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5. SOURCE CONTROL <br /> This project proposes to construct two new SFRs and driveways. Volume IV of the 2019 <br /> DOE Stormwater Management Manual was reviewed for specific BMPs required for this <br /> type of land-use. None of the activities or land uses contained in any of the chapters in <br /> Volume IV applies to this project. Therefore, no site/development specific source control <br /> BMPs are required for this project. <br /> 6. PRESERVATION OF NATURAL DRAINAGE SYSTEM <br /> By grading and then amending the site soils in the area of disturbance while ensuring the <br /> proposed grades maintain slopes in same direction as the current conditions, this will allow <br /> the site to absorb some of the future runoff and provide sheet flow of runoff to the south- <br /> southeast. This will mimic the existing conditions by maintaining the existing direction and <br /> condition of flow from this site. <br /> 7. ON-SITE STORMWATER MANAGEMENT <br /> List #1 in the SWMM volume 1 section 2.5.5 provides multiple BMP options for runoff <br /> management, conveyance BMPs and Discharge BMPs. Each option was reviewed for this <br /> project and the most suitable was selected. Standard Project Runoff Manage Options <br /> Lawn and Landscaped Areas: <br /> 1. Post-Construction Soil Quality and Depth: Required <br /> Roofs: <br /> 1. Full Dispersion: Not feasible due to site slopes exceeding 15% and not having the <br /> minimum f00-foot vegetated flow path for developed site runoff. <br /> • 2. Downspout Infiltration Systems: Not feasible due to existing site soils, excessive cuts <br /> required to lower high point on site adjacent to 57th. <br /> 3. Bioretention/Rain Gardens: Not feasible due to existing site soils and excessive cuts. <br /> 4. Downspout Dispersion: Not feasible due to existing off-site slopes exceeding 20%. <br /> 5. Perforated Stub-Out Connections: Selected with outfall from downspout conveyance <br /> system being discharged to level spreader at edge of off-site wetland. <br /> The As previously mentioned, the soils for this project wece4494144 are alderwood-urban land <br /> • complex and there will be a cut of approximately 10-feet in the front of the lots and 14-feet <br /> or more in the south side of the proposed SFRs. Therefore, the site soils cannot be used <br /> 'for1nfiltrafiori'for'this project. 'As a result, all hi-filtration-based BMPs are not feasible. <br /> Seahurst SP 18-1015 <br /> •'May'2020 Page 9 <br />