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9610 19th Avenue SE <br /> July 27, 2012 �r <br /> Revised September 18, 2012 <br /> Page 5 <br /> III. SITE DEVELOPMENT PLAN W/ ON-SITE STORMWATER MANAGEMENT <br /> On site design considerations: <br /> 1.) Retaining duff layer, native topsoil and natural vegetation to the maximum extent <br /> feasible. <br /> This project is being built on the minimum footprint possible for the storage facility <br /> proposed. To the maximum extent feasible, the west side of the site is being <br /> retained in a natural state. <br /> 2.) Retaining to the maximum extent practicable the features on the site that provide <br /> natural stormwater management. <br /> This project leaves all of the natural drainage elements on the west side of the site <br /> untouched, including the wetland buffer. <br /> 3.)Maintaining predevelopment flow path lengths and natural drainage patterns <br /> whenever possible. <br /> This project is being built on the minimum footprint possible for the storage facility <br /> proposed. To the maximum extent feasible, the west side of the site is being <br /> retained in a natural state. <br /> 4.) Keeping distances for overland flow short to promote sheet flow and minimize <br /> concentration of runoff. <br /> Based on the site layout, there are few opportunities to sheet flow disperse runoff. <br /> However, the site achieves relatively lengthy sheet flow times prior to collection in <br /> catch basins. <br /> 5.)Managing stormwater as close to its origin as possible. <br /> Since downspout dispersion and sheet flow dispersion are not feasible on this site <br /> traditional stormwater detention is proposed. <br /> 6.) Directing runoff to areas of permeable soils or natural depression areas to promote <br /> infiltration. <br /> Stormwater infiltration is not proposed on this project since there is limited <br /> infiltration capacity (0.25 inches/hour) and the detention pipe is under the building. <br /> 7.) Integrating numerous small, dispersed bioretention areas to capture, store and <br /> infiltrate stormwater on site. <br /> Open bioretention facilities are not possible in the layout of this project. <br /> 8.) Designing roads, parking tots and other proposed site features to follow the site's <br /> topographic contours in order to minimize cuts and fills and the resulting soil and <br /> vegetation disturbance and loss of topsoil or organic duff layer. <br /> This project has been designed to minimize earthwork and disturbance of subgrade. <br /> In fact, by minimizing the disturbance of the subgrade, this project is able to stay <br /> under the one acre threshold which requires the use of the WWHM3 stormwater <br /> model. <br /> Ph: (206)403-0933, email:jayd@deckerce.com <br />