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SECTION III: SITE DEVELOPMENT PLAN W/ON-SITE <br /> STORMWATER MANAGEMENT <br /> The proposal is to construct a commercial building to the south of the site and large <br /> parking area along with sidewalk. The existing building will remain. The access to the site <br /> will be from 40th Ave W. <br /> A Stormtech system SC-740 of capacity 5,504 CF will be located underneath the <br /> parking area near the northeast portion of the site is proposed to meet the flow control <br /> requirements conforming to the City of Everett requirements. The Stormtech system was <br /> sized using Western Washington Hydrology Model V 4.2.14 (WWHM). The roof and the <br /> yard drains will be connected to the onsite detention system. The outflow from the <br /> detention pipe will be discharged to the east. Runoff treatment would be obtained by an <br /> underground Biopod Biofilter manufactured by Oldcastle Infrastructure located <br /> downstream of detention. <br /> Per Minimum Requirement#5 (Section 1-2.5.5 of the SWMMWW), Post- <br /> Construction Soil Quality and Depth BMP T.5.13 is proposed to provide onsite stormwater <br /> management for the lawn and landscaped areas of the site.The following NPGIS BMP's <br /> shall be applied for roof to provide onsite stormwater management and must be considered <br /> in the following order per List#2: Full Dispersion,Bioretention, Downspout Dispersion, <br /> and then Perforated Stub-Out Connections. Full Dispersion is infeasible because the <br /> required native vegetation preservation could not be achieved for the nature of the project. <br /> Bioretention is not feasible because of the poor quality of the soil. Downspout Dispersion is <br /> not feasible because the required vegetated flow path required by the BMP could not be <br /> met. Perforated stub-out is also not possible because of the steep slopes. Therefore the roof <br /> drains will be connected directly to the onsite detention system. The following BMP's <br /> shall be applied to the other hard surfaces: Full dispersion, Permeable Pavement, <br /> Bioretention, and then Dispersion. Full dispersion,permeable pavement and Bioretention <br /> are not feasible because the onsite soils that contain"low infiltration capacity". Basic <br /> Dispersion is not feasible because the required vegetated flow path could not be met. The <br /> yard and roof drains will be connected towards an on-site detention system. <br /> Insight Engineering Co. -Stormwater Site Plan 11/27/18 <br /> - 10- <br />