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7. ON-SITE STORMWATER MANAGEMENT <br /> As documented in Section 1 of this report this project is required to meet Minimum <br /> Requirements 1-5. As a result, this project is required to use the On-Site Stormwater <br /> Management BMP's from Chapter 12 of Volume Ill in the 2010 COE SWMM. <br /> Per the COE SWMM the BMP's must be evaluated in the order they are listed. <br /> BMP's for roofs: <br /> 1. BMP 12.30 On-site infiltration areas: <br /> As previously mentioned in this report, the soils were found to be glacial till at a depth <br /> of 24 inches below grade. Glacial till has a very low permeability rate and does not <br /> infiltrate runoff effectively. Since this can be considered hard pan and was found less <br /> than 3 feet below grade, infiltration is not feasible for this site. <br /> 2. Downspout Dispersion Systems: <br /> All requirements for downspout dispersion can be met. Therefore, roof runoff will be <br /> dispersed via a combination of splash blocks and a dispersion trench. Two splash <br /> blocks are proposed on the southern side of the house. No more than 700 sf of roof <br /> area shall be directed to a single splash block. Runoff from splash blocks shall have a <br /> minimum of 50-foot vegetation flow path before reaching the northern property line. <br /> Due to limited flow path on the north side of the site, the remainder roof area shall be <br /> directed to a dispersion trench. The dispersion trench shall be sized using 10 linear <br /> feet per 70 sf of roof area. A 25-foot vegetated flow path is required before flows <br /> reach the property line. <br /> 3. Perforated Stub-out Connections <br /> Higher priority BMP selected. <br /> BMP's for other hard surfaces: <br /> 1. Sheet Flow Dispersion: <br /> Feasible and selected for this project. The driveway will sheet flow over amended soils <br /> to the north. A 2 foot wide transition zone shall be used. <br /> Lawn and Landscaped Areas: <br /> 1. Post-Construction Soil Quality and Depth: Required <br /> Any area of the site not proposed to be covered with impervious surfaces but graded or <br /> compacted will be treated to meet the criteria for BMP 12.20. Please refer to the <br /> engineering plans for basic soil amendment notes. <br /> Bayview SFR 18-0806 <br /> August 2018 Page 10 <br />