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Drainage and Erosion 935100034
Stormwater Review for Cole Residence Page 1 of 3 Date: 2/15/2022 To: Amanda Hunt, DCD From: John Fleming PE, JCPW Project: Cole Residence (BLD2021-00466, Assessor Parcel # 935100034, 865 Thorndyke Rd, Port Ludlow, WA 98365) Subject: JCPW Stormwater Site Plan Review and Comments APPLICATION REVIEW A. Stormwater Management Unified Development Code Requirement(s): The Jefferson County Unified Development Code, Sections 18.30.060, Grading and excavation standards and 18.30.070, Stormwater Management Standards both set standards for erosion and sedimentation control and stormwater management. The code adopts the requirements set forth by the most current version of the Washington State Department of Ecology, Stormwater Management Manual for Western Washington (SWMMWW). The most current version is the 2019 SWMMWW. JCPW Findings: Jefferson County Department of Community Development (DCD) has requested that the Public Works Department review a stormwater plan and support documents prepared for the Cole residence by James Cole dated 10/11/2021 (small project certification), 10/12/2021 (site map), 10/23/2021 (stormwater calculation worksheet), and Mark Keller PE dated 11/30/2021 (stormwater site plan). The most recent stormwater site plan and soil log prepared by Mark Keller PE were dated 1/27/2022. The site is mapped as with a landslide hazard and a seismic hazard area. A geological / geotechnical report was performed on the site by Gary Flowers licensed geologist, and Robert Pride PE dated 9/19/2005. The 0.43 acres site is vacant with an existing driveway and septic system. The new development plan calls for a 26’ x 40’ house ((1,040 square feet building roof area) and a 24’ x 46’ permeable asphalt driveway (1,104 square feet). This is a small project, and is subject to meeting Minimum Requirements #1 and #2 of the 2019 SWMMWW. The site conditions were characterized by the septic design with three soil test pits, with the closest to the proposed stormwater improvements having fine sand texture, and mottles at 48”, logged by Nathan Cleaver, licensed onsite wastewater treatment system designer on 2/24/2005. In the area of the proposed stormwater improvements, one post hole was logged by Mark Keller PE on 1/3/2022 as loamy sand to 48”. Stormwater Review for Cole Residence Page 2 of 3 The Plan proposes to meet requirements of the 2019 SWMMWW by implementing a stormwater pollution prevention plan during construction consisting of the following Best Management Practices (BMP’s) - BMP C105 Stabilized Construction Entrance; - BMP C120 Temporary and Permanent Seeding; - BMP C121 Mulching; - BMP C 123 Plastic Covering; - BMP C233 Silt Fence; and a permanent stormwater system consisting of - BMP T5.10A Downspout Full Infiltration trenches (88 linear feet of 2 feet wide, 18” thick, no deeper than 3 feet from existing grade) under the driveway for the roof area; - BMP T5.13 Post-Construction Soil Quality and Depth in the landscaped areas; - BMP T5.15 Permeable Asphalt Pavement the driveway. The project includes clearing, grading and/or excavation that results in the disturbance of less than 1 acre. Per the application it appears as though discharge of stormwater to waters of the State (as defined by WA State Department of Ecology) may not occur. JCPW Recommendations: 1. The proponent shall install the stormwater management facilities and implement the Best Management Practices (BMP’s) consisting of BMP C105 Stabilized Construction Entrance, BMP C120 Temporary and Permanent Seeding, BMP C121 Mulching, BMP C 123 Plastic Covering, BMP C233 Silt Fence, BMP T5.10A Downspout Full Infiltration trenches (88 linear feet of 2 feet wide, 18” thick, no deeper than 3 feet from existing grade) under the driveway for the roof area, BMP T5.13 Post-Construction Soil Quality and Depth in the landscaped areas, BMP T5.15 Permeable Asphalt Pavement the driveway. Construction shall conform with the 2019 edition of the WA State Dept of Ecology Stormwater Management Manual for Western Washington, and the documents prepared for the Cole residence by James Cole dated 10/11/2021 (small project certification), 10/12/2021 (site map), 10/23/2021 (stormwater calculation worksheet), and Mark Keller PE dated 1/27/2022 (stormwater site plan). 2. Prior to commencing land disturbing activity, the proponent shall notify Jefferson County Public Works (JCPW) and arrange a Preconstruction Meeting. 3. Before any construction begins on-site, erosion control facilities shall be installed. 4. In accordance with the Jefferson County Unified Development Code, Section 18.30.080 (1) (f): Clearing, grading, and construction of roads, bridges, utilities, and stormwater management facilities shall be inspected by JCPW. In order to enable the department to conduct inspections in a timely manner, the applicant shall notify the department in a timely manner regarding the project construction schedule. Typical Inspections: • Installation of temporary erosion and sediment control measures; (Required) • Clearing (and Grading) and road subgrade preparation; • Placing roadway gravel base; • Placing roadway crushed surfacing top course; Stormwater Review for Cole Residence Page 3 of 3 • Placing improved roadway surface (chip seal or asphalt concrete); • Construction of stormwater management facilities; (Required) -Infiltration trenches’ excavation bottom before placing drainrock; (Required) -Preformance testing of Permeable Pavement; (Required) • Final plat review. • (Additional inspections may be deemed necessary as project progresses.) 5. After construction is complete and prior to final DCD project approval, the proponent shall submit a letter to the Department of Community Development, from the Engineer of Record (EOR), certifying that the stormwater management facilities have been constructed per the approved plans & specifications. It is the responsibility of the proponent to schedule inspections with the EOR, his designee &/or qualified inspection firm(s), approved by the EOR, to provide for said final certification. 6. To ensure that the approved stormwater management facilities are appropriately maintained for the life of the project, prior to final project approval, the proponent shall enter into a Stormwater Management Facility Maintenance Agreement with Jefferson County. The Department of Community Development (DCD) will send a copy of the Agreement to the proponent which has been signed by the DCD Director. The proponent shall sign the Agreement before a notary, file it with the Jefferson County Auditor, and provide DCD with a copy of the recorded document. County Auditor 2022 recording fees are $203.50 for the first page and $1 for each additional page. B. Public Works Department Fees Requirement: Unified Development Code Requirement(s): The Jefferson County Unified Development Code Chapter 18.30.080(1)(u) authorizes the Public Works Department to assess fees in accordance with the Jefferson County Fee Schedule Ordinance for development review activities including application and plan review, inspections, meetings, hearings, and final review. • Prior to DCD project approval, the proponent shall pay all costs related to the Department’s application review, plan review, inspections, and preparation of the Stormwater Management Facility Maintenance Agreement. In accordance with the Jefferson County Public Works Department Fee Schedule, the Department’s hourly development review fee is $90 for 2021 and $95 for 2022. In the event that approval for the proposal is denied by Jefferson County or the proposal is not completed, the proponent shall still be responsible for paying the Department’s fee. Cole Stormwater forms, 5 pages DEPARTMENT OF COMMUNITY DEVELOPMENT 観 E_moI ArЛ rr,再 を｀ハ 称 rJ、健 ♂.A……●s∞n the QR code to a∝ess he digitai fo阿 1亀 STORMVATER CALCULATION WORKSHEET DF『ERMBNINS STORMWATER MANAGEMENT REQUBREMENTS:ThiS StOrmwater caiculation WOrksheet shouid be completed arst to ciassify the propOSal as'SmaW,″'medtumD″ or ″iarse.The size determines whethe『a Stormwater site Pian iS required in Con,unction with a Stand・ aione stormwater management pernllt app∥catlon,bunding permit app∥Cation,or other iand use apprOVal applicatton that invoives storrlwater review. The basic tnformation will also be he,pfui fOr completing a StOrmwater Slte Pian,r requi とo"J・ J′StV′b′,9o■′V′り IS anV activlw that resul`in movement of earth,or a change in the existlng so∥coVer (bOth VeBetatiVe and non‐vegetatiVe〕and′Or the eXISting soli tOp08raphy.Land diSturbin8 actiVlties include,but are nOt∥mited to dearing,8rading,1∥inB excavation,and compactiOn associated with Stab∥|〓ation 。f structureS and『。ad const『uttion. Ⅳat′ve v=伊 =:α P′。Л iS Vesetation cOmprised of plant species,other than noXIOus weeds,which reasonabiv could have been expected to natura∥v ocCur on the site.ExampleS include species Such as Doustas lr,western hemi∝k,western red Cedar,BIder,bIB・ lear mDple,and vine ttlaplaこ れrubs SuCh as wi∥ow,elderberrv,Saimonberry,and salal,herbaceOus plants such as SWOrd fern,fOam f!ower,and areweed. PARCCは',ROた Ci′AP'阻 NFNAM■ヒOtちらヽ600 3Lt PARCEL S〕ZEl].E..SITEL An aCre contain3 43.560 square reet,Mu∥ply he acreage by this lou『o.1DT物 sqnS鯰 o Of parcelin square reet s屹 。Or paに el_旦 握__acres 鰯 聯 漫絲財航Answer the fol10胡 ng two quesUOnS relatt tO OOnverslon Of native vegetation: 潔 期 詠瑠協 監「総 呂解 濫s? clrdα Yos O Ч∬露解縦苫耐 ″ 生し3電,″ 」0(仏 _SqA しConSt『UdiOn Sib fo「StR:dureS TempOratt consmmon area Total Land DIsturbance other∞『npacted sura∞,etc, D由 ∪M〕y=pa『kin9,roads,etc. L―=landscapl町 .etc. sqh sqれ 叩R indicate To的 iV。〕umoS Of P『OpOSed: (inCtudes BMP T5,13 EJШ ム塾ЩШQ) c囃 _ 日∥Ч。仲叩〕 随hndi septicね 蔽,ec,0(臼ぜゝ均91 _ We∥t ut∥itiest etc。______ 歯 n"心t強 ―い0旧 OR競 ―Reu V3口 19 ""IJを Dec 01 2021 Worttheet S SmalI Pro,eCt Ce面 偶cadon This cettncatiOn mav oniv be used if you answer yesto a∥ofthe quesdons below(Cirde ves or no)。Otherwise,a submittal prepared by a licensed engineer rnav be required. no If!ocated in a Seawaterintrusion Prote《粛on Zone(S,PZ),'am able to inttltrate stormwater onsite using a dry‐ weli or other method(fu∥diSpersion,downspout dispersion)。 permanent and tempo『att drainage on site is designed to divert Stornlwater away f『om my onsite sepSc systenl or anv neighboring onsite septic system. no no My prttect w∥i nOt discharge stormwater runofFinto a c前 頓cal area゛ncluding but not hmited toi g∞hazard area orits 30,foot burer,weuand Or Fish and VVild“fe Habitat ConseⅣaSon Area) no My proposalis a smali proiect,WhiCh means k wilicreate tess than 2,000 square feet of new,replaced,or new plus replaced irnpeⅣious surface area,and hasiess than 7,000 square feet oftand disturbing activttes as denned On the Stormwater Calculadon Worksheet. :understand that my prO,ect muStCOmply with Minimum Requirement静 2 in the Depattment of Ecolo研 Stormwater Management Manualas amended.l have read the Construcdon Stormwater Pollution PrevenSon Fact Sheet and w∥lirnplement Best Manage‐ ment prattices(BMP'S,aS apphcable to my proieCt・ i〔萬田玉盈H『ATlVE SIGttAIURE〕l tDATEⅢfiANDOWHER OR無 ,THOR12ED By signing the sma∥ of mv knowiedge. l as the applicant/owner attestthat the informadon projded herein is true and correctto the best ,ο //r/±99 Apphcant Signature Dec 01 2021 Cole stormwater plans, 4 pages Cole stormwater site plan, 1 pageFeb 15 2022 Cole stormwater soil log, 1 page Cole soil log from septic permit, 3 pages Cole geotechnical report, 8 pages V-4 Roof Downspout BMPs V-4.1 Introduction to Roof Downspout BMPs Roof downspout BMPs are simple pre-engineered designs for infiltrating and/or dispersing runoff from roof areas for the purposes of increasing opportunities for ground water recharge and reduc- tion of runoff volumes from development. Roof downspout BMPs include infiltration trenches, dry wells, and partial dispersion systems for use in individual lots, proposed plats, and short plats. Roof downspout BMPs are used in conjunction with, and in addition to, any Flow Control BMPs that may be necessary. They are included in the list of BMPs to consider if using the List Approach for compliance with I-3.4.5 MR5: On-Site Stormwater Management. How to Select Roof Downspout BMPs Large lots in rural areas (5 acres or greater) typically have enough area to disperse or infiltrate roof runoff. Lots created in urban areas will typically be smaller (about 8,000 square feet) and have a lim- ited amount of area in which to site infiltration or dispersion trenches. BMP T5.10A: Downspout Full Infiltration should be used in those soils that readily infiltrate. BMP T5.10B: Downspout Dispersion Systems should be used for urban lots located in less permeable soils, where infiltration is not feas- ible. Where BMP T5.10B: Downspout Dispersion Systems is not feasible because of very small lot size, or where there is a potential for creating drainage problems on adjacent lots, use BMP T5.10C: Perforated Stub-out Connections to connect downspouts with perforated stub-out connections to the street drainage system, which directs the runoff to a stormwater management facility. Where supported by appropriate soil infiltration tests, downspout full infiltration in finer soils may be practical using a larger infiltration system. Roof downspout BMPs can be applied to individual commercial lot developments when the percent impervious area and pollutant characteristics are comparable to those from residential lots. Note: Other innovative downspout control BMPs such as rain barrels, ornamental ponds, down- spout cisterns, or other downspout water storage devices may be used to supplement any of the BMPs in this chapter if approved by the reviewing authority. BMP T5.10A: Downspout Full Infiltration 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. Roof surfaces that comply with this BMP are considered to be "fully infiltrated" (i.e., zero percent effective imperviousness). 2019 Stormwater Management Manual for Western Washington Volume V -Chapter 4 -Page 705 Cole stormwater BMP T5.10A, 5 pages 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: l A professional soil scientist certified by the Soil Science Society of America (or an equi- valent national program) l A locally licensed on-site sewage designer l A suitably trained person working under the supervision of a professional engineer, geo- logist, 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 project 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. Complete additional site-specific testing on lots or sites containing outwash (coarse sand and cobbles to medium sand) and loam type soils. Individual 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. Identify 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. 3. Downspout full infiltration is considered feasible on lots or sites that meet all of the following: l 3 feet or more of permeable soil from the proposed final grade to the seasonal high ground water table. l 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. l The downspout full infiltration system can be designed to meet the minimum design cri- teria specified below. Setbacks Local governments may require specific setbacks in sites with slopes over 40%, 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 infiltration systems should be at least 10 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 set- back may be reduced to 15 feet based on a geotechnical evaluation, but in no instances may it 2019 Stormwater Management Manual for Western Washington Volume V -Chapter 4 -Page 706 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. Design Criteria Infiltration Trenches Figure V-4.1: Typical Downspout Infiltration Trench shows a typical downspout infiltration trench sys- tem, and Figure V-4.2: Alternative Downspout Infiltration 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. 1. The following minimum lengths (linear feet) per 1,000 square feet of roof area based on soil type may be used for sizing downspout infiltration trenches: o Coarse sands and cobbles: 20 LF o Medium sand: 30 LF o Fine sand, loamy sand: 75 LF o Sandy loam: 125 LF o Loam: 190 LF 2. Silt and clay type soils have a saturated hydraulic conductivity that is too small for adequate infiltration and are infeasible for downspout infiltration trenches. 3. The maximum length of the trench shall not exceed 100 feet from the inlet sump. 4. The minimum spacing between trench centerlines shall be 6 feet. 5. Filter fabric shall be placed over the drain rock as shown on Figure V-4.1: Typical Downspout Infiltration Trench prior to backfilling. 6. Infiltration trenches may be placed in fill material if: o the fill is placed and compacted under the direct supervision of a geotechnical engineer or professional civil engineer with geotechnical expertise, and o 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. Infiltration rates can be tested using the methods described in V-5.4 Determining the Design Infiltration Rate of the Native Soils. 7. Infiltration trenches should not be built on slopes steeper than 25% (4:1). A geotechnical ana- lysis and report may be required on slopes over 15%, or if the proposed trench is located within 200 feet of the top of a slope steeper than 40%, or in a landslide hazard area. 8. Infiltration trenches may be located under pavement if a small yard drain or catch basin with grate cover is placed at the end of the trench pipe such that overflow would occur out of the 2019 Stormwater Management Manual for Western Washington Volume V -Chapter 4 -Page 707 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 down- hill properties or drainage systems. This is intended to prevent saturation of the pavement in the event of system failure. 2019 Stormwater Management Manual for Western Washington Volume V -Chapter 4 -Page 708 Figure V-4.1: Typical Downspout Infiltration Trench 2019 Stormwater Management Manual for Western Washington Volume V -Chapter 4 -Page 709 BMP T5.15: Permeable Pavements Purpose and Definition Ecology accepts Permeable Pavement as having the potential to meet I-3.4.5 MR5: On-Site Storm- water Management, I-3.4.6 MR6: Runoff Treatment and I-3.4.7 MR7: Flow Control for the tributary drainage areas depending upon site conditions, configuration, and sizing. Pavement for vehicular and pedestrian travel occupies roughly twice the space of buildings. Storm- water from vehicular pavement can contain significant levels of solids, heavy metals, and hydro- carbon pollutants. Both pedestrian and vehicular pavements also contribute to increased peak flow durations and associated physical habitat degradation of streams and wetlands. Optimum man- agement of stormwater quality and quantity from paved surfaces is, therefore, critical for improving fresh and marine water conditions in Puget Sound. The general categories of permeable paving systems include: l Porous hot or warm-mix asphalt pavement (see Figure V-5.1: Example of a Permeable Pavement (Concrete or Asphalt) Section) is a flexible pavement similar to standard asphalt that uses a bituminous binder to adhere aggregate together. However, the fine material (sand and finer) is reduced or eliminated and, as a result, voids form between the aggregate in the pavement surface and allow water to infiltrate. l Pervious Portland cement concrete (see Figure V-5.1: Example of a Permeable Pave- ment (Concrete or Asphalt) Section) is a rigid pavement similar to conventional concrete that uses a cementitious material to bind aggregate together. However, the fine aggregate (sand) component is reduced or eliminated in the gradation and, as a result, voids form between the aggregate in the pavement surface and allow water to infiltrate. l Permeable interlocking concrete pavements (PICP) and aggregate pavers. (see Fig- ure V-5.2: Example of a Permeable Paver Section) PICPs are solid, precast, manufactured modular units. The solid pavers are (impervious) high-strength Portland cement concrete man- ufactured with specialized production equipment. Pavements constructed with these units cre- ate joints that are filled with permeable aggregates and installed on an open-graded aggregate bedding course. Aggregate pavers (sometime called pervious pavers) are a dif- ferent class of pavers from PICP. These include modular precast paving units made with sim- ilar sized aggregates bound together with Portland cement concrete with high-strength epoxy or other adhesives. Like PICP, the joints or openings in the units are filled with open-graded aggregate and placed on an open-graded aggregate bedding course. Aggregate pavers are intended for pedestrian use only. l Grid systems include those made of concrete or plastic. Concrete units are precast in a man- ufacturing facility, packaged and shipped to the site for installation. Plastic grids typically are delivered to the site in rolls or sections. The openings in both grid types are filled with topsoil and grass or permeable aggregate. Plastic grid sections connect together and are pinned into a dense-graded base, or are eventually held in place by the grass root structure. Both systems can be installed on an open-graded aggregate base as well as a dense-graded aggregate base. 2019 Stormwater Management Manual for Western Washington Volume V -Chapter 5 -Page 745 Cole stormwater BMP T5.15, 16 pages Figure V-5.1: Example of a Permeable Pavement (Concrete or Asphalt) Section 2019 Stormwater Management Manual for Western Washington Volume V -Chapter 5 -Page 746 Figure V-5.2: Example of a Permeable Paver Section 2019 Stormwater Management Manual for Western Washington Volume V -Chapter 5 -Page 747 Applications and Limitations Permeable pavements are an important integrated management practice within the LID approach and can be designed to accommodate pedestrian, bicycle and auto traffic while allowing Runoff Treatment and Flow Control of stormwater. Permeable pavements are appropriate in many applications where traditionally impermeable pave- ments have been used. Typical applications for permeable pavements include parking lots, side- walks, pedestrian and bike trails, driveways, residential access roads, and emergency and facility maintenance roads. Limitations to permeable pavements include: l No run-on from pervious surfaces is preferred. If runoff comes from minor or incidental per- vious areas, those areas must be fully stabilized. l Unless the pavement, base course, and subgrade have been designed to accept runoff from adjacent impervious surfaces, slope impervious runoff away from the permeable pavement to the maximum extent practicable. Sheet flow from up-gradient impervious areas is not recom- mended, but permissible if the permeable pavement area is > the impervious pavement area. l Soils must not be tracked onto the wear layer or the base course during construction. Infeasibility Criteria The following infeasibility criteria describe conditions that make permeable pavement infeasible when applying The List Approach within I-3.4.5 MR5: On-Site Stormwater Management. If a project proponent wishes to use a permeable pavement BMP even though one of the infeasibility criteria within this section are met, they may propose a functional design to the local government. These criteria also apply to impervious pavements that would employ stormwater collection from the surface of impervious pavement with redistribution below the pavement. Any of the following circumstances allow the designer to determine permeable pavement as "infeas- ible" when applying the The List Approach within I-3.4.5 MR5: On-Site Stormwater Management: l Citation of any of the following infeasibility criteria must be based on an evaluation of site-spe- cific conditions and a written recommendation from an appropriate licensed professional (e.g, engineer, geologist, hydrogeologist) o Where professional geotechnical evaluation recommends infiltration not be used due to reasonable concerns about erosion, slope failure, or down gradient flooding. o Within an area whose ground water drains into an erosion hazard, or landslide hazard area. o Where infiltrating and ponded water below new permeable pavement area would com- promise adjacent impervious pavements. o Where infiltrating water below a new permeable pavement area would threaten exist- ing below grade basements. 2019 Stormwater Management Manual for Western Washington Volume V -Chapter 5 -Page 748 o Where infiltrating water would threaten shoreline structures such as bulkheads. o Down slope of steep, erosion prone areas that are likely to deliver sediment. o Where fill soils are used that can become unstable when saturated. o On excessively steep slopes where water within the aggregate base layer or at the sub- grade surface cannot be controlled by detention structures and may cause erosion and structural failure, or where surface runoff velocities may preclude adequate infiltration at the pavement surface. o Where permeable pavements can not provide sufficient strength to support heavy loads at industrial facilities such as ports. o Where installation of permeable pavement would threaten the safety or reliability of pre- existing underground utilities, pre-existing underground storage tanks, or pre-existing road sub-grades. l The following infeasibility criteria are based on conditions such as topography and distances to predetermined boundaries. Citation of the following criteria do not need site-specific written recommendations from a licensed professional, although some may require professional ser- vices to determine: o Within an area designated as an erosion hazard, or landslide hazard. o Within 50 feet from the top of slopes that are greater than 20%. o For properties with known soil or ground water contamination (typically federal Super- fund sites or state cleanup sites under the Model Toxics Control Act (MTCA)): n Within 100 feet of an area known to have deep soil contamination; n Where ground water modeling indicates infiltration will likely increase or change the direction of the migration of pollutants in the ground water; n Wherever surface soils have been found to be contaminated unless those soils are removed within 10 horizontal feet from the infiltration area; n Any area where these facilities are prohibited by an approved cleanup plan under the state Model Toxics Control Act or Federal Superfund Law, or an envir- onmental covenant under Chapter 64.70 RCW. o Within 100 feet of a closed or active landfill. o Within 100 feet of a drinking water well, or a spring used for drinking water supply, if the permeable pavement is (or has run-on from) a pollution-generating hard surface. o Within 10 feet of a small on-site sewage disposal drainfield, including reserve areas, and grey water reuse systems. For setbacks from a “large on-site sewage disposal sys- tem”, see Chapter 246-272B WAC. o Within 10 feet of any underground storage tank and connecting underground pipes, regardless of tank size. As used in these criteria, an underground storage tank means any tank used to store petroleum products, chemicals, or liquid hazardous wastes of 2019 Stormwater Management Manual for Western Washington Volume V -Chapter 5 -Page 749 which 10% or more of the storage volume (including volume in the connecting piping system) is beneath the ground surface. o At multi-level parking garages, and over culverts and bridges. o Where the site design cannot avoid putting pavement in areas likely to have long-term excessive sediment deposition after construction (e.g., construction and landscaping material yards). o Where the subgrade slope exceeds 6 percent after reasonable efforts to grade. Where the permeable pavement wearing course slope exceeds 6 percent after reasonable efforts to design grade. o Where the native soils below a pollution-generating permeable pavement (e.g., road or parking lot) do not meet the criteria for Runoff Treatment in V-5.6 Site Suitability Cri- teria (SSC), or do not have adequate separation to ground water (or other imper- meable surface). If the local jurisdiction wishes to allow permeable pavement in areas where the native soils do not meet the site suitability criteria, installation of a 6" layer of sand that meets the size gradation (by weight) given in Table V-6.1: Sand Medium Spe- cification can be used to provide treatment. o Where seasonal high ground water or an underlying impermeable/low permeable layer would create saturated conditions within one foot of the bottom of the permeable pave- ment BMP. The bottom of the permable pavement BMP is the bottom of the lowest layer that has been designed to be part of the BMP, such as the lowest gravel base course or a sand layer used for treatment below the permeable pavement. o Where underlying soils are unsuitable for supporting traffic loads when saturated. Soils meeting a California Bearing Ratio of 5% are considered suitable for residential access roads. o Where appropriate field testing indicates soils have a measured (a.k.a., initial) native soil saturated hydraulic conductivity (Ksat) less than 0.3 inches per hour. See V-5.4 Determining the Design Infiltration Rate of the Native Soils. (Note: In these instances, unless other infeasibility restrictions apply, roads and parking lots may be built with an underdrain, preferably elevated within the base course, if Flow Control benefits are desired.) o Roads that receive more than very low traffic volumes. Roads with a projected average daily traffic volume of 400 vehicles or less are very low volume roads (AASHTO, 2001), (USDOT, 2013). Note: This infeasibility criterion does not extend to sidewalks and other non-traffic bearing surfaces. o Areas having more than very low truck traffic. Areas with very low truck traffic volumes are roads and other areas not subject to through truck traffic but may receive up to weekly use by utility trucks (e.g., garbage, recycling), daily school bus use, and multiple daily use by pick-up trucks, mail/parcel delivery trucks, and maintenance vehicles. Note: This infeasibility criterion does not extend to sidewalks and other non-traffic bearing sur- faces. o Where replacing existing impervious surfaces, unless the existing surface is a non- 2019 Stormwater Management Manual for Western Washington Volume V -Chapter 5 -Page 750 pollution generating surface over an outwash soil with a measured (initial) saturated hydraulic conductivity (Ksat) of four inches per hour or greater. o At sites that whose land use requires oil control BMPs per III-1.2 Choosing Your Runoff Treatment BMPs. o In areas with “industrial activity” as identified in 40 CFR 122.26(b)(14). o Where the risk of concentrated pollutant spills is more likely such as gas stations, truck stops, and industrial chemical storage sites. o Where routine, heavy applications of sand occur in frequent snow zones to maintain traction during weeks of snow and ice accumulation. l A local government may designate geographic areas within which permeable pavement, or certain types of permeable pavement, may be designated as infeasible due to year-round, sea- sonal or periodic high groundwater conditions, or due to inadequate infiltration rates. Desig- nations must be based upon a preponderance of field data, collected within the area of concern, that indicate a high likelihood of failure to achieve the minimum groundwater clear- ance or infiltration rates identified in the above infeasibility criteria. The local government must develop a technical report, and make it available upon request to Ecology. The technical report must be authored by (a) professional(s) with appropriate expertise (e.g., registered engineer, geologist, hydrogeologist, or certified soil scientist), and document the location and pertinent values/observations of data that were used to recommend the designation and boundaries for the geographic area. The types of pertinent data include, but are not limited to: o Standing water heights or evidence of recent saturated conditions in observation wells, test pits, test holes, and well logs. o Observations of areal extent and time of surface ponding, including local government or professional observations of high water tables, frequent or long durations of standing water, springs, wetlands, and/or frequent flooding. o Results of infiltration tests l In addition, a local government can map areas that meet a specific infeasibility criterion listed above provided they have an adequate data basis. Criteria that are most amenable to map- ping are: o Where land for permeable pavement is within an area designated by the local gov- ernment as an erosion hazard, or landslide hazard o Within 50 feet from the top of slopes that are greater than 20% and over 10 feet vertical relief o Within 100 feet of a closed or active landfill 2019 Stormwater Management Manual for Western Washington Volume V -Chapter 5 -Page 751 Design Criteria General Design Criteria l Ecology has listed below the critical design criteria you must consider when designing per- meable pavement. Local governments can adopt alternative design criteria, as long as it does not conflict with the criteria listed below. l You can find additional guidance for permeable pavement design in the Low Impact Devel- opment Technical Guidance Manual for Puget Sound (Hinman and Wulkan, 2012). Note that the Low Impact Development Technical Guidance Manual for Puget Sound (Hin- man and Wulkan, 2012) is for additional informational purposes only. You must follow the guid- ance within this manual if there are any discrepancies between this manual and the Low Impact Development Technical Guidance Manual for Puget Sound (Hinman and Wulkan, 2012). l Project submission requirements: Submit results of infiltration (Ksat) testing, ground water elevation testing (or other documentation and justification for the rates and hydraulic restric- tion layer clearances) with the Stormwater Site Plan as justification for the feasibility decision regarding permeable pavement, and as justification for assumptions made in the runoff mod- eling. If necessary, also submit documentation of meeting the criteria for Runoff Treatment in V-5.6 Site Suitability Criteria (SSC). l Legal documentation to track permeable pavement obligations: Where drainage plan sub- mittals include assumptions in regard to size and location of permeable pavement, approval of the plat or short-plat should identify the permeable pavement obligation of each lot; and the appropriate lots should have deed requirements for construction and maintenance of those BMPs. Permeable Pavement as Runoff Treatment Ecology recognizes the permeable pavement BMP as a basic treatment BMP (as further described in III-1.2 Choosing Your Runoff Treatment BMPs) if it meets either of the following criteria: l The native soils below the permeable pavement meet the criteria for Runoff Treatment per V- 5.6 Site Suitability Criteria (SSC). OR l The permeable pavement design includes a 6" layer of sand that meets the size gradation (by weight) given in Table V-6.1: Sand Medium Specification. Subgrade l Compact the subgrade to the minimum compaction necessary for structural stability. Two guidelines currently used to specify subgrade compaction are “firm and unyielding” (qual- itative), and 90- 92% Standard Proctor (quantitative). Subgrade should not be subject to com- paction beyond the qualitative and quantitative levels identified herein. Do not allow 2019 Stormwater Management Manual for Western Washington Volume V -Chapter 5 -Page 752 construction traffic and equipment onto the subgrade except when construction access on sub- grade is required for the pavement section installation. Follow back dumping approach as noted below. l To prevent compaction when installing the aggregate base, the following steps (back-dump- ing) should be followed: 1) the aggregate base is dumped onto the subgrade from the edge of the installation and aggregate is then pushed out onto the subgrade; 2) trucks then dump sub- sequent loads from on top of the aggregate base as the installation progresses. l Use on soil types A through C. Separation or Bottom Filter Layer (recommended but optional) l A layer of sand or crushed stone (0.5 inch or smaller) graded flat is recommended to promote infiltration across the surface, stabilize the base layer, protect underlying soil from compaction, and serve as a transition between the base course and the underlying geotextile material. Base Material l Local governments should adopt their own minimum base material requirements as they see necessary for support of flexible pavements. Many design combinations are possible. The material must be free draining. The municipality should determine and publish estimates of the void space for each standard base material allowed in their jurisdiction. l To increase infiltration, improve flow attenuation and reduce structural problems associated with subgrade erosion on slopes, impermeable check dams may be placed on the subgrade and below the permeable pavement surface (See Figure V-5.3: Example of a Check Dam Along a Sloped Section of Permeable Pavement). Check dams should have an overflow drain invert placed at the maximum ponding depth. The distance between berms will vary depend- ing on slope, Flow Control goals and cost. 2019 Stormwater Management Manual for Western Washington Volume V -Chapter 5 -Page 753 Figure V-5.3: Example of a Check Dam Along a Sloped Section of Permeable Pavement 2019 Stormwater Management Manual for Western Washington Volume V -Chapter 5 -Page 754 Wearing Layer l For all surface types, a minimum initial infiltration rate of 20 inches per hour is necessary. To improve the probability of long-term performance, significantly higher initial infiltration rates are desirable. l Porous Asphalt: Products must have adequate void spaces through which water can infilt- rate. A void space within the range of 16 – 25% is typical. l Pervious Concrete: Products must have adequate void spaces through which water can infiltrate. A void space within the range of 15 – 35% is typical.. l Grid/lattice systems filled with gravel, sand, or a soil of finer particles with or without grass: The fill material must be at least a minimum of 2 inches of sand, gravel, or soil. l Permeable Interlocking Concrete Pavement and Aggregate Pavers: Pavement joints should be filled with No. 8, 89 or 9 stone. Consult with paver manufacturer specifications to determine the appropriate material type and size. Drainage Conveyance Roads should still be designed with adequate drainage conveyance facilities as if the road surface was impermeable. Roads with base courses that extend below the surrounding grade should have a designed drainage flow path to safely move water away from the road prism and into the roadside drainage facilities. Use of perforated storm drains to collect and transport infiltrated water from under the road surface will result in less effective designs and less Flow Control benefit. Underdrains Note that if an underdrain is placed at or near the bottom of the aggregate base in a permeable pave- ment BMP, the permeable pavement is no longer considered an LID BMP and cannot be used to sat- isfy The List Approach within I-3.4.5 MR5: On-Site Stormwater Management. However, designs utilizing an underdrain that is elevated within the aggregate base course to protect the pavement wearing course from saturation is considered an LID BMP and can be used to satisfy The List Approach within I-3.4.5 MR5: On-Site Stormwater Management. Infiltration Test for Permeable Pavement Surface l Permeable pavement driveways can be tested by simply throwing a bucket of water on the sur- face. If anything other than a scant amount puddles or runs off the surface, additional testing is necessary prior to accepting the construction. l Permeable pavement roads may be initially tested with the bucket test described above. In addition, test the initial infiltration with a 6-inch ring, sealed at the base to the road surface, or with a sprinkler infiltrometer. Wet the road surface continuously for 10 minutes. Begin test to determine compliance with 20 inches per hour minimum rate. Use of ASTM C1701 or ASTM C1781, as appropriate, is also recommended. 2019 Stormwater Management Manual for Western Washington Volume V -Chapter 5 -Page 755 Determining the Native Soil Infiltration Rates Determining infiltration rates of the site soils is necessary to determine feasibility of designs that intend to infiltrate stormwater on-site. It is also necessary to estimate flow reduction benefits of such designs when using a continuous runoff model The certified soils professional or engineer can exercise discretion concerning the need for and extent of infiltration rate (saturated hydraulic conductivity, Ksat) testing. The professional can con- sider a reduction in the extent of infiltration (Ksat) testing if, in their judgment, information exists con- firming that the site is unconsolidated outwash material with high infiltration rates, and there is adequate separation from ground water. Refer to V-5.4 Determining the Design Infiltration Rate of the Native Soils for further guidance on the methods to determine the infiltration rate of the native soils. Field Testing Requirements Based Upon Project Size l Projects subject to Minimum Requirements #1 - #5: o A small-scale Pilot Infiltration Test (PIT) – or other small-scale tests as allowed by the local jurisdiction - should be performed for every 5,000 sq. ft. of permeable pavement, but not less than 1 test per site. Submit results as part of the Stormwater Site Plan to establish a basis for a feasibility decision. l Projects subject to Minimum Requirements #1 - #9: o A small-scale Pilot Infiltration Tests (PIT) - or other small-scale tests as allowed by the local jurisdiction - should be performed for every 5,000 sq. ft. of permeable pavement, but not less than 1 test per site. On residential developments, small-scale infiltration tests should be performed at every proposed lot, at least every 200 feet of roadway and within each length of road with significant differences in subsurface characteristics. However, if the site subsurface characterization - including soil borings across the development site - indicate consistent soil characteristics and depths to seasonal high ground water conditions, the number of test locations may be reduced to a frequency recommended by a geotechnical professional. Unless seasonal high ground water elevations across the site have already been determined, upon conclusion of the infiltration testing, infiltration sites should be over-excavated 1 foot to see any restrictive layers or ground water. Observations through a wet season can identify a seasonal ground water restriction. Perform infiltration testing in the soil profile at the estimated bottom elevation of base materials for the permeable pavement. If no base materials, (e.g., a pervious concrete sidewalk), perform the test- ing at the estimated bottom elevation of the pavement. Assignment of Appropriate Correction Factors If the design requires determination of a long-term (design) infiltration rate of the native soils (for example, to demonstrate compliance with the LID Performance Standard and/or the Flow Control 2019 Stormwater Management Manual for Western Washington Volume V -Chapter 5 -Page 756 Performance Standard), refer to V-5.4 Determining the Design Infiltration Rate of the Native Soils and the following additional guidance specific to permeable pavement BMPs: l The overlying permeable pavement provides excellent protection for the underlying native soil from sedimentation. Accordingly, when using The Simplified Approach to Calculating the Design Infiltration Rate of the Native Soils as described in V-5.4 Determining the Design Infiltration Rate of the Native Soils, the correction factor for the sub-grade soil does not have to take into consideration the extent of influent control and clogging over time. The correction factor to be applied to in-situ, small-scale infiltration test results for permeable pavement sites is determined by the site variability and number of locations tested, the quality of the aggreg- ate base material, and the method used to determine the initial Ksat. Using Table V-5.1: Cor- rection Factors to be Used With In-Situ Saturated Hydraulic Conductivity Measurements to Estimate Design Rates, the correction factor for permeable pavement design is revised based on this guidance as: Total Correction Factor, CFT = CFv x CFt x CFa where CFa is the partial correction factor determined by the quality of the pavement aggreg- ate base material. CFa ranges from 0.9 to 1.0. l Tests should be located and be at adequate frequency capable of producing a soil profile char- acterization that fully represents the infiltration capability where the permeable pavement is located. The partial correction factor CFV depends on the level of uncertainty that variable sub- surface conditions justify. If enough pilot infiltration tests are conducted across the permeable pavement subgrade to provide an accurate characterization, or the range of uncertainty is low (for example, conditions are known to be uniform through previous exploration and site geo- logical factors), then a partial correction factor CFV of one for site variability may be justified. Additionally, a partial correction factor CFa of 1 for the quality of pavement aggregate base material may be necessary if the aggregate base is clean washed material with 1% or less fines passing the 200 sieve. l If the level of uncertainty is high, a partial correction factor CFV near the low end of the range may be appropriate. Two example scenarios where a low CFV may be appropriate include: o Site conditions are highly variable due to a deposit of ancient landslide debris, or buried stream channels. In these cases, even with many explorations and several pilot infilt- ration tests, the level of uncertainty may still be high. o Conditions are variable, but few explorations and only one pilot infiltration test is con- ducted. That is, the number of explorations and tests conducted do not match the degree of site variability anticipated. Runoff Model Representation Note that if the project is using permeable pavement to only meet The List Approach within I-3.4.5 MR5: On-Site Stormwater Management, there is no need to model the permeable pavement in a continuous runoff model. 2019 Stormwater Management Manual for Western Washington Volume V -Chapter 5 -Page 757 The guidance below is to show compliance with the LID Performance Standard in I-3.4.5 MR5: On- Site Stormwater Management, or the standards in I-3.4.6 MR6: Runoff Treatment, I-3.4.7 MR7: Flow Control, and/or I-3.4.8 MR8: Wetlands Protection. Continuous runoff modeling software include specific modeling elements to use to model the storm- water for permeable pavement. Within these elements, the model user specifies pavement thickness and porosity, aggregate base material thickness and porosity, maximum allowed ponding depth, and the infiltration rate into the native soil. l For grades less than 2%, no adjustment to the below ground volumes are necessary. l For grades greater than 2% without internal dams within the base materials, the below ground storage volume must be adjusted as follows: o Permeable pavement surfaces that are below the surrounding grade and that are on a slope can be modeled as permeable pavement with an infiltration rate and a nominal depth. o The dimensions of the permeable pavement are: the length (parallel to and beneath the road) of the base materials that are below grade; the width of the below grade base materials; and an Effective Total Depth of 1 inch. If the continuous runoff model requires the permeable pavement to have an overflow riser to model overflows that occur should the available storage get exceeded, enter 0.04 ft (1/2 inch) for the “Riser Height” and a large Riser Diameter (say 1000 inches) to ensure that there is no head build up. o If a drainage pipe is embedded and elevated in the below grade base materials, the pipe should only have perforations on the lower half (below the spring line) or near the invert. Pipe volume and trench volume above the pipe invert cannot be assumed as available storage space. If a drainage pipe is placed at the bottom of the base material, the pavement is modeled as an impervious surface without any gravel trench. l For roads on a slope with internal dams within the base materials that are below grade, the below ground storage volume must be adjusted as follows: o Each stretch of permeable pavement (cell) that is separated by barriers can be modeled separately. For each cell, determine the average depth of water within the cell at which the barrier at the lower end will be overtopped. o Specify the dimensions of each cell of the below-grade base materials using the per- meable pavement dimension fields for: the “Pavement Length” (length of the cell par- allel to the road); the “Pavement Bottom Width”(width of the bottom of the base material); and the Effective Total Depth. In WWHM2012, the field entilted “Effective Volume Factor” is used by the program to calculate the effective storage volume within the below-grade base materials for roads on a slope. The Effective Volume Factor is the ratio of the average maximum water depth behind a check dam (typically at the middle of the pavement length) to the below-grade base materials depth. 2019 Stormwater Management Manual for Western Washington Volume V -Chapter 5 -Page 758 o Each cell should have its own tributary drainage area within the permeable pavement element that includes the road above it, any project site areas whose runoff drains onto and through the road (lateral flow soil or impervious basin), and any off-site areas. Rep- resent each drainage area with a permeable pavement icon and a lateral flow basin icon (if runon occurs). In the runoff modeling, similar designs throughout a development can be summed and represented as one large facility. For instance, walkways can be summed into one facility. Driveways with similar designs (and enforced through deed restrictions) can be summed into one facility. In these instances, a weighted average of the design infiltration rates (where within a factor of two) for each location may be used. The averages are weighted by the size of their drainage area. The design infilt- ration rate for each site is the measured Ksat multiplied by the appropriate correction factors. On the Permeable Pavement screen under “Infiltration”, there is a field that asks the following “Use Wetted Surface Area?” By default, it is set to “NO”. It should stay “NO” if the below-grade base material trench has sidewalls steeper than 2 horizontal to 1 vertical. Maintenance Please see Table V-A.22: Maintenance Standards - Permeable Pavement. Maintenance recommendations for all permeable pavement BMPs: l Erosion and introduction of sediment from surrounding land uses should be strictly controlled after construction by amending exposed soil with compost and mulch, planting exposed areas as soon as possible, and armoring outfall areas. l Surrounding landscaped areas should be inspected regularly and possible sediment sources controlled immediately. l Installations can be monitored for adequate or designed minimum infiltration rates by observing drainage immediately after heavier rainstorms for standing water or infiltration tests using ASTM C1701. l Clean permeable pavement surfaces to maintain infiltration capacity at least once or twice annually following recommendations below. l Utility cuts should be backfilled with the same aggregate base used under the permeable pav- ing to allow continued conveyance of stormwater through the base, and to prevent migration of fines from the standard base aggregate to the more open graded permeable base material (Diniz, 1980). l Ice build up on permeable pavement is reduced and the surface becomes free and clear more rapidly compared to conventional pavement. For western Washington, deicing and sand application may be reduced or eliminated and the permeable pavement installation should be assessed during winter months and the winter traction program developed from those obser- vations. Vacuum and sweeping frequency will likely be required more often if sand is applied. Porous asphalt and pervious concrete maintenance recommendations: 2019 Stormwater Management Manual for Western Washington Volume V -Chapter 5 -Page 759 l Clean surfaces using suction, sweeping with suction or high-pressure wash and suction (sweeping alone is minimally effective). Hand held pressure washers are effective for cleaning void spaces and appropriate for smaller areas such as sidewalks. l For large scale cleaning use vacuum surface cleaning machines (such as Cyclone, Elgin, etc.) for cleaning pervious concrete and porous asphalt. l Small utility cuts can be repaired with conventional asphalt or concrete if small batches of per- meable material are not available or are too expensive. Permeable paver maintenance recommendations: l ICPI recommends cleaning if the measured infiltration rate falls below 10 in/hr. l Use sweeping with suction when surface and debris are dry 1-2 times annually (see next bul- let for exception). Apply vacuum to a paver test section and adjust settings to remove all visible sediment without excess uptake of aggregate from paver openings or joints. If necessary replace No 8, 89 or 9 stone to specified depth within the paver openings. Washing or power washing should not be used to remove debris and sediment in the openings between the pavers (Smith, 2000). l For badly clogged installations, wet the surface and vacuumed aggregate to a depth that removes all visible fine sediment and replace with clean aggregate. l If necessary use No 8, 89 or 9 stone for winter traction rather than sand (sand will accelerate clogging). l Pavers can be removed individually and replaced when utility work is complete. l Replace broken pavers as necessary to prevent structural instability in the surface. l The structure of the top edge of the paver blocks reduces chipping from snowplows. For addi- tional protection, skids on the corner of plow blades are recommended. l For a model maintenance agreement see Permeable Interlocking Concrete Pavements: Design, Specifications, Construction, Maintenance (Smith, 2011). Plastic or concrete grid system maintenance recommendations: l Remove and replace top course aggregate if clogged with sediment or contaminated (vacuum trucks for stormwater collection basins can be used to remove aggregate). l Remove and replace grid segments where three or more adjacent rings are broken or dam- aged. l Replenish aggregate material in grid as needed. l Snowplows should use skids to elevate blades slightly above the gravel surface to prevent loss of top course aggregate and damage to plastic grid. l For grass installations, use normal turf maintenance procedures except do not aerate. Use very slow release fertilizers if needed. 2019 Stormwater Management Manual for Western Washington Volume V -Chapter 5 -Page 760 Maintenance Com- ponent Recommended Frequency a Condition when Maintenance is Needed (Stand- ards)Action Needed (Procedures) Inspection Routine Main- tenance vegetation man- agement protocols) Note that the inspection and routine maintenance frequencies listed above are recommended by Ecology. They do not supersede or replace the municipal stormwater permit requirements for inspection frequency required of municipal stormwater per- mittees for "stormwater treatment and flow control BMPs/facilities". a Frequency: A = Annually; B = Biannually (twice per year); M = Monthly; W = At least one visit should occur during the wet season (for debris/clog related maintenance, this inspection/maintenance visit should occur in the early fall, after deciduous trees have lost their leaves); S = Perform inspections after major storm events (24-hour storm event with a 10-year or greater recurrence interval). IPM - Integrated Pest Management ISA - International Society of Arboriculture Table V-A.21: Maintenance Standards - Bioretention Facilities (continued) Component Recommended Frequency a Condition when Maintenance is Needed (Standards)Action Needed (Procedures) Inspection Routine Maintenance Surface/Wearing Course Permeable Pave- ments, all A, S Runoff from adjacent pervious areas deposits soil, mulch or sediment on paving l Clean deposited soil or other materials from permeable pavement or other adjacent surfacing l Check if surface elevation of planted area is too high, or slopes towards pavement, and can be regraded (prior to regrading, protect permeable pavement by covering with temporary plastic and secure covering in place) l Mulch and/or plant all exposed soils that may erode to pavement surface Porous asphalt or per- vious concrete A or B None (routine maintenance) Clean surface debris from pavement surface using one or a combination of the following methods: l Remove sediment, debris, trash, vegetation, and other debris deposited onto pavement (rakes and leaf blowers can be used for removing leaves) l Vacuum/sweep permeable paving installation using: o Walk-behind vacuum (sidewalks) o High efficiency regenerative air or vacuum sweeper (roadways, parking lots) o ShopVac or brush brooms (small areas) l Hand held pressure washer or power washer with rotating brushes Follow equipment manufacturer guidelines for when equipment is most effective for cleaning permeable pavement. Dry weather is more effective for some equipment. Ab Surface is clogged: Ponding on surface or water flows off the permeable pavement surface dur- ing a rain event (does not infiltrate) l Review the overall performance of the facility (note that small clogged areas may not reduce overall per- formance of facility) l Test the surface infiltration rate using ASTM C1701 as a corrective maintenance indicator. Perform one test per installation, up to 2,500 square feet. Perform an additional test for each additional 2,500 square feet up to 15,000 square feet total. Above 15,000 square feet, add one test for every 10,000 square feet. l If the results indicate an infiltration rate of 10 inches per hour or less, then perform corrective maintenance to restore permeability. To clean clogged pavement surfaces, use one or combination of the following methods: Table V-A.22: Maintenance Standards - Permeable Pavement 2019 Stormwater Management Manual for Western Washington Volume V -Appendix A -Page 1025 Cole stormwater maintenance for permeable pavement, 5 pages Component Recommended Frequency a Condition when Maintenance is Needed (Standards)Action Needed (Procedures) Inspection Routine Maintenance o Combined pressure wash and vacuum system calibrated to not dislodge wearing course aggregate. o Hand held pressure washer or power washer with rotating brushes o Pure vacuum sweepers Note: If the annual/biannual routine maintenance standard to clean the pavement surface is conducted using equipment from the list above, corrective maintenance may not be needed. A Sediment present at the surface of the pave- ment l Assess the overall performance of the pavement system during a rain event. If water runs off the pavement and/or there is ponding then see above. l Determine source of sediment loading and evaluate whether or not the source can be reduced/eliminated. If the source cannot be addressed, consider increasing frequency of routine cleaning (e.g., twice per year instead of once per year). Summer Moss growth inhibits infiltration or poses slip safety hazard l Sidewalks: Use a stiff broom to remove moss in the summer when it is dry l Parking lots and roadways: Pressure wash, vacuum sweep, or use a combination of the two for cleaning moss from pavement surface. May require stiff broom or power brush in areas of heavy moss. A Major cracks or trip hazards and concrete spalling and raveling l Fill potholes or small cracks with patching mixes l Large cracks and settlement may require cutting and replacing the pavement section. Replace in-kind where feasible. Replacing porous asphalt with conventional asphalt is acceptable if it is a small percentage of the total facility area and does not impact the overall facility function. l Take appropriate precautions during pavement repair and replacement efforts to prevent clogging of adjacent porous materials Interlocking concrete paver blocks and aggregate pavers A or B None (routine maintenance) Clean pavement surface using one or a combination of the following methods: l Remove sediment, debris, trash, vegetation, and other debris deposited onto pavement (rakes and leaf blowers can be used for removing leaves) l Vacuum/sweep permeable paving installation using: o Walk-behind vacuum (sidewalks) o High efficiency regenerative air or vacuum sweeper (roadways, parking lots) o ShopVac or brush brooms (small areas) Note: Vacuum settings may have to be adjusted to prevent excess uptake of aggregate from paver openings or joints. Vacuum surface openings in dry weather to remove dry, encrusted sediment. Ab Surface is clogged: Ponding on surface or water flows off the permeable pavement surface dur- ing a rain event (does not infiltrate) l Review the overall performance of the facility (note that small clogged areas may not reduce overall per- formance of facility) l Test the surface infiltration rate using ASTM C1701 as a corrective maintenance indicator. Perform one test per installation, up to 2,500 square feet. Perform an additional test for each additional 2,500 square feet up to 15,000 square feet total. Above 15,000 square feet, add one test for every 10,000 square feet. l If the results indicate an infiltration rate of 10 inches per hour or less, then perform corrective maintenance to restore permeability. Table V-A.22: Maintenance Standards - Permeable Pavement (continued) 2019 Stormwater Management Manual for Western Washington Volume V -Appendix A -Page 1026 Component Recommended Frequency a Condition when Maintenance is Needed (Standards)Action Needed (Procedures) Inspection Routine Maintenance l Clogging is usually an issue in the upper 2 to 3 centimeters of aggregate. Remove the upper layer of encrusted sediment, and fines, and/or vegetation from openings and joints between the pavers by mechanical means and/or suction equipment (e.g., pure vacuum sweeper). l Replace aggregate in paver cells, joints, or openings per manufacturer's recommendations A Sediment present at the surface of the pave- ment l Assess the overall performance of the pavement system during a rain event. If water runs off the pavement and/or there is ponding, then see above. l Determine source of sediment loading and evaluate whether or not the source can be reduced/eliminated. If the source cannot be addressed, consider increasing frequency of routine cleaning (e.g., twice per year instead of once per year). Summer Moss growth inhibits infiltration or poses slip safety hazard l Sidewalks: Use a stiff broom to remove moss in the summer when it is dry l Parking lots and roadways: Vacuum sweep or stiff broom/power brush for cleaning moss from pavement sur- face A Paver block missing or damaged Remove individual damaged paver blocks by hand and replace or repair per manufacturer's recommendations A Loss of aggregate material between paver blocks Refill per manufacturer's recommendations for interlocking paver sections A Settlement of surface May require resetting Open-celled paving grid with gravel A or B None (routine maintenance) l Remove sediment, debris, trash, vegetation, and other debris deposited onto pavement (rakes and leaf blowers can be used for removing leaves) l Follow equipment manufacturer guidelines for cleaning surface. Ab Aggregate is clogged: Ponding on surface or water flows off the permeable pavement surface during a rain event (does not infiltrate) l Use vacuum truck to remove and replace top course aggregate l Replace aggregate in paving grid per manufacturer's recommendations A Paving grid missing or damaged l Remove pins, pry up grid segments, and replace gravel l Replace grid segments where three or more adjacent rings are broken or damaged l Follow manufacturer guidelines for repairing surface. A Settlement of surface May require resetting A Loss of aggregate material in paving grid Replenish aggregate material by spreading gravel with a rake (gravel level should be maintained at the same level as the plastic rings or no more than 1/4 inch above the top of rings). See manufacturer's recommendations. A Weeds present l Manually remove weeds l Presence of weeds may indicate that too many fines are present (refer to Actions Needed under "Aggregate is clogged" to address this issue) Open-celled paving grid with grass A or B None (routine maintenance) l Remove sediment, debris, trash, vegetation, and other debris deposited onto pavement (rakes and leaf blowers can be used for removing leaves) l Follow equipment manufacturer guidelines for cleaning surface. Table V-A.22: Maintenance Standards - Permeable Pavement (continued) 2019 Stormwater Management Manual for Western Washington Volume V -Appendix A -Page 1027 Component Recommended Frequency a Condition when Maintenance is Needed (Standards)Action Needed (Procedures) Inspection Routine Maintenance Ab Aggregate is clogged: Ponding on surface or water flows off the permeable pavement surface during a rain event (does not infiltrate) Rehabilitate per manufacturer's recommendations. A Paving grid missing or damaged l Remove pins, pry up grid segments, and replace grass l Replace grid segments where three or more adjacent rings are broken or damaged l Follow manufacturer guidelines for repairing surface. A Settlement of surface May require resetting A Poor grass coverage in paving grid l Restore growing medium, reseed or plant, aerate, and/or amend vegetated area as needed l Traffic loading may be inhibiting grass growth; reconsider traffic loading if feasible As needed None (routine maintenance)Use a mulch mower to mow grass A None (routine maintenance) l Sprinkle a thin layer of compost on top of grass surface (1/2" top dressing) and sweep it in l Do not use fertilizer A Weeds present l Manually remove weeds l Mow, torch, or inoculate and replace with preferred vegetation Inlets/Outlets/Pipes Inlet/outlet pipe A Pipe is damaged Repair/replace A Pipe is clogged Remove roots or debris Underdrain pipe Clean pipe as needed Clean orifice at least bian- nually (may need more fre- quent cleaning during wet season) Plant roots, sediment or debris reducing capa- city of underdrain (may cause prolonged draw- down period) l Jet clean or rotary cut debris/roots from underdrain(s) l If underdrains are equipped with a flow restrictor (e.g., orifice) to attenuate flows, the orifice must be cleaned regularly Raised subsurface overflow pipe Clean pipe as needed Clean orifice at least bian- nually (may need more fre- quent cleaning during wet season) Plant roots, sediment or debris reducing capa- city of underdrain l Jet clean or rotary cut debris/roots from under-drain(s) l If underdrains are equipped with a flow restrictor (e.g., orifice) to attenuate flows, the orifice must be cleaned regularly Outlet structure A, S Sediment, vegetation, or debris reducing capa- city of outlet structure l Clear the blockage l Identify the source of the blockage and take actions to prevent future blockages Overflow B Native soil is exposed or other signs of erosion damage are present at discharge point Repair erosion and stabilize surface Aggregate Storage Reservoir Observation port A, S Water remains in the storage aggregate longer than anticipated by design after the end of a storm If immediate cause of extended ponding is not identified, schedule investigation of subsurface materials or other potential causes of system failure. Table V-A.22: Maintenance Standards - Permeable Pavement (continued) 2019 Stormwater Management Manual for Western Washington Volume V -Appendix A -Page 1028 Component Recommended Frequency a Condition when Maintenance is Needed (Standards)Action Needed (Procedures) Inspection Routine Maintenance Vegetation Adjacent large shrubs or trees As needed Vegetation related fallout clogs or will potentially clog voids l Sweep leaf litter and sediment to prevent surface clogging and ponding l Prevent large root systems from damaging subsurface structural components Once in May and Once in September Vegetation growing beyond facility edge onto sidewalks, paths, and street edge Edging and trimming of planted areas to control groundcovers and shrubs from overreaching the sidewalks, paths and street edge improves appearance and reduces clogging of permeable pavements by leaf litter, mulch and soil. Leaves, needles, and organic debris In fall (October to December) after leaf drop (1-3 times, depending on canopy cover) Accumulation of organic debris and leaf litter Use leaf blower or vacuum to blow or remove leaves, evergreen needles, and debris (i.e., flowers, blossoms) off of and away from permeable pavement Note that the inspection and routine maintenance frequencies listed above are recommended by Ecology. They do not supersede or replace the municipal stormwater permit requirements for inspection frequency required of municipal stormwater per- mittees for "stormwater treatment and flow control BMPs/facilities". a Frequency: A= Annually; B= Biannually (twice per year); S = Perform inspections after major storm events (24-hour storm event with a 10-year or greater recurrence interval). b Inspection should occur during storm event. Table V-A.22: Maintenance Standards - Permeable Pavement (continued) Activity Objective Schedule Notes Structural and Drainage Components Clear inlet pipes: Remove soil substrate, vegetation or other debris.Maintain free drain- age of inlet pipes.Twice annually. Inspect drain pipe: Check for cracks settling and proper alignment, and correct and re-compact soils or fill material surrounding pipe, if necessary. Maintain free drain- age of inlet pipes.Twice annually. Inspect fire ventilation points for proper operation Fire and safety.Twice annually. Maintain egress and ingress: Clear routes of obstructions and main- tained to design standards.Fire and safety.Twice annually. Insects: (see note) Roof garden design should provide drainage rates that do not allow pooling of water for periods that promote insect larvae development. If standing water is present for extended periods correct drainage problem. Chemical sprays should not be used. Prevent release of contaminants: Identify activities (mechanical systems maintenance, pet access, etc.) that can potentially release pollutants to the roof garden and establish agreements to prevent release. Water quality pro- tection. During construction of roof and then as determ- ined by inspection. Any cause of pollutant release should be corrected as soon as identified and the pollutant removed. Vegetation and Growth Medium Invasive or nuisance plants: Remove manually and without herb- icide applications. Promote selected plant growth and sur- vival, maintain aes- thetics. Twice annually.At a minimum, schedule weeding with inspections to coincide with important horticultural cycles (e.g., prior to major weed varieties dispersing seeds). Table V-A.23: Maintenance Standards - Vegetated Roofs 2019 Stormwater Management Manual for Western Washington Volume V -Appendix A -Page 1029 651866 PGS:2 AGR EWÆlRE MAMEMh"AN E When recordedpleasereturnto: JeffersonCounty Dept.ofCommunity Development 621 SheridanStreet PortTownsend,WA 98368 STORMWATER MANAGEMENT FACILITY MAINTENANCE AGREEMENT ThisMAINTENANCE AGREEMENT ismade thisÚ day of e_1s½A ,2022 by James Allan Cole and VirginiaBarnhill,hereinafterGUARANTOR and JeffersonCounty,a municipalcorporation, hereinafterGUARANTEE. 1.0 RECITALS 1.1GUARANTOR istheowner of certainrealpropertydescribedas Lot 7,Division5,ofthePlat of Bridgehaven,asrecordedinVolume 5,Pages 3-4,intheSection9,Township 27 North,Range 1 East,W.M.,JeffersonCounty,Washington;identifiedas Assessor'sParcelNumber 935100034; withaddress865 Thorndyke Rd,PortLudlow,WA 98365;and referredtointhisAgreement asthe PROPERTY. 1.2In conjunctionwith the GUARANTOR'S development of the PROPERTY under Jefferson County BuildingPermit BLD2021-00466,GUARANTEE has requiredand GUARANTOR has agreed to constructa stormwatermanagement facilitywhich includescollection,conveyance, treatment,and infiltrationfacilities(Permeable Asphalt,Downspout Full Infiltration).The stormwatermanagement facilityisdescribedand shown on attachedconstructiondrawing dated January27,2022 forGUARANTOR'S development of the PROPERTY thatison filewith the appropriateagency,division,employee,orrepresentativeofJeffersonCounty. 1.3 As a conditionof development approval,GUARANTOR has agreed to enterintothis MaintenanceAgreement ensuringthatthestormwatermanagement facilitywillbe constructedand maintainedinaccordancewiththeapprovedplans. 2.0 CONSTRUCTION AND MAINTENANCE GUARANTOR agreesto constructand maintaina stormwatermanagement facilityas shown on the constructiondrawing describedabove.The stormwater management facilityshall be maintainedand preservedby GUARANTOR untilsuch time as GUARANTOR,itsheirs, successors,or assignsand GUARANTEE agreethatthe facilityshould be dismantled,altered, abandoned,orremoved. 3.0 NO REMOVAL No partofthe stormwatermanagement facilityshallbe dismantled,altered,orremoved exceptas necessaryformaintenance,repairorreplacement. StormwaterManagementFacilityMaintenanceAgreement Page1of3 4.0 DISPUTE RESOLUTION Ifa disputearisesbetween thepartiesto thisAgreement regardingthe stormwatermanagement facility,GUARANTOR shallattemptto negotiatean appropriateresolutionwith GUARANTEE representedby the JeffersonCounty Engineer.If the disputecannot be resolvedat thatlevel, GUARANTOR may filean appealwiththeJeffersonCounty HearingExaminer asprovidedforin theJeffersonCounty UnifiedDevelopment Code. 5.0 ENFORCEMENT This Agreement may be enforcedby GUARANTEE inlaw or equityagainstGUARANTOR,its heirs,successorsand assigns. 6.0 SUCCESSORS AND ASSIGNS This Agreement shallrun with the PROPERTY and be bindingon GUARANTOR,itsheirs, successorsand assigns. 7.0 NOTICE GUARANTOR shallfilethisAgreement withtheJeffersonCounty Auditor. DATED thisM day of e c ,2022. GU NT R UA TOR STATE OF WASHINGTON COUNTY OF 14-tTS On thisdaypersonallyappearedbeforeme V t¾t®Ba©WL -tome known tobetheindividualdescribed inandwho executedtheforegoinginstrument,andacknowledgedthat signedthesameas -Enúr freeand voluntaryactanddeed,fortheusesandpurposesthereinmentioned. GIVEN undermy handandofficialsealthisd dayof N®'t ,20 onmurn,, NotaryPublicinandfortheStateofWashington . residingatµW50%6 gwA .E i NOTARY ap PUBLIC 2 MY COMMISSION EXPIRES saN ,20 lb ../O * WA ACC ED for;E F ON ''TY by:'""""' //2022 BrentButler Date JeffersonCoun Dept ofCommunity Development Director/UnifiedDevelopment Code Administrator StormwaterManagementFacilityMaintenanceAgreement Page2 of3 Stormwater Management Facility Maintenance Agreement Page 3 of 3 Feb 15 2022