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Home My WebLink AboutSWP272254 ^ITV OF RENTON c RECEIVED MAY 15 1996 BUILDING DIVISION :.;:::.;:::::.. ::::::... . .: ............................... tiw4/% ;a»>;>`��`: :: :iiii;';(>;??i?;;;a>i; iy;;>� ';! ;<;i�>!i: isi; <i<<:' '"``��_»` `< "` OUR JOB NO. 5131 MAY 10, 1996 '�,�R'Y JAC Oes of k�ti ti Prepared For. 1 ?JERRY SOLOMON is 694 94 201 SOUTH 7TH STREET ONAL RENTON, WA 98055 1EXPIRES 10/10/ Prepared By: BARGHAUSEN CONSULTING ENGINEERS, INC. 1 821 5 72ND AVENUE SOUTH KENT, WASHINGTON 98032 m�¢GHAVS�2 (206) 251 -6222 o = CIVIL ENGINEERING, LAND PLANNING, SURVEYING, ENVIRONMENTAL SERVICES & r �' 1.0 CORE AND SPECIAL REQUIREMENTS The following is a synopsis of the core requirements and special requirements for drainage projects in King County and how we meet these requirements: Core Requirement No. 1: Discharge at the Natural Location _ The discharge from a proposed project site must occur at the natural location. Response: The existing site runoff drains toward a ditch along the north property line. This ditch has no outlet to it, so most runoff currently infiltrates. This project proposes to discharge to the storm drainage system on the south side of the site within South Grady Way, of which most of the surrounding property drains to. Core Requirement No. 2: Off-Site Analysis All proposed projects must identify the upstream tributary drainage area and perform a downstream analysis. Levels of analysis required depend on the problems identified or predicted. At a minimum, a Level I analysis must be submitted with the initial permit application. Response: An off-site analysis was performed and submitted for this project with the initial drainage report. Please refer to that report. Core Requirement No. 3: Runoff Control Proposed projects must provide runoff control to limit the developed conditions, peak rates of runoff to the predevelopment, peak rates for specific design storm events based on the runoff of defined existing site conditions, and install biofiltration measures. Response: Detention has been provided for this project to limit the release rates for developed conditions to the predevelopment rate. Biofiltration was not utilized. In lieu of biofiltration, a coalescing plate oil/water separator was utilized. Core Requirement No. 4: Conveyance System All conveyance systems for proposed projects must be analyzed, designed and constructed for existing tributary off-site runoff and developed on-site runoff from the proposed project.. Response: The conveyance systems were sized for the 25-year/24-hour storm event for this project and the off-site conveyance system was checked for 100-year storm conveyance from the surrounding contributing area and the additional new on-site contributing area. Core Requirement No. 5: Temporary Erosion and Sedimentation Control All projects that require engineered drainage plans shall provide temporary erosion and sedimentation control measures that minimize the transport of sediments to drainage facilities, water resources, and adjacent properties. Page 1 of 4 5131.010 [JJ/kn/ks] Response: We have provided temporary erosion and sedimentation control measures as required. Core Requirement No. 6: Maintenance and Operation Maintenance of all drainage facilities constructed and modified by a proposed project is the responsibility of the developing owner, except King County may assume maintenance of drainage facilities constructed for formation of plats and divisions, planned unit developments, and some short plat subdivisions 2 years after construction approval. Response: Not applicable. Core Requirement No. 7: Bonds and Liability All drainage facilities for proposed projects except drainage stub out connections, downspout roof drain infiltration systems, and downspout dispersion systems for single-family residential lots must be constructed in conformance with the bond and liability requirements of King County Code 9.04.100. Response: Not applicable. In addition to the 7 core requirements, 12 special requirements may apply to the proposed project. Following is a listing in response to these special requirements: Special Requirement No. 1: Critical Drainage Area Threshold: If a proposed project lies within a designated critical drainage area as indicated on the critical drainage area maps. Response: The proposed project does not lie within a designated critical drainage area. Special Requirement No. 2: Compliance with an Existing Master Drainage Plan Threshold: If a proposed project lies within an area covered by an approved master drainage plan. Response: This project does not lie within an area covered by an approved master drainage plan. Special Requirement No. 3: Conditions Requiring a Master Drainage Plan Response: This project does not require a master drainage plan. Page 2 of 4 5131.010[JJ/kn/ks] Special Requirement No. 4: Adopted Basin or Community Plan If a proposed project lies within an area with an adopted basin or community plan. Response: This project does not lie within an adopted basin or community plan area. Special Requirement No. 5: Special Water Quality Controls Threshold: If any threshold discharge area of the proposed project contains more than 1 acre of new impervious surface that will be subject to vehicle use or storage of chemicals and proposes direct discharge of runoff to a regional facility, receiving water, lake, wetland, or closed depression without on-site peak rate runoff control, or proposes discharge of runoff through overland flow or on-site infiltration into a Class I or II stream or Class I wetland within a 1-mile radius downstream from the project site. Response: This threshold is not exceeded. Special Requirement No. 6: Coalescing Plate Oil/Water Separators Threshold: If a proposed project will construct more than 5 acres of impervious surface in any threshold discharge area, will be subject to petroleum storage or transfer or high vehicular use more than 2,500 vehicle trips per day or heavy equipment use storage or maintenance. Response: This threshold is not exceeded. Special Requirement No. 7: Closed Depression Threshold: If a proposed project will discharge runoff to an existing closed depression and has greater than 5,000 square feet of water surface area at overflow elevation. Response: This threshold is not exceeded. Special Requirement No. 8: Use of Lakes, Wetlands, or Closed Depressions for Peak Rate Runoff Control Response: This threshold is not exceeded. Special Requirement No. 9: Delineation of 100-Year Floodplain Threshold: If a proposed project contains or abuts a stream, wetland, or closed depression or if other City of Renton regulations require a study of flood hazards. Response: This threshold is not exceeded. Page 3 of 4 5131.010 [JJ/kn/ks] Special Requirement No. 10: Flood Protection Facilities for Types 1 and 2 Streams Response: This project does not contain or abut a Class 1 or 2 stream. Special Requirement No. 11: Geotechnical Analysis and Report Threshold: If a project proposes to construct a pond or an infiltration system within 200 feet from the top of a steep slope or on a steep slope with a gradient steeper 15 percent or using a berm higher than 6 feet or modify existing flood protection facilities. Response: This threshold is not exceeded. Special Requirement No. 12: Soils Analysis and Report Threshold: If the soils underlying the project have not been mapped or if existing soil maps are in error or not of sufficient resolution to allow the proper engineering analysis of the proposed site to be performed. Response: A soils analysis has been prepared for this site by a professional civil engineer with expertise in soils to verify and/or map the underlying soils by addressing them as described in the King County SWM manual. 2.0 SUPPLEMENTAL CONVEYANCE CALCULATIONS See the following pages of this Supplemental Drainage Report for a description and calculations to determine capacity and peak flow to the 12-inch concrete storm pipe crossing South Grady Way. Page 4 of 4 5131.010 [JJ/kn/ks] 0L'o 'vi »»» , ..... LAC Z-1 . H. woo ✓1 = Q, ('1 b✓ ✓r�c�,�► ►v� 5 �G i-.�4 loll N�>; S l/ ��hww e a c /J Gc., v- o Lv Ido (� 's 0,a I 1 /i S/QA RarnhAllc Pn Ff1n1 nPPrS _iFRPY SQL OMAN f AR I]FAI FRSNTP I00 YEAR FLOW IN S. ARAf1Y WAY m=e=ss===a:mmcc mCs=semosocm====ca==oe=o;o_==m c.ammxsesxxmmmaam=c smx_-..a- BASIN SIIMMARY BASIN ID: 1oontJ NAMF: IQO YR OFII TN ARATIV WAY SRIIN MFTNO(1O1 OAY TnTAL AREA_ _ _ _ , . 1 _ I d Arrr a RASFFL OWS: (l1_00 r f a RATNFAI I TVPF. . . . : IISFRI PFRt1TQIIS AREA PRPnTPTTATTON_ _ _ I qn inrhAG APFA. _ 0.00 Arrpg T T MF TAITFAt1AI _ _ _ In no min TTMF QF (.ON(.F 70 min TMPFR UTnilq AREA ---- ABSTRACTION COJ_FF! M_?n AREA_ _ 1 _ 14 Acres f'.N_ . _ _ 9R_on PFAk; RATE: 1 _ 11 rfa l)OI : 0 7q Ar--f4 TTMF: d701 min