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Home My WebLink About502171004 Stormwater MgmtDEC, APPROVED STORMWATER PLAN DEC 6 2002 Property Owner: ~.i SA ~_~zIQ'T--~) Telephone: Address: i'~'Z~.'~ ~¢~D,~ ~¢_~x,/~ ~ ~ ~ALk..A~kMA Assessor'sParcelNumber: ~og.- ~-/i- ex:>4 ~, ~_>Z. - t-il- 01~ Building Permit or Septic Permit Application Number (if applicable):, ,, Brief Project Description: _cS'~c-r' ~l ~ ~A~ ~t~~ Site Location: Person Responsible for BMP Installation and Maintenance: Address: Telephone: Describe/check the Best Management Practices (BMPs) that you will implement during land disturbing activities or construction to control erosion and prevent sediment from entering water bodies (marine waters, streams, rivers, lakes, or wetlands) or impacting adjacent property or roads. Please check the measures you plan to implement and show their approximate location on the site plan. You may also propose measures other than those listed. AAach additional sheets, if more space is required. [] Stabilize construction access route. Limit construction vehicles to one route, if feasible. Provide a stabilized construction access by applying quarry spalls, ballast, or crushed rock to minimize tracking sediment onto roads. (See attached illustration fi.om Stormwater Management Manual.) If sediment is transported onto roads, they will be cleaned thoroughly. Minimize the extent of land disturbing activity and preserve existing vegetation. Preserve buffers of well-established vegetation between disturbed areas and property boundaries, roads, water bodies, and designated critical areas (wetlands, fish and wildlife habitat areas, landslide or erosion hazard area, etc.). SPESC Instructions--Short Form Revised July 17, 2002 3 EROSION AND SEDIMENT CONTROL WORKSHEET [] [] [] [] [] Phase clearing so that only areas that are actively being worked are uncovered. Start and complete land disturbing activities and stabilize the site between April 1 and September 30. Stabilization means that disturbed areas will have well-established plant cover or be landscaped to minimize erosion. Stabilize exposed soil Exposed and unworked soil will be covered within 2 days between October 1 and March 31 and within 7 days between April 1 and September 30. [ ] Cover exposed soil with a minimum of 2 inches of straw or hay or other material approved for this purpose. [ ] Cover soil stockpiles with plastic sheeting and locate away from water bodies, roads, and property lines. [ ] Place gravel base on roads, driveways, and parking areas after clearing and subgrade preparation. Protect adjacent properties and water bodies from sediment deposition: [ ] Place straw or hay bales in ditches and drainage ways down slope from areas of land disturbing activity to filter runoff before it leaves the project site or enters water bodies. (See attached illustrations from Stormwater Management Manual.) [ ] Install a filter fence down slope from areas of land disturbing activity to filter runoff before it leaves the project site or enters water bodies. (See attached illustration from Stormwater Management Manual.) Regularly inspect and maintain all BMPs especially after storms events. Describe other erosion and sediment control Best Management Practices. Be specific as to design and specifications. SPESC Instructions--Short Form Revised JuIy 17, 2002 4 EROSION AND SEDIMENT CONTROL WORKSHEET Describe how disturbed areas will be permanently stabilized (seeded, landscaped, apply gravel base to roadways, etc.) Describe how runoff from impervious surfaces will be controlled (disperse to vegetated areas to infiltrate, dry well, infiltration trench, route runoff to existing drainage facilities, etc.). SPESC Instructions--Short Form Revised July 17, 2002 5 EROSION AND SEDIMENT CONTROL WORKSHEET Specify your construction sequence. Describe the timing of all land disturbing activities (clearing and grading, construction, installation of drainage facilities, landscaping, etc.) and Best Management Practices. Describe proposed maintenance of BMPs. The Best Management Practices proposed above will be implemented to control erosion, sediment, and stormwater runoff. I will notify the Jefferson County for inspections as required. ~ ~46~ ~ ~!~ 1~ Signature of Owner/Agent ~ Date SPESC Instructions--Short Fom~ Revised July 17, 2002 A i. TEl:INA TI VE . _DEBII NB P.O. Box 4459, Sou[h Colby, WA (360) 769-0098 25 November 2002 Stacie Hoskins Jefferson County Department of Community Development 621 Sheridan Street Port Townsend, WA 98368 DEC 22002 JEFFERSON COUNTY DEPT. OF COMMUNITY DEVELOPMENT RE: Bemtsen - Duckabush River Property (MLA020452) Dear Ms Hoskins, The following is bdef analysis of the proposed drainage improvements for the construction of a single-family residence (SFR) on the above referenced parcel(s). The total net increase in impervious area is 4,642 square feet (SI:) and the total disturbed area (including existing structures and improvement that will remain) is 26,099 SF. This project classifies as a "Small Parcel Development". PARCEL DESCRIPTION The irregular shaped subject parcel is located in a portion of the North East comer of Section 17, Township 25N, Range 2 West, Willamette Meridian, Jefferson County Washington (Figure 1). The parcel accesses Duckabush Road from the northeast and is bound by the Duckabush River along portions of the southem and western boundaries. Site topography slopes generally from northeast to southwest towards the dver. The project consists of two tax parcels; 502-171-012 & 502-171-004. The total area of these two parcels is approximately 20.92 acres (Ac). The project parcel is broken (topographically) into two large benches with a smaller, intermediate bench between the two. The uppermost bench is an area which contains remnants of previous buildings. The lower bench is a "pasture" like area, which fronts the dver. PROPOSEDIMPROVEMENTS The project proposal is to construct an SFR with a detached garage/shop in the area that was previously developed. There are currently remnants of four structures in the area of the proposed SFR. These structures include; a collapsed bam, a small shed, a chicken coop, a concrete slab, which is assumed to be the foundation of a previous residence, and a did/gravel ddveway from Duckabush Road to witltiCf approximately 50 feet of the Duckabush River. The total existing impervious area is approximately 17,957 SF (0.41 Ac). The proposed improvements will include SFR, garage/shop, patio area, driveway/parking area, septic system, well and utilities. The total new impervious area is approximately 7,621 SF (0.17 Ac). The proposed improvements will include the demolition/removal of some of the existing structures. This removal would include; the collapsed barn, the concrete house slab, the small shed and the section of existing ddveway that extends from the building area to the dyer. The total impervious are to be removed is approximately 2,979 SF (0.07 Ac). The net increase in impervious area is approximately 4,642 SF (0.11 Ac). The total impervious area after development will be approximately 22,599 SF (0.52 Ac), which includes portions of the existing access road and the chicken coop which will remain. The proposed development area is 2.48% of the total parcel area. SOILS EXPLORATION A total of nine (9) soil logs have been dug on the parcel to evaluate soils from an on-site sewage disposal standpoint as well as for determination of stormwater mitigation BMP's (Figure 2). "Soil Evaluation" sheets have provided for each log. Exposed banks and cuts were also examined for soil structure. Site soils vaded from shallow gravelly sand to deep medium sands. Three of the test holes were dug on the upper bench; one behind (northeast of) the old bam (SL-5), two in front of (southwest of) the old barn (SL-I&2). SL-5 yielded gravelly loamy sand to sandy loam overlying a mottled clay loam at 34 inches. SL-1 & 2 show medium gravelly sand overlying hardpan. The hardpan varied from 15 - 24 inches below the surface. One soil log (SL..4) was dug in the intermediate bench area. This log showed gravelly sandy loam to loamy sand overlying hardpan at a depth of 33 inches. The bank between the intermediate and lower benches shows cemented hardpan at 24 inches below the surface. Three soil logs (SL-3, SL-9 & SL-10) were dug in the lower bench area. These logs yielded medium gravelly sand to a depth of 34 inches; overlying a mottled sandy clay loam extending to a depth of 50 inches. Moisture was evident at approximately 36 inches. Two additional soil logs were located on benches near the North property line (SL-6) and near the gated entrance off Duckabush Road (SL-8). SL-6 yielded sandy loam to 42" with roots to 36". SL-8 yielded gravelly loamy sand to 36". Your examination of the road cut near SL-8 indicated approximately 4'-5' of permeable soil. Subsequent survey work has shown the lower bench area, in the vicinity of SL-3, to be within the 100-year flood plain area. Conversations with the Jefferson County Health Department indicate that this area in the flood plain area is suitable for on-site sewage disposal if adequate pretreatment is utilized. DRAINFIELD LOCATION Based on the soil explorations, site topography and economic considerations, the lower bench area is the most practical area for an on-site sewage disposal system. This has been reviewed by the Jefferson County Health Department and has been given verbal approval based on the information shown on this plan. , STORMWATER MITIGATION In selecting stormwater mitigation BMP's, the intent is to allow construction of the proposed SFR while minimizing impacts to the surrounding environment and at the same time protecting sensitive areas. As described above, the soils in the area of the proposed SFR are inadequate for infiltration. The proposed drainage improvements will utilize dispersion and infiltration to provide water quality and quantity mitigation. Stormwater runoff from the residence and garage/shop will be collected and directed to a dispersion trench as shown on the plans. This dispersion trench will disperse the runoff across natural vegetation to a localized depression below the proposed SFR. The depression is located within the previously described lO0-year flood plain. This dispersion trench will also serve to direct runoff away from septic system pretreatment components which are to be located outside the flood plain. Stormwater runoff from the driveway/parking area will be routed through a roadside bioflltration swale and then dispersed through native vegetation towards Wetland C. This system should provide adequate water quality mitigation while preventing short-circuiting the wetland. Both dispersion systems will promote limited infiltration and utilize the natural vegetation for water quality mitigation. CONCLUSION Given the numerous site constraints and regulatory restrictions on this site we feel that the proposed improvements as shown are consistent with standard practice and promote good environmental stewardship. If you have any questions or require additional information, please call. Sincerely, Kim S. May, P.E. Cc: Lisa Bemtsen TOPO! map printed on 06/12/02 from "Washington.tpo" and "Untitled. tpg" s01ooomE. 502ooomE. s03ooomE, s04ooomE. WGS84 Zone 10T $06OOOmE. WG$04 Zone lOT o06ooomE. Stormwater Calculations _NEW Structures (all roof area) Driveway Sidewalks Patios Covered/Solid Decks Other Total New IMPERVIOUS. ,SU RFAC_E_ z:~ ?_~ sq/ft Z ~ r:%z;~ ~:~ sq/ft sq]ft sq/~ EXISTING Structures (alt roof area) Ddveway Sidewalks Patios Covered/Solid Decks Other Total Existing .sq/ft sq/ft sq/ft · sq/ft TOTAL NEW + TOTAL EXISTING* ~ ~, ~-~ ~ .sq/ft ¢¢ ~ .. ~L.b~ ~ *¥his amount will bo used to check to~l tot coverage ease also indi~te the amount of land disturbing activin, in addition to the creation of im~ious surface, that will take ace: ~ND DISTURBING ACTIVt~ DrainfieM area cleared, ~ ~ ~ sq/~ Well, Stm~ures, UtiliZes, etc. ~~ sq~ Ddveway [ ~, ~ s~ Other sq~ Total Land Disturbance ~ L42>':::~~ .sqlft ALTERNATIVE DESIGNS P.o, Box 4459 SOUTH COLBY, WA 98384 (360) 769-0098 SHEET NO. CALCULATED BY CHECKED ~.Y SCALE ALTERNATIVE DESIGNS P.O. Box 4459 SOUTH COLBY, WA 98384 (360) 769-0098 SHEET NO. '""' OF. CALCULATED BY ~--------_~v'"'~,~ DATE CHECKED BY DATE SCALE