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6. 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. <br /> 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 not having 65% preserved vegetation. <br /> 2. Downspout infiltration: Downspout Infiltration Systems: Feasible. All design criteria <br /> can be met for downspout infiltration via an infiltration trench. In addition, the infiltration <br /> feasibility map provided by the City of Everett shows that the area of the proposed infiltration <br /> trench is not infeasible for infiltration. For.these reasons, infiltration has been selected for <br /> the roof of the SFR. <br /> 3. Bioretention/Rain Gardens: Higher priority option selected. <br /> 4. Downspout Dispersion: Higher priority option selected. <br /> 5. Perforated Stub-Out Connections: Higher priority option selected. <br /> As previously mentioned, the soils for this project are considered to be type fine sand to a <br /> depth of 48 inches. Since this soil type is feasible for infiltration, the proposed roof surfaces <br /> will be infiltrated on-site. The amount of infiltration trench required was determined by the <br /> soil type and the requirement stated in section 3.1.1 of the SMMWW. Per section 3.1 the <br /> soil type is classified as "fine sand" and shall be sized using 75 linear feet of trench per <br /> 1,000 sf of roof area for a 2 foot wide trench. The proposed roof surfaces total approximately <br /> 3,244 sf, therefore the infiltration trench will be 70 feet long and 7 feet wide. <br /> Pyatak Duplex 18-0622 <br /> August 2017 Page 9 <br />