HomeMy WebLinkAboutGEO2020-00074 - GEO Geological Review - 10/16/2020 74
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PLANNING
Belfair Administration Building
Stormwater Management Report
RECEIVED
OCT 16 2020
615 W. Alder Street
Prepared for
Washington State Department of Natural Resources
950 Farman Ave. N.
Enumclaw,WA 98022-9282
v WASHINGTON STATE DEPT OF
nATURAL
RESOURCES
Prepared by
Parametrix
1019 39th Avenue SE,Suite 100
Puyallup,WA 98374
T.253.604.6600 F. 1.855.542.6353
www.parametrix.com
06-15-2020 1214-1795-028
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CITATION
OVAIAjq
Parametrix. 2020. Belfair Administration Building
Stormwater Management Report. Prepared by Parametrix,
Puyallup,WA.06-15-2020.
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Belfair Administration Building
Stormwater Management Report
Washington State Department of Natural Resources
CERTIFICATION
The technical material and data contained in this document were prepared under the supervision and
direction of the undersigned, whose seal, as a professional engineer licensed to practice as such, is
affixed below.
i
, .
Prepared by Zac Garrard, EIT
Checked by Sam Nielson, P.E.
Approved by Sam Nielson, P.E.
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Belfair Administration Building
Stormwater Management Report
Washington State Department of Natural Resources
TABLE OF CONTENTS
1. PROJECT OVERVIEW...............................................................................................................2
2. EXISTING SITE HYDROLOGY....................................................................................................2
3. DEVELOPED SITE HYDROLOGY................................................................................................3
4. BASIC REQUIREMENTS...........................................................................................................3
4.1 Minimum Requirements#1:Stormwater Site Plan.........................................................................3
4.2 Minimum Requirements#2:Construction Stormwater Pollution Prevention (CSWPPP)...............4
4.3 Minimum Requirements#3:Source Control of Pollution...............................................................4
4.4 Minimum Requirements#4: Preservation of Natural Drainage Systems........................................5
4.5 Minimum Requirements#5:On-Site Management........................................................................5
S. OTHER PERMITS.....................................................................................................................5
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Belfair Administration Building
Stormwater Management Report
Washington State Department of Natural Resources
ACRONYMS
BMPs best management practices
CFS cubic feet per second
Ecology Washington State Department of Ecology
EPSC erosion prevention and sediment control
hrs hours
LF linear feet
LID low-impact development
NPDES National Pollutant Discharges Elimination System
NPGIS Non-Pollution Generating Impervious Surface
NRCS National Resource Conservation Service
PGIS pollution generating impervious surfaces
ROW right-of-way
SF square feet
SWMMWW Stormwater Management Manual for Western Washington
SWPPP Stormwater Pollution Prevention Plan
TMDL Total Maximum Daily Loads
TSS total suspended solids
WRIA Water Resource Inventory Area
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Belfair Administration Building
Stormwater Management Report
Washington State Department of Natural Resources
1. PROJECT OVERVIEW
The Belfair Administration Building project proposes to construct an administration office building,
paved accessible parking spot, concrete sidewalk,and a gravel parking lot in a partially developed site
located off of Sand Hill Road in Belfair,Washington.The proposed addition will be constructed on
existing Department of Natural Resources(DNR)property as seen in Figure 1.
Proposed construction activities include:
• Constructing an office building
• Installing concrete sidewalks to the building
• Improving a gravel driveway connection
• Installing domestic water, storm drain lines,and septic system.
• Demolition and site grading
• Constructing a gravel infiltration trench
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Mission Creek® ,
CorrecWns Cener
PROJECT
PROJECT LOCATION
LOCATION
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Figure 1 Vicinity Map(N.T.S.)
To incorporate low-impact development(LID)best management practices(BMPs),the site's stormwater
facilities include minimizing pollution generating impervious surfaces(PGIS)and a gravel infiltration
trench to manage all runoff generated from the site's proposed improved surfaces. Full dispersion will
manage all runoff generated from PGIS and native infiltration within the infiltration trench will manage
runoff generated from the site's non-pollution generating impervious surfaces(NPGIS).
This stormwater report has been prepared based on the requirements of the 2019 Stormwater
Management Manual for Western Washington(SWMMWW)to meet the stormwater requirements for
Mason County.
2. EXISTING SITE HYDROLOGY
The project is located on a partially developed lot in Belfair,WA in Mason County.The site is relatively
flat in the gravel surfaced areas sloping gradually to the northwest towards forested areas.The western
edge of the site is forested before dropping drastically into a heavily,wooded drainage ravine.The
developed portions of the site include gravel roads, parking, and material storage areas.There are a
series of existing maintenance and storage sheds and office buildings located throughout the site.The
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Belfair Administration Building
Stormwater Management Report
Washington State Department of Natural Resources
undeveloped areas are wooded remains of the surrounding forests.The undeveloped portions of the
site were covered in various vegetation including grasses,ferns, and, stands of trees.
Runoff from existing developed areas generally sheds to the west into wooded vegetation aligning Sand
Hill Road. Runoff will be infiltrated or evaporated once collecting in depressed areas, and in high rainfall
events, Mission Creek is the outfall that will convey runoff into Hood Canal.
A geotechnical investigation report indicates that on-site soils consist of various compositions of glacial
till. The till contains densely compacted sands,gravels, and clays from glacial activity in the region. The
soils identified as Class B and hydrologically categorized as well draining. Groundwater was not
encountered during site investigation, but historical well logs indicate that the groundwater level ranges
from 70-to 150-feet below ground surface. Perched groundwater layers are a possibility, but none were
encountered. Infiltration tests were not performed.
3 , DEVELOPED SITE HYDROLOGY
The Belfair Administration Building project will construct an administration office building, paved
accessible parking spot, concrete sidewalk, and a gravel parking lot to replace an existing building.
Grading will be minimal with primary activities being excavation for the building's foundation and
preparation of sidewalk forms.The existing office building will remain in use as the proposed
administration building is constructed. Following completion and relocation of resources into the new
structure, the older building will be demolished and debris removed from the site.
The site will maintain existing drainage patterns throughout the majority of the site as the developed
site is relatively levelled gravel surfacing, which will be regraded following construction. Stormwater will
collect and sheet flow on the gravel surface to the west through vegetated brush and into the nearby
woods. Full dispersion will manage all runoff generated from the replaced gravel surfaces associated
with the final grading. Runoff generated from the buildings' roofs will be collected in gutters, piped into
a roof drain storm line, and conveyed into a gravel infiltration/dispersion trench.The roof drain storm
line is the only stormwater conveyance network proposed.
4 , BASIC REQUIREMENTS
Per the SWMMWW, construction activities within Western Washington that disturb greater than 2,000
SF but less than 5,000 SF or more of land are required to implement minimum requirements during the
construction process to limit adverse impacts on the site and surrounding areas.The project proposes
constructing or replacing 4,665 SF of impervious surfaces,which triggers compliance with Minimum
Requirements 1 through 5 from the SWMMWW for all new and replaced surfaces and land disturbed.
The following Minimum Requirements will be met include:
4.1 Minimum Requirements #1: Stormwater Site Plat
Preparation of this stormwater management plan in accordance with the SWMMWW outlines and
satisfies this criterion.The proposed development activities are indicated in the Belfair Administration
Building civil design plan set submitted separately. Stormwater elements are outlined within this report
in conjunction with the plan set.
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Stormwater Management Report
Washington State Department of Natural Resources
4.2 Minimum Requirements # 2:Construction Stormwater
Pollution Prevention (CSWPPP)
These thirteen erosion control requirements below must be met evaluated for the project applicability
and implemented prior to and during any ground-clearing and construction activities: Mark Clearing
Limits
1. Establish Construction Access
3. Control Flow Rates
4. Install Sediment Controls
5. Stabilize Soils
6. Protect Slopes
7. Protect Drain Inlets
8. Stabilize Channels and Outlets
9. Control Pollutants
10. Control Dewatering
11. Maintain BMPs
12. Manage the Project
13. Protect Low Impact Development BMPs(Infiltration BMPs)
A Construction Stormwater Pollution Prevention Plan(CSWPPP) is attached as Appendix C.Appropriate
BMPs are included in the CSWPPP with necessary details to meet the thirteen CSWPPP elements. It is
the contractor's responsibility to follow the CSWPPP, utilize the BMPs indicated throughout the duration
of the project's completion,and maintain an updated CSWPPP on-site for reference as amendments are
incorporated.
4.3 Minimum Requirements #3: Source Control of Pollution
The source-control BMPs listed below give a broad overview of measures that will be taken to prevent
stormwater from coming into contact with pollutants on-site, both during and after construction
activities:
• To minimize dust generation during construction,soil will be wetted down with water prior to
ground disturbance.All generated waste must be properly disposed of.
• Loose aggregate chunks and dust will be swept or shoveled and collected (not hosed down a
storm drain)for recycling or proper disposal.
• A Spill Prevention Countermeasures and Control Plan (SPCC) Plan is required from the
contractor to mitigate any potential spills or leaks from construction materials, machinery, and
equipment during construction.
• Runoff fully dispersed off-site with flow through a minimum of 25-feet of native vegetation with
a flow path less than 150-feet per BMP F6.42.Sediment and pollutants are deposited within the
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vegetation as it flows downhill.Vegetation shall be preserved and maintained to meet
dispersion requirements.
4.4 Minimum Requirements #4: Preservation of Natural
Drainage Systems
Natural drainage patterns and discharges from the project site at the natural location will be maintained
to the maximum extent practicable.As previously mentioned,the site will maintain existing drainage
patterns by reworking the existing gravel parking lot to continue dispersing runoff to the west matching
existing conditions. Runoff generated from the buildings' roofs will be collected in gutters, piped into a
roof drain storm line, and conveyed into a gravel infiltration/dispersion trench.Water will collect,fill the
trench, and distribute overflow runoff to the west of the site through grassy slopes adjacent.
4.5 Minimum Requirements #5: On-Site Management
To reduce the amount of disruption of the natural hydrologic characteristics of the site on-site
stormwater management practices will be implemented.As previously mentioned, runoff generated
from the parking surfaces will match existing conditions of dispersion across the impervious areas into
vegetated woods. Runoff attributed to the proposed building's roof will be collected in gutters, piped
into a roof drain storm line, and conveyed into a gravel infiltration/dispersion trench.The runoff will
infiltrate into the surrounding soil strata or collect and overflow into a grassy hillside and disperse away
from the building.As a result of these practices, runoff will continue to be contained within the site and
the immediate vicinity as it does prior to proposed construction activities.
S. OTHER PERMITS
Permits required or anticipated for this project are listed below.
• No other permits are known at this time
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Belfair Administration Building
Stormwater Management Report
Washington State Department of Natural Resources
Appendix A
Geotechnical Investigation Report
6 06-15-2020 1 214-1795-028
Technical Memorandum
TO: Sam Nielson PE CommunityBuilding Senior Engineer, Parametrix Inc.
E
FROM: Barsha Pradhan, EIT, and Benjamin Ford, PE
DATE: June 19, 2020
RE: Geologic Hazard Assessment
Washington State Department of Natural Resources Administration Building
Belfair, Washington
Project No. 0193082.010.011
Introduction
This technical memorandum summarizes the results of a geologic hazard assessment completed by Landau
Associates, Inc. (LAI) in support of the Washington State Department of Natural Resources (DNR; project
owner) Administration Building project in Belfair, Washington.The assessment was completed in
accordance with the requirements in Chapter 8.52.140 of the Mason County Municipal Code (MCMC).
Services were provided in accordance with the scope outlined in the Subconsultant Agreement for
Professional Services between LAI and Parametrix, Inc. (project civil engineer), executed May 26, 2020.
Project Understanding
Based on information provided by representatives of DNR and Parametrix, LAI understands that an existing
administration building will be demolished and replaced with a prefabricated structure,which will also be
used for administrative purposes.The new administration building will be located at 3420 Northeast
Sandhill Road in Belfair, Washington (Mason County Parcel No. 123180060000; site; Figure 1).The new
building will be constructed south of the existing building, in an area that was previously graded and
developed.
Per the MCMC, a geologic hazard assessment is required for proposed developments that will be located
within 250 feet (ft) of potential geologic hazard areas (GHAs). The new building will be located
approximately 60 ft east of the top of a 35 to 45 percent slope. Mason County (County) has identified the
slope as a potential GHA. Minimal grading will be required during construction. Clearing and grubbing of
native vegetation adjacent to, and within,the potential GHA will not be required. The approximate
locations of the new administration building and slope (potential GHA) are shown on Figure 2.
To satisfy the County's reporting requirements, Parametrix requested that LAI perform a geologic hazard
assessment in accordance with the MCMC.
Geologic Conditions
Geologic information for the site and the surrounding area was obtained from the Geologic Map of the
Belfair 7.5-minute Quadrangle, Mason, Kitsap, and Pierce Counties, Washington (Polenz 2009). Subsurface
deposits at the proposed building site are mapped as Vashon stade glacial till (Qgt), a highly compact
mixture of clay, silt, sand, gravel, and cobbles. Glacial till in this region typically consists of 1 to 6 ft of
14 LANDAU
ASSOCIATES 955 Malin Lane SW,Suite B • Tumwater,Washington 98501 (360)791-3178
Landau Associates
weathered till (ablation till)overlying highly compact, unweathered lodgement till.Surface geology along
the adjacent steep slope is mapped as glacial till overlying pre-Vashon gravel (Qpg),a unit that includes
sand,gravel,and minor silt. Like glacial till, pre-Vashon gravel is glacially overridden and highly compact.
Surface Conditions
The site currently is developed with the existing administration building,which can be accessed from the
north via a gravel-surfaced road. Gravel surfacing surrounds the existing building and is present across the
proposed building footprint. Managed forestland is located east of the site.The first 70 ft of forest consists
of 15-to 20-ft-tall reprod trees then transitions to mature trees. Dense underbrush consisting of salal
(Gaultheria shallon), huckleberry(Gaylussacia), and rhododendron are also present within the forest.The
site is bordered to the south and west by the Mission Creek Corrections Center(MCCC).Site topography is
generally flat with a 55-to 60-ft-tall slope located east of the proposed building footprint. Existing site
features are shown on Figure 2.
Subsurface Conditions
LAI reviewed publicly available geologic information for the site, including one well report and three
geotechnical exploration logs (Ecology;accessed June 16, 2020;Attachment 1). Logs of the historical well
(installed for MCCC)and geotechnical explorations(completed for DNR) indicate that the mapped geology
is consistent with actual site subsurface conditions. Based on LAI's review of the logs, 1 to 2 ft of
weathered till overlying highly compact glacial till was observed in the historical geotechnical explorations.
LAI estimates that the dense/compact glacial till, reported on the exploration logs, will be encountered
within 2 to 5 ft of ground surface.
Groundwater Conditions
Based on LAI's review of the well report (Attachment 1),site groundwater levels are approximately 70 to
150 ft below ground surface.Although not noted on the well report, minor perched groundwater layers
may be present at shallow depths within the glacial till or pre-Vashon gravel units. No springs or perched
groundwater conditions were observed at the site during LAI's June 2,2020 site reconnaissance.
Geologic Hazard Assessment
LAI visited the site on June 2,2020 to observe existing conditions. During the site visit, LAI observed no
groundwater seeps, hummocky ground,ground cracks,terraced topography, bowed/arched trees,or other
geomorphic expressions indicative of current or previous slope movement. Based on LAI's measurements,
recorded with a hand-held inclinometer,the slope adjacent to the site is inclined at a 35 to 45 percent
grade(Figure 2).
LAI reviewed available mapping data and found that no historical slope instability/landslide activity had
been recorded for the site. However, mass wasting/landslide deposits are mapped approximately 850 ft
Geologic Hazard Assessment
DNR Administration Building 2 June 19,2020
Landau Associates
southwest and 1,100 ft north of the site (Polenz et al. 2009). No recent/active landslides were noted at the
site or within the immediate vicinity.
The MCMC defines geologically hazardous areas as areas exhibiting one or more of the following
conditions:
1. Indications of earth movement, such as debris slides, earthflows, slumps, and rock falls.
2. Artificially oversteepened or unengineered slopes (i.e., cuts or fills).
3. Slopes containing soft or potentially liquefiable soils.
4. Oversteepened or otherwise unstable areas as a result of stream incision, stream bank erosion, and
undercutting by wave action.
5. Slopes greater than 15 percent with:
a. intersecting geologic contacts with a relatively permeable sediment overlying a relatively
impermeable sediment or bedrock (e.g., sand overlying clay) and
b. springs or groundwater seepage.
6. A slope of 40 percent or steeper with a vertical relief of 10 ft or more, except areas composed of
consolidated rock. A slope is delineated by establishing its toe and top and measured by averaging
the inclination over at least 10 ft of vertical relief.
Per the above conditions,the slope east of the site is considered a GHA. The slope has a grade of more
than 40 percent and a vertical relief of 10 ft or more. LAI recommends including a minimum 50-ft buffer of
undisturbed native vegetation, as allowed by Section 8.52.140(D)(6)(b) of the MCMC.The proposed buffer
is shown on Figure 2.
The risk for long-term slope erosion and surficial sliding is considered negligible, provided the buffer
remains undisturbed. Development plans should include measures to control erosion and surface water
flow, during and post construction. Onsite stormwater management facilities should disperse runoff fully
before it reaches the buffer.
Based on the results of LAI's geologic review and site reconnaissance,the proposed building location is
considered suitable from a geologic standpoint.The slope consists of highly compact glacial till and
appears to be stable. Provided a minimum 50-ft buffer is implemented, the site is expected to have a low
risk for landslide activity, and the proposed development will not have an adverse impact on the GHA.
In LAI's opinion and per its discussions with the County, a landslide hazard geotechnical report, as
described in Chapter 8,52.140 of the MCMC, should not be required. In its geologic hazard assessment, LAI
sufficiently assessed the presence of the GHA and the impact the proposed administration building could
have on the GHA.
Use of This Technical Memorandum
Landau Associates prepared this technical memorandum for the exclusive use of the Washington State
Department of Natural Resources and Parametrix, Inc. for specific application to the Washington State
Geologic Hazard Assessment
DNR Administration Building 3 June 19,2020
r
Landau Associates
Department of Natural Resources Administration Building project in Belfair,Washington. No other party is
entitled to rely on the information,conclusions,and recommendations included in this document without
the express written consent of Landau Associates. Further,the reuse of information,conclusions,and
recommendations provided herein for extensions of the project or for any other project,without review
and authorization by Landau Associates, shall be at the user's sole risk. Landau Associates warrants that
within the limitations of scope,schedule,and budget, its services have been provided in a manner
consistent with that level of care and skill ordinarily exercised by members of the profession currently
practicing in the same locality under similar conditions as this project. Landau Associates makes no other
warranty,either express or implied.
Closing
We trust that this technical memorandum provides you with sufficient information to proceed with the
project. If you have questions or comments, or if we can be of further service, please contact the
undersigned at(360)791-3178 or at bford@landauinc.com.
LANDAU ASSOCIATES, INC.
Barsha Pradhan W14 JA r
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Benjamin Ford, PE
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[\\OLYMPIAI\PROJECTS\0193\082.010\R\DNR ADMINISTRATION BUILDING TECHNICAL MEMORANDUM 6.19.2020.DOC%]
Attachments: Figure 1.Vicinity Map
Figure 2. Site Plan
Attachment 1. Historical Boring Logs
Attachment 2. Geological Assessment Submittal Checklist
References
County. 2020.Title 8. Environmental Policy. Chapter 8.52. Resource Ordinance. Ordinance No. 8.52.140
Geologically Hazardous Areas. Mason County Municipal Code.June 12.
Ecology. Washington State Well Report Viewer. Washington State Department of Ecology. Accessed June
16, 2020.Available online at:
https://appswr.ecology.wa.gov/wellconstruction/map/WCLSWebMap/defauit.aspx.
Geologic Hazard Assessment
DNR Administration Building 4 June 19,2020
Landau Associates
Polenz, M. 2009. Geologic Map of the Belfair 7.5-minute Quadrangle, Mason, Kitsap, and Pierce Counties,
Washington. Washington Division of Geology and Earth Resources.July.
Geologic Hazard Assessment
DNR Administration Building 5 June 19,2020
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ASSOCIATES Belfair, Washington
ATTACHMENT 1
Historical Boring Logs
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DEPT. OF ECOLO
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SCALE: V-_�- PAGE _OF _
ECY 050-12(Rev.7106) Ecology Is an Ewal Opportunity Empkryer
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0
aai WATER WELL REPORT
ECOLOGY
Vrh101
_ ECOLOGY Origltrl8 f copy-Ecology, 2-copy-owner, 3~copy-drifter CURRENT
Q! Notice of Intent No.WE09919
Construction/Decommission rx"in circle) 3,4�, r n�^7
nX Construction `7 L• / Unique Ecology Well ID Tag No. APM063
ran Decommission ORIGINAL INSTALLATION G2-21634
❑ Water Right Permit No.
W Notice of Intent Number MISSION CREEK CORRECTION CENTER
C PROPOSEDuSE: ❑Domestic ❑ Industrial ❑Municipal Property Owner Name
0 ❑Dewaw El inigaii. El Test well a other Well Street Address 3420 NE SAND HILT,RD
C TYPE OF WORK Owners number ofwell(ifmore than one) City BELFAIR County MASON
0 Q New well ❑ Reconditioned Method: ❑Dug ❑Bored ❑ Driven
a ❑ Deepened ❑ e ❑■It Jetted LocationSE—I/4-1I4NE 1/4 Sec 13 Twn2R 02W EorI ❑ Check
E DIMENSIONS:Diameter of wcn inches,drilled R. (s,t,r Still REQUIRED) wwM[] One
Depth ofcormilctcd well
CONSTRUCTION DETAILS Lat Min/Sec
Cam 9 welded 8 Diem.Born+I ft.to 18 ft. i at/iAng Lan Deg
botoned. El Liner installed Diam.from ft.to R. Long Deg Long Min/Sec
❑Threaded Diam.From ft.to ft. Tax Parcel No.(Required) 223130030000
t Perforsdons- ❑Yes ❑a No CONSTRUCTION OR DECOMMISSION PROCEDURE
J..t
Ir Type ofpetforator used Formation:Describe by color,character,size of material and structure,and the kind and
0 SIZE ofperfs in.by in.and no.ofperfs from ft.to R. nature of the material in each stratum penetrated,with at least one entry for each shwas
` of infomration. (USE ADDITIONAL SHEETS IF NECESSARY.)
'� : QYcs []No ❑x K-Pere I.acatiao 181
C MnufacturcesName JOHNSON MATERIAL- FROM TO
C9 Type S/S Model No. TOP SOIL 0 2
Diam.7 Slot size.070 from 181 fl.to 9! 5 _R. BROWN CLAY AND GRAVEL. 2 22
Diam. Slot size from ft.to ft. BROWN CEMENTED SAND/GRAVEL 22 38
Q Gravel/Fitterpedted: ❑ Yes El No Size ofgravel/snd BROWN CEMENTED SAND/GRAVEL 38
Materials placed from ft,to ft. W/LFSIONS CLAY 69
t Surface Seal: ❑a Yes ❑ No To what depth? 18+ fl. BROWN GRAVEL 1/2INCH BIRDSEYE WB 69 74
BENTONITE BROWN CLAY 74 81
Materiel used in seal BROWN CEMENTED SAND/GRAVEL g 1 123
Did any strole contain unusable water? ❑Yea 0 No
� BROWN I/2 BIRDSEYE MINUS GRAVEL WB 123 127
CU Typeofwater? Depthofstreta GREY CLAY WITH GRAVEL 127 134
L Method of sealing strata off BROWN CEMENTED SAND/GRAVELS 134 177
PUMP:Mnufechuers Name BROWN CEMENTED GRAVEL WITH 177
Type: H.P. FRACTURED LESIONS WB 197
WATER LEVELS: Lndsurfeoe elevation above mean sea level ft.
O Static level 148 ft.below top of well Date 06/30/09 0
Z Artesian presAae lbs.per square inch Date _
H Artesian wafer is controlled by (cap,valve,etc.)
as
7>'
0 WELL TESTS: Drawdown is amount water level is lowered below static level
V Was a pump test me&? 17 Yes ❑ No Ifym by whom?AQUA PUM PS r.
Yield: 60 gAimin.with 26 ft.diatvdown after 4.5 his.
Yield: gaUmin,with ft.drowdowo after his. b
0 Yield: galAnin.with ft.drawdown after his.
ORecoverydato(rkne taken as zero when pump fumed off)(water level measured from well --)0
(� top to water kvel)
LU Time Water Level Time Water Level Time Water level
%_ 0 MIN 163 2 154 3 151.4
0 4 150.3 5 149.2 10 148.7
♦a 15 148.4 20 148.3
Date of test
Bailer Test galJmin.with fl.drawduwn after his.
L_ Airiest 35 gal./rain.with stem sal at 181 ft.for 4 hrs.
L
M Artesian Bow &p.m. Date
d) Temperature of water Was a chemical analysis made? Q Yes ❑No Start Date 06/15/2009 Completed Date 06/30/09
0 WELL CONSTRUCTION CERTIFICATION: 1 constructed and/or accept responsibility for construction of this well,and its compliance with all Washington well
= construction standards.Materials used and the information reported above are true to my best knowledge and belief.
ElDriller❑Engineer❑Trainee Name(P RD ER Drilling Company AQUA.PUMPS AND WELL DRILLING,INC.
Driller/Enginecr/Trainee Signature a 6 Address 242 ALPINE VIEW LANE
Driller or trainee License No. 22t2
City,State,'Lip PORT ANGELES. WA 98362
IF TRAINEE:Drillers License No:
Contractors
Drillers Signature. Registration No. AQUAPPW911BZ Date 07/09/2009
ECY 050-1-20(Rev 06108)Ijyou need this document in an alrenate format,please call the Water Resources Program at 360-407-6600.
Persons with hearing loss can call 711 for Washington Relay Service. Persons with a speech disability can call 877-833-6341.1) MOAL
ATTACHMENT 2
Geological Assessment Submittal Checklist
MASON COUNTY
COMMUNITY SERVICES Geological Assessment
Cuilli ng.Planning.fnvocnmenlal Health,Commumny Health
Instructions:
This checklist must be submitted with a Geological Assessment and completed, signed,and stamped by the licensed
professional(s)who prepared the Geological Assessment for review by Mason County pursuant to the Mason County
Resource Ordinance. If an item is found not applicable,the report should explain the basis for the conclusion.
Note:Unless specifically documented,this report does not provide compliance to the International Residential Code Sections
R403.1.7 for foundations on or adjacent to slopes, Section R403.1.8 for expansive soils or section 1806.7.1 of the International
Building Code Section for Foundations on or adjacent to slopes.
Applicant/Owner A091- Parcel# VL3160060=
Site Address 3420 bAJJDAJt L �-bAI - 4Et V-A 11L
(1) A discussion of geologic conditions in the general vicinity of the proposed development,with geologic unit
designation based on referenced maps.
Located on page(s) �-
(2) (a)A discussion of the ground water conditions at the site,
Located on page(s) -L.
(b) A discussion of the estimated depth to water,
Located on page(s) -I—
(c) A discussion of the quantity of surface seepage,
Located on page(s) 2
(d) A discussion of the upslope geomorphology,
' 3
Located on page(s)
(e) A discussion of location of upland waterbodies and wetlands.
Located on page(s) Nk
(3) The approximate depth to hard or dense competent soil, e.g.glacial till or outwash sand.
Located on page(s) Z- ; 7
(4) A discussion of any geomorphic expression of past slope instability(presence of hummocky ground or ground
cracks,terraced topography indicative of landslide block movement, bowed or arched trees indicating
downslope movement, etc.).
Located on page(s) �. 1
(5) A discussion of the history of landslide activity in the vicinity, as available in the referenced maps and records.
Located on page(s) 3
(6) An opinion on whether the proposed development is within the landslide hazard area or its associated buffer or
setback and the potential for landslide activity at the site in light of the proposed development.
Located on page(s) 3
(7) A recommendation by the preparer whether a Geotechnical Report should be required to further evaluate site
conditions and the proposed development of the subject property.
Rev. February 2018
K
Located on page(s) y
(8) If the presence of a hazard is determined within 300 feet of the proposed development, then the following are
delineated on a geologic map/site map:
(a) the area of the proposed development,
Located on Map(s) FIbV -6 I
(b) the boundaries of the landslide hazard area(top, both sides,and toe),
Located on Map(s) Fl[WA-E I-
(c) the associated buffers(top,both sides, and toe),
Located on Map(s) F14OVE 7-
(d) building or other setbacks(top, both sides,and toe).
Located on Map(s) F«!Vt-t Z
(9) A site map drawn to scale showing the property boundaries,scale, north arrow,and the location and nature of
existing and proposed development on the site.
Located on Map(s)
I, dENuk Kim ' I 'D hereby certify under penalty of perjury that I am a
civil engineer licensed in the State of Washington with specialized knowledge of geotechnical/geological engineering
or a geologist or engineering geologist licensed in the State of Washington with special knowledge of the local
conditions. I also certify that the Geological Assessment, dated ayWG ��. �� and entitled
KPLO` L RALIAa-fl A%1 iyir t0N - PNVL OfFtfO meets all the
requirements of the Mason County Resource Ordinance, Geologically Hazardous Areas Section, is complete and true,
that the assessment demonstrates conclusively that the risks posed by the landslide hazard can be mitigated through
the included geotechnical design recommendations,and that all hazards are mitigated in such a manner as to prevent
harm to property and public health and safety
PM�N JA r
of WAy
m y .1
q 6 9 44,E
ERE
SS�Q AL�N6 iD�Wltoto
(Signature and Stamp)
Page 2 of 2
Disclaimer:Mason County does not certify the quality of the work done in this Geological Assessment.
Belfair Administration Building
Stormwater Management Report
Washington State Department of Natural Resources
Appendix B
Civil Plans
06-15-20201214-1795-028 7
Washington State Department of Natural Resources
BelfairAd minis tration Building
Belfair, Washington
>ue 8
n
Nnbw r�.r
R - Mission Creek Q
g Corrections Center
PROJECT
LOCATION
PROJECT k
LOCATION GAS
�\O N RO U�mae{y
C'
0
?L
i
PROJECT LOCATION MAP VICINITY MAP
3
S
s
s
INDEX TO DRAWINGS
SHT NO. DWG NO. SHEET TITLE
01 G-01 COVER SHEET
02 G-02 GENERAL NOTES.LEGEND AND ABBREVIATIONS
03 OM-01 DEMOLITION,TESL AND CLEARING AND GRUBBING PLAN
i 04 DM02 DEMOLITION.TESC AND CLEARING AND GRUBBING DETAILS
!!� 05 HS-01 HARDSCAPE PLAN
D6 GR-01 GRADING AND STORM PLAN
07 UT-01 UTILITY PLAN
z
— OB O7-01 HARDSCAPE DETAILS
09 DT-02 UTILITY DETAILS
room
a UTILITIES LOCATE NOTE Knowwhers below.
s Cell before you dia
p THE LOCATION OF EXISTING UTILITIES SHOWN HEREON IS BASED ON INFORMATION OBTAINED FROM THE FIELD AND FROM RECORDS.
6 PARAMETRIX ASSUMES NO RESPONSIBILITY FOR EXACT LOCATION OF EXISTING UTILITIES SHOWN OR NOT SHOWN HEREON.
CONTRACTOR SHALL VERIFY THE EXACT SIZE,DEPTH,AND LOCATION OF EXISTING UTILITIES PRIOR TO CONSTRUCTION.CONTRACTOR 90% REVIEW SUBMITTAL
SHALL CALL FOR UNDERGROUND LOCATE AT 811 PRIOR TO START OF CONSTRUCTION.CONTRACTOR SHALL BE SOLELY RESPONSIBLE
5 FOR THE RELOCATION OF EXISTING UNDERGROUND UTILITIES DEPICTED OR NOT DEPICTED ON THESE PLANS. K"N 1E1 (� NOT FOR CONS T R U C T I O N
i REVISIONS DATE By DESIGNED B �� �a.�i_,_.'NAVE DRAWNG N0.
K. ECKER rammtrix
ONE INCH AT FULL SCALE.
DRAWN IF NOT,SCALE ACCORDINGLY ENGINEERING.PLANNING.ENVIAONMENTAtSCIENCES WASHINGTON STATE DEPARTMENT Ol of 09
K. BECKER FILE NAME � ` --�-CHECKED P51795028-CV OF NATURAL RESOURCES COVER SHEET
14 P1019 253.604.660D
53.6 4.660DAVENUE SE,SURE l00 I PUYAILUP,WA9837a BELFAIR ADMINISTRATION BUILDING G_0.1
eta-n95-o2B p \V�� WWW.PARA00
APPRovEO DATE wWw.PAfIAMFTRI%.COM BEIFAIR,WASHINGTON
JULY 2020
LEGEND-EXISTING ABBREVIATIONS GENERAL NOTES
BUILDING OUTLINE ADDL ADDITIONAL LF LINEAR FEET.LINEAR FOOT 1. THE CONTRACTOR IS RESPONSIBLE FOR FURNISHING AND INSTALLING ALL MATERIALS,LABOR,AND EQUIPMENT NECESSARY TO
ADJ ADJUSTABLE LG LENGTH LONG COMPLETE THE WORK SHOWN ON THESE DRAWINGS AND TO OBTAIN ACCEPTANCE BY THE COUNTY.
AGG AGGREGATE LN LINEAR
CATCH BASIN ALLOW ALLOWANCE.ALLOWABLE LN LANE 2, THE CONTRACTOR SHALL COORDINATE ALL CONSTRUCTION ACTIVITIES WITH ADJACENT PROPERTY OWNERS.DRIVEWAYS TO REMAIN
STORM MANHOLE AMT AMOUNT LT LEFT ACCESSIBLE AT ALL TIMES.
GAS VALVE ANG ANGLE LTG LIGHTING
AR,APPD ANGLE POINT APPROVED MAN MANUAL 3 INSTALL STRAW BALE BARRIERS SILT FENCE,WATTLES.SEDIMENT TRAPS,AND OTHER NECESSARY EROSION CONTROL MEASURES TO
FIRE HYDRANT APPROX APPROXIMATE MATL MATERIAL PREVENT EROSION AND KEEP SILT AND CONTAMINATED WATER FROM LEAVING THE PROJECT LIMITS.EROSION CONTROL MEASURES
LUMINARY APWA AMERICAN PUBLIC WORKS ASSOCIATION MH MANHOLE SHALL BE INSTALLED AND MAINTAINED PER MASON COUNTY AND DEPARTMENT OF ECOLOGY STANDARDS BY THE CONTRACTOR.
MAILBOX ARV AIR RELEASE VALVE MIN MINIMUM,MINUTE
180X AS%H ASPHALT RISC MISCELLANEOUS 4. ALL AREAS DISTURBED DURING CONSTRUCTION SHALL BE RESTORED TO THEIR ORIGINAL'PRELONSTRUCTKIN'STATE OR BETTER AS
DETERMINED BY THE OWNER AND COUNTY INSPECTOR.
ASSY ASSEMBLY MILES PER HOUR
POWER POLE ANCHOR A7B ASPHALT TREATED BASE MPH LEES
POWER POLE AVE AVENUE MTL METAL 5 ALL CONSTRUCTION MUST COMPLY WITH THE WSDOT STANDARD SPECIFICATION(LATEST EDITION)UNLESS OTHERWISE SUPERSEDED
POWER RISER AVG AVERAGE MIN MONITORING WELL BY COUNTY STANDARDS.
POWER VAULT BC BEGINNING OF CURVE,BUT CIRCLE N NORTH,NORTHING
BCR BEGINNING OF CURVE CENTER NIC NOT IN CONTRACT 6 MAINTAIN 10 MN HORIZONTAL AND I S'MN VERTICAL SEPARATION BETWEEN WATER AND SEWER MAINS UNLESS OTHERWISE NOTED.
BF BLIND FLANGE NO. NUMBER
SANITARY CLEANOUT BLDG BUILDING NITS NOT TO SCALE 7 A MINIMUM 64NCH SAND CUSHION IS REQUIRED FOR ANY UT1Dn LINE WITHIN 64NCHES OF ANOTHER UTILITY LINE AT CROSSING
SANITARY SEWER MANHOLE BLVD BOULEVARD P PUMP.POWER
SIGN sm BEAM.BENCH MARK PC POINT OF CURVATURE B. PIPE LENGTHS ARE FOR CALCULATION PURPOSES ONLY.BID QUANTITIES SHALL BE CALCULATED AS REQUIRED,
BID BLOW OFF PCC PORTLAND CEMENT CONCRETE
SIGNAL LUMINARY SOT BOTTOM PCV PRESSURE CONTROL VALVE 9 SYMBOLS ARE NOT TRUE SIZE
SURVEY MONUMENT BRG BEARING PERF PERFORATE,PERFORATED
TELEPHONE MANHOLE BVC BEGIN VERTICAL CURVE PH PHASE
CALC CALCULATION % POINT OF INTERSECTION.PRESSURE INDICATOR
TELEPHONE RISER CAP CAPACITY PNC POINT OF INTERSECTION FOR VERTICAL CURVE
WATER METER CB CATCH BASIN PP POWER POLE
WATER VALVE CCP CONCRETE CYLINDER PIPE PRV PRESSURE REGULATING VALVE.PRE
SSURE RELIEF VALVE.
CCSP CONCRETE LINED AND COATED STEEL PIPE PRESSURE REDUCING VALVE
CEM CEMENT PS PRESSURE SWITCH
ALIGNMENT RIGHT OF WAY LINE CHV CHECK VALVE PSI POUNDS PER SQUARE INCH
ASPHALT LINE CI CAST IRON PT POINT OF TANGENCY,POINT
DITCH CENTERLINE CP CAST IN PLACE,CAST IRON PIPE PV PLUG VALVE
CUR CLEAR.CLEARANCE PVI POINT OF VERTICAL INTERSECTION
FENCE•WOOD CND CONDUIT PVT PAVEMENT,PAVING.PRIVATE
EXISTING GRAVEL ROAD CO COUNTY,CLEANOUT PWR POWER
HIGH WATER MARK CONIC CONCRETE OTY QUANTITY
MINOR CONTOURS CONN CONNECT.CONNECTION DUAL QUALITY
i CONST CONSTRUCT,CONSTRUCTION R RISER
MAJOR CONTOURS CONT CONTINUE,CONTINUOUS RAD RADIUS
SANITARY SEWER LINE CONTR CONTRACTOR RCP REINFORCED CONCRETE PPE
STORM DRAIN LINE COORD COORDINATE RD ROAD.ROOF DRAIN
WATER BANK LINE CSBC CRUSHED SURFACING BASE COURSE RED REDUCER
WATER MAN CSTC CRUSHED SURFACING TOP COURSE REF REFERENCE
CTR CENTER REDD REQUIRED
RIGHT#-WAY BOUNDARY CUFT CUBIC FOOT,CUBIC FEET RET RETAINING,RETURN
8 CULV CULVERT REV REVERSE.REVISE
PROPERTY BOUNDARY
CV CONTROL VALVE ROT ROTATE
CY CUBIC YARD ROW RIGHT OF WAY
D DEPTH,DENSITY.DRAIN DRAINAGE FIT RIGHT
DBL DOUBLE RV RELIEF VALVE
DEG DEGREE RW RIGHT OF WAY
DEMO DEMOLITION S SOUTH
DEFT DEPARTMENT SCH SCHEDULE
LEGEND-PROPOSED DET DETAIL So STORM DRAIN
DI DUCTILE IRON SDMH STORM DRAIN MANHOLE
3
— ALIGNMENT CENTERLINE DIM DIAMETER SE SPOT EVALUATION
DIM DIM
AI ENSION SECT SECTION
WATER MN CAP Dip
DUCTILE IRON PIPE EEG SEGMENT
WATER PIPE FITTING DIST DISTANCE.DISTRICT SERV SERVICE
DSGN DESIGN SIG SIGNAL
WATER VALVE DWG DRAWING SL SLOPE,RAW SLUDGE
E EAST,EASTING SPA SPACE.SPACES
EA EACH SPEC SPECIFICATION
WATER MAIN EC END OF CURVE SPG SPACING
EL ELEVATION So SQUARE
.e ELL ELBOW SOFT SQUARE FOOT,SQUARE FEET
m FIRE HYDRANT EOP EDGE OF PAVEMENT SON SQUARE NCH,SQUARE INCHES
WATER SERVICE WAMETER EQUIP EQUIPMENT SOYD SQUARE YARD,SQUARE YARDS
EVC END VERTICAL CURVE SS SANITARY SEWER
`3 PRESSURE RELIEF VALVE EXIST EX EXISTING SSMH SANITARY SEWER MANHOLE
EL EXCAVATE ST STREET
a FCR FINE CRUSHED ROCK STA STATION
y FG FINISH GRADE STD STANDARD
FH FIRE HYDRANT SUR SURFACE
FIN FINISH.FINISHED SURV SURVEY
FL FLOW LINE SYS SYSTEM
DETAIL AND SECTION DESIGNATION FFIG T M FORCE E FLANGED TAN N EL TANGENT
f PHONE
G GAS TEMP TEMPERATURE.TEMPORARY
INDICATES DETAIL INDICATES SECTION GND GROUND THK THICK.THICKNESS
NUMBER 6 LETTER GR GRADE THRU THROUGH
GV GATE VALVE TOB TOP OF BANK
D H HIGH TOC TOP OF CONCRETE.TOP OF CURB
g INDICATES DRAWINGISHEET INDICATES DRAWING/SHEET HOR2 HORIZONTAL TOT TOTAL
WHERE DETAIL IS SHOWN WHERE SECTION IS SHOWN HT HEIGHT TOW TOP CA WALL
ID INSIDE DIAMETER TYP TYPICAL
.j IE INVERT ELEVATION UG UNDERGROUND
IN INCH LIP UTILITY POLE
INCL INCLUDE.INCLUDING UPR UPPER
8 DETAIL OR SECTION APPEARS ON INSTL INSTALL,INSTALLATION V VALVE,VENT,VOLT
THE SAME DRAWING/SHEET INT INTERIOR,INTERSECTION VAR VARIES.VARIABLE
INV INVERT VERT VERTICAL
JB JUNCTION BOX VOL VOLUME
INDICATES DETAIL NUMBER INDICATES SECTION LETTER JCT JUNCTION W WATER,WATT,WEST.WIDTH
$ LAT LATERAL.LATITUDE WD WIDE WOOD
)l
LB POUND WM WATER METER
SUBTITLE SUBTITLE LBL LABEL Ws WATER SURFACE
DETAIL �1 SECTION �1 WSDOT WASHINGTON STATE DEPARTMENT OF TRANSPORTATION
wr wEICHT
£ X
SCALE 4 SCALE 5 XSECT CROSS-SECTION
O YD YARD KROW whaC6 bBIOW.
INDICATES DRAWING/SHEET INDICATES DRAWING/SHEET YR YEAR Call before You ft.
WHERE DETAIL IS REFERRED TO J WHERE SECTION IS REFERRED TO
90%REVIEW SUBMITTAL
Prg.NJE� Ir� NOT FOR CONSTRUCTION
5
i REVISIONS DATE BY DESIGNED PROJECT NAME DRAINING NO.
K, BECKER Parametrix n ONE INCH AT FULL SCALE. 02 OF 09
DRAWN IF NOT,SCALE ACCORDINGLY /_ _ s0NMENTALSCNNCES WASHINGTON STATE DEPARTMENT GENERAL NOTES, LEGEND
K. BECKER FILE NAME4 ---- OF NATURAL RESOURCES
CHECKED PSI 795028— V /\ 1019 39TH AVENUE SE.SUITE 100 I"ALLUP,WA 98374 BELFAIR ADMINISTRATION BUILDING AND ABBREVIATIONS G-02
Nor_ \(J S
T2E14-1795-028 p \V("�� r 153.604.6600
APPROVED DA JULY 2020 ""+'raF:vn�ir.MKI BELFAIR,WASHINGTON
I
LEGEND
------CONSTRUCTION LIMITS
—p—p—p—SILT FENCE
REMOVE SITE FEATURE
CLEAR AND GRUB AS NECESSARY
®REMOVE EXISTING GRAVEL AREA
CONSTRUCTION NOTES
O7 MAINTAIN AND PROTECT EXISTING BUILDING DURING CONSTRUCTION
OF PROPOSED BUILDING.EXISTING BUILDING TO REMAIN OPERATIONAL
DURING CONSTRUCTION UNTIL PROPOSED BUILDING IS OPERATIONAL.
DEMOLISH AND REMOVE EXISTING BUILDING AFTER PROPOSED
BUILDING IS COMPLETE AND OPERATIONAL.
8 MAINTAIN AND PROTECT EXISTING UTILITY.
3 MAINTAIN AND PROTECT EXISTING UTILITY DURING CONSTRUCTION.
5 EXISTING UTILITY TO REMAIN IN USE UNTIL PROPOSED UTILITIES ARE
OPERATIONAL.cur,CAP AND ABANDON AND/OR REMOVE EXISTING
UTILITY AFTER PROPOSED BUILDING IS OPERATIONAL.
EXISTING
SHED 4O MAINTAIN AND PROTECT EXISTING BUILDING.
EXISTING O PRESERVE AND PROTECT EXISTING GRAVEL PARKING AREA
EXISTING SHED
WOOD -----------�
SHED 2
EXISTING OFFICE BUILDING I EXISTING COMMUNICATION VAULT GENERAL NOTES
II 1. PROTECT AND MAINTAIN EXISTING VEGETATION AND TREES
o � 1
2
2. STRAW BALE BARRIERS,WATTLES.AND OTHER NECESSARY TESC MEASURES
TO BE INSTALLED BY CONTRACTOR AS NEEDED OR AS DIRECTED BY OWNER,
SEE DETAILS ON SHEET DM-02.
\ee 3. INSTALL SILT FENCE BEFORE CLEARING AND GRUBBING BEGIN PER WSDOT
3 STD PLAN I30.10-02.ONLY SMALL AREAS OF CLEARING REQUIRED TO INSTALL
THE SILT FENCE IS ACCEPTABLE BEFORE THE SILT FENCE IS INSTALLED.SEE
i DETAIL ON SHEET DM-02.
o / 4. ALL DISTURBED AREAS TO BE STABILIZED TO PRECONSTRUCTION CONDITION
OR BETTER.
5. PRESERVE AND PROTECT EXISTING ASPHALT NOT SHOWN FOR REMOVAL.
' 6. MAINTAIN AND PROTECT ALL EXISTING UTILITIES UNLESS OTHERWISE NOTED
o l
/
ON THESE PLANS
EXISTING
z
I
STORAGE --
BUILDING
o
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s 2
U
II
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BUILDING j
SCALE IN FEET
0 0 20' 40' Knowwhars belOW,
Call before you dig.
o NOTE: 90% REVIEW SUBMITTAL
i SYMBOLS NOT TO SCALE
�lyK.N1Elp NOT FOR CONSTRUCTION
y [> REVISIONS DATE BY DESIGNED y��v PROJECT NAME DRAINING NO,
K. BECKER ONE INCH AT FULL SCALE. I t�S O.■tj�ft
DRAWN IF NOT,SCALE ACCORDINGLY ENGINEERING.PLANNING.ENVIRONMENTALSOENCES WASHINGTON STATE DEPARTMENT 03 OF 09
o K. BECKER ���� OF NATURAL RESOURCES DEMOLITION, TESC, AND
D„ECNED PS7795028—DM CLEARING AND GRUBBING PLAN
14 sa' 1019 39TH AVENUE SE,SUITE 300 1 PUYALIUP,WA 98374 BELFAIR ADMINISTRATION BUILDING D M-01
APPROVED 214-1795-02B C7 P W.604,6600
< DAILY 2020 WWW'PARAMETRIX.COM BELFAIR,WASHINGTON
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CHECKED PS1795028—DM o ,,,, 101939THAVENUE5E,5URE100 IPUYALLUP,WA98374 CLEARING AND GRUBBING PLAN DM-02
ND. AIR ADMINISTRATION BUILDING
APPROVED 214-1795-028 Q P253.6N.6600
DATEULY 2020 WWW.PARAMETRIX.COM BELFAIR,WASHINGTON
EXISTING GRAVEL PARKING AREA LEGEND
TO REMAIN AND PROVIDE PARKING j CEMENT CONCRETE
FOR PROPOSED BUILDING
GRAVEL
W + W LANDSPACE,MATCH EXISTING
EXISTING GRAVEL
Eo CONSTRUCTION NOTES
ADA PARKING STALL AND ACCESS AISLE
TO BE CONSTRUCTED AFTER PROPOSED 0 INSTALL CEMENT CONCRETE SIDEWALK PER W TD SDOT S .PLAN F-30.10-03 SEE
BUILDING IS OPERATIONAL AND 1f-vcl SHEET DT-01
DEMOLITION OF EXISTING BUILDING I��'L_JJ►�1�
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3 INSTALL ADA PARKING SIGNAGE ON BOLLARD PER DETAILS i AND 2 ON SHEET DT-01
2
GENERAL NOTES
3 RAMP PER
ARCHRECTURAL PLANS 1. CONTRACTOR SHALL FURNISH AND INSTALL ALL MATERIALS AND EQUIPMENT
5.0 15o' S.4' NECESSARY TO COMPLETE THIS WORK.
ci 2. CONTRACTOR TO VERIFY ALL EXISTING ELEVATIONS AND GRADES.
3 CONTRACTOR TO USE VERTICAL AND HORIZONTAL BENDS AS NEEDED.
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3 JULY 2020
I
GENERAL NOTES
1. CONTRACTOR SHALL FURNISH AND INSTALL ALL MATERIALS AND
EXISTING GRAVE EQUIPMENT NECESSARY TO COMPLETE THIS WOW(.
PARKING AREA
2. CONTRACTOR TO VERIFY ALL EXISTING ELEVATIONS AND GRADES
PRIOR TO START OF CONSTRUCTION.F VARIATIONS N GRADES ARE
PRESENT,CONTRACTOR SHALL NOTIFY OWNER AND ENGINEER TO
PROVIDE UPDATED DESIGN.
�- - ABBREVIATIONS
TC/69.00 TC 469.13 i SS BOTTOM OF STEP
FFE FINISHED FLOOR ELEVATION
TC TOP OF CONCRETE
MAX SLOPE IN A NY TS TOP OF STEP
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TC 469.13 -- TC 47011
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TC 489.16 1.0% 1.0%
a ° n
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ARCHITECTURAL PLAN BS 169.10
a TS/89.74
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BS 469.74
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SS 469.10 1.m
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4 REVISIONS DATE BY DESIGNED PROJECT NAME DRAWING NO.
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K. BECKER ---- OF NATURAL RESOURCES
CHECKED P51795028-HS �� �' 101939TH AVENUE St,SUITE 100IPUYALLUP,WA98374 BELFAIR ADMINISTRATION BUILDING GRADING AND STORM PLAN GR-01
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COMPLETE THIS WORK.MISCELLANEOUS EQUIPMENT NOT SHOWN OR IDENTIFIED BUT
NECESSARY TO COMPLETE INSTALLATION SHALL BE THE RESPONSIBILITY OF THE
CONTRACTOR.
2. CONTRACTOR SHALL VERIFY DIMENSIONS.ELEVATIONS AND LOCATIONS PRIOR 70
------------------ --- CONSTRUCTION.
I I 3 MAINTAIN 3 FEET MIN COVER OVER SEWER SERVICES FROM FINISHED GRADE UNLESS
OTHERWISE NOTED.
4. MAINTAIN 10 FEET MIN HORIZONTAL AND 1.5 FEET MN VERTICAL SEPARATION BETWEEN
I��gp I WATER AND SEWER MAINS UNLESS OTHERWISE NOTED.
5, A MINIMUM 61NCH SAND CUSHION IS REQUIRED FOR ANY UTILITY LINE WITHIN 6NCHES OF
ANOTHER UTILITY LINE AT CROSSING.
01
I I 6 PPE LENGTHS ARE FOR CALCULATION PURPOSES ONLY.BID QUANTITIES SHALL BE
EXISTING COMMUNICATION VAULT CALCULATED AS REWIRED.
/ I 7. POTHOLE AND VERIFY EXACT LOCATIONS OF UTILITIES PRIOR TO INSTALLATION OF UTILITIES.
/ I S. ALL CONSTRUCTION MUST COMPLY WITH WSOOT STANDARD SPECIFICATIONS(LATEST
——
____J EDITION),AND COUNTY,STATE,AND FEDERAL REGULATIONS.
9 SEWER SERVICE CONNECTIONS SHALL BE MINIMUM 2.0%SLOPE.CONTRACTOR SHALL
/ \ COORDINATE CONNECTION OF SEWER SERVICE WITH BUILDING ARCHITECTURAL PLANS.
10. SYMBOLS ARE NOT TRUE SIZE.
EXISTING UTLRV TO
11. CONTRACTOR TO USE VERTICAL AND HORIZONTAL BENDS AS NEEDED.
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PROPOSED UTILITIES
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EXISTING WATER MAIN -
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FRMIS FOR
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K. BECKER PLE NAME 5 Ixlxm PS1 795028—HS O --N-- OF NATURAL RESOURCES UTILITY PLAN
JOB N.. 1019 39TH AVENUE SE,SUITE 100 1 PUYALLUP,WA 98374 BELFAIR ADMINISTRATION BUILDING UT-01
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APPROVED DATE LY 2020 WVIVIYARAMETRIX.COM BELFAIR,WASHINGTON
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•i i i i NOTES:
I1 t f,'i ':{• I 1. EACH PARKING SPACE FOR THE DISABLED IS
REQUIRED TO BE IDENTIFIED BY A PERMANENT.
REFLECTORIZED SIGN WITH THE INTERNATIONAL
p i i i ••I SYMBOL OF ACCESSIBILITY.
3 i I�i I 2.THIS SIGN IS EQUAL TO A PORCELAIN ON STEEL
SIGN WITH BEADED TEXT,SIGN TO BE A MINIMUM
I'• •l L I+.• .I SIZE OF 70 SQUARE INCHES.
I I f 3.SIGN SHALL BE CENTERED ON THE INTERIOR END
i I l i i I OF THE PARKING SPACE,
B I r I I I �I
SOLLARD ADA PARKING SIGNAGE
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NO SCALE NO SCALEdig.
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Na. O� °mot 101939TH AVENUE SE,SUITE 1001PUYALLUPWA983 ' BELFAIR ADMINISTRATION BUILDING
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PoNG k COVER kV EXTEND k SPOOL 3'OF
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214-1795-028 p BELFAIR ADMINISTRATION BUILDING DT-02
APPROVED DA BELFAIR,WASHINGTON
< LY 2020
• Bel air Administration Building
9 i
Stormwater Management Report
Washington State Department of Natural Resources
Appendix C
Construction Stormwater Pollution Prevention Plan
(CSWPPP)
8 06-15-20201 214-1795-028
Construction Stormwater Pollution
Prevention Plan (CSWPPP)
Prepared for
Department of Natural Resources
950 Farman Ave. N.
Enumclaw,WA 98022-9282
�'ANINp��y
e WASHINGTON STATE DEPT Of
nATURAL
`•� ..�° RESOURCES
NATUIL
Prepared by
Parametrix
1019 39th Avenue SE,Suite 100
Puyallup,WA 98374
T.253.604.6600 F. 1.855.542.6353
www.parametrix.com
06-08-2020 1214-1795-028
CITATION
Parametrix. 2020. Construction Stormwater Pollution
Prevention Plan (CSWPPP). Prepared by Parametrix, Puyallup,
WA. 06-08-2020.
Construction Stormwater Pollution Prevention Plan(CSWPPP)
Department of Natural Resources
CERTIFICATION
The technical material and data contained in this document were prepared under the supervision and
direction of the undersigned,whose seal,as a professional engineer licensed to practice as such, is
affixed below.
Prepared by Zac Garrard, EIT
Checked by Sam Nielson, P.E.
Approved by Sam Nielson, P.E.
06-08-20201214-1795-028
Construction Stormwater Pollution Prevention Plan(CSWPPP)
Department of Natural Resources
TABLE OF CONTENTS
1. EROSION PREVENTION&SEDIMENT CONTROL REQUIREMENTS..............................................1
1.1 Objective of the Construction Stormwater Pollution Prevention Plan............................................1
1.2 Summary of Requirements..............................................................................................................1
1.3 Element#1: Marking Clearing Limits...............................................................................................1
1.4 Element#2: Establish Construction Access.....................................................................................2
1.5 Element#3:Control Flow Rates.......................................................................................................2
1.6 Element#4: Install Sediment Controls ............................................................................................2
1.7 Element#5:Stabilize Soils...............................................................................................................3
1.8 Element#6: Protect Slopes..............................................................................................................4
1.9 Element#7: Protect Drain Inlets......................................................................................................4
1.10 Element#8:Stabilize Channels and Outlets....................................................................................5
1.11 Element#9: Control Pollutants........................................................................................................5
1.12 Element#10: Control Dewatering...................................................................................................6
1.13 Element#11: Maintain BMPs..........................................................................................................6
1.14 Element#12: Manage the Project...................................................................................................6
1.14.1 Phasing of Construction...................................................................................................6
1.14.2 Seasonal Work Limitations..............................................................................................6
1.14.3 Inspection and Monitoring..............................................................................................7
1.14.4 Maintenance of the SWPPP.............................................................................................7
1.15 Element#13: Protect Low Impact Development BMPs(Infiltration BMPs)....................................7
2. PROJECT DESCRIPTION...........................................................................................................8
2.1 Location............................................................................................................................................8
2.2 Project Overview..............................................................................................................................8
3. EXISTING SITE CONDITIONS....................................................................................................8
3.1 Existing Topography and Vegetation...............................................................................................8
3.2 Existing Drainage System.................................................................................................................8
3.3 Adjacent Areas.................................................................................................................................8
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TABLE OF CONTENTS (CONTINUED)
4. CRITICAL AREAS.....................................................................................................................9
5. EROSION PROBLEM AREAS.....................................................................................................9
6. CONSTRUCTION PHASING......................................................................................................9
7. CONSTRUCTION SCHEDULE ....................................................................................................9
8. REPORTING AND RECORD KEEPING......................................................................................10
8.1 Record Keeping..............................................................................................................................10
8.1.1 Site Log Book.................................................................................................................10
8.1.2 Records Retention.........................................................................................................10
8.1.3 Updating the SWPPP.....................................................................................................10
8.2 Reporting.......................................................................................................................................it
8.2.1 Discharge Monitoring Reports.......................................................................................11
8.2.2 Notification of Noncompliance......................................................................................11
9. SITE PLAN............................................................................................................................12
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ACRONYMS
BMPs best management practices
CESCL Certified Erosion and Sediment Control Lead
CFS cubic feet per second
CSWPPP Construction Stormwater Pollution Prevention Plan
Ecology Washington State Department of Ecology
LID low-impact development
NPDES National Pollutant Discharges Elimination System
NPGIS Non-Pollution Generating Impervious Surface
NRCS National Resource Conservation Service
PGIS pollution generating impervious surfaces
SPCC Spill Prevention,Control, and Countermeasures
SWMMWW Stormwater Management Manual for Western Washington
TESC Temporary Erosion and Sediment Control
TMDL total maximum daily load
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1. EROSION PREVENTION & SEDIMENT CONTROL
REQUIREMENTS
1.1 Objective of the Construction Stormwater Pollution
Prevention Plan
The purpose of a Construction Stormwater Pollution Prevention Plan (CSWPPP) is to describe the
potential for pollution problems on a construction project.The CSWPPP also explains and illustrates the
measures to be taken on the construction site to manage these problems.This CSWPPP Plan is prepared
according to the guidance of the 2019 Stormwater Management Manual for Western Washington to
comply with Washington State Department of Ecology permit requirements.The Stormwater Manual
describes thirteen minimum site requirements of erosion prevention and sediment control.These
thirteen elements include: preserving vegetation/mark clearing limits,establish construction access,
control flow rates,install sediment controls,stabilize soils, protect slopes, protect drain inlets,stabilize
channels and outlets,control pollutants,control de-watering, maintain Best Management Practices
(BMPs),manage the project,and protect low-impact development BMPs.These elements have been
addressed as follows.
1.2 Summary of Requirements
The BMPs listed in this report,or their equivalent,are required.Any revisions by the contractor to the
BMPs listed in the SWPPP shall be approved by the Engineer.Therefore, if the contractor does not
require a BMP or needs to modify a BMP,the contractor shall document the reasons and update the
SWPPP to match what is being implemented in the field.A copy of the BMPs can be found in Appendix
A.
1.3 Element #1: Marking Clearing Limits
The clearing limits shall be marked prior to any clearing to restrict clearing to the approved limits.A high
visibility fence shall be installed to delineate the location and control access of each building/site to be
demolished prior to any work in accordance with BMP 103.The Contractor shall use best judgement
selecting of the type of fencing(high orange fencing,chain-link with placards,or high visible silt fence)to
be utilized based off public access to site location.
The native topsoil, natural vegetation, and existing trees shall be retained in an undisturbed state to the
maximum extent practicable. If it is not practicable to retain the native topsoil in place, it should be
stockpiled on-site,covered to prevent erosion,and replaced immediately upon completion of the
ground disturbing activities.The Contractor shall determine if construction is not possible due to
presence of vegetation/tree,and shall clear,grub,and dispose of accordingly.
Installation Schedule:Summer/Fall 2020
Inspection and Maintenance Plan:
• If the fencing or clearing limits are observed to be damaged or visibility is reduced, it shall be
repaired and/or replaced immediately, and visibility restored.
Responsible Staff:TBD
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1.4 Element #2: Establish Construction Access
Existing gravel and asphalt roads included within in the construction perimeter will be utilized as
construction access to the maximum extent feasible. Locations where the existing roads are to be
removed or intersections with an existing road not within the construction perimeter a stabilized
construction entrance shall be constructed to minimize the tracking of sediment onto any public road.
Construction vehicle access and exit shall be limited to one route, if feasible.This stabilized construction
entrance shall be constructed in accordance with the requirements of BMP C10S.
If sediment is tracked off-site, public roads shall be cleaned thoroughly at the end of each day, or more
frequently during wet weather. Sediment shall be removed from roads by shoveling or pickup sweeping
and shall be transported to a controlled sediment disposal area. Street washing will be allowed only
after sediment is removed.
Should tracking of sediments off-site continue to occur, wheel washes or construction road and parking
area stabilization may be needed (BMPs 106 and 107).
Installation Schedule: Fall/Summer 2020
Inspection and Maintenance Plan:
• If sediment or quarry spalls are observed being tracked onto pavement,then alternative
measures to keep the street free of sediment shall be used.This may include
replacement/cleaning of existing quarry spalls, street sweeping, an increase in the dimensions of
the entrance, or the installation of a wheel wash.
• If a wheel wash is installed,the wheel wash should start out the day with fresh water, and the
wash water should be changed a minimum once per day. The Contractor shall determine the
frequency of changing the wash water.
Responsible Staff: TBD
1.5 Element #3: Control Flow Rates
Stormwater runoff shall be observed during storm events to ensure flow rates or sediment loads are not
increased to cause erosion to adjacent properties or waterbodies. If flow rates are increased straw
wattles or other energy dispersion BMPs shall be constructed according to BMP C235.
Installation Schedule: Fall/Summer 2020
Inspection and Maintenance Plan:
• If wattles are utilized,the sediment collected shall be removed from the wattle when it reaches
greater than one-third the height of the wattle.
• Any damage to the temporary wattles shall be repaired or replaced.
Responsible Staff:TBD
1.6 Element #4: Install Sediment Controls
To minimize the discharge of pollutants offsite, erosion and sediment controls will be installed along site
perimeter as needed. Stormwater runoff from disturbed areas shall be routed through an appropriate
sediment removal BMP per the Contractor's best judgement prior to runoff discharging off-site or into
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drain inlets. Runoff from fully stabilized areas may be discharged without a sediment removal BMP but
must ensure downstream waterways are protected from erosion due to increases in the volume,
velocity,and peak flow rate of stormwater from the project site.Silt fence barriers shall be constructed
in accordance with BMP C233.
In addition to silt fencing,the following BMPs are may be implemented where appropriate:
• BMP C230—Straw Bale Barrier
• BMP C231—Brusher Barrier
• BMP C232—Gravel Filter Berm
• BMP C234—Vegetated Strip
• BMP C235—Straw Wattles
• BMP C240—Sediment Trap
• BMP C241—Temporary Sediment Pond
• BMP C 251—Construction Stormwater Filtration
Installation Schedule: Fall/Summer 2020
Inspection and Maintenance Plan:
• Repair any damage immediately.
• Intercept and convey all evident concentrated flows uphill of the silt fence to a sediment pond.
• Remove sediment deposits when the deposit reaches approximately one-third of the height of
the silt fence or install a second silt fence.
• Replace filter fabric that has deteriorated due to ultraviolet breakdown.
Responsible Staff:TBD
1.7 Element #5: Stabilize Soils
All exposed and unworked soils shall be stabilized by application of effective BMPs,which protect the
soil from the erosive forces of raindrop impact,flowing water,and from wind erosion. Demolition
schedule phasing shall be planned to reduce the amount of soil exposed during construction activity.
From October 1 through April 30, no soils shall remain exposed and un-worked for more than 2 days.
From May 1 to September 30, no soils shall remain exposed and un-worked for more than 7 days.This
condition applies to all soils on-site,whether at final grade or not.Soils to be stabilized at the end of
shifts prior to holidays or weekends based on weather forecasts per Contractor's best judgement.
In areas where the soils will remain un-worked for more than 30 days or have reached final grade,
seeding and mulching shall be used in accordance with BMPs C120 and C121. If the soil stockpile slope is
2H:1V or greater with at least 10 feet of vertical relief, nets,or blankets shall be used according to BMP
C122.Sod shall be used in accordance with BMP C124 for disturbed areas that require immediate
vegetative cover. Dust control shall be used as needed to prevent wind transport of dust from disturbed
soil surfaces and in accordance with BMP C140. Contractor to utilize available non-potable water from
on-site sources or provide water tanker in order to spray down disturbed soils to minimize dust
produced from construction activities.
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In addition, the following BMPs may be used to stabilize soils where appropriate:
• BMP C123—Plastic Covering
• BMPC125—Topsoiling
• BMPC130—Surface Roughening
• BMP C131—Gradient Terraces
Installation Schedule: Fall/Summer 2020
Inspection and Maintenance Plan:
• Reseed any seeded areas that fail to establish at least 80 percent cover. If reseeding is
ineffective, use an alternative method such as sodding, mulching, or nets/blankets to stabilize
soils.
• Reseed and protect by mulch any areas that experience erosion after achieving adequate cover.
• Supply seeded areas with adequate moisture, but do not water to the extent that runoff is
generated.
• If the grass is unhealthy,the cause shall be determined, and appropriate action taken to
reestablish a healthy groundcover. If it is impossible to establish a healthy groundcover due to
frequent saturation, instability, or some other cause, the sod shall be removed,the area seeded
with an appropriate mix, and protected with a net or blanket.
• Respray areas as needed to keep dust to a minimum.
Responsible Staff:TBD
Element #6: Protect Slopes
Slopes will be stabilized as indicated in Element#5 above. Cut and fill slopes shall be constructed in a
manner that will minimize erosion. In addition,the following BMPs may be implemented where
appropriate:
• BMP C200— Interceptor Dike and Swale
• BMP C205—Subsurface Drains
• BMP C206—Level Spreader
• BMP C207—Check Dams
Installation Schedule: Fall/Summer 2020
Inspection and Maintenance Plan:
• BMPs to be inspected after every runoff event to ensure that they are functioning correctly.
Responsible Staff:TBD
Element #7: Protect Drain Inlet,
All storm drain inlets made operable during construction, as well as all existing structures within the
project limits, shall be marked and protected so that stormwater runoff shall not enter the conveyance
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system without first being filtered or treated to remove sediment. Install catch basin sock filters or
approved equal as shown on the TESC Plans and in accordance with BMP C220 or WSDOT standard
1-40.20-00.
Contractor to prevent sediment and street wash water to enter storm drains without prior and
adequate treatment.
Installation Schedule: Fall/Summer 2020
Inspection and Maintenance Plan:
• Inlets to be inspected weekly at a minimum and daily during storm events.
• Inlet protection devices shall be cleaned and removed and replaced when sediment has filled
one-third of the available storage(unless a different standard is specified by the product
manufacturer).
• Do not wash sediment into storm drains while cleaning.
Responsible Staff:TBD
1.10 Element #8: Stabilize Channels and Outlets
Armoring materials such as riprap or check dams shall be installed in the roadside ditch adjacent to Main
Street for anticipated on-site runoff discharging towards. If the Contractor determines in the field that it
is appropriate to construct temporary drainage swales to convey runoff to approved stormwater control
facilities,the temporary drainage swales will provide stabilization, including armoring material,
adequate to prevent erosion of outlets, slopes,and downstream reaches.The Contractor to contact
Design Engineer for appropriate dimensions of conveyance channels if utilized.
Installation Schedule: Fall/Summer 2020
Inspection and Maintenance Plan:
• Inspect and repair as needed.
• Install channel lining if erosion is observed.
• Install check dams if concentrated flow rates are observed during and after a runoff event.
Responsible Staff:TBD
1.11 Element #9: Control Pollutants
All pollutants, including waste materials and demolition debris,that occur on-site during construction
shall be handled and disposed of in a manner that does not cause contamination of stormwater.
Maintenance and repair of heavy equipment and vehicles involving oil changes, hydraulic system drain
down,solvent and de-greasing cleaning operations,fuel tank drain down and removal,and other
activities which may result in discharge or spillage of pollutants to the ground or into stormwater runoff
must be conducted using spill prevention measures,such as drip pans. Emergency repairs may be
performed on-site using temporary plastic placed beneath,and if raining,over the vehicle.Application
of agricultural chemicals, including fertilizers and pesticides,shall be conducted in a manner and at
application rates that will not result in loss of chemical to stormwater runoff. Manufacturers'
recommendations shall be followed for application rates and procedures.
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Two source control BMPs will apply to this project:
• A Spill Prevention Control and Countermeasures Plan(prepared by Contractor)
• Street Sweeping(as needed during construction by Contractor)
Installation Schedule: Fall/Summer 2020
Inspection and Maintenance Plan:
• Contaminated surfaces shall be cleaned immediately following any discharge or spill incident.
• Source control BMPs shall be utilized to prevent the likelihood of pollutants being introduced
on-site.
Responsible Staff:TBD
1.12 Element #10: Control Dewatering
It is not anticipated that dewatering will be required for this project.
1.13 Element #11: Maintain BMPs
All temporary and permanent erosion and sediment control BMPs shall be maintained and repaired as
needed to ensure continued performance of their intended function.All maintenance and repair shall be
in accordance with BMPs.
Sediment control BMPs shall be inspected weekly or after a runoff-producing storm event during the dry
season and daily during the wet season.
All temporary erosion and sediment control BMPs shall be removed within 30 days after final site
stabilization is achieved,or after the temporary BMPs are no longer needed.Trapped sediment shall be
removed or stabilized on-site. Disturbed soil areas resulting from removal of BMPs or vegetation shall be
permanently stabilized.
1.14 Element #12: Manage the Project
1.14.1 Phasing of Construction
The project shall be phased where feasible in order to prevent,to the maximum extent practicable,the
transport of sediment from the site during construction. Revegetation of exposed areas and
maintenance of that vegetation shall be an integral part of the clearing activities for each phase.
1.14.2 Seasonal Work Limitations
From October 1 through April 30,clearing,grading,and other soil disturbing activities shall only be
permitted if silt-laden runoff will be prevented from leaving the construction site.
The following activities are exempt from the seasonal clearing and grading limitations:
• Routine maintenance and necessary repair of erosion and sediment control BMPs.
• Routine maintenance of public facilities or existing utility structures that do not expose the soil
or result in the removal of the vegetative cover to the soil;and
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• Activities where there is 100 percent infiltration of surface water runoff within the site in
approved and installed erosion and sediment control facilities.
1.14.3 Inspection and Monitoring
All BMPs shall be inspected, maintained,and repaired as needed to ensure continued performance of
their intended function.
Sampling and analysis of the stormwater discharges from the construction site may be necessary to
ensure compliance with standards.
Whenever inspection and/or monitoring reveals that the BMPs identified in the construction SWPPP are
inadequate,due to the actual discharge of or potential to discharge a significant amount of any
pollutant,the construction SWPPP shall be modified, as appropriate, in a timely manner.
Site inspections shall be conducted the identified CESCL.The CESCL must be on-site or on-call at all times
during the duration of construction activities.The CESCL must examine stormwater visually for the
presence of suspended sediment,turbidity,discoloration,and oil sheen,and it is upon the CESCL's
evaluation of the effectiveness of BMPs to determine if it is necessary to install, maintain,or repair
BMPs to improve quality of stormwater discharges.
The CESCL must inspect all areas disturbed by construction activities,all BMPs,and all stormwater
discharge points at least once every calendar week and within 24 hours of any discharge from the site.
The CESCL may reduce this inspection frequency for temporary stabilized or inactive sites to once every
calendar month through the duration of construction activities.
1.14.4 Maintenance of the SWPPP
The construction SWPPP shall be retained on-site or within reasonable access to the site.The
construction SWPPP shall be modified by the Contractor and/or Engineer whenever there is a significant
change in the design,construction,operation,or maintenance of any BMP.
1.15 Element #13: Protect Low Impact Development BMPs
(Infiltration BMPs)
Measures shall be made to protect the infiltration trench from sedimentation and compaction through
use of buffer zones, high visibility fencing,or silt fences. Following construction of the infiltration trench,
compaction by construction equipment or foot traffic shall be prevented.
Installation Schedule: Fall/Summer 2020
Inspection and Maintenance Plan:
The removal of sediment and any sediment-laden soils within the infiltration and replacing the
removed soils with design specification rock is required to meet design performance.
Responsible Staff:TBD
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2. PROJECT DESCRIPTION
2.1 Location
The project is located on a partially developed lot in Belfair,WA in Mason County. The site is relatively
flat in the gravel surfaced areas sloping gradually to the northwest towards forested areas.The western
edge of the site is forested before dropping drastically into a heavily,wooded drainage ravine.The
developed portions of the site include gravel roads, parking,and material storage areas.There are a
series of existing maintenance and storage sheds and office buildings located throughout the site.The
undeveloped areas are wooded remains of the surrounding forests.The undeveloped portions of the
site were covered in various vegetation including grasses,ferns,and,stands of trees.
2.2 Project Overview
The Belfair Administration Building project proposes to construct an administration office building,
paved accessible parking spot, concrete sidewalk, and a gravel parking lot in a partially developed site
located off of Sand Hill Road in Belfair,Washington.The proposed addition will be constructed on
existing Department of Natural Resources(DNR) property.
The Contractor shall manage,dispose,and reuse/recycle all waste and debris from construction
activities to an approved facility. Upon completion of the demolition work,all areas where topsoil has
been disturbed will be backfilled,graded, and hydro-seeded to establish a grass cover for the entire site.
The Contractor will blend and grade the backfill soils into the surrounding grade to ensure no ponding
and to provide positive drainage.
Total disturbed acreage:0.15-acres
3. EXISTING SITE CONDITIONS
3.1 Existing Topography and Vegetation
to the northwest towards forested
The site is relative) flat in the ravel surfaced areas sloping
Y g P g
areas.The western edge of the site is forested before dropping drastically into a heavily,wooded
drainage ravine.The developed portions of the site include gravel roads, parking,and material storage
areas.There are a series of existing maintenance and storage sheds and office buildings located
throughout the site.The undeveloped areas are wooded remains of the surrounding forests.The
undeveloped portions of the site were covered in various vegetation including grasses,ferns,and,
stands of trees.
3.2 Existing Drainage System
Runoff from existing developed areas generally sheds to the west into wooded vegetation aligning Sand
Hill Road. Runoff will be infiltrated or evaporated once collecting in depressed areas, and in high rainfall
events, Mission Creek is the outfall that will convey runoff into Hood Canal.
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3.3 Adjacent Areas
The surrounding property is a densely vegetated woods dropping to a drainage ravine to the east,gravel
access roads to the north,a corrections facility is the neighboring property to the southwest, and the
west is the wooded remains of a previous forest and the extension of the prison.
4. CRITICAL AREAS
There are no identified critical areas within 100 feet of the construction site area. Mission Creeek is
within 0.25-mile vicinity of the project site.
5. EROSION PROBLEM AREAS
Potential on-site erosion control problems are a possibility associated with construction activities. No
specific location is identified on the project site.The Contractor will closely observe the site during
construction and report any problems that may develop.
6. CONSTRUCTION PHASING
The project shall be phased where feasible in order to prevent,to the maximum extent practicable,the
transport of sediment from the site during construction. Revegetation of exposed areas and
maintenance of that vegetation shall be an integral part of the clearing activities for each site.Activities
shall begin on the south end of the site and work north to completion.The proposed addition will be
constructed following site preparation and foundation excavation,and once constructed the existing
structure will be demolished following a transfer of resources to the new building.
The Contractor will install the aforementioned erosion and sediment control BMPs prior to any
construction activities.
The Contractor will install site security fencing as needed to control access to each building/site being
demolished before the demolition begins.At locations where the public has no access the fence will be
the standard 4-foot-high orange plastic fence and at locations where the public has access,the fence
6-foot-high chain-link with placards.
At completion of the demolition and site restoration,workers will do a final policing of the area, picking
up any remaining debris,then remove the SWPPP control measures and security fencing.
7. CONSTRUCTION SCHEDULE
Construction Activity Date of Completion
Project Start Summer/Fall 2020
Install Erosion and Sediment Control BMPs Summer/Fall 2020
Notify Utility Providers for Shut-Off Summer/Fall 2020
Demolition Begin Summer/Fall 2020
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Final Stabilization Fall/Winter 2020
Remove Erosion and Sediment Control BMPs Fall/Winter 2020
Project End Fall/Winter 2020
8. REPORTING AND RECORD KEEPING
8.1 Record Keeping
8.1.1 Site Logbook
A site logbook will be maintained for all on-site construction activities and will include:
• A record of the implementation of the SWPPP and other permit requirements
• Site Inspections
• Sample Logs
8.1.2 Records Retention
Records will be retained during the life of the project and for a minimum of 3 years following the
termination of permit coverage in accordance with Special Condition SS.0 of the CSWGP.
Permit documentation to be retained on-site:
• CSWGP
• Permit Coverage Letter
• SWPPP
• Site Logbook
Permit documentation will be provided within 14 days of receipt of a written request from Ecology.A
copy of the SWPPP or access to the SWPPP will be provided to the public when requested in writing
accordance with Special Condition S5.G.2.b of the CSWGP.
8.1.3 Updating the SWPPP
The SWPPP will be modified if:
• Found ineffective in eliminating or significantly minimizing pollutants in stormwater discharges
from the site.
• There is a change in design,construction,operation,or maintenance at the construction site
that has,or could have,a significant effect on the discharge of pollutants to waters of the State.
The SWPPP will be modified within 7 days if inspections or investigations determine additional or
modified BMPs are necessary for compliance.An updated timeline for BMP implementation will be
prepared.
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8.2 Reporting
8.2.1 Discharge Monitoring Reports
Cumulative soil disturbance is 1 acre or larger;therefore, Discharge Monitoring Reports(DMRs)will be
submitted to Ecology monthly. If there was no discharge during a given monitoring period the DMR will
be submitted as required, reporting"No Discharge."The DMR due date is 15 days following the end of
each calendar month.
DMRs will be reported online through Ecology's WQWebDMR System.
https://www.ecology.wa.gov/Regulations-Permits/Guidance-technical-assistance/Water-guality-
permits-guidance/WQWebPortal-guidance
8.2.2 Notification of Noncompliance
If any of the terms and conditions of the permit is not met,and the resulting noncompliance may cause
a threat to human health or the environment,the following actions will be taken:
• Ecology will be notified within 24 hours of the failure to comply by calling the applicable regional
office ERTS phone number(regional office numbers listed below).
• Immediate action will be taken to prevent the discharge/pollution or otherwise stop or correct
the noncompliance. If applicable,sampling and analysis of any noncompliance will be repeated
immediately and the results submitted to Ecology within 5 days of becoming aware of the
violation.
• A detailed written report describing the noncompliance will be submitted to Ecology within
5 days, unless requested earlier by Ecology.
Any time turbidity sampling indicates turbidity is 250 NTUs or greater,or water transparency is 6 cm or
less,the Ecology Regional office will be notified by phone within 24 hours of analysis as required by
Special Condition SS.A of the CSWGP.
• Central Region at(509) 575-2490 for Benton,Chelan, Douglas, Kittitas, Klickitat,Okanogan,or
Yakima County
• Western Region at(509)329-3400 for Adams,Asotin,Columbia, Ferry, Franklin,Garfield,Grant,
Lincoln, Pend Oreille,Spokane,Stevens,Walla Walla,or Whitman County
• Northwest Region at(425)649-7000 for Island, King, Kitsap,San Juan,Skagit,Snohomish,or
Whatcom County
• Southwest Region at(360)407-6300 for Clallam,Clark,Cowlitz,Grays Harbor,Jefferson, Lewis,
Mason, Pacific, Pierce,Skamania,Thurston,or Wahkiakum
Include the following information:
1. Your name and phone number
2. Permit number
3. City/county of project
4. Sample results
06-08-2020 1 214-1795-028 11
Construction Stormwater Pollution Prevention Plan(CSWPPP)
Department of Natural Resources
5. Date and time of call
6. Date and time of sample
7. Project name
In accordance with Special Condition S4.D.S.b of the CSWGP,the Ecology regional office will be notified
if chemical treatment other than CO2 sparging is planned for adjustment of high pH water.
9. SITE PLAN
Refer to the Civil Plans for reference.
12 06-08-2020 1214-1795-028
Construction Stormwater Pollution Prevention Plan(CSWPPP)
Department of Natural Resources
Appendix A
Erosion and Sediment Control BMPs
06-08-20201 214-1795-028 1
4.1 Source Control BMPs
BMP C101: Preserving Natural Vegetation
Purpose The purpose of preserving natural vegetation is to reduce erosion wherever
practicable. Limiting site disturbance is the single most effective method
for reducing erosion. For example,conifers can hold up to about 50
percent of all rain that falls during a storm. Up to 20-30 percent of this rain
may never reach the ground but is taken up by the tree or evaporates.
Another benefit is that the rain held in the tree can be released slowly to the
ground after the storm.
Conditions of Use . Natural vegetation should be preserved on steep slopes,near
perennial and intermittent watercourses or swales,and on building
sites in wooded areas.
As required by local governments.
Design and Natural vegetation can be preserved in natural clumps or as individual
Installation trees, shrubs and vines.
Specifications
The preservation of individual plants is more difficult because heavy
equipment is generally used to remove unwanted vegetation. The points
to remember when attempting to save individual plants are:
• Is the plant worth saving? Consider the location,species,size,age,
vigor,and the work involved. Local governments may also have
ordinances to save natural vegetation and trees.
• Fence or clearly mark areas around trees that are to be saved. It is
preferable to keep ground disturbance away from the trees at least as
far out as the dripline.
Plants need protection from three kinds of injuries:
• Construction Equipment-This injury can be above or below the
ground level. Damage results from scarring, cutting of roots,and
compaction of the soil. Placing a fenced buffer zone around plants to
be saved prior to construction can prevent construction equipment
injuries.
• Grade Changes- Changing the natural ground level will alter grades,
which affects the plant's ability to obtain the necessary air,water,and
minerals. Minor fills usually do not cause problems although
sensitivity between species does vary and should be checked. Trees
can tolerate fill of 6 inches or less. For shrubs and other plants,the fill
should be less.
When there are major changes in grade, it may become necessary to
supply air to the roots of plants. This can be done by placing a layer of
gravel and a tile system over the roots before the fill is made. A tile
4-2 Volume H—Construction Stormwater Pollution Prevention February 2005
system protects a tree from a raised grade. The tile system should be
laid out on the original grade leading from a dry well around the tree
trunk. The system should then be covered with small stones to allow
air to circulate over the root area.
Lowering the natural ground level can seriously damage trees and
shrubs. The highest percentage of the plant roots are in the upper 12
inches of the soil and cuts of only 2-3 inches can cause serious injury.
To protect the roots it may be necessary to terrace the immediate area
around the plants to be saved. If roots are exposed,construction of
retaining walls may be needed to keep the soil in place. Plants can
also be preserved by leaving them on an undisturbed,gently sloping
mound. To increase the chances for survival,it is best to limit grade
changes and other soil disturbances to areas outside the dripline of the
plant.
• Excavations-Protect trees and other plants when excavating for
drainfields,power,water, and sewer lines. Where possible,the
trenches should be routed around trees and large shrubs. When this is
not possible,it is best to tunnel under them. This can be done with
hand tools or with power augers. If it is not possible to route the
trench around plants to be saved,then the following should be
observed:
Cut as few roots as possible. When you have to cut,cut clean. Paint
cut root ends with a wood dressing like asphalt base paint.
Backfill the trench as soon as possible.
Tunnel beneath root systems as close to the center of the main trunk to
preserve most of the important feeder roots.
Some problems that can be encountered with a few specific trees are:
• Maple, Dogwood, Red alder,Western hemlock,Western red cedar,
and Douglas fir do not readily adjust to changes in environment and
special care should be taken to protect these trees.
• The windthrow hazard of Pacific silver fir and madronna is high,while
that of Western hemlock is moderate. The danger of windthrow
increases where dense stands have been thinned. Other species(unless
they are on shallow,wet soils less than 20 inches deep)have a low
windthrow hazard.
• Cottonwoods,maples,and willows have water-seeking roots. These
can cause trouble in sewer lines and infiltration fields. On the other
hand,they thrive in high moisture conditions that other trees would
not.
• Thinning operations in pure or mixed stands of Grand fir,Pacific silver
fir,Noble fir, Sitka spruce, Western red cedar, Western hemlock,
February 2005 Volume ii—Construction Stormwater Pollution Prevention 4-3
Pacific dogwood, and Red alder can cause serious disease problems.
Disease can become established through damaged limbs,trunks,roots,
and freshly cut stumps. Diseased and weakened trees are also
susceptible to insect attack.
Maintenance . Inspect flagged and/or fenced areas regularly to make sure flagging or
Standards fencing has not been removed or damaged. If the flagging or fencing
has been damaged or visibility reduced, it shall be repaired or
replaced immediately and visibility restored.
If tree roots have been exposed or injured, "prune" cleanly with an
appropriate pruning saw or lopers directly above the damaged roots
and recover with native soils. Treatment of sap flowing trees (fir,
hemlock, pine, soft maples) is not advised as sap forms a natural
healing barrier.
4-4 Volume Il— Construction Stormwater Pollution Prevention February 2005
BMP C103: High Visibility Plastic or Metal Fence
Purpose Fencing is intended to: (1)restrict clearing to approved limits; (2)prevent
disturbance of sensitive areas,their buffers, and other areas required to be
left undisturbed; (3) limit construction traffic to designated construction
entrances or roads; and,(4)protect areas where marking with survey tape
may not provide adequate protection.
Conditions of Use To establish clearing limits,plastic or metal fence may be used:
• At the boundary of sensitive areas,their buffers, and other areas
required to be left uncleared.
• As necessary to control vehicle access to and on the site.
Design and . High visibility plastic fence shall be composed of a high-density
Installation polyethylene material and shall be at least four feet in height. Posts
Specifications for the fencing shall be steel or wood and placed every 6 feet on
center(maximum)or as needed to ensure rigidity. The fencing shall
be fastened to the post every six inches with a polyethylene tie. On
long continuous lengths of fencing,a tension wire or rope shall be
used as a top stringer to prevent sagging between posts. The fence
color shall be high visibility orange. The fence tensile strength shall
be 360 lbs./ft.using the ASTM D4595 testing method.
Metal fences shall be designed and installed according to the
manufacturer's specifications.
• Metal fences shall be at least 3 feet high and must be highly visible.
• Fences shall not be wired or stapled to trees.
Maintenance . If the fence has been damaged or visibility reduced, it shall be
Standards repaired or replaced immediately and visibility restored.
4-6 Volume!1—Construction Stormwater Pollution Prevention February 2005
BMP C105: Stabilized Construction Entrance
Pulvo.se Construction entrances are stabilized to reduce the amount of sediment
transported onto paved roads by vehicles or equipment by constructing a
stabilized pad of quarry spalls at entrances to construction sites.
Conditions of Use Construction entrances shall be stabilized wherever traffic will be leaving
a construction site and traveling on paved roads or other paved areas
within 1,000 feet of the site.
On large commercial,highway,and road projects,the designer should
include enough extra materials in the contract to allow for additional
stabilized entrances not shown in the initial Construction SWPPP. It is
difficult to determine exactly where access to these projects will take
place; additional materials will enable the contractor to install them where
needed.
Design and . See Figure 4.2 for details. Note: the 100' minimum length of the
Installation entrance shall be reduced to the maximum practicable size when the
Specifications size or configuration of the site does not allow the full length(100').
A separation geotextile shall be placed under the spalls to prevent
fine sediment from pumping up into the rock pad. The geotextile
shall meet the following standards:
Grab Tensile Strength(ASTM D4751) 200 psi min.
Grab Tensile Elongation(ASTM D4632) 30% max.
Mullen Burst Strength (ASTM D3786-80a) 400 psi min.
AOS(ASTM D4751) 20-45(U.S. standard sieve size)
• Consider early installation of the first lift of asphalt in areas that will
paved; this can be used as a stabilized entrance. Also consider the
installation of excess concrete as a stabilized entrance. During large
concrete pours,excess concrete is often available for this purpose.
• Hog fuel (wood-based mulch)may be substituted for or combined with
quarry spalls in areas that will not be used for permanent roads. Hog
fuel is generally less effective at stabilizing construction entrances and
should be used only at sites where the amount of traffic is very limited.
Hog fuel is not recommended for entrance stabilization in urban areas.
The effectiveness of hog fuel is highly variable and it generally
requires more maintenance than quarry spalls. The inspector may at
any time require the use of quarry spalls if the hog fuel is not
preventing sediment from being tracked onto pavement or if the hog
fuel is being carried onto pavement. Hog fuel is prohibited in
permanent roadbeds because organics in the subgrade soils cause
degradation of the subgrade support over time.
• Fencing(see BMPs C 103 and C 104)shall be installed as necessary to
restrict traffic to the construction entrance.
4-8 Volume ll—Construction Stormwater Pollution Prevention February 2005
• Whenever possible,the entrance shall be constructed on a firm,
compacted subgrade. This can substantially increase the effectiveness
of the pad and reduce the need for maintenance.
Maintenance • Quarry spalls(or hog fuel)shall be added if the pad is no longer in
Standards accordance with the specifications.
• If the entrance is not preventing sediment from being tracked onto
pavement,then alternative measures to keep the streets free of
sediment shall be used. This may include street sweeping, an increase
in the dimensions of the entrance,or the installation of a wheel wash.
• Any sediment that is tracked onto pavement shall be removed by
shoveling or street sweeping. The sediment collected by sweeping
shall be removed or stabilized on site. The pavement shall not be
cleaned by washing down the street, except when sweeping is
ineffective and there is a threat to public safety. If it is necessary to
wash the streets,the construction of a small sump shall be considered.
The sediment would then be washed into the sump where it can be
controlled.
• Any quarry spalls that are loosened from the pad,which end up on the
roadway shall be removed immediately.
• If vehicles are entering or exiting the site at points other than the
construction entrance(s),fencing(see BMPs C 103 and C 104)shall be
installed to control traffic.
• Upon project completion and site stabilization,all construction
accesses intended as permanent access for maintenance shall be
permanently stabilized.
Driveway shall meet the
requirements of the
permitting agency
It is recommended that
the entrance be
crowned so that runoff
aoS6 drains on the pad
r
°o.
i
Install driveway culvert
if there is a roadside
ditch present
4'-8"quarry spalls
Geotextile
12'min.thickness
Provide full width of
ingress/egress area
Figure 4.2—Stabilized Construction Entrance
February 2005 Volume ll— Construction Stormwater Pollution Prevention 4-9
BMP C106: Wheel Wash
Purpose Wheel washes reduce the amount of sediment transported onto paved
roads by motor vehicles.
Conditions of Use When a stabilized construction entrance(see BMP C105) is not preventing
sediment from being tracked onto pavement.
• Wheel washing is generally an effective BMP when installed with
careful attention to topography. For example,a wheel wash can be
detrimental if installed at the top of a slope abutting a right-of-way
where the water from the dripping truck can run unimpeded into the
street.
• Pressure washing combined with an adequately sized and surfaced pad
with direct drainage to a large 10-foot x 10-foot sump can be very
effective.
Design and Suggested details are shown in Figure 4.3. The Local Permitting
Installation Authority may allow other designs. A minimum of 6 inches of asphalt
Specifications treated base(ATB)over crushed base material or 8 inches over a good
subgrade is recommended to pave the wheel wash.
Use a low clearance truck to test the wheel wash before paving. Either a
belly dump or lowboy will work well to test clearance.
Keep the water level from 12 to 14 inches deep to avoid damage to truck
hubs and filling the truck tongues with water.
Midpoint spray nozzles are only needed in extremely muddy conditions.
Wheel wash systems should be designed with a small grade change, 6 to
12 inches for a 10-foot-wide pond,to allow sediment to flow to the low
side of pond to help prevent re-suspension of sediment. A drainpipe with
a 2-to 3-foot riser should be installed on the low side of the pond to allow
for easy cleaning and refilling. Polymers may be used to promote
coagulation and flocculation in a closed-loop system. Polyacrylamide
(PAM)added to the wheel wash water at a rate of 0.25 -0.5 pounds per
1,000 gallons of water increases effectiveness and reduces cleanup time.
If PAM is already being used for dust or erosion control and is being
applied by a water truck,the same truck can be used to change the wash
water.
Maintenance The wheel wash should start out the day with fresh water.
Standards The wash water should be changed a minimum of once per day. On
large earthwork jobs where more than 10-20 trucks per hour are
expected,the wash water will need to be changed more often.
Wheel wash or tire bath wastewater shall be discharged to a separate on-
site treatment system, such as closed-loop recirculation or land
application,or to the sanitary sewer with proper local sewer district
approval.
4-10 Volume 11—Construction Stormweter Pollution Prevention February 2005
/2"Schedule 40
1 '/2"schedule 40 for sprayers
II
2% 5:1 C5�: 1 1 2%
Slope Slope Slope
II
r,
II
SIApe
Wheel Wash Plan
1-16-716—
20' 15� 50'
Elevation View
Water level
�1 1:1 Slope
Section A-A
N.T.S.
Figure 4.3 Wheel Wash
Notes:
1. Asphalt construction entrance 6 in. asphalt treated base(ATB).
2. 3-inch trash pump with floats on the suction hose.
3. Midpoint spray nozzles, if needed.
4. 6-inch sewer pipe with butterfly valves. Bottom one is a drain. Locate top pipe's invert 1 foot
above bottom of wheel wash.
5. 8 foot x 8 foot sump with 5 feet of catch. Build so can be cleaned with trackhoe.
6. Asphalt curb on the low road side to direct water back to pond.
7. 6-inch sleeve under road.
8. Ball valves.
9. 15 foot.ATB apron to protect ground from splashing water.
February 2005 Volume 11— Construction Stormwater Pollution Prevention 4-11
BMP C107: Construction Road/Parking Area Stabilization
Purpose Stabilizing subdivision roads,parking areas,and other onsite vehicle
transportation routes immediately after grading reduces erosion caused by
construction traffic or runoff.
Conditions of Use ' Roads or parking areas shall be stabilized wherever they are constructed,
whether permanent or temporary,for use by construction traffic.
Fencing(see BMPs C 103 and C 104)shall be installed, if necessary,to
limit the access of vehicles to only those roads and parking areas that
are stabilized.
Design and • On areas that will receive asphalt as part of the project, install the first
Installation lift as soon as possible.
Specifications . A 6-inch depth of 2-to 4-inch crushed rock, gravel base,or crushed
surfacing base course shall be applied immediately after grading or
utility installation. A 4-inch course of asphalt treated base(ATB)may
also be used, or the road/parking area may be paved. It may also be
possible to use cement or calcium chloride for soil stabilization. If
cement or cement kiln dust is used for roadbase stabilization,pH
monitoring and BMPs are necessary to evaluate and minimize the
effects on stormwater. If the area will not be used for permanent roads,
parking areas,or structures,a 6-inch depth of hog fuel may also be
used,but this is likely to require more maintenance. Whenever
possible,construction roads and parking areas shall be placed on a firm,
compacted subgrade.
Temporary road gradients shall not exceed 15 percent. Roadways shall
be carefully graded to drain. Drainage ditches shall be provided on each
side of the roadway in the case of a crowned section,or on one side in the
case of a super-elevated section. Drainage ditches shall be directed to a
sediment control BMP.
• Rather than relying on ditches,it may also be possible to grade the road
so that runoff sheet-flows into a heavily vegetated area with a well-
developed topsoil. Landscaped areas are not adequate. If this area has at
least 50 feet of vegetation,then it is generally preferable to use the
vegetation to treat runoff,rather than a sediment pond or trap. The 50
feet shall not include wetlands. If runoff is allowed to sheetflow through
adjacent vegetated areas,it is vital to design the roadways and parking
areas so that no concentrated runoff is created.
Storm drain inlets shall be protected to prevent sediment-laden water
entering the storm drain system(see BMP C220).
Maintenance • Inspect stabilized areas regularly,especially after large storm events.
Standards . Crushed rock,gravel base,hog fuel,etc. shall be added as required to
maintain a stable driving surface and to stabilize any areas that have
eroded.
Following construction,these areas shall be restored to pre-construction
condition or better to prevent future erosion.
4-12 Volume 11-Construction Stormwater Pollution Prevention February 2005
BMP C120: Temporary and Permanent Seeding
Purpose Seeding is intended to reduce erosion by stabilizing exposed soils. A
well-established vegetative cover is one of the most effective methods of
reducing erosion.
Conditions of Use • Seeding may be used throughout the project on disturbed areas that
have reached final grade or that will remain unworked for more than
30 days.
• Channels that will be vegetated should be installed before major
earthwork and hydroseeded with a Bonded Fiber Matrix. The
vegetation should be well established(i.e., 75 percent cover)before
water is allowed to flow in the ditch. With channels that will have
high flows,erosion control blankets should be installed over the
hydroseed. If vegetation cannot be established from seed before water
is allowed in the ditch,sod should be installed in the bottom of the
ditch over hydromulch and blankets.
Retention/detention ponds should be seeded as required.
• Mulch is required at all times because it protects seeds from heat,
moisture loss,and transport due to runoff.
All disturbed areas shall be reviewed in late August to early September
and all seeding should be completed by the end of September.
Otherwise,vegetation will not establish itself enough to provide more
than average protection.
• At final site stabilization, all disturbed areas not otherwise vegetated or
stabilized shall be seeded and mulched. Final stabilization means the
completion of all soil disturbing activities at the site and the
establishment of a permanent vegetative cover,or equivalent
permanent stabilization measures(such as pavement,riprap, gabions
or geotextiles)which will prevent erosion.
Design and • Seeding should be done during those seasons most conducive to
Installation growth and will vary with the climate conditions of the region.
Specifications Local experience should be used to determine the appropriate
seeding periods.
• The optimum seeding windows for western Washington are April 1
through June 30 and September 1 through October 1. Seeding that
occurs between July 1 and August 30 will require irrigation until 75
percent grass cover is established. Seeding that occurs between
October 1 and March 30 will require a mulch or plastic cover until
75 percent grass cover is established.
• To prevent seed from being washed away,confirm that all required
surface water control measures have been installed.
February 2005 Volume 11— Construction Stormwater Pollution Prevention 4-13
• The seedbed should be firm and rough. All soil should be roughened
no matter what the slope. If compaction is required for engineering
purposes, slopes must be track walked before seeding. Backblading or
smoothing of slopes greater than 4:1 is not allowed if they are to be
seeded.
• New and more effective restoration-based landscape practices rely on
deeper incorporation than that provided by a simple single-pass
rototilling treatment. Wherever practical the subgrade should be
initially ripped to improve long-term permeability,infiltration, and
water inflow qualities. At a minimum,permanent areas shall use soil
amendments to achieve organic matter and permeability performance
defined in engineered soil/landscape systems. For systems that are
deeper than 8 inches the rototilling process should be done in multiple
lifts,or the prepared soil system shall be prepared properly and then
placed to achieve the specified depth.
• Organic matter is the most appropriate form of"fertilizer"because it
provides nutrients(including nitrogen,phosphorus,and potassium) in
the least water-soluble form. A natural system typically releases 2-10
percent of its nutrients annually. Chemical fertilizers have since been
formulated to simulate what organic matter does naturally.
• In general, 10-4-6 N-P-K(nitrogen-phosphorus-potassium)fertilizer
can be used at a rate of 90 pounds per acre. Slow-release fertilizers
should always be used because they are more efficient and have fewer
environmental impacts. It is recommended that areas being seeded for
final landscaping conduct soil tests to determine the exact type and
quantity of fertilizer needed. This will prevent the over-application of
fertilizer. Fertilizer should not be added to the hydromulch machine
and agitated more than 20 minutes before it is to be used. If agitated
too much,the slow-release coating is destroyed.
• There are numerous products available on the market 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 is a good source of
long-term, slow-release,available nitrogen.
• Hydroseed applications shall include a minimum of 1,500 pounds per
acre of mulch with 3 percent tackifier. Mulch may be made up of 100
percent: cottonseed meal; fibers made of wood,recycled cellulose,
hemp, and kenaf; compost; or blends of these. Tackifier shall be plant-
based, such as guar or alpha plantago,or chemical-based such as
polyacrylamide or polymers. Any mulch or tackifier product used
shall be installed per manufacturer's instructions. Generally,mulches
come in 40-50 pound bags. Seed and fertilizer are added at time of
application.
4-14 Volume 11—Construction Stormwater Pollution Prevention February 2005
• Mulch is always required for seeding. Mulch can be applied on top of
the seed or simultaneously by hydroseeding.
• On steep slopes, Bonded Fiber Matrix(BFM)or Mechanically Bonded
Fiber Matrix (MBFM)products should be used. BFM/MBFM
products are applied at a minimum rate of 3,000 pounds per acre of
mulch with approximately 10 percent tackifier. Application is made
so that a minimum of 95 percent soil coverage is achieved. Numerous
products are available commercially and should be installed per
manufacturer's instructions. Most products require 24-36 hours to
cure before a rainfall and cannot be installed on wet or saturated soils.
Generally,these products come in 40-50 pound bags and include all
necessary ingredients except for seed and fertilizer.
BFMs and MBFMs have some advantages over blankets:
• No surface preparation required;
• Can be installed via helicopter in remote areas;
• On slopes steeper than 2.5:1,blanket installers may need to be roped
and harnessed for safety;
• They are at least$1,000 per acre cheaper installed.
In most cases,the shear strength of blankets is not a factor when used on
slopes,only when used in channels. BFMs and MBFMs are good
alternatives to blankets in most situations where vegetation establishment
is the goal.
• 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. One way to
overcome this is to increase seed quantities by up to 50 percent.
• Vegetation establishment can also be enhanced by dividing the
hydromulch operation into two phases:
1. Phase 1- Install all seed and fertilizer with 25-30 percent mulch
and tackifier onto soil in the first lift;
2. Phase 2-Install the rest of the mulch and tackifier over the first lift.
An alternative is to install the mulch, seed, fertilizer, and tackifier in one
lift. Then, spread or blow straw over the top of the hydromulch at a rate of
about 800-1000 pounds per acre. 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:
1. Irrigation
2. Reapplication of mulch
3. Repair of failed slope surfaces
February 2005 Volume 11-Construction Stormwater Pollution Prevention 4-15
This technique works with standard hydromulch(1,500 pounds per acre
minimum)and BFM/MBFMs(3,000 pounds per acre minimum).
• Areas to be permanently landscaped shall provide a healthy topsoil
that reduces the need for fertilizers,improves overall topsoil quality,
provides for better vegetal health and vitality, improves hydrologic
characteristics, and reduces the need for irrigation. This can be
accomplished in a number of ways:
Recent research has shown that the best method to improve till soils is
to amend these soils with compost. The optimum mixture is
approximately two parts soil to one part compost. This equates to 4
inches of compost mixed to a depth of 12 inches in till soils. Increasing
the concentration of compost beyond this level can have negative
effects on vegetal health,while decreasing the concentrations can
reduce the benefits of amended soils. Please note: The compost should
meet specifications for Grade A quality compost in Ecology
Publication 94-038.
Other soils, such as gravel or cobble outwash soils,may require
different approaches. Organics and fines easily migrate through the
loose structure of these soils. Therefore,the importation of at least 6
inches of quality topsoil,underlain by some type of filter fabric to
prevent the migration of fines,may be more appropriate for these soils.
Areas that already have good topsoil, such as undisturbed areas,do not
require soil amendments.
• Areas that will be seeded only and not landscaped may need compost
or meal-based mulch included in the hydroseed in order to establish
vegetation. Native topsoil should be re-installed on the disturbed soil
surface before application.
• Seed that is installed as a temporary measure may be installed by hand
if it will be covered by straw,mulch,or topsoil. Seed that is installed
as a permanent measure may be installed by hand on small areas
(usually less than 1 acre)that will be covered with mulch,topsoil,or
erosion blankets. The seed mixes listed below include recommended
mixes for both temporary and permanent seeding. These mixes,with
the exception of the wetland mix,shall be applied at a rate of 120
pounds per acre. This rate can be reduced if soil amendments or slow-
release fertilizers are used. Local suppliers or the local conservation
district should be consulted for their recommendations because the
appropriate mix depends on a variety of factors, including location,
exposure, soil type, slope, and expected foot traffic. Alternative seed
mixes approved by the local authority may be used.
4-16 Volume 11—Construction Stormwater Pollution Prevention February 2005
Table 4.1 represents the standard mix for those areas where just a
temporary vegetative cover is required.
Table 4.1
Temporary Erosion Control Seed Mix
%Wei ht %Puri %Germination
Chewings or annual blue grass 40 98 90
Festuca rubra var.commutata or Poa anna
Perennial rye- 50 98 90
Lolium perenne
Redtop or colonial bentgrass 5 92 85
Agrostis alba or Agrostis tenuis
White dutch clover 5 98 90
Trifolium re ens
Table 4.2 provides just one recommended possibility for landscaping seed.
Table 4.2
Landscaping Seed Mix
%Weight %Purl %Germination
Perennial rye blend 70 98 90
Lolium perenne
Chewings and red fescue blend 30 98 90
Festuca rubra var.commutata
or Festuca rubra
This turf seed mix in Table 4.3 is for dry situations where there is no need
for much water. The advantage is that this mix requires very little
maintenance.
Table 4.3
Low-Growing Turf Seed Mix
`% Weight %Purity `V.Germination
Dwarf tall fescue(several varieties) 45 98 90
Festuca arundinacea var.
Dwarf perennial rye(Barclay) 30 98 90
Lolium perenne var,barcl
Red fescue 20 98 90
Festuca rubra
Colonial bentgrass 5 98 90
A rostis tenuis
Table 4.4 presents a mix recommended for bioswales and other
intermittently wet areas.
Table 4.4
Bioswale Seed Mix"
Weight "/0 Purity '%Germination
Tall or meadow fescue 75-80 98 90
Festuca arundinacea or Festuca elatior
Seaside/Creeping bentgrass 10-15 92 85
Agrostis palustris
Redtopbentgrass 5-10 90 80
Agrostis alba or A rostis gigantea
*Modified Briargreen,Inc. Hydroseeding Guide Wetlands Seed Mix
February 2005 Volume ll—Construction Stormwater Pollution Prevention 4-17
The seed mix shown in Table 4.5 is a recommended low-growing,
relatively non-invasive seed mix appropriate for very wet areas that are
not regulated wetlands. Other mixes may be appropriate,depending on
the soil type and hydrology of the area. Recent research suggests that
bentgrass(agrostis sp.)should be emphasized in wet-area seed mixes.
Apply this mixture at a rate of 60 pounds per acre.
Table 4.5
Wet Area Seed Mix"
N1ei(,ht Purity "4,Germination
Tall or meadow fescue 60-70 98 90
Festuca arundinacea or
Festuca elatior
Seaside/Creeping bentgrass 10-15 98 85
Agrostis palustris
Meadow foxtail 10-15 90 80
Alepocurus pratensis
Alsike clover 1-6 98 90
Tri olium h bridum
Redtop bentgrass 1-6 92 85
A rostis alba
*Modified Briargreen,Inc.Hydroseeding Guide Wetlands Seed Mix
The meadow seed mix in Table 4.6 is recommended for areas that will be
maintained infrequently or not at all and where colonization by native
plants is desirable. Likely applications include rural road and utility right-
of-way. Seeding should take place in September or very early October in
order to obtain adequate establishment prior to the winter months. The
appropriateness of clover in the mix may need to be considered, as this can
be a fairly invasive species. If the soil is amended,the addition of clover
may not be necessary.
Table 4.6
Meadow Seed Mix
'.Weight °%, Purih %Germination
Redtop or Oregon bentgrass 20 92 85
Agrostis alba or A rostis oregonensis
Red fescue 70 98 90
Festuca rubra
White dutch clover 10 98 90
Di olium re ens
Maintenance • Any seeded areas that fail to establish at least 80 percent cover(100
Standards percent cover for areas that receive sheet or concentrated flows)shall
be reseeded. If reseeding is ineffective, an alternate method, such as
sodding,mulching,or nets/blankets, shall be used. If winter weather
prevents adequate grass growth,this time limit may be relaxed at the
discretion of the local authority when sensitive areas would otherwise
be protected.
4-18 Volume 11— Construction Stormwater Pollution Prevention February 2005
• After adequate cover is achieved,any areas that experience erosion
shall be reseeded and protected by mulch. If the erosion problem is
drainage related,the problem shall be fixed and the eroded area
reseeded and protected by mulch.
• Seeded areas shall be supplied with adequate moisture,but not watered
to the extent that it causes runoff.
February 2005 Volume 11—Construction Stormwater Pollution Prevention 4-19
BMP C121 : Mulching
Purpose
Mulching soils provides immediate temporary protection from erosion. Mulch also enhances plant
establishment by conserving moisture, holding fertilizer, seed, and topsoil in place, and moderating soil
temperatures. There is an enormous variety of mulches that can be used. This section discusses only
the most common types of mulch.
Conditions of Use
As a temporary cover measure, mulch should be used:
• For less than 30 days on disturbed areas that require cover.
• At all times for seeded areas, especially during the wet season and during the hot summer months.
• Duringthe wet season on slopes steeper than 3H:1 V with more than 10 feet of vertical relief.
P P
Mulch may be applied at any time of the year and must be refreshed periodically.
• For seeded areas mulch may be made up of 100 percent: cottonseed meal; fibers made of wood,
recycled cellulose, hemp, kenaf; compost; or blends of these. Tackifier shall be plant-based, such
as guar or alpha plantago, or chemical-based such as polyacrylamide or polymers. Any mulch or
tackifier product used shall be installed per manufacturer's instructions. Generally, mulches come
in 40-50 pound bags. Seed and fertilizer are added at time of application.
Design and Installation Specifications
For mulch materials, application rates, and specifications, see Table II-4.1.8 Mulch Standards and
Guidelines. Always use a 2-inch minimum mulch thickness; increase the thickness until the ground is
95% covered (i.e. not visible under the mulch layer). Note: Thickness may be increased for disturbed
areas in or near sensitive areas or other areas highly susceptible to erosion.
Where the option of"Compost" is selected, it should be a coarse compost that meets the following size
gradations when tested in accordance with the U.S. Composting Council "Test Methods for the
Examination of Compost and Composting" (TMECC) Test Method 02.02-B.
Coarse Compost
Minimum Percent passing 3" sieve openings 100%
Minimum Percent passing 1" sieve openings 90%
Minimum Percent passing 1/4" sieve openings 70%
Minimum Percent passing '/4" sieve openings 40%
Mulch used within the ordinary high-water mark of surface waters should be selected to minimize
potential flotation of organic matter. Composted organic materials have higher specific gravities
(densities) than straw, wood, or chipped material. Consult Hydraulic Permit Authority (HPA) for mulch
mixes if applicable.
Maintenance Standards
• The thickness of the cover must be maintained.
• Any areas that experience erosion shall be remulched and/or protected with a net or blanket. If the
erosion problem is drainage related, then the problem shall be fixed and the eroded area
remulched.
Table 11-4.1.8 Mulch Standards and Guidelines
Mulch Quality Application Remarks
Material Standards Rates
Cost-effective protection when applied with adequate
thickness. Hand-application generally requires greater
thickness than blown straw. The thickness of straw may be
reduced by half when used in conjunction with seeding. In
Air-dried; free 2"-3" thick; windy areas straw must be held in place by crimping, using a
from 5 bales per tackifier, or covering with netting. Blown straw always has to be
Straw undesirable 1,000 sf or held in place with a tackifier as even light winds will blow it
seed and 2-3 tons per away. Straw, however, has several deficiencies that should be
coarse acre considered when selecting mulch materials. It often introduces
material. and/or encourages the propagation of weed species and it has
no significant long-term benefits It should also not be used
within the ordinary high-water elevation of surface waters (due
to flotation).
Approx. 25-
No growth 30 Ibs per Shall be applied with hydromulcher. Shall not be used without
Hydromulch inhibiting 1,000 sf or seed and tackifier unless the application rate is at least
factors. 1,500 - doubled. Fibers longer than about 3/4 - 1 inch clog hydromulch
2,000 Ibs equipment. Fibers should be kept to less than 3/4 inch.
per acre
Mulch Quality Application Remarks
Material Standards Rates
No visible
water or dust
during More effective control can be obtained by increasing thickness
handling. 2" thick to 3". Excellent mulch for protecting final grades until
Must be min.; landscaping because it can be directly seeded or tilled into soil
produced per approx. 100 as an amendment. Compost used for mulch has a coarser size
Compost WAC 173- tons per gradation than compost used for BMP C125: Topsoilingl
350, Solid acre mpostinq or BMP T5.13: Post-Construction Soil Quality
Waste (approx. Depth. It is more stable and practical to use in wet areas and
Handling )yar
Standards, yard) per during rainy weather conditions. Do not use near wetlands or but may have near phosphorous impaired water bodies.
up to 35%
biosolids.
Average size
shall be
several This is a cost-effective way to dispose of debris from clearing
inches. and grubbing, and it eliminates the problems associated with
Chipped Gradations burning. Generally, it should not be used on slopes above
Site from fines to 6 2" thick approx. 10% because of its tendency to be transported by
Vegetation inches in min.; runoff. It is not recommended within 200 feet of surface waters.
length for If seeding is expected shortly after mulch, the decomposition of
texture, the chipped vegetation may tie up nutrients important to grass
variation, and establishment.
interlocking
properties.
No visible
water or dust
during
handling. 2" thick This material is often called "hog or hogged fuel". The use of
Wood- Must be min.; mulch ultimately improves the organic matter in the soil.
based Purchased approx. 100 Special caution is advised regarding the source and
Mulch or from a tons per composition of wood-based mulches. Its preparation typically
Wood supplier with acre does not provide any weed seed control, so evidence of
Straw a Solid Waste (approx. residual vegetation in its composition or known inclusion of
Handling 800 lbs. per weed plants or seeds should be monitored and prevented (or
Permit or one cubic yard) minimized).
exempt from
solid waste
regulations.
A blend of
loose, long, Cost-effective protection when applied with adequate
thin wood thickness. A minimum of 95-percent of the wood strand shall
Wood pieces derived from have lengths between 2 and 10-inches, with a width and
native conifer
Strand 2" thick min. thickness between 1/16 and 3/8-inches. The mulch shall not
Mulch contain resin, tannin, or other compounds in quantities that
or deciduous would be detrimental to plant life. Sawdust or wood shavings
trees with high length- shall not be used as mulch. (WSDOT specification (9-14.4(4))
�
to-width ratio.
BMP C122: Nets and Blankets
Purpose
Erosion control nets and blankets are intended to prevent erosion and hold seed and mulch in place on
steep slopes and in channels so that vegetation can become well established. In addition, some nets
and blankets can be used to permanently reinforce turf to protect drainage ways during high flows. Nets
(commonly called matting) are strands of material woven into an open, but high-tensile strength net (for
example, coconut fiber matting). Blankets are strands of material that are not tightly woven, but instead
form a layer of interlocking fibers, typically held together by a biodegradable or photodegradable netting
(for example, excelsior or straw blankets). They generally have lower tensile strength than nets, but
cover the ground more completely. Coir (coconut fiber) fabric comes as both nets and blankets.
Conditions of Use
Erosion control nets and blankets should be used:
• To aid permanent vegetated stabilization of slopes 2H:1 V or greater and with more than 10 feet of
vertical relief.
• For drainage ditches and swales (highly recommended). The application of appropriate netting or
blanket to drainage ditches and swales can protect bare soil from channelized runoff while
vegetation is established. Nets and blankets also can capture a great deal of sediment due to their
open, porous structure. Nets and blankets can be used to permanently stabilize channels and may
provide a cost-effective, environmentally preferable alternative to riprap. 100 percent synthetic
blankets manufactured for use in ditches may be easily reused as temporary ditch liners.
Disadvantages of blankets include:
• Surface preparation required.
• On slopes steeper than 2.5H:1 V, blanket installers may need to be roped and harnessed for safety.
• They cost at least $4,000-6,000 per acre installed.
Advantages of blankets include:
• Installation without mobilizing special equipment.
• Installation by anyone with minimal training
• Installation in stages or phases as the project progresses.
• Installers can hand place seed and fertilizer as they progress down the slope.
• Installation in any weather.
• There are numerous types of blankets that can be designed with various parameters in mind.
Those parameters include: fiber blend, mesh strength, longevity, biodegradability, cost, and
availability.
Design and Installation Specifications
• See Figure II-4.1.3 Channel Installation and Figure II-4.1.4 Slope Installation for typical orientation
and installation of blankets used in channels and as slope protection. Note: these are typical only;
all blankets must be installed per manufacturer's installation instructions.
• Installation is critical to the effectiveness of these products. If good ground contact is not achieved,
runoff can concentrate under the product, resulting in significant erosion.
• Installation of Blankets on Slopes:
1. Complete final grade and track walk up and down the slope.
2. Install hydromulch with seed and fertilizer.
3. Dig a small trench, approximately 12 inches wide by 6 inches deep along the top of the
slope.
4. Install the leading edge of the blanket into the small trench and staple approximately
every 18 inches. NOTE: Staples are metal, "U"-shaped, and a minimum of 6 inches
long. Longer staples are used in sandy soils. Biodegradable stakes are also available.
5. Roll the blanket slowly down the slope as installer walks backwards. NOTE: The
blanket rests against the installer's legs. Staples are installed as the blanket is unrolled.
It is critical that the proper staple pattern is used for the blanket being installed. The
blanket is not to be allowed to roll down the slope on its own as this stretches the
blanket making it impossible to maintain soil contact. In addition, no one is allowed to
walk on the blanket after it is in place.
6. If the blanket is not long enough to cover the entire slope length, the trailing edge of the
upper blanket should overlap the leading edge of the lower blanket and be stapled. On
steeper slopes, this overlap should be installed in a small trench, stapled, and covered
with soil.
• With the variety of products available, it is impossible to cover all the details of appropriate use and
installation. Therefore, it is critical that the design engineer consult the manufacturer's information
and that a site visit takes place in order to ensure that the product specified is appropriate.
Information is also available at the following web sites:
1. WSDOT (Section 3.2.4):
http://www.wsdot.wa.gov/NR/rdonlyres/3B41 E087-FA86-4717-932D-
D7A8556CCD57/0/ErosionTrainingManual.pdf
2. Texas Transportation Institute:
http://www.txdot.gov/business/doing_business/product_evaluation/erosion_control.htm
• 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 certain circumstances.
• In general, most nets (e.g., jute matting) require mulch in order to prevent erosion because they
have a fairly open structure. Blankets typically do not require mulch because they usually provide
complete protection of the surface.
• Extremely steep, unstable, wet, or rocky slopes are often appropriate candidates for use of
synthetic blankets, as are riverbanks, beaches and other high-energy environments. If synthetic
blankets are used, the soil should be hydromulched first.
• 100-percent biodegradable blankets are available for use in sensitive areas. These organic
blankets are usually held together with a paper or fiber mesh and stitching which may last up to a
year.
• Most netting used with blankets is photodegradable, meaning they break down under sunlight (not
UV stabilized). However, this process can take months or years even under bright sun. Once
vegetation is established, sunlight does not reach the mesh. It is not uncommon to find non-
degraded netting still in place several years after installation. This can be a problem if maintenance
requires the use of mowers or ditch cleaning equipment. In addition, birds and small animals can
become trapped in the netting.
Maintenance Standards
• Maintain good contact with the ground. Erosion must not occur beneath the net or blanket.
• Repair and staple any areas of the net or blanket that are damaged or not in close contact with the
ground.
• Fix and protect eroded areas if erosion occurs due to poorly controlled drainage.
Figure 11-4.1.3 Channel Installation
O , 0-
go
2014 Figure II-4.1.3 pdf download
Figure II-4.1.4 Slope Installation
2014 Figure II-4.1.4 pdf download
Washington State Department of Ecology
2012 Stormwater Management Manual for Western Washington, as Amended in December 2014 (The 2014 SWMMWW)
Anchor in 6"x 6" min.
trench and staple at
12" intervals
Min.2"overlap
Min. 6"overlap
Staple overlaps
max. 5"spacing
Bring material down to a level
area, turn the end under 4"
and staple at 12" intervals
Notes:
1. Slope surface shall be smooth before placement for
proper soil contact.
2. Stapling pattern as per manufacturer's recommendations.
3. Do not stretch blankets/mattings tight-allow the rolls to
mold to any irregularities.
4. For slopes less than 31-1:1 V, rolls may be placed in
horizontal strips.
5. If there is a berm at the top of the slope, anchor upslope
of the berm.
6. Lime, fertilize, and seed before installation. Planting of
shrubs, trees, etc. should occur after installation.
NOT TO SCALE
Figure II-4.1 .4
Slope Installation
DEPARTMENT OF Revised June 2015
ECOLOGY Please see http://www.ecy.wa.gov/copyright.html for copyright notice including permissions,
State of Washington limitation of liability, and disclaimer.
BMP C123: Plastic Covering
Purpose Plastic covering provides immediate, short-term erosion protection to
slopes and disturbed areas.
Conditions of • Plastic covering may be used on disturbed areas that require cover
U.se measures for less than 30 days,except as stated below.
• Plastic is particularly useful for protecting cut and fill slopes and
stockpiles. Note: The relatively rapid breakdown of most polyethylene
sheeting makes it unsuitable for long-term(greater than six months)
applications.
• Clear plastic sheeting can be used over newly-seeded areas to create a
greenhouse effect and encourage grass growth if the hydroseed was
installed too late in the season to establish 75 percent grass cover,or if
the wet season started earlier than normal. Clear plastic should not be
used for this purpose during the summer months because the resulting
high temperatures can kill the grass.
• Due to rapid runoff caused by plastic sheeting,this method shall not be
used upslope of areas that might be adversely impacted by
concentrated runoff. Such areas include steep and/or unstable slopes.
• While plastic is inexpensive to purchase,the added cost of installation,
maintenance,removal, and disposal make this an expensive material,
up to$1.50-2.00 per square yard.
• Whenever plastic is used to protect slopes,water collection measures
must be installed at the base of the slope. These measures include
plastic-covered berms, channels,and pipes used to covey clean
rainwater away from bare soil and disturbed areas. At no time is clean
runoff from a plastic covered slope to be mixed with dirty runoff from
a project.
• Other uses for plastic include:
1. Temporary ditch liner;
2. Pond liner in temporary sediment pond;
3. Liner for beamed temporary fuel storage area if plastic is not
reactive to the type of fuel being stored;
4. Emergency slope protection during heavy rains; and,
5. Temporary drainpipe("elephant trunk")used to direct water.
4-26 Volume !I-Construction Stormwater Pollution Prevention February 2005
Design and Plastic slope cover must be installed as follows:
Installation 1. Run plastic up and down slope,not across slope;
Specifications
2. Plastic may be installed perpendicular to a slope if the slope length
is less than 10 feet;
3. Minimum of 8-inch overlap at seams;
4. On long or wide slopes,or slopes subject to wind,all seams should
be taped;
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 pound a wooden stake through each to hold them in
place;
7. Inspect plastic for rips, tears,and open seams regularly and repair
immediately. This prevents high velocity runoff from contacting
bare soil which causes extreme erosion;
8. Sandbags may be lowered into place tied to ropes. However, all
sandbags must be staked in place.
• Plastic sheeting shall have a minimum thickness of 0.06 millimeters.
• If erosion at the toe of a slope is likely, a gravel berm,riprap,or other
suitable protection shall be installed at the toe of the slope in order to
reduce the velocity of runoff.
Maintenance • Torn sheets must be replaced and open seams repaired.
Standards
• If the plastic begins to deteriorate due to ultraviolet radiation,it must
be completely removed and replaced.
• When the plastic is no longer needed, it shall be completely removed.
• Dispose of old tires appropriately.
February 2005 Volume 11—Construction Stormwater Pollution Prevention 4-27
o
BMP C125: Topsoiling / Composting
Purpose
Topsoiling and composting provide a suitable growth medium for final site stabilization with vegetation.
While not a permanent cover practice in itself, topsoiling and composting are an integral component of
providing permanent cover in those areas where there is an unsuitable soil surface for plant growth. Use
this BMP in conjunction with other BMPs such as seeding, mulching, or sodding. Note that this BMP is
functionally the same as BMP T5.13: Post-Construction Soil Quality and Dep h_which is required for all
disturbed areas that will be developed as lawn or landscaped areas at the completed project site.
Native soils and disturbed soils that have been organically amended not only retain much more
stormwater, but they also serve as effective biofilters for urban pollutants and, by supporting more
vigorous plant growth, reduce the water, fertilizer and pesticides needed to support installed landscapes.
Topsoil does not include an subsoils but only the material from the to several inches including organic
P Y Y P 9
debris.
Conditions of Use
• Permanent landscaped areas shall contain healthy topsoil that reduces the need for fertilizers,
improves overall topsoil quality, provides for better vegetal health and vitality, improves hydrologic
characteristics, and reduces the need for irrigation.
• Leave native soils and the duff layer undisturbed to the maximum extent practicable. Stripping of
existing, properly functioning soil system and vegetation for the purpose of topsoiling during
construction is not acceptable. Preserve existing soil systems in undisturbed and uncompacted
conditions if functioning properly.
• Areas that already have good topsoil, such as undisturbed areas, do not require soil amendments.
• Restore, to the maximum extent practical, native soils disturbed during clearing and grading to a
condition equal to or better than the original site condition's moisture-holding capacity. Use on-site
native topsoil, incorporate amendments into on-site soil, or import blended topsoil to meet this
requirement.
• Topsoiling is a required procedure when establishing vegetation on shallow soils, and soils of
critically low pH (high acid) levels.
• Beware of where the topsoil comes from, and what vegetation was on site before disturbance,
invasive plant seeds may be included and could cause problems for establishing native plants,
landscaped areas, or grasses.
• Topsoil from the site will contain mycorrhizal bacteria that are necessary for healthy root growth
and nutrient transfer. These native mycorrhiza are acclimated to the site and will provide optimum
conditions for establishing grasses. Use commercially available mycorrhiza products when using
off-site topsoil.
Design and Installation Specifications
Meet the following requirements for disturbed areas that will be developed as lawn or landscaped areas
at the completed project site:
• Maximize the depth of the topsoil wherever possible to provide the maximum possible infiltration
capacity and beneficial growth medium. Topsoil shall have:
o A minimum depth of 8-inches. Scarify subsoils below the topsoil layer at least 4-inches with
some incorporation of the upper material to avoid stratified layers, where feasible. Ripping or
re-structuring the subgrade may also provide additional benefits regarding the overall
infiltration and interflow dynamics of the soil system.
o A minimum organic content of 10% dry weight in planting beds, and 5% organic matter
content in turf areas. Incorporate organic amendments to a minimum 8-inch depth except
where tree roots or other natural features limit the depth of incorporation.
• A pH between 6.0 and 8.0 or matching the pH of the undisturbed soil.
o If blended topsoil is imported, then fines should be limited to 25 percent passing through a
200 sieve.
o Mulch planting beds with 2 inches of organic material
• Accomplish the required organic content, depth, and pH by returning native topsoil to the site,
importing topsoil of sufficient organic content, and/or incorporating organic amendments. When
using the option of incorporating amendments to meet the organic content requirement, use
compost that meets the compost specification for Bioretention (See BMP T7.30: Bioretention Cells,
Swales, and Planter Boxes), with the exception that the compost may have up to 35% biosolids or
manure.
• Sections three through seven of the document entitled, Guidelines and Resources for
Implementing Soil Quality and Depth BMP T5.13 in WDOE Stormwater Management Manual for
Western Washington, provides useful guidance for implementing whichever option is chosen. It
includes guidance for pre-approved default strategies and guidance for custom strategies. Check
with your local jurisdiction concerning its acceptance of this guidance. It is available through the
organization, Soils for Salmon. As of this printing the document may be found at:
http://www.soilsforsalmon.org/pdf/Soil_BMP_Manual.�df.
• The final composition and construction of the soil system will result in a natural selection or
favoring of certain plant species over time. For example, incorporation of topsoil may favor
grasses, while layering with mildly acidic, high-carbon amendments may favor more woody
vegetation.
• Allow sufficient time in scheduling for topsoil spreading prior to seeding, sodding, or planting.
• Take care when applying top soil to subsoils with contrasting textures. Sandy topsoil over clayey
subsoil is a particularly poor combination, as water creeps along the junction between the soil
layers and causes the topsoil to slough. If topsoil and subsoil are not properly bonded, water will
not infiltrate the soil profile evenly and it will be difficult to establish vegetation. The best method to
prevent a lack of bonding is to actually work the topsoil into the layer below for a depth of at least 6
inches.
• Field exploration of the site shall be made to determine if there is surface soil of sufficient quantity
and quality to justify stripping. Topsoil shall be friable and loamy (loam, sandy loam, silt loam,
sandy clay loam, and clay loam). Avoid areas of natural ground water recharge.
• Stripping shall be confined to the immediate construction area. A 4-inch to 6-inch stripping depth is
common, but depth may vary depending on the particular soil. All surface runoff control structures
shall be in place prior to stripping.
• Do not place topsoil while in a frozen or muddy condition, when the subgrade is excessively wet, or
when conditions exist that may otherwise be detrimental to proper grading or proposed sodding or
seeding.
• In any areas requiring grading remove and stockpile the duff layer and topsoil on site in a
designated, controlled area, not adjacent to public resources and critical areas. Stockpiled topsoil
is to be reapplied to other portions of the site where feasible.
• Locate the topsoil stockpile so that it meets specifications and does not interfere with work on the
site. It may be possible to locate more than one pile in proximity to areas where topsoil will be
used.
Stockpiling of topsoil shall occur in the following manner:
o Side slopes of the stockpile shall not exceed 2H:1 V.
o Between October 1 and April 30:
■ An interceptor dike with gravel outlet and silt fence shall surround all topsoil.
■ Within 2 days complete erosion control seeding, or covering stockpiles with clear
plastic, or other mulching materials.
o Between May 1 and September 30:
■ An interceptor dike with gravel outlet and silt fence shall surround all topsoil if the
stockpile will remain in place for a longer period of time than active construction
grading.
■ Within 7 days complete erosion control seeding, or covering stockpiles with clear
plastic, or other mulching materials.
• When native topsoil is to be stockpiled and reused the following should apply to ensure that the
mycorrhizal bacterial, earthworms, and other beneficial organisms will not be destroyed:
1. Re-install topsoil within 4 to 6 weeks.
2. Do not allow the saturation of topsoil with water.
3. Do not use plastic covering.
Maintenance Standards
• Inspect stockpiles regularly, especially after large storm events. Stabilize any areas that have
eroded.
• Establish soil quality and depth toward the end of construction and once established, protect from
compaction, such as from large machinery use, and from erosion.
• Plant and mulch soil after installation.
• Leave plant debris or its equivalent on the soil surface to replenish organic matter.
• Reduce and adjust, where possible, the use of irrigation, fertilizers, herbicides and pesticides,
rather than continuing to implement formerly established practices.
Washington State Department of Ecology
2012 Stormwater Management Manual for Western Washington, as Amended in December 2014 (The 2014 SWMMWW)
BMP C130: Surface Roughening
Purpose
Surface roughening aids in the establishment of vegetative cover, reduces runoff velocity, increases
infiltration, and provides for sediment trapping through the provision of a rough soil surface. Horizontal
depressions are created by operating a tiller or other suitable equipment on the contour or by leaving
slopes in a roughened condition by not fine grading them.
Use this BMP in conjunction with other BMPs such as seeding, mulching, or sodding.
Conditions for Use
• All slopes steeper than 3H:1 V and greater than 5 vertical feet require surface roughening to a
depth of 2 to 4 inches prior to seeding..
• Areas that will not be stabilized immediately may be roughened to reduce runoff velocity until
seeding takes place.
• Slopes with a stable rock face do not require roughening.
• Slopes where mowing is planned should not be excessively roughened.
Design and Installation Specifications
There are different methods for achieving a roughened soil surface on a slope, and the selection of an
appropriate method depends upon the type of slope. Roughening methods include stair-step grading,
grooving, contour furrows, and tracking. See Figure II-4.1.5 Surface Rough niagJby Trackingan
Contour Furrows for tracking and contour furrows. Factors to be considered in choosing a method are
slope steepness, mowing requirements, and whether the slope is formed by cutting or filling.
• Disturbed areas that will not require mowing may be stair-step graded, grooved, or left rough after
filling.
• Stair-step grading is particularly appropriate in soils containing large amounts of soft rock. Each
"step" catches material that sloughs from above, and provides a level site where vegetation can
become established. Stairs should be wide enough to work with standard earth moving equipment.
Stair steps must be on contour or gullies will form on the slope.
• Areas that will be mowed (these areas should have slopes less steep than 3H:1 V) may have small
furrows left by disking, harrowing, raking, or seed-planting machinery operated on the contour.
• Graded areas with slopes steeper than 3H:1 V but less than 2H:1 V should be roughened before
seeding. This can be accomplished in a variety of ways, including "track walking," or driving a
crawler tractor up and down the slope, leaving a pattern of cleat imprints parallel to slope contours.
• Tracking is done by operating equipment up and down the slope to leave horizontal depressions in
the soil.
Maintenance Standards
• Areas that are graded in this manner should be seeded as quickly as possible.
• Regular inspections should be made of the area. If rills appear, they should be re-graded and re-
seeded immediately.
Figure 11-4.1.5 Surface Roughening by Tracking and Contour Furrows
2014 Figure II-4.1.5 pdf download
Washington State Department of Ecology
2012 Stormwater Management Manual for Western Washington, as Amended in December 2014 (The 2014 SWMMWW).
a-
a.-
�-
a-
a
a
Tracking with machinery up and down
the slope provides grooves that will
a
catch seed, rainfall, and reduce runoff. e a s a a
a a a
a
Tracking
50' 6" min �—
(15m) (150mm)
3
a1 Contour Furrows
Maximum
Grooves will catch seed, fertilizer,
mulch, rainfall, and decrease runoff.
NOT TO SCALE
Figure II-4. 1 .5
Surface Roughening by Tracking
and Contour Furrows
DEPARTMENT OF Revised June 2015
ECOLOGYPlease see http://www.ecy.wa.govlcopyright.html for copyright notice including permissions,
State of Washington limitation of liability, and disclaimer.
BMP C131 : Gradient Terraces
Purpose
Gradient terraces r r e e aces educe erosion damage by intercepting surface runoff and conducting it to a stable
outlet at a non-erosive velocity.
Conditions of Use
• Gradient terraces normally are limited to denuded land having a water erosion problem. They
should not be constructed on deep sands or on soils that are too stony, steep, or shallow to permit
practical and economical installation and maintenance. Gradient terraces may be used only where
suitable outlets are or will be made available. See Figure II-4.1.6 Gradient Terraces for gradient
terraces.
Design and Installation Specifications
• The maximum vertical spacing of gradient terraces should be determined by the following method:
VI = (0.8)s + y
Where:
VI = vertical interval in feet
s = land rise per 100 feet, expressed in feet
y = a soil and cover variable with values from 1.0 to 4.0
Values of"y" are influenced by soil erodibility and cover practices. The lower values are applicable
to erosive soils where little to no residue is left on the surface. The higher value is applicable only
to erosion-resistant soils where a large amount of residue (1'/2 tons of straw/acre equivalent) is on
the surface.
• The minimum constructed cross-section should meet the design dimensions.
• The top of the constructed ridge should not be lower at any point than the design elevation plus the
specified overfill for settlement. The opening at the outlet end of the terrace should have a cross
section equal to that specified for the terrace channel.
• Channel grades may be either uniform or variable with a maximum grade of 0.6 feet per 100 feet
length (0.6%). For short distances, terrace grades may be increased to improve alignment. The
channel velocity should not exceed that which is nonerosive for the soil type.
• All gradient terraces should have adequate outlets. Such an outlet may be a grassed waterway,
vegetated area, or tile outlet. In all cases the outlet must convey runoff from the terrace or terrace
system to a point where the outflow will not cause damage. Vegetative cover should be used in the
outlet channel.
• The design elevation of the water surface of the terrace should not be lower than the design
elevation of the water surface in the outlet at their junction, when both are operating at design flow.
• Vertical spacing determined by the above methods may be increased as much as 0.5 feet or 10
percent, whichever is greater, to provide better alignment or location, to avoid obstacles, to adjust
for equipment size, or to reach a satisfactory outlet. The drainage area above the terrace should
not exceed the area that would be drained by a terrace with normal spacing.
• The terrace should have enough capacity to handle the peak runoff expected from a 2-year, 24-
hour design storm without overtopping.
• The terrace cross-section should be proportioned to fit the land slope. The ridge height should
include a reasonable settlement factor. The ridge should have a minimum top width of 3 feet at the
design height. The minimum cross-sectional area of the terrace channel should be 8 square feet
for land slopes of 5 percent or less, 7 square feet for slopes from 5 to 8 percent, and 6 square feet
for slopes steeper than 8 percent. The terrace can be constructed wide enough to be maintained
using a small vehicle.
Maintenance Standards
• Maintenance should be performed as needed. Terraces should be inspected regularly; at least
once a year, and after large storm events.
Figure II-4.1.6 Gradient Terraces
2014 Figure II-4.1.6 pdf download
Washington State Department of Ecology
2012 Stormwater Management Manual for Western Washington, as Amended in December 2014 (The 2014 SWMMWW)
Slope to adequate outlet a�• -I I —) I ,
� III=III-
,
10 min. -III
-III-III;
I-
50
III-III_
III III- �
'-III-III-III-I I I-
�' E II I II 11-
NOT TO SCALE
Figure II-4.1 .6
Gradient Terraces
DEPARTMENT OF Revised June 2015
ECOLOGY Please see httpJ/www.ecy.wa.gov/copyright.htmi for copyright notice including permissions,
State of Washington limitation of liability, and disclaimer.
BMP C140: Dust Control
Purpose Dust control prevents wind transport of dust from disturbed soil surfaces
onto roadways,drainage ways, and surface waters.
Conditions of Use • In areas(including roadways)subject to surface and air movement of
dust where on-site and off-site impacts to roadways,drainage ways,or
surface waters are likely.
Design and • Vegetate or mulch areas that will not receive vehicle traffic. In areas
Installation where planting, mulching,or paving is impractical, apply gravel or
Specifications landscaping rock.
Limit dust generation by clearing only those areas where immediate
activity will take place, leaving the remaining area(s)in the original
condition, if stable. Maintain the original ground cover as long as
practical.
• Construct natural or artificial windbreaks or windscreens. These may
be designed as enclosures for small dust sources.
• Sprinkle the site with water until surface is wet. Repeat as needed. To
prevent carryout of mud onto street,refer to Stabilized Construction
Entrance(BMP C105).
Irrigation water can be used for dust control. Irrigation systems should
be installed as a first step on sites where dust control is a concern.
• Spray exposed soil areas with a dust palliative, following the
manufacturer's instructions and cautions regarding handling and
application. Used oil is prohibited from use as a dust suppressant.
Local governments may approve other dust palliatives such as calcium
chloride or PAM.
• PAM(BMP C126)added to water at a rate of 0.5 lbs.per 1,000
gallons of water per acre and applied from a water truck is more
effective than water alone. This is due to the increased infiltration of
water into the soil and reduced evaporation. In addition, small soil
particles are bonded together and are not as easily transported by wind.
Adding PAM may actually reduce the quantity of water needed for
dust control, especially in eastern Washington. Since the wholesale
cost of PAM is about$4.00 per pound,this is an extremely cost-
effective dust control method.
Techniques that can be used for unpaved roads and lots include:
• Lower speed limits. High vehicle speed increases the amount of dust
stirred up from unpaved roads and lots.
• Upgrade the road surface strength by improving particle size, shape,
and mineral types that make up the surface and base materials.
4-40 Volume 11—Construction Stormwater Pollution Prevention February 2005
• Add surface gravel to reduce the source of dust emission. Limit the
amount of fine particles(those smaller than .075 mm)to 10 to 20
percent.
• Use geotextile fabrics to increase the strength of new roads or roads
undergoing reconstruction.
• Encourage the use of alternate,paved routes, if available.
• Restrict use by tracked vehicles and heavy trucks to prevent damage to
road surface and base.
• Apply chemical dust suppressants using the admix method,blending
the product with the top few inches of surface material. Suppressants
may also be applied as surface treatments.
• Pave unpaved permanent roads and other trafficked areas.
• Use vacuum street sweepers.
• Remove mud and other dirt promptly so it does not dry and then turn
into dust.
• Limit dust-causing work on windy days.
• Contact your local Air Pollution Control Authority for guidance and
training on other dust control measures. Compliance with the local Air
Pollution Control Authority constitutes compliance with this BMP.
Maintenance Respray area as necessary to keep dust to a minimum.
Standards
February 2005 Volume 11- Construction Stormwater Pollution Prevention 4-41
BMP C200: Interceptor Dike and Swale
Purpose
Provide a ridge of compacted soil, or a ridge with an upslope swale, at the top or base of a disturbed
slope or along the perimeter of a disturbed construction area to convey stormwater. Use the dike and/or
swale to intercept the runoff from unprotected areas and direct it to areas where erosion can be
controlled. This can prevent storm runoff from entering the work area or sediment-laden runoff from
leaving the construction site.
Conditions of Use
Where the runoff from an exposed site or disturbed slope must be conveyed to an erosion control facility
which can safely convey the stormwater.
• Locate upslope of a construction site to prevent runoff from entering disturbed area.
• When placed horizontally across a disturbed slope, it reduces the amount and velocity of runoff
flowing down the slope.
• Locate downslope to collect runoff from a disturbed area and direct water to a sediment basin.
Design and Installation Specifications
• Dike and/or swale and channel must be stabilized with temporary or permanent vegetation or other
channel protection during construction.
• Channel requires a positive grade for drainage; steeper grades require channel protection and
check dams.
• Review construction for areas where overtopping may occur.
• Can be used at top of new fill before vegetation is established.
• May be used as a permanent diversion channel to carry the runoff.
• Sub-basin tributary area should be one acre or less.
• Design capacity for the peak volumetric flow rate calculated using a 10-minute time step from a 10-
year, 24-hour storm, assuming a Type 1A rainfall distribution, for temporary facilities. Alternatively,
use 1.6 times the 10-year, 1-hour flow indicated by an approved continuous runoff model. For
facilities that will also serve on a permanent basis, consult the local government's drainage
requirements.
Interceptor dikes shall meet the following criteria:
• Top Width: 2 feet minimum.
• Height: 1.5 feet minimum on berm.
• Side Slope: 2H:1 V or flatter.
• Grade: Depends on topography, however, dike system minimum is 0.5%, and maximum is 1%.
• Compaction: Minimum of 90 percent ASTM D698 standard proctor.
• Horizontal Spacing of Interceptor Dikes:
Average Slope Slope Percent Flowpath Length
20H:1 V or less 3-5% 300 feet
(10 to 20)H:lV 5-10% 200 feet
(4 to 10)H:1 V 10-25% 100 feet
(2 to 4)H:1 V 25-50% 50 feet
• Stabilization: depends on velocity and reach
• Slopes <5%: Seed and mulch applied within 5 days of dike construction (see BMP C121:
Mulching).
• Slopes 5 -40%: Dependent on runoff velocities and dike materials. Stabilization should be done
immediately using either sod or riprap or other measures to avoid erosion.
• The upslope side of the dike shall provide positive drainage to the dike outlet. No erosion shall
occur at the outlet. Provide energy dissipation measures as necessary. Sediment-laden runoff
must be released through a sediment trapping facility.
• Minimize construction traffic over temporary dikes. Use temporary cross culverts for channel
crossing.
Interceptor swales shall meet the following criteria:
• Bottom Width: 2 feet minimum; the cross-section bottom shall be level.
• Depth: 1-foot minimum.
• Side Slope: 2H:1 V or flatter.
• Grade: Maximum 5 percent, with positive drainage to a suitable outlet (such as a sediment pond).
• Stabilization: Seed as per BMP C120: Temporary and Permanent Seeding, or BMP C202:_Channel
Lining, 12 inches thick riprap pressed into the bank and extending at least 8 inches vertical from
the bottom.
Inspect diversion dikes and interceptor swales once a week and after every rainfall. Immediately remove
sediment from the flow area.
Damage caused by construction traffic or other activity must be repaired before the end of each working
day.
Check outlets and make timely repairs as needed to avoid gully formation. When the area below the
temporary diversion dike is permanently stabilized, remove the dike and fill and stabilize the channel to
blend with the natural surface.
Washington State Department of Ecology
2012 Stormwater Management Manual for Westem Washingto,as Amended in December 2014 (The 2014 SWMMWW)
BMP C205: Subsurface Drains
Purpose
To intercept, collect, and convey ground water to a satisfactory outlet, using a perforated pipe or conduit
below the ground surface. Subsurface drains are also known as "french drains." The perforated pipe
provides a dewatering mechanism to drain excessively wet soils, provide a stable base for construction,
improve stability of structures with shallow foundations, or to reduce hydrostatic pressure to improve
slope stability.
Conditions of Use
Use when excessive water must be removed from the soil. The soil permeability, depth to water table
and impervious layers are all factors which may govern the use of subsurface drains.
Design and Installation Specifications
Relief drains are used either to lower the water table in large, relatively flat areas, improve the growth of
vegetation, or to remove surface water.
Relief drains are installed along a slope and drain in the direction of the slope.
They can be installed in a grid pattern, a herringbone pattern, or a random pattern.
• Interceptor drains are used to remove excess ground water from a slope, stabilize steep slopes,
and lower the water table immediately below a slope to prevent the soil from becoming saturated.
Interceptor drains are installed perpendicular to a slope and drain to the side of the slope.
They usually consist of a single pipe or series of single pipes instead of a patterned layout.
• Depth and spacing of interceptor drains - The depth of an interceptor drain is determined
primarily by the depth to which the water table is to be lowered or the depth to a confining layer.
For practical reasons, the maximum depth is usually limited to 6 feet, with a minimum cover of 2
feet to protect the conduit.
• The soil should have depth and sufficient permeability to permit installation of an effective drainage
system at a depth of 2 to 6 feet.
• An adequate outlet for the drainage system must be available either by gravity or by pumping.
• The quantity and quality of discharge needs to be accounted for in the receiving stream (additional
detention may be required).
• This standard does not apply to subsurface drains for building foundations or deep excavations.
• The capacity of an interceptor drain is determined by calculating the maximum rate of ground
water flow to be intercepted. Therefore, it is good practice to make complete subsurface
investigations, including hydraulic conductivity of the soil, before designing a subsurface drainage
system.
• Size of drain - Size subsurface drains to carry the required capacity without pressure flow.
Minimum diameter for a subsurface drain is 4 inches.
• The minimum velocityrequired to prevent silting is 1.4 ft./sec. The line shall be graded to achieve
q P 9
this velocity at a minimum. The maximum allowable velocity using a sand-gravel filter or envelope
is 9 ft/sec.
• Filter material and fabric shall be used around all drains for proper bedding and filtration of fine
materials. Envelopes and filters should surround the drain to a minimum of 3-inch thickness.
• The outlet of the subsurface drain shall empty into a sediment pond through a catch basin. If free
of sediment, it can then empty into a receiving channel, swale, or stable vegetated area adequately
protected from erosion and undermining.
• The trench shall be constructed on a continuous grade with no reverse grades or low spots.
• Soft or yielding soils under the drain shall be stabilized with gravel or other suitable material.
• Backfilling shall be done immediately after placement of the pipe. No sections of pipe shall remain
uncovered overnight or during a rainstorm. Backfill material shall be placed in the trench in such a
manner that the drain pipe is not displaced or damaged.
• Do not install permanent drains near trees to avoid the tree roots that tend to clog the line. Use
solid pipe with watertight connections where it is necessary to pass a subsurface drainage system
through a stand of trees.
• Outlet - Ensure that the outlet of a drain empties into a channel or other watercourse above the
normal water level.
• Secure an animal guard to the outlet end of the pipe to keep out rodents.
• Use outlet pipe of corrugated metal, cast iron, or heavy-duty plastic without perforations and at
least 10 feet long. Do not use an envelope or filter material around the outlet pipe, and bury at
least two-thirds of the pipe length.
• When outlet velocities exceed those allowable for the receiving stream, outlet protection must be
provided.
Maintenance Standards
Subsurface drains shall be checked periodically to ensure that they are free-flowing and not clogged with
sediment or roots.
• The outlet shall be kept clean and free of debris.
• Surface inlets shall be kept open and free of sediment and other debris.
• Trees located too close to a subsurface drain often clog the system with their roots. If a drain
becomes clogged, relocate the drain or remove the trees as a last resort. Drain placement should
be planned to minimize this problem.
• Where drains are crossed by heavy vehicles, the line shall be checked to ensure that it is not
crushed.
Washington State Department of Ecology
2012 Stormwater Management Manual for Western Washington, as Amended in December 2014 (The 2014 SWMMWW)
BMP C207: Check Dams
Purpose
Construction of small dams across a swale or ditch reduces the velocity of concentrated flow and
dissipates energy at the check dam.
Conditions of Use
Where temporary channels or permanent channels are not yet vegetated, channel lining is infeasible,
and/or velocity checks are required.
• Check dams may not be placed in streams unless approved by the State Department of Fish and
Wildlife. Check dams may not be placed in wetlands without approval from a permitting agency.
• Do not place check dams below the expected backwater from any salmonid bearing water
between October 1 and May 31 to ensure that there is no loss of high flow refuge habitat for
overwintering juvenile salmonids and emergent salmonid fry.
• Construct rock check dams from appropriately sized rock. The rock used must be large enough to
stay in place given the expected design flow through the channel. The rock must be placed by
hand or by mechanical means (no dumping of rock to form dam) to achieve complete coverage of
the ditch or swale and to ensure that the center of the dam is lower than the edges.
• Check dams may also be constructed of either rock or pea-gravel filled bags. Numerous new
products are also available for this purpose. They tend to be re-usable, quick and easy to install,
effective, and cost efficient.
• Place check dams perpendicular to the flow of water.
• The dam should form a triangle when viewed from the side. This prevents undercutting as water
flows over the face of the dam rather than falling directly onto the ditch bottom.
• Before installing check dams impound and bypass upstream water flow away from the work area.
Options for bypassing include pumps, siphons, or temporary channels.
• Check dams in association with sumps work more effectively at slowing flow and retaining
sediment than just a check dam alone. A deep sump should be provided immediately upstream of
the check dam.
• In some cases, if carefully located and designed, check dams can remain as permanent
installations with very minor regrading. They may be left as either spillways, in which case
accumulated sediment would be graded and seeded, or as check dams to prevent further
sediment from leaving the site.
• The maximum spacing between the dams shall be such that the toe of the upstream dam is at the
same elevation as the top of the downstream dam.
• Keep the maximum height at 2 feet at the center of the dam.
• Keep the center of the check dam at least 12 inches lower than the outer edges at natural ground
elevation.
• Keep the side slopes of the check dam at 2H:1 V or flatter.
• Key the stone into the ditch banks and extend it beyond the abutments a minimum of 18 inches to
avoid washouts from overflow around the dam.
• Use filter fabric foundation under a rock or sand bag check dam. If a blanket ditch liner is used,
filter fabric is not necessary. A piece of organic or synthetic blanket cut to fit will also work for this
purpose.
• In the case of grass-lined ditches and swales, all check dams and accumulated sediment shall be
removed when the grass has matured sufficiently to protect the ditch or swale - unless the slope of
the swale is greater than 4 percent. The area beneath the check dams shall be seeded and
mulched immediately after dam removal.
• Ensure that channel appurtenances, such as culvert entrances below check dams, are not subject
to damage or blockage from displaced stones. Figure 11-4.2.7_Rock_Check_Dam depicts a typical
rock check dam.
Maintenance Standards
Check dams shall be monitored for performance and sediment accumulation during and after each
runoff producing rainfall. Sediment shall be removed when it reaches one half the sump depth.
• Anticipate submergence and deposition above the check dam and erosion from high flows around
the edges of the dam.
• If significant erosion occurs between dams, install a protective riprap liner in that portion of the
channel.
Approved as Equivalent
Ecology has approved products as able to meet the requirements of BMP C207: Check Dams. The
products did not pass through the Technology Assessment Protocol — Ecology (TAPE) process. Local
jurisdictions may choose not to accept this product approved as equivalent, or may require additional
testing prior to consideration for local use. The products are available for review on Ecology's website at
http://www.ecy.wa.gov/programs/wq/stormwater/newtech/equiva lent.htmI
Figure 11-4.2.7 Rock Check Dam
1�
2014 Figure II-4.2.7 pdf download
Washington State Department of Ecology
2012 Stormwater Management Manual for Western Washington, as Amended in December 2014 (The 2014 SWMMWW)
View Looking Upstream
stream
A 18„
12" (0.5m)
(150mm)
Note: �:°�' ''
Key stone into channel banks and extend it / /•/ /
beyond the abutments a minimum of 18"
(0.5m)to prevent flow around dam. A
Section A-A
24" (0.6m) o,
•QO �o
XX
8'(2.4m)
Spacing Between Check Dams
'L' =the distance such that points
'A'and'B'are of equal elevation.
Point'A' Point'B'
' o
NOT TO SCALE
Figure II-4.2.7
Rock Check Dam
DEPARTMENT OF Revised July 2015
ECOLOGY Please see http://www.ecy.wa.gov/copyright.html for copyright notice including permissions,
State of Washington limitation of liability, and disclaimer.
BMP C220: Storm Drain Inlet Protection
Purpose To prevent coarse sediment from entering drainage systems prior to
permanent stabilization of the disturbed area.
Conditions of Use Where storm drain inlets are to be made operational before permanent
stabilization of the disturbed drainage area. Protection should be provided
for all storm drain inlets downslope and within 500 feet of a disturbed or
construction area,unless the runoff that enters the catch basin will be
conveyed to a sediment pond or trap. Inlet protection may be used
anywhere to protect the drainage system. It is likely that the drainage
system will still require cleaning.
Table 4.9 lists several options for inlet protection. All of the methods for
storm drain inlet protection are prone to plugging and require a high
frequency of maintenance. Drainage areas should be limited to 1 acre or
less. Emergency overflows may be required where stormwater ponding
would cause a hazard. If an emergency overflow is provided,additional
m end-of-pipe treatment may be required.
Table 4.9
Storm Drain Inlet Protetion
Applicable for
Type of Inlet Emergency Paved/ Earthen
Protection Overflow Surfaces Conditions of Use
Drop Inlet Protection
Excavated drop inlet Yes, Earthen Applicable for heavy flows. Easy
protection temporary to maintain. Large area
flooding will Requirement: 30'X 307acre
occur
Block and gravel drop Yes Paved or Earthen Applicable for heavy concentrated
inlet protection flows. Will not pond.
Gravel and wire drop No Applicable for heavy concentrated
inlet protection flows. Will pond. Can withstand
traffic.
Catch basin filters Yes Paved or Earthen Frequent maintenance required.
Curb Inlet Protection
Curb inlet protection Small capacity Paved Used for sturdy,more compact
with a wooden weir overflow installation.
Block and gravel curb Yes Paved Sturdy,but limited filtration.
inlet protection
Culvert Inlet Protection
Culvert inlet sediment 18 month expected life.
trap
4-82 Volume 11—Construction Stormwater Pollution Prevention February 2005
Design and Excavated Drop Inlet Protection-An excavated impoundment around the
Installation storm drain. Sediment settles out of the stormwater prior to entering the
Specifications storm drain.
• Depth 1-2 ft as measured from the crest of the inlet structure.
• Side Slopes of excavation no steeper than 2:1.
• Minimum volume of excavation 35 cubic yards.
• Shape basin to fit site with longest dimension oriented toward the
longest inflow area.
• Install provisions for draining to prevent standing water problems.
• Clear the area of all debris.
• Grade the approach to the inlet uniformly.
• Drill weep holes into the side of the inlet.
• Protect weep holes with screen wire and washed aggregate.
• Seal weep holes when removing structure and stabilizing area.
• It may be necessary to build a temporary dike to the down slope side
of the structure to prevent bypass flow.
Block and Gravel Filter-A barrier formed around the storm drain inlet
with standard concrete blocks and gravel. See Figure 4.14.
Height 1 to 2 feet above inlet.
• Recess the first row 2 inches into the ground for stability.
Support subsequent courses by placing a 2x4 through the block
opening.
Do not use mortar.
• Lay some blocks in the bottom row on their side for dewatering the
pool.
Place hardware cloth or comparable wire mesh with %z-inch openings
over all block openings.
Place gravel just below the top of blocks on slopes of 2:1 or flatter.
An alternative design is a gravel donut.
Inlet slope of 3:1.
• Outlet slope of 2:1.
• 1-foot wide level stone area between the structure and the inlet.
Inlet slope stones 3 inches in diameter or larger.
• Outlet slope use gravel ''/z-to%-inch at a minimum thickness of 1-foot.
February 2005 Volume 11— Construction Stormwater Pollution Prevention 4-83
Plan View A
Drain
Grate Q OQ 4° .�p o�p
O 0 C
p p
ono o � O O
••Q4°c�0��
°••°' a.Oq�. •°o Concrete
O °moo, o Block
•i�00Q0�4QoQ�6�
a �S° ,
Q 4°O�
0
'Q°
� •'°; ° Gravel
•rJ g0 a
0 o Backfill
o�0
a
,�� o° °00� .�Q •00�4
y�o
Section A - A Concrete Block _Wire Screen or
Filter Fabric
Gravel Backfill Overflow
Water Ponding Height
0 0 •,o
• Water
Drop Inlet \\\\\ N\11\\\\\
Notes:
1.Drop inlet sediment barriers are to be used for small,nearly level drainage areas.(less than 5%)
2.Excavate a basin of sufficient size adjacent to the drop inlet.
3.The top of the structure(ponding height)must be well below the ground elevation downslope to prevent
runoff from bypassing the inlet. A temporary dike may be necessary on the dowslopc side of the structure.
Figure 4.14—Block and Gravel Filter
Gravel and Wire Mesh Filter- A gravel barrier placed over the top of the
inlet. This structure does not provide an overflow.
• Hardware cloth or comparable wire mesh with t/2-inch openings.
• Coarse aggregate.
• Height 1-foot or more, 18 inches wider than inlet on all sides.
• Place wire mesh over the drop inlet so that the wire extends a
minimum of 1-foot beyond each side of the inlet structure.
• if more than one strip of mesh is necessary, overlap the strips.
• Place coarse aggregate over the wire mesh.
• The depth of the gravel should be at least 12 inches over the entire
inlet opening and extend at least 18 inches on all sides.
4-84 Volume 11—Construction Stormwater Pollution Prevention February 2005
Catchbasin Filters-Inserts should be designed by the manufacturer for
use at construction sites. The limited sediment storage capacity increases
the amount of inspection and maintenance required,which may be daily
for heavy sediment loads. The maintenance requirements can be reduced
by combining a catchbasin filter with another type of inlet protection.
This type of inlet protection provides flow bypass without overflow and
therefore may be a better method for inlets located along active rights-of-
way.
• 5 cubic feet of storage.
• Dewatering provisions.
• High-flow bypass that will not clog under normal use at a construction
site.
• The catchbasin filter is inserted in the catchbasin just below the
grating.
Curb Inlet Protection with Wooden Weir—Barrier formed around a curb
inlet with a wooden frame and gravel.
• Wire mesh with '/2-inch openings.
• Extra strength filter cloth.
• Construct a frame.
• Attach the wire and filter fabric to the frame.
• Pile coarse washed aggregate against wire/fabric.
• Place weight on frame anchors.
Block and Gravel Curb Inlet Protection—Barrier formed around an inlet
with concrete blocks and gravel. See Figure 4.14.
• Wire mesh with %z-inch openings.
• Place two concrete blocks on their sides abutting the curb at either side
of the inlet opening. These are spacer blocks.
• Place a 2x4 stud through the outer holes of each spacer block to align
the front blocks.
• Place blocks on their sides across the front of the inlet and abutting the
spacer blocks.
• Place wire mesh over the outside vertical face.
• Pile coarse aggregate against the wire to the top of the barrier.
Curb and Gutter Sediment Barrier—Sandbag or rock berm(riprap and
aggregate)3 feet high and 3 feet wide in a horseshoe shape. See Figure
4.16.
• Construct a horseshoe shaped berm, faced with coarse aggregate if
using riprap, 3 feet high and 3 feet wide,at least 2 feet from the inlet.
• Construct a horseshoe shaped sedimentation trap on the outside of the
berm sized to sediment trap standards for protecting a culvert inlet.
February 2005 Volume 11— Construction Stormwater Pollution Prevention 4-85
Maintenance • Catch basin filters should be inspected frequently,especially after
Standards storm events. If the insert becomes clogged, it should be cleaned or
replaced.
• For systems using stone filters: If the stone filter becomes clogged
with sediment,the stones must be pulled away from the inlet and
cleaned or replaced. Since cleaning of gravel at a construction site
may be difficult,an alternative approach would be to use the clogged
stone as fill and put fresh stone around the inlet.
• Do not wash sediment into storm drains while cleaning. Spread all
excavated material evenly over the surrounding land area or stockpile
and stabilize as appropriate.
4-86 Volume 11—Construction Stormwater Pollution Prevention February 2005
O
LL
U
Q
U
J
}
m
5"MAX.
DRAINAGE GRATE
TRIM
GRATE FRAME
DRAINAGE GRATE
D \ -RECTANGULAR GRATE SHOWN
SEDIMENT AND DEBRIS -
4 v '
OVERFLOW BYPASS
t v
BELOW INLET GRATE DEVICE
v
FILTERED rr
WATER
BELOW INLET GRATE DEVICE
0
D
D
D D
D D D
SECTION VIEW
ki---Ai o
BMP C231 : Brush Barrier
Purpose
The purpose of brush barriers is to reduce the transport of coarse sediment from a construction site by
providing a temporary physical barrier to sediment and reducing the runoff velocities of overland flow.
Conditions of Use
• Brush barriers may be used downslope of all disturbed areas of less than one-quarter acre.
• Brush barriers are not intended to treat concentrated flows, nor are they intended to treat
substantial amounts of overland flow. Any concentrated flows must be conveyed through the
drainage system to a sediment pond. The only circumstance in which overland flow can be treated
solely by a brush barrier, rather than by a sediment pond, is when the area draining to the barrier is
small.
• Brush barriers should only be installed on contours.
Design and Installation Specifications
• Height 2 feet (minimum) to 5 feet (maximum).
• Width 5 feet at base (minimum) to 15 feet (maximum).
• Filter fabric (geotextile) may be anchored over the brush berm to enhance the filtration ability of the
barrier. Ten-ounce burlap is an adequate alternative to filter fabric.
• Chipped site vegetation, composted mulch, or wood-based mulch (hog fuel) can be used to
construct brush barriers.
• A 100 percent biodegradable installation can be constructed using 10-ounce burlap held in place
by wooden stakes. Figure _ll-4.2.11 Brush Barrier depicts a typical brush barrier.
Maintenance Standards
• There shall be no signs of erosion or concentrated runoff under or around the barrier. If
concentrated flows are bypassing the barrier, it must be expanded or augmented by toed-in filter
fabric.
• The dimensions of the barrier must be maintained.
Figure 11-4.2.11 Brush Barrier
2014 Figure 11 4.2.11 pdf download
Washington State Department of Ecology
2012 Stormwater Management Manual for Western Washington, as Amended in December 2014 (The 2014 SWMMWW),
If required, drape filter fabric over
brush and secure in 4"x4"min.
trench with compacted backfill \
\ Anchor downhill edge of
filter fabric with stakes,
sandbags, or equivalent
2' min. height
III�I_
Min. 5'wide brush barrier with
max. 6"diameter woody debris.
Alternatively topsoil strippings
may be used to form the barrier.
NOT TO SCALE
Figure II-4.2. 11
Brush Barrier
DEPARTMENT OF Revised September 2015
ECOLOGY Please see http://Www.ecy.wa.gov/copyright.html for copyright notice including permissions,
State of Washington limitation of liability, and disclaimer.
BMP C232: Gravel Filter Berm
Purpose
A gravel filter berm is constructed on rights-of-way or traffic areas within a construction site to retain
sediment by using a filter berm of gravel or crushed rock.
Conditions of Use
Where a temporary measure is needed to retain sediment from rights-of-way or in traffic areas on
construction sites.
Design and Installation Specifications
• Berm material shall be %to 3 inches in size, washed well-grade gravel or crushed rock with less
than 5 percent fines.
• Spacing of berms:
o Every 300 feet on slopes less than 5 percent
o Every 200 feet on slopes between 5 percent and 10 percent
o Every 100 feet on slopes greater than 10 percent
• Berm dimensions:
0 1 foot high with 3H:1 V side slopes
0 8 linear feet per 1 cfs runoff based on the 10-year, 24-hour design storm
Maintenance Standards
• Regular inspection is required. Sediment shall be removed and filter material replaced as needed.
Washington State Department of Ecology
2012 Stormwater Management Manual for Western Washing, as Amended in December 2014 (The 2014 SWMMWWI
BMP C233: Silt Fence
Purpose Use of a silt fence reduces the transport of coarse sediment from a
construction site by providing a temporary physical barrier to sediment
and reducing the runoff velocities of overland flow. See Figure 4.19 for
details on silt fence construction.
Conditions of Use Silt fence may be used downslope of all disturbed areas.
• Silt fence is not intended to treat concentrated flows, nor is it intended
to treat substantial amounts of overland flow. Any concentrated flows
must be conveyed through the drainage system to a sediment pond.
The only circumstance in which overland flow can be treated solely by
a silt fence,rather than by a sediment pond, is when the area draining
to the fence is one acre or less and flow rates are less than 0.5 cfs.
• Silt fences should not be constructed in streams or used in V-shaped
ditches. They are not an adequate method of silt control for anything
deeper than sheet or overland flow.
Joints in filter fabric shall be spliced at
posts.Use staples,wire rings or 2"x2"by 14 Ga.wire or
equivalent to attach fabric to posts equivalent,if standard
strength fabric used I
Filter fabric--
II I
II I N
II I
II
C
T ;:W -6'maxim T �Minimum 4"x4"trench E
N
Backtill trench with native soil �
Post spacing may be increased or 3/4"-1.5"washed gravel
to 8'if wire backing is used
2"x2"wood posts,steel fence
posts,or equivalent
Figure 4.19- Silt Fence
Design and • Drainage area of 1 acre or less or in combination with sediment basin
Installation in a larger site.
Specifications
• Maximum slope steepness(normal(perpendicular)to fence line) 1:1.
• Maximum sheet or overland flow path length to the fence of 100 feet.
• No flows greater than 0.5 cfs.
• The geotextile used shall meet the following standards. All geotextile
properties listed below are minimum average roll values(i.e.,the test
result for any sampled roll in a lot shall meet or exceed the values
shown in Table 4.10):
4-94 Volume 11-Construction Stormwater Pollution Prevention February 2005
Table 4.10
Geotextile Standards
Polymeric Mesh AOS 0.60 mm maximum for slit film woven(#30 sieve). 0.30
(ASTM D4751) mm maximum for all other geotextile types(#50 sieve).
0.15 mm minimum for all fabric types(#100 sieve).
Water Permittivity 0.02 sec" minimum
(ASTM D4491)
Grab Tensile Strength 180 lbs.Minimum for extra strength fabric.
(ASTM D4632) 1001bs minimum for standard strength fabric.
i
Grab Tensile Strength 30%maximum
(ASTM D4632)
Ultraviolet Resistance 70%minimum
(ASTM D4355)
• Standard strength fabrics shall be supported with wire mesh, chicken
wire, 2-inch x 2-inch wire, safety fence,or jute mesh to increase the
strength of the fabric. Silt fence materials are available that have
synthetic mesh backing attached.
• Filter fabric material shall contain ultraviolet ray inhibitors and
stabilizers to provide a minimum of six months of expected usable
construction life at a temperature range of 0°F.to 120T.
• 100 percent biodegradable silt fence is available that is strong, long
lasting,and can be left in place after the project is completed, if
permitted by local regulations.
• Standard Notes for construction plans and specifications follow. Refer
to Figure 4.19 for standard silt fence details.
The contractor shall install and maintain temporary silt fences at the
locations shown in the Plans. The silt fences shall be constructed in
the areas of clearing,grading,or drainage prior to starting those
activities. A silt fence shall not be considered temporary if the silt
fence must function beyond the life of the contract. The silt fence
shall prevent soil carried by runoff water from going beneath,through,
or over the top of the silt fence,but shall allow the water to pass
through the fence.
The minimum height of the top of silt fence shall be 2 feet and the
maximum height shall be 2'/2 feet above the original ground surface.
The geotextile shall be sewn together at the point of manufacture,or at
an approved location as determined by the Engineer,to form geotextile
lengths as required. All sewn seams shall be located at a support post.
Alternatively,two sections of silt fence can be overlapped,provided
the Contractor can demonstrate,to the satisfaction of the Engineer,that
the overlap is long enough and that the adjacent fence sections are
close enough together to prevent silt laden water from escaping
through the fence at the overlap.
February 2005 Volume It— Construction Stormwater Pollution Prevention 4-95
The geotextile shall be attached on the up-slope side of the posts and
support system with staples,wire,or in accordance with the
manufacturer's recommendations. The geotextile shall be attached to
the posts in a manner that reduces the potential for geotextile tearing at
the staples,wire,or other connection device. Silt fence back-up
support for the geotextile in the form of a wire or plastic mesh is
dependent on the properties of the geotextile selected for use. If wire
or plastic back-up mesh is used,the mesh shall be fastened securely to
the up-slope of the posts with the geotextile being up-slope of the
mesh back-up support.
The geotextile at the bottom of the fence shall be buried in a trench to
a minimum depth of 4 inches below the ground surface. The trench
shall be backfilled and the soil tamped in place over the buried portion
of the geotextile, such that no flow can pass beneath the fence and
scouring can not occur. When wire or polymeric back-up support
mesh is used,the wire or polymeric mesh shall extend into the trench a
minimum of 3 inches.
The fence posts shall be placed or driven a minimum of 18 inches. A
minimum depth of 12 inches is allowed if topsoil or other soft
subgrade soil is not present and a minimum depth of 18 inches cannot
be reached. Fence post depths shall be increased by 6 inches if the
fence is located on slopes of 3:1 or steeper and the slope is
perpendicular to the fence. If required post depths cannot be obtained,
the posts shall be adequately secured by bracing or guying to prevent
overturning of the fence due to sediment loading.
Silt fences shall be located on contour as much as possible,except at
the ends of the fence,where the fence shall be turned uphill such that
the silt fence captures the runoff water and prevents water from
flowing around the end of the fence.
If the fence must cross contours,with the exception of the ends of the
fence,gravel check dams placed perpendicular to the back of the fence
shall be used to minimize concentrated flow and erosion along the
back of the fence. The gravel check dams shall be approximately 1-
foot deep at the back of the fence. It 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. The gravel check dams
shall consist of crushed surfacing base course, gravel backfill for
walls,or shoulder ballast. The gravel check dams shall be located
every 10 feet along the fence where the fence must cross contours.
The slope of the fence line where contours must be crossed shall not
be steeper than 3:1.
Wood,steel or equivalent posts shall be used. Wood posts shall have
minimum dimensions of 2 inches by 2 inches by 3 feet minimum
length,and shall be free of defects such as knots, splits,or gouges.
4-96 Volume 11— Construction Stormwater Pollution Prevention February 2005
Steel posts shall consist of either size No. 6 rebar or larger,ASTM A
120 steel pipe with a minimum diameter of 1-inch,U, T,L,or C shape
steel posts with a minimum weight of 1.351bs./ft.or other steel posts
having equivalent strength and bending resistance to the post sizes
listed. The spacing of the support posts shall be a maximum of 6 feet.
Fence back-up 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 ultraviolet radiation as the geotextile it supports.
• Silt fence installation using the slicing method specification details
follow. Refer to Figure 4.20 for slicing method details.
The base of both end posts must be at least 2 to 4 inches above the top
of the silt fence 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.
Install posts 3 to 4 feet apart in critical retention areas and 6 to 7 feet
apart in standard applications.
Install posts 24 inches deep on the downstream side of the silt fence,
and as close as possible to the fabric,enabling posts to support the
fabric from upstream water pressure.
Install posts with the nipples facing away from the silt fence fabric.
Attach the 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. In
addition,each tie should be positioned to hang on a post nipple when
tightening to prevent sagging.
Wrap approximately 6 inches of fabric around the end posts and secure
with 3 ties.
No more than 24 inches of a 36-inch fabric is allowed above ground
level.
The rope lock system must be used in all ditch check applications.
The installation should be checked and corrected for any deviation
before compaction. Use a flat-bladed shovel to tuck fabric deeper into
the ground if necessary.
Compaction is vitally important for effective results. Compact the soil
immediately next to the silt fence 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.
February 2005 Volume 11—Construction Stormwater Pollution Prevention 4-97
• Any damage shall be repaired immediately.
Maintenance If concentrated flows are evident uphill of the fence, they must be
Standards intercepted and conveyed to a sediment pond.
• It is important to check the uphill side of the fence for signs of the
fence clogging and acting as a barrier to flow and then causing
channelization of flows parallel to the fence. If this occurs, replace the
fence or remove the trapped sediment.
• Sediment deposits shall either be removed when the deposit reaches
approximately one-third the height of the silt fence, or a second silt
fence shall be installed.
• If the filter fabric(geotextile) has deteriorated due to ultraviolet
breakdown it shall be replaced.
►.nding height POST SPACING:
lwaw.=4' 7'raa> on e"n runs
IF fa1a.an Pooling aoas .............. .. ...............Topol Fabric
Bell
Attach fabric a 14
...beard side of Pon fr
FLOW---—
0"..ever each old..r r POST DEPTH:
set Mice at.4 Was. As nook eNow pound
with doelce osssrt.4 i Y faMlc leovo pound
ea P•.J.or prooeor
100%c 1.9%...vocY.n DogaW
tlmdaeslwrp'
ATTACH ENT OMM:
//
//\//\// /\�/\\\ a Gather fabric at polls.I needed.
a Ullhe three tlw per post,as v4hln lop a'of fabric.
•Padit each tie aaporWy*
p xwlu p holes.erWally
•mm o lls of r apart.
i \ \ •Narp each w on a and poa rllppb llplt«+seas•►!•
No more than 24"of a 36'fabric use cable ties OObO or wA et•.
is allowed above ground.
Rol of$1111I fence
-0— OPpfation
Poe
Wiggled
alter
compaction
Fatafc
1 srt Fence
TJ-•b
WAIWIMR;16_K��A,
2�-3�fTIR1
aJC Q it v a\a .�\ \'�\'�\,.��. .\
71
Hofleontel tdtleel porrll %Chg blade
(76 mm aid" (1 B mm width) Completed Ira skillon
Vibratory plow k not acceptable because of hodrontel compaction
Figure 4.20—Silt Fence Installation by Slicing Method
4-98 Volume lI—Construction Stormwater Pollution Prevention February 2005
BMP C234: Vegetated Strip
Purpose
Vegetated strips reduce the transport of coarse sediment from a construction site by providing a
temporary physical barrier to sediment and reducing the runoff velocities of overland flow.
Conditions of Use
• Vegetated strips may be used downslope of all disturbed areas.
• Vegetated strips are not intended to treat concentrated flows, nor are they intended to treat
substantial amounts of overland flow. Any concentrated flows must be conveyed through the
drainage system to a sediment pond. The only circumstance in which overland flow can be treated
solely by a strip, rather than by a sediment pond, is when the following criteria are met (see Table
II-4.2.4 Contributing Drainage Area for Vegetated Strips):
Table 11-4.2.4 Contributing Drainage Area for Vegetated Strip_
Average Contributing Area Average Contributing Area Max Contributing area Flowpath
Slope Percent Slope Length
1.5H : 1 V or flatter 67% or flatter 100 feet
2H : 1 V or flatter 50% or flatter 115 feet
4H : 1V or flatter 25% or flatter 150 feet
6H : 1 V or flatter 16.7% or flatter 200 feet
1 OH : 1 V or flatter 10% or flatter 250 feet
Design and Installation Specifications
• The vegetated strip shall consist of a minimum of a 25-foot flowpath length continuous strip of
dense vegetation with topsoil. Grass-covered, landscaped areas are generally not adequate
because the volume of sediment overwhelms the grass. Ideally, vegetated strips shall consist of
undisturbed native growth with a well-developed soil that allows for infiltration of runoff.
• The slope within the strip shall not exceed 4H:1 V.
• The uphill boundary of the vegetated strip shall be delineated with clearing limits.
Maintenance Standards
• Any areas damaged by erosion or construction activity shall be seeded immediately and protected
by mulch.
• If more than 5 feet of the original vegetated strip width has had vegetation removed or is being
eroded, sod must be installed.
• If there are indications that concentrated flows are traveling across the buffer, surface water
controls must be installed to reduce the flows entering the buffer, or additional perimeter protection
must be installed.
Washington State Department of Ecology
2012 Stormwater Management Manual for Western Washington, as Amended in December 2014 (The 2014 SWMMWW)
BMP C235: Wattles
Purpose
Wattles are temporary erosion and sediment control barriers consisting of straw, compost, or other
material that is wrapped in biodegradable tubular plastic or similar encasing material. They reduce the
velocity and can spread the flow of rill and sheet runoff, and can capture and retain sediment. Wattles
are typically 8 to 10 inches in diameter and 25 to 30 feet in length. Wattles are placed in shallow
trenches and staked along the contour of disturbed or newly constructed slopes. See -Figure II-4.2.14
Wattles for typical construction details. WSDOT Standard Plan 1-30.30-00 also provides information on
Wattles (http://www.wsdot.wa.gov/Design/Standards/Plans.htm#Sectioni)
Conditions of Use
• Use wattles:
o In disturbed areas that require immediate erosion protection.
o On exposed soils during the period of short construction delays, or over winter months.
o On slopes requiring stabilization until permanent vegetation can be established.
• The material used dictates the effectiveness period of the wattle. Generally, Wattles are typically
effective for one to two seasons.
• Prevent rilling beneath wattles by properly entrenching and abutting wattles together to prevent
water from passing between them.
Design Criteria
• Install wattles perpendicular to the flow direction and parallel to the slope contour.
• Narrow trenches should be dug across the slope on contour to a depth of 3- to 5-inches on clay
soils and soils with gradual slopes. On loose soils, steep slopes, and areas with high rainfall, the
trenches should be dug to a depth of 5- to 7- inches, or 1/2 to 2/3 of the thickness of the wattle.
• Start building trenches and installing wattles from the base of the slope and work up. Spread
excavated material evenly along the uphill slope and compacted using hand tamping or other
methods.
• Construct trenches at intervals of 10- to 25-feet depending on the steepness of the slope, soil type,
and rainfall. The steeper the slope the closer together the trenches.
• Install the wattles snugly into the trenches and abut tightly end to end. Do not overlap the ends.
• Install stakes at each end of the wattle, and at 4-foot centers along entire length of wattle.
• If required, install pilot holes for the stakes using a straight bar to drive holes through the wattle
and into the soil.
• Wooden stakes should be approximately 3/4 x 3/4 x 24 inches min. Willow cuttings or 3/8-inch
rebar can also be used for stakes.
• Stakes should be driven through the middle of the wattle, leaving 2 to 3 inches of the stake
protruding above the wattle.
Maintenance Standards
• Wattles may require maintenance to ensure they are in contact with soil and thoroughly
entrenched, especially after significant rainfall on steep sandy soils.
Figure 11-4.2.14 Wattles
aN'
2014 Figure II-4.2.14 pdf download
• Inspect the slope after significant storms and repair any areas where wattles are not tightly abutted
or water has scoured beneath the wattles.
Approved as Equivalent
Ecology has approved products as able to meet the requirements of BMP C235: Wattles. The products
did not pass through the Technology Assessment Protocol — Ecology (TAPE) process. Local jurisdictions
may choose not to accept this product approved as equivalent, or may require additional testing prior to
consideration for local use. The products are available for review on Ecology's website at
http.Ryomy.ecy.wa.gov/programs/wq/stormwater/newtech/equivalent.htmI
Washington State Department of Ecology
2012 Stormwater Management Manual for Western Washington, as Amended in December 2014 (The 2014 SWMMWW)
3'-4'
—(1.2m)
\i,\
Straw rolls must be
placed along slope r�� �/ Adjacent rolls
contours \ shall tightly abut
10'-25'(3-8m)
i
Spacing depends
on soil type and
slope steepness Sediment, organic matter,
and native seeds are
captured behind the rolls.
3"-5"(75-125mm)
00
� r
Live Stake \
—7Y_ 1"x 1"Stake \\%\
��� l/ (25 x 25mm)
�\ NOTE:
r 1. Straw roll installation requires the placement and secure staking
of the roll in a trench, 3"-5" (75-125mm)deep, dug on contour.
Runoff must not be allowed to run under or around roll. NOT TO SCALE
Figure II-4.2.14
Wattles
DEPARTMENT OF Revised November 2015
ECOLOGY Please see http://www.ecy.wa.gov/copyright.html for copyright notice including permissions,
State of Washington limitation of liability, and disclaimer.
BMP C240: Sediment Trap
Purpose A sediment trap is a small temporary ponding area with a gravel outlet
used to collect and store sediment from sites cleared and/or graded 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 Prior to leaving a construction site, sormwater runoff must pass through a
sediment pond or trap or other appropriate sediment removal best
management practice. Non-engineered sediment traps may be used on-site
prior to an engineered sediment trap or sediment pond to provide
additional sediment removal capacity.
It is 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
site area is permanently protected against erosion by vegetation and/or
structures.
Sediment traps and ponds 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.
Whenever possible, sediment-laden water shall be discharged into onsite,
relatively level,vegetated areas(see BMP C234—Vegetated Strip). This
is the only way to effectively remove fine particles from runoff unless
chemical treatment or filtration is used. This can be particularly useful
after initial treatment in a sediment trap or pond. The areas of release
must be evaluated on a site-by-site basis in order to determine appropriate
locations for and methods of releasing runoff. Vegetated wetlands shall
not be used for this purpose. Frequently, it may be possible to pump water
from the collection point at the downhill end of the site to an upslope
vegetated area. Pumping shall only augment the treatment system,not
replace it,because of the possibility of pump failure or runoff volume in
excess of pump capacity.
All projects that are constructing permanent facilities for runoff quantity
control should use the rough-graded or final-graded permanent facilities
for traps and ponds. This includes combined facilities and infiltration
facilities. When permanent facilities are used as temporary sedimentation
facilities,the surface area requirement of a sediment trap or pond must be
met. If the surface area requirements are larger than the surface area of
the permanent facility,then the trap or pond shall be enlarged to comply
with the surface area requirement. The permanent pond shall also be
divided into two cells as required for sediment ponds.
4-102 Volume 11—Construction Stormwater Pollution Prevention February 2005
f f
Either a permanent control structure or the temporary control structure
(described in BMP C241, Temporary Sediment Pond)can be used. If a
permanent control structure is used, it may be advisable to partially restrict
the lower orifice with gravel to increase residence time while still allowing
dewatering of the pond. A shut-off valve may be added to the control
structure to allow complete retention of stormwater in emergency
situations. In this case, an emergency overflow weir must be added.
A skimmer may be used for the sediment trap outlet if approved by the
Local Permitting Authority.
Design and • See Figures 4.22 and 4.23 for details.
Installation • If permanent runoff control facilities are part of the project,they
Specifications
should be used for sediment retention.
• 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 = Design inflow based on the peak discharge from the
developed 2-year runoff event from the contributing
drainage area as computed in the hydrologic analysis. The
10-year peak flow shall be used if the project size,expected
timing and duration of construction,or downstream
conditions warrant a higher level of protection. If no
hydrologic analysis is required,the Rational Method may
be used.
Vs = The settling velocity of the soil particle of interest. The
0.02 mm(medium silt)particle with an assumed density of
2.65 g/cm3 has been selected as the particle of interest and
has a settling velocity(Vs)of 0.00096 f/sec.
FS = A safety factor of 2 to account for non-ideal settling.
Therefore,the equation for computing surface area becomes:
SA = 2 x Q2/0.00096 or
2080 square feet per cfs of inflow
Note: Even if permanent facilities are used,they must still have a
surface area that is at least as large as that derived from the above
formula. If they do not,the pond must be enlarged.
• To aid in determining sediment depth, all sediment traps shall have a
staff gauge with a prominent mark 1-foot above the bottom of the trap.
February 2005 Volume 11— Construction Stormwater Pollution Prevention 4-103
• 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.
Maintenance • Sediment shall be removed from the trap when it reaches 1-foot in
Standards depth.
• Any damage to the pond embankments or slopes shall be repaired.
Surface area determine 4�� Min.i
at top of weir
\ _ _ _ Lt 1'Min.Overflow
7 T I'Min.
\'S' I'Min.
3.5'-5'
� 1.5'Min. l�
Flat Bottom RipRap
%"-1.5" 2"4'Rock
Washed gravel
Note:Trap may be formed by berm or by Geotexble
partial or complete excavation
Discharge to stabilized
conveyance, outlet,or
level spreader
Figure 4.22 Cross Section of Sediment Trap
-------- 6'Min.
'1 Min.depth overflow spillway
=1 1=1 1=1 1=1 1=1 1=1 y =1 11=1 I El I IM I M 11=1
III— ��
Native soil or !� =1 I I I 1' Min. V depth
compacted backfill I.E I I —) I 2"4"rock
III III III-1 I I-1 I I III III III III Min. V depth 3/4"-1.5"
Geotextile =1 I I=1 I I=1 I I=1 I I-1 I I-1 I I=1 I I- I=1 washed gravel
Figure 4.23 Sediment Trap Outlet
4-104 Volume ll—Construction Stormwater Pollution Prevention February 2005
1
BMP C241: Temporary Sediment Pond
Purpose Sediment ponds remove sediment from runoff originating from disturbed
areas of the site. Sediment ponds are typically designed to remove
sediment no smaller than medium silt(0.02 mm). Consequently,they
usually reduce turbidity only slightly.
Conditions of Use Prior to leaving a construction site, stormwater runoff must pass through a
sediment pond or other appropriate sediment removal best management
practice.
A sediment pond shall be used where the contributing drainage area is 3
acres or more. Ponds must be used in conjunction with erosion control
practices to reduce the amount of sediment flowing into the basin.
Design and • Sediment basins must be installed only on sites where failure of the
Installation structure would not result in loss of life,damage to homes or
Specifications buildings,or interruption of use or service of public roads or utilities.
Also,sediment traps and ponds are attractive to children and can be
very dangerous. Compliance with local ordinances regarding health
and safety must be addressed. If fencing of the pond is required,the
type of fence and its location shall be shown on the ESC plan.
• Structures having a maximum storage capacity at the top of the dam of
10 acre-ft(435,600 ft)or more are subject to the Washington Dam
Safety Regulations(Chapter 173-175 WAC).
• See Figure 4.24,Figure 4.25,and Figure 4.26 for details.
• If permanent runoff control facilities are part of the project,they
should be used for sediment retention. The surface area requirements
of the sediment basin must be met. This may require enlarging the
permanent basin to comply with the surface area requirements. If a
permanent control structure is used,it may be advisable to partially
restrict the lower orifice with gravel to increase residence time while
still allowing dewatering of the basin.
• Use of infiltration facilities for sedimentation basins during
construction tends to clog the soils and reduce their capacity to
infiltrate. If infiltration facilities are to be used,the sides and bottom
of the facility must only be rough excavated to a minimum of 2 feet
above final grade. Final grading of the infiltration facility shall occur
only when all contributing drainage areas are fully stabilized. The
infiltration pretreatment facility should be fully constructed and used
with the sedimentation basin to help prevent clogging.
• Determining Pond Geometry
Obtain the discharge from the hydrologic calculations of the peak flow
for the 2-year runoff event(Q2). The 10-year peak flow shall be used
if the project size,expected timing and duration of construction,or
downstream conditions warrant a higher level of protection. If no
hydrologic analysis is required,the Rational Method may be used.
February 2005 Volume 11— Construction Stormwater Pollution Prevention 4-105
Determine the required surface area at the top of the riser pipe with the
equation:
SA = 2 x Q2/0.00096 or
2080 square feet per cfs of inflow
See BMP C240 for more information on the derivation of the surface
area calculation.
The basic geometry of the pond can now be determined using the
following design criteria:
• Required surface area SA(from Step 2 above)at top of riser.
• Minimum 3.5-foot depth from top of riser to bottom of pond.
• Maximum 3:1 interior side slopes and maximum 2:1 exterior slopes.
The interior slopes can be increased to a maximum of 2:1 if fencing is
provided at or above the maximum water surface.
• One foot of freeboard between the top of the riser and the crest of the
emergency spillway.
• Flat bottom.
• Minimum 1-foot deep spillway.
• Length-to-width ratio between 3:1 and 6:1.
• Sizing of Discharge Mechanisms.
The outlet for the basin consists of a combination of principal and
emergency spillways. These outlets must pass the peak runoff expected
from the contributing drainage area for a 100-year storm. If,due to site
conditions and basin geometry,a separate emergency spill-way is not
feasible,the principal spillway must pass the entire peak runoff expected
from the 100-year storm. However,an attempt to provide a separate
emergency spillway should always be made. The runoff calculations
should be based on the site conditions during construction. The flow
through the dewatering orifice cannot be utilized when calculating the
100-year storm elevation because of its potential to become clogged;
therefore,available spillway storage must begin at the principal spillway
riser crest.
The principal spillway designed by the procedures contained in this
standard will result in some reduction in the peak rate of runoff.
However,the riser outlet design will not adequately control the basin
discharge to the predevelopment discharge limitations as stated in
Minimum Requirement#7: Flow Control. However,if the basin for a
permanent stormwater detention pond is used for a temporary
sedimentation basin,the control structure for the permanent pond can be
used to maintain predevelopment discharge limitations. The size of the
basin,the expected life of the construction project,the anticipated
downstream effects and the anticipated weather conditions during
construction, should be considered to determine the need of additional
discharge control. See Figure 4.28 for riser inflow curves.
4-106 Volume 11— Construction Stormwater Pollution Prevention February 2005
J
Key divider into slope
to prevent flow
arourp*qw 4. -Sediment iser it
The pond length shall be 3 to 6 _
times the maximum pond width Emergency overflow
so
Po length ism P.
Inflow
Sift fence or Discharge to stabilized
equivalent divider conveyance,outlet,or
level spreader
Note:Pond may be formed by berm or
by partial or complete excavation
Figure 4.24-Sediment Pond Plan View
Riser pipe
(principal spillway) Crest of
open at top with 6'min.Width
eme en spillway
trash rack j
�_ ;• �, Embankment compacted 95%
- — Dewatering device \ r -"-`=`- rvious materials such as
1� 4 detail(see riser _ _ _ _
_II ) - = gravel or clean sand shall
not be used
Discharge to stabilized
Wire-backed silt fence Dewatering Concrete base
staked ha ball wrapped orifice conveyance outlet or
with filter fabric,or (see riser detail) level spreader
equivalent divider
Figure 4.25-Sediment Pond Cross Section
Polyethylene cap Provide adequate
strapping
Perforated polyethylene -
drainage tubing,diameter = Corrugated
min.2"larger than metal riser
dewatering orifice.
Tubing shall comply = 3.5"min.
Waterti
with ASTM F667 and = ght
Dewatering orifice,schedule,
AASHTO M294 = coupling Tack weld 40 steel stub min.
Diameter as per calculations
6"min. r---
18"min. I Altematively,metal stakes
Concrete base and wire may be used to
prevent flotation
�--2X riser dia.Min.--
Figure 4.26-Sediment Pond Riser Detail
February 2005 Volume 11- Construction Stormwater Pollution Prevention 4-107
100
72 54 48
1-r 7;;POO �*n 1100
ff 42
36
33
00000 30
-1000 27 _
24
m
0100
lei
21 �
c
0 18 000
0000,
m
m
10
m
10
d 15
f
u
a
p 12
00100 10
1
0.1 HEAD IN FEET (measulred from crest of riser) 10
G..b=9.739 DH312
Q orjfiee=3.782 D:H 112
0 in cis, D and H in feet
Slope change occurs at weir-orifice transition
Figure 4.27-Riser Inflow Curves
4-108 Volume 11-Construction Stormwater Pollution Prevention February 2005
Principal Spillway: Determine the required diameter for the principal
spillway(riser pipe). The diameter shall be the minimum necessary to
pass the pre-developed 10-year peak flow(Q 10). Use Figure 4.28 to
determine this diameter(h = l-foot). Note:A permanent control structure
may be used instead of a temporary riser.
Emergency Overflow Spillway: Determine the required size and design
of the emergency overflow spillway for the developed 100-year peak flow
using the method contained in Volume III.
Dewatering Orifice: Determine the size of the dewatering orifice(s)
(minimum 1-inch diameter)using a modified version of the discharge
equation for a vertical orifice and a basic equation for the area of a circular
orifice. Determine the required area of the orifice with the following
equation:
A.,(2h)0.s
A° 0.6x3600Tg 0.5
where Ao = orifice area(square feet)
As = pond surface area(square feet)
h = head of water above orifice(height of riser in feet)
T = dewatering time(24 hours)
g = acceleration of gravity(32.2 feet/second)
Convert the required surface area to the required diameter D of the orifice:
D=24x A° =13.54x A°
The vertical,perforated tubing connected to the dewatering orifice must be
at least 2 inches larger in diameter than the orifice to improve flow
characteristics. The size and number of perforations in the tubing should
be large enough so that the tubing does not restrict flow. The orifice
should control the flow rate.
• Additional Design Specifications
The pond shall be divided into two roughly equal volume cells by a
permeable divider that will reduce turbulence while allowing
movement of water between cells. The divider shall be at least one-
half the height of the riser and a minimum of one foot below the top of
the riser. Wire-backed,2-to 3-foot high, extra strength filter fabric
supported by treated 4"x4"s can be used as a divider. Alternatively,
staked straw bales wrapped with filter fabric(geotextile)may be used.
If the pond is more than 6 feet deep,a different mechanism must be
proposed. A riprap embankment is one acceptable method of
separation for deeper ponds. Other designs that satisfy the intent of
February 2005 Volume 11—Construction Stormwater Pollution Prevention 4-109
v �
this provision are allowed as long as the divider is penneable,
structurally sound, and designed to prevent erosion under or around
the barrier.
To aid in determining sediment depth, one-foot intervals shall be
prominently marked on the riser.
If an embankment of more than 6 feet is proposed, the pond must
comply with the criteria contained in Volume III regarding dam safety
for detention BMPs.
• The most common structural failure of sedimentation basins is caused
by piping. Piping refers to two phenomena: (1) water seeping through
fine-grained soil, eroding the soil grain by grain and forming pipes or
tunnels; and, (2)water under pressure flowing upward through a
granular soil with a head of sufficient magnitude to cause soil grains to
lose contact and capability for support.
The most critical construction sequences to prevent piping will be:
1. Tight connections between riser and barrel and other pipe
connections.
2. Adequate anchoring of riser.
3. Proper soil compaction of the embankment and riser footing.
4. Proper construction of anti-seep devices.
Maintenance • Sediment shall be removed from the pond when it reaches 1—foot in
Standards depth.
• Any damage to the pond embankments or slopes shall be repaired.
4-110 Volume 11-Construction Stormwater Pollution Prevention February 2005
1
BMP C251 : Construction Stormwater Filtration
Purpose
Filtration removes sediment from runoff originating from disturbed areas of the site.
Background Information:
Filtration with sand media has been used for over a century to treat water and wastewater. The use of
sand filtration for treatment of stormwater has developed recently, generally to treat runoff from streets,
parking lots, and residential areas. The application of filtration to construction stormwater treatment is
currently under development.
Conditions of Use
Traditional BMPs used to control soil erosion and sediment loss from sites under development may not
be adequate to ensure compliance with the water quality standard for turbidity in the receiving water.
Filtration may be used in conjunction with gravity settling to remove sediment as small as fine silt (0.5
pm). The reduction in turbidity will be dependent on the particle size distribution of the sediment in the
stormwater. In some circumstances, sedimentation and filtration may achieve compliance with the water
quality standard for turbidity.
The use of construction stormwater filtration does not require approval from Ecology as long as
treatment chemicals are not used. Filtration in conjunction with polymer treatment requires testing under
the Chemical Technology Assessment Protocol — Ecology (CTAPE) before it can be initiated. Approval
from the appropriate regional Ecology office must be obtained at each site where polymers use is
proposed prior to use. For more guidance on stormwater chemical treatment see BM_P_C250:
Construction Stormwater Chemical Treatment.
Design and Installation Specifications
Two types of filtration systems may be applied to construction stormwater treatment: rapid and slow.
Rapid sand filters are the typical system used for water and wastewater treatment. They can achieve
relatively high hydraulic flow rates, on the order of 2 to 20 gpm/sf, because they have automatic
backwash systems to remove accumulated solids. In contrast, slow sand filters have very low hydraulic
rates, on the order of 0.02 gpm/sf, because they do not have backwash systems. Slow sand filtration
has generally been used to treat stormwater. Slow sand filtration is mechanically simple in comparison to
rapid sand filtration but requires a much larger filter area.
Filtration Equipment. Sand media filters are available with automatic backwashing features that can
filter to 50 pm particle size. Screen or bag filters can filter down to 5 pm. Fiber wound filters can remove
r �
particles down to 0.5 pm. Filters should be sequenced from the largest to the smallest pore opening.
Sediment removal efficiency will be related to particle size distribution in the stormwater.
Treatment Process Description. Stormwater is collected at interception point(s) on the site and is
diverted to an untreated stormwater sediment pond or tank for removal of large sediment and storage of
the stormwater before it is treated by the filtration system. The untreated stormwater is pumped from the
trap, pond, or tank through the filtration system in a rapid sand filtration system. Slow sand filtration
systems are designed as flow through systems using gravity.
Maintenance Standards
Rapid sand filters typically have automatic backwash systems that are triggered by a pre-set pressure
drop across the filter. If the backwash water volume is not large or substantially more turbid than the
untreated stormwater stored in the holding pond or tank, backwash return to the untreated stormwater
pond or tank may be appropriate. However, other means of treatment and disposal may be necessary.
• Screen, bag, and fiber filters must be cleaned and/or replaced when they become clogged.
• Sediment shall be removed from the storage and/or treatment ponds as necessary. Typically,
sediment removal is required once or twice during a wet season and at the decommissioning of the
ponds.
Sizing Criteria for Flow-Through Treatment Systems for Flow Control Exempt Water
Bodies:
When sizing storage ponds or tanks for flow-through systems for flow control exempt water bodies the
treatment system capacity should be a factor. The untreated stormwater storage pond or tank should be
sized to hold 1.5 times the runoff volume of the 10-year, 24-hour storm event minus the treatment
system flowrate for an 8-hour period. For a chitosan-enhanced sand filtration system, the treatment
system flowrate should be sized using a hydraulic loading rate between 6-8 gpm/ft2. Other hydraulic
loading rates may be more appropriate for other systems. Bypass should be provided around the
chemical treatment system to accommodate extreme storms. Runoff volume shall be calculated using
the methods presented in Chapter III-2 - Hydrologic Analysis. Worst-case conditions (i.e., producing the
most runoff) should be used for analyses (most likely conditions present prior to final landscaping).
Sizing Criteria for Flow Control Water Bodies:
Sites that must implement flow control for the developed site condition must also control stormwater
release rates during construction. Construction site stormwater discharges shall not exceed the
discharge durations of the pre-developed condition for the range of pre-developed discharge rates from
112 of the 2-year flow through the 10-year flow as predicted by an approved continuous runoff model.
The pre-developed condition to be matched shall be the land cover condition immediately prior to the
development project. This restriction on release rates can affect the size of the storage pond, the
filtration system, and the flow rate through the filter system.
The following is how WWHM can be used to determine the release rates from the filtration systems:
1. Determine the pre-developed flow durations to be matched by entering the land use area
under the "Pre-developed" scenario in WWHM. The default flow range is from '/2 of the 2-year
flow through the 10-year flow.
2. Enter the post developed land use area in the "Developed Unmitigated" scenario in WWHM.
3. Copy the land use information from the "Developed Unmitigated" to "Developed Mitigated"
scenario.
4. There are two possible ways to model stormwater filtration systems:
a. The stormwater filtration system uses an untreated stormwater storage pond/tank
and the discharge from this pond/tank is pumped to one or more filters. In-line
filtration chemicals would be added to the flow right after the pond/tank and
before the filter(s). Because the discharge is pumped, WWHM can't generate a
stage/storage /discharge (SSD) table for this system. This system is modeled the
same way as described in BMP C250: Construction Stormwater Chemical
Treatment and is as follows:
While in the "Developed Mitigated" scenario, add a pond element under the basin
element containing the post-developed land use areas. This pond element
represents information on the available untreated stormwater storage and
discharge from the filtration system. In cases where the discharge from the
filtration system is controlled by a pump, a stage/storage/discharge (SSD) table
representing the pond must be generated outside WWHM and imported into
WWHM. WWHM can route the runoff from the post-developed condition through
this SSD table (the pond) and determine compliance with the flow duration
standard. This would be an iterative design procedure where if the initial SSD
table proved to be out of compliance, the designer would have to modify the SSD
table outside WWHM and re-import in WWHM and route the runoff through it
again. The iteration will continue until a pond that enables compliance with the
flow duration standard is designed.
Notes on SSD table characteristics:
■ The pump discharge rate would likely be initially set at just below '/2 if the 2-
year flow from the pre-developed condition. As runoff coming into the
untreated stormwater storage pond increases and the available untreated
stormwater storage volume gets used up, it would be necessary to increase
the pump discharge rate above '/z of the 2-year. The increase(s) above '/2 of
the 2-year must be such that they provide some relief to the untreated
stormwater storage needs but at the same time they will not cause
violations of the flow duration standard at the higher flows. The final design
SSD table will identify the appropriate pumping rates and the corresponding
stage and storages.
■ When building such a flow control system, the design must ensure that any
automatic adjustments to the pumping rates will be as a result of changes to
the available storage in accordance with the final design SSD table.
b. The stormwater filtration system uses a storage pond/tank and the discharge from
this pond/tank gravity flows to the filter. This is usually a slow sand filter system
and it is possible to model it in WWHM as a Filter element or as a combination of
Pond and Filter element placed in series. The stage/storage/discharge table(s)
may then be generated within WWHM as follows:
i. While in the "Developed Mitigated" scenario, add a Filter element
under the basin element containing the post-developed land use
areas. The length and width of this filter element would have to be the
same as the bottom length and width of the upstream untreated
stormwater storage pond/tank.
ii. In cases where the length and width of the filter is not the same as
those for the bottom of the upstream untreated stormwater storage
tank/pond, the treatment system may be modeled as a Pond element
followed by a Filter element. By having these two elements, WWHM
would then generate a SSD table for the storage pond which then
gravity flows to the Filter element. The Filter element downstream of
the untreated stormwater storage pond would have a storage
component through the media, and an overflow component for when
the filtration capacity is exceeded.
WWHM can route the runoff from the post-developed condition through the
treatment systems in 4b and determine compliance with the flow duration
standard. This would be an iterative design procedure where if the initial sizing
estimates for the treatment system proved to be inadequate, the designer would
49
have to modify the system and route the runoff through it again. The iteration
would continue until compliance with the flow duration standard is achieved.
5. It should be noted that the above procedures would be used to meet the flow control
requirements. The filtration system must be able to meet the runoff treatment requirements. It
is likely that the discharge flow rate of/z of the 2-year or more may exceed the treatment
capacity of the system. If that is the case, the untreated stormwater discharge rate(s) (i.e.,
influent to the treatment system) must be reduced to allow proper treatment. Any reduction in
the flows would likely result in the need for a larger untreated stormwater storage volume.
If system design does not allow you to discharge at the slower rates as described above and if the site
has a retention or detention pond that will serve the planned development, the discharge from the
treatment system may be directed to the permanent retention/detention pond to comply with the flow
control requirements. In this case, the untreated stormwater storage pond and treatment system will be
sized according to the sizing criteria for flow-through treatment systems for flow control exempt
waterbodies described earlier except all discharges (water passing through the treatment system and
stormwater bypassing the treatment system) will be directed into the permanent retention/detention
pond. If site constraints make locating the untreated stormwater storage pond difficult, the permanent
retention/detention pond may be divided to serve as the untreated stormwater discharge pond and the
post-treatment flow control pond. A berm or barrier must be used in this case so the untreated water
does not mix with the treated water. Both untreated stormwater storage requirements, and adequate
post-treatment flow control must be achieved. The post-treatment flow control pond's revised
dimensions must be entered into the WWHM and the WWHM must be run to confirm compliance with
the flow control requirement.
Washington State Department of Ecology
2012 Stormwater Management Manual for Western Washington, as Amended in December 2014 The 2014 SWMMWW).
GEO ,140- ZWD-7
Mason County Review Checklist
For a Geological Assessment
Instructions:
This checklist is intended to assist Staff in the review of a Geological Assessment.Ifie Assessment is reviewed for
completeness with respect to the Resource Ordinance. If an item is found to be not applicable,the report should
explain the basis for the conclusion.The Assessment is also reviewed for clarity and consistency. If the drawings,
discussion, or recommendations are not understandable,they should be clarified. If they do not appear internally
consistent or consistent with the application or observations on site, this needs to be corrected or explained. If
resolution is not achieved with the author, staff should refer the case to the Planning Manager or Director.
Applicant's Name: f dP-1 n T y-A&y 4 / C e-,SD V 1&—c-
Permit#; !:l' &2J?0(�l Q1 Parcel Vs:lZ-;5 10 OD'(Q d�OC7
Date(s)of the Document(s)reviewed: Id hOWU
1. A discussion of geologic conditions in the general vicinity of the proposed development,with geologic unit
designation based on referenced maps.
OK? Comment:
2. (a) A discussion of the ground water conditions at the site,
OK?_�Comment:
(b) A discussion of the estimated depth to water,
OK? _Comment:
(c) A discussion of the quantity of surface seepage;
OK?_Comment:
(d) A discussion of the upslope geomorphology,
OK? ✓ Comment:
(e) A discussion of location of upland waterbodies and wetlands.
OK? Comment:
3. The approximate depth to hard or dense competent soil, e.g. glacial till or outwash sand.
OK?_ Comment:
4. A discussion of any geomorphic expression of past slope instability(presence of hummocky ground or ground
cracks, terraced topography indicative of landslide block movement, bowed or arched trees indicating
downslope movement, etc.).
OK? Comment:
5. A discussion of the history of landslide activity in the vicinity, as available in the referenced maps and records.
OK? Comment:
6. An opinion on whether the proposed development is within the landslide hazard area or its associated buffer or
setback and the potential for landslide activity at the site in light of the proposed development.
OK? Comment:
7. A recommendation by the preparer whether a Geotechnical-Report should be required to further evaluate site
conditions and the oposed development of the subject property.
OK? Comment:
8. If the presence of a hazard is determined within 300 feet of the proposed development, then the following are
delineated on a geologic map/site map:
Page 1 of 2 Form Effective June 2008
(a) the area of the proposed develo ent,
OK? Comment: Z
(b) the boundaries of the landslide hazard area(top, both sides, and toe),
OK? Comment Z
-(c) the associated buffers (top, bo h ' es, and toe)
OK? Comment: Q LJY4-1
(d) building or other-setbacks(top, b th sides, and toe).
OK? Comment: ✓-L v
9. A site map drawn to scale showing the property boundaries, scale, north arrow, and the location and nature of
existing and proposed development on the site.
OK?_�„/_Comment:
Are the Documents signed and stamped? By whom? Y
License#: cense type:--r/ 7
FIRST REVIEW A proved ❑ Need more info.
If not approved, what is the next action/recommendation for further action?
Reviewed by , on .Time spent in review:
SECOND REVIEW/UPDATE ❑ Approved ❑ Need more info.
If not approved, what is the next action/recommendation for further action?
Reviewed by , on Time spent in second review:
THIRD REVIEW/UPDATE ❑ Approved ❑ Need more info.
If not approved, what is the next action/recommendation for further action?
Reviewed by , on .Time spent in third review:
Disclaimer.Mason County does not certify the quality of the work done in this Geological Assessment
4
Page 2 of 2 Form Effective June 2008
Gcn,?-07c) t
-Db07
Technical Memorandum
TO: Sam Nielson, PE, Community Building Senior Engineer, Parametrix, Inc.
FROM: Barsha Pradhan, EIT, and Benjamin Ford, PE
DATE: June 19, 2020
RE: Geologic Hazard Assessment
Washington State Department of Natural Resources Administration Building
Belfair, Washington
Project No. 0193082.010.011
Introduction
This technical memorandum summarizes the results of a geologic hazard assessment completed by Landau
Associates, Inc. (LAI) in support of the Washington State Department of Natural Resources (DNR; project
owner)Administration Building project in Belfair, Washington.The assessment was completed in
accordance with the requirements in Chapter 8.52.140 of the Mason County Municipal Code (MCMC).
Services were provided in accordance with the scope outlined in the Subconsultant Agreement for
Professional Services between LAI and Parametrix, Inc. (project civil engineer), executed May 26, 2020.
Project Understanding
Based on information provided by representatives of DNR and Parametrix, LAI understands that an existing
administration building will be demolished and replaced with a prefabricated structure, which will also be
used for administrative purposes. The new administration building will be located at 3420 Northeast
Sandhill Road in Belfair, Washington (Mason County Parcel No. 123180060000; site; Figure 1).The new
building will be constructed south of the existing building, in an area that was previously graded and
developed.
Per the MCMC, a geologic hazard assessment is required for proposed developments that will be located
within 250 feet (ft) of potential geologic hazard areas (GHAs). The new building will be located
approximately 60 ft east of the top of a 35 to 45 percent slope. Mason County (County) has identified the
slope as a potential GHA. Minimal grading will be required during construction. Clearing and grubbing of
native vegetation adjacent to, and within, the potential GHA will not be required.The approximate
locations of the new administration building and slope (potential GHA) are shown on Figure 2.
To satisfy the County's reporting requirements, Parametrix requested that LAI perform a geologic hazard
assessment in accordance with the MCMC.
Geologic Conditions
Geologic information for the site and the surrounding area was obtained from the Geologic Map of the
Belfair 7.5-minute Quadrangle, Mason, Kitsap, and Pierce Counties, Washington (Polenz 2009). Subsurface
deposits at the proposed building site are mapped as Vashon stade glacial till (Qgt), a highly compact
mixture of clay, silt, sand, gravel, and cobbles. Glacial till in this region typically consists of 1 to 6 ft of
14 LANDAU
ASSOCIATES 955 Malin Lane SW,Suite B • Tumwater,Washington 98501 (360)791-3178
Landau Associates
weathered till(ablation till)overlying highly compact, unweathered lodgement till.Surface geology along
the adjacent steep slope is mapped as glacial till overlying pre-Vashon gravel (Qpg),a unit that includes
sand,gravel,and minor silt. Like glacial till, pre-Vashon gravel is glacially overridden and highly compact.
Surface Conditions
The site currently is developed with the existing administration building,which can be accessed from the
north via a gravel-surfaced road. Gravel surfacing surrounds the existing building and is present across the
proposed building footprint. Managed forestland is located east of the site.The first 70 ft of forest consists
of 15-to 20-ft-tall reprod trees then transitions to mature trees. Dense underbrush consisting of salal
(Gaultheria shallon), huckleberry(Gaylussacia),and rhododendron are also present within the forest.The
site is bordered to the south and west by the Mission Creek Corrections Center(MCCC).Site topography is
generally flat with a 55-to 60-ft-tall slope located east of the proposed building footprint. Existing site
features are shown on Figure 2.
Subsurface Conditions
LAI reviewed publicly available geologic information for the site, including one well report and three
geotechnical exploration logs (Ecology;accessed June 16, 2020;Attachment 1). Logs of the historical well
(installed for MCCC)and geotechnical explorations(completed for DNR) indicate that the mapped geology
is consistent with actual site subsurface conditions. Based on LAI's review of the logs, 1 to 2 ft of
weathered till overlying highly compact glacial till was observed in the historical geotechnical explorations.
LAI estimates that the dense/compact glacial till, reported on the exploration logs, will be encountered
within 2 to 5 ft of ground surface.
Groundwater Conditions
Based on LAI's review of the well report (Attachment 1),site groundwater levels are approximately 70 to
150 ft below ground surface.Although not noted on the well report, minor perched groundwater layers
may be present at shallow depths within the glacial till or pre-Vashon gravel units. No springs or perched
groundwater conditions were observed at the site during LAI's June 2, 2020 site reconnaissance.
Geologic Hazard Assessment
LAI visited the site on June 2, 2020 to observe existing conditions. During the site visit, LAI observed no
groundwater seeps, hummocky ground,ground cracks,terraced topography, bowed/arched trees,or other
geomorphic expressions indicative of current or previous slope movement. Based on LAI's measurements,
recorded with a hand-held inclinometer,the slope adjacent to the site is inclined at a 35 to 45 percent
grade(Figure 2).
LAI reviewed available mapping data and found that no historical slope instability/landslide activity had
been recorded for the site. However, mass wasting/landslide deposits are mapped approximately 850 ft
Geologic Hazard Assessment
DNR Administration Building 2 June 19,2020
Landau Associates
southwest and 1,100 ft north of the site (Polenz et al. 2009). No recent/active landslides were noted at the
site or within the immediate vicinity.
The MCMC defines geologically hazardous areas as areas exhibiting one or more of the following
conditions:
1. Indications of earth movement, such as debris slides, earthflows, slumps, and rock falls.
2. Artificially oversteepened or unengineered slopes (i.e., cuts or fills).
3. Slopes containing soft or potentially liquefiable soils.
4. Oversteepened or otherwise unstable areas as a result of stream incision, stream bank erosion, and
undercutting by wave action.
5. Slopes greater than 15 percent with:
a. intersecting geologic contacts with a relatively permeable sediment overlying a relatively
impermeable sediment or bedrock (e.g., sand overlying clay) and
b. springs or groundwater seepage.
6. A slope of 40 percent or steeper with a vertical relief of 10 ft or more, except areas composed of
consolidated rock. A slope is delineated by establishing its toe and top and measured by averaging
the inclination over at least 10 ft of vertical relief.
Per the above conditions,the slope east of the site is considered a GHA. The slope has a grade of more
than 40 percent and a vertical relief of 10 ft or more. LAI recommends including a minimum 50-ft buffer of
undisturbed native vegetation, as allowed by Section 8.52.140(D)(6)(b) of the MCMC. The proposed buffer
is shown on Figure 2.
The risk for long-term slope erosion and surficial sliding is considered negligible, provided the buffer
remains undisturbed. Development plans should include measures to control erosion and surface water
flow, during and post construction. Onsite stormwater management facilities should disperse runoff fully
before it reaches the buffer.
Based on the results of LAI's geologic review and site reconnaissance,the proposed building location is
considered suitable from a geologic standpoint.The slope consists of highly compact glacial till and
appears to be stable. Provided a minimum 50-ft buffer is implemented, the site is expected to have a low
risk for landslide activity, and the proposed development will not have an adverse impact on the GHA.
In LAI's opinion and per its discussions with the County, a landslide hazard geotechnical report, as
described in Chapter 8.52.140 of the MCMC, should not be required. In its geologic hazard assessment, LAI
sufficiently assessed the presence of the GHA and the impact the proposed administration building could
have on the GHA.
Use of This Technical Memorandum
Landau Associates prepared this technical memorandum for the exclusive use of the Washington State
Department of Natural Resources and Parametrix, Inc. for specific application to the Washington State
Geologic Hazard Assessment
DNR Administration Building 3 June 19,2020
Landau Associates
Department of Natural Resources Administration Building project in Belfair,Washington. No other party is
entitled to rely on the information,conclusions,and recommendations included in this document without
the express written consent of Landau Associates. Further,the reuse of information, conclusions, and
recommendations provided herein for extensions of the project or for any other project,without review
and authorization by Landau Associates,shall be at the user's sole risk. Landau Associates warrants that
within the limitations of scope, schedule,and budget, its services have been provided in a manner
consistent with that level of care and skill ordinarily exercised by members of the profession currently
practicing in the same locality under similar conditions as this project. Landau Associates makes no other
warranty,either express or implied.
Closing
We trust that this technical memorandum provides you with sufficient information to proceed with the
project. If you have questions or comments, or if we can be of further service, please contact the
undersigned at(360)791-3178 or at bford@landauinc.com.
LANDAU ASSOCIATES, INC.
Barsha Pradhan �N JA r
Staff EIT � pF wQS O
Benjamin Ford, PE q 6 9
Associate
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BP/AMW/BJF/mcs
i\\OLVMPIA2\PROJECTS\0193\082.010\R\DNR ADMINISTRATION BUILDING TECHNICAL MEMORANDUM 6.19.2020.DOCXI
Attachments: Figure 1. Vicinity Map
Figure 2. Site Plan
Attachment 1. Historical Boring Logs
Attachment 2. Geological Assessment Submittal Checklist
References
County. 2020.Title 8. Environmental Policy.Chapter 8.52. Resource Ordinance. Ordinance No. 8.52.140
Geologically Hazardous Areas. Mason County Municipal Code.June 12.
Ecology.Washington State Well Report Viewer. Washington State Department of Ecology. Accessed June
16, 2020.Available online at:
https://a ppswr.ecology.wa.gov/weliconstruction/map/WCLSWebMap/defau lt.aspx.
Geologic Hazard Assessment
DNR Administration Building 4 June 19,2020
Landau Associates
Polenz, M. 2009. Geologic Map of the Belfair 7.5-minute Quadrangle, Mason, Kitsap, and Pierce Counties,
Washington. Washington Division of Geology and Earth Resources.July.
Geologic Hazard Assessment
DNR Administration Building 5 June 19,2020
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Geologic Hazard Assessment Figure
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LANDAU Administration Building Vicinity Map 1
ASSOCIATES Belfair,Washington