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Lester loams. These soils are of Hydrolagic Soil Group {HSG�Type C,and have restricted <br /> infilt�ation rates{additional sails information is included in Appendix A). Hydric soils are <br /> present in tfie low/wetland areas. <br /> The site generally drains from north to south into surrounding wetlands (Figure 1,Appendix B); <br /> runoff ftom Wayzata Blvd. is conveyed to the wetlands by road ditches and wi11 not pass <br /> through the site. The wetlands are part of a larger wetland complex tied together south of <br /> Highway 212; all site runoff enters the wetland complex, and overall drainage patterns are to <br /> be maintained after development. <br /> 3. PROPOSED STORMWATER MANAGEMENT <br /> The proposeci site will be graded to drain to storm sewer for conveyance to the new <br /> stormwater management area (Figure 2,Appendix 8). Nearly all new impervious area runoff <br /> will be treated in the biofiltration BMP, including that from all new street surfaces. <br /> 3.1 VOLUME CONT`ROL <br /> The required treatment WQV of 1"fram the site impervious areas will be met with a single <br /> biofiltration area at the western edge of the development. A wet pond forebay adjacent to <br /> the filtration shelf will provide pretreatment for the biafilter. Orainage from all but the <br /> backyards of the sauthem row of houses will be conveyed to the treatment area. The filter <br /> wiU cansist of 18 inches of filtration topsoil media (50-659�o sand, 20-359�o topsoil, 5-109�0 <br /> compost)with a rock-encased 4" underdrain. The fo{lowing calculation shows the infiftration <br /> volume required for this site, as well as what will be provided wlth the current design. <br /> MPCA Water Qualihr Volume Calculation: <br /> 1.0"x lmpervlous Area=0.0833 x 95,860 sq.ft. =7,990 cu.ft.=0.183 ac ft <br /> Tota!Filter Valume Required=0.183 ac ft <br /> Total Filter Volume Provided=0.184 ac ft <br /> A conservative hydrauilc conductivity/filtration rate of 1.Q inches/haur for the ftlter media, <br /> and the required 48 hour drawdown time,yiefds a footprint of 2,000 sq. ft to adequately filter <br /> the WQV (see WQV design event in HydroCAD output, Appendix C). Runaff enter(ng the wet <br /> pool will overflow onto the biofilt�atlon shelf until a depth af 1.05' is reached,at which point <br /> discharge will begin over the weir in the outlet control structure {OCS). Filtered water will <br /> pass through the underdrain to the downstream side of the weir within the OCS. <br /> The wet pond fo�ebay wiN provide a treatment pool voiume of 7,970 cu.ft., or 100�0 of the <br /> WQV (see volurne below Starting Water Surface Efevation,Appendix C}. A submerged outlet <br /> Eisinger Meadow-SWMP Page I 2 <br /> March 2016 <br />