SWPPP (2)
Civil Engineers ● Structural Engineers ● Landscape Architects ● Community Planners ● Land Surveyors
Construction Stormwater
Pollution Prevention Plan
PREPARED FOR:
Mr. Evan Mann
Copper Ridge LLC
PO Box 73790
Puyallup, WA 98373-0790
PROJECT:
Crystal Springs Preliminary Plat
Yelm, Washington
2210633.10
PREPARED BY:
Michael Lesmeister, PE
Project Engineer
REVIEWED BY:
J. Matthew Weber, PE.
Principal
DATE
March 2022
Construction Stormwater
Pollution Prevention Plan
PREPARED FOR:
Mr. Evan Mann
Copper Ridge LLC
PO Box 73790
Puyallup, WA 98373-0790
PROJECT:
Crystal Springs Preliminary Plat
Yelm, Washington
2210633.10
PREPARED BY:
Michael Lesmeister, PE
Project Engineer
REVIEWED BY:
J. Matthew Weber, PE.
Principal
DATE:
March 2022
I hereby state that this Construction
Stormwater Pollution Prevention Plan for
Crystal Springs Plat project has been
prepared by me or under my supervision,
and meets the standard of care and
expertise that is usual and customary in
this community for professional
engineers. I understand that City of Yelm
does not and will not assume liability for
the sufficiency, suitability, or performance
of drainage facilities prepared by me.
03/28/2022
Construction Stormwater Pollution Prevention Plan
Crystal Springs Preliminary Plat
2210633.10
Table of Contents
Section Page
1.0 Introduction .................................................................................................................................... 1
2.0 Project Description ........................................................................................................................ 2
3.0 Existing Site Conditions ................................................................................................................ 2
4.0 Adjacent Areas and Drainage ....................................................................................................... 2
5.0 Critical Areas .................................................................................................................................. 2
6.0 Soils ................................................................................................................................................. 2
7.0 Potential Erosion Problems .......................................................................................................... 2
8.0 Construction Stormwater Pollution Prevention Elements ......................................................... 3
8.1 Mark Clearing Limits ........................................................................................................... 3
8.2 Establish Construction Access ............................................................................................ 3
8.3 Control Flow Rates.............................................................................................................. 3
8.4 Install Sediment Controls .................................................................................................... 3
8.5 Stabilize Soils ...................................................................................................................... 3
8.6 Protect Slopes ..................................................................................................................... 3
8.7 Protect Drain Inlets.............................................................................................................. 4
8.8 Stabilize Channels and Outlets ........................................................................................... 4
8.9 Control Pollutants ................................................................................................................ 4
8.10 Control Dewatering ............................................................................................................. 6
8.11 Maintain BMPs .................................................................................................................... 6
8.12 Manage the Project ............................................................................................................. 6
8.13 Protect Low Impact Development BMPs ............................................................................ 7
9.0 Construction Sequence and Phasing .......................................................................................... 7
9.1 Construction Sequence ....................................................................................................... 7
9.2 Construction Phasing .......................................................................................................... 8
10.0 Construction Schedule .................................................................................................................. 8
11.0 Financial/Ownership Responsibilities ......................................................................................... 8
12.0 Certified Erosion and Sediment Control Lead (CESCL) ............................................................ 8
Construction Stormwater Pollution Prevention Plan
Crystal Springs Preliminary Plat
2210633.10
Exhibits
Exhibit 1
NRCS Soils Map
Exhibit 2
TESC Calculations
Exhibit 3
Inspection Logs
Exhibit 4
Selected Best Management Practices (BMPs)
Construction Stormwater Pollution Prevention Plan
Crystal Springs Preliminary Plat 1
2210633.10
1.0 Introduction
In 1972, Congress passed the Federal Water Pollution Control Act (FWPCA), also known as the
Clean Water Act (CWA), to restore and maintain the quality of the nation's waterways. The
ultimate goal was to make sure that rivers and streams were fishable, swimmable, and drinkable.
In 1987, the Water Quality Act (WQA) added provisions to the CWA that allowed the
Environmental Protection Agency (EPA) to govern stormwater discharges from construction sites.
The National Pollutant Discharge Elimination System (NPDES) General Permit includes
provisions for development of a Stormwater Pollution Prevention Plan (SWPPP) to maximize the
potential benefits of pollution prevention and sediment and erosion control measures at
construction sites.
The proposed project will disturb more than 1 acre of area, and therefore is required to obtain an
NPDES General Permit for Stormwater Associated with Construction Activities.
The most recent Department of Ecology Stormwater Management Manual for Western
Washington (SMMWW), as adopted by the City of Yelm, requires a Construction Stormwater
Pollution Prevention Plan (CSWPPP) for projects that add or replace more than 2,000 square feet
of impervious surface. The proposed project will exceed this threshold; therefore, a CSWPPP is
required.
Development, implementation, and maintenance of the CSWPPP will provide the selected
General Contractor with the framework for reducing soil erosion and minimizing pollutants in
stormwater during construction. The CSWPPP will:
• Define the characteristics of the site and the type of construction that will occur.
• Describe the practices that will be implemented to control erosion and the release of
pollutants in stormwater.
• Create an implementation schedule to ensure that the practices descr ibed in this CSWPPP
are in fact implemented, and to evaluate the plan's effectiveness in reducing erosion,
sediment, and pollutant levels in stormwater discharged from the site.
• Describe the final stabilization/termination design to minimize erosion and prevent
stormwater impacts after construction is complete.
This CSWPPP:
• Identifies the CSWPPP Coordinator with a description of this person's duties.
• Identifies the Stormwater Pollution Prevention Team (SWPP Team) that will assist in
implementation of the CSWPPP during construction.
• Describes the existing site conditions, including existing land use, soil types at the site, and
the location of surface waters that are located on or next to the site.
• Identifies the body or bodies of water that will receive runoff from the construction site,
including the ultimate body of water that receives the stormwater.
• Identifies the drainage areas and potential stormwater contaminants.
• Describes the stormwater management controls and various Best Management Practices
(BMPs) necessary to reduce erosion, sediment, and pollutants in stormwater discharge.
• Describes the facility monitoring plan and how controls will be coordinated with construction
activities.
• Describes the implementation schedule and provisions for amendment of the plan.
Construction Stormwater Pollution Prevention Plan
Crystal Springs Preliminary Plat 2
2210633.10
2.0 Project Description
This CSWPPP accompanies the civil engineering plans submitted for a site development permit
for the proposed project, Crystal Springs Plat. The 4.89-acre site is located in Section 19,
Township 17 North, Range 02 East, W. M. The Thurston County tax parcel number associated
with the project is 22719210403. The project includes the addition of 30 residential lots for single-
family homes, a new roadway and sidewalks, sewer, water services, and stormwater facilities to
treat and dispose of the project's stormwater. The proposed roadway features and utilities will be
extended from NW Crystal Springs Road, as well as connecting to Woodland Court SE
3.0 Existing Site Conditions
The site is presently covered with grass and a few deciduous trees, along with an existing
building on the south end of the site, with slopes ranging from 0 to 5 percent The existing
residence and outbuildings, located in the center of the site, will be demolished. Presently, the
site infiltrates directly into the ground with no offsite runoff.
4.0 Adjacent Areas and Drainage
Review of available GIS topographic information and topographic survey data indicates that there
is minimal potential of runoff from pervious surfaces of adjacent properties. The entire proposed
project runoff will be infiltrated on-site. To our knowledge there are no existing or anticipated
impacts to the downstream basin area.
5.0 Critical Areas
The project site is within an aquifer recharge area.
To our knowledge, no environmentally sensitive areas, including creeks, lakes, ponds, wetlands,
ravines, gullies, steep slopes, or springs, are located on or immediately down gradient of the
property.
6.0 Soils
Site soils are identified by the Natural Resources Conservation Service (NRCS) Web Soil Survey
as Spanaway gravelly sandy loam, a Type A soil . This soil is characterized as very deep,
somewhat excessively drained.
Earth Solutions NW conducted a site investigation to confirm subsurface soil conditions and
establish a design infiltration rate. Soil test holes were dug in the vicinity of the proposed
infiltration basins of the project and observations confirm that the soil types match the SCS soil
description. A soil log map showing the location of the test holes is included in the geotechnical
report. The report recommends a design infiltration rate of 36 inches per hour. Please see Exhibit
5 for the complete Earth Solutions NW report.
7.0 Potential Erosion Problems
There are no known historical erosion problems on the site. There are no known potential
erosion problems that will be created onsite.
Construction Stormwater Pollution Prevention Plan
Crystal Springs Preliminary Plat 3
2210633.10
8.0 Construction Stormwater Pollution Prevention Elements
The purpose of this section is to describe how each of the 1 3 Construction Stormwater Pollution
Prevention elements has been addressed and to identify the type and location of BMPs used to
satisfy the required element. If an element is not applicable to the project, a reason is provided.
8.1 Mark Clearing Limits
Prior to beginning land-disturbing activities, clearing limits will be marked with high visibility plastic
or metal fence (BMP C103). Significant vegetation to remain will be marked and protected by
fencing.
8.2 Establish Construction Access
The existing paved driveway access from Crystal Springs St. NW will serve as the sites
construction entrance (BMP C105). If sediment tracking should occur, the Contractor will be
required to sweep the impacted roadways. Dump trucks hauling material to and from the site will
be covered by a tarp.
8.3 Control Flow Rates
An infiltration sediment trap (BMP C240) will utilize infiltration to control flows during construction.
The proposed sediment trap will infiltrate 100-percent of construction phase runoff with a
maximum design water depth of less than 3ft in the 10-year design event. Sizing of the facility is
found in Exhibit 2.
8.4 Install Sediment Controls
As part of the initial construction activities, BMPs will be installed to trap sediment onsite. The
identified BMPs include sediment trap (BMP C240) and silt fencing (BMP C233).
8.5 Stabilize Soils
To protect soil from the erosive forces of raindrops, flowing water, and wind, the following BMPs
will be implemented:
• All disturbed areas that will remain unworked will be stabilized with temporary hydroseed
(BMP C120) or mulch (BMP C121) within 2 days (October 1 - April 30) or 7 days (May 1 -
September 30).
• After fertilizing, all areas that will not be impacted by construction will be seeded
(BMP C120).
• Topsoil stockpiles will be stabilized with plastic coverings (BMP C123).
• Dust control (BMP C140) will be provided by sprinkling the site with water.
• Permanent erosion control measures will include site paving and seeding of exposed soils.
8.6 Protect Slopes
Slopes on the site will be protected to minimize erosion. Temporary and permanent seeding
(BMP C120) will be used to reduce erosion of exposed soils on slopes. Runoff collection
methods include temporary interceptor swales (BMP C200).
Construction Stormwater Pollution Prevention Plan
Crystal Springs Preliminary Plat 4
2210633.10
8.7 Protect Drain Inlets
Proposed drain inlets shall be protected until final site stabilization. Any storm drain inlets
downstream shall be protected so that surface water runoff does not enter the conveyance
system without first being filtered. Inlets shall be inspected weekly, at a minimum, and daily
during storm events. Storm Drain Inlet Protection (BMP C220) will be provided.
8.8 Stabilize Channels and Outlets
Interceptor swales are proposed for the project to divert stormwater away from the construction
area and direct it to the sediment traps. Stabilized channels will be provided for interceptor
swales descending the slopes associated with the proposed daylight lots . Outlets to the sediment
traps will be stabilized to prevent erosion and check dams (BMP C207) will be provided.
8.9 Control Pollutants
All waste materials will be collected and stored in a securely closed metal dumpster. All trash
and construction debris from the site will be deposited in the dumpster. The dumpster will be
emptied a minimum of once per week, and the trash will be hauled to the local landfill. No
construction materials will be buried onsite. All personnel will be instructed regarding the correct
procedure for waste disposal. All sanitary waste will be collected from the portable un its a
minimum of three times per week. Good housekeeping and spill control practices will be followed
during construction to minimize stormwater contamination from petroleum products, fertilizers,
and concrete.
Table 1 below lists several pollutants that are commonly found on construction sites that have the
potential to contaminate storm runoff. These pollutants will be present, mainly in areas of building
and pavement construction. The Contractor and the CSWPPP/TESC coordinator will be
responsible for identifying areas where these pollutants are being used and monitor runoff coming
from these areas. Pollutant sources will be covered with plastic if contaminated runoff is
observed from these areas. If contaminated runoff is found in the sediment trap or soils, the
Certified Erosion and Sedimentation Control Lead (CESCL) will direct the Contractor to remove
the polluted water/soil and dispose of it in an approved area offsite.
Table 1 – Potential Construction Site Stormwater Pollutants
Trade Name Material Chemical/Physical
Description(1)
Stormwater Pollutants(1)
Pesticides (insecticides,
fungicides, herbicide,
rodenticides)
Various colored to colorless
liquid, powder, pellets, or grains
Chlorinated hydrocarbons,
organophosphates, carbamates,
arsenic
Fertilizer Liquid or solid grains Nitrogen, phosphorous
Plaster White granules or powder Calcium sulphate, calcium
carbonate, sulfuric acid
Cleaning solvents Colorless, blue, or yellow-green
liquid
Perchloroethylene, methylene
chloride, trichloroethylene,
petroleum distillates
Asphalt Black solid Oil, petroleum distillates
Concrete White solid Limestone, sand
Glue, adhesives White or yellow liquid Polymers, epoxies
Paints Various colored liquid Metal oxides, Stoddard solvent,
talc, calcium carbonate, arsenic
Curing compounds Creamy white liquid Naphtha
Wastewater from construction
equipment washing
Water Soil, oil & grease, solids
Construction Stormwater Pollution Prevention Plan
Crystal Springs Preliminary Plat 5
2210633.10
Trade Name Material Chemical/Physical
Description(1)
Stormwater Pollutants(1)
Wood preservatives Clear amber or dark brown
liquid
Stoddard solvent, petroleum
distillates, arsenic, copper,
chromium
Hydraulic oil/fluids Brown oily petroleum
hydrocarbon
Mineral oil
Gasoline Colorless, pale brown or pink
petroleum hydrocarbon
Benzene, ethyl benzene, toluene,
xylene, MTBE
Diesel fuel Clear, blue-green to yellow
liquid
Petroleum distillate, oil & grease,
naphthalene, xylenes
Kerosene Pale yellow liquid petroleum
hydrocarbon
Coal oil, petroleum distillates
Antifreeze/coolant Clear green/yellow liquid Ethylene glycol, propylene glycol,
heavy metals (copper, lead, zinc)
Erosion Solid Particles Soil, Sediment
(1) Data obtained from MSDS when available
8.9.1 Required BMPs
The following BMPs or equivalent measures are required of all businesses and agencies during
concrete pouring and asphalt application at temporary sites:
• Employees must be educated on the pollution hazards of concrete and asphalt application and
cutting.
• Loose aggregate chunks and dust must be swept or shoveled and collected (not hosed down a
storm drain) for recycling or proper disposal at the end of each work day, especially at work
sites such as streets, driveways, parking lots, sidewalks, curbs, and gutters where rain can
readily pick up the loose material and carry it to the nearest stormwater conveyance. Small
amounts of excess concrete, grout, and mortar can be disposed of in the trash.
• Storm drain covers or similarly effective containment devices must be placed over all
nearby drains at the beginning of each day. Shovel or vacuum slurry and remove from the
site. All accumulated runoff and solids must be collected and properly disposed at the end
of each workday, or more often if necessary.
• Exposed aggregate washing, where the top layer of unhardened concrete is hosed or
scraped off to leave a rough finish, must be done with a mechanism for containment and
collection of the discarded concrete slurry (such as the storm drain covers mentioned
above). The easiest way to contain the wash water will be to direct the washings to a hole
in the ground where the water can percolate into the ground and the solids later covered
with soil.
• If directed to a drain, a catch basin filter insert must be used to remove the solids. This is
especially useful if the activity must proceed on rainy days.
• Cleaning of concrete application and mixing equipment or concrete vehicles on the work
site must be done in a designated area where the rinse water is controlled. The rinse water
must either be collected for proper disposal or put into a hole in the ground where the water
can percolate away and the solids later covered with soil or recovered and disposed or
recycled.
The use of any treatment BMP must not result in the violation of groundwater, surface water, or
drinking water quality standards.
Construction Stormwater Pollution Prevention Plan
Crystal Springs Preliminary Plat 6
2210633.10
8.10 Control Dewatering
Dewatering is not anticipated for the project.
8.11 Maintain BMPs
Temporary and permanent erosion and sediment control BMPs shall be maintained and repaired
as needed to assure performance of their intended functions.
Sediment control BMPs such as silt fencing, slope blankets, and drain inlet protection shall be
inspected weekly or after a runoff-producing event. Temporary erosion and sediment control
BMPs will be removed within 30 days after final site stabilization is achieved. The following
inspection and maintenance practices will be used to maintain erosion and sediment controls:
• Built-up sediment will be removed from silt fencing when it has reached one-third the height
of the fence.
• Silt fences will be inspected for depth of sediment, tears in the fabric, and attachment to the
fence posts, and to determine that fence posts are firmly in the ground. Accumulated
sediment will be removed from behind the fence.
• Check dams will be inspected for depth of sediment. Accumulated sediment will be
removed when it reaches 6 inches in depth.
• Temporary and permanent seeding will be inspected for bare spots, washouts, and healthy
growth.
• The Contractor Certified Erosion and Sedimentation Control Lead (CESCL) (BMP C160)
will provide erosion control inspection services and stormwater disposal monitoring through
construction. The City Inspector will be notified of daily construction activities and
scheduled meetings between the Erosion Control Inspector and the Contractor.
The maintenance inspection report will be made after each inspection. Copies of the report forms
to be completed by the CSWPPP coordinator are attached as Exhibit 3 of this CSWPPP.
Completed forms will be provided to the City Inspector and will also be maintained onsite during
the entire construction project. If construction activities or design modifications are made to the
site plan that could impact stormwater, or if AHBL determines that the measures are not
adequate to prevent erosion and the discharge of sediment from the site (based on turbidity
measurements), this CSWPPP will be amended appropriately. The amended CSWPPP will have
a description of the new activities that contribute to the increased pollutant loading and the
planned source control activities.
8.12 Manage the Project
The following practices will be required during construction to properly manage activities:
• Comply with seasonal work limitations.
• Inspect, maintain, and repair BMPs.
• Identify a CESCL (BMP C160).
• Maintain the CSWPPP onsite at all times, including narrative and plans.
Construction Stormwater Pollution Prevention Plan
Crystal Springs Preliminary Plat 7
2210633.10
8.13 Protect Low Impact Development BMPs
• Proposed infiltration location will be protected from construction vehicles and equipment to
the maximum extent practical.
• Proposed sediment traps designed to not impact infiltration interface of future infiltration
facility.
• All Low Impact Development (LID) BMPs should be kept clean of sediment and equipment
to the maximum extent practical.
9.0 Construction Sequence and Phasing
9.1 Construction Sequence
The construction sequence is described below:
1. Stake/flag clearing and construction limits.
2. Arrange and attend a pre-construction meeting with City of Yelm.
3. Install construction entrance.
4. Provide demolition as required to install all temporary erosion control BMPs according to
the TESC plan. Install inlet sediment protection in existing catch basins.
5. Provide all perimeter erosion control and site barrier fencing including filter fabric fence
prior to start of any clearing or grading activities.
6. Excavate temporary TESC ponds (protect subgrades from compaction – used for
infiltration).
7. Demolish remainder of existing site features as designated for demolition on the plans.
8. Maintain erosion control measures as site development progresses.
9. Rough grade site and provide erosion control BMPs to stabilize the site and direct all
surface runoff to the TESC plans.
10. Apply erosion control mulch and seeding, straw mulch or equal to areas that will not be
brought to final grade or permanently vegetated within 7 days of exposure, during the dry
season and 2 days of exposure during the wet season (October 1 – Aril 30).
11. Relocate erosion control measures or install new measures so that as the site conditions
change, the erosion and sediment control is always in accordance with the SWPPP
minimum requirements.
12. Construct storm system and misc. utilities and install inlet sediment protectio n to new catch
basins.
13. Fine grade asphalt paved areas, place curb and gutters, and pave.
14. After site is stabilized, complete bio-retention construction:
Construction Stormwater Pollution Prevention Plan
Crystal Springs Preliminary Plat 8
2210633.10
14.1. Scarify bio-retention sub-grade (do not compact bio-retention bottoms). Schedule
geotechnical engineer for infiltration testing to ensure bio-retention functions per design.
Provide infiltration testing to include a minimum of 2 tests per bio-retention system.
14.2. Upon approval of infiltration testing results, provide bio-retention treatment soil mix
per plans. Bio-retention soil mix placement and bio-retention excavation shall not be
conducted during wet or saturated conditions.
15. Provide landscape plantings and final bio-retention stabilization per landscape design.
16. Remove remaining temporary erosion control items once site has been stabilized and upon
approval from the city.
17. Perform final close-out items as required by city and owner.
9.2 Construction Phasing
No phasing is proposed. The proposed construction will be done as one project.
10.0 Construction Schedule
Construction is anticipated to begin in Summer 2022 and be completed in Spring 2023. Based on
the construction schedule, construction may be ongoing during the wet season. During
construction, measures will be taken to prevent the transportation of sediment from the site to
receiving waters. These measures include the use of, but are not limited to, the BMPs listed in
Exhibit 4.
11.0 Financial/Ownership Responsibilities
The Developer is the party responsible for initiation of bonds and other financial securities. The
project must comply with City of Yelm financial liability requirements.
12.0 Certified Erosion and Sediment Control Lead (CESCL)
The General Contractor shall be required to provide a CESCL prior to permit issuance. The
CESCL can be identified at the preconstruction meeting. Once this individual is identified, the
City Inspector will be notified.
The contractor will designate their CESCL here:
Name: _____________________________________________
Address: _____________________________________________
Phone: _____________________________________________
Fax Number: _____________________________________________
The CESCL is required to meet Washington State Department of Ecology certification
requirements. The City Inspector will be provided with CESCL information.
The duties of the CESCL include:
Construction Stormwater Pollution Prevention Plan
Crystal Springs Preliminary Plat 9
2210633.10
• Implementing the CSWPPP/TESC plan with the aid of the SWPP Team.
• Overseeing maintenance practices identified as BMPs in the CSWPPP.
• Conducting or providing for inspection and monitoring activities.
• Sampling stormwater for turbidity using a turbidity meter.
• Identifying other potential pollutant sources and ensuring they are added to the plan.
• Identifying any deficiencies in the CSWPPP and ensuring they are corrected.
• Ensuring that any changes in construction plans are addressed in the CSWPPP.
To aid in the implementation of the CSWPPP, the members of the SWPP Team include the
following: General Contractor, CESCL, City of Yelm Inspector, the geotechnical engineering
consultant, and AHBL.
The General Contractor will ensure that all housekeeping and monitoring procedures are
implemented, while the CESCL will ensure the integrity of the structural BMPs. The SWPP Team
will observe construction and erosion control practices and rec ommend revisions or additions to
the CSWPPP and drawings.
This analysis is based on data and records either supplied to or obtained by AHBL, Inc. These
documents are referenced within the text of the analysis. The analysis has been prepared utilizing
procedures and practices within the standard accepted practices of the industry. We conclude that this
project, as proposed, will not create any new problems within the existing downstream drainage system.
This project will not noticeably aggravate any existing downstream problems due to either water quality or
quantity.
AHBL, Inc.
Michael Lesmeister, PE
ML/
March 2022
Q:\2021\2210633\10_CIV\NON_CAD\REPORTS\SWPPP\20220326 Rpt (SWPPP) 2210633.10.docx
Construction Stormwater Pollution Prevention Plan
Crystal Springs Preliminary Plat
2210633.10
Exhibit 1
NRCS Soils Map
Soil Map—Thurston County Area, Washington
(A-2)
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
10/5/2021
Page 1 of 35199540519956051995805199600519962051996405199660519968051997005199720519974051997605199780519980051995405199560519958051996005199620519964051996605199680519970051997205199740519976051997805199800530070530090530110530130530150530170530190530210530230
530070 530090 530110 530130 530150 530170 530190 530210 530230
46° 57' 4'' N 122° 36' 17'' W46° 57' 4'' N122° 36' 9'' W46° 56' 55'' N
122° 36' 17'' W46° 56' 55'' N
122° 36' 9'' WN
Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 10N WGS84
0 35 70 140 210
Feet
0 10 20 40 60
Meters
Map Scale: 1:766 if printed on B portrait (11" x 17") sheet.
Soil Map may not be valid at this scale.
MAP LEGEND MAP INFORMATION
Area of Interest (AOI)
Area of Interest (AOI)
Soils
Soil Map Unit Polygons
Soil Map Unit Lines
Soil Map Unit Points
Special Point Features
Blowout
Borrow Pit
Clay Spot
Closed Depression
Gravel Pit
Gravelly Spot
Landfill
Lava Flow
Marsh or swamp
Mine or Quarry
Miscellaneous Water
Perennial Water
Rock Outcrop
Saline Spot
Sandy Spot
Severely Eroded Spot
Sinkhole
Slide or Slip
Sodic Spot
Spoil Area
Stony Spot
Very Stony Spot
Wet Spot
Other
Special Line Features
Water Features
Streams and Canals
Transportation
Rails
Interstate Highways
US Routes
Major Roads
Local Roads
Background
Aerial Photography
The soil surveys that comprise your AOI were mapped at
1:24,000.
Warning: Soil Map may not be valid at this scale.
Enlargement of maps beyond the scale of mapping can cause
misunderstanding of the detail of mapping and accuracy of soil
line placement. The maps do not show the small areas of
contrasting soils that could have been shown at a more detailed
scale.
Please rely on the bar scale on each map sheet for map
measurements.
Source of Map: Natural Resources Conservation Service
Web Soil Survey URL:
Coordinate System: Web Mercator (EPSG:3857)
Maps from the Web Soil Survey are based on the Web Mercator
projection, which preserves direction and shape but distorts
distance and area. A projection that preserves area, such as the
Albers equal-area conic projection, should be used if more
accurate calculations of distance or area are required.
This product is generated from the USDA-NRCS certified data as
of the version date(s) listed below.
Soil Survey Area: Thurston County Area, Washington
Survey Area Data: Version 15, Aug 31, 2021
Soil map units are labeled (as space allows) for map scales
1:50,000 or larger.
Date(s) aerial images were photographed: Jul 18, 2020—Jul 20,
2020
The orthophoto or other base map on which the soil lines were
compiled and digitized probably differs from the background
imagery displayed on these maps. As a result, some minor
shifting of map unit boundaries may be evident.
Soil Map—Thurston County Area, Washington
(A-2)
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
10/5/2021
Page 2 of 3
Map Unit Legend
Map Unit Symbol Map Unit Name Acres in AOI Percent of AOI
110 Spanaway gravelly sandy
loam, 0 to 3 percent slopes
4.5 63.1%
111 Spanaway gravelly sandy
loam, 3 to 15 percent slopes
2.6 36.9%
Totals for Area of Interest 7.1 100.0%
Soil Map—Thurston County Area, Washington A-2
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
10/5/2021
Page 3 of 3
Construction Stormwater Pollution Prevention Plan
Crystal Springs Preliminary Plat
2210633.10
Exhibit 2
TESC Calculations
History Cleared: 13:14:25 Saturday, March 26, 2022
LPOOLCOMPUTE [Pond] SUMMARY using Puls
Start of live storage: 333.0000 ft
Dev Event Summary
Record Id: Dev
Event Match Q (cfs)Peak Q (cfs)Peak Stg (ft)Vol (cf)Vol (acft)Time to Empty
10 year 0.2167 0.2167 335.5026 1909.82 0.0438 26.83
Event Peak Q (cfs)Peak T (hrs)Hyd Vol (acft)Area (ac)Method Raintype
2 year 0.5301 8.00 0.1872 1.5500 SBUH TYPE1A
other 0.5595 8.00 0.1984 1.5500 SBUH TYPE1A
5 year 0.6797 8.00 0.2439 1.5500 SBUH TYPE1A
10 year 0.8346 8.00 0.3020 1.5500 SBUH TYPE1A
25 year 0.9920 8.00 0.3611 1.5500 SBUH TYPE1A
100 year 1.1513 8.00 0.4210 1.5500 SBUH TYPE1A
Design Method SBUH Rainfall type TYPE1A
Hyd Intv 10.00 min Peaking Factor 484.00
Abstraction Coeff 0.20
Pervious Area (AMC 2)0.34 ac DCIA 1.21 ac
Pervious CN 72.00 DC CN 98.00
Pervious TC 32.22 min DC TC 6.65 min
Pervious CN Calc
Description SubArea Sub cn
Pervious 0.34 ac 72.00
Pervious Composited CN (AMC 2)72.00
Pervious TC Calc
Type Description Length Slope Coeff Misc TT
Sheet Short prairie grass and lawns.: 0.15 300.00 ft 1.25%0.1500 2.50 in 32.22 min
Pervious TC 32.22 min
Directly Connected CN Calc
Description SubArea Sub cn
Hard Surface 1.21 ac 98.00
DC Composited CN (AMC 2)98.00
Page 1 of 2
3/26/2022file:///Q:/2021/2210633/10_CIV/NON_CAD/CALCS/StormShed/20220325%20TESC.html
Record Id: Pond Dimensions
Licensed to: AHBL
Directly Connected TC Calc
Type Description Length Slope Coeff Misc TT
Sheet Smooth Surfaces.: 0.011 100.00 ft 1.25%0.0110 2.50 in 1.65 min
Fixed Ditch 5.00 min
Directly Connected TC 6.65min
Descrip:Prototype Record Increment 0.10 ft
Start El.333.0000 ft Max El.336.0000 ft
Length 52.0000 ft Width 5.0000 ft
Length ss1 3.00h:1v Length ss2 3.0000h:1v
Width ss1 3.00h:1v Width ss2 3.0000h:1v
Only consider bottom area for infiltration
Stage Storage Rating Curve
333.0000 ft 0.0000 cf 334.6000 ft 902.9120 cf
333.1000 ft 27.7220 cf 334.7000 ft 995.1460 cf
333.2000 ft 58.9360 cf 334.8000 ft 1092.0240 cf
333.3000 ft 93.7140 cf 334.9000 ft 1193.6180 cf
333.4000 ft 132.1280 cf 335.0000 ft 1300.0000 cf
333.5000 ft 174.2500 cf 335.1000 ft 1411.2420 cf
333.6000 ft 220.1520 cf 335.2000 ft 1527.4160 cf
333.7000 ft 269.9060 cf 335.3000 ft 1648.5940 cf
333.8000 ft 323.5840 cf 335.4000 ft 1774.8480 cf
333.9000 ft 381.2580 cf 335.5000 ft 1906.2500 cf
334.0000 ft 443.0000 cf 335.6000 ft 2042.8720 cf
334.1000 ft 508.8820 cf 335.7000 ft 2184.7860 cf
334.2000 ft 578.9760 cf 335.8000 ft 2332.0640 cf
334.3000 ft 653.3540 cf 335.9000 ft 2484.7780 cf
334.4000 ft 732.0880 cf 336.0000 ft 2643.0000 cf
Page 2 of 2
3/26/2022file:///Q:/2021/2210633/10_CIV/NON_CAD/CALCS/StormShed/20220325%20TESC.html
Construction Stormwater Pollution Prevention Plan
Crystal Springs Preliminary Plat
2210633.10
Exhibit 3
Inspection Logs
Construction Stormwater Pollution Prevention Plan
Crystal Springs Preliminary Plat
2210633.10
Crystal Springs Plat
Construction Stormwater Pollution Prevention Plan
Inspection and Maintenance Report Form
To be completed every 7 days and within 24 hours of a rainfall event of 0.5 inches or more
Inspector: Date:
Inspector's Qualifications:
Days since last rainfall: Amount of last rainfall: inches
Stabilization Measures
Drainage Area Date Since
Last
Disturbance
Date of
Disturbance
Stabilized
(yes/No)
Stabilized With Condition
Stabilization required:
To be performed by: On or before:
Construction Stormwater Pollution Prevention Plan
Crystal Springs Preliminary Plat
2210633.10
Crystal Springs Plat
Construction Stormwater Pollution Prevention Plan
Inspection and Maintenance Report Form
Perimeter Structural Controls:
Date:
Silt Fence
Drainage Area
Perimeter
Has Silt Reached 1/3 of
Fence Height?
Is Fence Properly
Secured?
Is There Evidence of
Washout or
Overtopping?
Maintenance required for silt fence and straw bales:
To be performed by: On or before:
Construction Stormwater Pollution Prevention Plan
Crystal Springs Preliminary Plat
2210633.10
Crystal Springs Plat
Construction Stormwater Pollution Prevention Plan
Inspection and Maintenance Report Form
Changes required to the pollution prevention plan:
Reasons for changes:
I certify under penalty of law that this document and all attachments were prepared under my
direction or supervision in accordance with a system designed to assure that qualified personnel
properly gathered and evaluated the information submitted. Based on my inquiry of the person
or persons who manage the system, or those persons directly responsible for gathering the
information, the information submitted is, to the best of my knowledge and belief, true, accurate,
and complete. I am aware that there are significant penalties for submitting false information,
including the possibility of fine and imprisonment for knowing violations.
Signature: Date: ____________________
Construction Stormwater Pollution Prevention Plan
Crystal Springs Preliminary Plat
2210633.10
Exhibit 4
Selected Best Management Practices (BMPs)
• High Visibility Fence (BMP C103)
• Stabilized Construction Access (BMP C105)
• Temporary and Permanent Seeding (BMP C120)
• Mulching (BMP C121)
• Nets and Blankets (BMP C122)
• 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)
• Concrete Washout Area (BMP C154)
• Certified Erosion and Sediment Control Lead (BMP C160)
• Scheduling (BMP C162)
• Interceptor Dike and Swale (BMP C200)
• Riprap Channel Lining (BMP C202)
• Check Dams (BMP C207)
• Outlet Protection (BMP C209)
• Inlet Protection (BMP C220)
• Silt Fence (BMP C233)
• Sediment Trap (BMP C240)
BMP C103: High-Visibility Fence
Purpose
High-visibility fencing is intended to:
l Restrict clearing to approved limits.
l Prevent disturbance of sensitive areas, their buffers, and other areas required to be left undis-
turbed.
l Limit construction traffic to designated construction entrances, exits, or internal roads.
l 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:
l At the boundary of sensitive areas, their buffers, and other areas required to be left uncleared.
l 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: Silt Fence 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.
2019 Stormwater Management Manual for Western Washington
Volume II -Chapter 3 -Page 274
Maintenance Standards
If the fence has been damaged or visibility reduced, it shall be repaired or replaced immediately and
visibility restored.
BMP C105: Stabilized Construction Access
Purpose
Stabilized construction accesses are established to reduce the amount of sediment transported onto
paved roads outside the project site by vehicles or equipment. This is done by constructing a sta-
bilized pad of quarry spalls at entrances and exits for project sites.
Conditions of Use
Construction accesses shall be stabilized wherever traffic will be entering or leaving a construction
site if paved roads or other paved areas are within 1,000 feet of the site.
For residential subdivision construction sites, provide a stabilized construction access for each res-
idence, 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 and configuration.
On large commercial, highway, and road projects, the designer should include enough extra mater-
ials in the contract to allow for additional stabilized accesses 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 II-3.1: Stabilized Construction Access for details. Note: the 100’ minimum length of the
access shall be reduced to the maximum practicable size when the size or configuration of the site
does not allow the full length (100’).
Construct stabilized construction accesses with a 12-inch thick pad of 4-inch to 8-inch quarry spalls,
a 4-inch course of asphalt treated base (ATB), or use existing pavement. Do not use crushed con-
crete, cement, or calcium chloride for construction access stabilization because these products raise
pH levels in stormwater and concrete discharge to waters of the State is prohibited.
A separation geotextile shall be placed under the spalls to prevent fine sediment from pumping up
into the rock pad. The geotextile shall meet the standards listed in Table II-3.2: Stabilized Con-
struction Access Geotextile Standards.
Geotextile Property Required Value
Grab Tensile Strength (ASTM D4751)200 psi min.
Table II-3.2: Stabilized Construction Access
Geotextile Standards
2019 Stormwater Management Manual for Western Washington
Volume II -Chapter 3 -Page 275
Geotextile Property Required Value
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)
Table II-3.2: Stabilized Construction Access
Geotextile Standards (continued)
l Consider early installation of the first lift of asphalt in areas that will be paved; this can be used
as a stabilized access. Also consider the installation of excess concrete as a stabilized access.
During large concrete pours, excess concrete is often available for this purpose.
l Fencing (see BMP C103: High-Visibility Fence) shall be installed as necessary to restrict
traffic to the construction access.
l Whenever possible, the access shall be constructed on a firm, compacted subgrade. This can
substantially increase the effectiveness of the pad and reduce the need for maintenance.
l Construction accesses should avoid crossing existing sidewalks and back of walk drains if at
all possible. If a construction access must cross a sidewalk or back of walk drain, the full length
of the sidewalk and back of walk drain must be covered and protected from sediment leaving
the site.
Alternative Material Specification
WSDOT has raised safety concerns about the Quarry Spall rock specified above. WSDOT observes
that the 4-inch to 8-inch rock sizes can become trapped between Dually truck tires, and then
released off-site at highway speeds. WSDOT has chosen to use a modified specification for the rock
while continuously verifying that the Stabilized Construction Access remains effective. To remain
effective, the BMP must prevent sediment from migrating off site. To date, there has been no per-
formance testing to verify operation of this new specification. Jurisdictions may use the alternative
specification, but must perform increased off-site inspection if they use, or allow others to use, it.
Stabilized Construction Accesses may use material that meets the requirements of WSDOT's Stand-
ard Specifications for Road, Bridge, and Municipal Construction Section 9-03.9(1) (WSDOT, 2016)
for ballast except for the following special requirements.
The grading and quality requirements are listed in Table II-3.3: Stabilized Construction Access
Alternative Material Requirements.
Sieve Size Percent Passing
2½″99-100
Table II-3.3: Stabilized
Construction Access
Alternative Material
Requirements
2019 Stormwater Management Manual for Western Washington
Volume II -Chapter 3 -Page 276
Sieve Size Percent Passing
2″65-100
¾″40-80
No. 4 5 max.
No. 100 0-2
% Fracture 75 min.
Table II-3.3: Stabilized
Construction Access
Alternative Material
Requirements
(continued)
l All percentages are by weight.
l The sand equivalent value and dust ratio requirements do not apply.
l The fracture requirement shall be at least one fractured face and will apply the combined
aggregate retained on the No. 4 sieve in accordance with FOP for AASHTO T 335.
Maintenance Standards
Quarry spalls shall be added if the pad is no longer in accordance with the specifications.
l If the access is not preventing sediment from being tracked onto pavement, then alternative
measures to keep the streets free of sediment shall be used. This may include replace-
ment/cleaning of the existing quarry spalls, street sweeping, an increase in the dimensions of
the access, or the installation of BMP C106: Wheel Wash.
l Any sediment that is tracked onto pavement shall be removed by shoveling or street sweep-
ing. The sediment collected by sweeping shall be removed or stabilized on site. The pavement
shall not be cleaned by washing down the street, except when high efficiency sweeping is inef-
fective and there is a threat to public safety. If it is necessary to wash the streets, the con-
struction 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.
l Perform street sweeping by hand or with a high efficiency sweeper. Do not use a non-high effi-
ciency mechanical sweeper because this creates dust and throws soils into storm systems or
conveyance ditches.
l Any quarry spalls that are loosened from the pad, which end up on the roadway shall be
removed immediately.
l If vehicles are entering or exiting the site at points other than the construction access(es),
BMP C103: High-Visibility Fence shall be installed to control traffic.
2019 Stormwater Management Manual for Western Washington
Volume II -Chapter 3 -Page 277
l Upon project completion and site stabilization, all construction accesses intended as per-
manent access for maintenance shall be permanently stabilized.
2019 Stormwater Management Manual for Western Washington
Volume II -Chapter 3 -Page 278
Figure II-3.1: Stabilized Construction Access
2019 Stormwater Management Manual for Western Washington
Volume II -Chapter 3 -Page 279
Approved as Functionally Equivalent
Ecology has approved products as able to meet the requirements of this BMP. The products did not
pass through the Technology Assessment Protocol – Ecology (TAPE) process. Local jurisdictions
may choose not to accept these products, or may require additional testing prior to consideration for
local use. Products that Ecology has approved as functionally equivalent are available for review on
Ecology’s website at:
https://ecology.wa.gov/Regulations-Permits/Guidance-technical-assistance/Stormwater-per-
mittee-guidance-resources/Emerging-stormwater-treatment-technologies
2019 Stormwater Management Manual for Western Washington
Volume II - Chapter 3 - Page 280
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 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
pro-tection.
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 sta-
bilization 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. See BMP T5.13: Post-Construction Soil
Quality and Depth.
Design and Installation Specifications
General
l 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 the top of hydroseed. Before allowing water to flow in vegetated channels,
establish 75 percent vegetation cover. If vegetated channels cannot be established by seed
2019 Stormwater Management Manual for Western Washington
Volume II -Chapter 3 -Page 284
before water flow; install sod in the channel bottom — over top of hydromulch and erosion con-
trol blankets.
l Confirm the installation of all required surface water control measures to prevent seed from
washing away.
l Hydroseed applications shall include a minimum of 1,500 pounds per acre of mulch with 3 per-
cent tackifier. See BMP C121: Mulching for specifications.
l Areas that will have seeding only and not landscaping may need compost or meal-based
mulch included in the hydroseed in order to establish vegetation. Re-install native topsoil on
the disturbed soil surface before application. See BMP T5.13: Post-Construction Soil Quality
and Depth.
l 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.
l Enhance vegetation establishment by dividing the hydromulch operation into two phases:
o Phase 1- Install all seed and fertilizer with 25-30 percent mulch and tackifier onto soil in
the first lift.
o Phase 2- Install the rest of the mulch and tackifier over the first lift.
Or, enhance vegetation by:
o Installing the mulch, seed, fertilizer, and tackifier in one lift.
o Spread or blow straw over the top of the hydromulch at a rate of 800-1000 pounds per
acre.
o 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:
o Irrigation.
o Reapplication of mulch.
o Repair of failed slope surfaces.
This technique works with standard hydromulch (1,500 pounds per acre minimum) and Bon-
ded Fiber Matrix/ Mechanically Bonded Fiber Matrix (BFM/MBFMs) (3,000 pounds per acre
minimum).
l Seed may be installed by hand if:
o Temporary and covered by straw, mulch, or topsoil.
o Permanent in small areas (usually less than 1 acre) and covered with mulch, topsoil, or
erosion blankets.
l The seed mixes listed in Table II-3.4: Temporary and Permanent Seed Mixes include
2019 Stormwater Management Manual for Western Washington
Volume II -Chapter 3 -Page 285
recommended mixes for both temporary and permanent seeding.
l Apply these mixes, with the exception of the wet area seed mix, at a rate of 120 pounds per
acre. This rate can be reduced if soil amendments or slow-release fertilizers are used. Apply
the wet area seed mix at a rate of 60 pounds per acre.
l Consult the local suppliers or the local conservation district for their recommendations. 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,
depending on the soil type and hydrology of the area.
Common Name Latin Name % Weight % Purity % Germination
Temporary Erosion Control Seed Mix
A standard mix for areas requiring a temporary vegetative cover.
Chewings or
annual 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
Landscaping Seed Mix
A recommended mix for landscaping seed.
Perennial rye blend Lolium perenne 70 98 90
Chewings and red
fescue blend
Festuca rubra var.
commutata or Fes-
tuca rubra
30 98 90
Low-Growing Turf Seed Mix
A turf seed mix for dry situations where there is no need for watering. This mix requires very little main-
tenance.
Dwarf tall fescue
(several varieties)
Festuca arundin-
acea 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
Bioswale Seed Mix
A seed mix for bioswales and other intermittently wet areas.
Tall or meadow fes-Festuca arundin-75-80 98 90
Table II-3.4: Temporary and Permanent Seed Mixes
2019 Stormwater Management Manual for Western Washington
Volume II -Chapter 3 -Page 286
Common Name Latin Name % Weight % Purity % Germination
cue acea or Festuca
elatior
Seaside/Creeping
bentgrass Agrostis palustris 10-15 92 85
Redtop bentgrass Agrostis alba or
Agrostis gigantea 5-10 90 80
Wet Area Seed Mix
A low-growing, relatively non-invasive seed mix appropriate for very wet areas that are not regulated wet-
lands. Consult Hydraulic Permit Authority (HPA) for seed mixes if applicable.
Tall or meadow fes-
cue
Festuca arundin-
acea or Festuca
elatior
60-70 98 90
Seaside/Creeping
bentgrass Agrostis palustris 10-15 98 85
Meadow foxtail Alepocurus praten-
sis 10-15 90 80
Alsike clover Trifolium hybridum 1-6 98 90
Redtop bentgrass Agrostis alba 1-6 92 85
Meadow Seed Mix
A recommended meadow seed mix for infrequently maintained areas or non-maintained areas where col-
onization by native plants is desirable. Likely applications include rural road and utility right-of-way. Seed-
ing should take place in September or very early October in order to obtain adequate establishment prior to
the winter months. Consider the appropriateness of clover, a fairly invasive species, in the mix. Amending
the soil can reduce the need for clover.
Redtop or Oregon
bentgrass
Agrostis alba or
Agrostis ore-
gonensis
20 92 85
Red fescue Festuca rubra 70 98 90
White dutch clover Trifolium repens 10 98 90
Table II-3.4: Temporary and Permanent Seed Mixes (continued)
Roughening and Rototilling
l The seedbed should be firm and rough. Roughen all soil no matter what the slope. Track walk
slopes before seeding if engineering purposes require compaction. Backblading or smoothing
of slopes greater than 4H:1V is not allowed if they are to be seeded.
l Restoration-based landscape practices require deeper incorporation than that provided by a
simple single-pass rototilling treatment. Wherever practical, initially rip the subgrade to
improve long-term permeability, infiltration, and water inflow qualities. At a minimum,
2019 Stormwater Management Manual for Western Washington
Volume II -Chapter 3 -Page 287
permanent areas shall use soil amendments to achieve organic matter and permeability per-
formance 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
l Conducting soil tests to determine the exact type and quantity of fertilizer is recommended.
This will prevent the over-application of fertilizer.
l Organic matter is the most appropriate form of fertilizer because it provides nutrients (includ-
ing nitrogen, phosphorus, and potassium) in the least water-soluble form.
l In general, use 10-4-6 N-P-K (nitrogen-phosphorus-potassium) fertilizer at a rate of 90
pounds per acre. Always use slow-release fertilizers because they are more efficient and
have fewer environmental impacts. Do not add fertilizer to the hydromulch machine, or agit-
ate, more than 20 minutes before use. Too much agitation destroys the slow-release coating.
l There are numerous products available that take the place of chemical 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
l On steep slopes use Bonded Fiber Matrix (BFM) or Mechanically Bonded Fiber Matrix
(MBFM) products. Apply BFM/MBFM products at a minimum rate of 3,000 pounds per acre
with approximately 10 percent tackifier. Achieve a minimum of 95 percent soil coverage during
application. Numerous products are available commercially. Most products require 24-36
hours to cure before rainfall and cannot be installed on wet or saturated soils. Generally,
products come in 40-50 pound bags and include all necessary ingredients except for seed and
fertilizer.
l Install products per manufacturer's instructions.
l BFMs and MBFMs provide good alternatives to blankets in most areas requiring vegetation
establishment. Advantages over blankets include:
o BFM and MBFMs do not require surface preparation.
o Helicopters can assist in installing BFM and MBFMs in remote areas.
o On slopes steeper than 2.5H:1V, blanket installers may require ropes and harnesses
for safety.
o Installing BFM and MBFMs can save at least $1,000 per acre compared to blankets.
2019 Stormwater Management Manual for Western Washington
Volume II -Chapter 3 -Page 288
Maintenance Standards
Reseed any seeded areas that fail to establish at least 75 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, nets, or blankets.
l Reseed and protect by mulch any areas that experience erosion after achieving adequate
cover. Reseed and protect by mulch any eroded area.
l Supply seeded areas with adequate moisture, but do not water to the extent that it causes run-
off.
Approved as Functionally Equivalent
Ecology has approved products as able to meet the requirements of this BMP. The products did not
pass through the Technology Assessment Protocol – Ecology (TAPE) process. Local jurisdictions
may choose not to accept these products, or may require additional testing prior to consideration for
local use. Products that Ecology has approved as functionally equivalent are available for review on
Ecology’s website at:
https://ecology.wa.gov/Regulations-Permits/Guidance-technical-assistance/Stormwater-per-
mittee-guidance-resources/Emerging-stormwater-treatment-technologies
BMP C121: Mulching
Purpose
Mulching soils provides immediate temporary protection from erosion. Mulch also enhances plant
establishment by conserving moisture, holding fertilizer, seed, and topsoil in place, and moderating
soil temperatures. There are a variety of mulches that can be used. This section discusses only the
most common types of mulch.
Conditions of Use
As a temporary cover measure, mulch should be used:
l For less than 30 days on disturbed areas that require cover.
l At all times for seeded areas, especially during the wet season and during the hot summer
months.
l 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:
l cottonseed meal;
l fibers made of wood, recycled cellulose, hemp, or kenaf;
2019 Stormwater Management Manual for Western Washington
Volume II -Chapter 3 -Page 289
l compost;
l or blends of these.
Tackifier shall be plant-based, such as guar or alpha plantago, or chemical-based such as poly-
acrylamide or polymers.
Generally, mulches come in 40-50 pound bags. Seed and fertilizer are added at time of application.
Recycled cellulose may contain polychlorinated biphenyl (PCBs). Ecology recommends that
products should be evaluated for PCBs prior to use.
Refer to BMP C126: Polyacrylamide (PAM) for Soil Erosion Protection for conditions of use. PAM
shall not be directly applied to water or allowed to enter a water body.
Any mulch or tackifier product used shall be installed per the manufacturer’s instructions.
Design and Installation Specifications
For mulch materials, application rates, and specifications, see Table II-3.6: Mulch Standards and
Guidelines. Consult with the local supplier or the local conservation district for their recom-
mendations. Increase the application rate until the ground is 95% covered (i.e. not visible under the
mulch layer). Note: Thickness may be increased for disturbed areas in or near sensitive areas or
other areas highly susceptible to erosion.
Where the option of “Compost” is selected, it should be a coarse compost that meets the size grad-
ations listed in Table II-3.5: Size Gradations of Compost as Mulch Material when tested in accord-
ance with Test Method 02.02-B found in Test Methods for the Examination of Composting and
Compost (Thompson, 2001).
Sieve Size Percent Passing
3"100%
1"90% - 100%
3/4"70% - 100%
1/4"40% - 100%
Table II-3.5: Size Gradations of Compost as Mulch Material
Mulch used within the ordinary high-water mark of surface waters should be selected to minimize
potential flotation of organic matter. Composted organic materials have higher specific gravities
(densities) than straw, wood, or chipped material. Consult the Hydraulic Permit Authority (HPA) for
mulch mixes if applicable.
Maintenance Standards
The thickness of the mulch 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.
2019 Stormwater Management Manual for Western Washington
Volume II -Chapter 3 -Page 290
Mulch Mater-
ial Guideline Description
Straw
Quality
Standards Air-dried; free from undesirable seed and coarse material.
Application
Rates 2"-3" thick; 5 bales per 1,000 sf or 2-3 tons per acre
Remarks
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 flot-
ation).
Hydromulch
Quality
Standards No growth inhibiting factors.
Application
Rates Approx. 35-45 lbs per 1,000 sf or 1,500 - 2,000 lbs per acre
Remarks
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 3/4 - 1 inch clog hydromulch equipment. Fibers should be kept to less
than 3/4 inch.
Compost
Quality
Standards
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.
Application
Rates 2" thick min.; approx. 100 tons per acre (approx. 750 lbs per cubic yard)
Remarks
More effective control can be obtained by increasing thickness to 3". Excel-
lent mulch for protecting final grades until landscaping because it can be dir-
ectly seeded or tilled into soil as an amendment. Compost used for mulch
has a coarser size gradation than compost used for BMP C125: Topsoiling
/ Composting or BMP T5.13: Post-Construction Soil Quality and Depth. It
is more stable and practical to use in wet areas and during rainy weather
conditions. Do not use near wetlands or near phosphorous impaired water
bodies.
Chipped
Site Veget-
ation
Quality
Standards
Gradations from fines to 6 inches in length for texture, variation, and inter-
locking properties. Include a mix of various sizes so that the average size
is between 2- and 4- inches.
Application
Rates 2" thick min.;
Table II-3.6: Mulch Standards and Guidelines
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Mulch Mater-
ial Guideline Description
Remarks
This is a cost-effective way to dispose of debris from clearing and grub-
bing, 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 sur-
face waters. If permanent seeding or planting is expected shortly after
mulch, the decomposition of the chipped vegetation may tie up nutrients
important to grass establishment.
Note: thick application of this material over existing grass, herbaceous spe-
cies, and some groundcovers could smother and kill vegetation.
Wood-
Based
Mulch
Quality
Standards
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 reg-
ulations.
Application
Rates 2" thick min.; approx. 100 tons per acre (approx. 750 lbs. per cubic yard)
Remarks
This material is often called "wood straw" or "hog 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
Quality
Standards
A blend of loose, long, thin wood pieces derived from native conifer or
deciduous trees with high length-to-width ratio.
Application
Rates 2" thick min.
Remarks
Cost-effective protection when applied with adequate thickness. A min-
imum of 95-percent of the wood strand shall have lengths between 2 and
10-inches, with a width and thickness between 1/16 and 1/2-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. [Specification 9-14.4(4) from the Standard Specifications
for Road, Bridge, and Municipal Construction (WSDOT, 2016)
Table II-3.6: Mulch Standards and Guidelines (continued)
BMP C122: Nets and Blankets
Purpose
Erosion control nets and blankets are intended to prevent erosion and hold seed and mulch in place
on steep slopes and in channels so that vegetation can become well established. In addition, some
nets and blankets can be used to permanently reinforce turf to protect drainage ways during high
flows.
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Nets (commonly called matting) are strands of material woven into an open, but high-tensile strength
net (for example, coconut fiber matting). Blankets are strands of material that are not tightly woven,
but instead form a layer of interlocking fibers, typically held together by a biodegradable or pho-
todegradable netting (for example, excelsior or straw blankets). They generally have lower tensile
strength than nets, but cover the ground more completely. Coir (coconut fiber) fabric comes as both
nets and blankets.
Conditions of Use
Erosion control netting and blankets shall be made of natural plant fibers unaltered by synthetic
materials.
Erosion control nets and blankets should be used:
l To aid permanent vegetated stabilization of slopes 2H:1V or greater and with more than 10
feet of vertical relief.
l For drainage ditches and swales (highly recommended). The application of appropriate net-
ting or blanket to drainage ditches and swales can protect bare soil from channelized runoff
while vegetation is established. Nets and blankets also can capture a great deal of sediment
due to their open, porous structure. Nets and blankets can be used to permanently stabilize
channels and may provide a cost-effective, environmentally preferable alternative to riprap.
Disadvantages of nets and blankets include:
l Surface preparation is required.
l On slopes steeper than 2.5H:1V, net and blanket installers may need to be roped and har-
nessed for safety.
l They cost at least $4,000-6,000 per acre installed.
Advantages of nets and blankets include:
l Installation without mobilizing special equipment.
l Installation by anyone with minimal training
l Installation in stages or phases as the project progresses.
l Installers can hand place seed and fertilizer as they progress down the slope.
l Installation in any weather.
l There are numerous types of nets and blankets that can be designed with various parameters
in mind. Those parameters include: fiber blend, mesh strength, longevity, biodegradability,
cost, and availability.
An alternative to nets and blankets in some limited conditions is BMP C202: Riprap Channel Lining.
Ensure that BMP C202: Riprap Channel Lining is appropriate before using it as a substitute for nets
and blankets.
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Design and Installation Specifications
l See Figure II-3.3: Channel Installation (Clackamas County et al., 2008) and Figure II-3.4:
Slope Installation for typical orientation and installation of nets and blankets used in channels
and as slope protection. Note: these are typical only; all nets and blankets must be installed
per manufacturer’s installation instructions.
l Installation is critical to the effectiveness of these products. If good ground contact is not
achieved, runoff can concentrate under the product, resulting in significant erosion.
l Installation of nets and blankets on slopes:
1. Complete final grade and track walk up and down the slope.
2. Install hydromulch with seed and fertilizer.
3. Dig a small trench, approximately 12 inches wide by 6 inches deep along the top of the
slope.
4. Install the leading edge of the net/blanket into the small trench and staple approximately
every 18 inches. NOTE: Staples are metal, “U”-shaped, and a minimum of 6 inches
long. Longer staples are used in sandy soils. Biodegradable stakes are also available.
5. Roll the net/blanket slowly down the slope as the installer walks backward. NOTE: The
net/blanket rests against the installer’s legs. Staples are installed as the net/blanket is
unrolled. It is critical that the proper staple pattern is used for the net/blanket being
installed. The net/blanket is not to be allowed to roll down the slope on its own as this
stretches the net/blanket, making it impossible to maintain soil contact. In addition, no
one is allowed to walk on the net/blanket after it is in place.
6. If the net/blanket is not long enough to cover the entire slope length, the trailing edge of
the upper net/blanket should overlap the leading edge of the lower net/blanket and be
stapled. On steeper slopes, this overlap should be installed in a small trench, stapled,
and covered with soil.
l With the variety of products available, it is impossible to cover all the details of appropriate use
and installation. Therefore, it is critical that the designer consult the manufacturer's inform-
ation and that a site visit takes place in order to ensure that the product specified is appro-
priate. Information is also available in WSDOT's Standard Specifications for Road, Bridge,
and Municipal Construction Division 8-01 and Division 9-14 (WSDOT, 2016).
l Use jute matting in conjunction with mulch (BMP C121: Mulching). Excelsior, woven straw
blankets and coir (coconut fiber) blankets may be installed without mulch. There are many
other types of erosion control nets and blankets on the market that may be appropriate in cer-
tain circumstances.
l In general, most nets (e.g., jute matting) require mulch in order to prevent erosion because
they have a fairly open structure. Blankets typically do not require mulch because they usually
provide complete protection of the surface.
l Extremely steep, unstable, wet, or rocky slopes are often appropriate candidates for use of
synthetic blankets, as are riverbanks, beaches and other high-energy environments. If
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synthetic blankets are used, the soil should be hydromulched first.
l 100-percent biodegradable blankets are available for use in sensitive areas. These organic
blankets are usually held together with a paper or fiber mesh and stitching which may last up
to a year.
l Most netting used with blankets is photodegradable, meaning it breaks down under sunlight
(not UV stabilized). However, this process can take months or years even under bright sun.
Once vegetation is established, sunlight does not reach the mesh. It is not uncommon to find
non-degraded netting still in place several years after installation. This can be a problem if
maintenance requires the use of mowers or ditch cleaning equipment. In addition, birds and
small animals can become trapped in the netting.
Maintenance Standards
l Maintain good contact with the ground. Erosion must not occur beneath the net or blanket.
l Repair and staple any areas of the net or blanket that are damaged or not in close contact with
the ground.
l Fix and protect eroded areas if erosion occurs due to poorly controlled drainage.
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Figure II-3.3: Channel Installation
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Figure II-3.4: Slope Installation
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BMP C123: Plastic Covering
Purpose
Plastic covering provides immediate, short-term erosion protection to slopes and disturbed areas.
Conditions of Use
Plastic covering may be used on disturbed areas that require cover measures for less than 30 days,
except as stated below.
l Plastic is particularly useful for protecting cut and fill slopes and stockpiles. However, the rel-
atively rapid breakdown of most polyethylene sheeting makes it unsuitable for applications
greater than six months.
l Due to rapid runoff caused by plastic covering, do not use this method upslope of areas that
might be adversely impacted by concentrated runoff. Such areas include steep and/or
unstable slopes.
l Plastic sheeting may result in increased runoff volumes and velocities, requiring additional on-
site measures to counteract the increases. Creating a trough with wattles or other material
can convey clean water away from these areas.
l To prevent undercutting, trench and backfill rolled plastic covering products.
l Although the plastic material is inexpensive to purchase, the cost of installation, maintenance,
removal, and disposal add to the total costs of this BMP.
l Whenever plastic is used to protect slopes, install water collection measures at the base of the
slope. These measures include plastic-covered berms, channels, and pipes used to convey
clean rainwater away from bare soil and disturbed areas. Do not mix clean runoff from a
plastic covered slope with dirty runoff from a project.
l Other uses for plastic include:
o Temporary ditch liner.
o Pond liner in temporary sediment pond.
o Liner for bermed temporary fuel storage area if plastic is not reactive to the type of fuel
being stored.
o Emergency slope protection during heavy rains.
o Temporary drainpipe (“elephant trunk”) used to direct water.
Design and Installation Specifications
l Plastic slope cover must be installed as follows:
1. Run plastic up and down the slope, not across the slope.
2. Plastic may be installed perpendicular to a slope if the slope length is less than 10 feet.
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3.Provide a minimum of 8-inch overlap at the seams.
4.On long or wide slopes, or slopes subject to wind, tape all seams.
5.Place plastic into a small (12-inch wide by 6-inch deep) slot trench at the top of the slope
and backfill with soil to keep water from flowing underneath.
6.Place sand filled burlap or geotextile bags every 3 to 6 feet along seams and tie them
together with twine to hold them in place.
7.Inspect plastic for rips, tears, and open seams regularly and repair immediately. This
prevents high velocity runoff from contacting bare soil, which causes extreme erosion.
8.Sandbags may be lowered into place tied to ropes. However, all sandbags must be
staked in place.
l Plastic sheeting shall have a minimum thickness of 0.06 millimeters.
l If erosion at the toe of a slope is likely, a gravel berm, riprap, or other suitable protection shall
be installed at the toe of the slope in order to reduce the velocity of runoff.
Maintenance Standards
l Torn sheets must be replaced and open seams repaired.
l Completely remove and replace the plastic if it begins to deteriorate due to ultraviolet radi-
ation.
l Completely remove plastic when no longer needed.
l Dispose of old tires used to weight down plastic sheeting appropriately.
Approved as Functionally Equivalent
Ecology has approved products as able to meet the requirements of this BMP. The products did not
pass through the Technology Assessment Protocol – Ecology (TAPE) process. Local jurisdictions
may choose not to accept these products, or may require additional testing prior to consideration for
local use. Products that Ecology has approved as functionally equivalent are available for review on
Ecology’s website at:
https://ecology.wa.gov/Regulations-Permits/Guidance-technical-assistance/Stormwater-per-
mittee-guidance-resources/Emerging-stormwater-treatment-technologies
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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
Use dust control in areas (including roadways) subject to surface and air movement of dust where
on-site or off-site impacts to roadways, drainage ways, or surface waters are likely.
Design and Installation Specifications
l Vegetate or mulch areas that will not receive vehicle traffic. In areas where planting, mulching,
or paving is impractical, apply gravel or landscaping rock.
l Limit dust generation by clearing only those areas where immediate activity will take place,
leaving the remaining area(s) in the original condition. Maintain the original ground cover as
long as practical.
l Construct natural or artificial windbreaks or windscreens. These may be designed as enclos-
ures for small dust sources.
l Sprinkle the site with water until the surface is wet. Repeat as needed. To prevent carryout of
mud onto the street, refer to BMP C105: Stabilized Construction Access and BMP C106:
Wheel Wash.
l Irrigation water can be used for dust control. Irrigation systems should be installed as a first
step on sites where dust control is a concern.
l Spray exposed soil areas with a dust palliative, following the manufacturer’s instructions and
cautions regarding handling and application. Used oil is prohibited from use as a dust sup-
pressant. Local governments may approve other dust palliatives such as calcium chloride or
PAM.
l PAM (BMP C126: Polyacrylamide (PAM) for Soil Erosion Protection) added to water at a rate
of 0.5 pounds per 1,000 gallons of water per acre and applied from a water truck is more effect-
ive 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 trans-
ported by wind. Adding PAM may reduce the quantity of water needed for dust control. Note
that the application rate specified here applies to this BMP, and is not the same application
rate that is specified in BMP C126: Polyacrylamide (PAM) for Soil Erosion Protection, but the
downstream protections still apply.
Refer to BMP C126: Polyacrylamide (PAM) for Soil Erosion Protection for conditions of use.
PAM shall not be directly applied to water or allowed to enter a water body.
l Contact your local Air Pollution Control Authority for guidance and training on other dust con-
trol measures. Compliance with the local Air Pollution Control Authority constitutes
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compliance with this BMP.
l Use vacuum street sweepers.
l Remove mud and other dirt promptly so it does not dry and then turn into dust.
l Techniques that can be used for unpaved roads and lots include:
o Lower speed limits. High vehicle speed increases the amount of dust stirred up from
unpaved roads and lots.
o Upgrade the road surface strength by improving particle size, shape, and mineral types
that make up the surface and base materials.
o 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.
o Use geotextile fabrics to increase the strength of new roads or roads undergoing recon-
struction.
o Encourage the use of alternate, paved routes, if available.
o 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.
o Limit dust-causing work on windy days.
o Pave unpaved permanent roads and other trafficked areas.
Maintenance Standards
Respray area as necessary to keep dust to a minimum.
BMP C150: Materials on Hand
Purpose
Keep quantities of erosion prevention and sediment control materials on the project site at all times
to be used for regular maintenance and emergency situations such as unexpected heavy rains. Hav-
ing these materials on-site reduces the time needed to replace existing or implement new BMPs
when inspections indicate that existing BMPs are not meeting the Construction SWPPP require-
ments. In addition, contractors can save money by buying some materials in bulk and storing them at
their office or yard.
Conditions of Use
l 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
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pipe, sandbags, geotextile fabric and steel “T” posts.
l Materials should be stockpiled and readily available before any site clearing, grubbing, or
earthwork begins. A large contractor or project proponent could keep a stockpile of materials
that are available for use on several projects.
l 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.
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:
l Clear Plastic, 6 mil
l Drainpipe, 6 or 8 inch diameter
l Sandbags, filled
l Straw Bales for mulching
l Quarry Spalls
l Washed Gravel
l Geotextile Fabric
l Catch Basin Inserts
l Steel "T" Posts
l Silt fence material
l Straw Wattles
Maintenance Standards
l 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.
l Re-stock materials 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 dis-
charge to waters of the State is prohibited. Use this BMP to minimize and eliminate concrete, con-
crete process water, and concrete slurry from entering waters of the State.
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Conditions of Use
Any time concrete is used, utilize these management practices. Concrete construction project com-
ponents include, but are not limited to:
l Curbs
l Sidewalks
l Roads
l Bridges
l Foundations
l Floors
l Runways
Disposal options for concrete, in order of preference are:
1. Off-site disposal
2. Concrete wash-out areas (see BMP C154: Concrete Washout Area)
3. De minimus washout to formed areas awaiting concrete
Design and Installation Specifications
l Wash concrete truck drums at an approved off-site location or in designated concrete
washout areas only. Do not wash out concrete trucks onto the ground (including formed areas
awaiting concrete), or into storm drains, open ditches, streets, or streams. Refer to BMP
C154: Concrete Washout Area for information on concrete washout areas.
o 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 as allowed in BMP C154: Concrete Washout Area.
l Wash small concrete handling equipment (e.g. hand tools, screeds, shovels, rakes, floats,
trowels, and wheelbarrows) into designated concrete washout areas or into formed areas
awaiting concrete pour.
l At no time shall concrete be washed off into the footprint of an area where an infiltration fea-
ture will be installed.
l Wash equipment difficult to move, such as concrete paving machines, in areas that do not dir-
ectly drain to natural or constructed stormwater conveyance or potential infiltration areas.
l Do not allow washwater from areas, such as concrete aggregate driveways, to drain directly
(without detention or treatment) to natural or constructed stormwater conveyances.
l Contain washwater and leftover product in a lined container when no designated concrete
washout areas (or formed areas, allowed as described above) are available. Dispose of con-
tained concrete and concrete washwater (process water) properly.
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l Always use forms or solid barriers for concrete pours, such as pilings, within 15-feet of surface
waters.
l Refer to BMP C252: Treating and Disposing of High pH Water for pH adjustment require-
ments.
l Refer to the Construction Stormwater General Permit (CSWGP) for pH monitoring require-
ments if the project involves one of the following activities:
o Significant concrete work (as defined in the CSWGP).
o The use of soils amended with (but not limited to) Portland cement-treated base,
cement kiln dust or fly ash.
o Discharging stormwater to segments of water bodies on the 303(d) list (Category 5) for
high pH.
Maintenance Standards
Check containers for holes in the liner daily during concrete pours and repair the same day.
BMP C152: Sawcutting and Surfacing Pollution
Prevention
Purpose
Sawcutting and surfacing operations generate slurry and process water that contains fine particles
and high pH (concrete cutting), both of which can violate the water quality standards in the receiving
water. Concrete spillage or concrete discharge to waters of the State is prohibited. Use this BMP to
minimize and eliminate process water and slurry created through sawcutting or surfacing from enter-
ing waters of the State.
Conditions of Use
Utilize these management practices anytime sawcutting or surfacing operations take place. Saw-
cutting and surfacing operations include, but are not limited to:
l Sawing
l Coring
l Grinding
l Roughening
l Hydro-demolition
l Bridge and road surfacing
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Design and Installation Specifications
l Vacuum slurry and cuttings during cutting and surfacing operations.
l Slurry and cuttings shall not remain on permanent concrete or asphalt pavement overnight.
l Slurry and cuttings shall not drain to any natural or constructed drainage conveyance includ-
ing stormwater systems. This may require temporarily blocking catch basins.
l Dispose of collected slurry and cuttings in a manner that does not violate ground water or sur-
face water quality standards.
l Do not allow process water generated during hydro-demolition, surface roughening or similar
operations to drain to any natural or constructed drainage conveyance including stormwater
systems. Dispose of process water in a manner that does not violate ground water or surface
water quality standards.
l Handle and dispose of cleaning waste material and demolition debris in a manner that does
not cause contamination of water. Dispose of sweeping material from a pick-up sweeper at an
appropriate disposal site.
Maintenance Standards
Continually monitor operations to determine whether slurry, cuttings, or process water could enter
waters of the state. If inspections show that a violation of water quality standards could occur, stop
operations and immediately implement preventive measures such as berms, barriers, secondary
containment, and/or vacuum trucks.
BMP C153: Material Delivery, Storage, and
Containment
Purpose
Prevent, reduce, or eliminate the discharge of pollutants to the stormwater system or watercourses
from material delivery and storage. Minimize the storage of hazardous materials on-site, store mater-
ials in a designated area, and install secondary containment.
Conditions of Use
Use at construction sites with delivery and storage of the following materials:
l Petroleum products such as fuel, oil and grease
l Soil stabilizers and binders (e.g., Polyacrylamide)
l Fertilizers, pesticides and herbicides
l Detergents
l Asphalt and concrete compounds
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l Hazardous chemicals such as acids, lime, adhesives, paints, solvents, and curing compounds
l Any other material that may be detrimental if released to the environment
Design and Installation Specifications
l The temporary storage area should be located away from vehicular traffic, near the con-
struction entrance(s), and away from waterways or storm drains.
l Safety Data Sheets (SDS) should be supplied for all materials stored. Chemicals should be
kept in their original labeled containers.
l Hazardous material storage on-site should be minimized.
l Hazardous materials should be handled as infrequently as possible.
l During the wet weather season (Oct 1 – April 30), consider storing materials in a covered
area.
l Materials should be stored in secondary containments, such as an 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 con-
crete mixing trays.
l Do not store chemicals, drums, or bagged materials directly on the ground. Place these items
on a pallet and, when possible, within secondary containment.
l If drums must be kept uncovered, store them at a slight angle to reduce ponding of rainwater
on the lids to reduce corrosion. Domed plastic covers are inexpensive and snap to the top of
drums, preventing water from collecting.
l Liquids, petroleum products, and substances listed in 40 CFR Parts 110, 117, or 302 shall be
stored in approved containers and drums and shall not be overfilled. Containers and drums
shall be stored in temporary secondary containment facilities.
l 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 capa-
city of the largest container within its boundary, whichever is greater.
l Secondary containment facilities shall be impervious to the materials stored therein for a min-
imum contact time of 72 hours.
l Sufficient separation should be provided between stored containers to allow for spill cleanup
and emergency response access.
l During the wet weather season (Oct 1 – April 30), each secondary containment facility shall
be covered during non-working days, prior to and during rain events.
l Keep material storage areas clean, organized and equipped with an ample supply of appro-
priate spill clean-up material (spill kit).
l The spill kit should include, at a minimum:
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o 1-Water Resistant Nylon Bag
o 3-Oil Absorbent Socks 3”x 4’
o 2-Oil Absorbent Socks 3”x 10’
o 12-Oil Absorbent Pads 17”x19”
o 1-Pair Splash Resistant Goggles
o 3-Pair Nitrile Gloves
o 10-Disposable Bags with Ties
o Instructions
Maintenance Standards
l 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.
l Re-stock spill kit materials as needed.
BMP C154: Concrete Washout Area
Purpose
Prevent or reduce the discharge of pollutants from concrete waste to stormwater by conducting
washout off-site, or performing on-site washout in a designated area.
Conditions of Use
Concrete washout areas are implemented on construction projects where:
l Concrete is used as a construction material
l It is not possible to dispose of all concrete wastewater and washout off-site (ready mix plant,
etc.).
l Concrete truck drums are washed on-site.
Note that auxiliary concrete truck components (e.g. chutes and hoses) and small concrete
handling equipment (e.g. hand tools, screeds, shovels, rakes, floats, trowels, and wheel-
barrows) may be washed into formed areas awaiting concrete pour.
At no time shall concrete be washed off into the footprint of an area where an infiltration feature will
be installed.
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Design and Installation Specifications
Implementation
l Perform washout of concrete truck drums at an approved off-site location or in designated con-
crete washout areas only.
l Do not wash out concrete onto non-formed areas, or into storm drains, open ditches, streets,
or streams.
l Wash equipment difficult to move, such as concrete paving machines, in areas that do not dir-
ectly drain to natural or constructed stormwater conveyance or potential infiltration areas.
l Do not allow excess concrete to be dumped on-site, except in designated concrete washout
areas as allowed above.
l Concrete washout areas may be prefabricated concrete washout containers, or self-installed
structures (above-grade or below-grade).
l 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.
l 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.
l Self-installed above-grade structures should only be used if excavation is not practical.
l Concrete washout areas shall be constructed and maintained in sufficient quantity and size to
contain all liquid and concrete waste generated by washout operations.
Education
l Discuss the concrete management techniques described in this BMP with the ready-mix con-
crete supplier before any deliveries are made.
l Educate employees and subcontractors on the concrete waste management techniques
described in this BMP.
l Arrange for the contractor’s superintendent or Certified Erosion and Sediment Control Lead
(CESCL) to oversee and enforce concrete waste management procedures.
l A sign should be installed adjacent to each concrete washout area to inform concrete equip-
ment operators to utilize the proper facilities.
Contracts
Incorporate requirements for concrete waste management into concrete supplier and subcontractor
agreements.
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Location and Placement
l Locate concrete washout areas at least 50 feet from sensitive areas such as storm drains,
open ditches, water bodies, or wetlands.
l Allow convenient access to the concrete washout area for concrete trucks, preferably near the
area where the concrete is being poured.
l If trucks need to leave a paved area to access the concrete washout area, prevent track-out
with a pad of rock or quarry spalls (see BMP C105: Stabilized Construction Access). These
areas should be far enough away from other construction traffic to reduce the likelihood of acci-
dental damage and spills.
l The number of concrete washout areas you install should depend on the expected demand
for storage capacity.
l On large sites with extensive concrete work, concrete washout areas should be placed in mul-
tiple locations for ease of use by concrete truck drivers.
Concrete Truck Washout Procedures
l Washout of concrete truck drums shall be performed in designated concrete washout areas
only.
l Concrete washout from concrete pumper bins can be washed into concrete pumper trucks
and discharged into designated concrete washout areas or properly disposed of off-site.
Concrete Washout Area Installation
l Concrete washout areas should be constructed as shown in the figures below, with a recom-
mended minimum length and minimum width of 10 ft, but with sufficient quantity and volume to
contain all liquid and concrete waste generated by washout operations.
l 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.
l Lath and flagging should be commercial type.
l Liner seams shall be installed in accordance with manufacturers’ recommendations.
l 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
l Inspect and verify that concrete washout areas are in place prior to the commencement of con-
crete work.
l Once concrete wastes are washed into the designated washout area and allowed to harden,
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the concrete should be broken up, removed, and disposed of per applicable solid waste reg-
ulations. Dispose of hardened concrete on a regular basis.
l During periods of concrete work, inspect the concrete washout areas daily to verify continued
performance.
o Check overall condition and performance.
o Check remaining capacity (% full).
o If using self-installed concrete washout areas, verify plastic liners are intact and side-
walls are not damaged.
o If using prefabricated containers, check for leaks.
l Maintain the concrete washout areas to provide adequate holding capacity with a minimum
freeboard of 12 inches.
l Concrete washout areas must be cleaned, or new concrete washout areas must be con-
structed and ready for use once the concrete washout area is 75% full.
l If the concrete washout area is nearing capacity, vacuum and dispose of the waste material in
an approved manner.
l Do not discharge liquid or slurry to waterways, storm drains or directly onto ground.
l Do not discharge to the sanitary sewer without local approval.
l Place a secure, non-collapsing, non-water collecting cover over the concrete washout
area prior to predicted wet weather to prevent accumulation and overflow of pre-
cipitation.
l Remove and dispose of hardened concrete and return the structure to a functional con-
dition. Concrete may be reused on-site or hauled away for disposal or recycling.
l When you remove materials from a self-installed concrete washout area, build a new struc-
ture; or, if the previous structure is still intact, inspect for signs of weakening or damage, and
make any necessary repairs. Re-line the structure with new plastic after each cleaning.
Removal of Concrete Washout Areas
l When concrete washout areas are no longer required for the work, the hardened concrete,
slurries and liquids shall be removed and properly disposed of.
l Materials used to construct concrete washout areas shall be removed from the site of the work
and disposed of or recycled.
l Holes, depressions or other ground disturbance caused by the removal of the concrete
washout areas shall be backfilled, repaired, and stabilized to prevent erosion.
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Figure II-3.7: Concrete Washout Area with Wood Planks
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Figure II-3.8: Concrete Washout Area with Straw Bales
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Figure II-3.9: Prefabricated Concrete Washout Container w/Ramp
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BMP C160: Certified Erosion and Sediment Control
Lead
Purpose
The project proponent designates at least one person as the responsible representative in charge of
erosion and sediment control (ESC), and water quality protection. The designated person shall be
responsible for ensuring compliance with all local, state, and federal erosion and sediment control
and water quality requirements. Construction sites one acre or larger that discharge to waters of the
State must designate a Certified Erosion and Sediment Control Lead (CESCL) as the responsible
representative.
Conditions of Use
A CESCL shall be made available on projects one acre or larger that discharge stormwater to sur-
face waters of the state. Sites less than one acre may have a person without CESCL certification
conduct inspections.
The CESCL shall:
l Have a current certificate proving attendance in an erosion and sediment control training
course that meets the minimum ESC training and certification requirements established by
Ecology.
Ecology has provided the minimum requirements for CESCL course training, as well as a list
of ESC training and certification providers at:
https://ecology.wa.gov/Regulations-Permits/Permits-certifications/Certified-erosion-sed-
iment-control
OR
l Be a Certified Professional in Erosion and Sediment Control (CPESC). For additional inform-
ation go to:
http://www.envirocertintl.org/cpesc/
Specifications
l CESCL certification shall remain valid for three years.
l The CESCL shall have authority to act on behalf of the contractor or project proponent and
shall be available, or on-call, 24 hours per day throughout the period of construction.
l The Construction SWPPP shall include the name, telephone number, fax number, and
address of the designated CESCL. See II-2 Construction Stormwater Pollution Prevention
Plans (Construction SWPPPs).
l A CESCL may provide inspection and compliance services for multiple construction projects
in the same geographic region, but must be on site whenever earthwork activities are
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occurring that could generate release of turbid water.
l Duties and responsibilities of the CESCL shall include, but are not limited to the following:
o Maintaining a permit file on site at all times which includes the Construction SWPPP
and any associated permits and plans.
o Directing BMP installation, inspection, maintenance, modification, and removal.
o Updating all project drawings and the Construction SWPPP with changes made.
o Completing any sampling requirements including reporting results using electronic Dis-
charge Monitoring Reports (WebDMR).
o Facilitate, participate in, and take corrective actions resulting from inspections per-
formed by outside agencies or the owner.
o Keeping daily logs, and inspection reports. Inspection reports should include:
n Inspection date/time.
n Weather information; general conditions during inspection and approximate
amount of precipitation since the last inspection.
n Visual monitoring results, including a description of discharged stormwater. The
presence of suspended sediment, turbid water, discoloration, and oil sheen shall
be noted, as applicable.
n Any water quality monitoring performed during inspection.
n General comments and notes, including a brief description of any BMP repairs,
maintenance or installations made as a result of the inspection.
n A summary or list of all BMPs implemented, including observations of all
erosion/sediment control structures or practices. The following shall be noted:
1. Locations of BMPs inspected.
2. Locations of BMPs that need maintenance.
3. Locations of BMPs that failed to operate as designed or intended.
4. Locations of where additional or different BMPs are required.
BMP C162: Scheduling
Purpose
Sequencing a construction project reduces the amount and duration of soil exposed to erosion by
wind, rain, runoff, and vehicle tracking.
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Conditions of Use
The construction sequence schedule is an orderly listing of all major land-disturbing activities
together with the necessary erosion and sedimentation control measures planned for the project.
This type of schedule guides the contractor on work to be done before other work is started so that
serious erosion and sedimentation problems can be avoided.
Following a specified work schedule that coordinates the timing of land-disturbing activities and the
installation of control measures is perhaps the most cost-effective way of controlling erosion during
construction. The removal of ground cover leaves a site vulnerable to erosion. Construction sequen-
cing that limits land clearing, provides timely installation of erosion and sedimentation controls, and
restores protective cover quickly can significantly reduce the erosion potential of a site.
Design Considerations
l Minimize construction during rainy periods.
l Schedule projects to disturb only small portions of the site at any one time. Complete grading
as soon as possible. Immediately stabilize the disturbed portion before grading the next por-
tion. Practice staged seeding in order to revegetate cut and fill slopes as the work progresses.
II-3.3 Construction Runoff BMPs
BMP C200: Interceptor Dike and Swale
Purpose
Provide a dike of compacted soil or a swale at the top or base of a disturbed slope or along the peri-
meter 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 con-
struction site.
Conditions of Use
Use an interceptor dike or swale where runoff from an exposed site or disturbed slope must be con-
veyed to an erosion control BMP which can safely convey the stormwater.
l Locate upslope of a construction site to prevent runoff from entering the disturbed area.
l When placed horizontally across a disturbed slope, it reduces the amount and velocity of run-
off flowing down the slope.
l Locate downslope to collect runoff from a disturbed area and direct it to a sediment BMP (e.g.
BMP C240: Sediment Trap or BMP C241: Sediment Pond (Temporary)).
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Design and Installation Specifications
l Dike and/or swale and channel must be stabilized with temporary or permanent vegetation or
other channel protection during construction.
l Steep grades require channel protection and check dams.
l Review construction for areas where overtopping may occur.
l Can be used at the top of new fill before vegetation is established.
l May be used as a permanent diversion channel to carry the runoff.
l Contributing area for an individual dike or swale should be one acre or less.
l Design the dike and/or swale to contain flows calculated by one of the following methods:
o Single Event Hydrograph Method: The peak volumetric flow rate calculated using a 10-
minute time step from a Type 1A, 10-year, 24-hour frequency storm for the worst-case
land cover condition.
OR
o Continuous Simulation Method: The 10-year peak flow rate, as determined by an
approved continuous runoff model with a 15-minute time step for the worst-case land
cover condition.
Worst-case land cover conditions (i.e., producing the most runoff) should be used for analysis
(in most cases, this would be the land cover conditions just prior to final landscaping).
Interceptor Dikes
Interceptor dikes shall meet the following criteria:
l Top Width: 2 feet minimum.
l Height: 1.5 feet minimum on berm.
l Side Slope: 2H:1V or flatter.
l Grade: Depends on topography, however, dike system minimum is 0.5%, and maximum is
1%.
l Compaction: Minimum of 90 percent ASTM D698 standard proctor.
l Stabilization: Depends on velocity and reach. Inspect regularly to ensure stability.
l Ground Slopes <5%: Seed and mulch applied within 5 days of dike construction (see BMP
C121: Mulching).
l Ground Slopes 5 - 40%: Dependent on runoff velocities and dike materials. Stabilization
should be done immediately using either sod or riprap, or other measures to avoid erosion.
l The upslope side of the dike shall provide positive drainage to the dike outlet. No erosion shall
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occur at the outlet. Provide energy dissipation measures as necessary. Sediment-laden runoff
must be released through a sediment trapping facility.
l Minimize construction traffic over temporary dikes. Use temporary cross culverts for channel
crossing.
l See Table II-3.8: Horizontal Spacing of Interceptor Dikes Along Ground Slope for recom-
mended horizontal spacing between 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
Table II-3.8: Horizontal Spacing of
Interceptor Dikes Along Ground
Slope
Interceptor Swales
Interceptor swales shall meet the following criteria:
l Bottom Width: 2 feet minimum; the cross-section bottom shall be level.
l Depth: 1-foot minimum.
l Side Slope: 2H:1V or flatter.
l Grade: Maximum 5 percent, with positive drainage to a suitable outlet (such as BMP C241:
Sediment Pond (Temporary)).
l Stabilization: Seed as per BMP C120: Temporary and Permanent Seeding, or BMP C202:
Riprap Channel Lining, 12 inches thick riprap pressed into the bank and extending at least 8
inches vertical from the bottom.
Maintenance Standards
l Inspect diversion dikes and interceptor swales once a week and after every rainfall. Imme-
diately remove sediment from the flow area.
l Damage caused by construction traffic or other activity must be repaired before the end of
each working day.
l 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 sta-
bilize the channel to blend with the natural surface.
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BMP C202: Riprap Channel Lining
Purpose
To protect channels by providing a channel liner using riprap.
Conditions of Use
Use this BMP when natural soils or vegetated stabilized soils in a channel are not adequate to pre-
vent channel erosion.
Use this BMP when a permanent ditch or pipe system is to be installed and a temporary measure is
needed.
An alternative to riprap channel lining is BMP C122: Nets and Blankets.
The Federal Highway Administration recommends not using geotextile liners whenever the slope
exceeds 10 percent or the shear stress exceeds 8 lbs/ft2.
Design and Installation Specifications
l Since riprap is typically used where erosion potential is high, construction must be sequenced
so that the riprap is put in place with the minimum possible delay.
l Disturb areas awaiting riprap only when final preparation and placement of the riprap can fol-
low immediately behind the initial disturbance. Where riprap is used for outlet protection, the
riprap should be placed before or in conjunction with the construction of the pipe or channel so
that it is in place when the pipe or channel begins to operate.
l The designer, after determining the riprap size that will be stable under the flow conditions,
shall consider that size to be a minimum size and then, based on riprap gradations actually
available in the area, select the size or sizes that equal or exceed the minimum size. The pos-
sibility of drainage structure damage by others shall be considered in selecting a riprap size,
especially if there is nearby water or a gully in which to toss the stones.
l Stone for riprap shall consist of field stone or quarry stone of approximately rectangular
shape. The stone shall be hard and angular and of such quality that it will not disintegrate on
exposure to water or weathering and it shall be suitable in all respects for the purpose inten-
ded. See Section 9-13 of WSDOT's Standard Specifications for Road, Bridge, and Municipal
Construction (WSDOT, 2016).
l A lining of engineering filter fabric (geotextile) shall be placed between the riprap and the
underlying soil surface to prevent soil movement into or through the riprap. The geotextile
should be keyed in at the top of the bank.
l Filter fabric shall not be used on slopes greater than 1.5H:1V as slippage may occur. It should
be used in conjunction with a layer of coarse aggregate (granular filter blanket) when the
riprap to be placed is 12 inches and larger.
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Maintenance Standards
Replace riprap as needed.
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BMP C207: Check Dams
Purpose
Construction of check dams across a swale or ditch reduces the velocity of concentrated flow and dis-
sipates energy at the check dam.
Conditions of Use
Use check dams where temporary or permanent channels are not yet vegetated, channel lining is
infeasible, and/or velocity checks are required.
l Check dams may not be placed in streams unless approved by the State Department of Fish
and Wildlife.
l Check dams may not be placed in wetlands without approval from a permitting agency.
l 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.
Design and Installation Specifications
l 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 (do not dump the rock to form the dam) to achieve
complete coverage of the ditch or swale and to ensure that the center of the dam is lower than
the edges.
l 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.
l Place check dams perpendicular to the flow of water.
l The check dam should form a triangle when viewed from the side. This prevents undercutting
as water flows over the face of the check dam rather than falling directly onto the ditch bottom.
l Before installing check dams, impound and bypass upstream water flow away from the work
area. Options for bypassing include pumps, siphons, or temporary channels.
l Check dams combined with sumps work more effectively at slowing flow and retaining sed-
iment than a check dam alone. A deep sump should be provided immediately upstream of the
check dam.
l In some cases, if carefully located and designed, check dams can remain as permanent install-
ations with very minor regrading. They may be left as either spillways, in which case accu-
mulated sediment would be graded and seeded, or as check dams to prevent further
sediment from leaving the site.
l The maximum spacing between check dams shall be such that the downstream toe of the
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upstream dam is at the same elevation as the top of the downstream dam.
l Keep the maximum height at 2 feet at the center of the check dam.
l Keep the center of the check dam at least 12 inches lower than the outer edges at natural
ground elevation.
l Keep the side slopes of the check dam at 2H:1V or flatter.
l 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.
l 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.
l 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.
l Ensure that channel appurtenances, such as culvert entrances below check dams, are not
subject to damage or blockage from displaced stones.
l See Figure II-3.16: Rock Check Dam.
Maintenance Standards
Check dams shall be monitored for performance and sediment accumulation during and after each
rainfall that produces runoff. Sediment shall be removed when it reaches one half the sump depth.
l Anticipate submergence and deposition above the check dam and erosion from high flows
around the edges of the dam.
l If significant erosion occurs between dams, install a protective riprap liner in that portion of the
channel. See BMP C202: Riprap Channel Lining.
Approved as Functionally Equivalent
Ecology has approved products as able to meet the requirements of this BMP. The products did not
pass through the Technology Assessment Protocol – Ecology (TAPE) process. Local jurisdictions
may choose not to accept these products, or may require additional testing prior to consideration for
local use. Products that Ecology has approved as functionally equivalent are available for review on
Ecology’s website at:
https://ecology.wa.gov/Regulations-Permits/Guidance-technical-assistance/Stormwater-per-
mittee-guidance-resources/Emerging-stormwater-treatment-technologies
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Figure II-3.16: Rock Check Dam
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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
Use outlet protection at the outlets of all ponds, pipes, ditches, or other conveyances that discharge
to a natural or manmade drainage feature such as a stream, wetland, lake, or ditch.
Design and Installation Specifications
l The receiving channel at the outlet of a pipe shall be protected from erosion by lining a min-
imum of 6 feet downstream and extending up the channel sides a minimum of 1–foot above
the maximum tailwater elevation, or 1-foot above the crown, whichever is higher. For pipes lar-
ger than 18 inches in diameter, the outlet protection lining of the channel shall be four times
the diameter of the outlet pipe.
l Standard wingwalls, tapered outlets, and paved channels should also be considered when
appropriate for permanent culvert outlet protection (WSDOT, 2015).
l BMP C122: Nets and Blankets or BMP C202: Riprap Channel Lining provide suitable options
for lining materials.
l With low flows, BMP C201: Grass-Lined Channels can be an effective alternative for lining
material.
l The following guidelines shall be used for outlet protection with riprap:
o If the discharge velocity at the outlet is less than 5 fps, use 2-inch to 8-inch riprap. Min-
imum thickness is 1-foot.
o For 5 to 10 fps discharge velocity at the outlet, use 24-inch to 48-inch riprap. Minimum
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thickness is 2 feet.
o For outlets at the base of steep slope pipes (pipe slope greater than 10 percent), use an
engineered energy dissipator.
o Filter fabric or erosion control blankets should always be used under riprap to prevent
scour and channel erosion. See BMP C122: Nets and Blankets.
l Bank stabilization, bioengineering, and habitat features may be required for disturbed areas.
This work may require a Hydraulic Project Approval (HPA) from the Washington State Depart-
ment of Fish and Wildlife. See I-2.11 Hydraulic Project Approvals.
Maintenance Standards
l Inspect and repair as needed.
l Add rock as needed to maintain the intended function.
l Clean energy dissipator if sediment builds up.
BMP C220: Inlet Protection
Purpose
Inlet protection prevents coarse sediment from entering drainage systems prior to permanent sta-
bilization of the disturbed area.
Conditions of Use
Use inlet protection at inlets that are operational before permanent stabilization of the disturbed
areas that contribute runoff to the inlet. Provide protection for all storm drain inlets downslope and
within 500 feet of a disturbed or construction area, unless those inlets are preceded by a sediment
trapping BMP.
Also consider inlet protection for lawn and yard drains on new home construction. These small and
numerous drains coupled with lack of gutters can add significant amounts of sediment into the roof
drain system. If possible, delay installing lawn and yard drains until just before landscaping, or cap
these drains to prevent sediment from entering the system until completion of landscaping. Provide
18-inches of sod around each finished lawn and yard drain.
Table II-3.10: Storm Drain Inlet Protection lists several options for inlet protection. All of the methods
for inlet protection tend to plug and require a high frequency of maintenance. Limit contributing drain-
age areas for an individual inlet to one acre or less. If possible, provide emergency overflows with
additional end-of-pipe treatment where stormwater ponding would cause a hazard.
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Type of Inlet Pro-
tection
Emergency
Overflow
Applicable for
Paved/ Earthen Sur-
faces
Conditions of Use
Drop Inlet Protection
Excavated drop
inlet protection
Yes, temporary
flooding may
occur
Earthen
Applicable for heavy flows. Easy
to maintain. Large area requirement:
30'x30'/acre
Block and gravel
drop inlet pro-
tection
Yes Paved or Earthen Applicable for heavy concentrated flows.
Will not pond.
Gravel and wire
drop inlet pro-
tection
No Paved or Earthen 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 pro-
tection with
wooden weir
Small capacity
overflow Paved Used for sturdy, more compact install-
ation.
Block and gravel
curb inlet pro-
tection
Yes Paved Sturdy, but limited filtration.
Culvert Inlet Protection
Culvert inlet sed-
iment trap N/A N/A 18 month expected life.
Table II-3.10: Storm Drain Inlet Protection
Design and Installation Specifications
Excavated Drop Inlet Protection
Excavated drop inlet protection consists of an excavated impoundment around the storm drain inlet.
Sediment settles out of the stormwater prior to entering the storm drain. Design and installation spe-
cifications for excavated drop inlet protection include:
l Provide a depth of 1-2 ft as measured from the crest of the inlet structure.
l Slope sides of excavation should be no steeper than 2H:1V.
l Minimum volume of excavation is 35 cubic yards.
l Shape the excavation to fit the site, with the longest dimension oriented toward the longest
inflow area.
l Install provisions for draining to prevent standing water.
l Clear the area of all debris.
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l Grade the approach to the inlet uniformly.
l Drill weep holes into the side of the inlet.
l Protect weep holes with screen wire and washed aggregate.
l Seal weep holes when removing structure and stabilizing area.
l Build a temporary dike, if necessary, to the down slope side of the structure to prevent bypass
flow.
Block and Gravel Filter
A block and gravel filter is a barrier formed around the inlet with standard concrete blocks and gravel.
See Figure II-3.17: Block and Gravel Filter. Design and installation specifications for block gravel fil-
ters include:
l Provide a height of 1 to 2 feet above the inlet.
l Recess the first row of blocks 2-inches into the ground for stability.
l Support subsequent courses by placing a pressure treated wood 2x4 through the block open-
ing.
l Do not use mortar.
l Lay some blocks in the bottom row on their side to allow for dewatering the pool.
l Place hardware cloth or comparable wire mesh with ½-inch openings over all block openings.
l Place gravel to just below the top of blocks on slopes of 2H:1V or flatter.
l An alternative design is a gravel berm surrounding the inlet, as follows:
o Provide a slope of 3H:1V on the upstream side of the berm.
o Provide a slope of 2H:1V on the downstream side of the berm.
o Provide a 1-foot wide level stone area between the gravel berm and the inlet.
o Use stones 3 inches in diameter or larger on the upstream slope of the berm.
o Use gravel ½- to ¾-inch at a minimum thickness of 1-foot on the downstream slope of
the berm.
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Figure II-3.17: Block and Gravel Filter
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Gravel and Wire Mesh Filter
Gravel and wire mesh filters are gravel barriers placed over the top of the inlet. This method does not
provide an overflow. Design and installation specifications for gravel and wire mesh filters include:
l Use a hardware cloth or comparable wire mesh with ½-inch openings.
o Place wire mesh over the drop inlet so that the wire extends a minimum of 1-foot bey-
ond each side of the inlet structure.
o Overlap the strips if more than one strip of mesh is necessary.
l Place coarse aggregate over the wire mesh.
o Provide at least a 12-inch depth of aggregate over the entire inlet opening and extend at
least 18-inches on all sides.
Catch Basin Filters
Catch basin filters are designed by manufacturers for construction sites. The limited sediment stor-
age capacity increases the amount of inspection and maintenance required, which may be daily for
heavy sediment loads. To reduce maintenance requirements, combine a catch basin filter with
another type of inlet protection. This type of inlet protection provides flow bypass without overflow
and therefore may be a better method for inlets located along active rights-of-way. Design and install-
ation specifications for catch basin filters include:
l Provides 5 cubic feet of storage.
l Requires dewatering provisions.
l Provides a high-flow bypass that will not clog under normal use at a construction site.
l Insert the catch basin filter in the catch basin just below the grating.
Curb Inlet Protection with Wooden Weir
Curb inlet protection with wooden weir is an option that consists of a barrier formed around a curb
inlet with a wooden frame and gravel. Design and installation specifications for curb inlet protection
with wooden weirs include:
l Use wire mesh with ½-inch openings.
l Use extra strength filter cloth.
l Construct a frame.
l Attach the wire and filter fabric to the frame.
l Pile coarse washed aggregate against the wire and fabric.
l Place weight on the frame anchors.
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Block and Gravel Curb Inlet Protection
Block and gravel curb inlet protection is a barrier formed around a curb inlet with concrete blocks and
gravel. See Figure II-3.18: Block and Gravel Curb Inlet Protection. Design and installation spe-
cifications for block and gravel curb inlet protection include:
l Use wire mesh with ½-inch openings.
l Place two concrete blocks on their sides abutting the curb at either side of the inlet opening.
These are spacer blocks.
l Place a 2x4 stud through the outer holes of each spacer block to align the front blocks.
l Place blocks on their sides across the front of the inlet and abutting the spacer blocks.
l Place wire mesh over the outside vertical face.
l Pile coarse aggregate against the wire to the top of the barrier.
2019 Stormwater Management Manual for Western Washington
Volume II -Chapter 3 -Page 361
Figure II-3.18: Block and Gravel Curb Inlet Protection
2019 Stormwater Management Manual for Western Washington
Volume II -Chapter 3 -Page 362
Curb and Gutter Sediment Barrier
Curb and gutter sediment barrier is a sandbag or rock berm (riprap and aggregate) 3 feet high and 3
feet wide in a horseshoe shape. See Figure II-3.19: Curb and Gutter Barrier. Design and installation
specifications for curb and gutter sediment barrier include:
l Construct a horseshoe shaped berm, faced with coarse aggregate if using riprap, 3 feet high
and 3 feet wide, at least 2 feet from the inlet.
l Construct a horseshoe shaped sedimentation trap on the upstream side of the berm. Size the
trap to sediment trap standards for protecting a culvert inlet.
2019 Stormwater Management Manual for Western Washington
Volume II -Chapter 3 -Page 363
Figure II-3.19: Curb and Gutter Barrier
2019 Stormwater Management Manual for Western Washington
Volume II -Chapter 3 -Page 364
Maintenance Standards
l Inspect all forms of inlet protection frequently, especially after storm events. Clean and
replace clogged catch basin filters. For rock and gravel filters, pull away the rocks from the
inlet and clean or replace. An alternative approach would be to use the clogged rock as fill and
put fresh rock around the inlet.
l Do not wash sediment into storm drains while cleaning. Spread all excavated material evenly
over the surrounding land area or stockpile and stabilize as appropriate.
Approved as Functionally Equivalent
Ecology has approved products as able to meet the requirements of this BMP. The products did not
pass through the Technology Assessment Protocol – Ecology (TAPE) process. Local jurisdictions
may choose not to accept these products, or may require additional testing prior to consideration for
local use. Products that Ecology has approved as functionally equivalent are available for review on
Ecology’s website at:
https://ecology.wa.gov/Regulations-Permits/Guidance-technical-assistance/Stormwater-per-
mittee-guidance-resources/Emerging-stormwater-treatment-technologies
2019 Stormwater Management Manual for Western Washington
Volume II -Chapter 3 -Page 365
BMP C233: Silt Fence
Purpose
Silt fence reduces the transport of coarse sediment from a construction site by providing a temporary
physical barrier to sediment and reducing the runoff velocities of overland flow.
Conditions of Use
Silt fence may be used downslope of all disturbed areas.
l Silt fence shall prevent sediment carried by runoff from going beneath, through, or over the
top of the silt fence, but shall allow the water to pass through the fence.
l Silt fence is not intended to treat concentrated flows, nor is it intended to treat substantial
amounts of overland flow. Convey any concentrated flows through the drainage system to a
sediment trapping BMP.
l Do not construct silt fences in streams or use in V-shaped ditches. Silt fences do not provide
an adequate method of silt control for anything deeper than sheet or overland flow.
2019 Stormwater Management Manual for Western Washington
Volume II -Chapter 3 -Page 370
Figure II-3.22: Silt Fence
2019 Stormwater Management Manual for Western Washington
Volume II -Chapter 3 -Page 371
Design and Installation Specifications
l Use in combination with other construction stormwater BMPs.
l Maximum slope steepness (perpendicular to the silt fence line) 1H:1V.
l Maximum sheet or overland flow path length to the silt fence of 100 feet.
l Do not allow flows greater than 0.5 cfs.
l Use geotextile fabric that meets the following standards. All geotextile properties listed below
are minimum average roll values (i.e., the test result for any sampled roll in a lot shall meet or
exceed the values shown in Table II-3.11: Geotextile Fabric Standards for Silt Fence):
Geotextile Property Minimum Average Roll Value
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
Table II-3.11: Geotextile Fabric Standards for Silt Fence
l Support standard strength geotextiles with wire mesh, chicken wire, 2-inch x 2-inch wire,
safety fence, or jute mesh to increase the strength of the geotextile. Silt fence materials are
available that have synthetic mesh backing attached.
l Silt fence material shall contain ultraviolet ray inhibitors and stabilizers to provide a minimum
of six months of expected usable construction life at a temperature range of 0°F to 120°F.
l One-hundred percent biodegradable silt fence is available that is strong, long lasting, and can
be left in place after the project is completed, if permitted by the local jurisdiction.
l Refer to Figure II-3.22: Silt Fence for standard silt fence details. Include the following Stand-
ard 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.
2019 Stormwater Management Manual for Western Washington
Volume II -Chapter 3 -Page 372
3. The silt fence shall have a 2-feet min. and a 2½-feet max. height above the original
ground surface.
4. The geotextile fabric shall be sewn together at the point of manufacture to form fabric
lengths as required. Locate all sewn seams at support posts. Alternatively, two sections
of silt fence can be overlapped, provided that the overlap is long enough and that the
adjacent silt fence sections are close enough together to prevent silt laden water from
escaping through the fence at the overlap.
5. Attach the geotextile fabric on the up-slope side of the posts and secure with staples,
wire, or in accordance with the manufacturer's recommendations. Attach the geotextile
fabric to the posts in a manner that reduces the potential for tearing.
6. Support the geotextile fabric with wire or plastic mesh, dependent on the properties of
the geotextile selected for use. If wire or plastic mesh is used, fasten the mesh securely
to the up-slope side of the posts with the geotextile fabric up-slope of the mesh.
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 geotextile fabric it
supports.
8. Bury the bottom of the geotextile fabric 4-inches min. below the ground surface. Backfill
and tamp soil in place over the buried portion of the geotextile fabric, so that no flow can
pass beneath the silt fence and scouring cannot occur. When wire or polymeric back-up
support mesh is used, the wire or polymeric mesh shall extend into the ground 3-inches
min.
9. Drive or place the silt fence posts into the ground 18-inches min. A 12–inch min. depth
is allowed if topsoil or other soft subgrade soil is not present and 18-inches 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 pre-
vent overturning of the fence due to sediment loading.
10. Use wood, steel or equivalent posts. The spacing of the support posts shall be a max-
imum of 6-feet. Posts shall consist of either:
l Wood with minimum dimensions of 2 inches by 2 inches by 3 feet. Wood shall be
free of defects such as knots, splits, or gouges.
l No. 6 steel rebar or larger.
l ASTM A 120 steel pipe with a minimum diameter of 1-inch.
l U, T, L, or C shape steel posts with a minimum weight of 1.35 lbs./ft.
l Other steel posts having equivalent strength and bending resistance to the post
sizes listed above.
11. Locate silt fences on contour as much as possible, except at the ends of the fence,
2019 Stormwater Management Manual for Western Washington
Volume II -Chapter 3 -Page 373
where the fence shall be turned uphill such that the silt fence captures the runoff water
and prevents water from flowing around the end of the fence.
12. If the fence must cross contours, with the exception of the ends of the fence, place
check dams perpendicular to the back of the fence to minimize concentrated flow and
erosion. The slope of the fence line where contours must be crossed shall not be
steeper than 3H:1V.
l Check dams shall be approximately 1-foot deep at the back of the fence. Check
dams shall be continued perpendicular to the fence at the same elevation until
the top of the check dam intercepts the ground surface behind the fence.
l Check dams shall consist of crushed surfacing base course, gravel backfill for
walls, or shoulder ballast. Check dams shall be located every 10 feet along the
fence where the fence must cross contours.
l Refer to Figure II-3.23: Silt Fence Installation by Slicing Method for slicing method details. The
following are specifications for silt fence installation using the slicing method:
1. The base of both end posts must be at least 2- to 4-inches above the top of the geo-
textile fabric on the middle posts for ditch checks to drain properly. Use a hand level or
string level, if necessary, to mark base points before installation.
2. Install posts 3- to 4-feet apart in critical retention areas and 6- to 7-feet apart in standard
applications.
3. Install posts 24-inches deep on the downstream side of the silt fence, and as close as
possible to the geotextile fabric, enabling posts to support the geotextile fabric from
upstream water pressure.
4. Install posts with the nipples facing away from the geotextile fabric.
5. Attach the geotextile fabric to each post with three ties, all spaced within the top 8-
inches of the fabric. Attach each tie diagonally 45 degrees through the fabric, with each
puncture at least 1-inch vertically apart. Each tie should be positioned to hang on a post
nipple when tightening to prevent sagging.
6. Wrap approximately 6-inches of the geotextile fabric around the end posts and secure
with 3 ties.
7. No more than 24-inches of a 36-inch geotextile fabric is allowed above ground level.
8. Compact the soil immediately next to the geotextile fabric with the front wheel of the
tractor, skid steer, or roller exerting at least 60 pounds per square inch. Compact the
upstream side first and then each side twice for a total of four trips. Check and correct
the silt fence installation for any deviation before compaction. Use a flat-bladed shovel
to tuck the fabric deeper into the ground if necessary.
2019 Stormwater Management Manual for Western Washington
Volume II -Chapter 3 -Page 374
Figure II-3.23: Silt Fence Installation by Slicing Method
2019 Stormwater Management Manual for Western Washington
Volume II -Chapter 3 -Page 375
Maintenance Standards
l Repair any damage immediately.
l Intercept and convey all evident concentrated flows uphill of the silt fence to a sediment trap-
ping BMP.
l Check the uphill side of the silt fence for signs of the fence clogging and acting as a barrier to
flow and then causing channelization of flows parallel to the fence. If this occurs, replace the
fence and remove the trapped sediment.
l Remove sediment deposits when the deposit reaches approximately one-third the height of
the silt fence, or install a second silt fence.
l Replace geotextile fabric that has deteriorated due to ultraviolet breakdown.
2019 Stormwater Management Manual for Western Washington
Volume II -Chapter 3 -Page 376
BMP C240: Sediment Trap
Purpose
A sediment trap is a small temporary ponding area with a gravel outlet used to collect and store sed-
iment from sites during construction. Sediment traps, along with other perimeter controls, shall be
installed before any land disturbance takes place in the drainage area.
Conditions of Use
l Sediment traps are intended for use on sites where the tributary drainage area is less than 3
acres, with no unusual drainage features, and a projected build-out time of six months or less.
The sediment trap is a temporary measure (with a design life of approximately 6 months) and
shall be maintained until the tributary area is permanently protected against erosion by veget-
ation and/or structures.
l Sediment traps are only effective in removing sediment down to about the medium silt size
fraction. Runoff with sediment of finer grades (fine silt and clay) will pass through untreated,
emphasizing the need to control erosion to the maximum extent first.
l Projects that are constructing permanent Flow Control BMPs, or Runoff Treatment BMPs
that use ponding for treatment, may use the rough-graded or final-graded permanent BMP
footprint for the temporary sediment trap. When permanent BMP footprints are used as tem-
porary sediment traps, the surface area requirement of the sediment trap must be met. If the
surface area requirement of the sediment trap is larger than the surface area of the per-
manent BMP, then the sediment trap shall be enlarged beyond the permanent BMP footprint
to comply with the surface area requirement.
2019 Stormwater Management Manual for Western Washington
Volume II -Chapter 3 -Page 383
l A floating pond skimmer may be used for the sediment trap outlet if approved by the Local Per-
mitting Authority.
l Sediment traps may not be feasible on utility projects due to the limited work space or the
short-term nature of the work. Portable tanks may be used in place of sediment traps for utility
projects.
Design and Installation Specifications
l See Figure II-3.26: Cross Section of Sediment Trap and Figure II-3.27: Sediment Trap Outlet
for details.
l To determine the sediment trap geometry, first calculate the design surface area (SA) of the
trap, measured at the invert of the weir. Use the following equation:
SA = FS(Q2/Vs)
where
Q2 =
o Option 1 - Single Event Hydrograph Method:
Q2 = Peak volumetric flow rate calculated using a 10-minute time step from a Type 1A,
2-year, 24-hour frequency storm for the developed condition. The 10-year peak volu-
metric flow rate shall be used if the project size, expected timing and duration of con-
struction, or downstream conditions warrant a higher level of protection.
o Option 2 - For construction sites that are less than 1 acre, the Rational Method may be
used to determine Q2.
Vs = The settling velocity of the soil particle of interest. The 0.02 mm (medium silt) particle with
an assumed density of 2.65 g/cm3 has been selected as the particle of interest and has a set-
tling velocity (Vs) of 0.00096 ft/sec.
FS = A safety factor of 2 to account for non-ideal settling.
Therefore, the equation for computing sediment trap surface area becomes:
SA = 2 x Q2/0.00096
or
2080 square feet per cfs of inflow
l Sediment trap depth shall be 3.5 feet minimum from the bottom of the trap to the top of the
overflow weir.
l To aid in determining sediment depth, all sediment traps shall have a staff gauge with a prom-
inent mark 1-foot above the bottom of the trap.
2019 Stormwater Management Manual for Western Washington
Volume II -Chapter 3 -Page 384
l Design the discharge from the sediment trap by using the guidance for discharge from tem-
porary sediment ponds in BMP C241: Sediment Pond (Temporary).
Maintenance Standards
l Sediment shall be removed from the trap when it reaches 1-foot in depth.
l Any damage to the trap embankments or slopes shall be repaired.
2019 Stormwater Management Manual for Western Washington
Volume II -Chapter 3 -Page 385
Figure II-3.26: Cross Section of Sediment Trap
2019 Stormwater Management Manual for Western Washington
Volume II -Chapter 3 -Page 386
Figure II-3.27: Sediment Trap Outlet
2019 Stormwater Management Manual for Western Washington
Volume II -Chapter 3 -Page 387
Construction Stormwater Pollution Prevention Plan
Crystal Springs Preliminary Plat
2210633.10
Exhibit 5
Geotechnical Report
Earth Solutions NW, LLC, October 6, 2021
EarthSolutionsNWLLC
EarthSolutions
NW LLC
15365 N.E.90th Street,Suite 100 Redmond,WA 98052
(425)449-4704 Fax (425)449-4711
www.earthsolutionsnw.com
Geotechnical Engineering
Construction Observation/Testing
Environmental Services
GEOTECHNICAL ENGINEERING STUDY
CRYSTAL SPRINGS
714 CRYSTAL SPRINGS STREET NORTHWEST
YELM,WASHINGTON
ES-8113
PREPARED FOR
COPPER RIDGE, LLC
October 6, 2021
_________________________
Scott S. Riegel, L.G., L.E.G.
Senior Project Manager
________________________
Kyle R. Campbell, P.E.
Principal Engineer
GEOTECHNICAL ENGINEERING STUDY
CRYSTAL SPRINGS
714 CRYSTAL SPRINGS STREET NORTHWEST
YELM, WASHINGTON
ES-8113
Earth Solutions NW, LLC
15365 Northeast 90th Street, Suite 100
Redmond, Washington 98052
Phone: 425-449-4704 | Fax: 425-449-4711
www.earthsolutionsnw.com
10/06/2021
Geotechnical-Engineering Report
Important Information about This
Subsurface problems are a principal cause of construction delays, cost overruns, claims, and disputes.
While you cannot eliminate all such risks, you can manage them. The following information is provided to help.
The Geoprofessional Business Association (GBA)
has prepared this advisory to help you – assumedly
a client representative – interpret and apply this
geotechnical-engineering report as effectively as
possible. In that way, you can benefit from a lowered
exposure to problems associated with subsurface
conditions at project sites and development of
them that, for decades, have been a principal cause
of construction delays, cost overruns, claims,
and disputes. If you have questions or want more
information about any of the issues discussed herein,
contact your GBA-member geotechnical engineer.
Active engagement in GBA exposes geotechnical
engineers to a wide array of risk-confrontation
techniques that can be of genuine benefit for
everyone involved with a construction project.
Understand the Geotechnical-Engineering Services
Provided for this Report
Geotechnical-engineering services typically include the planning,
collection, interpretation, and analysis of exploratory data from
widely spaced borings and/or test pits. Field data are combined
with results from laboratory tests of soil and rock samples obtained
from field exploration (if applicable), observations made during site
reconnaissance, and historical information to form one or more models
of the expected subsurface conditions beneath the site. Local geology
and alterations of the site surface and subsurface by previous and
proposed construction are also important considerations. Geotechnical
engineers apply their engineering training, experience, and judgment
to adapt the requirements of the prospective project to the subsurface
model(s). Estimates are made of the subsurface conditions that
will likely be exposed during construction as well as the expected
performance of foundations and other structures being planned and/or
affected by construction activities.
The culmination of these geotechnical-engineering services is typically a
geotechnical-engineering report providing the data obtained, a discussion
of the subsurface model(s), the engineering and geologic engineering
assessments and analyses made, and the recommendations developed
to satisfy the given requirements of the project. These reports may be
titled investigations, explorations, studies, assessments, or evaluations.
Regardless of the title used, the geotechnical-engineering report is an
engineering interpretation of the subsurface conditions within the context
of the project and does not represent a close examination, systematic
inquiry, or thorough investigation of all site and subsurface conditions.
Geotechnical-Engineering Services are Performed
for Specific Purposes, Persons, and Projects,
and At Specific Times
Geotechnical engineers structure their services to meet the specific
needs, goals, and risk management preferences of their clients. A
geotechnical-engineering study conducted for a given civil engineer
will not likely meet the needs of a civil-works constructor or even a
different civil engineer. Because each geotechnical-engineering study
is unique, each geotechnical-engineering report is unique, prepared
solely for the client.
Likewise, geotechnical-engineering services are performed for a specific
project and purpose. For example, it is unlikely that a geotechnical-
engineering study for a refrigerated warehouse will be the same as
one prepared for a parking garage; and a few borings drilled during
a preliminary study to evaluate site feasibility will not be adequate to
develop geotechnical design recommendations for the project.
Do not rely on this report if your geotechnical engineer prepared it:
• for a different client;
• for a different project or purpose;
• for a different site (that may or may not include all or a portion of
the original site); or
• before important events occurred at the site or adjacent to it;
e.g., man-made events like construction or environmental
remediation, or natural events like floods, droughts, earthquakes,
or groundwater fluctuations.
Note, too, the reliability of a geotechnical-engineering report can
be affected by the passage of time, because of factors like changed
subsurface conditions; new or modified codes, standards, or
regulations; or new techniques or tools. If you are the least bit uncertain
about the continued reliability of this report, contact your geotechnical
engineer before applying the recommendations in it. A minor amount
of additional testing or analysis after the passage of time – if any is
required at all – could prevent major problems.
Read this Report in Full
Costly problems have occurred because those relying on a geotechnical-
engineering report did not read the report in its entirety. Do not rely on
an executive summary. Do not read selective elements only. Read and
refer to the report in full.
You Need to Inform Your Geotechnical Engineer
About Change
Your geotechnical engineer considered unique, project-specific factors
when developing the scope of study behind this report and developing
the confirmation-dependent recommendations the report conveys.
Typical changes that could erode the reliability of this report include
those that affect:
• the site’s size or shape;
• the elevation, configuration, location, orientation,
function or weight of the proposed structure and
the desired performance criteria;
• the composition of the design team; or
• project ownership.
As a general rule, always inform your geotechnical engineer of project
or site changes – even minor ones – and request an assessment of their
impact. The geotechnical engineer who prepared this report cannot accept
responsibility or liability for problems that arise because the geotechnical
engineer was not informed about developments the engineer otherwise
would have considered.
Most of the “Findings” Related in This Report
Are Professional Opinions
Before construction begins, geotechnical engineers explore a site’s
subsurface using various sampling and testing procedures. Geotechnical
engineers can observe actual subsurface conditions only at those specific
locations where sampling and testing is performed. The data derived from
that sampling and testing were reviewed by your geotechnical engineer,
who then applied professional judgement to form opinions about
subsurface conditions throughout the site. Actual sitewide-subsurface
conditions may differ – maybe significantly – from those indicated in
this report. Confront that risk by retaining your geotechnical engineer
to serve on the design team through project completion to obtain
informed guidance quickly, whenever needed.
This Report’s Recommendations Are
Confirmation-Dependent
The recommendations included in this report – including any options or
alternatives – are confirmation-dependent. In other words, they are not
final, because the geotechnical engineer who developed them relied heavily
on judgement and opinion to do so. Your geotechnical engineer can finalize
the recommendations only after observing actual subsurface conditions
exposed during construction. If through observation your geotechnical
engineer confirms that the conditions assumed to exist actually do exist,
the recommendations can be relied upon, assuming no other changes have
occurred. The geotechnical engineer who prepared this report cannot assume
responsibility or liability for confirmation-dependent recommendations if you
fail to retain that engineer to perform construction observation.
This Report Could Be Misinterpreted
Other design professionals’ misinterpretation of geotechnical-
engineering reports has resulted in costly problems. Confront that risk
by having your geotechnical engineer serve as a continuing member of
the design team, to:
• confer with other design-team members;
• help develop specifications;
• review pertinent elements of other design professionals’ plans and
specifications; and
• be available whenever geotechnical-engineering guidance is needed.
You should also confront the risk of constructors misinterpreting this
report. Do so by retaining your geotechnical engineer to participate in
prebid and preconstruction conferences and to perform construction-
phase observations.
Give Constructors a Complete Report and Guidance
Some owners and design professionals mistakenly believe they can shift
unanticipated-subsurface-conditions liability to constructors by limiting
the information they provide for bid preparation. To help prevent
the costly, contentious problems this practice has caused, include the
complete geotechnical-engineering report, along with any attachments
or appendices, with your contract documents, but be certain to note
conspicuously that you’ve included the material for information purposes
only. To avoid misunderstanding, you may also want to note that
“informational purposes” means constructors have no right to rely on
the interpretations, opinions, conclusions, or recommendations in the
report. Be certain that constructors know they may learn about specific
project requirements, including options selected from the report, only
from the design drawings and specifications. Remind constructors
that they may perform their own studies if they want to, and be sure to
allow enough time to permit them to do so. Only then might you be in
a position to give constructors the information available to you, while
requiring them to at least share some of the financial responsibilities
stemming from unanticipated conditions. Conducting prebid and
preconstruction conferences can also be valuable in this respect.
Read Responsibility Provisions Closely
Some client representatives, design professionals, and constructors do
not realize that geotechnical engineering is far less exact than other
engineering disciplines. This happens in part because soil and rock on
project sites are typically heterogeneous and not manufactured materials
with well-defined engineering properties like steel and concrete. That
lack of understanding has nurtured unrealistic expectations that have
resulted in disappointments, delays, cost overruns, claims, and disputes.
To confront that risk, geotechnical engineers commonly include
explanatory provisions in their reports. Sometimes labeled “limitations,”
many of these provisions indicate where geotechnical engineers’
responsibilities begin and end, to help others recognize their own
responsibilities and risks. Read these provisions closely. Ask questions.
Your geotechnical engineer should respond fully and frankly.
Geoenvironmental Concerns Are Not Covered
The personnel, equipment, and techniques used to perform an
environmental study – e.g., a “phase-one” or “phase-two” environmental
site assessment – differ significantly from those used to perform a
geotechnical-engineering study. For that reason, a geotechnical-engineering
report does not usually provide environmental findings, conclusions, or
recommendations; e.g., about the likelihood of encountering underground
storage tanks or regulated contaminants. Unanticipated subsurface
environmental problems have led to project failures. If you have not
obtained your own environmental information about the project site,
ask your geotechnical consultant for a recommendation on how to find
environmental risk-management guidance.
Obtain Professional Assistance to Deal with
Moisture Infiltration and Mold
While your geotechnical engineer may have addressed groundwater,
water infiltration, or similar issues in this report, the engineer’s
services were not designed, conducted, or intended to prevent
migration of moisture – including water vapor – from the soil
through building slabs and walls and into the building interior, where
it can cause mold growth and material-performance deficiencies.
Accordingly, proper implementation of the geotechnical engineer’s
recommendations will not of itself be sufficient to prevent
moisture infiltration. Confront the risk of moisture infiltration by
including building-envelope or mold specialists on the design team.
Geotechnical engineers are not building-envelope or mold specialists.
Copyright 2019 by Geoprofessional Business Association (GBA). Duplication, reproduction, or copying of this document, in whole or in part, by any means whatsoever, is strictly
prohibited, except with GBA’s specific written permission. Excerpting, quoting, or otherwise extracting wording from this document is permitted only with the express written permission of
GBA, and only for purposes of scholarly research or book review. Only members of GBA may use this document or its wording as a complement to or as an element of a report of any kind.
Any other firm, individual, or other entity that so uses this document without being a GBA member could be committing negligent or intentional (fraudulent) misrepresentation.
Telephone: 301/565-2733
e-mail: info@geoprofessional.org www.geoprofessional.org
October 6, 2021
ES-8113
Copper Ridge, LLC
P.O. Box 73790
Puyallup, Washington 98373
Attention: Mr. Evan Mann
Dear Mr. Mann:
Earth Solutions NW, LLC (ESNW) is pleased to present this report supporting the planned
residential development for Yelm, Washington. In our opinion, the proposed residential
development is feasible from a geotechnical standpoint. Based on the conditions observed
during our fieldwork, the subject site is underlain primarily by recessional outwash deposits that
are suitable for infiltration. The proposed structures can be supported on conventional spread
and continuous foundations bearing on competent native soil, recompacted native soil, or new
structural fill placed directly on competent native soil. In general, competent native soil suitable
for support of foundations will likely be encountered at depths of about two to four feet below the
existing ground surface (bgs). Where loose or unsuitable soil conditions are exposed at
foundation subgrade elevations, compaction of soils to the specifications of structural fill, or
overexcavation and replacement with suitable structural fill, will likely be necessary.
This report provides recommendations for foundation subgrade preparation, foundation and
retaining wall design parameters, drainage, infiltration recommendations, the suitability of the on-
site soils for use as structural fill, and other geotechnical recommendations.
The opportunity to be of service to you is appreciated. If you have any questions regarding the
content of this geotechnical engineering study, please call.
Sincerely,
EARTH SOLUTIONS NW, LLC
Scott S. Riegel, L.G., L.E.G.
Senior Project Manager
15365 N.E. 90th Street, Suite 100 • Redmond, WA 98052 •(425) 449-4704 • FAX (425) 449-4711
Earth Solutions NW LLC
Geotechnical Engineering, Construction
Observation/Testing and Environmental Services
Earth Solutions NW, LLC
Table of Contents
ES-8113
PAGE
INTRODUCTION ................................................................................. 1
General..................................................................................... 1
Project Description ................................................................. 1
SITE CONDITIONS ............................................................................. 2
Surface ..................................................................................... 2
Subsurface .............................................................................. 2
Topsoil and Fill ............................................................. 2
Native Soil ..................................................................... 3
Geologic Setting ........................................................... 3
Groundwater ................................................................. 3
Geologically Hazardous Areas .............................................. 3
DISCUSSION AND RECOMMENDATIONS ....................................... 3
General..................................................................................... 3
Site Preparation and Earthwork ............................................. 4
Temporary Erosion Control ......................................... 4
In-Situ Soils .................................................................. 4
Wet Season Grading .................................................... 4
Structural Fill ................................................................ 4
Excavations and Slopes .............................................. 5
Foundations ............................................................................ 5
Seismic Design Considerations ............................................ 6
Slab-on-Grade Floors ............................................................. 7
Retaining Walls ....................................................................... 7
Drainage................................................................................... 8
Infiltration Evaluation ................................................... 8
Test Method .................................................................. 8
Test Results .................................................................. 9
Soil Types and Site Variability .................................... 9
Restrictive Layer .......................................................... 9
Summary and Recommendations............................... 9
Utility Support and Trench Backfill ....................................... 10
Pavement Sections ................................................................. 10
LIMITATIONS ...................................................................................... 11
Additional Services ................................................................. 11
Earth Solutions NW, LLC
Table of Contents
Cont’d
ES-8113
GRAPHICS
Plate 1 Vicinity Map
Plate 2 Test Pit Location Plan
Plate 3 Retaining Wall Drainage Detail
Plate 4 Footing Drain Detail
APPENDICES
Appendix A Subsurface Exploration
Test Pit Logs
Appendix B Laboratory Test Results
Earth Solutions NW, LLC
GEOTECHNICAL ENGINEERING STUDY
CRYSTAL SPRINGS
714 CRYSTAL SPRINGS STREET NORTHWEST
YELM, WASHINGTON
ES-8113
INTRODUCTION
General
This report was prepared for the proposed residential development to be constructed at 714
Crystal Springs Street Northwest in Yelm, Washington. The purpose of this study was to provide
geotechnical recommendations for the proposed development. Our scope of services for
completing this geotechnical engineering study included the following:
Observing, logging, and sampling test pits for purposes of characterizing site soil and
groundwater conditions;
Laboratory testing of soil samples collected at the test pit locations;
Engineering analyses and recommendations for the proposed development, and;
Preparation of this report.
The following documents and resources were reviewed as part of our report preparation:
Geologic Map of the Centralia Quadrangle, Washington, 1987;
Conceptual Site Plan, undated;
Web Soil Survey (WSS) online resource, maintained by the Natural Resources
Conservation Service under the United States Department of Agriculture, and;
Yelm Municipal Code Title 18.21: Critical Areas and Resource Lands.
Project Description
Based on review of the referenced plans, the subject site will be redeveloped with up to 30 single-
family residences and associated improvements. Grading plans were not available at the time
this report was prepared; however, given the low topographic relief on this site, we anticipate
grading may include cuts and fills of up to about five feet with deeper excavations required to
install underground utilities.
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At the time this report was prepared, specific building load values were not available; however,
we anticipate the proposed residential structures will consist of relatively lightly loaded wood
framing supported on conventional foundations. Based on our experience with similar
developments, we estimate wall loads on the order of 1 to 2 kips per linear foot and slab-on-grade
loading of 150 pounds per square foot (psf). The feasibility of infiltrating runoff into native soils is
being investigated as part of the project plans.
If the above design assumptions are incorrect or change, ESNW should be contacted to review
the recommendations in this report. ESNW should review the final design to verify the
geotechnical recommendations provided in this report have been incorporated into the plans.
SITE CONDITIONS
Surface
The subject site is located east of Crystal Springs Street Northwest in Yelm, Washington, as
illustrated on the Vicinity Map (Plate 1). The site consists of a single tax parcel (Thurston County
Parcel Number 22719210403) currently developed with a single-family residence, barn, detached
garage, and associated improvements. The majority of the subject site is lightly to moderately
vegetated with tall grass, and sparse trees and general landscaping around existing buildings.
Topography is relatively level, with less than about five feet of total elevation change across the
site.
Subsurface
A representative of ESNW observed, logged, and sampled six test pits, excavated at accessible
locations within the proposed development area, on August 31, 2021, using a trackhoe and
operator provided by the client. The approximate locations of the test pits are depicted on Plate
2 (Test Pit Location Plan). Please refer to the test pit logs provided in Appendix A for a more
detailed description of subsurface conditions. Representative soil samples collected at the test
pit locations were analyzed in general accordance with Unified Soil Classification System (USCS)
and United States Department of Agriculture (USDA) methods and procedures.
Topsoil and Fill
Topsoil was observed extending to depths of approximately 6 to 12 inches below existing grades.
The topsoil thickness is variable and vegetation roots often extend below the topsoil zone into
the underlying weathered native soil. The topsoil was characterized by dark brown color and fine
organic material. Topsoil is not suitable for use as structural fill nor should it be mixed with
material to be used as structural fill. Topsoil or otherwise unsuitable material can be used in
landscape areas if desired.
Fill was not encountered within the test pits; however, fill is likely present near the existing
structures to some degree. If fill is encountered during construction, ESNW should be consulted
to verify the suitability for support of the proposed structures and/or reuse as structural fill.
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Native Soil
Underlying the topsoil, native soils consisted primarily of medium dense to dense poorly and well-
graded gravel with variable sand (USCS: GP and GW respectively). The native soils were
generally encountered in a damp to moist condition and extended to the maximum exploration
depth of 13 feet below ground surface (bgs). We encountered scattered large cobbles and small
boulders at the test pit locations.
Geologic Setting
The referenced geologic map resource identifies recessional outwash, specifically Vashon drift
gravel (Qdvg), across the site and surrounding areas. The referenced WSS resource identifies
Spanaway gravelly sandy loam (Map Unit Symbols: 110 and 111) across the site and surrounding
areas. Spanaway gravelly loam was formed in outwash plains. Based on our field observations,
native soils on site are generally consistent with the geologic setting outlined in this section.
Groundwater
Groundwater was not encountered, at the time of our exploration (August 31, 2021).
Groundwater seepage rates and elevations fluctuate depending on many factors, including
precipitation duration and intensity, the time of year, and soil conditions. In general, groundwater
flow rates are higher during the wetter, winter, spring, and early summer months.
Geologically Hazardous Areas
As part of this report, the subject property was evaluated for the presence of geologically
hazardous areas in general accordance with the applicable Yelm municipal code. Based on our
investigation, the site does not lie within or is immediately adjacent to geologically hazardous
areas.
DISCUSSION AND RECOMMENDATIONS
General
In our opinion, the proposed residential structures can be supported on conventional spread and
continuous foundations bearing on undisturbed competent native soil, recompacted native soil or
new structural fill placed directly on competent native soil. Competent soils suitable for support
of foundations are anticipated to be exposed at depths of about two to four feet below existing
grades across the majority of the site. Slab-on-grade floors should be supported on competent
native soil, re-compacted native soil, or new structural fill. Organic material exposed at subgrade
elevations must be removed below design elevation and grades restored with structural fill.
Where loose, organic or other unsuitable materials are encountered at or below the footing
subgrade elevation, the material should be removed and replaced with structural fill, as
necessary.
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This study has been prepared for the exclusive use of Copper Ridge, LLC and their
representatives. No warranty, expressed or implied, is made. This study has been prepared in
a manner consistent with the level of care and skill ordinarily exercised by other members of the
profession currently practicing under similar conditions in this area.
Site Preparation and Earthwork
Site preparation activities will consist of installing temporary erosion control measures and
performing clearing and site stripping. Grading activities will likely consist of cuts and fills on the
order five feet with the deeper cuts associated with stormwater facilities and utility excavations.
Temporary Erosion Control
Temporary construction entrances and drive lanes, consisting of at least six inches of quarry
spalls, should be considered in order to minimize off-site soil tracking and to provide a temporary
road surface. Temporary slopes and stockpiles should be covered when not in use. Silt fencing
should be installed along the margins of the property. Temporary infiltration swales and galleries
can be considered for control of stormwater. Erosion control measures should conform to the
applicable Washington State Department of Ecology and City of Yelm/Thurston County
standards.
In-Situ Soils
The majority of the soils encountered during our subsurface exploration have a low to moderate
sensitivity to moisture and were generally in a damp to moist condition at the time of the
exploration on August 2021. Soils encountered during site excavations that are excessively over
the optimum moisture content will require aeration or treatment prior to placement and
compaction. Conversely, soils that are substantially below the optimum moisture content will
require moisture conditioning through the addition of water prior to use as structural fill. An ESNW
representative should determine the suitability of in-situ soils for use as structural fill at the time
of construction.
Wet Season Grading
If grading takes place during the wet season surface water could collect and degrade site soils if
not property controlled. The contractor should establish temporary drainage control measures,
such as swales and ponds, prior to extended wet weather. ESNW should be consulted during
construction to provide temporary drainage control recommendations.
Structural Fill
Structural fill is defined as compacted soil placed in foundation, slab-on-grade, and roadway
areas. Fills placed to construct permanent slopes and throughout retaining wall and utility trench
backfill areas are considered structural fill as well. Soils placed in structural areas should be
placed in loose lifts of 12 inches or less and compacted to a relative compaction of 95 percent,
based on the laboratory maximum dry density as determined by the Modified Proctor Method
(ASTM D1557). More stringent compaction specifications may be required for utility trench
backfill zones depending on the responsible utility district or jurisdiction.
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Excavations and Slopes
The Federal Occupation Safety and Health Administration (OSHA) and the Washington Industrial
Safety and Health Act (WISHA) provide soil classification in terms of temporary slope inclinations.
Soils that exhibit a high compressive strength are allowed steeper temporary slope inclinations
than are soils that exhibit lower strength characteristics.
Based on the soil conditions encountered at the test pit locations, site soils are classified as Type
C by OSHA. New fill should also be considered Type C soil. Temporary slopes over four feet in
height in Type C soils must be sloped no steeper than (1.5H:1V). Steeper temporary slopes may
be feasible and should be evaluated by ESNW during construction. Where encountered, the
presence of groundwater seepage may cause caving of temporary slopes. ESNW should
observe site excavations to confirm soil types and allowable slope inclinations. If the
recommended temporary slope inclinations cannot be achieved, temporary shoring may be
necessary to support excavations, particularly utility trench excavations.
Permanent slopes should be planted with vegetation to enhance stability and to minimize erosion
and should maintain a gradient of 2H:1V or flatter. An ESNW representative should observe
temporary and permanent slopes to confirm the slope inclinations are suitable for the exposed
soil conditions. Supplementary recommendations with respect to excavations and slopes may
be provided as conditions warrant.
Foundations
The proposed residential structures can be supported on conventional spread and continuous
footings bearing on undisturbed competent native soil, recompacted native soil, or new structural
fill placed directly on competent native soil. Based on the soil conditions encountered at the test
sites, competent soils suitable for support of foundations are anticipated to be exposed at depths
of about two to four feet below existing grades across the majority of the site. Where loose or
unsuitable soil conditions are observed at foundation subgrade elevations, compaction of the
soils to the specifications of structural fill, or overexcavation and replacement with granular
structural fill will be necessary. Organic material exposed at foundation subgrade elevations must
be removed and grades restored with structural fill.
Provided the structures will be supported as described above, the following parameters can be
used for design of the new foundations:
Allowable soil bearing capacity 2,500 psf
Passive earth pressure 300 pcf (equivalent fluid)
Coefficient of friction 0.40
A one-third increase in the allowable soil bearing capacity can be assumed for short-term wind
and seismic loading conditions.
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With structural loading as expected, total settlement in the range of 1.0 inch is anticipated, with
differential settlement of about 0.5 inch. The majority of the settlements should occur during
construction, as dead loads are applied.
Seismic Design Considerations
The 2018 International Building Code (2018 IBC) recognizes the most recent edition of the
Minimum Design Loads for Buildings and Other Structures manual (ASCE 7-16) for seismic
design, specifically with respect to earthquake loads. Based on the soil conditions encountered
at the test pit locations, the parameters and values provided below are recommended for seismic
design per the 2018 IBC.
Parameter Value
Site Class D*
Mapped short period spectral response acceleration, S S (g) 1.291
Mapped 1-second period spectral response acceleration, S 1 (g) 0.466
Short period site coefficient, Fa 1
Long period site coefficient, Fv 1.88†
Adjusted short period spectral response acceleration, S MS (g) 1.291
Adjusted 1-second period spectral response acceleration, S M1 (g) 0.876†
Design short period spectral response acceleration, S DS (g) 0.861
Design 1-second period spectral response acceleration, S D1 (g) 0.584†
* Assumes medium dense native soil conditions, encountered to a maximum depth of 13 feet bgs during the August
2021 field exploration, remain medium dense or better to at least 100 feet bgs.
† Values assume Fv may be determined using linear interpolation per Table 11.4-2 in ASCE 7-16.
As indicated in the table footnote, several of the seismic design values provided above are
dependent on the assumption that site-specific ground motion analysis (per Section 11.4.8 of
ASCE 7-16) will not be required for the subject project. ESNW recommends the validity of this
assumption be confirmed at the earliest available opportunity during the planning and early
design stages of the project. Further discussion between the project structural engineer, the
project owner, and ESNW may be prudent to determine the possible impacts to the structural
design due to increased earthquake load requirements under the 2018 IBC. ESNW can provide
additional consulting services to aid with design efforts, including supplementary geotechnical
and geophysical investigation, upon request.
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Liquefaction is a phenomenon where saturated or loose soil suddenly loses internal strength and
behaves as a fluid. This behavior is in response to increased pore water pressures resulting from
an earthquake or another intense ground shaking. In our opinion, site susceptibility to liquefaction
may be considered low. The depth of the local groundwater table and the gradation and relatively
dense characteristics of the native soil were the primary bases for this opinion.
Slab-on-Grade Floors
Slab-on-grade floors for the proposed residential structures should be supported on a firm and
unyielding subgrade. Unstable or yielding areas of the subgrade should be recompacted, or
overexcavated and replaced with suitable structural fill, prior to construction of the slab.
A capillary break consisting of a minimum of four inches of free-draining crushed rock or gravel
should be placed below the slab. The free-draining material should have a fines content of 5
percent or less (percent passing the Number 200 sieve, based on the minus three-quarter-inch
fraction). In areas where slab moisture is undesirable, installation of a vapor barrier below the
slab should be considered. If a vapor barrier is to be utilized, it should be a material specifically
designed for use as a vapor barrier and should be installed in accordance with the specifications
of the manufacturer.
Retaining Walls
Retaining walls must be designed to resist earth pressures and applicable surcharge loads. The
following parameters can be used for retaining wall design:
Active earth pressure (unrestrained condition) 35 pcf
At-rest earth pressure (restrained condition) 55 pcf
Traffic surcharge (passenger vehicles) 70 psf (rectangular distribution)
Passive earth pressure 300 pcf
Coefficient of friction 0.40
Seismic surcharge 8H*
* Where H equals the retained height.
Additional surcharge loading from adjacent foundations, sloped backfill, retaining walls, or other
loads should be included in the retaining wall design. Drainage should be provided behind
retaining walls such that hydrostatic pressures do not develop. If drainage is not provided,
hydrostatic pressures should be included in the wall design.
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Retaining walls should be backfilled with at least 18 inches of free-draining material or suitable
sheet drainage that extends along the height of the wall. The upper one foot of the wall backfill
can consist of a less permeable soil, if desired. A perforated drain pipe should be placed along
the base of the wall and connected to an approved discharge location. A typical retaining wall
drainage detail is provided on Plate 3.
Drainage
Based on our field observations, the native soils generally consisted of well-drained, poorly to
well-graded gravels with slightly variable sand contents. Because of the generally well-drained
nature of the native gravels, significant groundwater is not anticipated to be encountered within
shallow site excavations. ESNW should be consulted during preliminary grading to identify areas
of seepage (if present) and provide recommendations to reduce the potential for instability related
to seepage effects.
Finish grades must be designed to direct surface drain water away from structures and slopes.
The grade adjacent to buildings should be sloped away from the buildings at a gradient of at least
2 percent for a horizontal distance of at least 10 feet or more as setbacks allow. Water must not
be allowed to pond adjacent to structures or slopes. Based on our field observations, it may be
feasible to eliminate foundation drains, provided clean, well-drained deposits are exposed at
footing subgrade elevation. However, confirmation should be provided by ESNW at the time of
construction. A typical foundation drain detail is provided on Plate 4.
Infiltration Evaluation
We conducted in-situ pilot infiltration tests (PITs) at the two areas proposed for infiltration within
the overall development. The PITs were completed at test pit locations TP-1 and TP-4 within
native soils about 8 to 10 feet below existing grades. As indicated in the Subsurface section of
this report, native soils encountered during our fieldwork were characterized primarily as
Spanaway gravels with variable sand content. Based upon the results of USDA textural analyses
performed on representative soil samples, native soils may also be classified chiefly as extremely
gravelly coarse sand. Irrespective of gravel content, fines contents within the native gravels were
generally less than one percent.
Test Method
The bottom of each PIT area was set at the approximate design facility bottom as recommended
in the Method 1 Field Test Methods section of Appendix III-A. Water was metered into each PIT
area using a pump fed hose to develop a constant head of about one foot. The hydraulic head
was maintained until the water truck was emptied (3,800-gallon capacity), and measurements of
flow for each test area was monitored by our field staff. Upon completion of the constant head
soaking period, the water source was removed and each test area was allowed to drain. Upon
drained conditions, the test pits were advanced to the limits of the excavator to determine soil
stratigraphy and check for groundwater.
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Test Results
Our testing yielded measured (unfactored) infiltration rates of between 90 and 180 inches per
hour (iph). The correction factors below were applied to the measured rates.
Correction Factor Value
Test Method 0.5
Geometry 0.9*
Plugging 0.9
* This value is estimated based on typical pond geometry and uses information collected during the testing.
The total correction factor applied to the measured infiltration rates was 0.4. The resulting long-
term (design) infiltration rate is 36 iph. These rates were calculated using the lowest measured
infiltration rate.
Soil Types and Site Variability
We conducted USDA textural analyses of representative soil samples collected at the PIT areas.
On this basis, the majority of the native soil within the proposed areas consist of extremely
gravelly coarse sand. The samples collected at the tested locations indicated consistent soil
types across the site, with low variability.
Restrictive Layer
On this site, the restrictive layer is groundwater, as the alluvial sand and gravel persisted to the
maximum exploration depth at each location. The groundwater was not identified on this site at
the test pit locations during our fieldwork.
Summary and Recommendations
From a geotechnical standpoint, it is our opinion that the native gravels are suitable for infiltration.
The low soil variability consisting of a consistent thick layer of sand and gravel and low fines
contents within the gravels are the basis of this conclusion. Based on the results of our PIT
program, a long-term infiltration rate of 36 iph may be used for the current infiltration trench design
that will expose coarse gravel soils. Successful performance of the infiltration systems requires
that the base of the facility (receptor soils) exposed sandy soils similar to those encountered at
the test depth. The minimum vertical separation and corresponding trench base elevations
detailed in the referenced groundwater summary should be incorporated into facility designs.
ESNW should review final designs to confirm the recommendations provided in this letter report
are incorporated. ESNW should be retained to observe construction of the infiltration facility
areas during grading to confirm conditions are as anticipated. This site is identified as a highly
susceptible critical aquifer recharge area per YMC section 18.21.070 and will require
performance standards within this section to be met as part of the project design.
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Utility Support and Trench Backfill
In our opinion, the soils observed at the test pit locations are generally suitable for support of
utilities. The native soils observed at the test pit locations are likely suitable for use as structural
backfill in the utility trench excavations. Utility trench backfill should be placed and compacted to
the specifications of structural fill provided in this report, or to the applicable requirements of
presiding jurisdiction. Native sands and gravels used as backfill should be appropriately moisture
conditioned through the addition of water to mitigate the settlement potential.
Native soils proposed for use as utility trench backfill should contain aggregate of six inches in
diameter or less. Caving of the trench sidewalls should be expected and will require temporary
shoring to ensure safety is maintained during utility installation.
Pavement Sections
The performance of site pavements is largely related to the condition of the underlying subgrade.
To ensure adequate pavement performance, the subgrade should be in a firm and unyielding
condition when subjected to proofrolling with a loaded dump truck. Structural fill in pavement
areas should be compacted to the specifications detailed in the Site Preparation and Earthwork
section of this report. It is possible that soft, wet, or otherwise unsuitable subgrade areas may
still exist after base grading activities. Areas of unsuitable or yielding subgrade conditions may
require remedial measures such as overexcavation and replacement with structural fill or thicker
crushed rock sections prior to pavement.
For relatively lightly loaded pavements subjected to automobiles and occasional truck traffic, the
following sections can be considered for preliminary design:
Two inches of hot mix asphalt (HMA) placed over four inches of CRB, or;
Two inches of HMA placed over three inches of asphalt treated base (ATB).
Heavier traffic areas generally require thicker pavement sections depending on site usage,
pavement life expectancy, and site traffic. For preliminary design purposes, the following
pavement sections for occasional truck traffic areas can be considered:
Three inches of HMA placed over six inches of crushed rock base (CRB), or;
Three inches of HMA placed over four-and-one-half inches of ATB.
The HMA, CRB and ATB materials should conform to WSDOT specifications. Thurston
County/City of Yelm minimum pavement requirements may supersede our recommendations and
may require thicker pavement sections.
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Earth Solutions NW, LLC
LIMITATIONS
The recommendations and conclusions provided in this geotechnical engineering study are
professional opinions consistent with the level of care and skill that is typical of other members in
the profession currently practicing under similar conditions in this area. A warranty is not
expressed or implied. Variations in the soil and groundwater conditions observed at the test pit
locations may exist and may not become evident until construction. ESNW should reevaluate
the conclusions in this geotechnical engineering study if variations are encountered.
Additional Services
ESNW should have an opportunity to review the final design with respect to the geotechnical
recommendations provided in this report. ESNW should also be retained to provide testing and
consultation services during construction.
Drwn.MRS
Checked SKH Date Sept.2021
Date 09/20/2021 Proj.No.8113
Plate 1
Earth Solutions NWLLC
Geotechnical Engineering,Construction
EarthSolutionsNWLLC
EarthSolutions
NW LLC Observation/Testing and Environmental Services
Vicinity Map
Crystal Springs
Yelm,Washington
Reference:
Thurston County,Washington
OpenStreetMap.org
NORTH
NOTE:This plate may contain areas of color.ESNW cannot be
responsible for any subsequent misinterpretation of the information
resulting from black &white reproductions of this plate.
Yelm
SITE
Plate
Proj.No.
Date
Checked By
Drwn.ByEarthSolutionsNWLLCGeotechnicalEngineering,ConstructionObservation/TestingandEnvironmentalServicesEarthSolutionsNWLLCEarthSolutionsNWLLCMRS
SKH
09/20/2021
8113
2TestPitLocationPlan CrystalSpringsYelm,WashingtonLEGEND
Approximate Location of
ESNW Test Pit,Proj.No.
ES-8113,Aug.2021
Subject Site
Existing Building
NORTH
0 75 150
Sc ale in Feet1"=150'
NOTE:This plate may contain areas of color.ESNW cannot be
responsible for any subsequent misinterpretation of the information
resulting from black &white reproductions of this plate.
NOTE:The graphics shown on this plate are not intended for design
purposes or precise scale measurements,but only to illustrate the
approximate test locations relative to the approximate locations of
existing and /or proposed site features.The information illustrated
is largely based on data provided by the client at the time of our
study.ESNW cannot be responsible for subsequent design changes
or interpretation of the data by others.
TP-1
95TH C
OURT S.E.W OODLANDCOURT S.E.TP-1
TP-2
TP-3
TP-4
TP-5
TP-6
330
334
330
334
N.W.RHOTONROADN.W.CRYSTALSPRINGSSTREET
Geotechnical Engineering,Construction
Observation/Testing and Environmental Services
Drwn.CAM
Checked SSR Date Oct.2021
Date 10/06/2021 Proj.No.8113
Plate 3
Earth Solutions NWLLCEarthSolutionsNWLLC
EarthSolutions
NW LLC
NOTES:
Free-draining Backfill should consist
of soil having less than 5 percent fines.
Percent passing No.4 sieve should be
25 to 75 percent.
Sheet Drain may be feasible in lieu
of Free-draining Backfill,per ESNW
recommendations.
Drain Pipe should consist of perforated,
rigid PVC Pipe surrounded with 1-inch
Drain Rock.
LEGEND:
Free-draining Structural Backfill
1-inch Drain Rock
18"Min.
Structural
Fill
Perforated Rigid Drain Pipe
(Surround in Drain Rock)
SCHEMATIC ONLY -NOT TO SCALE
NOT A CONSTRUCTION DRAW ING
Retaining Wall Drainage Detail
Crystal Springs
Yelm,Washington
Geotechnical Engineering,Construction
Observation/Testing and Environmental Services
Drwn.CAM
Checked SSR Date Oct.2021
Date 10/06/2021 Proj.No.8113
Plate 4
Earth Solutions NWLLCEarthSolutionsNWLLC
EarthSolutions
NW LLC
Slope
Perforated Rigid Drain Pipe
(Surround in Drain Rock)
18"Min.
NOTES:
Do NOT tie roof downspouts
to Footing Drain.
Surface Seal to consist of
12"of less permeable,suitable
soil.Slope away from building.
LEGEND:
Surface Seal:native soil or
other low-permeability material.
1-inch Drain Rock
SCHEMATIC ONLY -NOT TO SCALE
NOT A CONSTRUCTION DRAW ING
Footing Drain Detail
Crystal Springs
Yelm,Washington
Earth Solutions NW, LLC
Appendix A
Subsurface Exploration
Test Pit Logs
ES-8113
The subsurface conditions at the site were explored by excavating six test pits at the approximate
locations illustrated on Plate 2 of this report. The test pit logs are provided in this Appendix. The
subsurface exploration was completed on August 31, 2021 to a maximum depth of 13 feet below
existing grades.
Logs of the explorations observed by ESNW are presented in Appendix A. The final logs
represent the interpretations of the field logs and the results of laboratory analyses. The
stratification lines on the logs represent the approximate boundaries between soil types. In
actuality, the transitions may be more gradual.
GRAVEL
AND
GRAVELLY
SOILS
CLAYEY GRAVELS, GRAVEL - SAND -
CLAY MIXTURES
WELL-GRADED SANDS, GRAVELLY
SANDS, LITTLE OR NO FINES
POORLY-GRADED SANDS,
GRAVELLY SAND, LITTLE OR NO
FINES
SILTY SANDS, SAND - SILT
MIXTURES
CLAYEY SANDS, SAND - CLAY
MIXTURES
INORGANIC SILTS AND VERY FINE
SANDS, ROCK FLOUR, SILTY OR
CLAYEY FINE SANDS OR CLAYEY
SILTS WITH SLIGHT PLASTICITY
INORGANIC CLAYS OF LOW TO
MEDIUM PLASTICITY, GRAVELLY
CLAYS, SANDY CLAYS, SILTY CLAYS,
LEAN CLAYS
ORGANIC SILTS AND ORGANIC
SILTY CLAYS OF LOW PLASTICITY
INORGANIC SILTS, MICACEOUS OR
DIATOMACEOUS FINE SAND OR
SILTY SOILS
INORGANIC CLAYS OF HIGH
PLASTICITY
SILTS
AND
CLAYS
MORE THAN 50%
OF MATERIAL IS
LARGER THAN
NO. 200 SIEVE
SIZE
MORE THAN 50%
OF MATERIAL IS
SMALLER THAN
NO. 200 SIEVE
SIZE
MORE THAN 50%
OF COARSE
FRACTION
PASSING ON NO.
4 SIEVE
MORE THAN 50%
OF COARSE
FRACTION
RETAINED ON NO.
4 SIEVE
SOIL CLASSIFICATION CHART
(APPRECIABLE
AMOUNT OF FINES)
(APPRECIABLE
AMOUNT OF FINES)
(LITTLE OR NO FINES)
FINE
GRAINED
SOILS
SAND
AND
SANDY
SOILS
SILTS
AND
CLAYS
ORGANIC CLAYS OF MEDIUM TO
HIGH PLASTICITY, ORGANIC SILTS
PEAT, HUMUS, SWAMP SOILS WITH
HIGH ORGANIC CONTENTS
LETTERGRAPH
SYMBOLSMAJOR DIVISIONS
COARSE
GRAINED
SOILS
TYPICAL
DESCRIPTIONS
WELL-GRADED GRAVELS, GRAVEL -
SAND MIXTURES, LITTLE OR NO
FINES
POORLY-GRADED GRAVELS,
GRAVEL - SAND MIXTURES, LITTLE
OR NO FINES
SILTY GRAVELS, GRAVEL - SAND -
SILT MIXTURES
CLEAN
GRAVELS
GRAVELS WITH
FINES
CLEAN SANDS
(LITTLE OR NO FINES)
SANDS WITH
FINES
LIQUID LIMIT
LESS THAN 50
LIQUID LIMIT
GREATER THAN 50
HIGHLY ORGANIC SOILS
DUAL SYMBOLS are used to indicate borderline soil classifications.
The discussion in the text of this report is necessary for a proper understanding of the nature
of the material presented in the attached logs.
GW
GP
GM
GC
SW
SP
SM
SC
ML
CL
OL
MH
CH
OH
PT
Earth Solutions NW LLC
GB
MC = 2.5%
MC = 2.3%
Fines = 1.2%
MC = 3.8%
Fines = 0.3%
TPSL
GP
GP
Dark brown TOPSOIL, abundant roots
Brown poorly graded GRAVEL with sand, medium dense, damp
-abundant cobbles and small boulders present throughout
-minor caving to BOH
[USDA Classification: extremely gravelly coarse SAND]
-infiltration test
Brown poorly graded GRAVEL, dense, damp
[USDA Classification: extremely gravelly coarse SAND]
Test pit terminated at 13.0 feet below existing grade. No groundwater encountered during
excavation. Caving observed from 5.0 to 13.0 feet.
1.0
11.5
13.0
NOTES Depth of Topsoil & Sod 12": field grass
LOGGED BY SKH
EXCAVATION METHOD
EXCAVATION CONTRACTOR Client Provided
CHECKED BY SSR
DATE STARTED 8/31/21 COMPLETED 8/31/21
GROUND WATER LEVEL:
GROUND ELEVATION +-334
LONGITUDE -122.60337 LATITUDE 46.95015
AT TIME OF EXCAVATION
SAMPLE TYPENUMBERDEPTH(ft)0
5
10
PAGE 1 OF 1
TEST PIT NUMBER TP-1
PROJECT NUMBER ES-8113 PROJECT NAME Crystal Springs
GENERAL BH / TP / WELL - 8113.GPJ - GRAPHICS TEMPLATE.GDT - 10/6/21Earth Solutions NW, LLC
15365 N.E. 90th Street, Suite 100
Redmond, Washington 98052
Telephone: 425-449-4704
Fax: 425-449-4711
TESTS
U.S.C.S.MATERIAL DESCRIPTION
GRAPHICLOG
MC = 3.6%
MC = 9.3%
Fines = 0.9%
MC = 3.0%
Fines = 0.4%
TPSL
GP
Dark brown TOPSOIL, abundant roots
Brown poorly graded GRAVEL with sand, medium dense, damp
-abundant cobbles and small boulders present throughout
-minor caving from 3.5' to BOH
-becomes moist
[USDA Classification: extremely gravelly coarse SAND]
-becomes damp
[USDA Classification: extremely gravelly coarse SAND]
Test pit terminated at 11.5 feet below existing grade. No groundwater encountered during
excavation. Caving observed from 3.5 feet to BOH.
1.0
11.5
NOTES Depth of Topsoil & Sod 12": field grass
LOGGED BY SKH
EXCAVATION METHOD
EXCAVATION CONTRACTOR Client Provided
CHECKED BY SSR
DATE STARTED 8/31/21 COMPLETED 8/31/21
GROUND WATER LEVEL:
GROUND ELEVATION +-334
LONGITUDE -122.60344 LATITUDE 46.95049
AT TIME OF EXCAVATION
SAMPLE TYPENUMBERDEPTH(ft)0
5
10
PAGE 1 OF 1
TEST PIT NUMBER TP-2
PROJECT NUMBER ES-8113 PROJECT NAME Crystal Springs
GENERAL BH / TP / WELL - 8113.GPJ - GRAPHICS TEMPLATE.GDT - 10/6/21Earth Solutions NW, LLC
15365 N.E. 90th Street, Suite 100
Redmond, Washington 98052
Telephone: 425-449-4704
Fax: 425-449-4711
TESTS
U.S.C.S.MATERIAL DESCRIPTION
GRAPHICLOG
MC = 1.4%
Fines = 0.4%
MC = 1.8%
Fines = 0.4%
TPSL
GW
GW
Dark brown TOPSOIL, abundant roots
Brown well-graded GRAVEL with sand, medium dense, damp
[USDA Classification: extremely gravelly coarse SAND]
-abundant cobbles and small boulders present throughout
-becomes very dense
-minor caving from 8' to BOH
Brown well-graded GRAVEL, dense, damp
[USDA Classification: extremely gravelly coarse SAND]
Test pit terminated at 11.0 feet below existing grade. No groundwater encountered during
excavation. Caving observed from 8.0 feet to BOH.
1.0
9.0
11.0
NOTES Depth of Topsoil & Sod 12": field grass
LOGGED BY SKH
EXCAVATION METHOD
EXCAVATION CONTRACTOR Client Provided
CHECKED BY SSR
DATE STARTED 8/31/21 COMPLETED 8/31/21
GROUND WATER LEVEL:
GROUND ELEVATION +-333
LONGITUDE -122.60414 LATITUDE 46.95036
AT TIME OF EXCAVATION
SAMPLE TYPENUMBERDEPTH(ft)0
5
10
PAGE 1 OF 1
TEST PIT NUMBER TP-3
PROJECT NUMBER ES-8113 PROJECT NAME Crystal Springs
GENERAL BH / TP / WELL - 8113.GPJ - GRAPHICS TEMPLATE.GDT - 10/6/21Earth Solutions NW, LLC
15365 N.E. 90th Street, Suite 100
Redmond, Washington 98052
Telephone: 425-449-4704
Fax: 425-449-4711
TESTS
U.S.C.S.MATERIAL DESCRIPTION
GRAPHICLOG
MC = 1.8%
MC = 2.1%
Fines = 0.7%
MC = 3.5%
Fines = 0.4%
TPSL
GW
GP
Dark brown TOPSOIL, abundant roots
Brown well-graded GRAVEL with sand, medium dense, damp
-abundant cobbles and small boulders present throughout
-minor caving from 4' to BOH
-infiltration test
[USDA Classification: extremely gravelly coarse SAND]
Brown poorly graded GRAVEL with sand, medium dense, damp
[USDA Classification: extremely gravelly coarse SAND]
Test pit terminated at 11.0 feet below existing grade. No groundwater encountered during
excavation. Caving observed from 4.0 feet to BOH.
1.0
9.5
11.0
NOTES Depth of Topsoil & Sod 12": field grass
LOGGED BY SKH
EXCAVATION METHOD
EXCAVATION CONTRACTOR Client Provided
CHECKED BY SSR
DATE STARTED 8/31/21 COMPLETED 8/31/21
GROUND WATER LEVEL:
GROUND ELEVATION +-331
LONGITUDE -122.60413 LATITUDE 46.95006
AT TIME OF EXCAVATION
SAMPLE TYPENUMBERDEPTH(ft)0
5
10
PAGE 1 OF 1
TEST PIT NUMBER TP-4
PROJECT NUMBER ES-8113 PROJECT NAME Crystal Springs
GENERAL BH / TP / WELL - 8113.GPJ - GRAPHICS TEMPLATE.GDT - 10/6/21Earth Solutions NW, LLC
15365 N.E. 90th Street, Suite 100
Redmond, Washington 98052
Telephone: 425-449-4704
Fax: 425-449-4711
TESTS
U.S.C.S.MATERIAL DESCRIPTION
GRAPHICLOG
MC = 2.4%
MC = 1.7%
Fines = 0.1%
MC = 2.8%
TPSL
GP
Dark brown TOPSOIL, abundant fine roots
Brown poorly graded GRAVEL with sand, dense, damp
-abundant cobbles and small boulders present throughout
-minor caving from 4' to 6'
-minor mottling
-major caving from 6' to BOH
[USDA Classification: extremely gravelly coarse SAND]
Test pit terminated at 10.5 feet below existing grade. No groundwater encountered during
excavation. Caving observed from 4.0 feet to BOH.
0.5
10.5
NOTES Depth of Topsoil & Sod 6": field grass
LOGGED BY SKH
EXCAVATION METHOD
EXCAVATION CONTRACTOR Client Provided
CHECKED BY SSR
DATE STARTED 8/31/21 COMPLETED 8/31/21
GROUND WATER LEVEL:
GROUND ELEVATION +-332
LONGITUDE -122.60331 LATITUDE 46.9495
AT TIME OF EXCAVATION
SAMPLE TYPENUMBERDEPTH(ft)0
5
10
PAGE 1 OF 1
TEST PIT NUMBER TP-5
PROJECT NUMBER ES-8113 PROJECT NAME Crystal Springs
GENERAL BH / TP / WELL - 8113.GPJ - GRAPHICS TEMPLATE.GDT - 10/6/21Earth Solutions NW, LLC
15365 N.E. 90th Street, Suite 100
Redmond, Washington 98052
Telephone: 425-449-4704
Fax: 425-449-4711
TESTS
U.S.C.S.MATERIAL DESCRIPTION
GRAPHICLOG
GB
MC = 2.1%
MC = 2.9%
Fines = 0.7%
MC = 3.8%
TPSL
GP
Dark brown TOPSOIL, abundant fine roots
Brown poorly graded GRAVEL with sand, medium dense, damp
-abundant cobbles and small boulders present throughout
-minor caving from 4.5' to BOH
[USDA Classification: extremely gravelly coarse SAND]
-becomes moist
Test pit terminated at 12.5 feet below existing grade. No groundwater encountered during
excavation. Caving observed from 4.5 feet to BOH.
1.0
12.5
NOTES Depth of Topsoil & Sod 12": field grass
LOGGED BY SKH
EXCAVATION METHOD
EXCAVATION CONTRACTOR Client Provided
CHECKED BY SSR
DATE STARTED 8/31/21 COMPLETED 8/31/21
GROUND WATER LEVEL:
GROUND ELEVATION +-331
LONGITUDE -122.60438 LATITUDE 46.94935
AT TIME OF EXCAVATION
SAMPLE TYPENUMBERDEPTH(ft)0
5
10
PAGE 1 OF 1
TEST PIT NUMBER TP-6
PROJECT NUMBER ES-8113 PROJECT NAME Crystal Springs
GENERAL BH / TP / WELL - 8113.GPJ - GRAPHICS TEMPLATE.GDT - 10/6/21Earth Solutions NW, LLC
15365 N.E. 90th Street, Suite 100
Redmond, Washington 98052
Telephone: 425-449-4704
Fax: 425-449-4711
TESTS
U.S.C.S.MATERIAL DESCRIPTION
GRAPHICLOG
Earth Solutions NW, LLC
Appendix B
Laboratory Test Results
ES-8113
0
5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
90
95
100
0.0010.010.1110100
3
D100
140
Specimen Identification
1
fine
6
HYDROMETER
304
1.2
0.3
0.9
0.4
0.4
101/2
COBBLES
Specimen Identification
4
coarse
20 401.5 8 14
USDA: Brown Extremely Gravelly Coarse Sand. USCS: GP with Sand.
USDA: Brown Extremely Gravelly Coarse Sand. USCS: GP.
USDA: Brown Extremely Gravelly Coarse Sand. USCS: GP with Sand.
USDA: Brown Extremely Gravelly Coarse Sand. USCS: GP with Sand.
USDA: Brown Extremely Gravelly Coarse Sand. USCS: GW with Sand.
6 60
PERCENT FINER BY WEIGHTD10
6.934
12.226
10.116
11.877
7.12
14.952
25.97
27.313
26.824
18.742
GRAIN SIZE DISTRIBUTION
100
18.27
15.34
33.69
22.41
15.61
LL
TP-01
TP-01
TP-02
TP-02
TP-03
0.818
1.693
0.811
1.197
1.2
3/4
U.S. SIEVE OPENING IN INCHES U.S. SIEVE NUMBERS
GRAVEL SAND
37.5
75
75
75
37.5
%Silt
3.93
3.40
4.62
4.39
2.25
TP-01
TP-01
TP-02
TP-02
TP-03
2 2003
Cc CuClassification
%Clay
16
PID60 D30
coarse SILT OR CLAYfinemedium
GRAIN SIZE IN MILLIMETERS
3/8 50
7.0ft.
13.0ft.
8.0ft.
11.5ft.
2.0ft.
7.00ft.
13.00ft.
8.00ft.
11.50ft.
2.00ft.
PL
PROJECT NUMBER ES-8113 PROJECT NAME Crystal Springs
GRAIN SIZE USDA ES-8113 CRYSTAL SPRINGS.GPJ GINT US LAB.GDT 9/9/21Earth Solutions NW, LLC
15365 N.E. 90th Street, Suite 100
Redmond, Washington 98052
Telephone: 425-449-4704
Fax: 425-449-4711
0
5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
90
95
100
0.0010.010.1110100
3
D100
140
Specimen Identification
1
fine
6
HYDROMETER
304
0.4
0.7
0.4
0.1
0.7
101/2
COBBLES
Specimen Identification
4
coarse
20 401.5 8 14
USDA: Brown Extremely Gravelly Coarse Sand. USCS: GW.
USDA: Brown Extremely Gravelly Coarse Sand. USCS: GW with Sand.
USDA: Brown Extremely Gravelly Coarse Sand. USCS: GP with Sand.
USDA: Brown Extremely Gravelly Coarse Sand. USCS: GP.
USDA: Brown Extremely Gravelly Coarse Sand. USCS: GP.
6 60
PERCENT FINER BY WEIGHTD10
16.792
7.591
9.26
10.206
15.784
24.998
18.42
21.805
22.982
28.324
GRAIN SIZE DISTRIBUTION
100
5.16
16.56
24.81
4.27
10.23
LL
TP-03
TP-04
TP-04
TP-05
TP-06
4.849
1.112
0.879
5.383
2.768
3/4
U.S. SIEVE OPENING IN INCHES U.S. SIEVE NUMBERS
GRAVEL SAND
37.5
37.5
37.5
75
75
%Silt
2.33
2.81
4.47
0.84
3.18
TP-03
TP-04
TP-04
TP-05
TP-06
2 2003
Cc CuClassification
%Clay
16
PID60 D30
coarse SILT OR CLAYfinemedium
GRAIN SIZE IN MILLIMETERS
3/8 50
11.0ft.
8.0ft.
11.0ft.
7.0ft.
7.0ft.
11.00ft.
8.00ft.
11.00ft.
7.00ft.
7.00ft.
PL
PROJECT NUMBER ES-8113 PROJECT NAME Crystal Springs
GRAIN SIZE USDA ES-8113 CRYSTAL SPRINGS.GPJ GINT US LAB.GDT 9/9/21Earth Solutions NW, LLC
15365 N.E. 90th Street, Suite 100
Redmond, Washington 98052
Telephone: 425-449-4704
Fax: 425-449-4711
Earth Solutions NW, LLC
Report Distribution
ES-8113
EMAIL ONLY Copper Ridge, LLC
P.O. Box 73790
Puyallup, Washington 98373
Attention: Mr. Evan Mann