APPROVED SWPPP Report+2.4.2022_10.52.48_AM+2662073P a g e | 1
Table of Contents
1 Project Information .............................................................................................................. 4
1.1 Existing Conditions ...................................................................................................... 4
1.2 Proposed Construction Activities .................................................................................. 5
2 Construction Stormwater Best Management Practices (BMPs) ........................................... 7
2.1 The 13 Elements .......................................................................................................... 8
2.1.1 Element 1: Preserve Vegetation / Mark Clearing Limits ........................................ 8
2.1.2 Element 2: Establish Construction Access ............................................................ 9
2.1.3 Element 3: Control Flow Rates ............................................................................10
2.1.4 Element 4: Install Sediment Controls ...................................................................11
2.1.5 Element 5: Stabilize Soils ....................................................................................12
2.1.6 Element 6: Protect Slopes....................................................................................13
2.1.7 Element 7: Protect Drain Inlets ............................................................................14
2.1.8 Element 8: Stabilize Channels and Outlets ..........................................................15
2.1.9 Element 9: Control Pollutants ...............................................................................16
2.1.10 Element 10: Control Dewatering ..........................................................................20
2.1.11 Element 11: Maintain BMPs .................................................................................21
2.1.12 Element 12: Manage the Project ..........................................................................22
2.1.13 Element 13: Protect Low Impact Development (LID) BMPs .................................23
3 Pollution Prevention Team .................................................................................................26
4 Monitoring and Sampling Requirements ............................................................................27
4.1 Site Inspection ............................................................................................................27
4.2 Stormwater Quality Sampling ......................................................................................27
4.2.1 Turbidity Sampling ...............................................................................................27
4.2.2 pH Sampling ........................................................................................................29
5 Discharges to 303(d) or Total Maximum Daily Load (TMDL) Waterbodies .........................30
5.1 303(d) Listed Waterbodies ..........................................................................................30
5.2 TMDL Waterbodies .....................................................................................................30
6 Reporting and Record Keeping ..........................................................................................31
6.1 Record Keeping ..........................................................................................................31
6.1.1 Site Log Book ......................................................................................................31
6.1.2 Records Retention ...............................................................................................31
6.1.3 Updating the SWPPP ...........................................................................................31
6.2 Reporting ....................................................................................................................32
6.2.1 Discharge Monitoring Reports ..............................................................................32
6.2.2 Notification of Noncompliance ..............................................................................32
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List of Tables
Table 1 – Summary of Site Pollutant Constituents ................................................................ 5
Table 2 – Pollutants ................................................................................................................16
Table 3 – pH-Modifying Sources ............................................................................................17
Table 4 – Dewatering BMPs ....................................................................................................20
Table 5 – Management ............................................................................................................22
Table 6 – BMP Implementation Schedule .................................... Error! Bookmark not defined.
Table 7 – Team Information ....................................................................................................26
Table 8 – Turbidity Sampling Method ....................................................................................27
Table 9 – pH Sampling Method ..............................................................................................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
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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
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1 Project Information
Project/Site Name: Bracket’s Reserve
Street/Location: 9105/9109/9125 240th Street SW
City: Edmonds, WA 98026
Subdivision: Portion of Lots 3, 4 and 5 of Block 13, Hansbury’s Sound View Tracts
Receiving waterbody:
Puget Sound
1.1 Existing Conditions
Total acreage (including support activities such as off-site equipment staging yards, material
storage areas, borrow areas).
Total acreage: 2.7 ac. (includes Right-of-Way redevelopment area)
Disturbed acreage: 2.0 ac. (includes off-site utilities and frontage improvements)
Existing structures: 3 Existing Residences, to be removed.
Landscape Topography:
The site is located on a knoll and slopes off in nearly all directions. Slopes range greatly with
the side slopes of the knoll reaching slopes up to 66% grade. In accordance with the project’s
site-specific geotechnical engineering study by Earth Solutions NW, LLC the on-site soils consist
of silty sand (USCS: SM) glacial till deposits. The subject site is underlain by glacial till deposits
(Qvt, Vashon till soils). Full soils description is included in the project’s site specific
geotechnical engineering study by Earth Solutions NW, LLC.
Existing Vegetation: Large Single Family lots with lawn and several mature trees.
Critical Areas (wetlands, streams, high erosion risk, steep or difficult to stabilize slopes):
There are no known wetlands on-site. However, there is a documented existing wetland area
west of the site and appears to potentially be an existing wetland area south of the site on
private property. The westerly wetland is located on the Madrona School site and has been
documented as a Category III depressional wetland with a 60-foot buffer. The westerly wetland
is about 75 to 100 feet away and thus the 60-foot buffer does not extend to the project.
The potential southerly wetland area is located on private property south of 240th St SW and
east of 92nd Ave W. Wetland Resources Environmental Consulting has estimated that the
southerly wetland to be a type III or IV wetland. The buffer from a wetland on the south side of
240th St SW would be interrupted by the 240th St SW improvements and would not extend to
the project site (per ECDC 23.40.220.C.4.). See additional offsite wetland discussion include in
the project’s Critical Area Reconnaissance Report prepared by Wetland Resources
Environmental Consulting.
List of known impairments for 303(d) listed or Total Maximum Daily Load (TMDL) for the
receiving waterbody:
None Known
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Table 1 includes a list of suspected and/or known contaminants associated with the construction
activity.
Table 1 – Summary of Site Pollutant Constituents
Constituent (Pollutant) Location Depth Concentration
None Known
1.2 Proposed Construction Activities
Description of site development (example: subdivision):
The total site consists of about 107,474 sf (2.467 acres) and is currently occupied by three existing
single-family residence and detached garage with access driveways off 240th Street SW. The existing
houses are surrounded by grass lawn, garden, and landscape areas with several large mature trees
throughout the site. The site is surrounded by single family residences to the east and north;
Madrona K-8 School to the west; and 240th St SW to the south.
The proposed project includes the construction of 11 single-family residences and associated
frontage improvements, driveways, and utilities. All existing structures and impervious surface
onsite will be removed/replaced with the site development; landscaping and grass lawn around the
new residence will stabilize the site upon building construction.
Description of construction activities (example: site preparation, demolition, excavation):
Install SWPPP BMPs, demo/raze all existing residences and site improvements, mass grading and
road pre-grade, excavate and install detention vault, install utilities (storm, sewer, water, power,
etc.), install curb, gutter, sidewalk and road pavement, final fine grade, landscape, building
construction and final site stabilization.
Description of site drainage including flow from and onto adjacent properties. Must be consistent
with Site Map in Appendix A:
UPSTREAM ANALYSIS: There are no upstream basin areas to the site.
DOWNSTREAM ANALYSIS: The project site is located on a knoll that slopes off in nearly every
direction. Generally, the site is made up of two site sub-basins. A north sub-basin that includes the
site areas that slope off to the north and west ultimately flows west to a depressional wetland area
located on the adjacent Madrona School property; and a south site sub-basin that includes the runoff
that flows east and south from the site which is routed to the existing stormwater pipe system along
240th St SW. The city’s municipal separate storm sewer system (MS4) along 240th St SW flows west
along the project’s frontage and then turns and continues south in an open ditch along the east side
of 92nd Ave W (private road). The wetland area on the Madrona School site west of the project site
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in the north site sub-basin is a depressional wetland that has an overflow connected to the 240th St
SW MS4 located about 85 feet west of the site; therefore, the project’s runoff flows are in the same
threshold discharge area in accordance with the City’s drainage manual (DOE 2014) definition.
The open ditch along the east side of 92nd Ave W flows south through residential private property in
a collection of culverts and open channels. The stormwater system bends westerly and continues
westerly through the Bracket Apartment Homes complex and enters the City’s MS4 system along
Firdale Ave near 243rd Pl SW (about 2,800 feet from the project site). The stormwater system in
Firdale Ave bends back north along 100th Ave W and combines with the Edmonds Way main trunk
stormwater system (about 1.4 miles from the project site). The Edmonds Way stormwater system
continues northwesterly and eventually discharges to the Puget Sound about 3.4 miles from the site.
Developed Site Basin Summary: The proposed development includes the construction of 11
residential unit lots with typical onsite utilities, and stormwater flow control and water quality
treatment facilities. Additional off-site improvements will include frontage improvements along
240th Street SW (per City of Edmonds standards).
The project proposes to create and/or replace 50,050 sf of hard surface with the complete site
development, all existing onsite hard surface will be removed with the project site development. All
of the new/replace hard surface will be routed to the stormwater treatment (filters) and flow control
(detention vault) facilities in the site’s south sub-basin.
Description of final stabilization (example: extent of revegetation, paving, landscaping):
Upon the site improvement construction (roads and utilities) and building construction the exposed
soils will be revegetated with urban residential landscaping and grass lawn.
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2 Construction Stormwater Best Management Practices (BMPs)
Refer to the project’s approved TESC plans included in the Appendix A. Alternate
County approved BMPs shall be utilized in the event the BMP(s) listed below are
deemed ineffective or inappropriate during construction to satisfy the requirements set
forth in the General NPDES Permit (Appendix C). To avoid potential erosion and
sediment control issues that may cause a violation(s) of the NPDES Construction
Stormwater permit, the Certified Erosion and Sediment Control Lead will promptly
initiate the implementation of alternative BMPs after the first sign that existing BMPs are
ineffective or failing.
BMPs must be consistent with the most current edition of the Stormwater
Management Manual for Western Washington (SWMMWW) or other Ecology-
approved manual.
Note the location of each BMP on your Site Map in Appendix A.
Include the corresponding Ecology source control BMPs and runoff conveyance
and treatment BMPs in Appendix B.
o SWMMWW Volume II Chapter 4 Sections 4.1 and 4.2:
https://fortress.wa.gov/ecy/publications/SummaryPages/1410055.html ,or
o SWMMEW Chapter 7 Section 7.3.1 and 7.3.2:
http://www.ecy.wa.gov/biblio/0410076.html
If it can be justified that a particular element does not apply to the project site, include a
written justification in lieu of the BMP description in the text for the appropriate element.
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.
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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.
Trees 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. In general, natural vegetation and
native topsoil shall be retained in an undisturbed state to the maximum extent possible.
The BMPs relevant to marking the clearing limits that will be applied for this project
include:
Preserving Natural Vegetation (BMP C101)
Buffer Zones (BMP C102)
High Visibility Plastic or Metal Fence (BMP C103)
Silt Fence (BMP C233)
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2.1.2 Element 2: Establish Construction Access
Construction access or activities occurring on unpaved areas shall be minimized, yet
where necessary, access points shall be stabilized to minimize the tracking of sediment
onto public roads, and wheel washing, street sweeping, and street cleaning shall be
employed to prevent sediment from entering state waters. All wash wastewater shall be
controlled on site.
Limit vehicle access to one route, if possible.
Recycled concrete used to establish construction ingress or egress may be a
stormwater pollutant source that requires treatment prior to discharge.
Street sweeping, street cleaning, or wheel wash/tire baths may be necessary if the
stabilized construction access is not effective. All wheel wash wastewater shall be
controlled on-site and CANNOT be discharged into waters of the State.
Install site ingress/egress stabilization BMPs according to BMP C105.
The specific BMPs related to establishing construction access that will be used on this
project include:
Stabilized Construction Entrance (BMP C105)
Construction Road/Parking Area Stabilization (BMP C107)
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2.1.3 Element 3: Control Flow Rates
In order to protect the properties and waterways downstream of the project site,
stormwater discharges from the site will be controlled. In general, discharge rates of
stormwater from the site will be controlled where increases in impervious area or soil
compaction during construction could lead to downstream erosion, or where necessary
to meet local agency stormwater discharge requirements (e.g. discharge to combined
sewer systems). The specific BMPs for flow control that shall be used on this project
include:
Interceptor Dikes and Swales (BMP C200)
Check Dams (BMP C207)
Silt Fence (BMP C233)
Sediment Trap (BMP C240)
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2.1.4 Element 4: Install Sediment Controls
All stormwater runoff from disturbed areas shall pass through an appropriate sediment
removal BMP before leaving the construction site or prior to being discharged to the
public conveyance system.
In addition, sediment will be removed from paved areas in and adjacent to construction
work areas manually or using mechanical sweepers, as needed, to minimize tracking of
sediments on vehicle tires away from the site and to minimize wash-off of sediments from
adjacent streets in runoff.
In some cases, sediment discharge in concentrated runoff can be controlled using
permanent stormwater BMPs (e.g., infiltration swales, ponds, trenches). Sediment loads
can limit the effectiveness of some permanent stormwater BMPs, such as those used for
infiltration or biofiltration; however, those BMPs designed to remove solids by settling (wet
ponds or detention ponds) can be used during the construction phase. When permanent
stormwater BMPs will be used to control sediment discharge during construction, the
structure will be protected from excessive sedimentation with adequate erosion and
sediment control BMPs. Any accumulated sediment shall be removed after construction
is complete and the permanent stormwater BMP will be restabilized with vegetation per
applicable design requirements once the remainder of the site has been stabilized. The
specific BMPs to be used for controlling sediment on this project include:
Interceptor Dikes and Swales (BMP C200)
Check Dams (BMP C207)
Storm Drain Inlet Protection (BMP C220)
Silt Fence (BMP C233)
Sediment Trap (BMP C240)
During construction a sediment trap/pond in the location of the stormwater detention
vault near the southwest corner of the site shall be installed. The surface area of the
sediment trap/pond is determined by calculating the runoff rate of the 2-year return
period developed storm event. The following equation shows the calculated required
surface area.
Surface Area (SF) = 2,080 * Q2
where: Q2 = design inflow for the collected developed site (cfs)
The 2-year return period developed flow rate for the collected site development area is
0.367 cfs. The minimum required surface area for sediment trap/pond is 2,080 * 0.367 =
764 square feet. Once constructed, the detention vault can be used for sediment control.
See Construction SWPPP plans in Appendix A of this Report.
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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. The project site is located west of the
Cascade Mountain Crest. As such, no soils shall remain exposed and unworked for
more than 7 days during the dry season (May 1 to September 30) and 2 days during the
wet season (October 1 to April 30). Regardless of the time of year, all soils shall be
stabilized at the end of the shift before a holiday or weekend if needed based on
weather forecasts.
In general, cut and fill slopes will be stabilized as soon as possible and soil stockpiles
will be temporarily covered with plastic sheeting. 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.
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: May 2022 End date: October 2024
Will you construct during the wet season?
Yes No
The specific BMPs for soil stabilization that shall be used on this project include:
Temporary and Permanent Seeding (BMP C120)
Mulching (BMP C121)
Plastic Covering (BMP C123)
Dust Control (BMP C140)
Early application of gravel base on areas to be paved
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2.1.6 Element 6: Protect Slopes
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.
If using the Western Washington Hydrology Model (WWHM) to predict flows, bare soil areas
should be modeled as “landscaped area”.
All cut and fill slopes will be designed, constructed, and protected in a manner than minimizes
erosion. The following specific BMPs will be used to protect slopes for this project:
Temporary and Permanent Seeding (BMP C120)
Mulching (BMP C121)
Plastic Covering (BMP C123)
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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 street wash water
separate from entering storm drains until treatment can be provided. Inlet protection will be
implemented for all drainage inlets and culverts that could potentially be impacted by sediment-
laden runoff on and near the project site. The following inlet protection measures will be applied
on this project.
Keep in mind inlet protection may function well for coarse sediment but is less effective in
filtering finer particles and dissolved constituents. 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.
Inlets will be inspected weekly at a minimum and daily during storm events.
The following inlet protection measures will be applied on this project.
Storm Drain Inlet Protection (BMP C220)
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2.1.8 Element 8: Stabilize Channels and Outlets
Clean stormwater discharge shall be released to the existing stormwater pipe can catch basin
system along the south boundary of the site. No open channel or point discharge to the open
surface shall be allowed.
West of the Cascade Mountains Crest
On-site conveyance channels 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.
If using the WWHM to predict flows, bare soil areas should be modeled as “landscaped area”.
See Full Storm Drainage Report by RAM Engineering Inc. dated March 1, 2016 for peak storm
event flows.
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.
The specific BMPs for channel and outlet stabilization that shall be used on this project include:
Grass-Lined Channels (BMP C201)
Check Dams (BMP C207)
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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)
Turbidity (clays and silty soils)
pH Control (concrete pour, washouts, etc.)
Petroleum hydrocarbons (fuels, ex. contaminated soils, etc.)
The site contractor and CESCL shall document and report any pollutants encounter on-site.
Documentation of pollutants shall describe how you will handle and dispose of all pollutants,
including waste materials and demolition debris, in a manner that does not cause contamination
of stormwater; describe how you will cover, contain, and protect from vandalism all chemicals,
liquid products, petroleum products, and other polluting materials; and escribe how you will
manage known contaminants to prevent their discharge with stormwater to waters of the State
(i.e., treatment system, off-site disposal).
Each documentation report shall include:
1. List and describe BMPs:
2. Installation Schedules:
3. Inspection and Maintenance plan:
4. Responsible Staff:
Will maintenance, fueling, and/or repair of heavy equipment and vehicles occur on-site?
Yes No
If yes, describe spill prevention and control measures in place while conducting maintenance,
fueling, and repair of heavy equipment and vehicles.
If yes, also provide the total volume of fuel on-site and capacity of the secondary containment
for each fuel tank. Secondary containment structures shall be impervious.
Will wheel wash or tire bath system BMPs be used during construction?
Yes No
If yes, provide disposal methods for wastewater generated by BMPs. If discharging to the
sanitary sewer, include the approval letter from your local sewer district under Correspondence
in Appendix C.
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Will pH-modifying sources be present on-site?
Yes No If yes, check the source(s).
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
Other (i.e., calcium lignosulfate)
Describe BMPs you will use to prevent pH-modifying sources from contaminating stormwater.
Adjust pH of stormwater if outside the range of 6.5 to 8.5 su.
Obtain written approval from Ecology before using chemical treatment with the
exception of CO2 or dry ice to modify pH.
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.
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. 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
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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.
Chemical storage:
Any chemicals stored in the construction areas will conform to the
appropriate source control BMPs listed in Volume IV of the
Ecology stormwater manual. In Western WA, all chemicals shall
have cover, containment, and protection provided on site, per
BMP C153 for Material Delivery, Storage and Containment in
SWMMWW 2005
Application of agricultural chemicals, including fertilizers and
pesticides, shall be conducted in a manner and at application
rates that will not result in loss of chemical to stormwater runoff.
Manufacturers’ recommendations for application procedures and
rates shall be followed.
Excavation and tunneling spoils dewatering waste:
Dewatering BMPs and BMPs specific to the excavation and
tunneling (including handling of contaminated soils) are discussed
under Element 10.
Demolition:
Dust released from demolished sidewalks, buildings, or structures
will be controlled using Dust Control measures (BMP C140).
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).
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Process water and slurry resulting from saw cutting and surfacing
operations will be prevented from entering the waters of the State
by implementing Saw cutting and Surfacing Pollution Prevention
measures (BMP C152).
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). Concrete wash out
areas shall not be allowed on bare dirt or allowed to drain to bare
dirt or the storm system.
Sanitary wastewater:
Portable sanitation facilities will be firmly secured, regularly
maintained, and emptied when necessary.
Wheel wash or tire bath wastewater shall be discharged to a
separate on-site treatment system or to the sanitary sewer as part
of Wheel Wash implementation (BMP C106).
Solid Waste:
Solid waste will be stored in secure, clearly marked containers.
Other:
Other BMPs will be administered as necessary to address any
additional pollutant sources on site.
The facility does not require a Spill Prevention, Control, and Countermeasure (SPCC)
Plan under the Federal regulations of the Clean Water Act (CWA).
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2.1.10 Element 10: Control Dewatering
Dewatering shall be placed within and around the foundation, shoring and utility
excavations. Contaminated (turbid or chemical) shall be contained and properly treated.
Water from foundations, vaults, and trenches with characteristics similar to stormwater
runoff shall be discharged into a controlled conveyance system before discharging to a
sediment pond or sediment pond. Clean dewatering water will not be routed through
stormwater sediment ponds.
Only clean, non-turbid dewatering water (such as well-point groundwater) may be
discharged to systems tributary to, or directly into, surface waters of the State, provided
the dewatering flow does not cause erosion or flooding of receiving waters.
Site contractor shall manage dewatering water to prevent the discharge of contaminants
to waters of the State, including dewatering water that has comingled with stormwater
(i.e., treatment system, off-site disposal).
Table 4 – Dewatering BMPs
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)
CESCL and/or contractor shall document and inspect the following information for each
dewatering BMP utilized during construction:
5. List and describe BMPs:
6. Installation Schedules:
7. Inspection and Maintenance plan:
8. Responsible Staff:
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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.
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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 | 23
Optional: Fill out Table 6 by listing the BMP associated with specific construction activities.
Identify the phase of the project (if applicable). To increase awareness of seasonal
requirements, indicate if the activity falls within the wet or dry season.
Table 6 – BMP Implementation Schedule
Phase of
Construction
Project
Stormwater BMPs Date Wet/Dry
Season
Initial Clearing and
Grading
High Visibility Plastic or Metal Fence
(BMP C103)
At start Wet or Dry
Initial Clearing and
Grading
Stabilized Construction Entrance
(BMP C105)
At start Wet or Dry
Initial Clearing and
Grading
Construction Road/Parking Area
Stabilization (BMP C107)
At start Wet or Dry
After Initial Site
Grading
Temporary and Permanent Seeding
(BMP C120)
During
Construction
Wet or Dry
After Initial Site
Grading
Mulching (BMP C121) During
Construction
Wet or Dry
After Initial Site
Grading
Plastic Covering (BMP C123) During
Construction
Wet or Dry
Initial Clearing and
Grading
Dust Control (BMP C140) During
Construction
Wet or Dry
Improvement
Construction
Concrete Handling (BMP C151) During
Construction
Wet or Dry
Initial Clearing and
Grading
Material Delivery, Storage and
Containment (BMP C153)
Prior to start Wet or Dry
Improvement
Construction
Concrete Washout Area (BMP C154) During
Construction
Wet or Dry
Initial Clearing and
Grading
Interceptor Dikes and Swales
(BMP C200)
During
Construction
Wet or Dry
Initial Clearing and
Grading
Check Dams (BMP C207) Prior to start Wet or Dry
Initial Clearing and
Grading
Storm Drain Inlet Protection
(BMP C220)
Prior to start Wet or Dry
Initial Clearing and
Grading
Silt Fence (BMP C233) Prior to start Wet or Dry
Initial Clearing and
Grading
Sediment Trap (BMP C240) Prior to start Wet or Dry
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Phase of
Construction
Project
Stormwater BMPs Date Wet/Dry
Season
P a g e | 25
2.1.13 Element 13: Protect Low Impact Development (LID) BMPs
Describe LIDs: Due to existing dense unweathered till (hard pan) soils observed at relatively shallow
depths (exhibit poor soil infiltration characteristics) and lack of minimum flow path lengths that do not
include steep slopes, no infiltration or dispersion BMPs are proposed. All disturbed pervious areas will
be amended per Snohomish County equivalent BMP T5.13 Post Construction Soils Quality and Depth.
Permittees must keep all heavy equipment off post construction amended soils (BMPT5.13) to avoid
over compaction. Areas used for stockpiles or laydown areas shall be “reconditioned” as needed to
maintain adequate post construction soils quality and depth (per BMP T5.13).
P a g e | 26
3 Pollution Prevention Team
Table 7 – Team Information
Title Name(s) Phone Number
Certified Erosion and
Sediment Control Lead
(CESCL)
Eric Strand
Pacific Ridge Homes (425) 375-3065
Resident Engineer Robert L. Long, PE
RAM Engineering, Inc. (425) 678-6960
Emergency Ecology
Contact Miya Spratt (360) 870-7853
Emergency Permittee/
Owner Contact
Eric Strand
Pacific Ridge Homes (425) 375-3065
Non-Emergency Owner
Contact
John Mirante
Pacific Ridge Homes (425) 939-1186
Monitoring Personnel To be Determined.
Ecology Regional Office Northwest Regional Office (425) 649-7000
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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
Create your own Site Inspection Form or use the Construction Stormwater Site Inspection Form
found on Ecology’s website.
http://www.ecy.wa.gov/programs/wq/stormwater/construction/index.html
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.
Numeric effluent limits may be required for certain discharges to 303(d) listed waterbodies. See
CSWGP Special Condition S8 and Section 5 of this template.
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) are indicated on the Site Map (see Appendix A) and in accordance with
the applicable requirements of the CSWGP.
4.2 Stormwater Quality Sampling
4.2.1 Turbidity Sampling
Requirements include calibrated turbidity meter or transparency tube to sample site discharges
for compliance with the CSWGP. Sampling will be conducted at all discharge points at least
once per calendar week.
Method for sampling turbidity: To be determined.
Table 8 – Turbidity Sampling Method
Turbidity Meter/Turbidimeter (required for disturbances 5 acres or greater in size)
Transparency Tube (option for disturbances less than 1 acre and up to 5 acres in size)
The benchmark for turbidity value is 25 nephelometric turbidity units (NTU) and a transparency
less than 33 centimeters.
P a g e | 28
If the discharge’s turbidity is 26 to 249 NTU or the transparency is less than 33 cm but equal to
or greater than 6 cm, the following steps will be conducted:
1. Review the SWPPP for compliance with Special Condition S9. Make appropriate
revisions within 7 days of the date the discharge exceeded the benchmark.
2. Immediately begin the process to fully implement and maintain appropriate source
control and/or treatment BMPs as soon as possible. Address the problems within 10
days of the date the discharge exceeded the benchmark. If installation of necessary
treatment BMPs is not feasible within 10 days, Ecology may approve additional time
when the Permittee requests an extension within the initial 10-day response period.
3. Document BMP implementation and maintenance in the site log book.
If the turbidity exceeds 250 NTU or the transparency is 6 cm or less at any time, the following
steps will be conducted:
1. Telephone the applicable Ecology Region’s Environmental Report Tracking System
(ERTS) number within 24 hours.
Central Region (Benton, Chelan, Douglas, Kittitas, Klickitat, Okanogan,
Yakima): (509) 575-2490
Eastern Region (Adams, Asotin, Columbia, Ferry, Franklin, Garfield, Grant,
Lincoln, Pend Oreille, Spokane, Stevens, Walla Walla, Whitman): (509) 329-3400
Northwest Region (King, Kitsap, Island, San Juan, Skagit, Snohomish,
Whatcom): (425) 649-7000
Southwest Region (Clallam, Clark, Cowlitz, Grays Harbor, Jefferson, Lewis,
Mason, Pacific, Pierce, Skamania, Thurston, Wahkiakum,): (360) 407-6300
2. Immediately begin the process to fully implement and maintain appropriate source
control and/or treatment BMPs as soon as possible. Address the problems within 10
days of the date the discharge exceeded the benchmark. If installation of necessary
treatment BMPs is not feasible within 10 days, Ecology may approve additional time
when the Permittee requests an extension within the initial 10-day response period
3. Document BMP implementation and maintenance in the site log book.
4. Continue to sample discharges daily until one of the following is true:
Turbidity is 25 NTU (or lower).
Transparency is 33 cm (or greater).
Compliance with the water quality limit for turbidity is achieved.
o 1 - 5 NTU over background turbidity, if background is less than 50 NTU
o 1% - 10% over background turbidity, if background is 50 NTU or greater
The discharge stops or is eliminated.
P a g e | 29
4.2.2 pH Sampling
pH monitoring is required for “Significant concrete work” (i.e., greater than 1000 cubic yards
poured or recycled concrete over the life of the project). The use of engineered soils (soil
amendments including but not limited to Portland cement-treated base [CTB], cement kiln dust
[CKD] or fly ash) also requires pH monitoring.
For significant concrete work, pH sampling will start the first day concrete is poured and
continue until it is cured, typically three (3) weeks after the last pour.
For engineered soils, pH sampling begins when engineered soils are first exposed to
precipitation and continues until the area is fully stabilized.
If the measured pH is 8.5 or greater, the following measures will be taken:
1. Prevent high pH water from entering storm sewer systems or surface water.
2. Adjust or neutralize the high pH water to the range of 6.5 to 8.5 su using appropriate
technology such as carbon dioxide (CO2) sparging (liquid or dry ice).
3. Written approval will be obtained from Ecology prior to the use of chemical treatment
other than CO2 sparging or dry ice.
Method for sampling pH:
Check the analysis method you will use:
Table 9 – pH Sampling Method
pH meter
pH test kit
Wide range pH indicator paper
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5 Discharges to 303(d) or Total Maximum Daily Load (TMDL)
Waterbodies
5.1 303(d) Listed Waterbodies
Is the receiving water 303(d) (Category 5) listed for turbidity, fine sediment, phosphorus, or pH?
Yes No
None known.
List the impairment(s):
If yes, discharges must comply with applicable effluent limitations in S8.C and S8.D of the
CSWGP.
5.2 TMDL Waterbodies
Waste Load Allocation for CWSGP discharges:
None
List and describe BMPs:
Discharges to TMDL receiving waterbodies will meet in-stream water quality criteria at the point
of discharge.
The Construction Stormwater General Permit Proposed New Discharge to an Impaired Water
Body form is included in Appendix F.
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6 Reporting and Record Keeping
6.1 Record Keeping
6.1.1 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
6.1.2 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
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.
6.1.3 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.
P a g e | 32
6.2 Reporting
6.2.1 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.
To sign up for WQWebDMR go to:
http://www.ecy.wa.gov/programs/wq/permits/paris/webdmr.html
6.2.2 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 immediately notified 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. Specific information to be included in the
noncompliance report is found in Special Condition S5.F.3 of the CSWGP.
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.
Northwest Region at (425) 649-7000 for Island, King, Kitsap, San Juan, Skagit,
Snohomish, or Whatcom County
1. Include the following information:
2. Your name and / Phone number
3. Permit number
4. City / County of project
5. Sample results
6. Date / Time of call
7. Date / Time of sample
8. 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.
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Appendix/Glossary
A. Site Map
BOUNDARY 1
11
4
3
2
6
5
1
999
9
7
49
10
8
998
BLOCK 12
HANBURY'S SOUND
VIEW TRACTS
V.7 / PG.20
LOT 5 LOT 4
EDMUNDS HIGHLANDS
REC. NO. 200404125344
TRACT 998
4
3
2
1
VILLAGER
REC. NO. 8112285001
5
9
7
10
4
3
2
6
5
1
9
11
TRACT 999
240TH ST SWROAD A92NDAVE W8
WASHINGTONREVISIONRAM
ENGINEERING, INC.
Civil Engineering / Land Planning
19109 36TH AVE W, SUITE 100
LYNNWOOD, WA 98036
PHONE: (425) 678-6960
WWW.RAMENGINEERINGINC.COM
SE1/4, SEC 31, TWP 27N, RGE 4E, W.M.BRACKET'S RESERVEPACIFIC RIDGE - DRH, LLCPLN2021-0037CITY OF EDMONDS20-024
15
APPROVED FOR CONSTRUCTION
CITY OF EDMONDS
PLN2021-0037 CLEARING, GRADING & TESC PLANTP-01
4
N
CONSTRUCTION SEQUENCE
GRADING QUANTITIES
CB INLET PROTECTION NOTE
FILTER FABRIC FENCE NOTE
TESC NOTE
STOCKPILE NOTE
SOILS NOTE
TREE LEGEND
OUTFALL 1:
TO EXISTING CATCHBASIN/CONVEYANCE SYSTEM
DISCHARGE MONITORING POINT
SYSTEM EVENTLY FLOWS NORTH TO EDMONDS
WAY AND DIRECT DISCHARGES TO PUGET
SOUND ABOUT 3.4 MILES FORM THE SITE
(DISCHARGE DOES NOT ENTER A STREAM)
ON SITE RUNOFF SHALL BE DIRECTED TO
PROPSED DETETNION VALUT PRIOR TO
DISCHARGE FROM TH SITE.
P a g e | 34
B. BMP Detail
BMP List:
High Visibility Plastic or Metal Fence (BMP C103)
Stabilized Construction Entrance (BMP C105)
Construction Road/Parking Area Stabilization (BMP C107)
Temporary and Permanent Seeding (BMP C120)
Mulching (BMP C121)
Plastic Covering (BMP C123)
Dust Control (BMP C140)
Materials On Hand (BMP C150)
Concrete Handling (BMP C151)
Sawcutting and Surfacing Pollution Prevention (BMP C152)
Material Delivery, Storage, and Containment (BMP C153)
Certified Erosion and Sediment Control Lead (BMP C160)
Interceptor Dikes and Swales (BMP C200)
Check Dams (BMP C207)
Storm Drain Inlet Protection (BMP C220)
Silt Fence (BMP C233)
Wattles (BMP C235)
Sediment Trap (BMP C240)
High pH Neutralization using CO2 (BMP C252)
pH control for High pH Water (BMP C253)
Additional resources and guidance can be found on the Ecology Construction Stormwater website at:
http://www.ecy.wa.gov/programs/wq/stormwater/construction/index.html
Volume II – Construction Stormwater Pollution Prevention - December 2014
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BMP C101: Preserving Natural Vegetation
Purpose The purpose of preserving natural vegetation is to reduce erosion wherever
practicable. Limiting site disturbance is the single most effective method
for reducing erosion. For example, conifers can hold up to about 50 percent of all rain that falls during a storm. Up to 20-30 percent of this rain
may never reach the ground but is taken up by the tree or evaporates.
Another benefit is that the rain held in the tree can be released slowly to
the ground after the storm.
Conditions of Use Natural vegetation should be preserved on steep slopes, near perennial and intermittent watercourses or swales, and on building sites in wooded
areas.
• As required by local governments.
• Phase construction to preserve natural vegetation on the project site for
as long as possible during the construction period.
Design and Installation Specifications
Natural vegetation can be preserved in natural clumps or as individual
trees, shrubs and vines.
The preservation of individual plants is more difficult because heavy
equipment is generally used to remove unwanted vegetation. The points
to remember when attempting to save individual plants are:
• Is the plant worth saving? Consider the location, species, size, age, vigor,
and the work involved. Local governments may also have ordinances to
save natural vegetation and trees.
• Fence or clearly mark areas around trees that are to be saved. It is
preferable to keep ground disturbance away from the trees at least as far out as the dripline.
Plants need protection from three kinds of injuries:
• Construction Equipment - This injury can be above or below the
ground level. Damage results from scarring, cutting of roots, and
compaction of the soil. Placing a fenced buffer zone around plants to be saved prior to construction can prevent construction equipment injuries.
• Grade Changes - Changing the natural ground level will alter grades,
which affects the plant's ability to obtain the necessary air, water, and
minerals. Minor fills usually do not cause problems although sensitivity between species does vary and should be checked. Trees can typically tolerate fill of 6 inches or less. For shrubs and other
plants, the fill should be less.
When there are major changes in grade, it may become necessary to
supply air to the roots of plants. This can be done by placing a layer of gravel and a tile system over the roots before the fill is made. A tile
Volume II – Construction Stormwater Pollution Prevention - December 2014
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system protects a tree from a raised grade. The tile system should be
laid out on the original grade leading from a dry well around the tree
trunk. The system should then be covered with small stones to allow
air to circulate over the root area.
Lowering the natural ground level can seriously damage trees and
shrubs. The highest percentage of the plant roots are in the upper 12
inches of the soil and cuts of only 2-3 inches can cause serious injury.
To protect the roots it may be necessary to terrace the immediate area
around the plants to be saved. If roots are exposed, construction of retaining walls may be needed to keep the soil in place. Plants can also
be preserved by leaving them on an undisturbed, gently sloping
mound. To increase the chances for survival, it is best to limit grade
changes and other soil disturbances to areas outside the dripline of the
plant.
• Excavations - Protect trees and other plants when excavating for
drainfields, power, water, and sewer lines. Where possible, the
trenches should be routed around trees and large shrubs. When this is
not possible, it is best to tunnel under them. This can be done with
hand tools or with power augers. If it is not possible to route the trench around plants to be saved, then the following should be observed:
Cut as few roots as possible. When you have to cut, cut clean. Paint
cut root ends with a wood dressing like asphalt base paint if roots will
be exposed for more than 24-hours.
Backfill the trench as soon as possible.
Tunnel beneath root systems as close to the center of the main trunk to
preserve most of the important feeder roots.
Some problems that can be encountered with a few specific trees are:
• Maple, Dogwood, Red alder, Western hemlock, Western red cedar,
and Douglas fir do not readily adjust to changes in environment and special care should be taken to protect these trees.
• The windthrow hazard of Pacific silver fir and madrona is high, while
that of Western hemlock is moderate. The danger of windthrow
increases where dense stands have been thinned. Other species (unless
they are on shallow, wet soils less than 20 inches deep) have a low windthrow hazard.
• Cottonwoods, maples, and willows have water-seeking roots. These
can cause trouble in sewer lines and infiltration fields. On the other
hand, they thrive in high moisture conditions that other trees would
not.
• Thinning operations in pure or mixed stands of Grand fir, Pacific silver
fir, Noble fir, Sitka spruce, Western red cedar, Western hemlock,
Pacific dogwood, and Red alder can cause serious disease problems.
Volume II – Construction Stormwater Pollution Prevention - December 2014
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Disease can become established through damaged limbs, trunks, roots,
and freshly cut stumps. Diseased and weakened trees are also
susceptible to insect attack.
Maintenance Standards Inspect flagged and/or fenced areas regularly to make sure flagging or fencing has not been removed or damaged. If the flagging or fencing
has been damaged or visibility reduced, it shall be repaired or
replaced immediately and visibility restored.
• If tree roots have been exposed or injured, “prune” cleanly with an
appropriate pruning saw or loppers directly above the damaged roots and recover with native soils. Treatment of sap flowing trees (fir, hemlock, pine, soft maples) is not advised as sap forms a natural
healing barrier.
BMP C102: Buffer Zones
Purpose Creation of an undisturbed area or strip of natural vegetation or an established suitable planting that will provide a living filter to reduce soil erosion and runoff velocities.
Conditions of Use Natural buffer zones are used along streams, wetlands and other bodies of
water that need protection from erosion and sedimentation. Vegetative
buffer zones can be used to protect natural swales and can be incorporated into the natural landscaping of an area.
Critical-areas buffer zones should not be used as sediment treatment areas.
These areas shall remain completely undisturbed. The local permitting
authority may expand the buffer widths temporarily to allow the use of the
expanded area for removal of sediment.
Design and Installation Specifications
• Preserving natural vegetation or plantings in clumps, blocks, or strips
is generally the easiest and most successful method.
• Leave all unstable steep slopes in natural vegetation.
• Mark clearing limits and keep all equipment and construction debris
out of the natural areas and buffer zones. Steel construction fencing is the most effective method in protecting sensitive areas and buffers.
Alternatively, wire-backed silt fence on steel posts is marginally
effective. Flagging alone is typically not effective.
• Keep all excavations outside the dripline of trees and shrubs.
• Do not push debris or extra soil into the buffer zone area because it will cause damage from burying and smothering.
• Vegetative buffer zones for streams, lakes or other waterways shall be
established by the local permitting authority or other state or federal
permits or approvals.
Maintenance Standards Inspect the area frequently to make sure flagging remains in place and the area remains undisturbed. Replace all damaged flagging immediately.
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BMP C103: High Visibility Fence
Purpose Fencing is intended to:
1. Restrict clearing to approved limits.
2. Prevent disturbance of sensitive areas, their buffers, and other areas required to be left undisturbed.
3. Limit construction traffic to designated construction entrances, exits,
or internal roads.
4. Protect areas where marking with survey tape may not provide
adequate protection.
Conditions of Use To establish clearing limits plastic, fabric, or metal fence may be used:
• At the boundary of sensitive areas, their buffers, and other areas
required to be left uncleared.
• As necessary to control vehicle access to and on the site.
Design and Installation Specifications
High visibility plastic fence shall be composed of a high-density polyethylene material and shall be at least four feet in height. Posts for
the fencing shall be steel or wood and placed every 6 feet on center
(maximum) or as needed to ensure rigidity. The fencing shall be fastened
to the post every six inches with a polyethylene tie. On long continuous
lengths of fencing, a tension wire or rope shall be used as a top stringer to prevent sagging between posts. The fence color shall be high visibility
orange. The fence tensile strength shall be 360 lbs./ft. using the ASTM
D4595 testing method.
If appropriate install fabric silt fence in accordance with BMP C233 to
act as high visibility fence. Silt fence shall be at least 3 feet high and must be highly visible to meet the requirements of this BMP.
Metal fences shall be designed and installed according to the
manufacturer's specifications.
Metal fences shall be at least 3 feet high and must be highly visible.
Fences shall not be wired or stapled to trees.
Maintenance Standards
If the fence has been damaged or visibility reduced, it shall be repaired or
replaced immediately and visibility restored.
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BMP C105: Stabilized Construction Entrance / Exit
Purpose Stabilized Construction entrances are established to reduce the amount of sediment transported onto paved roads by vehicles or equipment. This is
done by constructing a stabilized pad of quarry spalls at entrances and exits for construction sites.
Conditions of Use Construction entrances shall be stabilized wherever traffic will be entering or leaving a construction site if paved roads or other paved areas are
within 1,000 feet of the site.
For residential construction provide stabilized construction entrances for
each residence, rather than only at the main subdivision entrance. Stabilized surfaces shall be of sufficient length/width to provide vehicle
access/parking, based on lot size/configuration.
On large commercial, highway, and road projects, the designer should include enough extra materials in the contract to allow for additional stabilized entrances not shown in the initial Construction SWPPP. It is difficult to determine exactly where access to these projects will take place; additional materials will enable the contractor to install them where needed.
Design and Installation Specifications
See Figure 4.1.1 for details. Note: the 100’ minimum length of the entrance shall be reduced to the maximum practicable size when the size or configuration of the site does not allow the full length (100’).
Construct stabilized construction entrances with a 12-inch thick pad of 4-inch to 8-inch quarry spalls, a 4-inch course of asphalt treated base (ATB), or use existing pavement. Do not use crushed concrete, cement,
or calcium chloride for construction entrance stabilization because these products raise pH levels in stormwater and concrete discharge to surface
waters of the State is prohibited.
A separation geotextile shall be placed under the spalls to prevent fine
sediment from pumping up into the rock pad. The geotextile shall meet the following standards:
Grab Tensile Strength (ASTM D4751) 200 psi min.
Grab Tensile Elongation (ASTM D4632) 30% max.
Mullen Burst Strength (ASTM D3786-80a) 400 psi min.
AOS (ASTM D4751) 20-45 (U.S. standard sieve size)
• Consider early installation of the first lift of asphalt in areas that will paved; this can be used as a stabilized entrance. Also consider the
installation of excess concrete as a stabilized entrance. During large concrete pours, excess concrete is often available for this purpose.
Volume II – Construction Stormwater Pollution Prevention - December 2014
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• Fencing (see BMP C103) shall be installed as necessary to restrict
traffic to the construction entrance.
• Whenever possible, the entrance shall be constructed on a firm,
compacted subgrade. This can substantially increase the effectiveness of the pad and reduce the need for maintenance.
• Construction entrances should avoid crossing existing sidewalks and back of walk drains if at all possible. If a construction entrance must
cross a sidewalk or back of walk drain, the full length of the sidewalk and back of walk drain must be covered and protected from sediment
leaving the site.
Maintenance
Standards
Quarry spalls shall be added if the pad is no longer in accordance with
the specifications.
• If the entrance is not preventing sediment from being tracked onto
pavement, then alternative measures to keep the streets free of sediment shall be used. This may include replacement/cleaning of the
existing quarry spalls, street sweeping, an increase in the dimensions of the entrance, or the installation of a wheel wash.
• Any sediment that is tracked onto pavement shall be removed by shoveling or street sweeping. The sediment collected by sweeping
shall be removed or stabilized on site. The pavement shall not be cleaned by washing down the street, except when high efficiency
sweeping is ineffective and there is a threat to public safety. If it is necessary to wash the streets, the construction of a small sump to
contain the wash water shall be considered. The sediment would then be washed into the sump where it can be controlled.
• Perform street sweeping by hand or with a high efficiency sweeper. Do not use a non-high efficiency mechanical sweeper because this creates
dust and throws soils into storm systems or conveyance ditches.
• Any quarry spalls that are loosened from the pad, which end up on the
roadway shall be removed immediately.
• If vehicles are entering or exiting the site at points other than the
construction entrance(s), fencing (see BMP C103) shall be installed to control traffic.
• Upon project completion and site stabilization, all construction accesses intended as permanent access for maintenance shall be
permanently stabilized.
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Figure 4.1.1 – Stabilized Construction Entrance
Approved as
Equivalent
Ecology has approved products as able to meet the requirements of BMP
C105. The products did not pass through the Technology Assessment Protocol – Ecology (TAPE) process. Local jurisdictions may choose not
to accept this product approved as equivalent, or may require additional
testing prior to consideration for local use. The products are available for
review on Ecology’s website at
http://www.ecy.wa.gov/programs/wq/stormwater/newtech/equivalent.html
BMP C106: Wheel Wash
Purpose Wheel washes reduce the amount of sediment transported onto paved
roads by motor vehicles.
Conditions of Use When a stabilized construction entrance (see BMP C105) is not preventing sediment from being tracked onto pavement.
• Wheel washing is generally an effective BMP when installed with
careful attention to topography. For example, a wheel wash can be
detrimental if installed at the top of a slope abutting a right-of-way
where the water from the dripping truck can run unimpeded into the street.
Driveway shall meet the requirements of the permitting agency
It is recommended that the entrance be crowned so that runoff drains off the pad
Provide full width of ingress/egress area
12” min. thickness
Geotextile
4’ – 8” quarry spalls
Install driveway culvert if there is a roadside ditch present
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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
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stable driving surface and to stabilize any areas that have eroded.
Following construction, these areas shall be restored to pre-construction
condition or better to prevent future erosion.
Perform street cleaning at the end of each day or more often if necessary.
BMP C120: Temporary and Permanent Seeding
Purpose Seeding reduces erosion by stabilizing exposed soils. A well-established
vegetative cover is one of the most effective methods of reducing erosion.
Conditions of Use Use seeding throughout the project on disturbed areas that have reached
final grade or that will remain unworked for more than 30 days.
The optimum seeding windows for western Washington are April 1
through June 30 and September 1 through October 1.
Between July 1 and August 30 seeding requires irrigation until 75 percent
grass cover is established.
Between October 1 and March 30 seeding requires a cover of mulch with straw or an erosion control blanket until 75 percent grass cover is
established.
Review all disturbed areas in late August to early September and complete
all seeding by the end of September. Otherwise, vegetation will not
establish itself enough to provide more than average protection.
• Mulch is required at all times for seeding because it protects seeds
from heat, moisture loss, and transport due to runoff. Mulch can be applied on top of the seed or simultaneously by hydroseeding. See
BMP C121: Mulching for specifications.
• Seed and mulch, all disturbed areas not otherwise vegetated at final
site stabilization. Final stabilization means the completion of all soil
disturbing activities at the site and the establishment of a permanent
vegetative cover, or equivalent permanent stabilization measures (such
as pavement, riprap, gabions, or geotextiles) which will prevent erosion.
Design and Installation
Specifications
Seed retention/detention ponds as required.
Install channels intended for vegetation before starting major
earthwork and hydroseed with a Bonded Fiber Matrix. For vegetated
channels that will have high flows, install erosion control blankets over hydroseed. Before allowing water to flow in vegetated channels, establish 75 percent vegetation cover. If vegetated
channels cannot be established by seed before water flow; install sod
in the channel bottom—over hydromulch and erosion control
blankets.
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• Confirm the installation of all required surface water control measures
to prevent seed from washing away.
• Hydroseed applications shall include a minimum of 1,500 pounds per
acre of mulch with 3 percent tackifier. See BMP C121: Mulching for specifications.
• Areas that will have seeding only and not landscaping may need
compost or meal-based mulch included in the hydroseed in order to
establish vegetation. Re-install native topsoil on the disturbed soil
surface before application.
• When installing seed via hydroseeding operations, only about 1/3 of
the seed actually ends up in contact with the soil surface. This reduces the ability to establish a good stand of grass quickly. To overcome this,
consider increasing seed quantities by up to 50 percent.
• Enhance vegetation establishment by dividing the hydromulch
operation into two phases:
1. Phase 1- Install all seed and fertilizer with 25-30 percent mulch
and tackifier onto soil in the first lift.
2. Phase 2- Install the rest of the mulch and tackifier over the first lift.
Or, enhance vegetation by:
1. Installing the mulch, seed, fertilizer, and tackifier in one lift.
2. Spread or blow straw over the top of the hydromulch at a rate of 800-1000 pounds per acre.
3. Hold straw in place with a standard tackifier.
Both of these approaches will increase cost moderately but will greatly
improve and enhance vegetative establishment. The increased cost may be offset by the reduced need for:
• Irrigation.
• Reapplication of mulch.
• Repair of failed slope surfaces.
This technique works with standard hydromulch (1,500 pounds per acre minimum) and BFM/MBFMs (3,000 pounds per acre minimum).
• Seed may be installed by hand if:
• Temporary and covered by straw, mulch, or topsoil.
• Permanent in small areas (usually less than 1 acre) and covered with mulch, topsoil, or erosion blankets.
• The seed mixes listed in the tables below include recommended
mixes for both temporary and permanent seeding.
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• Apply these mixes, with the exception of the wetland mix, at a rate
of 120 pounds per acre. This rate can be reduced if soil
amendments or slow-release fertilizers are used.
• Consult the local suppliers or the local conservation district for their recommendations because the appropriate mix depends on a variety of factors, including location, exposure, soil type, slope,
and expected foot traffic. Alternative seed mixes approved by the
local authority may be used.
• Other mixes may be appropriate, depending on the soil type and hydrology of the area.
• Table 4.1.2 lists the standard mix for areas requiring a temporary
vegetative cover.
Table 4.1.2 Temporary Erosion Control Seed Mix
% Weight % Purity % Germination
Chewings or annual blue grass Festuca rubra var. commutata or Poa anna
40 98 90
Perennial rye -
Lolium perenne
50 98 90
Redtop or colonial bentgrass
Agrostis alba or Agrostis tenuis
5 92 85
White dutch clover
Trifolium repens
5 98 90
• Table 4.1.3 lists a recommended mix for landscaping seed.
Table 4.1.3
Landscaping Seed Mix
% Weight % Purity % Germination Perennial rye blend
Lolium perenne
70 98 90
Chewings and red fescue blend
Festuca rubra var. commutata
or Festuca rubra
30 98 90
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• Table 4.1.4 lists a turf seed mix for dry situations where there is no
need for watering. This mix requires very little maintenance.
Table 4.1.4
Low-Growing Turf Seed Mix
% Weight % Purity % Germination Dwarf tall fescue (several varieties)
Festuca arundinacea var.
45 98 90
Dwarf perennial rye (Barclay)
Lolium perenne var. barclay
30 98 90
Red fescue
Festuca rubra
20 98 90
Colonial bentgrass
Agrostis tenuis
5 98 90
• Table 4.1.5 lists a mix for bioswales and other intermittently wet areas.
Table 4.1.5 Bioswale Seed Mix*
% Weight % Purity % Germination
Tall or meadow fescue
Festuca arundinacea or Festuca elatior
75-80 98 90
Seaside/Creeping bentgrass Agrostis palustris 10-15 92 85
Redtop bentgrass Agrostis alba or Agrostis gigantea 5-10 90 80
* Modified Briargreen, Inc. Hydroseeding Guide Wetlands Seed Mix
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• Table 4.1.6 lists a low-growing, relatively non-invasive seed mix
appropriate for very wet areas that are not regulated wetlands. Apply
this mixture at a rate of 60 pounds per acre. Consult Hydraulic Permit
Authority (HPA) for seed mixes if applicable.
Table 4.1.6 Wet Area Seed Mix*
% Weight % Purity % Germination
Tall or meadow fescue
Festuca arundinacea or Festuca elatior
60-70 98 90
Seaside/Creeping bentgrass Agrostis palustris 10-15 98 85
Meadow foxtail Alepocurus pratensis 10-15 90 80
Alsike clover
Trifolium hybridum
1-6 98 90
Redtop bentgrass
Agrostis alba
1-6 92 85
* Modified Briargreen, Inc. Hydroseeding Guide Wetlands Seed Mix
• Table 4.1.7 lists a recommended meadow seed mix for infrequently
maintained areas or non-maintained areas where colonization by native plants is desirable. Likely applications include rural road and utility
right-of-way. Seeding should take place in September or very early
October in order to obtain adequate establishment prior to the winter
months. Consider the appropriateness of clover, a fairly invasive
species, in the mix. Amending the soil can reduce the need for clover.
Table 4.1.7 Meadow Seed Mix
% Weight % Purity % Germination
Redtop or Oregon bentgrass
Agrostis alba or Agrostis oregonensis
20 92 85
Red fescue
Festuca rubra
70 98 90
White dutch clover Trifolium repens 10 98 90
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• Roughening and Rototilling:
• The seedbed should be firm and rough. Roughen all soil no matter
what the slope. Track walk slopes before seeding if engineering
purposes require compaction. Backblading or smoothing of slopes greater than 4H:1V is not allowed if they are to be seeded.
• Restoration-based landscape practices require deeper incorporation
than that provided by a simple single-pass rototilling treatment.
Wherever practical, initially rip the subgrade to improve long-term
permeability, infiltration, and water inflow qualities. At a minimum, permanent areas shall use soil amendments to achieve
organic matter and permeability performance defined in
engineered soil/landscape systems. For systems that are deeper
than 8 inches complete the rototilling process in multiple lifts, or
prepare the engineered soil system per specifications and place to achieve the specified depth.
• Fertilizers:
• Conducting soil tests to determine the exact type and quantity of
fertilizer is recommended. This will prevent the over-application
of fertilizer.
• Organic matter is the most appropriate form of fertilizer because it
provides nutrients (including nitrogen, phosphorus, and potassium)
in the least water-soluble form.
• In general, use 10-4-6 N-P-K (nitrogen-phosphorus-potassium)
fertilizer at a rate of 90 pounds per acre. Always use slow-release fertilizers because they are more efficient and have fewer
environmental impacts. Do not add fertilizer to the hydromulch
machine, or agitate, more than 20 minutes before use. Too much
agitation destroys the slow-release coating.
• There are numerous products available that take the place of chemical fertilizers. These include several with seaweed extracts that are beneficial to soil microbes and organisms. If 100 percent
cottonseed meal is used as the mulch in hydroseed, chemical
fertilizer may not be necessary. Cottonseed meal provides a good
source of long-term, slow-release, available nitrogen.
• Bonded Fiber Matrix and Mechanically Bonded Fiber Matrix:
• On steep slopes use Bonded Fiber Matrix (BFM) or Mechanically
Bonded Fiber Matrix (MBFM) products. Apply BFM/MBFM
products at a minimum rate of 3,000 pounds per acre of mulch
with approximately 10 percent tackifier. Achieve a minimum of 95 percent soil coverage during application. Numerous products are available commercially. Installed products per manufacturer’s
instructions. Most products require 24-36 hours to cure before
rainfall and cannot be installed on wet or saturated soils.
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Generally, products come in 40-50 pound bags and include all
necessary ingredients except for seed and fertilizer.
• BFMs and MBFMs provide good alternatives to blankets in most
areas requiring vegetation establishment. Advantages over blankets include:
• BFM and MBFMs do not require surface preparation.
• Helicopters can assist in installing BFM and MBFMs in remote areas.
• On slopes steeper than 2.5H:1V, blanket installers may require ropes and harnesses for safety.
• Installing BFM and MBFMs can save at least $1,000 per acre compared to blankets.
Maintenance
Standards
Reseed any seeded areas that fail to establish at least 80 percent cover
(100 percent cover for areas that receive sheet or concentrated flows). If reseeding is ineffective, use an alternate method such as sodding,
mulching, or nets/blankets. If winter weather prevents adequate grass
growth, this time limit may be relaxed at the discretion of the local
authority when sensitive areas would otherwise be protected.
• Reseed and protect by mulch any areas that experience erosion after achieving adequate cover. Reseed and protect by mulch any eroded
area.
• Supply seeded areas with adequate moisture, but do not water to the
extent that it causes runoff.
Approved as Equivalent Ecology has approved products as able to meet the requirements of BMP C120. The products did not pass through the Technology Assessment
Protocol – Ecology (TAPE) process. Local jurisdictions may choose not to
accept this product approved as equivalent, or may require additional testing
prior to consideration for local use. The products are available for review on
Ecology’s website at http://www.ecy.wa.gov/programs/wq/stormwater/newtech/equivalent.html.
BMP C121: Mulching
Purpose Mulching soils provides immediate temporary protection from erosion.
Mulch also enhances plant establishment by conserving moisture, holding
fertilizer, seed, and topsoil in place, and moderating soil temperatures. There is an enormous variety of mulches that can be used. This section
discusses only the most common types of mulch.
Conditions of Use As a temporary cover measure, mulch should be used:
• For less than 30 days on disturbed areas that require cover.
• At all times for seeded areas, especially during the wet season and during the hot summer months.
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• During the wet season on slopes steeper than 3H:1V with more than
10 feet of vertical relief.
Mulch may be applied at any time of the year and must be refreshed
periodically.
• For seeded areas mulch may be made up of 100 percent: cottonseed
meal; fibers made of wood, recycled cellulose, hemp, kenaf; compost;
or blends of these. Tackifier shall be plant-based, such as guar or alpha
plantago, or chemical-based such as polyacrylamide or polymers. Any
mulch or tackifier product used shall be installed per manufacturer’s instructions. Generally, mulches come in 40-50 pound bags. Seed and
fertilizer are added at time of application.
Design and
Installation
Specifications
For mulch materials, application rates, and specifications, see Table 4.1.8.
Always use a 2-inch minimum mulch thickness; increase the thickness
until the ground is 95% covered (i.e. not visible under the mulch layer). Note: Thickness may be increased for disturbed areas in or near sensitive
areas or other areas highly susceptible to erosion.
Where the option of “Compost” is selected, it should be a coarse compost
that meets the following size gradations when tested in accordance with
the U.S. Composting Council “Test Methods for the Examination of Compost and Composting” (TMECC) Test Method 02.02-B.
Coarse Compost
Minimum Percent passing 3” sieve openings 100%
Minimum Percent passing 1” sieve openings 90%
Minimum Percent passing ¾” sieve openings 70%
Minimum Percent passing ¼” sieve openings 40%
Mulch used within the ordinary high-water mark of surface waters should
be selected to minimize potential flotation of organic matter. Composted
organic materials have higher specific gravities (densities) than straw,
wood, or chipped material. Consult Hydraulic Permit Authority (HPA) for mulch mixes if applicable.
Maintenance
Standards
• The thickness of the cover must be maintained.
• Any areas that experience erosion shall be remulched and/or protected
with a net or blanket. If the erosion problem is drainage related, then the problem shall be fixed and the eroded area remulched.
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Table 4.1.8 Mulch Standards and Guidelines
Mulch Material Quality Standards Application Rates Remarks
Straw Air-dried; free from
undesirable seed and
coarse material.
2"-3" thick; 5
bales per 1,000
sf or 2-3 tons per
acre
Cost-effective protection when applied with adequate thickness.
Hand-application generally requires greater thickness than
blown straw. The thickness of straw may be reduced by half
when used in conjunction with seeding. In windy areas straw
must be held in place by crimping, using a tackifier, or covering
with netting. Blown straw always has to be held in place with a tackifier as even light winds will blow it away. Straw, however, has several deficiencies that should be considered when selecting mulch materials. It often introduces and/or encourages the propagation of weed species and it has no significant long-term benefits. It should also not be used within the ordinary high-water elevation of surface waters (due to flotation).
Hydromulch No growth inhibiting factors. Approx. 25-30 lbs per 1,000 sf or 1,500 - 2,000
lbs per acre
Shall be applied with hydromulcher. Shall not be used without seed and tackifier unless the application rate is at least doubled. Fibers longer than about ¾-1 inch clog hydromulch equipment.
Fibers should be kept to less than ¾ inch.
Compost No visible water or
dust during
handling. Must be produced per WAC 173-350, Solid Waste Handling Standards, but may have up to 35% biosolids.
2" thick min.;
approx. 100 tons
per acre (approx. 800 lbs per yard)
More effective control can be obtained by increasing thickness
to 3". Excellent mulch for protecting final grades until
landscaping because it can be directly seeded or tilled into soil as an amendment. Compost used for mulch has a coarser size gradation than compost used for BMP C125 or BMP T5.13 (see Chapter 5 of Volume V of this manual) It is more stable and practical to use in wet areas and during rainy weather conditions. Do not use near wetlands or near phosphorous impaired water bodies.
Chipped Site Vegetation Average size shall be several inches. Gradations from
fines to 6 inches in
length for texture,
variation, and
interlocking
properties.
2" thick min.; This is a cost-effective way to dispose of debris from clearing and grubbing, and it eliminates the problems associated with burning. Generally, it should not be used on slopes above
approx. 10% because of its tendency to be transported by
runoff. It is not recommended within 200 feet of surface waters.
If seeding is expected shortly after mulch, the decomposition of
the chipped vegetation may tie up nutrients important to grass
establishment.
Wood-based Mulch or Wood Straw
No visible water or dust during handling. Must be purchased from a supplier with a Solid Waste Handling Permit or one exempt from solid waste regulations.
2” thick min.; approx. 100 tons per acre (approx. 800 lbs. per cubic yard)
This material is often called “hog or hogged fuel.” The use of mulch ultimately improves the organic matter in the soil. Special caution is advised regarding the source and composition of wood-based mulches. Its preparation typically does not provide any weed seed control, so evidence of residual vegetation in its composition or known inclusion of weed plants or seeds should be monitored and prevented (or minimized).
Wood Strand
Mulch
A blend of loose,
long, thin wood
pieces derived from
native conifer or deciduous trees with high length-to-width ratio.
2” thick min. Cost-effective protection when applied with adequate thickness.
A minimum of 95-percent of the wood strand shall have lengths
between 2 and 10-inches, with a width and thickness between
1/16 and ⅜-inches. The mulch shall not contain resin, tannin, or other compounds in quantities that would be detrimental to plant life. Sawdust or wood shavings shall not be used as mulch. (WSDOT specification (9-14.4(4))
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BMP C123: Plastic Covering
Purpose Plastic covering provides immediate, short-term erosion protection to
slopes and disturbed areas.
Conditions of Use Plastic covering may be used on disturbed areas that require cover measures for less than 30 days, except as stated below.
• Plastic is particularly useful for protecting cut and fill slopes and
stockpiles. Note: The relatively rapid breakdown of most polyethylene
sheeting makes it unsuitable for long-term (greater than six months)
applications.
• Due to rapid runoff caused by plastic covering, do not use this method
upslope of areas that might be adversely impacted by concentrated
runoff. Such areas include steep and/or unstable slopes.
• Plastic sheeting may result in increased runoff volumes and velocities,
requiring additional on-site measures to counteract the increases. Creating a trough with wattles or other material can convey clean
water away from these areas.
• To prevent undercutting, trench and backfill rolled plastic covering
products.
• While plastic is inexpensive to purchase, the added cost of installation, maintenance, removal, and disposal make this an expensive material, up to $1.50-2.00 per square yard.
• Whenever plastic is used to protect slopes install water collection
measures at the base of the slope. These measures include plastic-
covered berms, channels, and pipes used to covey clean rainwater away from bare soil and disturbed areas. Do not mix clean runoff from a plastic covered slope with dirty runoff from a project.
• Other uses for plastic include:
1. Temporary ditch liner.
2. Pond liner in temporary sediment pond.
3. Liner for bermed temporary fuel storage area if plastic is not reactive to the type of fuel being stored.
4. Emergency slope protection during heavy rains.
5. Temporary drainpipe (“elephant trunk”) used to direct water.
Design and Installation Specifications
• Plastic slope cover must be installed as follows:
1. Run plastic up and down slope, not across slope.
2. Plastic may be installed perpendicular to a slope if the slope length
is less than 10 feet.
3. Minimum of 8-inch overlap at seams.
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4. On long or wide slopes, or slopes subject to wind, tape all seams.
5. Place plastic into a small (12-inch wide by 6-inch deep) slot trench
at the top of the slope and backfill with soil to keep water from
flowing underneath.
6. Place sand filled burlap or geotextile bags every 3 to 6 feet along
seams and tie them together with twine to hold them in place.
7. Inspect plastic for rips, tears, and open seams regularly and repair
immediately. This prevents high velocity runoff from contacting
bare soil which causes extreme erosion.
8. Sandbags may be lowered into place tied to ropes. However, all
sandbags must be staked in place.
• Plastic sheeting shall have a minimum thickness of 0.06 millimeters.
• If erosion at the toe of a slope is likely, a gravel berm, riprap, or other
suitable protection shall be installed at the toe of the slope in order to reduce the velocity of runoff.
Maintenance Standards
• Torn sheets must be replaced and open seams repaired.
• Completely remove and replace the plastic if it begins to deteriorate
due to ultraviolet radiation.
• Completely remove plastic when no longer needed.
• Dispose of old tires used to weight down plastic sheeting
appropriately.
Approved as
Equivalent
Ecology has approved products as able to meet the requirements of BMP
C123. The products did not pass through the Technology Assessment
Protocol – Ecology (TAPE) process. Local jurisdictions may choose not to accept this product approved as equivalent, or may require additional
testing prior to consideration for local use. The products are available for
review on Ecology’s website at
http://www.ecy.wa.gov/programs/wq/stormwater/newtech/equivalent.html
BMP C124: Sodding
Purpose The purpose of sodding is to establish permanent turf for immediate
erosion protection and to stabilize drainage ways where concentrated
overland flow will occur.
Conditions of Use Sodding may be used in the following areas:
• Disturbed areas that require short-term or long-term cover.
• Disturbed areas that require immediate vegetative cover.
• All waterways that require vegetative lining. Waterways may also be
seeded rather than sodded, and protected with a net or blanket.
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BMP C140: Dust Control
Purpose Dust control prevents wind transport of dust from disturbed soil surfaces
onto roadways, drainage ways, and surface waters.
Conditions of Use • In areas (including roadways) subject to surface and air movement of dust where on-site and off-site impacts to roadways, drainage ways, or
surface waters are likely.
Design and
Installation
Specifications
• Vegetate or mulch areas that will not receive vehicle traffic. In areas
where planting, mulching, or paving is impractical, apply gravel or
landscaping rock.
• Limit dust generation by clearing only those areas where immediate
activity will take place, leaving the remaining area(s) in the original
condition. Maintain the original ground cover as long as practical.
• Construct natural or artificial windbreaks or windscreens. These may
be designed as enclosures for small dust sources.
• Sprinkle the site with water until surface is wet. Repeat as needed. To
prevent carryout of mud onto street, refer to Stabilized Construction
Entrance (BMP C105).
• Irrigation water can be used for dust control. Irrigation systems should
be installed as a first step on sites where dust control is a concern.
• Spray exposed soil areas with a dust palliative, following the
manufacturer’s instructions and cautions regarding handling and
application. Used oil is prohibited from use as a dust suppressant.
Local governments may approve other dust palliatives such as calcium
chloride or PAM.
• PAM (BMP C126) added to water at a rate of 0.5 lbs. per 1,000
gallons of water per acre and applied from a water truck is more
effective than water alone. This is due to increased infiltration of water
into the soil and reduced evaporation. In addition, small soil particles
are bonded together and are not as easily transported by wind. Adding PAM may actually reduce the quantity of water needed for dust
control. Use of PAM could be a cost-effective dust control method.
Techniques that can be used for unpaved roads and lots include:
• Lower speed limits. High vehicle speed increases the amount of dust
stirred up from unpaved roads and lots.
• Upgrade the road surface strength by improving particle size, shape,
and mineral types that make up the surface and base materials.
• Add surface gravel to reduce the source of dust emission. Limit the
amount of fine particles (those smaller than .075 mm) to 10 to 20
percent.
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• Use geotextile fabrics to increase the strength of new roads or roads
undergoing reconstruction.
• Encourage the use of alternate, paved routes, if available.
• Restrict use of paved roadways by tracked vehicles and heavy trucks to prevent damage to road surface and base.
• Apply chemical dust suppressants using the admix method, blending
the product with the top few inches of surface material. Suppressants
may also be applied as surface treatments.
• Pave unpaved permanent roads and other trafficked areas.
• Use vacuum street sweepers.
• Remove mud and other dirt promptly so it does not dry and then turn
into dust.
• Limit dust-causing work on windy days.
• Contact your local Air Pollution Control Authority for guidance and training on other dust control measures. Compliance with the local Air Pollution Control Authority constitutes compliance with this BMP.
Maintenance
Standards
Respray area as necessary to keep dust to a minimum.
BMP C150: Materials on Hand
Purpose Keep quantities of erosion prevention and sediment control materials on the project site at all times to be used for regular maintenance and
emergency situations such as unexpected heavy summer rains. Having
these materials on-site reduces the time needed to implement BMPs when
inspections indicate that existing BMPs are not meeting the Construction SWPPP requirements. In addition, contractors can save money by buying some materials in bulk and storing them at their office or yard.
Conditions of Use • Construction projects of any size or type can benefit from having
materials on hand. A small commercial development project could
have a roll of plastic and some gravel available for immediate protection of bare soil and temporary berm construction. A large
earthwork project, such as highway construction, might have several
tons of straw, several rolls of plastic, flexible pipe, sandbags,
geotextile fabric and steel “T” posts.
• Materials are stockpiled and readily available before any site clearing, grubbing, or earthwork begins. A large contractor or developer could
keep a stockpile of materials that are available for use on several
projects.
• If storage space at the project site is at a premium, the contractor could
maintain the materials at their office or yard. The office or yard must be less than an hour from the project site.
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Design and Installation
Specifications
Depending on project type, size, complexity, and length, materials and
quantities will vary. A good minimum list of items that will cover
numerous situations includes:
Material
Clear Plastic, 6 mil
Drainpipe, 6 or 8 inch diameter
Sandbags, filled
Straw Bales for mulching,
Quarry Spalls
Washed Gravel
Geotextile Fabric
Catch Basin Inserts
Steel “T” Posts
Silt fence material
Straw Wattles
Maintenance Standards • All materials with the exception of the quarry spalls, steel “T” posts, and gravel should be kept covered and out of both sun and rain.
• Re-stock materials used as needed.
BMP C151: Concrete Handling
Purpose Concrete work can generate process water and slurry that contain fine
particles and high pH, both of which can violate water quality standards in the receiving water. Concrete spillage or concrete discharge to surface
waters of the State is prohibited. Use this BMP to minimize and eliminate
concrete, concrete process water, and concrete slurry from entering waters
of the state.
Conditions of Use Any time concrete is used, utilize these management practices. Concrete construction projects include, but are not limited to, the following:
• Curbs
• Sidewalks
• Roads
• Bridges
• Foundations
• Floors
• Runways
Design and
Installation
• Assure that washout of concrete trucks, chutes, pumps, and internals is
performed at an approved off-site location or in designated concrete
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Specifications washout areas. Do not wash out concrete trucks onto the ground, or
into storm drains, open ditches, streets, or streams. Refer to BMP
C154 for information on concrete washout areas.
• Return unused concrete remaining in the truck and pump to the originating batch plant for recycling. Do not dump excess concrete on site, except in designated concrete washout areas.
• Wash off hand tools including, but not limited to, screeds, shovels,
rakes, floats, and trowels into formed areas only.
• Wash equipment difficult to move, such as concrete pavers in areas that do not directly drain to natural or constructed stormwater conveyances.
• Do not allow washdown from areas, such as concrete aggregate
driveways, to drain directly to natural or constructed stormwater
conveyances.
• Contain washwater and leftover product in a lined container when no
formed areas are available. Dispose of contained concrete in a manner
that does not violate ground water or surface water quality standards.
• Always use forms or solid barriers for concrete pours, such as pilings,
within 15-feet of surface waters.
• Refer to BMPs C252 and C253 for pH adjustment requirements.
• Refer to the Construction Stormwater General Permit for pH
monitoring requirements if the project involves one of the following
activities:
• Significant concrete work (greater than 1,000 cubic yards poured concrete or recycled concrete used over the life of a project).
• The use of engineered soils amended with (but not limited to)
Portland cement-treated base, cement kiln dust or fly ash.
• Discharging stormwater to segments of water bodies on the 303(d)
list (Category 5) for high pH.
Maintenance Standards
Check containers for holes in the liner daily during concrete pours and
repair the same day.
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BMP C153: Material Delivery, Storage and 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.
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.
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Material Storage Areas and Secondary Containment Practices:
• Liquids, petroleum products, and substances listed in 40 CFR Parts 110, 117, or 302 shall be stored in approved containers and drums and
shall not be overfilled. Containers and drums shall be stored in temporary secondary containment facilities.
• Temporary secondary containment facilities shall provide for a spill containment volume able to contain 10% of the total enclosed
container volume of all containers, or 110% of the capacity of the largest container within its boundary, whichever is greater.
• Secondary containment facilities shall be impervious to the materials stored therein for a minimum contact time of 72 hours.
• Secondary containment facilities shall be maintained free of accumulated rainwater and spills. In the event of spills or leaks,
accumulated rainwater and spills shall be collected and placed into drums. These liquids shall be handled as hazardous waste unless
testing determines them to be non-hazardous.
• Sufficient separation should be provided between stored containers to
allow for spill cleanup and emergency response access.
• During the wet weather season (Oct 1 – April 30), each secondary
containment facility shall be covered during non-working days, prior to and during rain events.
• Keep material storage areas clean, organized and equipped with an ample supply of appropriate spill clean-up material (spill kit).
• The spill kit should include, at a minimum:
• 1-Water Resistant Nylon Bag
• 3-Oil Absorbent Socks 3”x 4’
• 2-Oil Absorbent Socks 3”x 10’
• 12-Oil Absorbent Pads 17”x19”
• 1-Pair Splash Resistant Goggles
• 3-Pair Nitrile Gloves
• 10-Disposable Bags with Ties
• Instructions
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BMP 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 at an approved off-site location 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.
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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.
• Washout of concrete trucks shall be performed in designated areas
only.
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• 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).
• If using self-installed washout facilities, verify plastic liners are intact and sidewalls are not damaged.
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• 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.
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Figure 4.1.7a – Concrete Washout Area
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Figure 4.1.7b – Concrete Washout Area
Figure 4.1.8 – Prefabricated Concrete Washout Container w/Ramp
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BMP C250: Construction Stormwater
Chemical Treatment
BMP C251: Construction Stormwater
Filtration
BMP C252: High pH Neutralization
Using CO2
BMP C253: pH Control for High pH
Water
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 volumetric flow rate calculated using a
10-minute time step from a 10-year, 24-hour storm, assuming a Type 1A rainfall distribution, for temporary facilities. Alternatively, use 1.6
times the 10-year, 1-hour flow indicated by an approved continuous
runoff model. For facilities that will also serve on a permanent basis,
consult the local government’s drainage requirements.
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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.
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.
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• 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.
BMP C201: Grass-Lined Channels
Purpose To provide a channel with a vegetative lining for conveyance of runoff.
See Figure 4.2.1 for typical grass-lined channels.
Conditions of Use This practice applies to construction sites where concentrated runoff needs
to be contained to prevent erosion or flooding.
• When a vegetative lining can provide sufficient stability for the
channel cross section and at lower velocities of water (normally
dependent on grade). This means that the channel slopes are generally less than 5 percent and space is available for a relatively large cross
section.
• Typical uses include roadside ditches, channels at property boundaries,
outlets for diversions, and other channels and drainage ditches in low
areas.
• Channels that will be vegetated should be installed before major
earthwork and hydroseeded with a bonded fiber matrix (BFM). The
vegetation should be well established (i.e., 75 percent cover) before
water is allowed to flow in the ditch. With channels that will have high
flows, erosion control blankets should be installed over the hydroseed. If vegetation cannot be established from seed before water is allowed
in the ditch, sod should be installed in the bottom of the ditch in lieu of
hydromulch and blankets.
Design and
Installation Specifications
Locate the channel where it can conform to the topography and other
features such as roads.
• Locate them to use natural drainage systems to the greatest extent
possible.
• Avoid sharp changes in alignment or bends and changes in grade.
• Do not reshape the landscape to fit the drainage channel.
• The maximum design velocity shall be based on soil conditions, type of vegetation, and method of revegetation, but at no times shall
velocity exceed 5 feet/second. The channel shall not be overtopped by
the peak volumetric flow rate calculated using a 10-minute time step
from a 10-year, 24-hour storm, assuming a Type 1A rainfall
distribution. Alternatively, use 1.6 times the 10-year, 1-hour flow indicated by an approved continuous runoff model to determine a flow
rate which the channel must contain.
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Figure 4.2.6 – Detail of Level Spreader
BMP C207: Check Dams
Purpose Construction of small dams across a swale or ditch reduces the velocity of
concentrated flow and dissipates energy at the check dam.
Conditions of Use Where temporary channels or permanent channels are not yet vegetated,
channel lining is infeasible, and/or velocity checks are required.
• Check dams may not be placed in streams unless approved by the State Department of Fish and Wildlife. Check dams may not be placed in
wetlands without approval from a permitting agency.
• Do not place check dams below the expected backwater from any
salmonid bearing water between October 1 and May 31 to ensure that there is no loss of high flow refuge habitat for overwintering juvenile
salmonids and emergent salmonid fry.
• Construct rock check dams from appropriately sized rock. The rock
used must be large enough to stay in place given the expected design
flow through the channel. The rock must be placed by hand or by mechanical means (no dumping of rock to form dam) to achieve
complete coverage of the ditch or swale and to ensure that the center
of the dam is lower than the edges.
• Check dams may also be constructed of either rock or pea-gravel filled
bags. Numerous new products are also available for this purpose. They tend to be re-usable, quick and easy to install, effective, and cost
efficient.
• Place check dams perpendicular to the flow of water.
• The dam should form a triangle when viewed from the side. This
prevents undercutting as water flows over the face of the dam rather than falling directly onto the ditch bottom.
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• Before installing check dams impound and bypass upstream water
flow away from the work area. Options for bypassing include pumps,
siphons, or temporary channels.
• Check dams in association with sumps work more effectively at slowing flow and retaining sediment than just a check dam alone. A deep sump should be provided immediately upstream of the check
dam.
• In some cases, if carefully located and designed, check dams can
remain as permanent installations with very minor regrading. They may be left as either spillways, in which case accumulated sediment would be graded and seeded, or as check dams to prevent further
sediment from leaving the site.
• The maximum spacing between the dams shall be such that the toe of
the upstream dam is at the same elevation as the top of the downstream dam.
• Keep the maximum height at 2 feet at the center of the dam.
• Keep the center of the check dam at least 12 inches lower than the
outer edges at natural ground elevation.
• Keep the side slopes of the check dam at 2H:1V or flatter.
• Key the stone into the ditch banks and extend it beyond the abutments
a minimum of 18 inches to avoid washouts from overflow around the
dam.
• Use filter fabric foundation under a rock or sand bag check dam. If a
blanket ditch liner is used, filter fabric is not necessary. A piece of organic or synthetic blanket cut to fit will also work for this purpose.
• In the case of grass-lined ditches and swales, all check dams and
accumulated sediment shall be removed when the grass has matured
sufficiently to protect the ditch or swale - unless the slope of the swale
is greater than 4 percent. The area beneath the check dams shall be seeded and mulched immediately after dam removal.
• Ensure that channel appurtenances, such as culvert entrances below
check dams, are not subject to damage or blockage from displaced
stones. Figure 4.2.7 depicts a typical rock check dam.
Maintenance Standards Check dams shall be monitored for performance and sediment accumulation during and after each runoff producing rainfall. Sediment
shall be removed when it reaches one half the sump depth.
• Anticipate submergence and deposition above the check dam and
erosion from high flows around the edges of the dam.
• If significant erosion occurs between dams, install a protective riprap liner in that portion of the channel.
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Approved as Equivalent
Ecology has approved products as able to meet the requirements of BMP
C207. The products did not pass through the Technology Assessment
Protocol – Ecology (TAPE) process. Local jurisdictions may choose not
to accept this product approved as equivalent, or may require additional testing prior to consideration for local use. The products are available for
review on Ecology’s website at
http://www.ecy.wa.gov/programs/wq/stormwater/newtech/equivalent.html
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Figure 4.2.7 – Rock Check Dam
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Standards accumulation during and after each runoff producing rainfall.
Sediment shall be removed when it reaches one half the height of the
dam.
• Anticipate submergence and deposition above the triangular silt dam and erosion from high flows around the edges of the dam. Immediately repair any damage or any undercutting of the dam.
BMP C209: Outlet Protection
Purpose Outlet protection prevents scour at conveyance outlets and minimizes the
potential for downstream erosion by reducing the velocity of concentrated stormwater flows.
Conditions of use Outlet protection is required at the outlets of all ponds, pipes, ditches, or
other conveyances, and where runoff is conveyed to a natural or manmade
drainage feature such as a stream, wetland, lake, or ditch.
Design and Installation Specifications
The receiving channel at the outlet of a culvert shall be protected from erosion by rock lining a minimum of 6 feet downstream and extending up
the channel sides a minimum of 1–foot above the maximum tailwater
elevation or 1-foot above the crown, whichever is higher. For large pipes
(more than 18 inches in diameter), the outlet protection lining of the
channel is lengthened to four times the diameter of the culvert.
• Standard wingwalls, and tapered outlets and paved channels should
also be considered when appropriate for permanent culvert outlet
protection. (See WSDOT Hydraulic Manual, available through
WSDOT Engineering Publications).
• Organic or synthetic erosion blankets, with or without vegetation, are usually more effective than rock, cheaper, and easier to install. Materials can be chosen using manufacturer product specifications.
ASTM test results are available for most products and the designer can
choose the correct material for the expected flow.
• With low flows, vegetation (including sod) can be effective.
• The following guidelines shall be used for riprap outlet protection:
1. If the discharge velocity at the outlet is less than 5 fps (pipe slope
less than 1 percent), use 2-inch to 8-inch riprap. Minimum
thickness is 1-foot.
2. For 5 to 10 fps discharge velocity at the outlet (pipe slope less than 3 percent), use 24-inch to 48-inch riprap. Minimum thickness is 2
feet.
3. For outlets at the base of steep slope pipes (pipe slope greater than
10 percent), an engineered energy dissipater shall be used.
• Filter fabric or erosion control blankets should always be used under riprap to prevent scour and channel erosion.
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• New pipe outfalls can provide an opportunity for low-cost fish habitat
improvements. For example, an alcove of low-velocity water can be
created by constructing the pipe outfall and associated energy
dissipater back from the stream edge and digging a channel, over-widened to the upstream side, from the outfall. Overwintering juvenile
and migrating adult salmonids may use the alcove as shelter during
high flows. Bank stabilization, bioengineering, and habitat features
may be required for disturbed areas. This work may require a HPA.
See Volume V for more information on outfall system design.
Maintenance Standards • Inspect and repair as needed.
• Add rock as needed to maintain the intended function.
• Clean energy dissipater if sediment builds up.
BMP C220: Storm Drain Inlet Protection
Purpose Storm drain inlet protection prevents coarse sediment from entering
drainage systems prior to permanent stabilization of the disturbed area.
Conditions of Use Use storm drain inlet protection at inlets that are operational before
permanent stabilization of the disturbed drainage area. Provide protection for all storm drain inlets downslope and within 500 feet of a disturbed or
construction area, unless conveying runoff entering catch basins to a
sediment pond or trap.
Also consider inlet protection for lawn and yard drains on new home
construction. These small and numerous drains coupled with lack of gutters in new home construction can add significant amounts of sediment
into the roof drain system. If possible delay installing lawn and yard drains
until just before landscaping or cap these drains to prevent sediment from
entering the system until completion of landscaping. Provide 18-inches of
sod around each finished lawn and yard drain.
Table 4.2.2 lists several options for inlet protection. All of the methods for
storm drain inlet protection tend to plug and require a high frequency of
maintenance. Limit drainage areas to one acre or less. Possibly provide
emergency overflows with additional end-of-pipe treatment where
stormwater ponding would cause a hazard.
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Table 4.2.2 Storm Drain Inlet Protection
Type of Inlet Protection Emergency Overflow
Applicable for Paved/ Earthen Surfaces Conditions of Use
Drop Inlet Protection
Excavated drop inlet
protection
Yes,
temporary
flooding will
occur
Earthen Applicable for heavy flows. Easy
to maintain. Large area
Requirement: 30’ X 30’/acre
Block and gravel drop
inlet protection
Yes Paved or Earthen Applicable for heavy concentrated
flows. Will not pond.
Gravel and wire drop
inlet protection
No Applicable for heavy concentrated
flows. Will pond. Can withstand
traffic.
Catch basin filters Yes Paved or Earthen Frequent maintenance required.
Curb Inlet Protection
Curb inlet protection
with a wooden weir
Small capacity
overflow
Paved Used for sturdy, more compact
installation.
Block and gravel curb
inlet protection
Yes Paved Sturdy, but limited filtration.
Culvert Inlet Protection
Culvert inlet sediment
trap
18 month expected life.
Design and Installation Specifications
Excavated Drop Inlet Protection - An excavated impoundment around the
storm drain. Sediment settles out of the stormwater prior to entering the storm drain.
• Provide a depth of 1-2 ft as measured from the crest of the inlet
structure.
• Slope sides of excavation no steeper than 2H:1V.
• Minimum volume of excavation 35 cubic yards.
• Shape basin to fit site with longest dimension oriented toward the
longest inflow area.
• Install provisions for draining to prevent standing water problems.
• Clear the area of all debris.
• Grade the approach to the inlet uniformly.
• Drill weep holes into the side of the inlet.
• Protect weep holes with screen wire and washed aggregate.
• Seal weep holes when removing structure and stabilizing area.
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• Build a temporary dike, if necessary, to the down slope side of the
structure to prevent bypass flow.
Block and Gravel Filter - A barrier formed around the storm drain inlet
with standard concrete blocks and gravel. See Figure 4.2.8.
• Provide a height of 1 to 2 feet above inlet.
• Recess the first row 2-inches into the ground for stability.
• Support subsequent courses by placing a 2x4 through the block
opening.
• Do not use mortar.
• Lay some blocks in the bottom row on their side for dewatering the
pool.
• Place hardware cloth or comparable wire mesh with ½-inch openings
over all block openings.
• Place gravel just below the top of blocks on slopes of 2H:1V or flatter.
• An alternative design is a gravel donut.
• Provide an inlet slope of 3H:1V.
• Provide an outlet slope of 2H:1V.
• Provide a1-foot wide level stone area between the structure and the
inlet.
• Use inlet slope stones 3 inches in diameter or larger.
• Use gravel ½- to ¾-inch at a minimum thickness of 1-foot for the
outlet slope.
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Figure 4.2.8 – Block and Gravel Filter
Gravel and Wire Mesh Filter - A gravel barrier placed over the top of the
inlet. This structure does not provide an overflow.
• Use a hardware cloth or comparable wire mesh with ½-inch openings.
• Use coarse aggregate.
• Provide a height 1-foot or more, 18-inches wider than inlet on all sides.
• Place wire mesh over the drop inlet so that the wire extends a
minimum of 1-foot beyond each side of the inlet structure.
• Overlap the strips if more than one strip of mesh is necessary.
Ponding Height
Notes: 1. Drop inlet sediment barriers are to be used for small, nearly level drainage areas. (less than 5%) 2. Excavate a basin of sufficient size adjacent to the drop inlet. 3. The top of the structure (ponding height) must be well below the ground elevation downslope to prevent
runoff from bypassing the inlet. A temporary dike may be necessary on the downslope side of the structure.
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• Place coarse aggregate over the wire mesh.
• Provide at least a 12-inch depth of gravel over the entire inlet opening
and extend at least 18-inches on all sides.
Catchbasin Filters – Use inserts designed by manufacturers for construction sites. The limited sediment storage capacity increases the
amount of inspection and maintenance required, which may be daily for
heavy sediment loads. To reduce maintenance requirements combine a
catchbasin filter with another type of inlet protection. This type of inlet
protection provides flow bypass without overflow and therefore may be a better method for inlets located along active rights-of-way.
• Provides 5 cubic feet of storage.
• Requires dewatering provisions.
• Provides a high-flow bypass that will not clog under normal use at a
construction site.
• Insert the catchbasin filter in the catchbasin just below the grating.
Curb Inlet Protection with Wooden Weir – Barrier formed around a curb
inlet with a wooden frame and gravel.
• Use wire mesh with ½-inch openings.
• Use extra strength filter cloth.
• Construct a frame.
• Attach the wire and filter fabric to the frame.
• Pile coarse washed aggregate against wire/fabric.
• Place weight on frame anchors.
Block and Gravel Curb Inlet Protection – Barrier formed around a curb inlet with concrete blocks and gravel. See Figure 4.2.9.
• Use wire mesh with ½-inch openings.
• Place two concrete blocks on their sides abutting the curb at either side
of the inlet opening. These are spacer blocks.
• Place a 2x4 stud through the outer holes of each spacer block to align the front blocks.
• Place blocks on their sides across the front of the inlet and abutting the
spacer blocks.
• Place wire mesh over the outside vertical face.
• Pile coarse aggregate against the wire to the top of the barrier.
Curb and Gutter Sediment Barrier – Sandbag or rock berm (riprap and
aggregate) 3 feet high and 3 feet wide in a horseshoe shape. See Figure
4.2.10.
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• Construct a horseshoe shaped berm, faced with coarse aggregate if
using riprap, 3 feet high and 3 feet wide, at least 2 feet from the inlet.
• Construct a horseshoe shaped sedimentation trap on the outside of the
berm sized to sediment trap standards for protecting a culvert inlet.
Maintenance Standards
• Inspect catch basin filters frequently, especially after storm events.
Clean and replace clogged inserts. For systems with clogged stone
filters: pull away the stones from the inlet and clean or replace. An
alternative approach would be to use the clogged stone as fill and put
fresh stone around the inlet.
• Do not wash sediment into storm drains while cleaning. Spread all
excavated material evenly over the surrounding land area or stockpile
and stabilize as appropriate.
Approved as
Equivalent
Ecology has approved products as able to meet the requirements of BMP
C220. The products did not pass through the Technology Assessment Protocol – Ecology (TAPE) process. Local jurisdictions may choose not to accept this product approved as equivalent, or may require additional
testing prior to consideration for local use. The products are available for
review on Ecology’s website at
http://www.ecy.wa.gov/programs/wq/stormwater/newtech/equivalent.html
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Figure 4.2.9 – Block and Gravel Curb Inlet Protection
A
Plan View
Wire Screen orFilter Fabric Catch Basin
Curb Inlet
Concrete Block
Ponding Height
Overflow
2x4 Wood Stud(100x50 Timber Stud)
Concrete Block
Wire Screen orFilter Fabric
Curb Inlet
¾" Drain Gravel(20mm)
¾" Drain Gravel(20mm)Section A - A
Back of Curb Concrete Block
2x4 Wood Stud
Catch BasinBack of Sidewalk
NOTES:1. Use block and gravel type sediment barrier when curb inlet is located in gently sloping street segment, where water can pond and allow sediment to separate from runoff.2. Barrier shall allow for overflow from severe storm event.3. Inspect barriers and remove sediment after each storm event. Sediment and gravel must be removed from the traveled way immediately.
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Figure 4.2.10 – Curb and Gutter Barrier
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BMP C232: Gravel Filter Berm
Purpose A gravel filter berm is constructed on rights-of-way or traffic areas within
a construction site to retain sediment by using a filter berm of gravel or
crushed rock.
Conditions of Use Where a temporary measure is needed to retain sediment from rights-of-
way or in traffic areas on construction sites.
Design and
Installation
Specifications
• Berm material shall be ¾ to 3 inches in size, washed well-grade gravel
or crushed rock with less than 5 percent fines.
• Spacing of berms:
− Every 300 feet on slopes less than 5 percent
− Every 200 feet on slopes between 5 percent and 10 percent
− Every 100 feet on slopes greater than 10 percent
• Berm dimensions:
− 1 foot high with 3H:1V side slopes
− 8 linear feet per 1 cfs runoff based on the 10-year, 24-hour design
storm
Maintenance Standards • Regular inspection is required. Sediment shall be removed and filter
material replaced as needed.
BMP C233: Silt Fence
Purpose Use of a silt fence reduces the transport of coarse sediment from a construction site by providing a temporary physical barrier to sediment
and reducing the runoff velocities of overland flow. See Figure 4.2.12 for
details on silt fence construction.
Conditions of Use Silt fence may be used downslope of all disturbed areas.
• Silt fence shall prevent soil carried by runoff water from going beneath, through, or over the top of the silt fence, but shall allow the
water to pass through the fence.
• Silt fence is not intended to treat concentrated flows, nor is it intended
to treat substantial amounts of overland flow. Convey any
concentrated flows through the drainage system to a sediment pond.
• Do not construct silt fences in streams or use in V-shaped ditches. Silt
fences do not provide an adequate method of silt control for anything
deeper than sheet or overland flow.
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Figure 4.2.12 – Silt Fence
Design and
Installation Specifications
• Use in combination with sediment basins or other BMPs.
• Maximum slope steepness (normal (perpendicular) to fence line) 1H:1V.
• Maximum sheet or overland flow path length to the fence of 100 feet.
• Do not allow flows greater than 0.5 cfs.
• The geotextile used shall meet the following standards. All geotextile
properties listed below are minimum average roll values (i.e., the test result for any sampled roll in a lot shall meet or exceed the values shown in Table 4.2.3):
Table 4.2.3 Geotextile Standards
Polymeric Mesh AOS (ASTM D4751) 0.60 mm maximum for slit film woven (#30 sieve). 0.30 mm maximum for all other geotextile types (#50 sieve).
0.15 mm minimum for all fabric types (#100 sieve).
Water Permittivity (ASTM D4491) 0.02 sec-1 minimum
Grab Tensile Strength (ASTM D4632) 180 lbs. Minimum for extra strength fabric.
100 lbs minimum for standard strength fabric.
Grab Tensile Strength (ASTM D4632) 30% maximum
Ultraviolet Resistance
(ASTM D4355)
70% minimum
• Support standard strength fabrics with wire mesh, chicken wire, 2-inch x 2-inch wire, safety fence, or jute mesh to increase the strength of the
fabric. Silt fence materials are available that have synthetic mesh
backing attached.
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• Filter fabric material shall contain ultraviolet ray inhibitors and
stabilizers to provide a minimum of six months of expected usable
construction life at a temperature range of 0°F. to 120°F.
• One-hundred percent biodegradable silt fence is available that is strong, long lasting, and can be left in place after the project is completed, if permitted by local regulations.
• Refer to Figure 4.2.12 for standard silt fence details. Include the
following standard Notes for silt fence on construction plans and
specifications:
1. The contractor shall install and maintain temporary silt fences at
the locations shown in the Plans.
2. Construct silt fences in areas of clearing, grading, or drainage prior
to starting those activities.
3. The silt fence shall have a 2-feet min. and a 2½-feet max. height above the original ground surface.
4. The filter fabric shall be sewn together at the point of manufacture
to form filter fabric lengths as required. Locate all sewn seams at
support posts. Alternatively, two sections of silt fence can be
overlapped, provided the Contractor can demonstrate, to the satisfaction of the Engineer, that the overlap is long enough and
that the adjacent fence sections are close enough together to
prevent silt laden water from escaping through the fence at the
overlap.
5. Attach the filter fabric on the up-slope side of the posts and secure with staples, wire, or in accordance with the manufacturer's
recommendations. Attach the filter fabric to the posts in a manner
that reduces the potential for tearing.
6. Support the filter fabric with wire or plastic mesh, dependent on
the properties of the geotextile selected for use. If wire or plastic mesh is used, fasten the mesh securely to the up-slope side of the
posts with the filter fabric up-slope of the mesh.
7. Mesh support, if used, shall consist of steel wire with a maximum
mesh spacing of 2-inches, or a prefabricated polymeric mesh. The
strength of the wire or polymeric mesh shall be equivalent to or greater than 180 lbs. grab tensile strength. The polymeric mesh
must be as resistant to the same level of ultraviolet radiation as the
filter fabric it supports.
8. Bury the bottom of the filter fabric 4-inches min. below the ground
surface. Backfill and tamp soil in place over the buried portion of the filter fabric, so that no flow can pass beneath the fence and
scouring cannot occur. When wire or polymeric back-up support
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mesh is used, the wire or polymeric mesh shall extend into the
ground 3-inches min.
9. Drive or place the fence posts into the ground 18-inches min. A
12–inch min. depth is allowed if topsoil or other soft subgrade soil is not present and 18-inches cannot be reached. Increase fence post
min. depths by 6 inches if the fence is located on slopes of 3H:1V
or steeper and the slope is perpendicular to the fence. If required
post depths cannot be obtained, the posts shall be adequately
secured by bracing or guying to prevent overturning of the fence due to sediment loading.
10. Use wood, steel or equivalent posts. The spacing of the support
posts shall be a maximum of 6-feet. Posts shall consist of either:
• Wood with dimensions of 2-inches by 2-inches wide min. and a 3-feet min. length. Wood posts shall be free of defects such as knots, splits, or gouges.
• No. 6 steel rebar or larger.
• ASTM A 120 steel pipe with a minimum diameter of 1-inch.
• U, T, L, or C shape steel posts with a minimum weight of 1.35
lbs./ft.
• Other steel posts having equivalent strength and bending
resistance to the post sizes listed above.
11. Locate silt fences on contour as much as possible, except at the
ends of the fence, where the fence shall be turned uphill such that
the silt fence captures the runoff water and prevents water from
flowing around the end of the fence.
12. If the fence must cross contours, with the exception of the ends of the fence, place gravel check dams perpendicular to the back of the
fence to minimize concentrated flow and erosion. The slope of the
fence line where contours must be crossed shall not be steeper than
3H:1V.
• Gravel check dams shall be approximately 1-foot deep at the back of the fence. Gravel check dams shall be continued
perpendicular to the fence at the same elevation until the top of
the check dam intercepts the ground surface behind the fence.
• Gravel check dams shall consist of crushed surfacing base course, gravel backfill for walls, or shoulder ballast. Gravel
check dams shall be located every 10 feet along the fence
where the fence must cross contours.
• Refer to Figure 4.2.13 for slicing method details. Silt fence installation using the slicing method specifications:
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1. The base of both end posts must be at least 2- to 4-inches above the
top of the filter fabric on the middle posts for ditch checks to drain
properly. Use a hand level or string level, if necessary, to mark
base points before installation.
2. Install posts 3- to 4-feet apart in critical retention areas and 6- to 7-
feet apart in standard applications.
3. Install posts 24-inches deep on the downstream side of the silt
fence, and as close as possible to the filter fabric, enabling posts to
support the filter fabric from upstream water pressure.
4. Install posts with the nipples facing away from the filter fabric.
5. Attach the filter fabric to each post with three ties, all spaced
within the top 8-inches of the filter fabric. Attach each tie
diagonally 45 degrees through the filter fabric, with each puncture
at least 1-inch vertically apart. Each tie should be positioned to hang on a post nipple when tightening to prevent sagging.
6. Wrap approximately 6-inches of fabric around the end posts and
secure with 3 ties.
7. No more than 24-inches of a 36-inch filter fabric is allowed above
ground level.
Compact the soil immediately next to the filter fabric with the front
wheel of the tractor, skid steer, or roller exerting at least 60 pounds
per square inch. Compact the upstream side first and then each side
twice for a total of four trips. Check and correct the silt fence
installation for any deviation before compaction. Use a flat-bladed shovel to tuck fabric deeper into the ground if necessary.
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Figure 4.2.13 – Silt Fence Installation by Slicing Method
Maintenance Standards
• Repair any damage immediately.
• Intercept and convey all evident concentrated flows uphill of the silt
fence to a sediment pond.
• Check the uphill side of the fence for signs of the fence clogging and
acting as a barrier to flow and then causing channelization of flows parallel to the fence. If this occurs, replace the fence or remove the trapped sediment.
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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
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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
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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
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Perforated polyethylenedrainage tubing, diametermin. 2" larger thandewatering orifice.Tubing shall comply with ASTM F667 and AASHTO M294
Polyethylene cap Provide adequatestrapping
Dewatering orifice, schedule,40 steel stub min.Diameter as per calculations
Alternatively, metal stakesand wire may be used toprevent flotation
2X riser dia. Min.
Concrete base
Corrugatedmetal riser
Watertightcoupling
18" min.
6" min.
Tack weld
3.5" min.
Figure 4.2.20 – Sediment Pond Riser Detail
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Figure 4.2.21 – Riser Inflow Curves
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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
hAAso=
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:
ooAADx54.13x24==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
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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.
BMP C250: Construction Stormwater Chemical Treatment
Purpose This BMP applies when using stormwater chemicals in batch treatment or
flow-through treatment.
Turbidity is difficult to control once fine particles are suspended in
stormwater runoff from a construction site. Sedimentation ponds are
effective at removing larger particulate matter by gravity settling, but are ineffective at removing smaller particulates such as clay and fine silt.
Traditional erosion and sediment control BMPs may not be adequate to
ensure compliance with the water quality standards for turbidity in
receiving water.
Chemical treatment can reliably provide exceptional reductions of turbidity and associated pollutants. Chemical treatment may be required to
meet turbidity stormwater discharge requirements, especially when
construction is to proceed through the wet season.
Conditions of Use Formal written approval from Ecology is required for the use of chemical
treatment regardless of site size. The Local Permitting Authority may also
P a g e | 35
C. Correspondence
Pending.
P a g e | 36
D. Site Inspection Form
Create your own or download Ecology’s template:
http://www.ecy.wa.gov/programs/wq/stormwater/construction/index.html
Select Permit, Forms and Application to find the link to the Construction Stormwater Site Inspection
Form.
P a g e | 37
P a g e | 38
P a g e | 39
P a g e | 40
P a g e | 41
E. Construction Stormwater General Permit (CSWGP)
Pending as of February 2, 2022.
P a g e | 42
F. 303(d) List Waterbodies / TMDL Waterbodies Information
None known.
P a g e | 43
G. Contaminated Site Information
None known.
See Geotechnical Engineering Study by Associated Earth Sciences, Inc. dated June 18, 2022.
P a g e | 44
H. Engineering Calculations
See Stormwater Site Plan Report by RAM Engineering Inc. dated February 2, 2022.