HomeMy WebLinkAboutBLD2018-00042 - 05 STORMWATERo
DEPARTI\IENT OF COIVIM U NITY DE \,IELOP ENT
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DETERMINING STORMWATER MANAGEMENT REQUIREMENTS: This stormwater calculation worksheet should be completed first to
classify the proposal as "small," "medium," or "large." The size determines whether a Stormwater Site Plan is required in
conjunction with a stand-alone stormwater management permit application, building permit application. or other land use approval
application that involves stormwater review. The basic information will also be helpful for completing a Stormwater Site Plan, if
required
Lond-disturbinE activity is any activity that result; in movement of earth, or a change in the existing soil cover (both vegetative and
non-vegetative) and/or the existing soil topography. Land disturbing activities include, but are not limited to clearing, grading, filling,
excavation. and compaction associated with stabilization of structures and road construction.
Nstive vegetation is vegetation comprised on plant species. other than noxious weeds, that are indigenous to the coastal region of
the pacific Northwest and which reasonably could have been expected to naturally occur on the site. Examples include species such
as Douglas fir, western hemlock, western red cedar, alder, big-leaf maple, and vine maple; shrubs such as willow, elderberry,
salmonberry, and salal; herbaceous plants such as sword fern, foam flower, and fireweed.
lmperuious surface is a hard surface that either prevents or retards the entry of water into the soil mantle as under natural
conditions prior to development. A hard surface area which causes water to run off the surface in greater quantities or at an
increased rate of flow from the flow present under natural conditions prior to development. Common impervious surfaces include,
but are not limited to roof tops, walkways, patios, driveways, parking lots or storage areas, concrete or asphalt paving, gravel roads,
packed earthen materials, and oiled, macadam or other surfaces which similarly impede the natural infiltration of stormwater.
Itormwatsi :31: rytri<sie3t - REV 1f,i2f,2114
PARCEL SIZE (I.E.. SITE)
An acre contains 43,560 square feet. Multiply the acreage by this figure
Size of parcel in squa rereer*b1O sq/ft
Size of p^o"tQ-19 u"r""
LAND DIST{JRBING ACTIVNTY. COhIVERSIOhI OF hIATIVE VEGETATION. At\ID VOLIJME OF C[,,T/FII-L
Total Land Disturbance *Z
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1
project. lnclude in this calculation the area to be cleared for:
.fffin,tff3f,fuctures 77ts ,qft
6twt
Other compacted'surtaCe,
sqlft
sq/ft
sq/ft
"Yn 5o o sq/ft
sq/ft
Indicate Total Volurnes of Proposed
cut 9)ah
Well, utilities, etc +Drainfield, septic tank, etc.rl/ o0o
Lawn, landscaping, etc.+
Answer the following two questions related to
conversion of native vegetation:
Does the project convert To acres or more of
native vegetation to lawn or landscaped areas?
Circle: Yes
Does the project convert 2 1/z acras or more of
native vegetation to pasture?
Circle: Yes
Fa, .?.V lc (cu/yd)
Calculate the total area to be cleared, graded, filled,
excavated, and/or compacted for proposed development
Driveway,parking,roads,etc. l?00 sqtft
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ST'O RI\IU'ATE R CALC LTLAT I ON W'ORKSHEET
STORiV!W,qTER C,ALU LATIONS - IMPERVIOUS SU RF'ACE
TorAr- NEW + TorAt- ExtsrtNG* 5711 ,r,o -This amount will be used to check total lot coverage.
sq/ft
b"sq/ft
#-
Total New S'.?-rb
Sidewalks ''*
Patios -b
Other
Driveway, parking, roads, etc €"
+
EXISTING
Structures (all roof area) 4^ sqtft
Solid Decks
(without infi ltratron below)
TotalExisting # sqlft
(without infi ltration below)
Driveway, parking, roads, etc | ?OO sqlft
other Appp*l soo -sq/ft
}IEW
Structures (all roof area)
Sidewalks
Patios
Solid Decks
,1,b1? ,qrt
ILCz sqlt
-a*-,.? sq/ft
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The following questions will help determine whether the proposed project is considered developrnent or nedeveloPment
FURTHER II$STRUCTIONS: tf the answer is yes, the proposal is considered redevelopment and the attached Figure 2 should be used
to determine the applicable Minimum Requirements. lf the answer is no, the proposal is considered new development and the
attached Figure 1 should be used. At this juncture, the applicant should refer to the applicable Flow Chart to determine the
Minimum Requirements for stormwater management. DCD staff will help verify the classification of the project and the application
requirements.
For proponents of "small" projects who must comply only with Minimum Requirement #2-Construction Stormwater Pollution
prevention-an additional submittal is not required. The proponent is responsible for employing the 12 Elements to control erosion
and prevent sediment and other pollutants from leaving the site during the construction phase of the project. Pick up the
Construction Storrnwater Pollution Prevention (SWPP) Best Management Practices (BMPs) Packet. Proponents of "medium"
projects-those that must meet only Minimum Requirements #1 through #5-and for "large" projects-those that must meet all 10
Minimum Requirements-are required to submit a Stormwater Site Plan. DCD has prepared a submittal template of a Stormwater
Site plan, principally for rural residential projects. Complete the template in the Stormwater Site Plan Instructions and Submittal
Template or prepare a Stormwater Site Plan using the step-by-step guidance in the Stormwater Manogement Monuol-
APPLICANT S!GNATURE
DEVELOPMENT v. REDEVEI-OPMENT
Divide the total qig!!!g impervious surface above by the size of the parcel and convert to a percenta n", I L 'O
Does the site have 35% or more of existinq impervious surface?Circle:Yes n"K
By signing the Stormwater Calculation Worksheet, I as the applicant/owner attest that the information provided herein is true and correct to the
best of my knowledge. I also certify that this application is being made with the full knowledge and consent of all owners of the affected
property.
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(onre)NER oR AUIHORIZED REPRESENTAIIVE SIGNAIURE}(
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Table R402.X.1 Footnotes
For Sl: 1 foot .= 304.8 mm, ci .= continuous insulation, int .= intermediate framing.
' R-values are minimums. U-factors and SHGC are maximums. When insulation is installed in a cavity which is
less than the labelor design thickness of the insulation, the compressed R-value of the insulation from
Appendix Table 4101.4 shall not be less than the R-value specified in the table.
b The fenestration U-factor column excludes skylights. The SHGC column applies to all glazed fenestration.
'"LOlLS/IL+TB" means R-L0 continuous insulation on the exterior of the wall, or R-15 on the continuous
insulation on the interior of the wall, or R-21cavity insulation plus a thermal break between the slab and the
basement wall at the interior of the basement wall. "10/L5 f 2L.+TB" shall be permitted to be met with R-13
cavity insulation on the interior of the basement wall plus R-5 continuous insulation on the interior or
exterior of the wall. "10/L3" means R-10 continuous insulation on the interior or exterior of the home or R-
13 cavity insulation at the interior of the basement wall. "TB" means thermal break between floor slab and
basement wall.
o R-10 continuous insulation is required under heated slab on grade floors. See R402.2.9.1.
" There are no SHGC requirements in the Marine Zone.
r Reserved.
s Reserved.
h Reserved.
i The second R-value applies when more than half the insulation is on the interior of the mass wall.
I Reserved.
k For single rafter- or joist-vaulted ceilings, the insulation may be reduced to R-38.
' Reserved.
* lnt. (intermediate framing) denotes standard framing 16 inches on center with headers insulated with a
minimum of R-10 insulation.
Table R402.1.3 Footnote
" Nonfenestration U-factors shall be obtained from measurement, calculation or an approved source or as
specified in Section R402.1.3.
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DEPARTMENT OF COMMUNITY DEVELOPMENT
621 Sheridan Street, Port Townsend, WA 98368
Tel: 360.379.4450 | Fax: 360.379.4451
Web : www.co. iefferson.wa. us/communitydevel ooment
E-mail : dcd@co.iefferson.wa"us
STORIVTW'ATER SITE PI-AN SUBMITTAI TEMPLATE
l,lu#9b<mo trc pRolecr/npplcANT NAt\4E ( arv17 F[onss
Please answer all of the following questions to the best of your ability. Where the question calls for depiction on a site map, the
applicant may choose to either incorporate the elements into the general plot plan for the Master Land Use Application or to submit a
separate stormwater site plan map.
Project Overview
Describe the proposed developed conditions of the site. lndicate position and relative size of proposed improvements on the
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Existing Conditions Summary
Describe the existing topography. lrldicate contours on the site map2
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3. Describe the existing vegetation. lndicate native vegetation areas on the site map.
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4. Describe the soils. lndicate soil on the site m
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Describe the existing site hydrology (i.e., drainage; behavior of water on the site-above, below, and on the ground). lndicate
existing stormwater drainage to and from the site on the site map. Deprct separate drainage basins on the site map, if
applicable, and ildicate acreage of each.
5.
I 6E MAP
6. Describe any excess levels of noise generated by the proposed use or activity:
N A,.} eDtrgl-
Describe significant geographic features and critical areas (i.e., environmentally sensitive areas such as wetlands, streams
steep slopes, etc.) on tfre site. lndicate location on the site map. D O p€
stormwater site plan template - rev 121712015
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Describe the general vicinity of the site, including adjacent land uses and structures, utilities, roads, and sensitive/critical areas
(streams. wetlands. lakes. steeo slooes. etc.).
8.
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This portion of the Stormwater Site Plan consists of the selection and installation of the appropriate stormwater control BMPs
and facilities to remain in place after construction of the pro.lect is completed.
"Medium" size projects are required to have the totals calculated of all impervious surfaces, pollutiongenerating impervious
surfaces, and pollution-generating pervious surfaces to verify that the thresholds for treatment facilities and flow control
facilities are not exceeded.
Describe the developed site hydrology, as proposed. lndicfte whether stormwater will be fully dispersed (i.e., per BMP T5.30
in the Manual) or, if not, what types of stormwater flow control will be utilized for the site or specific threshold discharge areas
within the site. Locate these facilities on the site plan and differentiate proposed facilities from existing facilities.
Permanent Stormwater Control Plan
9
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10. lf the project requires the use of stormwater treatment facilities, describe the types of stormwater treatment facilities proposed
for use on the site. Locate these facilities on the site plan and differentiate proposed facilities from existing facilities. [-his is
normally for "large" projects or projects that involve the potential for dispersion of contaminants.l
11. Describe the performance goals and standards applicable to the project.
12. Describe the flow control system.
13. Describe the water quality system.
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14. Describe the conveyance analysis and design.
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15. Describe the source of fill material, physical characteristics of fill material, and deposition of excess material
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'16. Proposed methods of placement and compaction consistent with the applicable standards on Appendix Chapter 33 of the
Uniform Building Code.
17. Describe the proposed surfacing material
18. Describe methods for restoration of the site.
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19 An Operation and Maintenance Manual is required for each flow control and treatment facility. [This is normally required for
"large" projects only and only those for which facilities are required to control flow or treat runoff.l lf included, list the Manuals
here.
20. List here and include any special reports or studies conducted to prepare the Stormwater Site Plan
21 Ltst other necessary permits and approvals as required by other regulatory agencies. lf those permits or approvals include
conditions that affect the drainage plan or contain more restrictive drainage-related requirements, describe those conditions or
restnctrons here.
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stormwater site plan template - rev. '12l7i2015
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coNSTRUCTtON STORMWATER POLLUTTON PREVENTTON PLAN (SWPPP)
The Construction SWPPP addresses sediment and erosion control during construction. The BMPs indicated by the applicant in the
template that follows must be installed on the ground during all construction phases of the project The proponent is responsible for
preventing sediment and erosion impacts to environmentally sensitive areas and off-site areas. Consult the Construction Stormwater
Pollution Prevention (SWPP) Best Management Practices (BMPs) Packet for guidance, particularly wrth rural residential
development.
SECTION I- CONSTRUCTION SWPPP NARRATIVE
Construction Stormwater Pollution Plan Elements. Describe how each of the Construction SWPPP elements has been or
will be addressed. ldentify the type and location of BMPs used to satisfy the required element. lf an element is not applicable to
the proposal, justify in writing. Detailed descriptions of the 13 Elements are found at Volume ll Section 3.3.3 of the lVlanual
(beginning on page 3-1 1).
13 Required Elements - Construction SWPPP
1. Mark Clearing Limits.
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2. Establish Construction Access
3. Control Flow Rates
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4. lnstall Sediment Controls
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5. Stabilize Soils.A6 VWDW 'rr> Ptt;s-a-r eflt(Ti&
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6. Protect Slopes
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7. Protect Drain lnlets.
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13 Required Elements - Construction SWPPP (continued)
L Stabilize Channels and Outlets.
9. Control Pollutants.
10. Control De-Watering (the act of pumping groundwater or stormwater away from an active construction site).
11. Maintain Best Management Practices (BMPs)
{drr4- /!l.Ataq6,,;5 br-tP{g
12 lvlanage the Project.
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13. Protect Low lmpact Development BMP's
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2.Adjacent Areas.
a. Description of the adjacent areas that may be affected by site disturbance (e.g., streams, lakes, wetlands, residential
areas, roads).
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b. Description of the downstream drainage path leading from the site to the receiving body of water (minimum distance of 400
yards).
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3.Environmentally Sensitive Areas.
a. Description of environmentally sensitive areas that are on or adjacent to the site.
storruater site plan tsmplate - rey. '1217/2015 9
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b. Descrtption of special requirements for working in or near environmentally sensitive areas.
4. Erosion Problem Areas. Description of potential erosion problems on site in the context of the characteristics of the on-site
soils (e.9., erodibility,, depth, texture, soil structure).T€r'iTl 0LL4.t C ttJ\7P $ * l,ott t-,
+s[?t*l A,t * I Ltf Ol)
5 Construction Phasing.
a. ConstructionsequenceP rlo,r d, L L*bq lt€€\tc FpA ySoul
b. Construction phasing (if proposed)
6. Construction Schedule. Wet season is October 1 through April 30 (page2-20 of the Manual).
l. Provide a proposed construction schedule.
I ,$Lare otr rl6ad
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Wet Season Construction Activities.
a. Proposed wet season construction6*C 6 d Lry A,t,Ad ,e,l\F c, r-
b. Proposed wet construction activities for environmentally sensitive areas.
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7. Financial/Ownership Responsibilities.
a. ldentify the property owner for the initiation of bonds and/or other financial securities.
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b. Describe bonds and/or other evidence of financial responsibility for liability associated with erosion and sedimentation
impacts.
N
8. Engineering Calculations. Provide Design Calculations on a separate sheet for the following, if applicable
a. SedimentPonds/Traps.
b. Diversions.
c. Wateruvays.
d. Runoff/StormwaterDetention Calculations
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SECTION II- EROSION AND SEDIMENT CONTROL PLAN
Sediment and erosion control measures may be depicted on the master land use application plot plan, a stormwater site plan, and/or a
separate Construction SWPPP site plan. This is a checklist to ensure that the following are depicted on a site plan:
General.
a. Vicinity Map
b Jefferson County Approval Block
c. Erosion and Sediment Control Notes
2 Site Plan.
a. Legal description of subject property.
b. North arrow.
c. lndicate boundaries of existing vegetation (e.9., tree lines, pasture areas, etc.).
d. ldentify and label areas of potential erosion problems.
e. ldentify FEMA base flood boundaries and Shoreline Management boundaries (if applicable).
f. Show existing and proposed contours.
S. lndicate drainage basins and direction of flow for individual drainage areas.
h. Label final grade contours and identify developed condition drainage basins.
i. Delineate areas that are to be cleared and graded.
j. Show all cut and fill slopes indicating top and bottom of slope catch lines.
Conveyance Systems.
a. Designate locations for swales, interceptor trenches, or ditches.
b. Show all temporary and permanent drainage pipes, ditches, or cut-off trenches required for erosion & sediment control
c. Provide minimum slope and cover for all temporary pipes or call out pipe inverts.
d. Shows grades, dimensions, and direction of flow in all ditches, swales, culverts and pipes.
e. Provide details for bypassing off-site runoff around disturbed areas.
f. lndicate locations and outlets of any dewatering systems.
3
4. Location of Detention Best Management Practices (BMPs). ldentify location of detention BMPs
5. Erosion
a.
b.
d.
e.
f.
s
h.
i.
)
k.
t.
m.
and Sediment Control Facilities.
Show the locations of sediment trap(s), pond(s), pipes and structures.
Dimension pond berm widths and inside and outside pond slopes.
lndicate the trap/pond storage required and the depth, length, and width dimensions.
Provide typical section views through pond and outlet structure.
Provide typical details of gravel cone and standpipe, and/or other filtering devices.
Detail stabilization techniques for outleVinlet.
Detail control/restrictor device location and details.
Specify mulch and/or recommended cover of berms and slopes.
Provide rock specifications and detail for rock check dam(s), if applicable.
Specify spacing for rock check dams as required.
Provide front and side sections of typical rock check dams.
lndicate the locations and provide details and specifications for silt fabric.
Locate the construction entrance and provide a detail.
6. Detailed Drawings. Any structural practices used that are not referenced in the Ecology Manual should be explained and
illustrated with detailed drawings.
Other Pollutant BMPs. lndicate on the site plan the locations of BMPs to be used for the control of pollutants other than
sediment (e.9., concrete wash water).
7
Monitoring Locations. lndicate on the site plan the water quality sampling locations to be used for monitoring water quality on
the construction site. Sampling stations should be located upstream and downstream of the project site.
8
stormwater site plan len1lale - ev 12n12015 11
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Stormwater Site Plan Changes
lf the designer wishes to make changes or revisions to the originally approved Stormwater Site Plan, the proposed revisions shall be
submitted to DCD prior to construction. The submittal shall include substitute pages that include all proposed changes, revised
drawings showing any structural changes, and any other supporting information that explains and supports the reason for the change.
Final Corrected Plan Submittal
lf the project included construction of conveyance systems, treatment facilities, flow control facilities, or structural source control BMPs
(not standard on-site stormwater management BMPs), the applicant shall submit a final corrected plan ("as-builts") when the project is
completed. These should be engineering drawings (stamped by a licensed civil engineer) that accurately represent the project as
constructed.
APPLICANT SIGNATURE
By signing the Construction SWPPP worksheet, I as the applicanVowner attest that the information provided herein is true and
correct to the best of my knowledge. I also certify that this application is being made with the full knowledge and consent of all
owners of the affected property
(LANDowNER oR AUTHoRTzED REpRESENTATTvE StGNATURE)(DATE)
THIS SPACE MAY BE USED FOR ADDITIONAL NOTES, IF NEEDED
stormwater site plan template - rev 1 Z7l20 1 5 12
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DEPARTNIENT' OF COIUNIUI\IIT}' DE !:E,;li.lt.nd.r:,.ir;i:, Prf f.:,ili<c:-rri, iI \ r.){it,J
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ST'O R}IW'ATER CALCULATI O]V W'ORKSHEET
DETERMINING STORMWATER i
classify the proposal as .,smal
conjunction with a stand-alone
application that involves storm
required.
MANAGEMENT REQUIRTMENTS:
ll," "medium," or ,,large.,, The
stormwater management permit
twater review. The basic informa
This stormwater carcuration worksheet should be compreted first tosize determines whether a Stormwater Site plan is required inapplication, building permit application, or other land use approvalrtion will also be helpful for completing a stormwater site plan, if
that results in movement of earth, or a change in the existing soil cover (both vegetative andtopography' Land disturbing activities includ!, but are not li;ited to ctearing, grading, filling,with stabilization of structures and road construction.
Notive vegetotion is vegetation comprised on plant species, other than noxious weeds, that are indigenous to the coastar region ofthe Pacific Northwest and which reasonably could have u""n "*p".i"j to naturaily o..r.on-tr," site. Examples incrude species suchlJ,,3lIr;T,::":::i:if^:,"#:""'j,ffj:ili;T"::fj;,'iiil::t**::""oT*d,;:", shrubs such as ,,irro*, e,derberrv
Lond-disturbing rctivity is any activity
non-vegetative) and/or the existing soil
excavation, and compaction associated
lmperuious
prior to development. A hard surface area
surfoce is a hard surface that either prevents or retards the entry of water into the soil mantle as under naturalconditions
increased rate of flow from the flow present under natu ral
which
conditions prior to development. Common i
causes water to run off the surface in
mpervious surfaces inclu de,
greater quantities or at an
but are not limited to roof tops, walkways, patios, drivewa ys, parking lots or storage areas. concrete or asphalt paving, gravel roads.packed earthen materials. and oiled, macadam or other su
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MLA #eRotecr/aeerrceNT NAME d/?(o<ooo t 3 busr/dfl_DffO {-g,tAd/tFb
Size of prot'Q2i a ,"o,
Size of parcet in square s."147b1 O
An acre contains 43,560 square feet. Multiply the acreage by this figure
PARCEI- SIZE {i.E.. SITE}
sq/ft
Calculate the total area to be cleared, graded, filled,
::.,1?t",9, 3nfl9r compacted for prop6sed devetopmentpro1ecr. tnctucle in this calculation the area to be cleared for:{o*te rq$ft^,L{.co;;tru;tBn/rit" ro-r-"ir"t ur"" 77 B
"r1x
Total Land Disturbance
*L
G
sq/ft
sq/ft Cut ot,l"
sq/ft
Circle: yes
other compa "r.f"(#!{, ry'" 5O a lndicate Total Volumes of proposed:
Lawn, landscaping, etc +
Does the project convert 2 lz acresor more ofnative vegetation to pasture?
Answerthe following two questions related toconversion of native vegetailon:
Does the project convert Tq acresor more ofnative vegetation to lawn or landscapeO areasZ
Circle: yes
ps1 Ll lo
{cu/yd)
Well, utilities, etc. +
Drainfield, septic tank, etc. rl/ O gO
sq/ft
sq/ft
rfaces which similarly impede the natural i nfiltration of stormwater
b,
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Driveway, parking, roads, etc. I 7 00 sqn
oo
Total New Total Existing
TOTAL NEW + TOTAL EXISTING-"This amount will be used to check total lot coverage.
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sq/ft
"**6+4+qt 1
-b
#
Lo
*-5c] c2
+
*#
€
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Driveway, parking, roads, etc
other Ap'cpu
NEW
Structures (all roof area)
Sidewalks
Patios
Solid Decks
(without infi ltration below)
Driveway, parking, roads, etc
Other
Sidewalks
Patios
Solid Decks
(without infi ltration below)
The following questions will help determine whether the proposed project is considered development or redeyelopment
FURTIIER lttlsrRucrloNs: lf the answer is yes, the proposal is considered redevelopment and the attached Figure 2 should be usedto determine the applicable Minimum Requirements. lf the answer is no, the proposal is considered new development and theattached figure l should be used. At this juncture, the applicant should refer to the applicable Flow chart to determine theMinimumRequirementsforstormwatermanagement. DCDstaffwill helpverifytheclassificationoftheprojectandtheapplication
requ irements.
For proponents of "small" projects who must comply only with Minimum Requirement #2-construction stormwater pollution
Prevention-an additional submittal is not required. The proponent is responsible for employing the 12 Elements to control erosionand prevent sediment and other pollutants from leaving the site during the construction phase of the project. pick up theConstruction Stormwater Pollution Prevention (swPP) Best Management practices (BMps) packet. proponents of ,,medium,,
projects-those that must meet only Minimum Requirements #1 through #5-and for "large" projects-those that must meet all 10Minimum Requirements-are required to submit a stormwater site Plan. DCD has prepared a submittal template of a stormwatersite Plan, principally for rural residential projects. Complete the template in the storrnwater site plan lnstructions and submittalTemplate or prepare a Stormwater Site Plan using the step-by-step guidance in the Stormw oter Monogement Monual.
APPLICANT SIGNATT'RE
DEVELOPMENT v. REDEVEL0PMEilIT
Divide the total existinq impervious surface above by the size of the parcel and convert to a percenta g", I L "r,
Does the site have 35o/o or more of existinq impervious surface? circle:Yes n"E
By signing the Stormwater Calculation worksheet, I as the applicant/owner attest that the information
best of my knowledge. talso certify that this application is being made with the full
oR AUTHoRtzED REpRESENTATIvE SiGNAT'JRE)
(
(
(DArE)
property
provided herein is true and correct to the
knowledge and consent of all owners of the affected
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Table R402"1.1 Footnotes
Forsl; 1foot.= 304.8 mm, ci .= continuous insulation, int.= intermecliate framing.
'R-values are minimums. U-factors and SHGC are maximums. When insulation is installed in a cavity which is
less than the iabelor design thickness of the insulation, the compressed R-value of the insulation from
Appendix Table A101.4 shall not be less than the R-value specified in the table.
lo
rne f.nertration U-factor column excludes skylights, The SHGC column applies to all glazed fenestration.
'"10175121..+TB" means R-10 continuous insulation on the exterior of the wall, or R-1-5 0n the continuous
insulation on the interior of the wall, or R-2L cavity insulation plus a thermal break between the slab and the
basement wallat the interior of the basement wall. "10/15 f 21,.+TB" shall be permitted to be met with R-13
cavity insulation on the interior of the basement wall plus R-5 continuous insulation on the interior or
exterior of the wall. "10/1,3" means R-10 continuous insulation on the interior or exterior of the home or R-
L3 cavity insulation at the interior of the basement wall. "TB" means thermal break between floor slab and
basement wall.
' R-L0 continuous insulation is required under heated slab on grade floors. See R402.2.9.1.
" There are no SHGC requirements in the Marine Zone.
Reserved
Reserved
Reserved
'The second R-value applies when more than half the insulation is on the interior of the mass wall
i' Reserved
k Forsingle rafter- or joist-vaulted ceilings, the insulation may be reduced to R-3grReserved
* lnt. (intermediate framing) denotes standard framing L6 inches on center with headers insulated with a
minimum of R-10 insulation
Table R402.1.3 Footnote
" Nonfenestration U-factors shall be obtained from measurement, calculation or an approved source or as
specified in Section R402.1.3.
h
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DEPARTMENT OF COMMUNITY DEVELOPMENT
621 Sheridan Street, Port Townsend, WA 9g36g
Tel: 360 379.4450 | Fax: 360.379.4451
Y"b,
E-mail : dcd@co. iefferson.wa. us
STORMWATER SITE PLAN SUBMITTAL TENIPIATE
uu# ?b<mo ilz pnorecr/eppLtcANT NAME l-lo*,eE
Please answer all of the following questions to the best of your ability. Where the question calls for depiction on a site map, theapplicant may choose to either incorporate the elements into the general plot plan for ti're Master Land Use Application or to submit aseparate stormwater site plan map.
Project Overview
Describe the proposed developed conditions of the site. lndicate position and relative size of proposed improvements on thesite
)
uD LLL€€|D S L6 F"A ^,\l rl.€11A sI
!T!\.l^L
cate contours on2 siteDescribeexisti
Existing Conditions Summary
T
lndicate native areas on site3.the
r+o 13 €a > ALALb{zC
on the site m4. Describe the soils. lndicate soil
456 0
5.theDescribe SI te e.behavior waterof onexistinghydrologydrainage;the below onandsite-above,eth lndrcatend).grou
dstormwater fa to fromandexisting sitethe theonnage site map onbasins ethseparateDepict site ifdrainagemapandndicateofeach
M
of noise the use or6.a excess
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7 wetlands, streams,Describe csignificant features criand areasticalraphigeog envi(i.e sensitive suchareas ASronmentally
theon olocation n site IJ p€
storruater site plan temptate - rev. 1r,2015
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8 Describe the theofvicinitygeneral landadjacent and utilincluding ties,androads,sensitive/critica areaslakesetc.
Permanent Stornnvater Control plan
This portion of the Stormwater Site Plan consists of the selection and installation of the appropriate stormwater control BMpsand facilities to remain in place after construction of the project is completed.
"Medium" size projects are required to have the totals calculated of all impervious surfaces, pollutiongenerating impervious:'{99"t' and pollution-generating pervious surfaces to verify that the thresholds for treatment facilities and flow controlfacilities are not exceeded.
Describe the developed site hydrology, as proposed. lndiclte whether stormwater will be fully dispersed (i.e., per BMp T5.30in the Manual) or, if not, what types of stormwater flow conlrol will be utilized for the site or. id""irl! threshold discharge areaswithin the site. Locate these facilities on the site plan and differentiate proposed facilities from existing facilities.
9
3 D@G.nl,Ta\ 6r a,L
ft
lf the project requires the use of stormwater treatment
for use on the site. Locate these facilities on the site
1normally for "large" projects or projects that involve the
facilities, describe the types of stormwater treatment facilities proposed
plan and differentiate proposed facilities from existing facilities. ;ir,i, i,potential for dispersion of contaminants.l
10
11. Describe the performance goals and standards applicable to the pro.lect.
12. Describe the flow control system
13. Describe the water quality system
o
stormatsr sits plan tefiplate - rev. 1zfQo15
site,USES structures,
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14. Describe the conveyance analysis and design
U A
15. Describe the source of fill material, physical characteristics of fill material, and deposition of excess material
-1 l-r Fird SoxO /,rtLJf6S ,-$ i-r{+ N
AiaDfu*A*l+"iha-
16 Proposed methods of placement and compaction consistent with the applicable standards on Appendix Chapter 33 of the
Uniform Building Code.
17. Describe the proposed surfacing material
18. Describe methods for restoration of the site.
LEU EL AA€A1 fi ttaw.r.Ei": htoArC'
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19 An Operation and Maintenance Manual is required for each flow control and treatment facility. [-his is normally required for"large" projects only and only those for which facilities are required to control flow or treat runoff.l lf included, list the Manuals
here.
L)
20. List here and include any special reports or studies conducted to prepare the Stormwater Site Plan
21 List other necessary permits and approvals as required by other regulatory agencies. lf those permits or approvals include
conditions that affect the drainage plan or contain more restrictive drainage-related requirements, describe those conditions or
restrictions here.
L - IES{A d Q7.6.J>l b - oorzl
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CoNSTRUCT|ON STORMWATER POLLUT|ON PREVENTTON PLAN (Swppp)
The Construction SWPPP addresses sediment and erosion control during construction. The BMps indicated by the applicant in thetemplate that follows must be installed on the ground during all constructi'on phases of the prolect. The propon'ent is responsible forpreventing sediment and erosion impacts to environmentally sensitive areas and off-site areas. bonsult the Construction StornnvaterPollution Prevention (SWPP) Best Management Practices (BMPs) Packet for guidance, particularly with rural residentialdevelopment.
SECTION I - CONSTRUCTION SWPPP NARRATIVE
construction stormwater Pollution Plan Elements. Describe how each of the
will be addressed. ldentify the type and location of BMps used to satisfy the requ
the proposal, lustify in writing. Detailed descriptions of the '13 Elements are found
(beginning on page 3-1 1).
Construction SWPPP elements has been or
ired element. lf an element is not applicable to
I at Volume ll Section 3.3.3 of the Manual
13 Required Elements - Construction SWPPP
1. Mark Clearing Limits.
LA)E
2. Establish Construction Access.
LLgS D
3. Control Flow Rates
t"
o*1awlt lA€TvtoA\ Flart AJ*o
4. lnstall Sediment Controls
aturg6
5. Stabilize Soils
A Puretq r(11 E(( Al"l ra $ lJ-r
gTl A)
6. Protect Slopes
bt vr F-G;,^s,L € brL B1 Lqr o{4 U)Pt2
7. Protect Drain lnlets
(
8
stor|]mter sita plan tstrplate - cv 12712015
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13 Required Elements - Construction SWPPP (continued)
8. Stabilize Channels and Outlets.
9. Control Pollutants.
10 Control De-Watering (the act of pumping groundwater or stormwater away from an active construction site).
11. Maintain Best Management Practices (BMPs)
q)tLt- rttfl;rrg, p BrJ p/3
12. Manage the Project.
13. Protect Low lmpact Development BMP's
L-r tu,t- {lt-o*'*f lrL, ! farA."I-5 ^-dps
Adjacent Areas.
a. Description of the adjacent areas that may be affected by site disturbance (e.g., streams, lakes, wetlands, residential
areas, roads).
Description of the downstream drainage path leading from the site to the receiving body of water (minimum distance of 400yards).
2.
bL
b
-Tb l-u+Lvt7-fuf
Environmentally Sensitive Areas.
a. Description of environmentally sensitive areas that are on or adjacent to the site
3.
stcrMtar site plan tefiDlatB - .ev. 124120'15 9
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Description of special requirements for working in or near envrronmentally sensitive areas.b.
problems on site in the context of the characteristics of the on-site
itj rlf( 4i
4. Erosion Problem Areas. Description of potential erosion
soils (e.9., erodibility bility, depthlity,, texture, soil
Cri J{7g1l)?EAjTIAL {rttuut
9Lll{* 4-r rsrL^i br-.ff*d\
It
5
UILD l.-Ft^-,) +t*L..L
FttA fituL
b. Construction phasing (if proposed)
Construction Phasing.
a. ConstructionsequenceP ttox$ A,t"t %L
Wet season is October 1 through April 30 (page 2-20 of the Manual).
€ r:rt*&l
AP tt tu
construction activities for environmentally sensitive areas
6.
il
Proposed wet
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a.seasonF*f
O /-\{1LA1r,?,',t1 0f qgAd,
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$TE ,{, A4. I e*.t,t
Wet Season Construction Activities
Construction Schedule.
Provide a proposed construction schedule
b. Proposed wet
and/or other evidence of financial responsibility for liability associated with erosion and sedimentation
for the initiation of bonds and/or other financial securities
N
b Describe bonds
impacts.p
7. Financial/Orrnership Responsibilities
a. ldentify the property owner
Calculations. Provide Design Calculations on a separate sheet for the following, if applicable8.Engineering
Detention Calculations
a. Sediment Ponds/Traps.
b. Diversions.
c. Watenrays.
d. Runoff/Stormwater
stormwater site plan temptate - rev 121720.15
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SECTION II - EROSION AND SEDIMENT CONTROL PLAN
Sediment and erosion control measures may be depicted on the master land use application plot plan, a stormwater site plan, andlor aseparate Construction SWPPP site plan. This is a checklist to ensure that the following are depicied on a site plan:
,l General.
a. Vicinity Map
b. Jefferson County Approval Block
c. Erosion and Sediment Control Notes
2 Site Plan
a. Legal description of subject property.
b. North arrow.
c. lndicate boundaries of existing vegetation (e.g., tree lines, pasture areas, etc.).d. ldentify and label areas of potential erosion problems.
e. ldentify FEMA base flood boundaries and Shoreline Management boundaries (if applicable).f. Show existing and proposed contours.
s lndicate drainage basins and direction of flow for individual drainage areas.h. Label final grade contours and identify developed condition drainage basins.i. Delineate areas that are to be cleared and graded.
j. Show all cut and fill slopes indicating top and bottom of slope catch lines.
3. Conveyance Systems.
a. Designate locations for swales, interceptor trenches, or ditchesb. Show all temporary and permanent drainage pipes, ditches, or cut-off trenches required for erosion & sediment controlc. Provide minimum slope and cover for all temporary pipes or call out pipe inverts.d. Shows grades, dimensions, and direction of flow in all ditches, swales, culverts and pipes.e. Provide details for bypassing off-site runoff around disturbed areas.f. lndicate locations and outlets of any dewatering systems.
4. Location of Detention Best Management Practices (BMPs). ldentify location of detention BMps
5. Erosion and Sediment Control Facilities.
a. Show the locations of sediment trap(s), pond(s), pipes and structures.b. Dimension pond berm widths and inside and outside pond slopes.c. lndicate the trap/pond storage required and the depth, length, and width dimensions.d. Provide typical section views through pond and outlet structure.
e. Provide typical details of gravel cone and standpipe, and/or other filtering devices.f. Detail stabilization techniques for outleVinlet.
g. Detail control/restrictor device location and details.
h. Specify mulch and/or recommended cover of berms and slopes.
i. Provide rock specifications and detail for rock check dam(s), if applicable.j. Specify spacing for rock check dams as required.
k. Provide front and side sections of typical rock check dams.
l. lndicate the locations and provide details and specifications for silt fabric.
m. Locate the construction entrance and provide a detail.
6.Detailed Drawings. Any structural practices used that are not referenced in the Ecology Manual should be explained and
il lustrated with detailed drawings.
7 Other Pollutant BMPs. lndicate on the site plan the locations of BMPs to be used for the control of pollutants other than
sediment (e.9., concrete wash water).
8.Monitoring Locations.
the construction site. Sr
lndicate on the site plan the water quality sampling locations to be used for monitoring water quality on
ampling stations should be located upstream and downstream of the project site.
stormttr site plan terptate -.ev 12y72015 11
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Stormwater Site Plan Changes
lf the designer wishes to make changes or revisions to the originally approved Stormwater Site Plan, the proposed revisions shall besubmitted to DCD prior to construction. The submittal shall include substitute pages that include all proposed changes, reviseddrawings showing any structural changes, and any other supporting information that eiplains and supports the reason for th! change.
Final Corrected Ptan Submittal
lf the project included construction of conveyance systems, treatment facilities, flow control facilities, or structural source control BMps(not standard on-site stormwater management BMPs), the applicant shall submit a flnal corrected plan ("as-builts") when the project iscompleted. These should be engineering drawings (stamped by a licensed civil engineer) that accurately represent the pro.lect asconstructed.
APPLICANT SIGNATURE
By signing the Construction SWPPP worksheet, I as the applicanUowner attest that the information provided herein is true andcorrect to the best of my knowledge. I also certify that this application is being made with the full knowledge and consent of allowners of the affected property.
(LANDoWNER oR AUTHoRIZED REPRESENTATIVE SIGNATURE)
THIS SPACE MAY BE USED FOR ADDITIONAL NOTES, IF NEEDED
stortuatar sita plan teftplata - rev. 1ZzZ01S 12
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DEPARTMENT OF COMMUNITY DEVELOPMENT
621 Sheridan Street. Port Townsend, WA 98368
Tel: 360.379.4450 | Fax: 360.379.4451
Web: www. co. iefferson-wa.us/communitvdevelooment
E-mail : dcd@co.iefferson.wa. us
STORMWATER SITE PIAN INISTRUCTIONS AND SUBDIITTAL TEMPI.ATE
"Me dium" and "Lafge" Projects
[lncludes Construction Stormwater Pollution Prevention Plan (SWPPP) and Permanent Stormwater Control plant
The submittal template for a Stormwater Site Plan has been developed from information presented in the Department of
Ecology 2012 Stormwater Management Manual for Western Washington (Manual), which is the set of stormwater
management standards for new development and redevelopment in Jefferson County.
The Stormwater Site Plan, Minimum Requirement #1 in the Manual, is the comprehensive report containing all of the
technical information and analysis necessary to evaluate a proposed new development or redevelopment for compliance
with stormwater requirements. A Stormwater Site Plan is required for all "medium" and "large' projects. (For background
information, refer to the Stormwater Management lnformation Sheet.)
The Stormwater Site Plan includes a Construction Stormwater Pollution Prevention Plan (SWPPP - Minimum
Requirement #2) that addresses sediment and erosion control during construction and a Permanent Stormwater Control
Plan thal addresses stormwater on the project site in its developed condition through dispersion, infiltration, or, if
necessary, flow control and/or treatment facilities.
The steps for preparing and the content of a Stormwater Site Plan are summarized below and more fully described in
Chapter 3 of Volume I of the Manual. The attached submittal template is intended to be a format applicable io typical rural
residential construction. For these cases, completion and submittal of the template results in a complete land use
application.
THE TWO MAIN COMPONENTS OF A STORMWATER SITE PLAN
l. Construction Stormwater Pollution Prevention plan
A Construction Stormwater Pollution Prevention Plan (SWPPP) is a document that describes the potential for pollution
problems on a construction project and which explains and illustrates the measures to be taken to control these problems.
The basis for requiring a SWPPP, the twelve elements required to be in a SWPPP, the suggested step-by step procedure
to follow, and the suggested Best Management Practices (BMPs) to follow, are all described in Volume ll of the Manual.
A SWPPP consists of two sections, a narrative and the drawings. A description of the contents of the narrative and the
drawings sections, and checklists for each of these sections, are in Section 3.3 of Volume ll. For typical rural residential
pro.lects, DCD provides a Construction Stormwater Pollution Prevention (SWPP) Best Management Practices (BMPs) packet
to assist with the preparation of the Construction SWPPP.
ll. Permanent Stormwater Control Plan
A Permanent Stormwater Control Plan is a document that describes the basis for, and the means of implementing,
permanent Best Management Practices (BMPs) for flow control and treatment facilities after the project is completed. Thl
content of a Permanent Stormwater Control Plan is described in Section 3.1 .5 of Volume I of the Manual. The permanent
BMPs and facilities for flow control and treatment are described in Volumes lll, lV, and V of the Manual. The submittal
template is intended for rural residential projects that can fully disperse or infiltrate stormwater. The template may not be
appropnate or sufficient for applications involving larger or more complex projects.
stormtsr etB plao terytale - @v. 12J7QO15
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INSTRUCTIONS
To prepare a Stormwater Site Plan, follow the steps outlined below, complete the Stormwater Site Plan template, sign andsubmit together with the Master Land Use Application (MLA). This information may also be provided on oiher diagrams,plans, studies, or attachments submitted with the project application. lf so, please indicate such on this suppleirentalpermit application. As the template is designed mostly for rural residential development, it may not be as useful for alarger project as an independently prepared Stormwater Site Plan. For any particular project, the Administrator maywaive specific submittal requirements determined to be unnecessary for review of the application.
Note: Prior to filling out the submiftal temptate, read through these sfeps for preparing a Stormwater SitePlan. Preliminary or draft versions of the individual components may be helpfut in the case that
redesigning an original layout would result in a proposat that has less environmental impacts and is
significantly simpler in terms of meeting stormwater requirements. For exampte, if the proposal can
utilize the "full dispersion" BMP (T5.30 in the Manual), there is no need to provide for fiow control orflow treatment on the site. For more information on the easiesf way to meet stormwater
requirements, refer to the "Low lmpact Development" lnformatlon Sheef. BMPs used during the
construction phase and that are included in the Construction SWPPP may also be usefulas e/ements
of the Permanent Stormwater Control Plan.
STEP 1: GOLLECT AND ANALYZE INFORMATION ON EXISTING CONDITIoNS
Collect and review information on existing site conditions, including topography, drainage patterns, soils, ground cover, critical areas,
9!1rye1t areas, existing development, existing stormwater facilities. The Jefferson Colnty website provides an lnternet Map Server(lMS) function (http://www.co.jefferson.wa.us). lf available, a Development Review Division (DRD) planner may be able to assist you incollecting this information.
Analyze the information to determine site limitations, including:o Areas with high potential for erosion and sediment deposition (based on soil properties, slope, etc.);o Locations of sensitive and critical areas (e.g., vegetative buffers, wetlands, steep slopes, floodplains, geologically hazardous
areas, streams, susceptible aquifer recharge areas, etc.); andr The natural receiving waters to which the stormwater runoff either directly or eventually discharges.
This information will be useful in site design and in the completion of the Permanent Stormwater Control Plan and ConstructionSWPPP.
STEP 2: PREPARE PRELIMINARY DEVELOPMENT LAYOUT
Based upon the analysis of existing site conditions, locate the buildings, driveways, roads, parking lots, and landscaping features for theproposed development. Consider the following points when laying out the site:o Fit development to the terrain to minimize land disturbance; confine construction activities to the least area necessary andaway from critical areas;
o Preserve areas with natural vegetation (especially forested areas) as much as possible;
' On sites with a mix of soil types, locate impervious areas over less permeable soil (e.g., till) and try to restrict development
over more porous soils (e.9., outwash);o Cluster buildings together;
o Minimize impervious areas; and
. Maintain and utilize the natural drainage patterns.
The preliminary development layout will assist in determining threshold discharge areas for calculating whether size thresholds underMinimum Requirements #6, #7, and #8 (for "large" projects) are exceeded and as a basis for the drawings and maps required for theStormwater Site Plan.
o
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STEP 3: PERFORM AN OFF-SITE ANALYSIS
This step is for "large" proiects (i.e., adding 5,000 square feet or more of new impervious surface, converting Vo acres of pervious
surfaces to lawn or landscaped areas, or converting 2lz acres of forested area to pasture) at the discretion of the UDC Administrator.
See Volume l, Section 2.6.2 for more information.
STEP 4: REVIEW THE APPLICABLE MINIMUM REQUIREMENTS
The Stormwater Calculation Worksheet is a required submittal for all development and redevelopment land use applications.
Completing the Worksheet helps determine the broad category of the proposal-"small," "medium," or "large" project-and the
applicable Minimum Requirements. 'Small" projects need to meet Minimum Requirement #2 only. "Medium" piojects need to meet
Minimum Requirements #1 through #5. "Large' projects need to meet all the Minimum Requirements, #1 through it9. The Minimum
Requirements are as follows:
1. Preparation of Stormwater Site Plans (Chapter 3 of Manual) 6. Runoff Treatment2. construction Stormwater Pollution Prevention T. Flow control3. Source Control of Pollution B. Weflands protection4. Preservation of Natural Drainage Systems and Outfalls 9. Operations and Maintenance5. On-site Stormwater Management
The Manual provides descriptions and instructions in Volume l, Chapter 2. lnformation sheets, application materials, and DRD planners
can help describe the Minimum Requirements to applicants.
IVofe.' "Large" projects, as pai of meeting Minimum Requirements #6 - Runoff Treatment - and #7 - Flow Control, are
compared to Volume l, Chapter 2 in the Manual to determine whether on-site stormwater management BMPs are
sufficient or treatment facilities or flow control facilities are required. The flow control determination may necessitate use
of the Western Washington Hydrology Model managed by the Department of Ecology. Consutt Sectlons 2.5.6 and 2.5.7
of Volume l, Chapter 2 of the Manual for more information.
Again, the easlest way to meet stormwater requirements is to design the project so that natural drainage is preserved, impervious
surface is limited, and full dispersion (BMP T5.30) is implemented. By using "low impact development" technrques in the site design,the need for treatment and flow control facilities is eliminated, simplifying preparation of the Stormwater Site Plan and often the site
construction process itself. For more information on these techniques, consult the "Low lmpact Development" lnformation Sheet.
STEP 5: PREPARE A PERMANENT STORMWATER CONTROL PLAN
Select stormwater control BMPs and facilities that will serve the project site in its developed condition. The selection process is
presented in Volume l, Chapter 4. After consideration is given to how selected BMPs and facilities fit within and serve the entirepreliminary development layout, the designer may want to reconsider the site layout to reduce the need for construction of facilities or
the size of the facilities by reducing the amount of impervious surfaces created and increasing the areas to be left undisturbed. The
Permanent Stormwater Control Plan should contain the following sections (Section 3.1 .5 of Volume l, Chapter 3):o Existing Site Hydrology (i.e., the behavior of water on the site-above, below, and on the ground)o Developed Site Hydrology (special requirements for projects and threshold discharge areas within projects that requirement
treatment and flow facilities). Performance Standards and Goals. Flow Control System. Water Quality Systemr Conveyance System Analysis and Design
Essentially, in terms of site hydrology, the developed condition of the site should match the pre-developed condition, with is forested
land cover (unless reasonable, historic information is provided that indicates the site was praine prior to setflement). For 'large"
projects, totals of impervious surfaces, pollutiongenerating impervious surfaces, and pollution generatlng pervious surfaces must be
tabulated for each threshold discharge area for which on-site BMPs are the sole stormwater manigement ipproach.
storwater srts plan tsfiplato - rav 12712015 3
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srEP 6: PREPARE A CONSTRUCTTON STORMWATER POLLUT|ON PREVENTTON PLAN (Swppp)
The Construction SWPPP for projects adding or replacing 2,000 square feet of impervious surface or more or clearing 7,000 squarefeet or more (i.e., "medium" or "large" prolects), must contain sufficient information to demonstrate to the UDC Administrator that thepotential pollution problems have been adequately addressed for the proposed project. An adequate Construction Swppp includes anarrative and drawings. The narrative is a written statement to explain and ;ustify the pollution prevention decisions made for aparticular project. The narrative contains concise information conceming exlsting site conditions, construction schedules, and otherpertinent items that are not contained on the drawings. The drawings and notes describe where and when the various BMps should beinstalled, the performance the BMPs are expected to achieve, and actions to be taken if the performance goals are not achieved.There are 13 Elements that must be considered in the development of a Construction SWPdP, unless site conditions render thatelement unnecessary and the exemption from that element is clearly justified in the narrative. The 13 Elements cover the general waterquality protection strategies for limiting site impacts during construction and are described in detail in Section 2.5.2, Vo'iume I of theManual.
The 13 Elements of Minimum Requirement #2, Construction Stormwater Pollution Prevention, are:
o
1. Mark Clearing Limits2. Establish Construction Access3. Control Flow Rates4. lnstall Sediment Controls5. Stabilize Soils
6. Protect Slopes7. Protect Drain lnlets
8. Stabilize Channels and Ouflets9. Control Pollutants
1 0. Control De-watering
Maintain BMPs
Manage the Project
Protect Low lmpact Development
BMP's
11
12
13
For ease of use, the Stormwater Site Plan submittal template below includes a section that lists the'13 Elements and provides theopportunity to include sufficient information for rural residential and other relatively simple Construction SWppps. For more complexprojects, a separate narrative and set of plans may be preferred or required.
Volume ll of the Manual is dedicated to Construction Stormwater Pollution Prevention. A step-by-step BMp selection process and acomplete description of the BMPs applicable to each element is provided in Chapters g'anO +. Additionally, DiD provides aConstruction Stormwater Poltution Prevention (SWPP) Best Management Praciices (BMPs) packet that iummarizes the 12Elements and excerpts from the Manual sample sediment and erosion control measures for typical rural residential development. ThePacket should prove useful for completing the Construction SWPPP component of the submittii template.
On construction sites that infiltrate all stormwater runoff, the primary consideration in the preparation of the Construction SWppp is theprotection of the infiltration facilities from fine sediments during the construction phase and protection of ground water from otherpollutants. On construction sites that discharge to surface water, the primary consideration in the preparJtion of the ConstructionSWPPP is compliance with the State Water Quality Standards. The step-by-step procedure oulined in Volume ll, Section 3.2 isrecommended for the development of these Construction SWppps.
STEP 7: COMPLETE THE STORMWATER SITE PLAN
The Stormwater Site Plan encompasses the entire submittal to Jefferson County in conjunction with a land use or building permitapplication. The following documents or sections should be included:o Project Overviewo Existing Conditions Summary. Off-site Analysis Report (if required; usually for*large,, projects)o Permanent Stormwater Control Plan
' Special Reports and Studies (such as soil testing, wetland delineation, etc., if applicable)o Other Permits (approvals required by other regulatory agencies that include stormwater management conditions)
' Operation and Maintenance Manual (for each flow control and treatment facility, if applicable)o Bond Quantities Worksheet (for performance bond or other financial guarantee for proper construction and operation ofconstruction site BMPs and permanent drainage facilities, if required)
The submittal template below is designed for rural residential and other relatively small or simple projects. For larger and morecomplex projects-particularly those that involve stormwater treatment and/or flow control--more informaiion may be reiuired and anindependent stormwater Site Plan may be the preferable submittal format.
STEP 8: CHECK COMPLIANCE WITH ALL APPLICABLE MINIMUM REQUIREMENTS
A Stormwater Site Plan as designed and implemented should specifically fulfill all Minimum Requirements applicable to the project.The applicant should review to check that these requirements are satisfied and that all information provided is true and correct prior tosigning and submitting the Stormwater Site Plan. (The signature box appears at the end of the submittal template.)
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I ' ,rr-r.l .l Downspout Full tnfilOn Systems (BMP T5.l0A)o Page 2 of5
lll-3.{.{ Downspout Full lnfiltration Systems (BMP 75.{OA)
Downspout full infiltration systems are trench or drywell designs intended only for use in infiltrating runoff from roof
downspout drains. They are not designed to directly infiltrate runoff from pollutant-generating impervious surfaces.
Application
Projects subject to l-2.5.5 Minimum Reouirement #5: On-site Stormwater Manaoement must provide for individual
downspout full infiltration systems or full dispersion if feasible. Evaluate the feasibility, or applicability, of downspout full
infiltration unless full dispersion is proposed. Use the evaluation procedure below to determine the feasibility of downspout
full infiltration.
Runoff Modeling for Roof Downspout Full lnfiltration
lf roof runoff is infiltrated according to the requirements of this section, the roof area may be discounted from the project
area used for sizing stormwater facilities.
Procedure for Evaluating Feasibility
1. Have one of the following prepare a soils report to determine if soils suitable for infiltration are present on the
site:
" A professional soil scientist certified by the Soil Science Society of America (or an equivalent national
program)
. A locally licensed on-site sewage designer
" A suitably trained person working under the supervision of a professional engineer, geologist,
hydrogeologist, or engineering geologist registered in the State of Washington.
The report shall reference a sufficient number of soils logs to establish the type and limits of soils on the proiect
site. The report should at a minimum identify the limits of any outwash type soils (i.e., those meeting USDA soil
texture classes ranging from coarse sand and cobbles to medium sand) versus other soil types and include an
inventory of topsoil depth.
2. lf the lots or site does not have outwash or loam soils, and full dispersion is not feasible, then consider a rain
garden or bioretention BMPs (the next lower priority on-site stormwater management system).
3. Complete additional site-specific testing on lots or sites containing outwash (coarse sand and cobbles to
medium sand) and loam type soils.
lndividual lot or site tests must consist of at least one soils log at the location of the infiltration system, a
minimum of 4 feet in depth from the proposed grade and at least 1 foot below the expected bottom elevation of
the infiltration trench or dry well.
ldentify the NRCS series of the soil and the USDA textural class of the soil horizon through the depth of the log,
and note any evidence of high ground water level, such as mottling.
4. Downspout infiltration is considered feasible on lots or sites that meet all of the following:
. 3 feet or more of permeable soil from the proposed final grade to the seasonal high ground water table.
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III-3.1.1 Downspout Full Idlation Systems (BMP T5.l0A) O Page 3 of5
" At least 1-foot of clearance from the expected bottom elevation of the infiltration trench or dry well to the
seasonal high ground water table.
. The downspout full infiltration system can be designed to meet the minimum design criteria specified
below.
Fioure lll-3.1.2 Tyoical Downsoout lnflltration Trench shows a typical downspout infiltration trench system, and Fioure
lll-3.1.3 Alternative Downspout lnfiltration Trench System for Coarse Sand and Gravel presents an alternative infiltration
trench system for sites with coarse sand and cobble soils. These systems are designed as specified below.
General
1. The following minimum lengths (linear feet) pert ,000 square feet of roof area based on soil type may be used
for sizing downspout infiltration trenches.
Coarse sands and cobbles: 20 LF
Medium sand: 30 LF
Fine sand, loamy sand: 75 LF
Sandy loam: 125 LF
Loam: 190 LF
2. Maximum length of trench shall not exceed 100 feet from the inlet sump.
3. Minimum spacing between trench centerlines shall be 6 feet.
4. Filter fabric shall be placed over the drain rock as shown on Fiqure lll-3.'l .2 Tvpical Downspout lnfiltration
Trench prior to backfilling.
5. lnfiltration trenches may be placed in fill material if the fill is placed and compacted under the direct supervision
of a geotechnical engineer or professional civil engineer with geotechnical expertise, and if the measured
infiltration rate is at least 8 inches per hour. Trench length in fill must be 60 linear feet per 1,000 square feet of
roof area. lnfiltration rates can be tested using the methods described in Section 3.3.
6. lnfiltration trenches should not be built on slopes steeper than 25% (4:1). A geotechnical analysis and report
may be required on slopes over 15 percent or if located within 200 feet of the top of slope steeper than 40%, or
in a landslide hazard area.
7. Trenches may be located under pavement if a small yard drain or catch basin with grate cover is placed at the
end ofthe trench pipe such that overflow would occur out ofthe catch basin at an elevation at least one foot
below that of the pavement, and in a location which can accommodate the overflow without creating a
significant adverse impact to downhill properties or drainage systems. This is intended to prevent saturation of
the pavement in the event of system failure.
Design Criteria for lnfiltration Drywells
,1
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Design Criteria for lnfiltration Trenches
,III-3.1 .l Downspout Full lnnlton Systems (BMP T5.l0A)o Page 4 of5
Figure lll-3.1.4 Tvoical Downspout lnfiltration Drvwell shows a typical downspout infiltration drywell system. These systems
are designed as specified below.
General
1. Drywell bottoms must be a minimum of 1 foot above seasonal high ground water level or impermeable soil
layers.
2. When located in course sands and cobbles, drywells must contain a volume of gravel equal to or greater than
60 cubic feet per 1000 square feet of impervious surface served. Wren located in medium sands, drywells must
contain at least 90 cubic feet of gravel per 1,000 square feet of impervious surface served.
3. Drywells must be at least 48 inches in diameter (minimum) and deep enough to contain the gravel amounts
specified above for the soil type and impervious surface served.
4. Filter fabric (geotextile) must be placed on top of the drain rock and on trench or drywell sides prior to
backfilling.
5. Spacing between drywells must be a minimum of '10 feet.
6. Downspout infiltration drywells must not be built on slopes greater lhan 25o/o (4:1). Drywells may not be placed
on or above a landslide hazard area or on slopes greater than 15% without evaluation by a professional
engineer with geotechnical expertise or a licensed geologist, hydrogeologist, or engineering geologist, and with
jurisdiction approval.
Figure lll-3.{.2 Typical Downspout lnfiltration Trench
r! ::.--
2014 Fioure lll-3.1.2 odf download
Flguto lll-3.{.3 Alternatlve Downspout lnflltratlon Trcnch System for Goarse Sand and Gravel
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2014 Fioure lll-3.1.3 pdf download
Figure lll-3.'1.4 Typical Downspout lnfiltration Dryrwell
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2014 Fioure lll-3.1.4 pdf download
Setbacks
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III-3. l. I Downspout Full trOation Systems (BMP T5.l0A)o
Local governments may require specific setbacks in sites with slopes over 40o/o,land slide areas, open water features,
springs, wells, and septic tank drain fields. Adequate room for maintenance access and equipment should also be
considered. Examples of setbacks commonly used include the following:
1 . All inflltration systems should be at least 1 0 feet from any structure, property line, or sensitive area (except
slopes over 40%).
2. All infiltration systems must be at least 50 feet from the top of any slope over 40%. This setback may be
reduced to 15 feet based on a geotechnical evaluation, but in no instances may it be less than the buffer width
3. For sites with septic systems, infiltration systems must be downgradient of the drainfield unless the site
topography clearly prohibits subsurface flows from intersecting the drainfield.
,t
Washington State Department of Ecology
2012 Stormwater Manaoement Manual for Westem Washinoton, as Amended in December 2014 (The 2014 S\NMM\AAA/)
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Page 5 of5
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Plan View
4" rigid or 6" flexible
perforated pipe
roof
drain
(
I
I
t
sump w/solid lid
infiltration trench
roof drain
overflow
Profile View 4" rigid or 6" flexible
perforated pipe
splash block
CB sump
w/solid lid
6"
12"washed rock 1 /2" -3A"1 min
1 min
A fine mesh screen
varies
10'min S'rin. .-
Section A-A filter fabric compacted backfill
o
24"4" rigid or 6" flexible
perforated pipe
1
washed rock1Y2" -3/4"
24 NOT TO SCALE
DEPARTMENT OF
ECOLOGY
State of Washington
Figure lll-3.1 .2
Typical Downspout Infiltration Trench
Revised November 2015
Please see http://www.ecy.wa.gov/copyight.htmlfor copyright notice including permissions,
limitation of liability, and disclaimer.
t
)
A
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from roof
grass
overflow+-
6" min
1 /2" -3/i'
washed rock
18'min.
2'min.15'min.
Note: Same length dimensions and site
limitations as typical system
NOT TO SCALE
DEPARTMENT OF
ECOLOGY
State of Washington
Figure lll-3.1 .3
Alternative Downspout Infiltration Trench
System for Coarse Sand and Gravel
Revised November 2015
Please see http:/rfuww.ecy.wa.gov/copyight.htmlfor copyright notice including permissions,
limitation of liability, and disclaimer.
f--
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House
Roof
downspout
Catch basin
(yard drain)
_{r>
flow
Roof
downspout
Plan View
Roof
downspout Mark center of hole
with 1" capped PVC
or other means flush
with surfaceHouseOverflow
Splash block Topsoil
_*1'min
flow
Fine mesh screen Min.4" dia.
PVC pipe
Catch basin
(yard drain)4'min.
Sides of hole lined
with filter fabric
15'min.
Min. 1' above seasonal high groundwater table
Section View
NOT TO SCALE
o
48 lnch diameter
hole filled with 1/z
- 3" washed drain
rock
48 lnch diameter
hole filled wilh 1/z
- 3" washed drain
rock
DEPARTMENT OF
ECOLOGY
State of Washington
Figure Ill-3.1 .4
Typical Downspout Infiltration Drywell
Revised November 201 5
Please see hftp:/lwww.ecy.wa.gov/copyright.htmlfor copyright notice including permissions,
limitation of liability, and disclaimer.
I
oo
7131lO3
DEPARTMENToFGoMMUNITYDEVELoPMENT
ADMINISTRATIVE
WATE RGO NSERVATION MEAS URES LIST
To Promote Aquifer Recharge
and Prevent Seawater lntrusion
1. Roof and other intercepted precipitation shall be routed to on-site detention ponds
andlor other approved means and allowed to be released to the soil stowly'
z. Water collected from storm water and roof catchments may be used for watering
r"*n. uno gardens. Unless catchments water has been treated to meet drinking
*"i"i itrnirrds, there shall be no cross connections allowed between the potable
suPP|Y and imPounded water'
3- crouno water withdrawn from each property should not exceed a rate of three (3)
gallons Per minute'
4. lnstall water-conserving fixtures such as low flow toilets, faucets and shower
iurtti"tors and other water saving plumbing fixtures'
5. Landscaping should include xeriscaping and native vegetation with minimal amounts
of inigation.
6, use drip inigation, soaker hose systems and root irrigation.
T.Usewaterbasintechniquestowaterplants,shrubsandtrees.
8. Routinely water deeply and less frequently'
g.Weedcontrolisanimportantpartofwaterconservation"
10- For your landscaping select drought tolerant plants, shrubs and trees stay away from
heavY water consumers'
11. Limit the amount of irrigated lawn'
l2.Mulchyourgardenaswel|asisolatedplants,treesandshrubs.
13. Use shade and windbreaks to assist in water conservation.
14 Use low flow water closets, showerheads and water conserving dish and clothes
washers-
15. Use rainwater catchment systems that corral rainwater from manmade surfaces and
into storage.
16. lnstallwater-conserving devices such as low-volume toilets and plumbing fixtures.
17. onty 400 gallons per day o1 lels shou.ld be pumped from all exempt wells in
Seawaterlntrusion Protection Zones (SIPZ)'
18. Water softeners that contribute salt to groundwater through infiltration should not be
used in SIPZ.
19. Hose bibs (outdoor spigots) for outdoor water use should not be used in SIPZ'
[end]
PLEASE NOTE:THIS LIST IS A WORK IN PROGRESSAND MAY HAVE ADDITIONS I
DELETIONS MADE AT ANY TIME. USE CURRENT LIST.
o
2.5 MinimumRequirements
This section describes the minimum requirements for stormwater
management at development and redevelopment sites. Section 2.'[ should
be consulted to determine which requirements apply to any given project.
Figures 2.4.1 and2.4.2 shouid be consulted to determine whether the
minimum requirements apply to new surfaces, replaced surfaces, or new
and replaced surfaces. Volumes II through V of this manual present Best
Management Practices @MPs) for use in meeting the Minimum
Requirements'
Throughout this chapter, requirements are written in bold and
supplemental guidelines that serye as advice and other materials are
4! in bold'
2.5.1 Minimum Requirement #1: Preparation of stormwater
Site Plans
All projects meeting tbe thresholds in Section 2.4 shall prepare a
Stormwater Site Plan for tocal government review. Stormwater Site
plans shall use site-appropriate development principles' as required
and encouraged by local development codes, to retain native
vegetation and minimize impervious surfaces to the extent feasible.
Stormwater Site Plans shalt be prepared in accordance with Chaoter
I of this volume'
Objective
The 2,000 square feet threshold for hard surfaces and 7,000 square foot
ttreshold for land disturbance are chosen to capture most single family
home construction and their equivalent. Note that the scope of the
stormwater site plan only covers compliance with Minimum Requirements
#2 through #5 ifthe thresholds of5,000 square feet ofhard surface or
conversion of3/t acre ofvegetation to lawn or landscape, or conversion of
2.5 acres of vegetation to pastue are not exceeded'
S uP Pleme ntal g uide li n es
Projects proposed by departments and agencies within the local
government with jurisdiction must comply with this requirement. The
local govemment shall determine the process for ensuring proper project
review, inspection, and compliance by its own departments and agencies.
Volume I - Minimum Technical Requirements - August 2012
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thresholds. Local governments should be prepared to demonstrate that by
comparing the number and types of historical projects that would have
been regulated using the Ecology thresholds versus the local governrnent,s
thresholds.
Local govemments are allowed to instifute a stop-loss provision on the
application of stormwater requirements to replaced hard surfaces- A stop-
loss provision is an upper limit on the extent to which a requirement is
applied. For instance, there could be a maximum percentage of the
estimated total project costs that are dedicated to meeting stormwater
requirements. A project would not have to incuradditional ,stormwater
costs above that maximum though the standard redevelopment
requirements will not be fully achieved. The allowance fbr a stop-loss
provision pertains to the extent that treatment, flow control and wetlands
.. protection requirements are imposed on replaced hard surfaces. It does not'Epply to meeting stormwater requirements for new hard surfaces.
Loapl governments can also establish criteria for ailowing redevelopment
proj\s to pay a fee in lieu of constructing water quality or flow control
facilitidqon a redeveloped site. At a minimum, the fee should be the
equivalen\gf an engineering estimate ofthecost of meeting all applicable
stormwater r€suirements.for the.project. The local govemment should use
such funds for\e implementation of stormwater control projects that
would have simi\.benefits to the sarn'e receiving water as if the project
had constructed its teguired improvements. Expenditure of such funds is
subject to other state stalutory requirernents.
Ecology cautionslocal golqmments abour the potential long-term
consequences of allowing a.fep-in-lieu of stormwater facilities. Sites that
are allowedto pay a fee continile without stonnwater controls. If it is
determined, through fuiure basin planning for instanee, that controls on
such sites are necess4f to achieve water quality goals or iegal
requirements, the gublic may bear tht'posts for providing th-ose controls.
Underground utility projects that replac\the ground surface wirh in-kind
material or ma(erials with similar runoffiharacteristics should not be
subject to rgdevelopment requirements exclBt construction site erosion
control.
Local governments are also encouraged to review all road projects for
changes in elevations or drainage flowpath that cd\td cause flooding,
upland or sheam erosion, or changes to discharges to wetlands. For
example, adding curbs will result in redirecting flows and possibly causing
new downstream impacts. The local government should set project-
specific requirements to avoid or mitigate those impacts.
Volume I - Minimum Technical Requirements - August 2012
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2.5-2 Minimum Requirement#2: Construction Stormwater
Pollution Prevention (SWPP)
Thresholds
Allnewdevelopmentandredevelopmentprojectsareresponsiblefor
preventing .rotirn and discharge of sediment aud other pollutants
into receiving waters.
Proiects which result in 2,000 square feet or more of new plus
."pl."a hard surface area' or which disturb 7,000 square feet or
more of land nrust prepare a Construction SWPP Plan (SWPPP) as
part of the Stormwater Site Ptan (see Section 2'5-!)'
Projects that result in less than 21000 square feet ofnew plus replaced
hari surface area' or disturb less than ?1000 square feet ofland are
not required to prepare a Construction SWPPP, but must consider all
of rn* il e lu*"rt* of Construction Stormwater Pollution Prevention
and develop controls for all elements that pertain to the project site'
General Requirements
The swPPP shall include a narrative and drawings. All BMPs shall
beclearlyreferencedintheuarrativeandmarkedonthedrawings.
fne SWi'fp narrative shall include documentation to explain and
justifythepollutionpreventiondtcisionsmadefortheproject.Each
of tt* 13 elements must be considered and included in the
construction SWPPP unless site conditions render the element
unnecessaryandtheexemptionfromthatelementisclearlyjustified
in the narrative of the SWPPP. .{
clearing and grading activities for developments shall be permitted
only if Jonducied pursuant to an approved site development plan (d.g.,
,ubdiri*ion approval) that establishes permitted areas of clearing'
grading, cutti-ng, and fitling. These permitted clearing and grading
ir.r, oi,d "ny
oth", areas required to preserve critical or sensilive
areas, buffers, native grorvth protection easements' or tree retention
areasrhatlbeelelineatedonthesiteplansandthedevelopmentsite.
The srJlPPP shall be implemented beginning with initial land
disturbance and until linal stabilization. sediment and Erosion
control BMPs shall be consistent with the BMPs contained in chapters
3 and 4 of Volume II.
seasonal work Limitations - From october I through April30'
clearing, grading, and other soit disturbing activities shall only be
permitteJif shown to the satisfaction of the local permitting authority
it ut ,itt-lrden ruroff will be prevented from leaving the site through a
combination of the following:
l. Site conditions including existing vegetative coverage' slope' soil
type and proximity to receiving waters'
Yolume I - Minimum Technical Requirements - Attgust 2012
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2. Limitations otr activities and the extent of disturbed areas.
3. Proposed erosion and sediment control measures.
The following activities are exempt from the seasonal clearing and
grading limitations:
l. Routine maintenance and necessary repair of erosion anrl
sediment control BMPs.
2. Routine maintenance of pubric facilities or existing utirity
structures that do not expose the soil. or result in the remoyal of
the vegetative cover to soil.
3. Activities where there is one hundred percent infiltration of
surface water runoff within the site in approved and inslalled
erosion and sediment control facilities.
Project Requirements - Construction Swppp Elements
Element 7: Preserue Vegetation/Mark Clearing Limits
. Before beginning hnd disturbing activities, includingclearing and
grading, clearly mark all clear.ing limits, sensitive areas and tleir
buffers, and trees that are to be preserved within the construction
area.
. Retain the duff layer, native top soil, and nafirral vegetation in an
undisturbed state to the maximum degree practicable.
Element 2: Establish Construction Access
Lirnit construction vehicle access, a.ndr oxit to,ore route; if possi ble.
Stabilize access points with a pad of quarry spa[s, crushed rock,
or other equivalent BMPs, to minimize tracking of sediment onto
public roads.
Locate wheel wash or tire baths on site, if the stabilized
construction entrance is not effective in preventing tracking
sediment onto roads.
If sediment is tracked off site, clean the affected roadway
thoroughly at the end ofeach day, or more frequently ai necessary
(for example, during wet weather). Remove sedimeni from roads
by shoveling, sweeping, or pick up and transport the sediment to a
controlled sediment disposal area.
Conduct street washing only after sediment is removed in
accordance with the above bullet.
Volume I - Minimum Technical Reguirements - August 2012
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. Control street rvash wastervater by pumping back on-site' or
otherwise prevent it from discharging into systems tributary to
waters of the State.
Etement 3: Control Flow Rates
'Protectpropertiesandwaterwaysdownstreamofdevelopmentsitesfromerosionandtheassociateddischargeofturbidwaters
duetoincreasesinthevelocityandpeakvolumetricflowrateof
storm\ilater runoff from the project site'
. Where necessary to comply with the bullet above, construct
stormwater retention or detention facilities as one of the first steps
in grading. Assure that detention facilities function properly
beflre constructing site improvements (e.g. impervious surfaces).
.Ifpermanentinfiltrationpondsareusedforflowcontrolduring
construction, protect these facilities from siltation during the
construction Phase.
Element 4: tnstall Sediment Controls
rDesign,installoandmaintaineffectiveerosioncontrolsand
sedimentcontrolstominimizethedischargeofpollutants....
, Construct sediment controt BMPs (sediment ponds, traps, filters,
etc.) as one of the first steps in grading' These BMPs shall be
.. functionel before other land disturbing activities take place.
. Minimize sediment discharges from the site' The design'
installation and maintenance of erosion and sediment controls.-'
must address factors such as the amount, frequenry, intensity and
duration of precipitation, the nature of resulting stormwater
runoff, and soil claracteristics, including the range ofsoil particle
sizes expected to be present on the site'
. Direct stormwater runoff from disturbed areas through a
sediment pond or other appropriate sediment removal BMP'
before the runoffleaves o construction site or before discharge to
an infiltration facility. Runofffrom fully stabilized areas may be
dischargedwithoutasedimentremovalBMP,butmustmeetthe
flow control performance standard in Element #3' bullet #l'
. Locate BMPs intended to trap sediment on-site in a manner to
avoidinterferencewiththemovementofjuvenilesalmonids
attempting to enter off-channel areas or drainages'
. where feasible, design outlet slructures that withdraw inrpounded
storntlater from the surface to avoid discharging sediment that is
still suspended lower in the water column'
Vohtme I - Minimum Technical Requirements - August 2012
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Element 6: Stabilize Soi/s
' stabirize exposed and unworked soirs by apprication of effectiveBMps that prevent erosion. Appricabre gMis include, but ,r" notlimited to: temporary and permanent seeding, sodding, mulching,plastic covering, erosion contror fabrics and iiatring, ioit
-
application of poryacryramide (pAlvf), the earry appiicatio, ofgravel base early on areas to be paved, and dust coitrot.
r control stormwater volume and verocity within the site tominimize soil erosion.
r contror stormwater discharges, including both peak flow ratesand total stormwater volume, to minimizi erosion at outlets and tominimize downstream channel and stream bank erosion.
. Soils must not remain exposed and unworked for more than thetime periods set forth below to prevent erosion:
r During the dry season (May 1 _ Sept. 30): 7 days
o During the wet season (October I _ April 30): 2 days
r Stabilize soirs at the end of the shift before a horiday or weekend ifneeded based on tbe weather forecast.
o Stabilize soil stockpiles from erosion, protected with sedimenttrapping measures, and where possible, be located aw"y frrmstorm drain inlets, waterways and drainage channels. "
o Minimize the amount of soir exposed during construction activity.
o Minimize the disturbance of steep slopes.
r Minimize soir compaction and, unress infeasibre, preserve topsoir.
Element 6: Protect S/opes
. Design and construct cut-and-filr sropes in a manner to minimize
erosion. Appricabre practices incrudg but are not timited to,reducing continuous rength of srope with terracing and rliversions,reducing slope steepness, and roughening slope srirfac"s tfor-example, track walking).
' Divert off-site stormrvater (run'on) or,grouud water away from
slopes and disturbed areas with interceptor dikes, pip"r *olo,
swales. off-site stormwater shourd be managed ,.pairt.ry iro,nstormwater generated on the site.
. At the top of slopes, collect drainage in pipe slope drains orprotected channels to prevent erosion.
. Temporary pipe slope drains must handle the peak l0-minutevelocity offlow from a Type 1A, l0_year,24_hour frequer"y
Yolume I - Minimum Technical Requirements _ Augtut 201 2
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storm for the developed condition' Alternatively' the l0-year
and 1-hour flow rate predicted by an approved continuous
runoff model, increased by a factor of 1'6, may be used' The
hydrologicanalysismustusetheexistinglandcovercondition
for predicting flow rates from tributary areas outside the
project limits- For tributary areas on the project site' the
anaiysis must use the temporary or permanent proiect land
cover condition, whichever will produce the highest flow rates.
IfusingtheWesternWashingtonHydrologyModel(w}vIIM)
to predlct flows, bare soil areas should be modeled as
ttlandscaPed" area-
. Place excavated material on the uphill side of trenches, consistent
with safety and space considerations'
. Place check dams at regular intervals within constructed channels
that are cut down a sloPe.
ElementT: Protect Drain lnlets
protect all storm drain inlets made operatrle during construction
so that stormwater runoffshall not enter the conveyance system
without first being filtered or treated to remove sediment'
Clean or remove and reptace inlet protection devices when
sediment has filted one-third of the available storage (unless a
different standard is specified by the product manufacturer).
Element 8: Stabitize Channels and Outlets
. Design, construct, and stabilize all on-site conveyance channels.to
prevent erosion from the following expected peak flows:
. Channels must handle the peak 10-minute velocity of flow
from a Type lA, 10- yeer,24-hour frequency storm for the
developed condition. Alternatively, the 10-year, l-hour flow
rate indicated by an approved continuous runoff model,
increased by a factor of 1.5, may be used' The hydrologic
analysis must use the existing land cover condition for
pr.di.ting flow rates from tributary arees outside the project
ii-it.. For tributary areas on the project site, the analysis must
use the temporary or permanent project land cover condition,
whichever will produce the highest flow rates' If using the
Western Washington Hydrology Model (WWHM) to predict
flows, bare soil areas should be modeled as "landscaped area.
Provide stabilization, including armoring material, adequate to
prevent erosion ofoutlets, adjacent stream banks, slopes and
downstream reaches at the outlets of all conveyance systems.
Volunte I - Minimum Technical Requiremenls - August 2012
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Element 9: Control Pollutants
' Designr install, implement and maintain effective poilution
prevention measures to minimize the discharge of pollutants.
. Irandle and dispose of ail poilutants, incruding waste materiars
and demolition debris that occur on-site in a manner that does not
cause contamination of stormwater.
' Provide cov€r, containment, and protection from vandarism for arlchemicals, liquid products, petroleum products, and other
materials that have the potential to pose a threat to human healthor the environment.on-site fuering tanks must incrude secondary
containment. Secondary containment means placing tanla orcontainers within an impervious structure capabre of containing
1107o of the volume contained in the largest take rvithin thecontainment structure- Doubre-wailed tanks do not require
additional secondary containment.
. Conduct maintenance, fueling, and repair of heavy equipment and
vehicles using spill prevention and control -"rru.o. 'Ct"rn
contaminated surfaces immediatery fo[owing any spilr incident.
. Discharge whoer wash or tire bath wastewater to a separate on-sitetreatment system that prevents discharge to surface water, such asclosed-loop recirculation or upland application, or to the sanitary
sewer, with local sewer district approval.
' Appty fertilizers and pesticides in a manner and at apprication
rates that will not result in loss of chemical to stormwater runoff.Follow manufacturers' raber requirements for apprication rates
and procedures.
' use BMPs to prevent contamination of stormwater runoff by pHmodi$ing sources. The sources for this contamination inctudc, but
are nol limited to: bulk cement, cement kiln dust, fly ash, new
concrete washing and curing waters, waste streams generated
from concrete grinding ald sawing, exposed
"gg."g"'t" p.oa.rr"r,
dewatering concrete vaults, concrete pumping anA mir", wr*hrut
waters.
. Adjust the pH of stormwater if necessary to prevent violations ofwater quality standards.
. Assure that washout of concrete trucks is performed off-site or in
designated concrete washout areas only. Do.not wash out conci.t.
trucks onto the ground, or into storm drains, open ditches, streets,
or streams. Do not dump excess concrete on-site, except in
designated concrete washout areas. Concrete spillage or concrete
discharge to surface waters ofthe State is prohibited.
Volume I - Minimunr Technical Requirements - August 201 2
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r Obtain written apProval from Ecology before using chemical
treatment other than CO2 or dry ice to adjust pH'
Element 10: Control De-Watering
. Discharge foundation, vault, and trench de-watering water' which
has similar characteristics to stormwater runoff at the site, into a
controlled conveyance system before discharge to a sediment trap
or sediment Pond.
.Dischargeclean,non-turbidde-watering\uaterrsuchaswell-point
ground water, to systems tributary to, or directty into surface
iuters of the state, as specilied in Element #9, provided the de-
watering flow does not cause erosion or flooding of receiving
waters. Do not route clean dewatering water through stormwater
sediment ponds. Note that "surface waters of the State" may exist
on " "on,t.uction
site as well as offsitel for example, a creek
running through a site.
. Handle highly turbid or otherwise contaminated dewatering water
:,, septrrtelY from stormwater'
r Other treatment or disposal options may include:
1. Infiltration.
2, Transport off-site in a vehicle, such as a vacuum flush truck,
forlegaldisposalinamannerthatdoesnotpollutestate
waters.
3. Ecology-approved on-site chemical treatment or other suitable
treatment technologies.
4. sanitary or combined sewer discharge with local sewer district
approval, if there is no other option'
5. use of a sedimentation bag with outfall to a ditch or swale for
smalt volumes of localized dewatering'
Element 11: Maintain BMPs
. Maintain and repair all temporary and permanenl erosion and
sediment control BMPs as needed to assure continued
performance of their intended function in accordance with BMP
specifications.
. Remove all temporary erosion and sediment control BMPs within
30daysafterachievingfinalsitestabilizationorafterthe
temporary BMPs are no longer needed'
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Volume I - Minimum Technical Requirements _ Augutt 20lZ
Element 12: Manage The project
' Phase deveropment projects to the maximum degree practicabre
and take into account seasonal work limitations.
' Inspection and monitoring - rnspect, maintain ,and-repair a,BMPs as needed to assure continued performanc" of ih"irintended function. proiects regurated under the constructionstormwater Generar perrnit must conduct site inspections andmonitoring in accordance with Speciar condition sa ortr, ---
Construction Stormwater General permit.
' Maintaining an updated construction swppp - Maintain, update,and implement the SWPpp.
' Projects that disturb one or more acres must have site inspectionsconducted by a certified Brosion and Sediment controrieaJ(CESCL). project sites disturbing ress than one acre may have aCESCL or a person without CESCL certification condu.t
inspections- By the initiation of construction, the swppp mustidentify the GESCL or inspector, who must be present on*ite oron-call at all times.
' Th. cEscl- or inspector (project sites less than one acre) must havethe skills to assess the:
. site conditions and construction activities that courd impact thequality of stormwater.
' Effectiveness of erosion and sediment contol measures used tocontol the quality of stormwater discharges.
The GESCL or inspector must examine stormwater visuaily for thepresence of suspended sediment, furbidity, discoloration, and oil
--
sheen. They must evaluate the effectivenlss of BMps and determine ifit is necessary to install, maintain, or repair BMps to improve tr" -- "
quality of stormwater discharges.
Based on the resurts of the inspection, construction site operators mustcorrect the problems identified by:
' Reviewing the swppp for compriance with the r3 construction
SWPPP elements and making appropriate revisions *ithi;r;;;s
ofthe inspection.
. Immediately beginning the process of fully implementing and
maintaining appropriate soruce control and/or treatment BMps assoon as possible, addressing the probrems not Iater than within iodays of the inspection. If instailation of necessary treatment BMps
is not feasible within l0 days, the construction site op.ruto,,uy
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request an extension within the initiai l0-day response period.
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Volume l'- Minimum Technical Requirements - August 2012
_r
. Documenting BMP implementation and maintenance in the site log
book (sites larger than I acre)'
. The CESCL or inspector must inspect all areas disturbed by
"onrt*.tion
activiiies, all BMPs, ind all stormwaler discharge points
at least once eyery calendar week and within 24 hours ofany discharge
fromthesite.(Forpurposesofthiscondition,individualdischarge
events that last moie than one day do not require daily inspections' For
"*a*pI",
if a stormwater pond discharges continuously over thc course
of a we.k, only one inspection is required that week') The CESCL oT
inrp""to. may reduce the inspection frequency for temporary
Juilitir"a, inactive sites to once every calendar month'
Element 13: Protect Low tmpact Development BMPs
. Protect all Bioretention and Rain Garden BMPs from
sedimentation through installation and maintenance of erosion
and sediment control BMPs on portions of the site that drain into
the Bioretention and/or Rain Garden BMPs' Restore the BMPs to
their fully functioning condition if they accumulate sediment
' during construction. Restoring the BMP must include removal of
sedimint and any sedimentJaden Bioretention/rain garden soils,
,oa replacing thl removed soils with soils meeting the design
specification.
. Prevent compacting Bioretention and rain garden BMPs by
excluding construciion equipment and foot traffic' Protect
completed lawn and landscaped areas from compaction due to
construction equiPment'
. control erosion and avoid introducing sediment from surrounding
land uses onto permeable pavements' Do not allow muddy
construction equipment 'n th" base material or pavement' Do not
allow sediment-laten runoff onto permeable pavements or base
materials.
. Pavement fouled with sediments or no longer passing an initial
infiltration test must be cleaned using procedures in accordance
with this manuat or the manufacturer's procedures'
. Keep all heavy equipment offexisting soils under LID fa-cilities
that have b.", eic"v"ted to final grade to retain the infiltration
rate of the soils'
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Objective
To contror erosion and prevent scdiment and other porutanrs from reavingthe site during the construction- phase of a projecr. t, r,"* n [y funcrionatstormwater facilities and BMp's for the developed site upon
"Jr'pt.tion orconstruction.
S up p le me ntal G ui de lines
If a construction S\[?pp is found to be inadequate (with respecr toerosion and sediment control-requirements), then the pfun approrufAuthorityr within the Locar covernment stroua require thal other BMpsbe implemented, as appropriate.
The Plan Approval Authority may allow development of generic
construction SWppp's that appry to commonry'"onductei priii. *"aactivities, such as road surface replacement, that trigger tr,is minimu.requirement. They may also develop an abbreviat"Jlwppp r"*.ir",project sites that will disturb less than I acre.
Based on the information provicred andror locar wealher conditions, thelocal permitting a*thority may expand or restrict the seasonar ri*i,ution onsite disturbance. The rocal_permining authority shar take "nfo..rr"ntaction - such as a notice of violation, adminishative order, p"""lt;;;stop-work order under the following circumslances:
r If, during the course of any construction activity or soil disturbance
during rhe seasonar limitation period, sediment leaves tt e consiructionsite causing a violation of the surface water quality standard; or. If clearing and grading limits or erosion and sediment control
measures shown in the approved plan are not maintained.
coordination with Utilities and other contractors - The primary projecrproponent shall evaluate, with input from utilities and otirer.;;;i;;r,
the stormwater management requirements for the entire pr";rr,,l'".r"ir.g
the utilities, when preparing the Construction Swppp.
Erement #13, protect Low Impact Deveropment BMps, is not yet incrudedas a permit condition in the NpDES construction Stormwater'c.o".ui
Pennit. That permit is not schedured for reissuance untir Decemb.r, ior s.until that permit is reissued with erement #r3 added u, u p*rrii.ona-i,inn,
the element may be enforceabre onry through the requiremenr, oi-r*uistormwater codes thar may have been updated to inciude it. Municipal
Stormwater Permittees must incorporati this erement into rocal
requirements per the timelines in their Municipal stormwater permit.
' The Plan Approval Authority is defined as that department within a local government that has been delegatedauthority to approve stormwater site plans.
Volume I _ Minimum T'echnical Requirements _ August 2012
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2,5.3 Minimum Requirement #3: Source Gontrol of Pollution
All known, available and reasonable source control BMPs must be
"ppiita
to all projects. Source control BMPs must be selected'
aliign"a, and-maintained according to this manual'
Obiective
The intent of source control BMPs is to prevent stormwater fiom coming
ln""*"'.withpollutants.Theyareacost-effectivemeansofreducing
poif**o in stormwater, and, therefore, should be a first consideration in
all projects.
S upplemental Guidelines
An adopted and implemented basin plan or a Total Maximum Daily Load
iiil;i, also known as a Water Clean-up Plan) may be used to develop
morestringentsourcecontrolrequirementsthataretailoredtoaspecific
basin.
SourceControlBMPsincludeoperationalBMPsandStructuralSource
co"t'orBMPs.SeeVolumelVfordesigndetailsoftheseBMPs.For
construction sites, see Volume lI, Chapter 4'
Structural source control BMPs should be identified in the stormwater site
pi* _a should.be shown on all applicable plans submitted for local
gor.*rn.nt review and aPProval'
2.5.4MinimumRequirement#4:PreservationofNatural
Drainage SYstems and Outfalls
Natural drainage patterns shall be maintained, and discharges from
it "
pro5ect site shalt occur at the natural location' to the maximum
".i,irr,
practicable. The manner by which runoff is discharged from
the project site must not cause a significant adverse impact to
Jo*ttr"r- receiving waters and downgradient properties' All
outfalls require energy dissipation'
Obiective
Topreserveandutilizenaturaldrainagesystemstothefullestextent
i".uur. of the multiple stormwater benefits these systems provide; and to
prevent erosion at and downstream ofthe discharge location'
S upp leme nt al G uideline s
creating new drainage patterns results in more site disturbance and more
p"i.r,i^'f for erosion and sedimentation during and after construction'
Lr"uting new discharge points can create significant stream channel
erosion problems as the ieceiving water body typically must adjust to the
nL* no*t. Diversions can cause greater impacts than would otherwise
occur by discharging runoffat the natural location'
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where no conveyance system exists at the adjacent downgradient properryline and the discharge was previously unconcentrated flow or significantry
lower concentrated flow, then measures must be taken to prevenl--
'
downgradient impacts. Drainage easements from downstream property
owrers may be needed and should be obtained prior to upprorutoi
engineering plans.
The following discharge requirement is recommended:
where no conveyance system exists at the abutting dovvnstream properry
line and the natural (existing) discharge is unconcenrrated, any runoff
concentrated by the proposed project must be discharged as follows:
a) lfthe 100-year peak discharge is less than or equal to 0.2 cfs (0.3 clsusing l5 minute time steps) under existing
"onditions and will re maln
less than or equal to 0.2 cfs under deveroped conditions, then the
concentrated runoffmay be discharged onto a rock pad or to any other
system that serves to disperse flows.
b) Ifthe 10O-year peak discharge is tess than or equal to 0.5 cfi (0.75 cfsusing r5 minute time steps) under existing conditions and will remain
less than or equal to 0.5 cfs under developed conditiors, then the
concentrated runoffmay be discharged through a dispersal hench or
other dispersal system, provided the appricant can demonstrate that
there will be no significant adverse impact to downhill propefties ordrainage systems.
c) Ifthe I00-year peak discharge is greater than 0.5 cfs for either existing
or developed conditions, or if a significant adverse impact to
downgradient properties or drainage systems is likely, then a
conveyance system must be provided to convey the concentrated
runoffacross the downstream properties to an acceptable discharge
point (i.e., an enclo-sed drainage system or open drainage feature ivhere
concentrated runoffcan be discharged without significint adverse
impact).
Stormwater control or treatment structures should not be located within
the expected 25-year water level erevations for salmonid-bearing *rr.
such areas may provide off-channer habitat for juvenile ,otronlo, ,rJ
salmonid fry. Designs for outfall systems to protect against adverse
impacts from concentrated runoffare included in volume v, chapter 4.
2.5.5 Minimum Requirement IFS: On-site Stormwater
Management
Projects shall employ on-site stormwater Management BIVlps in
accordance with the following projects thresholds, standards, and liststo iufiltrate, disperse, and retain stormwater runoffon-site to the
extent feasible without causing flooding or erosion impacts.
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Projects qualifying as flow control cxempt in accordance with Section
2.S-i of tbis chapter do not have to achieve the LID performance
illoarra, nor consider bioretention' rain gardens, permeable
,rr"u-*o,, and fult dispersion if using List #l or List #2' flowever'
Iio* ptoi".ts must implement BMP T5'13; BMPs T5'l0A' B' or C;
anit BMP T5.1lor T5.12, if feasible'
Proiect Thresholds
Projects triggering only Minimum Requirements #1 through #5 shall
either:
a. use on-site stormwater Management BMPs from List #l for all
surfaces within each type of surface in List #1; or
b.DemonstratecompliancewiththeLlDPerformanceStandard.
Projects selecting this option cannot use Rain Gardens' They may
choose to use Bioretention BMPs as described in chapter 7 of
Volume V to achieve the LID Performance Standard'
Projects triggering Minimum Requirements #1 through #9' must meet
the requirements in Tnble 2.5't'
Volume I - Minimum Technical Requirements - August 2012
/14
NOTE: This table refers to the urban Growth Area ([lGA) as designated under the
er"*ft Management Act (GMA) (Chapter 36'?0A RCw.) of the-State of
;;il;;;;;. iitU* P.rrittee is located in a county that is not subiect to planning
,"J"t ,fr. GMA' the city limits shall be used instead'
IableZ,s.lon.siteStormwaterManagementRequirementsforProiectsTriggering
Minimum Requirements #t - #9
RequirementProject TYPe and Location
Low lmpact Development Performance
Standard and BMP T5.13; or List #2
(applicant oPtion).
New development on any parcel inside the
UGA, or new develoPment outside the
UGA on a Parcel less than 5 acres
Low Impact Development Performance
Standard and BMP T5.13.New development outside the UGA on a
parcel of5 acres or larger
Redevelopment on any parcel insidelhe
UGA, o. iedevelopment outside the UGA
on a parcel less than 5 acres
Low Impact Development Performance
Standard and BMP T5.13; or List #2
(applicant option).
Low Impact Development Performance
Standard and BMP T5.13.RedeveloPment outside the UGA on a
parcel of5 acres or larger
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Low Impact Development performance Standord
stormwater discharges shalr match devetoped discharge durations topre-deveroped durations for therange of pre-developel air"iurg"rates from goh oI the 2-year peak flow rciarn of the 2-yea. p."n noro.Refer to thc standard Frow contror Requirement section in'ltini*u,Requirement #7 for information about the assignm"nt or tn. p".-developed condition. project sites that must arso meet mininrrim
requirement #7 - flow contror - must match flow durations b.i""n87o of the 2-year flow through the full50-year flow.
List #l: On-site Stormwater Management BMps for projects TrtggeringMinimum Requirements #l through #S
For each surface, consider the BMp's in the order listed for lbat typeof surface. Use the first BMp that is considered feasibre. No rtt..0r_site stormwater Mauagement BMp is necessary for that surface.Feasibility shall be determined by evaluation against:
l. Design criteria, rimitations, and infeasibirity criteria identified foreach BMP in this manuall and
2. competing Needs criteria listed in Chapter 5 of vorume v of thismanual.
Lawn and landscaped areas:
o Post-construction Soir euarity and Depth in accordance withBMP T5.13 in Chapter 5 of Volume V
Roofs:
l. Full Dispersion in accordance with BMp T5.30 in chapter 5 ofVolume V, or Downspout Full Infiltration Systems i, *.ord"n""with BMp r5.l0A in section 3.1.r in chapter 3 0f vorume III
2. Rain Gardens in accordance with BMp rs.r4 in Chapter s ofVolume V, or Bioretention in accordance with Chapter 7 ofvorume v. The rain garden or bioretention facirity must hive ,minimum horizontar projected surface area berow the overflowwhich is at least So/" oI the area draining to it.
3. Downspout Dispersion Systems in accordance with BMp 15.108in Section 3.1.2 in Chapter3 of Volume III
4. Perforated stub-out connections in accordance with BMp rs.r0cin Section 3.1.3 in Chapter 3 of Volume IfI
Other Hard Surfaces:
1. Full Dispersion in accordance with BMp 15.30 in Chapter 5 ofVolume V
Volume I - Minimum Technical Requirements - August 2012
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2. Pernreable pavementr in accordance with BMP T5'15 in Chaptcr 5
oiVoturn" V, or Rain Gardens in accordance with BMP T5'14 in
Cfraptcr 5 of Volume V, or Bioretention in accordance with
itr"p,"r ? of of Votume V. The rain garden or bioretention facility
n,rri nrr" a minimum horizontal projected surface area belorv the
overflow which is at least 57o of the area draining to it'
3. Sheet Flow Dispersion in accordance with BMP T5'12' or
ConcentratedFtowDispersioninaccordancewithBMl'>T5'11in
ChaPter 5 of Volume V.
Lisl #2: on-site stormwaler Management BMPs for Proiects Triggering
Minimum Requirements #l through #9
For each surface, consider tbe BMPs in the order listed for that type
oi.urt "*.
use the first BMP that is considered feasible. No other 0n-
.i," Srrr-rnater Management BMP is necessary for that surface.
Feasibility shatl be deterrnined by evaluation against:
1. Design criteria, limitations, and infeasibility criteria identified for
each BMP in this manuall and
2. competing Needs criteria listed in chapter 5 of volurne v of this
manual-
Lawn and laudscaPed areas:
o post-construction soil Quatity antl Depth in accordance with
BMP T5.13 in ChaPter 5 of Volume V'
Roofs:
l. Full Dispersion in accordance with BMP T5.30 in chapter 5 of
volume V, or Downspout Fult lnfiltration systems in accordance
withBMPT5.l0AinSection3.l.linChapter3ofVolumeIII
2. Bioretention (see chapter 7 of volume v) facilities that have a
minimum horizontally projected surface area below the overflow
whichisatleast5o/oofthetotalsurfaceareadrainingtoit.
3. Downspout Dispersion systems in accordance with BMP T5.10B
in Section 3.1.2 in Chapter 3 of Volume III
4. Perforated Stub-out connections in accordance with BMP T5.l0C
in Section 3.1.3 in Chapter 3 of Volume III
Other llard Surfaces:
1. Full Dispersion in accordance with BMP T5.30 in chapter 5 of
Volume V
, This is not a requirerrot to pave these surfaces. where pavement is proposed, it must be permeable to the extent
f.*iUt. untut, full dispcrsion is employed'
Yolume I - Minimum Technical Requirements - August 2012
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2. Permeable pavement' in accordance with BMp r5.15 in chapter 5of Volume V
3. Bioretention BMP's (see chapter z, vorume v of the sMluww)
that have e minimum horizontalry projected surface area berow
the overflow which is at least s%o of the total surface area draining
to it.
4. Sheet FIow Dispersion in accordance with BMp T5.12, or
concentrated FIow Dispersion in accordance with gMp ts.tt inChapter 5 of Volume V.
Objective
To use practices distributed across a development that reduce the amount
of disruption of the natural hydrologic characteristics of the site.
S upplemental Guideltnes
"Flooding or erosion impacts" include flooding of septic systems, crawl
spaces, living areas, outbuildings, etc.; increased ice or algal growth on
sidewalks/roadways; earth movement/settlement ; erosion and other
potential damage.
Recent research indicates that traditional development techniques in
residential, commercial, and industrial land development.urr" gros
disruption of the natural hydrologic cycle with severe impacts tJwater and
water-related natural res,ources. Based upon gross level applications of
continuous runoff modeling and assumptions conceming'minimum fl ows
needed to maintain beneficial uses. watersheds must ret;in the majority oftheir natural vegetation cover and soils, and developments must minimize
their disruption of the natural hydrologic cycle in oider to avoid
significant natural resource degradation in lowland streams.
The BMPs described in Section 3.1 of volume III, and section 5.3.1 ofvolume v are likely insufficient by themselves to prevent significant
hydrologic disruptions and impacts to streams and their natuial resources.
Therefore, locat govemments should look for opportunities to change their
local development codes to minimize impervious surfaces and retaii
native vegetation in all development situations. Most importantly, to
maintain the beneficial uses of our lowland freshwater tyrt"*, *il]
require land use planning that targets retention of a majority of a creek,s
watershed in its natural condition, and retains most of the benefits of
headwater areas, connected wetlands, riparian, and floodplain areas.
Volume I - Minimum Technical Requirements - August 2012
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BMP T5.30: Ful! Dispersion
Purpose and
DeJinition
Applications and
Limitolions
o
This BMP allows for "fully dispersing" runoff from impervious surfaces
and cleared areas of development sites that protect at least 65% of the site
(or a threshold discharge area on the site) in a forest or native condition.
. Rural single family residential developments should use these
dispersion BMPs wherever possible to minimize effective impervious
surface to less than l0% of the development site.
. Other types of development that retain 65% of the site (or a threshold
discharge area on the site) in a forested or native condition may also
use these BMPs to avoid triggering the flow control facility
requirement.
. The preserved area may be a previously cleared area that has been
replanted in accordance with native vegetation landscape
specifications described within this BMP.
. The preserved area should be situated to minimize the clearing of
existing forest cover, to maximize the preservation of wetlands
(though the wetland area and any streams and lakes do not count
tbward the 65Yo forest or native condition area), and to buffer stream
corridors.
. The preserved area should be placed in a separate tract or protected
through recorded easements fbr individual lots.
. The preserved area should be shown on all property maps and should
be clearly marked during clearing and construction on the site.
. All trees within the preserved area at the time of permit application
shall be relained, aside from approved timber harvest activities
regulated under WAC Title 222, except for Class IV General Forest
Practices that are conversions from timberland to other uses, and the
removal ofdangerous or diseased trees.
. The preserved area may be used for passive recreation and related
facilities, including pedestrian and bicycle trails, nature viewing areas,
fishing and camping areas, and other similar activities that do not
require permanent structures, provided that cleared areas and areas of
compacted soil associated with these areas and facilities do not exceed
eight percent ofthe preserved area.
. The preserved iuea may contain utilities and utility easements, but not
septic systems. Utilities are defined as potable and wastewater
underground piping, underground wiring, and power and telephone
poles.
Yolume Y - Runof '[r"",T:;:BMPs - December 20]4
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Minimum Design Requiremenls for Residenlial Proiects
Developments that preserve 65Yo of a site (or a threshold discharge area of
a site) in a forested or native condition, can disperse runofffrom the
developed portion ofthe site into the native vegetation area as long as the
developed areas draining to the native vegetation do not have impervious
areas that exceed l0% ofthe entire site.
Where a development has less lhal65oh of a site available to maintain or
create into a forested or native condition, that area may still be used for
full dispersion of a portion of the developed area. The ratio of thc native
vegetation area to the impervious area, which is dispersed into the native
vegetation, must not be less than 65 to 10. The lawn and landscaping areas
associated with the impervious areas may also be dispersed into the native
vegetation area. The lawn and landscaped arca must comply with BMP
T5.13. All design requirements listed also must be met.
The portion of the developed area which is not managed through full
dispersion can be considered a separate project site. lt must be evaluated
against the thresholds in Figures 2.2 and 2.3 of Volume l, whichever is
appropriate, to determine the applicable minimum requirements.
Additional impervious areas above the l0olo are allowed, but should not
drain to the native vegetation area, and are subject to the thresholds,
treatment and flow control requirements of this stormwater manual.
Within the context of this dispersion option, the impervious surfaces that
are over and above the l0% maximum can be routed into an appropriately
sized dry well or into an infiltration basin that meets the flow control
standard and does not overflow into the forested or native vegetation area.
Runoffmust be dispersed into the native area in accordance with one or
more of the dispersion devices, and in accordance with the design criteria
and limits for those devices, cited in this BMP. A native vegetation flow
path ofat least 100 feet in length (25 feet for sheet flow from a non-native
pervious surface) must be available along the flowpath that runoff would
follow upon discharge from a dispersion device cited in this BMP. The
native vegetated flowpath must meet all of the following criteria:
. The flow path must be over native vegetated surface
. The flow path must be on-site or in an off'-site tract or easement area
reserved for such dispersion
. The slope of the flowpath must be no steeper than l5% for any 2O-foot
reach of the flowpath. Slopes up to 33% are allowed where level
spreaders are located upstream ofthe dispersion area and at sites
where vegetation can be established.
. The flowpath must be located between the dispersion device and any
downstream drainage feature such as a pipe, ditch, stream, river, pond,
lake, or wetland.
Volume V - Runof Treatment BMPs - December 2014
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. The flowpaths for adjacent dispersion devices must be sufficiently
spaced to prevent overlap of flows in the flowpath areas.
For sites with on-site sewage disposal systems, the discharge of runoff
from dispersion devices must be located downslope of the primary and
reserve drainfield areas. This requirement may be waived by the
pennitting jurisdiction if site topography clearly prevents discharged flows
from intersecting the drainfield.
Dispersion devices are not allowed in critical area buffers or on slopes
steeper than20o/o. Dispersion devices proposed on slopes steeper than
l5o/o or within 50 feet of a geologically hazardous area CRCW
36.70A.030(5) must be approved by a geotechnical engineer or
engineering geologist.
The dispersion of runoff must not create flooding or erosion impacts.
. Roof l)ownspouts
Roof surfaces that comply with the Downspout Full Infiltration BMP
T5.l0A, are considered to be "fully infiltrated" (i.e., zero percent
effective imperviousness). AII other roof surfaces are considered to be
"fully dispersed" (i.e., at or approaching zero percent effective
imperviousness) only if they are within a threshold discharge area that
is or will be more than 65% forested (or native vegetative cover) and
less than l0% impervious (total), AND ifthey either: l) comply with
the Downspout Dispersion requirements of BMP T5. l0B, but with
vegetated flow paths of 100 feet or more through the native vegetation
preserved area; or 2) disperse the roof runoff along with the road
runoff in accordance with the roadway dispersion BMP section below.
. Driveway Dispersion
Driveway surfaces are considered to be "fully dispersed" if they are
within a threshold discharge area that is or will be more than 65%
forested (or native vegetative cover) and less than l0% impervious
(total), AND if they either: 1) comply with BMP 5.1 I for concentrated
flow and BMP T5. l2 for sheet flow- and have flow palhs of 100 feet
or more through native vegetation; or, 2) disperse driveway runoff
along with the road runoffin accordance with the roadway dispersion
BMP section below.
. Roadway Dispersion BMPs
Roadway surfaces are considered to be "fully dispersed" if they are
within a threshold discharge area that is or will be more than 65Yo
forested (or native vegetative cover) and less than l0% impervious
(otal), AND if they comply with the following dispersion
requirements:
Volume V - Runof Treatment BMPs - December 2014
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