconut fiber) fabric comes as both
nets and blankets.
Conditions of Use Erosion control nets and blankets should be used:
• To aid permanent vegetated stabilization of slopes 2H:1V or greater
and with more than 10 feet of vertical relief.
• For drainage ditches and swales (highly recommended). The
application of appropriate netting or blanket to drainage ditches and
swales can protect bare soil from channelized runoff while vegetation
is established. Nets and blankets also can capture a great deal of
sediment due to their open, porous structure. Nets and blankets can be
used to permanently stabilize channels and may provide a cost-
effective, environmentally preferable alternative to riprap. 100 percent
synthetic blankets manufactured for use in ditches may be easily
reused as temporary ditch liners.
Disadvantages of blankets include:
• Surface preparation required.
• On slopes steeper than 2.5H:1V, blanket installers may need to be
roped and harnessed for safety.
• They cost at least $4,000-6,000 per acre installed.
Advantages of blankets include:
• Installation without mobilizing special equipment.
• Installation by anyone with minimal training
• Installation in stages or phases as the project progresses.
• Installers can hand place seed and fertilizer as they progress down the
slope.
• Installation in any weather.
• There are numerous types of blankets that can be designed with
various parameters in mind. Those parameters include: fiber blend,
mesh strength, longevity, biodegradability, cost, and availability.
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Design and
Installation
Specifications
• See Figure 4.1.3 and Figure 4.1.4 for typical orientation and
installation of blankets used in channels and as slope protection. Note:
these are typical only; all blankets must be installed per
manufacturer’s installation instructions.
• Installation is critical to the effectiveness of these products. If good
ground contact is not achieved, runoff can concentrate under the
product, resulting in significant erosion.
• Installation of Blankets on Slopes:
1. Complete final grade and track walk up and down the slope.
2. Install hydromulch with seed and fertilizer.
3. Dig a small trench, approximately 12 inches wide by 6 inches deep
along the top of the slope.
4. Install the leading edge of the blanket into the small trench and
staple approximately every 18 inches. NOTE: Staples are metal,
“U”-shaped, and a minimum of 6 inches long. Longer staples are
used in sandy soils. Biodegradable stakes are also available.
5. Roll the blanket slowly down the slope as installer walks
backwards. NOTE: The blanket rests against the installer’s legs.
Staples are installed as the blanket is unrolled. It is critical that the
proper staple pattern is used for the blanket being installed. The
blanket is not to be allowed to roll down the slope on its own as
this stretches the blanket making it impossible to maintain soil
contact. In addition, no one is allowed to walk on the blanket after
it is in place.
6. If the blanket is not long enough to cover the entire slope length,
the trailing edge of the upper blanket should overlap the leading
edge of the lower blanket and be stapled. On steeper slopes, this
overlap should be installed in a small trench, stapled, and covered
with soil.
• With the variety of products available, it is impossible to cover all the
details of appropriate use and installation. Therefore, it is critical that
the design engineer consult the manufacturer's information and that a
site visit takes place in order to ensure that the product specified is
appropriate. Information is also available at the following web sites:
1. WSDOT (Section 3.2.4):
http://www.wsdot.wa.gov/NR/rdonlyres/3B41E087-FA86-4717-
932D-D7A8556CCD57/0/ErosionTrainingManual.pdf
2. Texas Transportation Institute:
http://www.txdot.gov/business/doing_business/product_evaluation/
erosion_control.htm
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• Use jute matting in conjunction with mulch (BMP C121). Excelsior,
woven straw blankets and coir (coconut fiber) blankets may be
installed without mulch. There are many other types of erosion control
nets and blankets on the market that may be appropriate in certain
circumstances.
• In general, most nets (e.g., jute matting) require mulch in order to
prevent erosion because they have a fairly open structure. Blankets
typically do not require mulch because they usually provide complete
protection of the surface.
• Extremely steep, unstable, wet, or rocky slopes are often appropriate
candidates for use of synthetic blankets, as are riverbanks, beaches and
other high-energy environments. If synthetic blankets are used, the soil
should be hydromulched first.
• 100-percent biodegradable blankets are available for use in sensitive
areas. These organic blankets are usually held together with a paper or
fiber mesh and stitching which may last up to a year.
• Most netting used with blankets is photodegradable, meaning they
break down under sunlight (not UV stabilized). However, this process
can take months or years even under bright sun. Once vegetation is
established, sunlight does not reach the mesh. It is not uncommon to
find non-degraded netting still in place several years after installation.
This can be a problem if maintenance requires the use of mowers or
ditch cleaning equipment. In addition, birds and small animals can
become trapped in the netting.
Maintenance
Standards
• Maintain good contact with the ground. Erosion must not occur
beneath the net or blanket.
• Repair and staple any areas of the net or blanket that are damaged or
not in close contact with the ground.
• Fix and protect eroded areas if erosion occurs due to poorly controlled
drainage.
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Min. 2“Overlap
Slope surface shall be smooth beforeplacement for proper soil contact.
Stapling pattern as permanufacturer’s recommendations.
Do not stretch blankets/mattings tight -allow the rolls to mold to any irregularities.
For slopes less than 3H:1V, rollsmay be placed in horizontal strips.
If there is a berm at thetop of slope, anchorupslope of the berm.
Anchor in 6"x6" min. Trenchand staple at 12" intervals.
Min. 6" overlap.
Staple overlapsmax. 5" spacing.
Bring material down to a level area, turnthe end under 4" and staple at 12" intervals.
Lime, fertilize, and seed before installation.Planting of shrubs, trees, etc. Should occurafter installation.
Figure 4.1.3 – Channel Installation
Figure 4.1.4 – Slope Installation
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BMP C123: Plastic Covering
Purpose Plastic covering provides immediate, short-term erosion protection to
slopes and disturbed areas.
Conditions of
Use
Plastic covering may be used on disturbed areas that require cover
measures for less than 30 days, except as stated below.
• Plastic is particularly useful for protecting cut and fill slopes and
stockpiles. Note: The relatively rapid breakdown of most polyethylene
sheeting makes it unsuitable for long-term (greater than six months)
applications.
• Due to rapid runoff caused by plastic covering, do not use this method
upslope of areas that might be adversely impacted by concentrated
runoff. Such areas include steep and/or unstable slopes.
• Plastic sheeting may result in increased runoff volumes and velocities,
requiring additional on-site measures to counteract the increases.
Creating a trough with wattles or other material can convey clean
water away from these areas.
• To prevent undercutting, trench and backfill rolled plastic covering
products.
• While plastic is inexpensive to purchase, the added cost of
installation, maintenance, removal, and disposal make this an
expensive material, up to $1.50-2.00 per square yard.
• Whenever plastic is used to protect slopes install water collection
measures at the base of the slope. These measures include plastic-
covered berms, channels, and pipes used to covey clean rainwater
away from bare soil and disturbed areas. Do not mix clean runoff from
a plastic covered slope with dirty runoff from a project.
• Other uses for plastic include:
1. Temporary ditch liner.
2. Pond liner in temporary sediment pond.
3. Liner for bermed temporary fuel storage area if plastic is not
reactive to the type of fuel being stored.
4. Emergency slope protection during heavy rains.
5. Temporary drainpipe (“elephant trunk”) used to direct water.
Design and
Installation
Specifications
• Plastic slope cover must be installed as follows:
1. Run plastic up and down slope, not across slope.
2. Plastic may be installed perpendicular to a slope if the slope length
is less than 10 feet.
3. Minimum of 8-inch overlap at seams.
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4. On long or wide slopes, or slopes subject to wind, tape all seams.
5. Place plastic into a small (12-inch wide by 6-inch deep) slot trench
at the top of the slope and backfill with soil to keep water from
flowing underneath.
6. Place sand filled burlap or geotextile bags every 3 to 6 feet along
seams and tie them together with twine to hold them in place.
7. Inspect plastic for rips, tears, and open seams regularly and repair
immediately. This prevents high velocity runoff from contacting
bare soil which causes extreme erosion.
8. Sandbags may be lowered into place tied to ropes. However, all
sandbags must be staked in place.
• Plastic sheeting shall have a minimum thickness of 0.06 millimeters.
• If erosion at the toe of a slope is likely, a gravel berm, riprap, or other
suitable protection shall be installed at the toe of the slope in order to
reduce the velocity of runoff.
Maintenance
Standards
• Torn sheets must be replaced and open seams repaired.
• Completely remove and replace the plastic if it begins to deteriorate
due to ultraviolet radiation.
• Completely remove plastic when no longer needed.
• Dispose of old tires used to weight down plastic sheeting
appropriately.
Approved as
Equivalent
Ecology has approved products as able to meet the requirements of BMP
C123. The products did not pass through the Technology Assessment
Protocol – Ecology (TAPE) process. Local jurisdictions may choose not
to accept this product approved as equivalent, or may require additional
testing prior to consideration for local use. The products are available for
review on Ecology’s website at
http://www.ecy.wa.gov/programs/wq/stormwater/newtech/equivalent.html
BMP C124: Sodding
Purpose The purpose of sodding is to establish permanent turf for immediate
erosion protection and to stabilize drainage ways where concentrated
overland flow will occur.
Conditions of Use Sodding may be used in the following areas:
• Disturbed areas that require short-term or long-term cover.
• Disturbed areas that require immediate vegetative cover.
• All waterways that require vegetative lining. Waterways may also be
seeded rather than sodded, and protected with a net or blanket.
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Design and
Installation
Specifications
Sod shall be free of weeds, of uniform thickness (approximately 1-inch
thick), and shall have a dense root mat for mechanical strength.
The following steps are recommended for sod installation:
• Shape and smooth the surface to final grade in accordance with the
approved grading plan. The swale needs to be overexcavated 4 to 6
inches below design elevation to allow room for placing soil
amendment and sod.
• Amend 4 inches (minimum) of compost into the top 8 inches of the
soil if the organic content of the soil is less than ten percent or the
permeability is less than 0.6 inches per hour. See
http://www.ecy.wa.gov/programs/swfa/organics/soil.html for further
information.
• Fertilize according to the supplier's recommendations.
• Work lime and fertilizer 1 to 2 inches into the soil, and smooth the
surface.
• Lay strips of sod beginning at the lowest area to be sodded and
perpendicular to the direction of water flow. Wedge strips securely
into place. Square the ends of each strip to provide for a close, tight fit.
Stagger joints at least 12 inches. Staple on slopes steeper than 3H:1V.
Staple the upstream edge of each sod strip.
• Roll the sodded area and irrigate.
• When sodding is carried out in alternating strips or other patterns, seed
the areas between the sod immediately after sodding.
Maintenance
Standards
If the grass is unhealthy, the cause shall be determined and appropriate
action taken to reestablish a healthy groundcover. If it is impossible to
establish a healthy groundcover due to frequent saturation, instability, or
some other cause, the sod shall be removed, the area seeded with an
appropriate mix, and protected with a net or blanket.
BMP C125: Topsoiling / Composting
Purpose Topsoiling and composting provide a suitable growth medium for final
site stabilization with vegetation. While not a permanent cover practice in
itself, topsoiling and composting are an integral component of providing
permanent cover in those areas where there is an unsuitable soil surface
for plant growth. Use this BMP in conjunction with other BMPs such as
seeding, mulching, or sodding.
Native soils and disturbed soils that have been organically amended not
only retain much more stormwater, but they also serve as effective
biofilters for urban pollutants and, by supporting more vigorous plant
growth, reduce the water, fertilizer and pesticides needed to support
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installed landscapes. Topsoil does not include any subsoils but only the
material from the top several inches including organic debris.
Conditions of
Use
• Permanent landscaped areas shall contain healthy topsoil that reduces
the need for fertilizers, improves overall topsoil quality, provides for
better vegetal health and vitality, improves hydrologic characteristics,
and reduces the need for irrigation.
• Leave native soils and the duff layer undisturbed to the maximum
extent practicable. Stripping of existing, properly functioning soil
system and vegetation for the purpose of topsoiling during
construction is not acceptable. Preserve existing soil systems in
undisturbed and uncompacted conditions if functioning properly.
• Areas that already have good topsoil, such as undisturbed areas, do not
require soil amendments.
• Restore, to the maximum extent practical, native soils disturbed during
clearing and grading to a condition equal to or better than the original
site condition’s moisture-holding capacity. Use on-site native topsoil,
incorporate amendments into on-site soil, or import blended topsoil to
meet this requirement.
• Topsoiling is a required procedure when establishing vegetation on
shallow soils, and soils of critically low pH (high acid) levels.
• Beware of where the topsoil comes from, and what vegetation was on
site before disturbance, invasive plant seeds may be included and could
cause problems for establishing native plants, landscaped areas, or
grasses.
• Topsoil from the site will contain mycorrhizal bacteria that are
necessary for healthy root growth and nutrient transfer. These native
mycorrhiza are acclimated to the site and will provide optimum
conditions for establishing grasses. Use commercially available
mycorrhiza products when using off-site topsoil.
Design and
Installation
Specifications
Meet the following requirements for areas requiring disruption and
topsoiling:
• Maximize the depth of the topsoil wherever possible to provide the
maximum possible infiltration capacity and beneficial growth
medium. Topsoil shall have:
• A minimum depth of 8-inches. Scarify subsoils below the topsoil
layer at least 4-inches with some incorporation of the upper
material to avoid stratified layers, where feasible. Ripping or re-
structuring the subgrade may also provide additional benefits
regarding the overall infiltration and interflow dynamics of the soil
system.
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• A minimum organic content of 10% dry weight, and 5% organic
matter content in turf areas. Incorporate organic amendments to a
minimum 8-inch depth except where tree roots or other natural
features limit the depth of incorporation.
• A pH between 6.0 and 8.0 or matching the pH of the undisturbed
soil.
• If blended topsoil is imported, then fines should be limited to 25
percent passing through a 200 sieve.
• Accomplish the required organic content and pH by either returning
native topsoil to the site and/or incorporating organic amendments.
• To meet the organic content use compost that meets the definition
of “composted materials” in WAC 173-350-220. This code is
available online at:
http://apps.leg.wa.gov/WAC/default.aspx?cite=173-350-220.
The compost must also have an organic matter content of 35% to
65%, and a carbon to nitrogen ratio below 25H:1V.
The carbon to nitrogen ratio may be as high as 35H:1V for
plantings composed entirely of plants native to the Puget Sound
Lowlands region.
• For till soils use a mixture of approximately two parts soil to one
part compost. This equates to 4 inches of compost mixed to a depth
of 12 inches in till soils. Increasing the concentration of compost
beyond this level can have negative effects on vegetal health, while
decreasing the concentrations can reduce the benefits of amended
soils.
• Gravel or cobble outwash soils, may require different approaches.
Organics and fines easily migrate through the loose structure of
these soils. Therefore, the importation of at least 6 inches of
quality topsoil, underlain by some type of filter fabric to prevent
the migration of fines, may be more appropriate for these soils.
• The final composition and construction of the soil system will result in
a natural selection or favoring of certain plant species over time. For
example, incorporation of topsoil may favor grasses, while layering
with mildly acidic, high-carbon amendments may favor more woody
vegetation.
• Allow sufficient time in scheduling for topsoil spreading prior to
seeding, sodding, or planting.
• Take care when applying top soil to subsoils with contrasting textures.
Sandy topsoil over clayey subsoil is a particularly poor combination,
as water creeps along the junction between the soil layers and causes
the topsoil to slough. If topsoil and subsoil are not properly bonded,
water will not infiltrate the soil profile evenly and it will be difficult to
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establish vegetation. The best method to prevent a lack of bonding is
to actually work the topsoil into the layer below for a depth of at least
6 inches.
• Field exploration of the site shall be made to determine if there is
surface soil of sufficient quantity and quality to justify stripping.
Topsoil shall be friable and loamy (loam, sandy loam, silt loam, sandy
clay loam, and clay loam). Avoid areas of natural ground water
recharge.
• Stripping shall be confined to the immediate construction area. A 4-
inch to 6-inch stripping depth is common, but depth may vary
depending on the particular soil. All surface runoff control structures
shall be in place prior to stripping.
• Do not place topsoil while in a frozen or muddy condition, when the
subgrade is excessively wet, or when conditions exist that may
otherwise be detrimental to proper grading or proposed sodding or
seeding.
• In any areas requiring grading remove and stockpile the duff layer and
topsoil on site in a designated, controlled area, not adjacent to public
resources and critical areas. Stockpiled topsoil is to be reapplied to
other portions of the site where feasible.
• Locate the topsoil stockpile so that it meets specifications and does not
interfere with work on the site. It may be possible to locate more than
one pile in proximity to areas where topsoil will be used.
Stockpiling of topsoil shall occur in the following manner:
• Side slopes of the stockpile shall not exceed 2H:1V.
• Between October 1 and April 30:
• An interceptor dike with gravel outlet and silt fence shall
surround all topsoil.
• Within 2 days complete erosion control seeding, or covering
stockpiles with clear plastic, or other mulching materials.
• Between May 1 and September 30:
• An interceptor dike with gravel outlet and silt fence shall
surround all topsoil if the stockpile will remain in place for a
longer period of time than active construction grading.
• Within 7 days complete erosion control seeding, or covering
stockpiles with clear plastic, or other mulching materials.
• When native topsoil is to be stockpiled and reused the following
should apply to ensure that the mycorrhizal bacterial, earthworms, and
other beneficial organisms will not be destroyed:
1. Re-install topsoil within 4 to 6 weeks.
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2. Do not allow the saturation of topsoil with water.
3. Do not use plastic covering.
Maintenance
Standards
• Inspect stockpiles regularly, especially after large storm events.
Stabilize any areas that have eroded.
• Establish soil quality and depth toward the end of construction and
once established, protect from compaction, such as from large
machinery use, and from erosion.
• Plant and mulch soil after installation.
• Leave plant debris or its equivalent on the soil surface to replenish
organic matter.
• Reduce and adjust, where possible, the use of irrigation, fertilizers,
herbicides and pesticides, rather than continuing to implement
formerly established practices.
BMP C126: Polyacrylamide (PAM) for Soil Erosion Protection
Purpose Polyacrylamide (PAM) is used on construction sites to prevent soil
erosion.
Applying PAM to bare soil in advance of a rain event significantly reduces
erosion and controls sediment in two ways. First, PAM increases the soil’s
available pore volume, thus increasing infiltration through flocculation
and reducing the quantity of stormwater runoff. Second, it increases
flocculation of suspended particles and aids in their deposition, thus
reducing stormwater runoff turbidity and improving water quality.
Conditions of Use PAM shall not be directly applied to water or allowed to enter a water
body.
In areas that drain to a sediment pond, PAM can be applied to bare soil
under the following conditions:
• During rough grading operations.
• In Staging areas.
• Balanced cut and fill earthwork.
• Haul roads prior to placement of crushed rock surfacing.
• Compacted soil roadbase.
• Stockpiles.
• After final grade and before paving or final seeding and planting.
• Pit sites.
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The specific PAM copolymer formulation must be anionic. Cationic
PAM shall not be used in any application because of known
aquatic toxicity problems. Only the highest drinking water grade
PAM, certified for compliance with ANSI/NSF Standard 60 for
drinking water treatment, will be used for soil applications. Recent
media attention and high interest in PAM has resulted in some
entrepreneurial exploitation of the term "polymer." All PAM are
polymers, but not all polymers are PAM, and not all PAM products
comply with ANSI/NSF Standard 60. PAM use shall be reviewed and
approved by the local permitting authority.
• PAM designated for these uses should be "water soluble" or "linear" or
"non-crosslinked". Cross-linked or water absorbent PAM, polymerized
in highly acidic (pH<2) conditions, are used to maintain soil moisture
content.
• The PAM anionic charge density may vary from 2-30 percent; a value
of 18 percent is typical. Studies conducted by the United States
Department of Agriculture (USDA)/ARS demonstrated that soil
stabilization was optimized by using very high molecular weight (12-
15 mg/mole), highly anionic (>20% hydrolysis) PAM.
• PAM tackifiers are available and being used in place of guar and alpha
plantago. Typically, PAM tackifiers should be used at a rate of no more
than 0.5-1 lb. per 1000 gallons of water in a hydromulch machine. Some
tackifier product instructions say to use at a rate of 3 –5 lbs. per acre,
which can be too much. In addition, pump problems can occur at higher
rates due to increased viscosity.
Maintenance
Standards
• PAM may be reapplied on actively worked areas after a 48-hour
period.
• Reapplication is not required unless PAM treated soil is disturbed or
unless turbidity levels show the need for an additional application. If
PAM treated soil is left undisturbed a reapplication may be necessary
after two months. More PAM applications may be required for steep
slopes, silty and clayey soils (USDA Classification Type "C" and "D"
soils), long grades, and high precipitation areas. When PAM is applied
first to bare soil and then covered with straw, a reapplication may not
be necessary for several months.
• Loss of sediment and PAM may be a basis for penalties per RCW
90.48.080.
BMP C130: Surface Roughening
Purpose Surface roughening aids in the establishment of vegetative cover, reduces
runoff velocity, increases infiltration, and provides for sediment trapping
through the provision of a rough soil surface. Horizontal depressions are
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created by operating a tiller or other suitable equipment on the contour or
by leaving slopes in a roughened condition by not fine grading them.
Use this BMP in conjunction with other BMPs such as seeding, mulching,
or sodding.
Conditions for
Use
• All slopes steeper than 3H:1V and greater than 5 vertical feet
require surface roughening to a depth of 2 to 4 inches prior to
seeding..
• Areas that will not be stabilized immediately may be roughened to
reduce runoff velocity until seeding takes place.
• Slopes with a stable rock face do not require roughening.
• Slopes where mowing is planned should not be excessively roughened.
Design and
Installation
Specifications
There are different methods for achieving a roughened soil surface on a
slope, and the selection of an appropriate method depends upon the type of
slope. Roughening methods include stair-step grading, grooving, contour
furrows, and tracking. See Figure 4.1.5 for tracking and contour furrows.
Factors to be considered in choosing a method are slope steepness, mowing
requirements, and whether the slope is formed by cutting or filling.
• Disturbed areas that will not require mowing may be stair-step graded,
grooved, or left rough after filling.
• Stair-step grading is particularly appropriate in soils containing large
amounts of soft rock. Each "step" catches material that sloughs from
above, and provides a level site where vegetation can become
established. Stairs should be wide enough to work with standard earth
moving equipment. Stair steps must be on contour or gullies will form
on the slope.
• Areas that will be mowed (these areas should have slopes less steep
than 3H:1V) may have small furrows left by disking, harrowing,
raking, or seed-planting machinery operated on the contour.
• Graded areas with slopes steeper than 3H:1V but less than 2H:1V
should be roughened before seeding. This can be accomplished in a
variety of ways, including "track walking," or driving a crawler tractor
up and down the slope, leaving a pattern of cleat imprints parallel to
slope contours.
• Tracking is done by operating equipment up and down the slope to
leave horizontal depressions in the soil.
Maintenance
Standards
• Areas that are graded in this manner should be seeded as quickly as
possible.
• Regular inspections should be made of the area. If rills appear, they
should be re-graded and re-seeded immediately.
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Figure 4.1.5 – Surface Roughening by Tracking and Contour Furrows
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BMP C131: Gradient Terraces
Purpose Gradient terraces reduce erosion damage by intercepting surface runoff
and conducting it to a stable outlet at a non-erosive velocity.
Conditions of Use • Gradient terraces normally are limited to denuded land having a water
erosion problem. They should not be constructed on deep sands or on
soils that are too stony, steep, or shallow to permit practical and
economical installation and maintenance. Gradient terraces may be
used only where suitable outlets are or will be made available. See
Figure 4.1.6 for gradient terraces.
Design and
Installation
Specifications
• The maximum vertical spacing of gradient terraces should be
determined by the following method:
VI = (0.8)s + y
Where: VI = vertical interval in feet
s = land rise per 100 feet, expressed in feet
y = a soil and cover variable with values from 1.0 to 4.0
Values of “y” are influenced by soil erodibility and cover practices.
The lower values are applicable to erosive soils where little to no
residue is left on the surface. The higher value is applicable only to
erosion-resistant soils where a large amount of residue (1½ tons of
straw/acre equivalent) is on the surface.
• The minimum constructed cross-section should meet the design
dimensions.
• The top of the constructed ridge should not be lower at any point than
the design elevation plus the specified overfill for settlement. The
opening at the outlet end of the terrace should have a cross section
equal to that specified for the terrace channel.
• Channel grades may be either uniform or variable with a maximum
grade of 0.6 feet per 100 feet length (0.6%). For short distances,
terrace grades may be increased to improve alignment. The channel
velocity should not exceed that which is nonerosive for the soil type.
• All gradient terraces should have adequate outlets. Such an outlet may
be a grassed waterway, vegetated area, or tile outlet. In all cases the
outlet must convey runoff from the terrace or terrace system to a point
where the outflow will not cause damage. Vegetative cover should be
used in the outlet channel.
• The design elevation of the water surface of the terrace should not be
lower than the design elevation of the water surface in the outlet at
their junction, when both are operating at design flow.
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Slope to adequate outlet.
10' min.
• Vertical spacing determined by the above methods may be increased
as much as 0.5 feet or 10 percent, whichever is greater, to provide
better alignment or location, to avoid obstacles, to adjust for
equipment size, or to reach a satisfactory outlet. The drainage area
above the terrace should not exceed the area that would be drained by
a terrace with normal spacing.
• The terrace should have enough capacity to handle the peak runoff
expected from a 2-year, 24-hour design storm without overtopping.
• The terrace cross-section should be proportioned to fit the land slope.
The ridge height should include a reasonable settlement factor. The
ridge should have a minimum top width of 3 feet at the design height.
The minimum cross-sectional area of the terrace channel should be
8 square feet for land slopes of 5 percent or less, 7 square feet for
slopes from 5 to 8 percent, and 6 square feet for slopes steeper than
8 percent. The terrace can be constructed wide enough to be
maintained using a small vehicle.
Maintenance
Standards
• Maintenance should be performed as needed. Terraces should be
inspected regularly; at least once a year, and after large storm events.
Figure 4.1.6 – Gradient Terraces
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BMP C140: Dust Control
Purpose Dust control prevents wind transport of dust from disturbed soil surfaces
onto roadways, drainage ways, and surface waters.
Conditions of Use • In areas (including roadways) subject to surface and air movement of
dust where on-site and off-site impacts to roadways, drainage ways, or
surface waters are likely.
Design and
Installation
Specifications
• Vegetate or mulch areas that will not receive vehicle traffic. In areas
where planting, mulching, or paving is impractical, apply gravel or
landscaping rock.
• Limit dust generation by clearing only those areas where immediate
activity will take place, leaving the remaining area(s) in the original
condition. Maintain the original ground cover as long as practical.
• Construct natural or artificial windbreaks or windscreens. These may
be designed as enclosures for small dust sources.
• Sprinkle the site with water until surface is wet. Repeat as needed. To
prevent carryout of mud onto street, refer to Stabilized Construction
Entrance (BMP C105).
• Irrigation water can be used for dust control. Irrigation systems should
be installed as a first step on sites where dust control is a concern.
• Spray exposed soil areas with a dust palliative, following the
manufacturer’s instructions and cautions regarding handling and
application. Used oil is prohibited from use as a dust suppressant.
Local governments may approve other dust palliatives such as calcium
chloride or PAM.
• PAM (BMP C126) added to water at a rate of 0.5 lbs. per 1,000
gallons of water per acre and applied from a water truck is more
effective than water alone. This is due to increased infiltration of water
into the soil and reduced evaporation. In addition, small soil particles
are bonded together and are not as easily transported by wind. Adding
PAM may actually reduce the quantity of water needed for dust
control. Use of PAM could be a cost-effective dust control method.
Techniques that can be used for unpaved roads and lots include:
• Lower speed limits. High vehicle speed increases the amount of dust
stirred up from unpaved roads and lots.
• Upgrade the road surface strength by improving particle size, shape,
and mineral types that make up the surface and base materials.
• Add surface gravel to reduce the source of dust emission. Limit the
amount of fine particles (those smaller than .075 mm) to 10 to 20
percent.
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• Use geotextile fabrics to increase the strength of new roads or roads
undergoing reconstruction.
• Encourage the use of alternate, paved routes, if available.
• Restrict use of paved roadways by tracked vehicles and heavy trucks
to prevent damage to road surface and base.
• Apply chemical dust suppressants using the admix method, blending
the product with the top few inches of surface material. Suppressants
may also be applied as surface treatments.
• Pave unpaved permanent roads and other trafficked areas.
• Use vacuum street sweepers.
• Remove mud and other dirt promptly so it does not dry and then turn
into dust.
• Limit dust-causing work on windy days.
• Contact your local Air Pollution Control Authority for guidance and
training on other dust control measures. Compliance with the local Air
Pollution Control Authority constitutes compliance with this BMP.
Maintenance
Standards
Respray area as necessary to keep dust to a minimum.
BMP C150: Materials on Hand
Purpose Keep quantities of erosion prevention and sediment control materials on
the project site at all times to be used for regular maintenance and
emergency situations such as unexpected heavy summer rains. Having
these materials on-site reduces the time needed to implement BMPs when
inspections indicate that existing BMPs are not meeting the Construction
SWPPP requirements. In addition, contractors can save money by buying
some materials in bulk and storing them at their office or yard.
Conditions of Use • Construction projects of any size or type can benefit from having
materials on hand. A small commercial development project could
have a roll of plastic and some gravel available for immediate
protection of bare soil and temporary berm construction. A large
earthwork project, such as highway construction, might have several
tons of straw, several rolls of plastic, flexible pipe, sandbags,
geotextile fabric and steel “T” posts.
• Materials are stockpiled and readily available before any site clearing,
grubbing, or earthwork begins. A large contractor or developer could
keep a stockpile of materials that are available for use on several
projects.
• If storage space at the project site is at a premium, the contractor could
maintain the materials at their office or yard. The office or yard must
be less than an hour from the project site.
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Design and
Installation
Specifications
Depending on project type, size, complexity, and length, materials and
quantities will vary. A good minimum list of items that will cover
numerous situations includes:
Material
Clear Plastic, 6 mil
Drainpipe, 6 or 8 inch diameter
Sandbags, filled
Straw Bales for mulching,
Quarry Spalls
Washed Gravel
Geotextile Fabric
Catch Basin Inserts
Steel “T” Posts
Silt fence material
Straw Wattles
Maintenance
Standards
• All materials with the exception of the quarry spalls, steel “T” posts,
and gravel should be kept covered and out of both sun and rain.
• Re-stock materials used as needed.
BMP C151: Concrete Handling
Purpose Concrete work can generate process water and slurry that contain fine
particles and high pH, both of which can violate water quality standards in
the receiving water. Concrete spillage or concrete discharge to surface
waters of the State is prohibited. Use this BMP to minimize and eliminate
concrete, concrete process water, and concrete slurry from entering waters
of the state.
Conditions of Use Any time concrete is used, utilize these management practices. Concrete
construction projects include, but are not limited to, the following:
• Curbs
• Sidewalks
• Roads
• Bridges
• Foundations
• Floors
• Runways
Design and
Installation
• Wash out concrete truck chutes, pumps, and internals into formed
areas only. Assure that washout of concrete trucks is performed off-
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Specifications site or in designated concrete washout areas. Do not wash out concrete
trucks onto the ground, or into storm drains, open ditches, streets, or
streams. Refer to BMP C154 for information on concrete washout
areas.
• Return unused concrete remaining in the truck and pump to the
originating batch plant for recycling. Do not dump excess concrete on
site, except in designated concrete washout areas.
• Wash off hand tools including, but not limited to, screeds, shovels,
rakes, floats, and trowels into formed areas only.
• Wash equipment difficult to move, such as concrete pavers in areas
that do not directly drain to natural or constructed stormwater
conveyances.
• Do not allow washdown from areas, such as concrete aggregate
driveways, to drain directly to natural or constructed stormwater
conveyances.
• Contain washwater and leftover product in a lined container when no
formed areas are available,. Dispose of contained concrete in a manner
that does not violate ground water or surface water quality standards.
• Always use forms or solid barriers for concrete pours, such as pilings,
within 15-feet of surface waters.
• Refer to BMPs C252 and C253 for pH adjustment requirements.
• Refer to the Construction Stormwater General Permit for pH
monitoring requirements if the project involves one of the following
activities:
• Significant concrete work (greater than 1,000 cubic yards poured
concrete or recycled concrete used over the life of a project).
• The use of engineered soils amended with (but not limited to)
Portland cement-treated base, cement kiln dust or fly ash.
• Discharging stormwater to segments of water bodies on the 303(d)
list (Category 5) for high pH.
Maintenance
Standards
Check containers for holes in the liner daily during concrete pours and
repair the same day.
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BMP C152: Sawcutting and Surfacing Pollution Prevention
Purpose Sawcutting and surfacing operations generate slurry and process water
that contains fine particles and high pH (concrete cutting), both of which
can violate the water quality standards in the receiving water. Concrete
spillage or concrete discharge to surface waters of the State is prohibited.
Use this BMP to minimize and eliminate process water and slurry created
through sawcutting or surfacing from entering waters of the State.
Conditions of Use Utilize these management practices anytime sawcutting or surfacing
operations take place. Sawcutting and surfacing operations include, but
are not limited to, the following:
• Sawing
• Coring
• Grinding
• Roughening
• Hydro-demolition
• Bridge and road surfacing
Design and
Installation
Specifications
• Vacuum slurry and cuttings during cutting and surfacing operations.
• Slurry and cuttings shall not remain on permanent concrete or asphalt
pavement overnight.
• Slurry and cuttings shall not drain to any natural or constructed
drainage conveyance including stormwater systems. This may require
temporarily blocking catch basins.
• Dispose of collected slurry and cuttings in a manner that does not
violate ground water or surface water quality standards.
• Do not allow process water generated during hydro-demolition,
surface roughening or similar operations to drain to any natural or
constructed drainage conveyance including stormwater systems.
Dispose process water in a manner that does not violate ground water
or surface water quality standards.
• Handle and dispose cleaning waste material and demolition debris in a
manner that does not cause contamination of water. Dispose of
sweeping material from a pick-up sweeper at an appropriate disposal
site.
Maintenance
Standards
Continually monitor operations to determine whether slurry, cuttings, or
process water could enter waters of the state. If inspections show that a
violation of water quality standards could occur, stop operations and
immediately implement preventive measures such as berms, barriers,
secondary containment, and vacuum trucks.
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BMP C153: Material Delivery, Storage and Containment
Purpose Prevent, reduce, or eliminate the discharge of pollutants to the
stormwater system or watercourses from material delivery and storage.
Minimize the storage of hazardous materials on-site, store materials in a
designated area, and install secondary containment.
Conditions of Use These procedures are suitable for use at all construction sites with
delivery and storage of the following materials:
• Petroleum products such as fuel, oil and grease
• Soil stabilizers and binders (e.g. Polyacrylamide)
• Fertilizers, pesticides and herbicides
• Detergents
• Asphalt and concrete compounds
• Hazardous chemicals such as acids, lime, adhesives, paints, solvents
and curing compounds
• Any other material that may be detrimental if released to the
environment
Design and
Installation
Specifications
The following steps should be taken to minimize risk:
• Temporary storage area should be located away from vehicular traffic,
near the construction entrance(s), and away from waterways or storm
drains.
• Material Safety Data Sheets (MSDS) should be supplied for all
materials stored. Chemicals should be kept in their original labeled
containers.
• Hazardous material storage on-site should be minimized.
• Hazardous materials should be handled as infrequently as possible.
• During the wet weather season (Oct 1 – April 30), consider storing
materials in a covered area.
• Materials should be stored in secondary containments, such as earthen
dike, horse trough, or even a children’s wading pool for non-reactive
materials such as detergents, oil, grease, and paints. Small amounts of
material may be secondarily contained in “bus boy” trays or concrete
mixing trays.
• Do not store chemicals, drums, or bagged materials directly on the
ground. Place these items on a pallet and, when possible, and within
secondary containment.
• If drums must be kept uncovered, store them at a slight angle to reduce
ponding of rainwater on the lids to reduce corrosion. Domed plastic
covers are inexpensive and snap to the top of drums, preventing water
from collecting.
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Material Storage Areas and Secondary Containment Practices:
• Liquids, petroleum products, and substances listed in 40 CFR Parts
110, 117, or 302 shall be stored in approved containers and drums and
shall not be overfilled. Containers and drums shall be stored in
temporary secondary containment facilities.
• Temporary secondary containment facilities shall provide for a spill
containment volume able to contain 10% of the total enclosed
container volume of all containers, or 110% of the capacity of the
largest container within its boundary, whichever is greater.
• Secondary containment facilities shall be impervious to the materials
stored therein for a minimum contact time of 72 hours.
• Secondary containment facilities shall be maintained free of
accumulated rainwater and spills. In the event of spills or leaks,
accumulated rainwater and spills shall be collected and placed into
drums. These liquids shall be handled as hazardous waste unless
testing determines them to be non-hazardous.
• Sufficient separation should be provided between stored containers to
allow for spill cleanup and emergency response access.
• During the wet weather season (Oct 1 – April 30), each secondary
containment facility shall be covered during non-working days, prior
to and during rain events.
• Keep material storage areas clean, organized and equipped with an
ample supply of appropriate spill clean-up material (spill kit).
• The spill kit should include, at a minimum:
• 1-Water Resistant Nylon Bag
• 3-Oil Absorbent Socks 3”x 4’
• 2-Oil Absorbent Socks 3”x 10’
• 12-Oil Absorbent Pads 17”x19”
• 1-Pair Splash Resistant Goggles
• 3-Pair Nitrile Gloves
• 10-Disposable Bags with Ties
• Instructions
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BMP C200: Interceptor Dike and Swale
Purpose Provide a ridge of compacted soil, or a ridge with an upslope swale, at the
top or base of a disturbed slope or along the perimeter of a disturbed
construction area to convey stormwater. Use the dike and/or swale to
intercept the runoff from unprotected areas and direct it to areas where
erosion can be controlled. This can prevent storm runoff from entering the
work area or sediment-laden runoff from leaving the construction site.
Conditions of Use Where the runoff from an exposed site or disturbed slope must be conveyed
to an erosion control facility which can safely convey the stormwater.
• Locate upslope of a construction site to prevent runoff from entering
disturbed area.
• When placed horizontally across a disturbed slope, it reduces the
amount and velocity of runoff flowing down the slope.
• Locate downslope to collect runoff from a disturbed area and direct
water to a sediment basin.
Design and
Installation
Specifications
• Dike and/or swale and channel must be stabilized with temporary or
permanent vegetation or other channel protection during construction.
• Channel requires a positive grade for drainage; steeper grades require
channel protection and check dams.
• Review construction for areas where overtopping may occur.
• Can be used at top of new fill before vegetation is established.
• May be used as a permanent diversion channel to carry the runoff.
• Sub-basin tributary area should be one acre or less.
• Design capacity for the peak flow from a 10-year, 24-hour storm,
assuming a Type 1A rainfall distribution, for temporary facilities.
Alternatively, use 1.6 times the 10-year, 1-hour flow indicated by an
approved continuous runoff model. For facilities that will also serve on
a permanent basis, consult the local government’s drainage
requirements.
Interceptor dikes shall meet the following criteria:
Top Width 2 feet minimum.
Height 1.5 feet minimum on berm.
Side Slope 2H:1V or flatter.
Grade Depends on topography, however, dike system minimum is
0.5%, and maximum is 1%.
Compaction Minimum of 90 percent ASTM D698 standard proctor.
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Horizontal Spacing of Interceptor Dikes:
Average Slope Slope Percent Flowpath Length
20H:1V or less 3-5% 300 feet
(10 to 20)H:1V 5-10% 200 feet
(4 to 10)H:1V 10-25% 100 feet
(2 to 4)H:1V 25-50% 50 feet
Stabilization depends on velocity and reach
Slopes <5% Seed and mulch applied within 5 days of dike
construction (see BMP C121, Mulching).
Slopes 5 - 40% Dependent on runoff velocities and dike materials.
Stabilization should be done immediately using either sod
or riprap or other measures to avoid erosion.
• The upslope side of the dike shall provide positive drainage to the dike
outlet. No erosion shall occur at the outlet. Provide energy dissipation
measures as necessary. Sediment-laden runoff must be released
through a sediment trapping facility.
• Minimize construction traffic over temporary dikes. Use temporary
cross culverts for channel crossing.
Interceptor swales shall meet the following criteria:
Bottom Width 2 feet minimum; the cross-section bottom shall be
level.
Depth 1-foot minimum.
Side Slope 2H:1V or flatter.
Grade Maximum 5 percent, with positive drainage to a
suitable outlet (such as a sediment pond).
Stabilization Seed as per BMP C120, Temporary and
Permanent Seeding, or BMP C202, Channel
Lining, 12 inches thick riprap pressed into the bank
and extending at least 8 inches vertical from the
bottom.
• Inspect diversion dikes and interceptor swales once a week and after
every rainfall. Immediately remove sediment from the flow area.
• Damage caused by construction traffic or other activity must be
repaired before the end of each working day.
Check outlets and make timely repairs as needed to avoid gully formation.
When the area below the temporary diversion dike is permanently
stabilized, remove the dike and fill and stabilize the channel to blend with
the natural surface.
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BMP C201: Grass-Lined Channels
Purpose To provide a channel with a vegetative lining for conveyance of runoff.
See Figure 4.2.1 for typical grass-lined channels.
Conditions of Use This practice applies to construction sites where concentrated runoff needs
to be contained to prevent erosion or flooding.
• When a vegetative lining can provide sufficient stability for the
channel cross section and at lower velocities of water (normally
dependent on grade). This means that the channel slopes are generally
less than 5 percent and space is available for a relatively large cross
section.
• Typical uses include roadside ditches, channels at property boundaries,
outlets for diversions, and other channels and drainage ditches in low
areas.
• Channels that will be vegetated should be installed before major
earthwork and hydroseeded with a bonded fiber matrix (BFM). The
vegetation should be well established (i.e., 75 percent cover) before
water is allowed to flow in the ditch. With channels that will have high
flows, erosion control blankets should be installed over the hydroseed.
If vegetation cannot be established from seed before water is allowed
in the ditch, sod should be installed in the bottom of the ditch in lieu of
hydromulch and blankets.
Design and
Installation
Specifications
Locate the channel where it can conform to the topography and other
features such as roads.
• Locate them to use natural drainage systems to the greatest extent
possible.
• Avoid sharp changes in alignment or bends and changes in grade.
• Do not reshape the landscape to fit the drainage channel.
• The maximum design velocity shall be based on soil conditions, type
of vegetation, and method of revegetation, but at no times shall
velocity exceed 5 feet/second. The channel shall not be overtopped by
the peak runoff from a 10-year, 24-hour storm, assuming a Type 1A
rainfall distribution." Alternatively, use 1.6 times the 10-year, 1-hour
flow indicated by an approved continuous runoff model to determine a
flow rate which the channel must contain.
• Where the grass-lined channel will also function as a permanent
stormwater conveyance facility, consult the drainage conveyance
requirements of the local government with jurisdiction.
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• An established grass or vegetated lining is required before the channel
can be used to convey stormwater, unless stabilized with nets or
blankets.
• If design velocity of a channel to be vegetated by seeding exceeds 2
ft/sec, a temporary channel liner is required. Geotextile or special
mulch protection such as fiberglass roving or straw and netting
provides stability until the vegetation is fully established. See Figure
4.2.2.
• Check dams shall be removed when the grass has matured sufficiently
to protect the ditch or swale unless the slope of the swale is greater
than 4 percent. The area beneath the check dams shall be seeded and
mulched immediately after dam removal.
• If vegetation is established by sodding, the permissible velocity for
established vegetation may be used and no temporary liner is needed.
• Do not subject grass-lined channel to sedimentation from disturbed
areas. Use sediment-trapping BMPs upstream of the channel.
• V-shaped grass channels generally apply where the quantity of water is
small, such as in short reaches along roadsides. The V-shaped cross
section is least desirable because it is difficult to stabilize the bottom
where velocities may be high.
• Trapezoidal grass channels are used where runoff volumes are large
and slope is low so that velocities are nonerosive to vegetated linings.
(Note: it is difficult to construct small parabolic shaped channels.)
• Subsurface drainage, or riprap channel bottoms, may be necessary on
sites that are subject to prolonged wet conditions due to long duration
flows or a high water table.
• Provide outlet protection at culvert ends and at channel intersections.
• Grass channels, at a minimum, should carry peak runoff for temporary
construction drainage facilities from the 10-year, 24-hour storm
without eroding. Where flood hazard exists, increase the capacity
according to the potential damage.
• Grassed channel side slopes generally are constructed 3H:1V or flatter
to aid in the establishment of vegetation and for maintenance.
• Construct channels a minimum of 0.2 foot larger around the periphery
to allow for soil bulking during seedbed preparations and sod buildup.
Maintenance
Standards
During the establishment period, check grass-lined channels after every
rainfall.
• After grass is established, periodically check the channel; check it after
every heavy rainfall event. Immediately make repairs.
• It is particularly important to check the channel outlet and all road
crossings for bank stability and evidence of piping or scour holes.
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• Remove all significant sediment accumulations to maintain the
designed carrying capacity. Keep the grass in a healthy, vigorous
condition at all times, since it is the primary erosion protection for the
channel.
Figure 4.2.1 – Typical Grass-Lined Channels
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OVERCUTCHANNEL
2'(50mm) TOALLOW
BULKING DURING SEEDBED
PREPARATION
TYPICAL INSTALLATION
WITH EROSION CONTROL
BLANKETS OR TURF
REINFORCEMENT MATS
Intermittent Check Slot Longitudinal Anchor Trench
Shingle-lap spliced ends or begin new
roll in an intermittent check slot
Prepare soil and apply seed before
installing blankets, mats or other
temporary channel liner system
/
NOTES:
1 Design velocities exceeding 2 ft/sec (0.5m/sec) require temporary blankets, mats or similar liners
to protect seed and soil until vegetation becomes established.
2 Grass-lined channels with design velocities exceeding 6 ft/sec (2m/sec) should include turf reinforcement
mats.
Fig ure 4.2 .2 – Temporary Channel Liners
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Maintenance
Standards
Subsurface drains shall be checked periodically to ensure that they are
free-flowing and not clogged with sediment or roots.
• The outlet shall be kept clean and free of debris.
• Surface inlets shall be kept open and free of sediment and other debris.
• Trees located too close to a subsurface drain often clog the system
with their roots. If a drain becomes clogged, relocate the drain or
remove the trees as a last resort. Drain placement should be planned to
minimize this problem.
• Where drains are crossed by heavy vehicles, the line shall be checked
to ensure that it is not crushed.
BMP C206: Level Spreader
Purpose To provide a temporary outlet for dikes and diversions consisting of an
excavated depression constructed at zero grade across a slope. To convert
concentrated runoff to sheet flow and release it onto areas stabilized by
existing vegetation or an engineered filter strip.
Conditions of Use Used when a concentrated flow of water needs to be dispersed over a large
area with existing stable vegetation.
• Items to consider are:
1. What is the risk of erosion or damage if the flow may become
concentrated?
2. Is an easement required if discharged to adjoining property?
3. Most of the flow should be as ground water and not as surface
flow.
4. Is there an unstable area downstream that cannot accept additional
ground water?
• Use only where the slopes are gentle, the water volume is relatively
low, and the soil will adsorb most of the low flow events.
Design and
Installation
Specifications
Use above undisturbed areas that are stabilized by existing vegetation.
If the level spreader has any low points, flow will concentrate, create
channels and may cause erosion.
• Discharge area below the outlet must be uniform with a slope flatter
than 5H:1V.
• Outlet to be constructed level in a stable, undisturbed soil profile (not
on fill).
• The runoff shall not re-concentrate after release unless intercepted by
another downstream measure.
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Densely vegetated for aMin. of 100' and slopeless than 5:1
Pressure-Treated 2"x10"
1' Min.2:1 Max.3' Min.
• The grade of the channel for the last 20 feet of the dike or interceptor
entering the level spreader shall be less than or equal to 1 percent. The
grade of the level spreader shall be 0 percent to ensure uniform
spreading of storm runoff.
• A 6-inch high gravel berm placed across the level lip shall consist of
washed crushed rock, 2- to 4-inch or 3/4-inch to 1½-inch size.
• The spreader length shall be determined by estimating the peak flow
expected from the 10-year, 24-hour design storm. The length of the
spreader shall be a minimum of 15 feet for 0.1 cfs and shall increase
by 10 feet for each 0.1 cfs thereafter to a maximum of 0.5 cfs per
spreader. Use multiple spreaders for higher flows.
• The width of the spreader should be at least 6 feet.
• The depth of the spreader as measured from the lip should be at least 6
inches and it should be uniform across the entire length.
• Level spreaders shall be setback from the property line unless there is
an easement for flow.
• Level spreaders, when installed every so often in grassy swales, keep
the flows from concentrating. Materials that can be used include sand
bags, lumber, logs, concrete, and pipe. To function properly, the
material needs to be installed level and on contour. Figures
4.2.5Figure425 and 4.2.6 provide a cross-section and a detail of a level
spreader. A capped perforated pipe could also be used as a spreader.
Maintenance
Standards
The spreader should be inspected after every runoff event to ensure that it
is functioning correctly.
• The contractor should avoid the placement of any material on the
structure and should prevent construction traffic from crossing over
the structure.
• If the spreader is damaged by construction traffic, it shall be
immediately repaired.
Figure 4.2.5 – Cross Section of Level Spreader
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Figure 4.2.6 – Detail of Level Spreader
BMP C207: Check Dams
Purpose Construction of small dams across a swale or ditch reduces the velocity of
concentrated flow and dissipates energy at the check dam.
Conditions of Use Where temporary channels or permanent channels are not yet vegetated,
channel lining is infeasible, and/or velocity checks are required.
• Check dams may not be placed in streams unless approved by the State
Department of Fish and Wildlife. Check dams may not be placed in
wetlands without approval from a permitting agency.
• Do not place check dams below the expected backwater from any
salmonid bearing water between October 1 and May 31 to ensure that
there is no loss of high flow refuge habitat for overwintering juvenile
salmonids and emergent salmonid fry.
• Construct rock check dams from appropriately sized rock. The rock
used must be large enough to stay in place given the expected design
flow through the channel. The rock must be placed by hand or by
mechanical means (no dumping of rock to form dam) to achieve
complete coverage of the ditch or swale and to ensure that the center
of the dam is lower than the edges.
• Check dams may also be constructed of either rock or pea-gravel filled
bags. Numerous new products are also available for this purpose. They
tend to be re-usable, quick and easy to install, effective, and cost
efficient.
• Place check dams perpendicular to the flow of water.
• The dam should form a triangle when viewed from the side. This
prevents undercutting as water flows over the face of the dam rather
than falling directly onto the ditch bottom.
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• Before installing check dams impound and bypass upstream water
flow away from the work area. Options for bypassing include pumps,
siphons, or temporary channels.
• Check dams in association with sumps work more effectively at
slowing flow and retaining sediment than just a check dam alone. A
deep sump should be provided immediately upstream of the check
dam.
• In some cases, if carefully located and designed, check dams can
remain as permanent installations with very minor regrading. They
may be left as either spillways, in which case accumulated sediment
would be graded and seeded, or as check dams to prevent further
sediment from leaving the site.
• The maximum spacing between the dams shall be such that the toe of
the upstream dam is at the same elevation as the top of the downstream
dam.
• Keep the maximum height at 2 feet at the center of the dam.
• Keep the center of the check dam at least 12 inches lower than the
outer edges at natural ground elevation.
• Keep the side slopes of the check dam at 2H:1V or flatter.
• Key the stone into the ditch banks and extend it beyond the abutments
a minimum of 18 inches to avoid washouts from overflow around the
dam.
• Use filter fabric foundation under a rock or sand bag check dam. If a
blanket ditch liner is used, filter fabric is not necessary. A piece of
organic or synthetic blanket cut to fit will also work for this purpose.
• In the case of grass-lined ditches and swales, all check dams and
accumulated sediment shall be removed when the grass has matured
sufficiently to protect the ditch or swale - unless the slope of the swale
is greater than 4 percent. The area beneath the check dams shall be
seeded and mulched immediately after dam removal.
• Ensure that channel appurtenances, such as culvert entrances below
check dams, are not subject to damage or blockage from displaced
stones. Figure 4.2.7 depicts a typical rock check dam.
Maintenance
Standards
Check dams shall be monitored for performance and sediment
accumulation during and after each runoff producing rainfall. Sediment
shall be removed when it reaches one half the sump depth.
• Anticipate submergence and deposition above the check dam and
erosion from high flows around the edges of the dam.
• If significant erosion occurs between dams, install a protective riprap
liner in that portion of the channel.
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Approved as
Equivalent
Ecology has approved products as able to meet the requirements of BMP
C207. The products did not pass through the Technology Assessment
Protocol – Ecology (TAPE) process. Local jurisdictions may choose not
to accept this product approved as equivalent, or may require additional
testing prior to consideration for local use. The products are available for
review on Ecology’s website at
http://www.ecy.wa.gov/programs/wq/stormwater/newtech/equivalent.html
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Figure 4.2.7 – Rock Check Dam
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BMP C208: Triangular Silt Dike (TSD) (Geotextile-Encased Check Dam)
Purpose Triangular silt dikes may be used as check dams, for perimeter protection,
for temporary soil stockpile protection, for drop inlet protection, or as a
temporary interceptor dike.
Conditions of use • May be used on soil or pavement with adhesive or staples.
• TSDs have been used to build temporary:
1. sediment ponds;
2. diversion ditches;
3. concrete wash out facilities;
4. curbing;
5. water bars;
6. level spreaders; and,
7. berms.
Design and
Installation
Specifications
Made of urethane foam sewn into a woven geosynthetic fabric.
It is triangular, 10 inches to 14 inches high in the center, with a 20-inch to
28-inch base. A 2–foot apron extends beyond both sides of the triangle
along its standard section of 7 feet. A sleeve at one end allows attachment
of additional sections as needed.
• Install with ends curved up to prevent water from flowing around the
ends.
• The fabric flaps and check dam units are attached to the ground with
wire staples. Wire staples should be No. 11 gauge wire and should be
200 mm to 300 mm in length.
• When multiple units are installed, the sleeve of fabric at the end of the
unit shall overlap the abutting unit and be stapled.
• Check dams should be located and installed as soon as construction
will allow.
• Check dams should be placed perpendicular to the flow of water.
• When used as check dams, the leading edge must be secured with
rocks, sandbags, or a small key slot and staples.
• In the case of grass-lined ditches and swales, check dams and
accumulated sediment shall be removed when the grass has matured
sufficiently to protect the ditch or swale unless the slope of the swale
is greater than 4 percent. The area beneath the check dams shall be
seeded and mulched immediately after dam removal.
Maintenance • Triangular silt dams shall be inspected for performance and sediment
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Standards accumulation during and after each runoff producing rainfall.
Sediment shall be removed when it reaches one half the height of the
dam.
• Anticipate submergence and deposition above the triangular silt dam
and erosion from high flows around the edges of the dam. Immediately
repair any damage or any undercutting of the dam.
BMP C209: Outlet Protection
Purpose Outlet protection prevents scour at conveyance outlets and minimizes the
potential for downstream erosion by reducing the velocity of concentrated
stormwater flows.
Conditions of use Outlet protection is required at the outlets of all ponds, pipes, ditches, or
other conveyances, and where runoff is conveyed to a natural or manmade
drainage feature such as a stream, wetland, lake, or ditch.
Design and
Installation
Specifications
The receiving channel at the outlet of a culvert shall be protected from
erosion by rock lining a minimum of 6 feet downstream and extending up
the channel sides a minimum of 1–foot above the maximum tailwater
elevation or 1-foot above the crown, whichever is higher. For large pipes
(more than 18 inches in diameter), the outlet protection lining of the
channel is lengthened to four times the diameter of the culvert.
• Standard wingwalls, and tapered outlets and paved channels should
also be considered when appropriate for permanent culvert outlet
protection. (See WSDOT Hydraulic Manual, available through
WSDOT Engineering Publications).
• Organic or synthetic erosion blankets, with or without vegetation, are
usually more effective than rock, cheaper, and easier to install.
Materials can be chosen using manufacturer product specifications.
ASTM test results are available for most products and the designer can
choose the correct material for the expected flow.
• With low flows, vegetation (including sod) can be effective.
• The following guidelines shall be used for riprap outlet protection:
1. If the discharge velocity at the outlet is less than 5 fps (pipe slope
less than 1 percent), use 2-inch to 8-inch riprap. Minimum
thickness is 1-foot.
2. For 5 to 10 fps discharge velocity at the outlet (pipe slope less than
3 percent), use 24-inch to 48-inch riprap. Minimum thickness is 2
feet.
3. For outlets at the base of steep slope pipes (pipe slope greater than
10 percent), an engineered energy dissipater shall be used.
• Filter fabric or erosion control blankets should always be used under
riprap to prevent scour and channel erosion.
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• New pipe outfalls can provide an opportunity for low-cost fish habitat
improvements. For example, an alcove of low-velocity water can be
created by constructing the pipe outfall and associated energy
dissipater back from the stream edge and digging a channel, over-
widened to the upstream side, from the outfall. Overwintering juvenile
and migrating adult salmonids may use the alcove as shelter during
high flows. Bank stabilization, bioengineering, and habitat features
may be required for disturbed areas. This work may require a HPA.
See Volume V for more information on outfall system design.
Maintenance
Standards
• Inspect and repair as needed.
• Add rock as needed to maintain the intended function.
• Clean energy dissipater if sediment builds up.
BMP C220: Storm Drain Inlet Protection
Purpose Storm drain inlet protection prevents coarse sediment from entering
drainage systems prior to permanent stabilization of the disturbed area.
Conditions of Use Use storm drain inlet protection at inlets that are operational before
permanent stabilization of the disturbed drainage area. Provide protection
for all storm drain inlets downslope and within 500 feet of a disturbed or
construction area, unless conveying runoff entering catch basins to a
sediment pond or trap.
Also consider inlet protection for lawn and yard drains on new home
construction. These small and numerous drains coupled with lack of
gutters in new home construction can add significant amounts of sediment
into the roof drain system. If possible delay installing lawn and yard drains
until just before landscaping or cap these drains to prevent sediment from
entering the system until completion of landscaping. Provide 18-inches of
sod around each finished lawn and yard drain.
Table 4.2.2 lists several options for inlet protection. All of the methods for
storm drain inlet protection tend to plug and require a high frequency of
maintenance. Limit drainage areas to one acre or less. Possibly provide
emergency overflows with additional end-of-pipe treatment where
stormwater ponding would cause a hazard.
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Table 4.2.2
Storm Drain Inlet Protection
Type of Inlet
Protection
Emergency
Overflow
Applicable for
Paved/ Earthen
Surfaces Conditions of Use
Drop Inlet Protection
Excavated drop inlet protection Yes, temporary flooding will occur
Earthen Applicable for heavy flows. Easy to maintain. Large area Requirement: 30’ X 30’/acre
Block and gravel drop inlet protection Yes Paved or Earthen Applicable for heavy concentrated flows. Will not pond.
Gravel and wire drop inlet protection No Applicable for heavy concentrated flows. Will pond. Can withstand traffic.
Catch basin filters Yes Paved or Earthen Frequent maintenance required.
Curb Inlet Protection
Curb inlet protection with a wooden weir Small capacity overflow Paved Used for sturdy, more compact installation.
Block and gravel curb inlet protection
Yes Paved Sturdy, but limited filtration.
Culvert Inlet Protection
Culvert inlet sediment trap 18 month expected life.
Design and
Installation
Specifications
Excavated Drop Inlet Protection - An excavated impoundment around the
storm drain. Sediment settles out of the stormwater prior to entering the
storm drain.
• Provide a depth of 1-2 ft as measured from the crest of the inlet
structure.
• Slope sides of excavation no steeper than 2H:1V.
• Minimum volume of excavation 35 cubic yards.
• Shape basin to fit site with longest dimension oriented toward the
longest inflow area.
• Install provisions for draining to prevent standing water problems.
• Clear the area of all debris.
• Grade the approach to the inlet uniformly.
• Drill weep holes into the side of the inlet.
• Protect weep holes with screen wire and washed aggregate.
• Seal weep holes when removing structure and stabilizing area.
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• Build a temporary dike, if necessary, to the down slope side of the
structure to prevent bypass flow.
Block and Gravel Filter - A barrier formed around the storm drain inlet
with standard concrete blocks and gravel. See Figure 4.2.8.
• Provide a height of 1 to 2 feet above inlet.
• Recess the first row 2-inches into the ground for stability.
• Support subsequent courses by placing a 2x4 through the block
opening.
• Do not use mortar.
• Lay some blocks in the bottom row on their side for dewatering the
pool.
• Place hardware cloth or comparable wire mesh with ½-inch openings
over all block openings.
• Place gravel just below the top of blocks on slopes of 2H:1V or flatter.
• An alternative design is a gravel donut.
• Provide an inlet slope of 3H:1V.
• Provide an outlet slope of 2H:1V.
• Provide a1-foot wide level stone area between the structure and the
inlet.
• Use inlet slope stones 3 inches in diameter or larger.
• Use gravel ½- to ¾-inch at a minimum thickness of 1-foot for the
outlet slope.
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Figure 4.2.8 – Block and Gravel Filter
Gravel and Wire Mesh Filter - A gravel barrier placed over the top of the
inlet. This structure does not provide an overflow.
• Use a hardware cloth or comparable wire mesh with ½-inch openings.
• Use coarse aggregate.
• Provide a height 1-foot or more, 18-inches wider than inlet on all
sides.
• Place wire mesh over the drop inlet so that the wire extends a
minimum of 1-foot beyond each side of the inlet structure.
• Overlap the strips if more than one strip of mesh is necessary.
Ponding Height
Notes:
1. Drop inlet sediment barriers are to be used for small, nearly level drainage areas. (less than 5%)
2. Excavate a basin of sufficient size adjacent to the drop inlet.
3. The top of the structure (ponding height) must be well below the ground elevation downslope to prevent
runoff from bypassing the inlet. A temporary dike may be necessary on the downslope side of the structure.
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• Place coarse aggregate over the wire mesh.
• Provide at least a 12-inch depth of gravel over the entire inlet opening
and extend at least 18-inches on all sides.
Catchbasin Filters – Use inserts designed by manufacturers for
construction sites. The limited sediment storage capacity increases the
amount of inspection and maintenance required, which may be daily for
heavy sediment loads. To reduce maintenance requirements combine a
catchbasin filter with another type of inlet protection. This type of inlet
protection provides flow bypass without overflow and therefore may be a
better method for inlets located along active rights-of-way.
• Provides 5 cubic feet of storage.
• Requires dewatering provisions.
• Provides a high-flow bypass that will not clog under normal use at a
construction site.
• Insert the catchbasin filter in the catchbasin just below the grating.
Curb Inlet Protection with Wooden Weir – Barrier formed around a curb
inlet with a wooden frame and gravel.
• Use wire mesh with ½-inch openings.
• Use extra strength filter cloth.
• Construct a frame.
• Attach the wire and filter fabric to the frame.
• Pile coarse washed aggregate against wire/fabric.
• Place weight on frame anchors.
Block and Gravel Curb Inlet Protection – Barrier formed around a curb
inlet with concrete blocks and gravel. See Figure 4.2.9.
• Use wire mesh with ½-inch openings.
• Place two concrete blocks on their sides abutting the curb at either side
of the inlet opening. These are spacer blocks.
• Place a 2x4 stud through the outer holes of each spacer block to align
the front blocks.
• Place blocks on their sides across the front of the inlet and abutting the
spacer blocks.
• Place wire mesh over the outside vertical face.
• Pile coarse aggregate against the wire to the top of the barrier.
Curb and Gutter Sediment Barrier – Sandbag or rock berm (riprap and
aggregate) 3 feet high and 3 feet wide in a horseshoe shape. See Figure
4.2.10.
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• Construct a horseshoe shaped berm, faced with coarse aggregate if
using riprap, 3 feet high and 3 feet wide, at least 2 feet from the inlet.
• Construct a horseshoe shaped sedimentation trap on the outside of the
berm sized to sediment trap standards for protecting a culvert inlet.
Maintenance
Standards
• Inspect catch basin filters frequently, especially after storm events.
Clean and replace clogged inserts. For systems with clogged stone
filters: pull away the stones from the inlet and clean or replace. An
alternative approach would be to use the clogged stone as fill and put
fresh stone around the inlet.
• Do not wash sediment into storm drains while cleaning. Spread all
excavated material evenly over the surrounding land area or stockpile
and stabilize as appropriate.
Approved as
Equivalent
Ecology has approved products as able to meet the requirements of BMP
C220. The products did not pass through the Technology Assessment
Protocol – Ecology (TAPE) process. Local jurisdictions may choose not
to accept this product approved as equivalent, or may require additional
testing prior to consideration for local use. The products are available for
review on Ecology’s website at
http://www.ecy.wa.gov/programs/wq/stormwater/newtech/equivalent.html
Volume II – Construction Stormwater Pollution Prevention - August 2012
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Figure 4.2.9 – Block and Gravel Curb Inlet Protection
A
Plan View
Wire Screen or
Filter Fabric Catch Basin
Curb Inlet
Concrete Block
Ponding Height
Overflow
2x4 Wood Stud
(100x50 Timber Stud)
Concrete Block
Wire Screen or
Filter Fabric
Curb Inlet
¾" Drain Gravel
(20mm)
¾" Drain Gravel
(20mm)Section A - A
Back of Curb Concrete Block
2x4 Wood Stud
Catch BasinBack of Sidewalk
NOTES:
1. Use block and gravel type sediment barrier when curb inlet is located in gently sloping street segment,
where water can pond and allow sediment to separate from runoff.
2. Barrier shall allow for overflow from severe storm event.
3. Inspect barriers and remove sediment after each storm event. Sediment and gravel must be removed
from the traveled way immediately.
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Figure 4.2.10 – Curb and Gutter Barrier
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If required, drape filter fabricover brush and secure in 4"x4"min. trench with compactedbackfill.
Min. 5' wide brush barrier withmax. 6" diameter woody debris.Alternatively topsoil strippingsmay be used to form the barrier.
Anchor downhill edge offilter fabric with stakes,sandbags, or equivalent.
2' Min. Height
BMP C231: Brush Barrier
Purpose The purpose of brush barriers is to reduce the transport of coarse sediment
from a construction site by providing a temporary physical barrier to
sediment and reducing the runoff velocities of overland flow.
Conditions of Use • Brush barriers may be used downslope of all disturbed areas of less
than one-quarter acre.
• Brush barriers are not intended to treat concentrated flows, nor are
they intended to treat substantial amounts of overland flow. Any
concentrated flows must be conveyed through the drainage system to a
sediment pond. The only circumstance in which overland flow can be
treated solely by a brush barrier, rather than by a sediment pond, is
when the area draining to the barrier is small.
• Brush barriers should only be installed on contours.
Design and
Installation
Specifications
• Height 2 feet (minimum) to 5 feet (maximum).
• Width 5 feet at base (minimum) to 15 feet (maximum).
• Filter fabric (geotextile) may be anchored over the brush berm to
enhance the filtration ability of the barrier. Ten-ounce burlap is an
adequate alternative to filter fabric.
• Chipped site vegetation, composted mulch, or wood-based mulch (hog
fuel) can be used to construct brush barriers.
• A 100 percent biodegradable installation can be constructed using 10-
ounce burlap held in place by wooden stakes. Figure 4.2.11 depicts a
typical brush barrier.
Maintenance
Standards
• There shall be no signs of erosion or concentrated runoff under or
around the barrier. If concentrated flows are bypassing the barrier, it
must be expanded or augmented by toed-in filter fabric.
• The dimensions of the barrier must be maintained.
Figure 4.2.11 – Brush Barrier
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BMP C232: Gravel Filter Berm
Purpose A gravel filter berm is constructed on rights-of-way or traffic areas within
a construction site to retain sediment by using a filter berm of gravel or
crushed rock.
Conditions of Use Where a temporary measure is needed to retain sediment from rights-of-
way or in traffic areas on construction sites.
Design and
Installation
Specifications
• Berm material shall be ¾ to 3 inches in size, washed well-grade gravel
or crushed rock with less than 5 percent fines.
• Spacing of berms:
− Every 300 feet on slopes less than 5 percent
− Every 200 feet on slopes between 5 percent and 10 percent
− Every 100 feet on slopes greater than 10 percent
• Berm dimensions:
− 1 foot high with 3H:1V side slopes
− 8 linear feet per 1 cfs runoff based on the 10-year, 24-hour design
storm
Maintenance
Standards
• Regular inspection is required. Sediment shall be removed and filter
material replaced as needed.
BMP C233: Silt Fence
Purpose Use of a silt fence reduces the transport of coarse sediment from a
construction site by providing a temporary physical barrier to sediment
and reducing the runoff velocities of overland flow. See Figure 4.2.12 for
details on silt fence construction.
Conditions of Use Silt fence may be used downslope of all disturbed areas.
• Silt fence shall prevent soil carried by runoff water from going
beneath, through, or over the top of the silt fence, but shall allow the
water to pass through the fence.
• Silt fence is not intended to treat concentrated flows, nor is it intended
to treat substantial amounts of overland flow. Convey any
concentrated flows through the drainage system to a sediment pond.
• Do not construct silt fences in streams or use in V-shaped ditches. Silt
fences do not provide an adequate method of silt control for anything
deeper than sheet or overland flow.
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Figure 4.2.12 – Silt Fence
Design and
Installation
Specifications
• Use in combination with sediment basins or other BMPs.
• Maximum slope steepness (normal (perpendicular) to fence line)
1H:1V.
• Maximum sheet or overland flow path length to the fence of 100 feet.
• Do not allow flows greater than 0.5 cfs.
• The geotextile used shall meet the following standards. All geotextile
properties listed below are minimum average roll values (i.e., the test
result for any sampled roll in a lot shall meet or exceed the values
shown in Table 4.2.3):
Table 4.2.3
Geotextile Standards
Polymeric Mesh AOS
(ASTM D4751)
0.60 mm maximum for slit film woven (#30 sieve). 0.30
mm maximum for all other geotextile types (#50 sieve).
0.15 mm minimum for all fabric types (#100 sieve).
Water Permittivity
(ASTM D4491)
0.02 sec-1 minimum
Grab Tensile Strength
(ASTM D4632)
180 lbs. Minimum for extra strength fabric.
100 lbs minimum for standard strength fabric.
Grab Tensile Strength
(ASTM D4632)
30% maximum
Ultraviolet Resistance
(ASTM D4355)
70% minimum
• Support standard strength fabrics with wire mesh, chicken wire, 2-inch
x 2-inch wire, safety fence, or jute mesh to increase the strength of the
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fabric. Silt fence materials are available that have synthetic mesh
backing attached.
• Filter fabric material shall contain ultraviolet ray inhibitors and
stabilizers to provide a minimum of six months of expected usable
construction life at a temperature range of 0°F. to 120°F.
• One-hundred percent biodegradable silt fence is available that is
strong, long lasting, and can be left in place after the project is
completed, if permitted by local regulations.
• Refer to Figure 4.2.12 for standard silt fence details. Include the
following standard Notes for silt fence on construction plans and
specifications:
1. The contractor shall install and maintain temporary silt fences at
the locations shown in the Plans.
2. Construct silt fences in areas of clearing, grading, or drainage prior
to starting those activities.
3. The silt fence shall have a 2-feet min. and a 2½-feet max. height
above the original ground surface.
4. The filter fabric shall be sewn together at the point of manufacture
to form filter fabric lengths as required. Locate all sewn seams at
support posts. Alternatively, two sections of silt fence can be
overlapped, provided the Contractor can demonstrate, to the
satisfaction of the Engineer, that the overlap is long enough and
that the adjacent fence sections are close enough together to
prevent silt laden water from escaping through the fence at the
overlap.
5. Attach the filter fabric on the up-slope side of the posts and secure
with staples, wire, or in accordance with the manufacturer's
recommendations. Attach the filter fabric to the posts in a manner
that reduces the potential for tearing.
6. Support the filter fabric with wire or plastic mesh, dependent on
the properties of the geotextile selected for use. If wire or plastic
mesh is used, fasten the mesh securely to the up-slope side of the
posts with the filter fabric up-slope of the mesh.
7. Mesh support, if used, shall consist of steel wire with a maximum
mesh spacing of 2-inches, or a prefabricated polymeric mesh. The
strength of the wire or polymeric mesh shall be equivalent to or
greater than 180 lbs. grab tensile strength. The polymeric mesh
must be as resistant to the same level of ultraviolet radiation as the
filter fabric it supports.
8. Bury the bottom of the filter fabric 4-inches min. below the ground
surface. Backfill and tamp soil in place over the buried portion of
the filter fabric, so that no flow can pass beneath the fence and
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scouring cannot occur. When wire or polymeric back-up support
mesh is used, the wire or polymeric mesh shall extend into the
ground 3-inches min.
9. Drive or place the fence posts into the ground 18-inches min. A
12–inch min. depth is allowed if topsoil or other soft subgrade soil
is not present and 18-inches cannot be reached. Increase fence post
min. depths by 6 inches if the fence is located on slopes of 3H:1V
or steeper and the slope is perpendicular to the fence. If required
post depths cannot be obtained, the posts shall be adequately
secured by bracing or guying to prevent overturning of the fence
due to sediment loading.
10. Use wood, steel or equivalent posts. The spacing of the support
posts shall be a maximum of 6-feet. Posts shall consist of either:
• Wood with dimensions of 2-inches by 2-inches wide min. and
a 3-feet min. length. Wood posts shall be free of defects such
as knots, splits, or gouges.
• No. 6 steel rebar or larger.
• ASTM A 120 steel pipe with a minimum diameter of 1-inch.
• U, T, L, or C shape steel posts with a minimum weight of 1.35
lbs./ft.
• Other steel posts having equivalent strength and bending
resistance to the post sizes listed above.
11. Locate silt fences on contour as much as possible, except at the
ends of the fence, where the fence shall be turned uphill such that
the silt fence captures the runoff water and prevents water from
flowing around the end of the fence.
12. If the fence must cross contours, with the exception of the ends of
the fence, place gravel check dams perpendicular to the back of the
fence to minimize concentrated flow and erosion. The slope of the
fence line where contours must be crossed shall not be steeper than
3H:1V.
• Gravel check dams shall be approximately 1-foot deep at the
back of the fence. Gravel check dams shall be continued
perpendicular to the fence at the same elevation until the top of
the check dam intercepts the ground surface behind the fence.
• Gravel check dams shall consist of crushed surfacing base
course, gravel backfill for walls, or shoulder ballast. Gravel
check dams shall be located every 10 feet along the fence
where the fence must cross contours.
• Refer to Figure 4.2.13 for slicing method details. Silt fence installation
using the slicing method specifications:
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1. The base of both end posts must be at least 2- to 4-inches above the
top of the filter fabric on the middle posts for ditch checks to drain
properly. Use a hand level or string level, if necessary, to mark
base points before installation.
2. Install posts 3- to 4-feet apart in critical retention areas and 6- to 7-
feet apart in standard applications.
3. Install posts 24-inches deep on the downstream side of the silt
fence, and as close as possible to the filter fabric, enabling posts to
support the filter fabric from upstream water pressure.
4. Install posts with the nipples facing away from the filter fabric.
5. Attach the filter fabric to each post with three ties, all spaced
within the top 8-inches of the filter fabric. Attach each tie
diagonally 45 degrees through the filter fabric, with each puncture
at least 1-inch vertically apart. Each tie should be positioned to
hang on a post nipple when tightening to prevent sagging.
6. Wrap approximately 6-inches of fabric around the end posts and
secure with 3 ties.
7. No more than 24-inches of a 36-inch filter fabric is allowed above
ground level.
Compact the soil immediately next to the filter fabric with the front
wheel of the tractor, skid steer, or roller exerting at least 60 pounds
per square inch. Compact the upstream side first and then each side
twice for a total of four trips. Check and correct the silt fence
installation for any deviation before compaction. Use a flat-bladed
shovel to tuck fabric deeper into the ground if necessary.
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Figure 4.2.13 – Silt Fence Installation by Slicing Method
Maintenance
Standards
• Repair any damage immediately.
• Intercept and convey all evident concentrated flows uphill of the silt
fence to a sediment pond.
• Check the uphill side of the fence for signs of the fence clogging and
acting as a barrier to flow and then causing channelization of flows
parallel to the fence. If this occurs, replace the fence or remove the
trapped sediment.
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• Remove sediment deposits when the deposit reaches approximately
one-third the height of the silt fence, or install a second silt fence.
• Replace filter fabric that has deteriorated due to ultraviolet breakdown.
BMP C234: Vegetated Strip
Purpose Vegetated strips reduce the transport of coarse sediment from a
construction site by providing a temporary physical barrier to sediment
and reducing the runoff velocities of overland flow.
Conditions of Use • Vegetated strips may be used downslope of all disturbed areas.
• Vegetated strips are not intended to treat concentrated flows, nor are
they intended to treat substantial amounts of overland flow. Any
concentrated flows must be conveyed through the drainage system to a
sediment pond. The only circumstance in which overland flow can be
treated solely by a strip, rather than by a sediment pond, is when the
following criteria are met (see Table 4.2.4):
Table 4.2.4
Contributing Drainage Area for Vegetated Strips
Average Contributing
area Slope
Average Contributing area
Percent Slope
Max Contributing
area Flowpath Length
1.5H:1V or flatter 67% or flatter 100 feet
2H:1V or flatter 50% or flatter 115 feet
4H:1V or flatter 25% or flatter 150 feet
6H:1V or flatter 16.7% or flatter 200 feet
10H:1V or flatter 10% or flatter 250 feet
Design and
Installation
Specifications
• The vegetated strip shall consist of a minimum of a 25-foot flowpath
length continuous strip of dense vegetation with topsoil. Grass-
covered, landscaped areas are generally not adequate because the
volume of sediment overwhelms the grass. Ideally, vegetated strips
shall consist of undisturbed native growth with a well-developed soil
that allows for infiltration of runoff.
• The slope within the strip shall not exceed 4H:1V.
• The uphill boundary of the vegetated strip shall be delineated with
clearing limits.
Maintenance
Standards
• Any areas damaged by erosion or construction activity shall be
seeded immediately and protected by mulch.
• If more than 5 feet of the original vegetated strip width has had
vegetation removed or is being eroded, sod must be installed.
• If there are indications that concentrated flows are traveling across the
buffer, surface water controls must be installed to reduce the flows
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entering the buffer, or additional perimeter protection must be
installed.
BMP C235: Wattles
Purpose Wattles are temporary erosion and sediment control barriers consisting of
straw, compost, or other material that is wrapped in biodegradable tubular
plastic or similar encasing material. They reduce the velocity and can
spread the flow of rill and sheet runoff, and can capture and retain
sediment. Wattles are typically 8 to 10 inches in diameter and 25 to 30 feet
in length. Wattles are placed in shallow trenches and staked along the
contour of disturbed or newly constructed slopes. See Figure 4.2.14 for
typical construction details. WSDOT Standard Plan I-30.30-00 also
provides information on Wattles
(http://www.wsdot.wa.gov/Design/Standards/Plans.htm#SectionI)
Conditions of Use • Use wattles:
• In disturbed areas that require immediate erosion protection.
• On exposed soils during the period of short construction delays, or
over winter months.
• On slopes requiring stabilization until permanent vegetation can be
established.
• The material used dictates the effectiveness period of the wattle.
Generally, Wattles are typically effective for one to two seasons.
• Prevent rilling beneath wattles by properly entrenching and abutting
wattles together to prevent water from passing between them.
Design Criteria • Install wattles perpendicular to the flow direction and parallel to the
slope contour.
• Narrow trenches should be dug across the slope on contour to a depth
of 3- to 5-inches on clay soils and soils with gradual slopes. On loose
soils, steep slopes, and areas with high rainfall, the trenches should be
dug to a depth of 5- to 7- inches, or 1/2 to 2/3 of the thickness of the
wattle.
• Start building trenches and installing wattles from the base of the slope
and work up. Spread excavated material evenly along the uphill slope
and compacted using hand tamping or other methods.
• Construct trenches at intervals of 10- to 25-feet depending on the
steepness of the slope, soil type, and rainfall. The steeper the slope the
closer together the trenches.
• Install the wattles snugly into the trenches and abut tightly end to end.
Do not overlap the ends.
• Install stakes at each end of the wattle, and at 4-foot centers along
entire length of wattle.
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• If required, install pilot holes for the stakes using a straight bar to drive
holes through the wattle and into the soil.
• Wooden stakes should be approximately 3/4 x 3/4 x 24 inches min.
Willow cuttings or 3/8-inch rebar can also be used for stakes.
• Stakes should be driven through the middle of the wattle, leaving 2 to
3 inches of the stake protruding above the wattle.
Maintenance
Standards
• Wattles may require maintenance to ensure they are in contact with
soil and thoroughly entrenched, especially after significant rainfall on
steep sandy soils.
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Figure 4.2.14 – Wattles
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• Inspect the slope after significant storms and repair any areas where
wattles are not tightly abutted or water has scoured beneath the
wattles.
Approved as
Equivalent
Ecology has approved products as able to meet the requirements of BMP
C235. The products did not pass through the Technology Assessment
Protocol – Ecology (TAPE) process. Local jurisdictions may choose not
to accept this product approved as equivalent, or may require additional
testing prior to consideration for local use. The products are available for
review on Ecology’s website at
http://www.ecy.wa.gov/programs/wq/stormwater/newtech/equivalent.html
BMP C236: Vegetative Filtration
Purpose Vegetative Filtration may be used in conjunction with BMP C241
Temporary Sediment Ponds, BMP C206 Level Spreader and a pumping
system with surface intake to improve turbidity levels of stormwater
discharges by filtering through existing vegetation where undisturbed
forest floor duff layer or established lawn with thatch layer are present.
Vegetative Filtration can also be used to infiltrate dewatering waste from
foundations, vaults, and trenches as long as runoff does not occur.
Conditions of Use • For every five acre of disturbed soil use one acre of grass field, farm
pasture, or wooded area. Reduce or increase this area depending on
project size, ground water table height, and other site conditions.
• Wetlands shall not be used for filtration.
• Do not use this BMP in areas with a high ground water table, or in
areas that will have a high seasonal ground water table during the use
of this BMP.
• This BMP may be less effective on soils that prevent the infiltration of
the water, such as hard till.
• Using other effective source control measures throughout a
construction site will prevent the generation of additional highly turbid
water and may reduce the time period or area need for this BMP.
• Stop distributing water into the vegetated area if standing water or
erosion results.
Design Criteria • Find land adjacent to the project that has a vegetated field, preferably a
farm field, or wooded area.
• If the project site does not contain enough vegetated field area
consider obtaining permission from adjacent landowners (especially
for farm fields).
• Install a pump and downstream distribution manifold depending on the
project size. Generally, the main distribution line should reach 100 to
200-feet long (many large projects, or projects on tight soil, will
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require systems that reach several thousand feet long with numerous
branch lines off of the main distribution line).
• The manifold should have several valves, allowing for control over the
distribution area in the field.
• Install several branches of 4” schedule 20, swaged-fit common septic
tight-lined sewer line, or 6” fire hose, which can convey the turbid
water out to various sections of the field. See Figure 4.2.15.
• Determine the branch length based on the field area geography and
number of branches. Typically, branches stretch from 200-feet to
several thousand feet. Always, lay branches on contour with the slope.
• On uneven ground, sprinklers perform well. Space sprinkler heads so
that spray patterns do not overlap.
• On relatively even surfaces, a level spreader using 4-inch perforated
pipe may be used as an alternative option to the sprinkler head setup.
Install drain pipe at the highest point on the field and at various lower
elevations to ensure full coverage of the filtration area. Pipe should be
place with the holes up to allow for a gentle weeping of stormwater
evenly out all holes. Leveling the pipe by staking and using sandbags
may be required.
• To prevent the over saturation of the field area, rotate the use of
branches or spray heads. Do this as needed based on monitoring the
spray field.
• Monitor the spray field on a daily basis to ensure that over saturation
of any portion of the field doesn’t occur at any time. The presence of
standing puddles of water or creation of concentrated flows visually
signify that over saturation of the field has occurred.
• Since the operator is handling contaminated water, physically monitor
the vegetated spray field all the way down to the nearest surface water,
or furthest spray area, to ensure that the water has not caused overland
or concentrated flows, and has not created erosion around the spray
nozzle.
• Monitoring usually needs to take place 3-5 times per day to ensure
sheet-flow into state waters. Do not exceed water quality standards for
turbidity.
• Ecology strongly recommends that a separate inspection log be
developed, maintained and kept with the existing site logbook to aid
the operator conducting inspections. This separate “Field Filtration
Logbook” can also aid the facility in demonstrating compliance with
permit conditions.
Maintenance
Standards
• Inspect the spray nozzles daily, at a minimum, for leaks and plugging
from sediment particles.
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• If erosion, concentrated flows, or over saturation of the field occurs,
rotate the use of branches or spray heads or move the branches to a
new field location.
• Check all branches and the manifold for unintended leaks.
Flowpath Guidelines for Vegetative Filtration
Average Slope Average Area % Slope Estimated Flowpath
Length (ft)
1.5H:1V 67% 250
2H:1V 50% 200
4H:1V 25% 150
6H:1V 16.7% 115
10H:1V 10% 100
Figure 4.2.15 – Manifold and Braches in a wooded, vegetated spray field