21-102066-UP-SWPPP-2021-11-24-V2Construction Stormwater General Permit
Stormwater Pollution Prevention Plan
(SWPPP)
for
Smith Brothers Farms
Prepared for:
The Washington State Department of Ecology
Southwest Regional Office
Permittee / Owner Developer Operator / Contractor
Smith Brothers Farms
26401 79th Ave S
Kent, WA 98032
Fedway Associates II LP
34700 9th Ave S
Federal Way, WA 98003
TBD
34520 9th Ave S
Federal Way, WA 98003
Certified Erosion and Sediment Control Lead (CESCL)
Name Organization Contact Phone Number
TBD TBD TBD
SWPPP Prepared By
Name Organization Contact Phone Number
Daniel Casey
Barghausen Consulting
Engineers, Inc.
(425) 251-6222
SWPPP Preparation Date
11/12/2021
Project Construction Dates
Activity / Phase Start Date End Date
Phase 1 TBD TBD
P a g e | 1
Table of Contents
1 Project Information .............................................................................................................. 4
1.1 Existing Conditions ...................................................................................................... 4
1.2 Proposed Construction Activities .................................................................................. 4
2 Construction Stormwater Best Management Practices (BMPs) ........................................... 6
2.1 The 13 Elements .......................................................................................................... 6
2.1.1 Element 1: Preserve Vegetation / Mark Clearing Limits ........................................ 6
2.1.2 Element 2: Establish Construction Access ............................................................ 7
2.1.3 Element 3: Control Flow Rates ............................................................................. 9
2.1.4 Element 4: Install Sediment Controls ...................................................................11
2.1.5 Element 5: Stabilize Soils ....................................................................................13
2.1.6 Element 6: Protect Slopes....................................................................................15
2.1.7 Element 7: Protect Drain Inlets ............................................................................17
2.1.8 Element 8: Stabilize Channels and Outlets ..........................................................18
2.1.9 Element 9: Control Pollutants ...............................................................................19
2.1.10 Element 10: Control Dewatering ..........................................................................23
2.1.11 Element 11: Maintain BMPs .................................................................................24
2.1.12 Element 12: Manage the Project ..........................................................................25
2.1.13 Element 13: Protect Low Impact Development (LID) BMPs .................................25
3 Pollution Prevention Team .................................................................................................29
4 Monitoring and Sampling Requirements ............................................................................30
4.1 Site Inspection ............................................................................................................30
5 Reporting and Record Keeping ..........................................................................................30
5.1 Record Keeping ..........................................................................................................30
5.1.1 Site Log Book ......................................................................................................30
5.1.2 Records Retention ...............................................................................................30
5.1.3 Updating the SWPPP ...........................................................................................31
5.2 Reporting ....................................................................................................................31
5.2.1 Discharge Monitoring Reports ..............................................................................31
5.2.2 Notification of Noncompliance ..............................................................................31
List of Tables
Table 1 – Summary of Site Pollutant Constituents ..................................................................... 4
Table 2 – Pollutants ..................................................................................................................19
Table 3 – pH-Modifying Sources ...............................................................................................22
P a g e | 2
Table 4 – Dewatering BMPs ......................................................................................................23
Table 5 – Management .............................................................................................................25
Table 6 – BMP Implementation Schedule .................................................................................26
Table 7 – Team Information ......................................................................................................29
List of Appendices
Appendix/Glossary
A. Site Map
B. BMP Detail
C. Correspondence
D. Site Inspection Form
E. Construction Stormwater General Permit (CSWGP)
F. 303(d) List Waterbodies / TMDL Waterbodies Information
G. Contaminated Site Information
H. Engineering Calculations
P a g e | 3
List of Acronyms and Abbreviations
Acronym / Abbreviation Explanation
303(d) Section of the Clean Water Act pertaining to Impaired Waterbodies
BFO Bellingham Field Office of the Department of Ecology
BMP(s) Best Management Practice(s)
CESCL Certified Erosion and Sediment Control Lead
CO2 Carbon Dioxide
CRO Central Regional Office of the Department of Ecology
CSWGP Construction Stormwater General Permit
CWA Clean Water Act
DMR Discharge Monitoring Report
DO Dissolved Oxygen
Ecology Washington State Department of Ecology
EPA United States Environmental Protection Agency
ERO Eastern Regional Office of the Department of Ecology
ERTS Environmental Report Tracking System
ESC Erosion and Sediment Control
GULD General Use Level Designation
NPDES National Pollutant Discharge Elimination System
NTU Nephelometric Turbidity Units
NWRO Northwest Regional Office of the Department of Ecology
pH Power of Hydrogen
RCW Revised Code of Washington
SPCC Spill Prevention, Control, and Countermeasure
su Standard Units
SWMMEW Stormwater Management Manual for Eastern Washington
SWMMWW Stormwater Management Manual for Western Washington
SWPPP Stormwater Pollution Prevention Plan
TESC Temporary Erosion and Sediment Control
SWRO Southwest Regional Office of the Department of Ecology
TMDL Total Maximum Daily Load
VFO Vancouver Field Office of the Department of Ecology
WAC Washington Administrative Code
WSDOT Washington Department of Transportation
WWHM Western Washington Hydrology Model
P a g e | 4
1 Project Information
Project/Site Name: Smith Brothers Farms
Street/Location: 34520 9th Avenue South
City: Federal Way State: WA Zip code: 98003
Subdivision: N/A
Receiving waterbody: West Hylebos Wetland
1.1 Existing Conditions
Total acreage (including support activities such as off-site equipment staging yards, material
storage areas, borrow areas).
Total acreage: 4.20 ac
Disturbed acreage: 4.23 ac
Existing structures: The existing site is undeveloped with remanants of stockpiles of
previous clearing and grading operations throughout the site.
Landscape
topography:
The existing site generally steep, with approximately 40 feet of
vertical relief toward the south.
Drainage patterns: All stormwater drainage onsite is either infiltrated into the native
soils or captured by the various plant species.
Existing Vegetation: The majority of the site is covered various of plants and bushes.
Critical Areas: There are no critical areas associated with this site.
List of known impairments for 303(d) listed or Total Maximum Daily Load (TMDL) for the
receiving waterbody: There are no 303(d) listings for the receiving waterbody
Table 1 – Summary of Site Pollutant Constituents
Constituent
(Pollutant) Location Depth Max. Concentration
Detected (mg/kg)
1.2 Proposed Construction Activities
Description of site development (example: subdivision):
The proposed project will involve the addition of approximately 3 acres of new pavement and
impervious along with a stormwater infiltration gallery for flow control for the project site.
Description of construction activities (example: site preparation, demolition, excavation):
Construction activities will include site preparation, TESC installation, stormwater appurtenance
installation, paving and building construction.
P a g e | 5
Description of site drainage including flow from and onto adjacent properties. Must be
consistent with Site Map in Appendix A:
The existing site is generally sloping to the south, wiith soils consisting of fine grained silt and
gravel. All stormwater runoff is currently captured by native plant species and retained with in
the project site. There is no significant offsite tributary area to this project and it does not
contribute significant runoff to any adjacent properties.
Description of final stabilization (example: extent of revegetation, paving, landscaping):
With the completion of construction, the disturbed site area of 4.23 acres will be approximately
75% impervious paving and 25% lawn and landscaping.
P a g e | 6
2 Construction Stormwater Best Management Practices (BMPs)
The SWPPP is a living document reflecting current conditions and changes throughout the life
of the project. These changes may be informal (i.e., hand-written notes and deletions). Update
the SWPPP when the CESCL has noted a deficiency in BMPs or deviation from original design.
2.1 The 13 Elements
2.1.1 Element 1: Preserve Vegetation / Mark Clearing Limits
To protect adjacent properties and to reduce the area of soil exposed to construction, the limits
of construction will be clearly marked before land-disturbing activities begin. Areas that are to
be preserved, as well as all sensitive areas and their buffers, shall be clearly delineated, both in
the field and on the plans. A silt fence will be installed around the perimeter of the project site to
mark the limits of construction as well as protect surrounding properties from any possible
sediment laden runoff and grading will occur around the perimeter the site to insure there is no
runoff of any ponded stormwater.
List and describe BMPs:
BMP C102: Buffer Zones
BMP C233: Silt Fence
Installation Schedules: TBD
Inspection and Maintenance plan:
Buffer Zone Maintenance
• Inspect the area frequently to make sure flagging remains in place and the area remains
undisturbed.
• Replace all damaged flagging immediately.
Silt Fence Maintenance
• 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.
• 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.
Responsible Staff: Contractor/CESL
P a g e | 7
2.1.2 Element 2: Establish Construction Access
Access points shall be stabilized to minimize the tracking of sediment onto public roads, street
sweeping, and street cleaning shall be employed to prevent sediment from entering state
waters. One stabilized construction entrance will be installed to allow access from South 344th
Street on the north side of the site. Wheel washing will occur onsite if necessary depending on
conditions in order to prevent sediment from leaving the site. Street sweeping and street
cleaning may be necessary if the stabilized construction access and wheel wash are not
effective. The roads shall be swept daily should sediment collect on them. All wheel wash
wastewater shall be recycled on-site or disposed of to the sanitary sewer under permit.
List and describe BMPs:
BMP C105: Stabilized Construction Entrance
BMP C106: Wheel Wash (If needed)
Installation Schedules: TBD
Inspection and Maintenance plan:
Stabilized Construction Entrance Maintenance
• 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.
P a g e | 8
Wheel Wash Maintenance
• The wheel wash should start out the day with fresh water.
• The wash water should be changed a minimum of once per day. On large
earthwork jobs where more than 10-20 trucks per hour are expected, the
wash water will need to be changed more often.
Responsible Staff: Contractor/CESL
P a g e | 9
2.1.3 Element 3: Control Flow Rates
In order to protect the properties and waterways downstream of the project site, stormwater
from the site will be controlled by construction of a temporary sediment pond and installation of
silt fence as one of the first items of construction. Once the pond is constructed, stormwater
during construction will be captured through v-ditches with rock check dams in order to control
the flow of stormwater runoff before reaching the sediment pond. The sediment pond has been
adequately sized to provide surface area for sediment settlement per the DOE requirements
from BMP C241. A temporary riser will be provided during the TESC phase of construction to
discharge stormwater after sedimentation to the existing storm system west of the site.
Detention facilities must be functioning property before construction of site improvements.
Will you construct stormwater retention and/or detention facilities?
Yes No
Will you use permanent infiltration ponds or other low impact development (example: rain
gardens, bio-retention, porous pavement) to control flow during construction?
Yes No
List and describe BMPs:
BMP C241: Sediment Pond
BMP C207: Check Dams
BMP C235: Wattles
Installation Schedules: TBD
Inspection and Maintenance plan:
Sediment Pond/Trap Maintenance
• Sediment shall be removed from the trap/pond when it reaches 1-foot in depth.
• Any damage to the pond embankments or slopes shall be repaired.
Check Dam Maintenance
• 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.
Wattles Maintenance
• Wattles may require maintenance to ensure they are in contact with soil and thoroughly
entrenched, especially after significant rainfall on steep sandy soils.
P a g e | 10
• Inspect the slope after significant storms and repair any areas where wattles are not
tightly abutted or water has scoured beneath the wattles.
Responsible Staff: Contractor/CESL
P a g e | 11
2.1.4 Element 4: Install Sediment Controls
All stormwater runoff from disturbed areas shall be directed to the sediment pond from where it
will be discharged to the existing drainage system west of this site after sedimentation.
Constructing the silt fence followed by the sediment control pond is one of the first steps to
create the necessary gradients for flow to the trap/pond and to prevent off site discharge of
sediment. Rock check dams and v-ditches will be used to convey stormwater runoff into the
sediment pond to settle out sediment as well. The surface area requirements for the TESC pond
are met with the designed TESC plan. Additional sand filter treatment will be stationed on-site to
treat any flows as necessary to meet discharge requirements.
If the proposed sediment controls are ineffective as determined by the CESCL, they will
promptly initiate the implementation of one or more of the alternative BMPs listed in Appendix B.
List and describe BMPs:
BMP C207: Check Dams
BMP C233: Silt Fence
BMP C241: Temporary Sediment Pond
BMP C235: Wattles
Installation Schedules: TBD
Inspection and Maintenance plan:
Silt Fence Maintenance
• 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.
• 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.
Sediment Pond Maintenance
• Sediment shall be removed from the pond when it reaches 1-foot in depth.
• Any damage to the pond embankments or slopes shall be repaired.
P a g e | 12
Check Dam Maintenance
• 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.
Wattles Maintenance
• Wattles may require maintenance to ensure they are in contact with soil and thoroughly
entrenched, especially after significant rainfall on steep sandy soils.
• Inspect the slope after significant storms and repair any areas where wattles are not
tightly abutted or water has scoured beneath the wattles.
Responsible Staff: Contractor/CESL
P a g e | 13
2.1.5 Element 5: Stabilize Soils
Exposed and unworked soils shall be stabilized with the application of effective BMPs to prevent
erosion throughout the life of the project. In general, cut and fill slopes will be stabilized as soon
as possible and soil stockpiles will be stabilized temporary and permanent seeding. All
stockpiled soils shall be stabilized from erosion, protected with sediment trapping measures,
and where possible, be located away from storm drain inlets, waterways, and drainage
channels. To minimize the amount of soil exposed through the life of the project, grading will be
completed within a reasonable time frame. To minimize soil compaction, construction entrances
will be used as well as keeping heavy equipment and machinery off unpaved areas as much as
possible.
West of the Cascade Mountains Crest
Season Dates Number of Days Soils Can
be Left Exposed
During the Dry Season May 1 – September 30 7 days
During the Wet Season October 1 – April 30 2 days
Soils must be stabilized at the end of the shift before a holiday or weekend if needed based on
the weather forecast.
Anticipated project dates: Start date: TBD End date: TBD
Will you construct during the wet season?
Yes No
List and describe BMPs:
BMP 120: Temporary and Permanent Seeding
BMP C121: Mulching
BMP C140: Dust Control
Installation Schedules: TBD
Inspection and Maintenance plan:
Temporary and Permanent Seeding Maintenance
• 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.
P a g e | 14
• Supply seeded areas with adequate moisture, but do not water to the extent that it
causes runoff.
Dust Control Maintenance
• Respray area as necessary to keep dust to a minimum.
Mulching Maintenance
• 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.
Responsible Staff: Contractor/CESL
P a g e | 15
2.1.6 Element 6: Protect Slopes
All cut and fill slopes will be designed, constructed, and protected in a manner that minimizes
erosion. It is required that any temporary pipe slope drains must handle the peak 10-minute
flow rate from a Type 1A, 10-year, 24-hour frequency storm for the developed condition.
Alternatively, the 10-year, 1-hour flow rate predicted by an approved continuous runoff model,
increased by a factor of 1.6, may be used. The hydrologic analysis must use the existing land
cover condition for predicting flow rates from tributary areas outside the project limits. For
tributary areas on the project site, the analysis must use the temporary or permanent project
land cover condition, whichever will produce the highest flow rates. For modeling the condition
with the Western Washington Hydrology Model (WWHM) to predict flows, bare soil areas have
been modeled as “landscaped area”. Scouring will be reduced by using v-ditches with rock
check dams to convey stormwater to the sediment ponds on site. However, if the proposed
BMPs to protect slopes are ineffective as determined by the CESCL, they will promptly initiate
the implementation of one or more of the alternative BMPs listed in Appendix B.
Will steep slopes be present at the site during construction?
Yes No
List and describe BMPs:
BMP C120: Temporary and Permanent Seeding
BMP C207: Check Dams
Installation Schedules: TBD
Inspection and Maintenance plan:
Temporary and Permanent Seeding Maintenance
• 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.
Check Dam Maintenance
• 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.
P a g e | 16
• 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.
Responsible Staff: Contractor/CESL
P a g e | 17
2.1.7 Element 7: Protect Drain Inlets
All storm drain inlets and culverts made operable during construction shall be protected to
prevent unfiltered or untreated water from entering the drainage conveyance system. However,
the first priority is to keep all access roads clean of sediment and keep wash water separate
from entering storm drains until treatment can be provided. Storm Drain Inlet Protection (BMP
C220) will be implemented for all drainage inlets and culverts that could potentially be impacted
by sediment-laden runoff on and near the project site. If this is deemed ineffective by the
CESCL, additional BMPs may be necessary, as listed in Appendix B. Inlet protection is the last
component of a treatment train and protection of drain inlets include additional sediment and
erosion control measures. Inlet protection devices will be cleaned (or removed and replaced),
when sediment has filled the device by one third (1/3) or as specified by the manufacturer.
List and describe BMPs:
BMP C220: Storm Drain Inlet Protection
Installation Schedules: TBD
Inspection and Maintenance plan:
Storm Drain Inlet Protection Maintenance
• 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.
• Inlets to be inspected weekly and a minimum of daily during storm events
Responsible Staff: Contractor/CESL
P a g e | 18
2.1.8 Element 8: Stabilize Channels and Outlets
For construction stormwater conveyance, v-ditches with rock check dams will be installed to
stabilize channels. Stabilization, including armoring material, adequate to prevent erosion of
outlets, adjacent streambanks, slopes, and downstream reaches shall be provided at the outlets
of all conveyance systems. As such, all temporary on-site conveyance channels shall be
designed, constructed, and stabilized to prevent erosion from the expected peak 10 minute
velocity of flow from a Type 1A, 10-year, 24-hour frequency storm for the developed condition.
Alternatively, the 10-year, 1-hour flow rate predicted by an approved continuous runoff model,
increased by a factor of 1.6, may be used. The hydrologic analysis must use the existing land
cover condition for predicting flow rates from tributary areas outside the project limits. For
tributary areas on the project site, the analysis must use the temporary or permanent project
land cover condition, whichever will produce the highest flow rates. If using the WWHM to
predict flows, bare soil areas should be modeled as “landscaped area”.
Provide stabilization, including armoring material, adequate to prevent erosion of outlets,
adjacent stream banks, slopes, and downstream reaches, will be installed at the outlets of all
conveyance systems.
List and describe BMPs:
BMP C207: Check Dams
Installation Schedules: TBD
Inspection and Maintenance plan:
Check Dam Maintenance
• 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.
Responsible Staff: Contractor/CESL
P a g e | 19
2.1.9 Element 9: Control Pollutants
The following pollutants are anticipated to be present on-site:
Table 2 – Pollutants
Pollutant (List pollutants and source, if applicable)
Hydraulic fluid - May be present on site with construction equipment.
Diesel - May be present on site with construction equipment.
Motor Oil - May be present on site with construction equipment.
All pollutants, including waste materials and demolition debris, that occur onsite shall be
handled and disposed of in a manner that does not cause contamination of stormwater. Good
housekeeping and preventative measures will be taken to ensure that the site will be kept clean,
well-organized, and free of debris. Chemicals, liquid products, petroleum products, and other
polluting materials will be kept covered, stored appropriately, and locked when not in use to
prevent vandalism or misuse of these materials that may pollute state waters. Treatement as
described in section 1.2 of this report will be implemented as necessary to control pollutants
found on-site.
If required, BMPs to be implemented to control specific sources of pollutants are discussed
below. Vehicles, construction equipment, and/or petroleum product storage/dispensing:
• All vehicles, equipment, and petroleum product storage/dispensing areas
will be inspected regularly to detect any leaks or spills, and to identify
maintenance needs to prevent leaks or spills.
• On-site fueling tanks and petroleum product storage containers shall
include secondary containment.
• Spill prevention measures, such as drip pans, will be used when
conducting maintenance and repair of vehicles or equipment.
• In order to perform emergency repairs on site, temporary plastic will be
placed beneath and, if raining, over the vehicle.
• Contaminated surfaces shall be cleaned immediately following any
discharge or spill incident.
• Storm drain inlets vulnerable to stormwater discharge carrying dust, soil,
or debris will be protected using Storm Drain Inlet Protection (BMP C220
as described above for Element 7).
• Process water and slurry resulting from sawcutting and surfacing
operations will be prevented from entering the waters of the State by
implementing Sawcutting and Surfacing Pollution Prevention measures
(BMP C152).
P a g e | 20
Concrete and grout:
• Process water and slurry resulting from concrete work will be prevented
from entering the waters of the State by implementing Concrete Handling
measures (BMP C151).
List and describe BMPs:
BMP C151: Concrete Handling
Installation Schedules: TBD
Inspection and Maintenance plan:
Concrete Handling Maintenance
• Check containers for holes in the liner daily during concrete pours and repair the same
day.
Responsible Staff: Contractor/CESL
Will maintenance, fueling, and/or repair of heavy equipment and vehicles occur on-site?
Yes No
In order to prevent spills and minimize risk, the following list should be applied
• 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.
• 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.
P a g e | 21
List and describe BMPs:
BMP C153: Material Delivery, Storage and Containment
Installation Schedules: TBD
Inspection and Maintenance plan:
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
Responsible Staff: Contractor/CESL
Will wheel wash or tire bath system BMPs be used during construction?
Yes No
The disposal method is discharging to the sanitary sewer, the approval letter from the sewer
district will be filed under Correspondence in Appendix C of this document.
List and describe BMPs:
BMP C106: Wheel Wash (If needed)
Installation Schedules: TBD
Inspection and Maintenance plan:
Wheel Wash Maintenance
• The wheel wash should start out the day with fresh water.
• The wash water should be changed a minimum of once per day. On large
earthwork jobs where more than 10-20 trucks per hour are expected, the
wash water will need to be changed more often.
Responsible Staff: Contractor/CESL
P a g e | 22
Will pH-modifying sources be present on-site?
Yes No
Table 3 – pH-Modifying Sources
None
Bulk cement
Cement kiln dust
Fly ash
Other cementitious materials
New concrete washing or curing waters
Waste streams generated from concrete grinding and sawing
Exposed aggregate processes
Dewatering concrete vaults
Concrete pumping and mixer washout waters
Recycled concrete
Recycled concrete stockpiles
Other (i.e., calcium lignosulfate) [please describe: ]
List and describe BMPs: N/A
Installation Schedules: N/A
Inspection and Maintenance plan: N/A
Responsible Staff: N/A
Concrete trucks must not be washed out onto the ground, or into storm drains, open ditches,
streets, or streams. Excess concrete must not be dumped on-site, except in designated
concrete washout areas with appropriate BMPs installed.
Will uncontaminated water from water-only based shaft drilling for construction of building, road,
and bridge foundations be infiltrated provided the wastewater is managed in a way that prohibits
discharge to surface waters?
Yes No
List and describe BMPs: N/A
Installation Schedules: N/A
Inspection and Maintenance plan: N/A
Responsible Staff: N/A
P a g e | 23
2.1.10 Element 10: Control Dewatering
No dewatering is anticipated to be required for the project site. However, if construction
dewatering is required, all water will be treated in accordance with Department of Ecology
standards before discharge.
Infiltration
Transport off-site in a vehicle (vacuum truck for legal disposal)
Ecology-approved on-site chemical treatment or other suitable treatment technologies
Sanitary or combined sewer discharge with local sewer district approval (last resort)
Use of sedimentation bag with discharge to ditch or swale (small volumes of localized
dewatering)
List and describe BMPs: N/A
Installation Schedules: N/A
Inspection and Maintenance plan: N/A
Responsible Staff: N/A
P a g e | 24
2.1.11 Element 11: Maintain BMPs
All temporary and permanent Erosion and Sediment Control (ESC) BMPs shall be maintained
and repaired as needed to ensure continued performance of their intended function.
Maintenance and repair shall be conducted in accordance with each particular BMP
specification (see Volume II of the SWMMWW or Chapter 7 of the SWMMEW).
Visual monitoring of all BMPs installed at the site will be conducted at least once every calendar
week and within 24 hours of any stormwater or non-stormwater discharge from the site. If the
site becomes inactive and is temporarily stabilized, the inspection frequency may be reduced to
once every calendar month.
All temporary ESC BMPs shall be removed within 30 days after final site stabilization is
achieved or after the temporary BMPs are no longer needed.
Trapped sediment shall be stabilized on-site or removed. Disturbed soil resulting from removal
of either BMPs or vegetation shall be permanently stabilized.
Additionally, protection must be provided for all BMPs installed for the permanent control of
stormwater from sediment and compaction. BMPs that are to remain in place following
completion of construction shall be examined and restored to full operating condition. If
sediment enters these BMPs during construction, the sediment shall be removed and the facility
shall be returned to conditions specified in the construction documents.
P a g e | 25
2.1.12 Element 12: Manage the Project
The project will be managed based on the following principles:
• Projects will be phased to the maximum extent practicable and seasonal work limitations
will be taken into account.
• Inspection and monitoring:
o Inspection, maintenance and repair of all BMPs will occur as needed to ensure
performance of their intended function.
o Site inspections and monitoring will be conducted in accordance with Special
Condition S4 of the CSWGP. Sampling locations are indicated on the Site Map.
Sampling station(s) are located in accordance with applicable requirements of
the CSWGP.
• Maintain an updated SWPPP.
o The SWPPP will be updated, maintained, and implemented in accordance with
Special Conditions S3, S4, and S9 of the CSWGP.
As site work progresses the SWPPP will be modified routinely to reflect changing site
conditions. The SWPPP will be reviewed monthly to ensure the content is current.
Table 5 – Management
Design the project to fit the existing topography, soils, and drainage patterns
Emphasize erosion control rather than sediment control
Minimize the extent and duration of the area exposed
Keep runoff velocities low
Retain sediment on-site
Thoroughly monitor site and maintain all ESC measures
Schedule major earthwork during the dry season
Other (please describe)
P a g e | 26
2.1.13 Element 13: Protect Low Impact Development BMPs
This project proposes infiltration facilities that will require additional protections to ensure that they
perform as intended. This project will protect all On-Site Stormwater Management (LID BMPs) by:
a) Protection of LID BMPs from sedimentation will be accomplished through the installation and
maintenance of erosion and sediment control BMPs. This project will implement a temporary
sediment pond and/or the final detention pond in order to collect stormwater runoff during the
clearing and grading construction phase and reduce the amount of sediment leaving the project
site. These facilities will be maintained to fully functionality as sediment collects during
construction.
b) Protection of LID BMPs from compaction by construction equipment and foot traffic. The
location of proposed infiltration facilities has been included on the TESC plans and shall be
protected to the greatest extent feasible by avoiding compaction of the soils and avoiding
stormwater runoff from entering the proposed infiltration area until site development work is
complete.
c) Protection of LID BMPs from sediment-laden runoff to base materials by collection of
stormwater runoff and conveyance to the proposed sediment control facilities. Muddy
construction equipment shall be prohibited from base materials (proposed subgrade) or LID
BMP designated areas.
d) Protection of LID BMPs infiltration performance will be accomplished by cleaning using the
procedures in accordance with the Department of Ecology’s Stormwater Management Manual
for Western Washington.
e) Protection of LID BMPs shall be accomplished by prohibiting all heavy equipment off existing
soils under proposed LID BMP locations that are close to final grade. Restricing where
construction equipment can be staged helps retain the long term design infiltration rate of the
soils.
List and describe BMPs:
BMP C200 Interceptor Dike and Swale
BMP C207 Check Dams
BMP C233 Silt Fence
Installation Schedules: TBD
Inspection and Maintenance plan:
Interceptor Dike and Swale Maintenance
· Inspect diversion dikes and interceptor swales once a week and after every rainfall.
Immediately remove sediment from the flow area.
P a g e | 27
· 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.
Check Dam Maintenance
• 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.
Silt Fence Maintenance
• 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.
• 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.
Responsible Staff: Contractor/CESL
P a g e | 28
Table 6 – BMP Implementation Schedule
Phase of
Construction
Project
Stormwater BMPs Date Wet/Dry
Season
TBD C105 – Construction Entrance
C220 – Storm Drain Inlet Protection
C235 – Wattles
C233 – Silt Fence
C241 – Sediment Pond
C207 – Check Dams
C251 – Construction Stormwater Filtration
C120 – Temporary and Permanent Seeding
C140 – Dust Control
C151 – Concrete Handling
C200 – Interceptor Dikes and Swales
C220 – Storm Drain Inlet Protection
C233 – Silt Fence
C240 – Temporary Sediment Pond
TBD TBD
P a g e | 29
3 Pollution Prevention Team
Table 7 – Team Information
Title Name(s) Phone Number
Certified Erosion and
Sediment Control Lead
(CESCL)
TBD
Resident Engineer Ben Eldridge (425) 251-6222
Emergency Ecology
Contact
Southwest Regional Office: WA
Emergency Management Division
1-800-258-5990
Emergency Permittee/
Owner Contact
TBD
Non-Emergency Owner
Contact
TBD
Monitoring Personnel TBD TBD
Ecology Regional Office Southwest Regional Office (360) 407-6300
P a g e | 30
4 Monitoring and Sampling Requirements
Monitoring includes visual inspection, sampling for water quality parameters of concern, and
documentation of the inspection and sampling findings in a site log book. A site log book will be
maintained for all on-site construction activities and will include:
· A record of the implementation of the SWPPP and other permit requirements
· Site inspections
· Stormwater sampling data
File a blank form under Appendix D.
The site log book must be maintained on-site within reasonable access to the site and be made
available upon request to Ecology or the local jurisdiction.
4.1 Site Inspection
Site inspections will be conducted at least once every calendar week and within 24 hours
following any discharge from the site. For sites that are temporarily stabilized and inactive, the
required frequency is reduced to once per calendar month.
The discharge point(s) to the sanitary sewer are indicated on the Site Map (see Appendix A)
and in accordance with the applicable requirements of the CSWGP.
Monitoring will be in accordance with City of Federal Way requiremetns as needed.
5 Reporting and Record Keeping
5.1 Record Keeping
5.1.1 Site Log Book
A site log book will be maintained for all on-site construction activities and will include:
· A record of the implementation of the SWPPP and other permit requirements
· Site inspections
· Sample logs
5.1.2 Records Retention
Records will be retained during the life of the project and for a minimum of three (3) years
following the termination of permit coverage in accordance with Special Condition S5.C of the
CSWGP.
Permit documentation to be retained on-site:
· CSWGP
· Permit Coverage Letter
· SWPPP
P a g e | 31
· Site Log Book
Permit documentation will be provided within 14 days of receipt of a written request from
Ecology. A copy of the SWPPP or access to the SWPPP will be provided to the public when
requested in writing in accordance with Special Condition S5.G.2.b of the CSWGP.
5.1.3 Updating the SWPPP
The SWPPP will be modified if:
· Found ineffective in eliminating or significantly minimizing pollutants in stormwater
discharges from the site.
· There is a change in design, construction, operation, or maintenance at the construction
site that has, or could have, a significant effect on the discharge of pollutants to waters
of the State.
The SWPPP will be modified within seven (7) days if inspection(s) or investigation(s) determine
additional or modified BMPs are necessary for compliance. An updated timeline for BMP
implementation will be prepared.
5.2 Reporting
5.2.1 Discharge Monitoring Reports
Cumulative soil disturbance is one (1) acre or larger; therefore, Discharge Monitoring
Reports (DMRs) will be submitted to Ecology monthly. If there was no discharge during a given
monitoring period the DMR will be submitted as required, reporting “No Discharge”. The DMR
due date is fifteen (15) days following the end of each calendar month.
DMRs will be reported online through Ecology’s WQWebDMR System.
5.2.2 Notification of Noncompliance
If any of the terms and conditions of the permit is not met, and the resulting noncompliance may
cause a threat to human health or the environment, the following actions will be taken:
1. Ecology will be notified within 24-hours of the failure to comply by calling the applicable
Regional office ERTS phone number (Regional office numbers listed below).
2. Immediate action will be taken to prevent the discharge/pollution or otherwise stop or
correct the noncompliance. If applicable, sampling and analysis of any noncompliance
will be repeated immediately and the results submitted to Ecology within five (5) days of
becoming aware of the violation.
3. A detailed written report describing the noncompliance will be submitted to Ecology
within five (5) days, unless requested earlier by Ecology.
P a g e | 32
Anytime turbidity sampling indicates turbidity is 250 NTUs or greater, or water transparency is 6
cm or less, the Ecology Regional office will be notified by phone within 24 hours of analysis as
required by Special Condition S5.A of the CSWGP.
· Central Region at (509) 575-2490 for Benton, Chelan, Douglas, Kittitas, Klickitat,
Okanogan, or Yakima County
· Eastern Region at (509) 329-3400 for Adams, Asotin, Columbia, Ferry, Franklin,
Garfield, Grant, Lincoln, Pend Oreille, Spokane, Stevens, Walla Walla, or Whitman
County
· Northwest Region at (425) 649-7000 for Island, King, Kitsap, San Juan, Skagit,
Snohomish, or Whatcom County
· Southwest Region at (360) 407-6300 for Clallam, Clark, Cowlitz, Grays Harbor,
Jefferson, Lewis, Mason, Pacific, Pierce, Skamania, Thurston, or Wahkiakum
Include the following information:
1. Your name and / Phone number
2. Permit number
3. City / County of project
4. Sample results
5. Date / Time of call
6. Date / Time of sample
7. Project name
In accordance with Special Condition S4.D.5.b of the CSWGP, the Ecology Regional office will
be notified if chemical treatment other than CO2 sparging is planned for adjustment of high pH
water.
P a g e | 33
Appendix/Glossary
A. Site Map
B. BMP Detail
C. Correspondence
D. Site Inspection Form
E. Construction Stormwater General Permit (CSWGP)
F. 303(d) List Waterbodies / TMDL Waterbodies Information
G. Contaminated Site Information
H. Engineering Calculations
VANCOVER SHEET
C1 SCALE: 1"=40'SITE
VANT.E.S.C. PLANC3SCALE: 1"=40'
TESC RISER12" TEMP. RISEREX. CBTYPE 2-48" W/STANDARD GRATET.E.S.C. NOTES AND DETAILS
C4
Volume II – Construction Stormwater Pollution Prevention - August 2012
4-6
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.
Volume II – Construction Stormwater Pollution Prevention - August 2012
4-7
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.
Volume II – Construction Stormwater Pollution Prevention - August 2012
4-8
• 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.
Volume II – Construction Stormwater Pollution Prevention - August 2012
4-9
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
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
Volume II – Construction Stormwater Pollution Prevention - August 2012
4-12
BMP C107: Construction Road/Parking Area Stabilization
Purpose Stabilizing subdivision roads, parking areas, and other on-site vehicle
transportation routes immediately after grading reduces erosion caused by
construction traffic or runoff.
Conditions of Use Roads or parking areas shall be stabilized wherever they are constructed,
whether permanent or temporary, for use by construction traffic.
• High Visibility Fencing (see BMP C103) shall be installed, if
necessary, to limit the access of vehicles to only those roads and
parking areas that are stabilized.
Design and
Installation
Specifications
• On areas that will receive asphalt as part of the project, install the first
lift as soon as possible.
• A 6-inch depth of 2- to 4-inch crushed rock, gravel base, or crushed
surfacing base course shall be applied immediately after grading or
utility installation. A 4-inch course of asphalt treated base (ATB) may
also be used, or the road/parking area may be paved. It may also be
possible to use cement or calcium chloride for soil stabilization. If
cement or cement kiln dust is used for roadbase stabilization, pH
monitoring and BMPs (BMPs C252 and C253) are necessary to
evaluate and minimize the effects on stormwater. If the area will not be
used for permanent roads, parking areas, or structures, a 6-inch depth of
hog fuel may also be used, but this is likely to require more
maintenance. Whenever possible, construction roads and parking areas
shall be placed on a firm, compacted subgrade.
• Temporary road gradients shall not exceed 15 percent. Roadways shall
be carefully graded to drain. Drainage ditches shall be provided on
each side of the roadway in the case of a crowned section, or on one
side in the case of a super-elevated section. Drainage ditches shall be
directed to a sediment control BMP.
• Rather than relying on ditches, it may also be possible to grade the
road so that runoff sheet-flows into a heavily vegetated area with a
well-developed topsoil. Landscaped areas are not adequate. If this area
has at least 50 feet of vegetation that water can flow through, then it is
generally preferable to use the vegetation to treat runoff, rather than a
sediment pond or trap. The 50 feet shall not include wetlands or their
buffers. If runoff is allowed to sheetflow through adjacent vegetated
areas, it is vital to design the roadways and parking areas so that no
concentrated runoff is created.
• Storm drain inlets shall be protected to prevent sediment-laden water
entering the storm drain system (see BMP C220).
Maintenance
Standards
Inspect stabilized areas regularly, especially after large storm events.
Crushed rock, gravel base, etc. shall be added as required to maintain a
Volume II – Construction Stormwater Pollution Prevention - August 2012
4-13
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.
Volume II – Construction Stormwater Pollution Prevention - August 2012
4-14
• 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.
Volume II – Construction Stormwater Pollution Prevention - August 2012
4-15
• 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
Volume II – Construction Stormwater Pollution Prevention - August 2012
4-16
• 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
Volume II – Construction Stormwater Pollution Prevention - August 2012
4-17
• 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
Volume II – Construction Stormwater Pollution Prevention - August 2012
4-18
• 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.
Volume II – Construction Stormwater Pollution Prevention - August 2012
4-19
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
Volume II – Construction Stormwater Pollution Prevention - August 2012
4-26
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.
Volume II – Construction Stormwater Pollution Prevention - August 2012
4-27
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.
Volume II – Construction Stormwater Pollution Prevention - August 2012
4-28
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
Volume II – Construction Stormwater Pollution Prevention - August 2012
4-29
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.
Volume II – Construction Stormwater Pollution Prevention - August 2012
4-30
• 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
Volume II – Construction Stormwater Pollution Prevention - August 2012
4-31
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.
Volume II – Construction Stormwater Pollution Prevention - August 2012
4-32
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.
Volume II – Construction Stormwater Pollution Prevention - August 2012
4-33
• Sites having a winter shut down. In the case of winter shut down, or
where soil will remain unworked for several months, PAM should be
used together with mulch.
Design and
Installation
Specifications
PAM may be applied with water in dissolved form. The preferred
application method is the dissolved form.
PAM is to be applied at a maximum rate of 2/3 pound PAM per 1,000
gallons water (80 mg/L) per 1 acre of bare soil. Table 4.1.9 can be used to
determine the PAM and water application rate for a disturbed soil area.
Higher concentrations of PAM do not provide any additional effectiveness.
Table 4.1.9
PAM and Water Application Rates
Disturbed Area (ac) PAM (lbs) Water (gal)
0.50 0.33 500
1.00 0.66 1,000
1.50 1.00 1,500
2.00 1.32 2,000
2.50 1.65 2,500
3.00 2.00 3,000
3.50 2.33 3,500
4.00 2.65 4,000
4.50 3.00 4,500
5.00 3.33 5,000
The Preferred Method:
• Pre-measure the area where PAM is to be applied and calculate the
amount of product and water necessary to provide coverage at the
specified application rate (2/3 pound PAM/1000 gallons/acre).
• PAM has infinite solubility in water, but dissolves very slowly.
Dissolve pre-measured dry granular PAM with a known quantity of
clean water in a bucket several hours or overnight. Mechanical mixing
will help dissolve the PAM. Always add PAM to water - not water to
PAM.
• Pre-fill the water truck about 1/8 full with water. The water does not
have to be potable, but it must have relatively low turbidity – in the
range of 20 NTU or less.
• Add PAM /Water mixture to the truck
• Completely fill the water truck to specified volume.
• Spray PAM/Water mixture onto dry soil until the soil surface is
uniformly and completely wetted.
An Alternate Method:
Volume II – Construction Stormwater Pollution Prevention - August 2012
4-34
PAM may also be applied as a powder at the rate of 5 lbs. per acre. This
must be applied on a day that is dry. For areas less than 5-10 acres, a hand-
held “organ grinder” fertilizer spreader set to the smallest setting will
work. Tractor-mounted spreaders will work for larger areas.
The following shall be used for application of powdered PAM:
• Powered PAM shall be used in conjunction with other BMPs and not
in place of other BMPs.
• Do not use PAM on a slope that flows directly into a stream or
wetland. The stormwater runoff shall pass through a sediment control
BMP prior to discharging to surface waters.
• Do not add PAM to water discharging from site.
• When the total drainage area is greater than or equal to 5 acres, PAM
treated areas shall drain to a sediment pond.
• Areas less than 5 acres shall drain to sediment control BMPs, such as a
minimum of 3 check dams per acre. The total number of check dams
used shall be maximized to achieve the greatest amount of settlement
of sediment prior to discharging from the site. Each check dam shall
be spaced evenly in the drainage channel through which stormwater
flows are discharged off-site.
• On all sites, the use of silt fence shall be maximized to limit the
discharges of sediment from the site.
• All areas not being actively worked shall be covered and protected
from rainfall. PAM shall not be the only cover BMP used.
• PAM can be applied to wet soil, but dry soil is preferred due to less
sediment loss.
• PAM will work when applied to saturated soil but is not as effective as
applications to dry or damp soil.
• Keep the granular PAM supply out of the sun. Granular PAM loses its
effectiveness in three months after exposure to sunlight and air.
• Proper application and re-application plans are necessary to ensure
total effectiveness of PAM usage.
• PAM, combined with water, is very slippery and can be a safety
hazard. Care must be taken to prevent spills of PAM powder onto
paved surfaces. During an application of PAM, prevent over-spray
from reaching pavement as pavement will become slippery. If PAM
powder gets on skin or clothing, wipe it off with a rough towel rather
than washing with water-this only makes cleanup messier and take
longer.
• Some PAMs are more toxic and carcinogenic than others. Only the
most environmentally safe PAM products should be used.
Volume II – Construction Stormwater Pollution Prevention - August 2012
4-35
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
Volume II – Construction Stormwater Pollution Prevention - August 2012
4-36
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.
Volume II – Construction Stormwater Pollution Prevention - August 2012
4-37
Figure 4.1.5 – Surface Roughening by Tracking and Contour Furrows
Volume II – Construction Stormwater Pollution Prevention - August 2012
4-28
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
Volume II – Construction Stormwater Pollution Prevention - August 2012
4-29
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.
Volume II – Construction Stormwater Pollution Prevention - August 2012
4-30
• 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
Volume II – Construction Stormwater Pollution Prevention - August 2012
4-31
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.
Volume II – Construction Stormwater Pollution Prevention - August 2012
4-32
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.
Volume II – Construction Stormwater Pollution Prevention - August 2012
4-13
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.
Volume II – Construction Stormwater Pollution Prevention - August 2012
4-41
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.
Volume II – Construction Stormwater Pollution Prevention - August 2012
4-42
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.
Volume II – Construction Stormwater Pollution Prevention - August 2012
4-42
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-
Volume II – Construction Stormwater Pollution Prevention - August 2012
4-43
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.
Volume II – Construction Stormwater Pollution Prevention - August 2012
4-44
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.
Volume II – Construction Stormwater Pollution Prevention - August 2012
4-45
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.
Volume II – Construction Stormwater Pollution Prevention - August 2012
4-46
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
Volume II – Construction Stormwater Pollution Prevention - August 2012
4-47
BMP C154: Concrete Washout Area
Purpose Prevent or reduce the discharge of pollutants to stormwater from concrete
waste by conducting washout off-site, or performing on-site washout in a
designated area to prevent pollutants from entering surface waters or
ground water.
Conditions of Use Concrete washout area best management practices are implemented on
construction projects where:
• Concrete is used as a construction material
• It is not possible to dispose of all concrete wastewater and washout
off-site (ready mix plant, etc.).
• Concrete trucks, pumpers, or other concrete coated equipment are
washed on-site.
• Note: If less than 10 concrete trucks or pumpers need to be washed out
on-site, the washwater may be disposed of in a formed area awaiting
concrete or an upland disposal site where it will not contaminate
surface or ground water. The upland disposal site shall be at least 50
feet from sensitive areas such as storm drains, open ditches, or water
bodies, including wetlands.
Design and
Installation
Specifications
Implementation
The following steps will help reduce stormwater pollution from concrete
wastes:
• Perform washout of concrete trucks off-site or in designated concrete
washout areas only.
• Do not wash out concrete trucks onto the ground, or into storm drains,
open ditches, streets, or streams.
• Do not allow excess concrete to be dumped on-site, except in
designated concrete washout areas.
• Concrete washout areas may be prefabricated concrete washout
containers, or self-installed structures (above-grade or below-grade).
• Prefabricated containers are most resistant to damage and protect
against spills and leaks. Companies may offer delivery service and
provide regular maintenance and disposal of solid and liquid waste.
• If self-installed concrete washout areas are used, below-grade
structures are preferred over above-grade structures because they are
less prone to spills and leaks.
• Self-installed above-grade structures should only be used if excavation
is not practical.
Volume II – Construction Stormwater Pollution Prevention - August 2012
4-48
Education
• Discuss the concrete management techniques described in this BMP
with the ready-mix concrete supplier before any deliveries are made.
• Educate employees and subcontractors on the concrete waste
management techniques described in this BMP.
• Arrange for contractor’s superintendent or Certified Erosion and
Sediment Control Lead (CESCL) to oversee and enforce concrete
waste management procedures.
• A sign should be installed adjacent to each temporary concrete
washout facility to inform concrete equipment operators to utilize the
proper facilities.
Contracts
Incorporate requirements for concrete waste management into concrete
supplier and subcontractor agreements.
Location and Placement
• Locate washout area at least 50 feet from sensitive areas such as storm
drains, open ditches, or water bodies, including wetlands.
• Allow convenient access for concrete trucks, preferably near the area
where the concrete is being poured.
• If trucks need to leave a paved area to access washout, prevent track-
out with a pad of rock or quarry spalls (see BMP C105). These areas
should be far enough away from other construction traffic to reduce
the likelihood of accidental damage and spills.
• The number of facilities you install should depend on the expected
demand for storage capacity.
• On large sites with extensive concrete work, washouts should be
placed in multiple locations for ease of use by concrete truck drivers.
On-site Temporary Concrete Washout Facility, Transit Truck
Washout Procedures:
• Temporary concrete washout facilities shall be located a minimum of
50 ft from sensitive areas including storm drain inlets, open drainage
facilities, and watercourses. See Figures 4.1.7 and 4.1.8.
• Concrete washout facilities shall be constructed and maintained in
sufficient quantity and size to contain all liquid and concrete waste
generated by washout operations.
• Approximately 7 gallons of wash water are used to wash one truck
chute.
• Approximately 50 gallons are used to wash out the hopper of a
concrete pump truck.
Volume II – Construction Stormwater Pollution Prevention - August 2012
4-49
• Washout of concrete trucks shall be performed in designated areas
only.
• Concrete washout from concrete pumper bins can be washed into
concrete pumper trucks and discharged into designated washout area
or properly disposed of off-site.
• Once concrete wastes are washed into the designated area and allowed
to harden, the concrete should be broken up, removed, and disposed of
per applicable solid waste regulations. Dispose of hardened concrete
on a regular basis.
• Temporary Above-Grade Concrete Washout Facility
• Temporary concrete washout facility (type above grade) should be
constructed as shown on the details below, with a recommended
minimum length and minimum width of 10 ft, but with sufficient
quantity and volume to contain all liquid and concrete waste
generated by washout operations.
• Plastic lining material should be a minimum of 10 mil
polyethylene sheeting and should be free of holes, tears, or other
defects that compromise the impermeability of the material.
• Temporary Below-Grade Concrete Washout Facility
• Temporary concrete washout facilities (type below grade) should
be constructed as shown on the details below, with a recommended
minimum length and minimum width of 10 ft. The quantity and
volume should be sufficient to contain all liquid and concrete
waste generated by washout operations.
• Lath and flagging should be commercial type.
• Plastic lining material shall be a minimum of 10 mil polyethylene
sheeting and should be free of holes, tears, or other defects that
compromise the impermeability of the material.
• Liner seams shall be installed in accordance with manufacturers’
recommendations.
• Soil base shall be prepared free of rocks or other debris that may
cause tears or holes in the plastic lining material.
Maintenance
Standards
Inspection and Maintenance
• Inspect and verify that concrete washout BMPs are in place prior to the
commencement of concrete work.
• During periods of concrete work, inspect daily to verify continued
performance.
• Check overall condition and performance.
• Check remaining capacity (% full).
Volume II – Construction Stormwater Pollution Prevention - August 2012
4-50
• If using self-installed washout facilities, verify plastic liners are
intact and sidewalls are not damaged.
• If using prefabricated containers, check for leaks.
• Washout facilities shall be maintained to provide adequate holding
capacity with a minimum freeboard of 12 inches.
• Washout facilities must be cleaned, or new facilities must be
constructed and ready for use once the washout is 75% full.
• If the washout is nearing capacity, vacuum and dispose of the waste
material in an approved manner.
• Do not discharge liquid or slurry to waterways, storm drains or
directly onto ground.
• Do not use sanitary sewer without local approval.
• Place a secure, non-collapsing, non-water collecting cover over the
concrete washout facility prior to predicted wet weather to prevent
accumulation and overflow of precipitation.
• Remove and dispose of hardened concrete and return the structure
to a functional condition. Concrete may be reused on-site or hauled
away for disposal or recycling.
• When you remove materials from the self-installed concrete washout,
build a new structure; or, if the previous structure is still intact, inspect
for signs of weakening or damage, and make any necessary repairs.
Re-line the structure with new plastic after each cleaning.
Removal of Temporary Concrete Washout Facilities
• When temporary concrete washout facilities are no longer required for
the work, the hardened concrete, slurries and liquids shall be removed
and properly disposed of.
• Materials used to construct temporary concrete washout facilities shall
be removed from the site of the work and disposed of or recycled.
• Holes, depressions or other ground disturbance caused by the removal
of the temporary concrete washout facilities shall be backfilled,
repaired, and stabilized to prevent erosion.
Volume II – Construction Stormwater Pollution Prevention - August 2012
4-51
Figure 4.1.7a – Concrete Washout Area
Volume II – Construction Stormwater Pollution Prevention - August 2012
4-52
Figure 4.1.7b – Concrete Washout Area
Figure 4.1.8 – Prefabricated Concrete Washout Container w/Ramp
Volume II – Construction Stormwater Pollution Prevention - August 2012
4-57
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.
Volume II – Construction Stormwater Pollution Prevention - August 2012
4-58
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.
Volume II – Construction Stormwater Pollution Prevention - August 2012
4-73
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.
Volume II – Construction Stormwater Pollution Prevention - August 2012
4-74
• 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.
Volume II – Construction Stormwater Pollution Prevention - August 2012
4-75
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
Volume II – Construction Stormwater Pollution Prevention - August 2012
4-76
Figure 4.2.7 – Rock Check Dam
Volume II – Construction Stormwater Pollution Prevention - August 2012
4-79
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.
Volume II – Construction Stormwater Pollution Prevention - August 2012
4-80
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.
Volume II – Construction Stormwater Pollution Prevention - August 2012
4-81
• 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.
Volume II – Construction Stormwater Pollution Prevention - August 2012
4-82
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.
Volume II – Construction Stormwater Pollution Prevention - August 2012
4-83
• 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.
Volume II – Construction Stormwater Pollution Prevention - August 2012
4-84
• 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
4-85
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.
Volume II – Construction Stormwater Pollution Prevention - August 2012
4-86
Figure 4.2.10 – Curb and Gutter Barrier
Volume II – Construction Stormwater Pollution Prevention - August 2012
4-88
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.
Volume II – Construction Stormwater Pollution Prevention - August 2012
4-104
BMP C241: Temporary Sediment Pond
Purpose Sediment ponds remove sediment from runoff originating from disturbed
areas of the site. Sediment ponds are typically designed to remove
sediment no smaller than medium silt (0.02 mm). Consequently, they
usually reduce turbidity only slightly.
Conditions of Use Prior to leaving a construction site, stormwater runoff must pass through a
sediment pond or other appropriate sediment removal best management
practice.
A sediment pond shall be used where the contributing drainage area is 3
acres or more. Ponds must be used in conjunction with erosion control
practices to reduce the amount of sediment flowing into the basin.
Design and
Installation
Specifications
• Sediment basins must be installed only on sites where failure of the
structure would not result in loss of life, damage to homes or
buildings, or interruption of use or service of public roads or utilities.
Also, sediment traps and ponds are attractive to children and can be
very dangerous. Compliance with local ordinances regarding health
and safety must be addressed. If fencing of the pond is required, the
type of fence and its location shall be shown on the ESC plan.
• Structures having a maximum storage capacity at the top of the dam of
10 acre-ft (435,600 ft3) or more are subject to the Washington Dam
Safety Regulations (Chapter 173-175 WAC).
• See Figures 4.2.18, 4.2.19, and 4.2.20 for details.
• If permanent runoff control facilities are part of the project, they
should be used for sediment retention. The surface area requirements
of the sediment basin must be met. This may require temporarily
enlarging the permanent basin to comply with the surface area
requirements. The permanent control structure must be temporarily
replaced with a control structure that only allows water to leave the
pond from the surface or by pumping. The permanent control structure
must be installed after the site is fully stabilized. .
• Use of infiltration facilities for sedimentation basins during
construction tends to clog the soils and reduce their capacity to
infiltrate. If infiltration facilities are to be used, the sides and bottom of
the facility must only be rough excavated to a minimum of 2 feet
above final grade. Final grading of the infiltration facility shall occur
only when all contributing drainage areas are fully stabilized. The
infiltration pretreatment facility should be fully constructed and used
with the sedimentation basin to help prevent clogging.
• Determining Pond Geometry
Obtain the discharge from the hydrologic calculations of the peak flow
for the 2-year runoff event (Q2). The 10-year peak flow shall be used if
Volume II – Construction Stormwater Pollution Prevention - August 2012
4-105
the project size, expected timing and duration of construction, or
downstream conditions warrant a higher level of protection. If no
hydrologic analysis is required, the Rational Method may be used.
Determine the required surface area at the top of the riser pipe with the
equation:
SA = 2 x Q2/0.00096 or
2080 square feet per cfs of inflow
See BMP C240 for more information on the derivation of the surface
area calculation.
The basic geometry of the pond can now be determined using the
following design criteria:
• Required surface area SA (from Step 2 above) at top of riser.
• Minimum 3.5-foot depth from top of riser to bottom of pond.
• Maximum 3H:1V interior side slopes and maximum 2H:1V exterior
slopes. The interior slopes can be increased to a maximum of 2H:1V if
fencing is provided at or above the maximum water surface.
• One foot of freeboard between the top of the riser and the crest of the
emergency spillway.
• Flat bottom.
• Minimum 1-foot deep spillway.
• Length-to-width ratio between 3:1 and 6:1.
• Sizing of Discharge Mechanisms.
The outlet for the basin consists of a combination of principal and
emergency spillways. These outlets must pass the peak runoff
expected from the contributing drainage area for a 100-year storm. If,
due to site conditions and basin geometry, a separate emergency spill-
way is not feasible, the principal spillway must pass the entire peak
runoff expected from the 100-year storm. However, an attempt to
provide a separate emergency spillway should always be made. The
runoff calculations should be based on the site conditions during
construction. The flow through the dewatering orifice cannot be
utilized when calculating the 100-year storm elevation because of its
potential to become clogged; therefore, available spillway storage
must begin at the principal spillway riser crest.
The principal spillway designed by the procedures contained in this
standard will result in some reduction in the peak rate of runoff.
However, the riser outlet design will not adequately control the basin
discharge to the predevelopment discharge limitations as stated in
Minimum Requirement #7: Flow Control. However, if the basin for a
permanent stormwater detention pond is used for a temporary
Volume II – Construction Stormwater Pollution Prevention - August 2012
4-106
Riser pipe(principal spillway)open at top withtrash rackper Fig 4.4.4E
Dewatering device
(see riser detail)
Wire-backed silt fencestaked haybales wrappedwith filter fabric, orequivalent divider
Dewatering
orifice Concrete base
(see riser detail)
Discharge to stabilized
conveyance outlet or
level spreader
Embankment compacted 95%
pervious materials such as
gravel or clean sand shall
not be used
6' min. WidthCrest of
emergency spillway
Key divider into slopeto prevent flowaround sides
The pond length shall be 3 to 6
times the maximum pond width Emergency overflow
spillway
Discharge to stabilizedconveyance, outlet, orlevel spreader
Note: Pond may be formed by berm or
by partial or complete excavation
Inflow
Pond length
Silt fence or
equivalent divider
Riser pipe
sedimentation basin, the control structure for the permanent pond can
be used to maintain predevelopment discharge limitations. The size of
the basin, the expected life of the construction project, the anticipated
downstream effects and the anticipated weather conditions during
construction, should be considered to determine the need of additional
discharge control. See Figure 4.2.21 for riser inflow curves.
Figure 4.2.18 – Sediment Pond Plan View
Figure 4.2.19 – Sediment Pond Cross Section
Volume II – Construction Stormwater Pollution Prevention - August 2012
4-107
Perforated polyethylene
drainage tubing, diameter
min. 2" larger than
dewatering orifice.
Tubing shall comply
with ASTM F667 and
AASHTO M294
Polyethylene cap Provide adequate
strapping
Dewatering orifice, schedule,
40 steel stub min.
Diameter as per calculations
Alternatively, metal stakes
and wire may be used to
prevent flotation
2X riser dia. Min.
Concrete base
Corrugated
metal riser
Watertight
coupling
18" min.
6" min.
Tack weld
3.5" min.
Figure 4.2.20 – Sediment Pond Riser Detail
Volume II – Construction Stormwater Pollution Prevention - August 2012
4-108
Figure 4.2.21 – Riser Inflow Curves
Volume II – Construction Stormwater Pollution Prevention - August 2012
4-109
Principal Spillway: Determine the required diameter for the principal
spillway (riser pipe). The diameter shall be the minimum necessary to pass
the site’s 15-minute, 10-year flowrate. If using the Western Washington
Hydrology Model (WWHM), Version 2 or 3, design flow is the 10-year (1
hour) flow for the developed (unmitigated) site, multiplied by a factor of
1.6. Use Figure 4.2.21 to determine this diameter (h = 1-foot). Note: A
permanent control structure may be used instead of a temporary riser.
Emergency Overflow Spillway: Determine the required size and design
of the emergency overflow spillway for the developed 100-year peak flow
using the method contained in Volume III.
Dewatering Orifice: Determine the size of the dewatering orifice(s)
(minimum 1-inch diameter) using a modified version of the discharge
equation for a vertical orifice and a basic equation for the area of a circular
orifice. Determine the required area of the orifice with the following
equation:
5.0
5.0
3600x6.0
)2(
Tg
hAAs
o =
where Ao = orifice area (square feet)
As = pond surface area (square feet)
h = head of water above orifice (height of riser in feet)
T = dewatering time (24 hours)
g = acceleration of gravity (32.2 feet/second2)
Convert the required surface area to the required diameter D of the orifice:
o
o AADx54.13x24==π
The vertical, perforated tubing connected to the dewatering orifice must be
at least 2 inches larger in diameter than the orifice to improve flow
characteristics. The size and number of perforations in the tubing should
be large enough so that the tubing does not restrict flow. The orifice
should control the flow rate.
• Additional Design Specifications
The pond shall be divided into two roughly equal volume cells by a
permeable divider that will reduce turbulence while allowing
movement of water between cells. The divider shall be at least one-
half the height of the riser and a minimum of one foot below the top of
the riser. Wire-backed, 2- to 3-foot high, extra strength filter fabric
supported by treated 4"x4"s can be used as a divider. Alternatively,
staked straw bales wrapped with filter fabric (geotextile) may be used.
If the pond is more than 6 feet deep, a different mechanism must be
proposed. A riprap embankment is one acceptable method of
Volume II – Construction Stormwater Pollution Prevention - August 2012
4-110
separation for deeper ponds. Other designs that satisfy the intent of this
provision are allowed as long as the divider is permeable, structurally
sound, and designed to prevent erosion under or around the barrier.
To aid in determining sediment depth, one-foot intervals shall be
prominently marked on the riser.
If an embankment of more than 6 feet is proposed, the pond must
comply with the criteria contained in Volume III regarding dam safety
for detention BMPs.
• The most common structural failure of sedimentation basins is caused
by piping. Piping refers to two phenomena: (1) water seeping through
fine-grained soil, eroding the soil grain by grain and forming pipes or
tunnels; and, (2) water under pressure flowing upward through a
granular soil with a head of sufficient magnitude to cause soil grains to
lose contact and capability for support.
The most critical construction sequences to prevent piping will be:
1. Tight connections between riser and barrel and other pipe
connections.
2. Adequate anchoring of riser.
3. Proper soil compaction of the embankment and riser footing.
4. Proper construction of anti-seep devices.
Maintenance
Standards
• Sediment shall be removed from the pond when it reaches 1–foot in
depth.
• Any damage to the pond embankments or slopes shall be repaired.
Applicable information to be inserted here as needed.
Construction Stormwater Site Inspection Form
Page 1
Project Name Permit # Inspection Date Time
Name of Certified Erosion Sediment Control Lead (CESCL) or qualified inspector if less than one acre
Print Name:
Approximate rainfall amount since the last inspection (in inches):
Approximate rainfall amount in the last 24 hours (in inches):
Current Weather Clear Cloudy Mist Rain Wind Fog
A. Type of inspection: Weekly Post Storm Event Other
B. Phase of Active Construction (check all that apply):
Pre Construction/installation of erosion/sediment controls Clearing/Demo/Grading Infrastructure/storm/roads
Concrete pours Vertical Construction/buildings Utilities
Offsite improvements Site temporary stabilized Final stabilization
C. Questions:
1. Were all areas of construction and discharge points inspected? Yes No
2. Did you observe the presence of suspended sediment, turbidity, discoloration, or oil sheen Yes No
3. Was a water quality sample taken during inspection? (refer to permit conditions S4 & S5) Yes No
4. Was there a turbid discharge 250 NTU or greater, or Transparency 6 cm or less?* Yes No
5. If yes to #4 was it reported to Ecology? Yes No
6. Is pH sampling required? pH range required is 6.5 to 8.5. Yes No
If answering yes to a discharge, describe the event. Include when, where, and why it happened; what action was taken,
and when.
*If answering yes to # 4 record NTU/Transparency with continual sampling daily until turbidity is 25 NTU or less/ transparency is 33
cm or greater.
Sampling Results: Date:
Parameter Method (circle one) Result Other/Note
NTU cm pH
Turbidity tube, meter, laboratory
pH Paper, kit, meter
Construction Stormwater Site Inspection Form
Page 2
D. Check the observed status of all items. Provide “Action Required “details and dates.
Element # Inspection BMPs
Inspected
BMP needs
maintenance
BMP
failed
Action
required
(describe in
section F)
yes no n/a
1
Clearing
Limits
Before beginning land disturbing
activities are all clearing limits,
natural resource areas (streams,
wetlands, buffers, trees) protected
with barriers or similar BMPs? (high
visibility recommended)
2
Construction
Access
Construction access is stabilized
with quarry spalls or equivalent
BMP to prevent sediment from
being tracked onto roads?
Sediment tracked onto the road
way was cleaned thoroughly at the
end of the day or more frequent as
necessary.
3
Control Flow
Rates
Are flow control measures installed
to control stormwater volumes and
velocity during construction and do
they protect downstream
properties and waterways from
erosion?
If permanent infiltration ponds are
used for flow control during
construction, are they protected
from siltation?
4
Sediment
Controls
All perimeter sediment controls
(e.g. silt fence, wattles, compost
socks, berms, etc.) installed, and
maintained in accordance with the
Stormwater Pollution Prevention
Plan (SWPPP).
Sediment control BMPs (sediment
ponds, traps, filters etc.) have been
constructed and functional as the
first step of grading.
Stormwater runoff from disturbed
areas is directed to sediment
removal BMP.
5
Stabilize
Soils
Have exposed un-worked soils
been stabilized with effective BMP
to prevent erosion and sediment
deposition?
Construction Stormwater Site Inspection Form
Page 3
Element # Inspection BMPs
Inspected
BMP needs
maintenance
BMP
failed
Action
required
(describe in
section F)
yes no n/a
5
Stabilize Soils
Cont.
Are stockpiles stabilized from erosion,
protected with sediment trapping
measures and located away from drain
inlet, waterways, and drainage
channels?
Have soils been stabilized at the end of
the shift, before a holiday or weekend
if needed based on the weather
forecast?
6
Protect
Slopes
Has stormwater and ground water
been diverted away from slopes and
disturbed areas with interceptor dikes,
pipes and or swales?
Is off-site storm water managed
separately from stormwater generated
on the site?
Is excavated material placed on uphill
side of trenches consistent with safety
and space considerations?
Have check dams been placed at
regular intervals within constructed
channels that are cut down a slope?
7
Drain Inlets
Storm drain inlets made operable
during construction are protected.
Are existing storm drains within the
influence of the project protected?
8
Stabilize
Channel and
Outlets
Have all on-site conveyance channels
been designed, constructed and
stabilized to prevent erosion from
expected peak flows?
Is stabilization, including armoring
material, adequate to prevent erosion
of outlets, adjacent stream banks,
slopes and downstream conveyance
systems?
9
Control
Pollutants
Are waste materials and demolition
debris handled and disposed of to
prevent contamination of stormwater?
Has cover been provided for all
chemicals, liquid products, petroleum
products, and other material?
Has secondary containment been
provided capable of containing 110%
of the volume?
Were contaminated surfaces cleaned
immediately after a spill incident?
Were BMPs used to prevent
contamination of stormwater by a pH
modifying sources?
Construction Stormwater Site Inspection Form
Page 4
Element # Inspection BMPs
Inspected
BMP needs
maintenance
BMP
failed
Action
required
(describe in
section F)
yes no n/a
9
Cont.
Wheel wash wastewater is handled
and disposed of properly.
10
Control
Dewatering
Concrete washout in designated areas.
No washout or excess concrete on the
ground.
Dewatering has been done to an
approved source and in compliance
with the SWPPP.
Were there any clean non turbid
dewatering discharges?
11
Maintain
BMP
Are all temporary and permanent
erosion and sediment control BMPs
maintained to perform as intended?
12
Manage the
Project
Has the project been phased to the
maximum degree practicable?
Has regular inspection, monitoring and
maintenance been performed as
required by the permit?
Has the SWPPP been updated,
implemented and records maintained?
13
Protect LID
Is all Bioretention and Rain Garden
Facilities protected from
sedimentation with appropriate BMPs?
Is the Bioretention and Rain Garden
protected against over compaction of
construction equipment and foot
traffic to retain its infiltration
capabilities?
Permeable pavements are clean and
free of sediment and sediment laden-
water runoff. Muddy construction
equipment has not been on the base
material or pavement.
Have soiled permeable pavements
been cleaned of sediments and pass
infiltration test as required by
stormwater manual methodology?
Heavy equipment has been kept off
existing soils under LID facilities to
retain infiltration rate.
E. Check all areas that have been inspected.
All in place BMPs All disturbed soils All concrete wash out area All material storage areas
All discharge locations All equipment storage areas All construction entrances/exits
Construction Stormwater Site Inspection Form
Page 5
F. Elements checked “Action Required” (section D) describe corrective action to be taken. List the element number;
be specific on location and work needed. Document, initial, and date when the corrective action has been completed
and inspected.
Element
#
Description and Location Action Required Completion
Date
Initials
Attach additional page if needed
Sign the following certification:
“I certify that this report is true, accurate, and complete, to the best of my knowledge and belief”
Inspected by: (print) (Signature) Date:
Title/Qualification of Inspector:
Applicable information to be inserted here as needed.
Applicable information to be inserted here as needed.
Applicable information to be inserted here as needed.
Project:
BCE #:
REQUIRED SURFACE AREA Flow cfs
SA = (2,080)(Q 10)=2,960 SF Q2*1.423
Q10 2.081
PRINCIPAL SPILLWAY SIZING Q100 2.9744
D = [(Q10 ) / (3.782)(H)0.5]0.5 =0.742 FT
=8.90 IN KEY
*H MIN (DEFAULT 1)=1 FT INPUT
∴ USE RISER DIAMETER 12 INCHES OUTPUT
CHECK
EMERGENCY OVERFLOW SPILLWAY
L = [Q100 / (3.21)(H)1.5] - 2.4H =1.42 FT
*H MIN (DEFAULT .5)=0.5 FT
∴ USE SPILLWAY LENGTH 5 FEET
DEWATERING ORIFICE
A0 = (S.A.)(2H)0.5/(0.6)(3,600)(T)(g)0.5 =0.027 SF
DIAM. = 13.54 (A 0)0.5 =2.21 IN
*H MIN (DEFAULT 3.5')=3.5 FT
∴ USE ORIFICE DIAMETER 2.21"
Smith Brothers Farms
21537
TESC Calculations
*IF CONSTRUCTION TAKES PLACE OUTSIDE THE WET SEASON IN SUMMER MONTHS, Q2 IS ALLOWED TO SIZE POND S.A.
P:\21000s\21537\engineering\Storm\WWHM\21537-TESC CALCS