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Silver Lake Plaza <br />Minimum Requirement # 6: Runoff Treatment <br />Due to the site proposing more than 5,000 sf, of new/replaced pollution generating hard <br />surfaces, runoff treatment is required. Due to the project consisting of a commercial site, <br />enhanced water quality treatment is required. Detained runoff from approximately <br />22,430 sf of paved driving and parking areas along with detained non -pollution <br />generating runoff from approximately 9,872 sf. of roof and sidewalk areas and 8,597 sf. <br />of lawn area is to pass through the proposed water quality treatment BMP. The site <br />requires enhanced treatment; therefore, per BMP T8.30 "Linear Sand Filters" and BMP <br />T8.11 "Large Sand Filter Basin," a post -detention 48'x3' large linear sand filter with a <br />minimum 95% water quality treatment rate (95.78% designed) has been selected for this <br />project. Refer to Detention and -Water Quality Sizing Calculations later in this report for <br />large linear sand filter sizing calculations. <br />Minimum Requirement # 7: Flow Control <br />Due to the site proposing more than 10,000 sf. of new hardscape, flow control is required. <br />Flow control is to be provided by a 6' diameter underground detention pipe located in the <br />southern portion of the site with a large linear sand filter located post detention. Note <br />that approximately 1,922 sf. of site area, consisting of mainly minor sidewalk and <br />landscaping area along the west and northern side of the new building bypass the <br />detention facility. This bypass area has been factored into the point of compliance <br />criteria for detention sizing along with upstream runoff from the adjacent properties to <br />the east of the site. Refer below for basin description and impervious area breakdown. <br />Refer to the "Detention Calculations" in the following sections for detention sizing <br />calculations (pre and post bypass). <br />Site Summary <br />Total Property/disturbance Area = 40,899 sf. (0.939 Ac.) <br />Upstream Basin = 7,000 sf. (0.161 Ac.) <br />Total Basin Area = 47,899 sf. (1.100 Ac.) <br />Upstream Basin <br />Ex. Lawn Area = 7,000 sf. (0.161 Ac.) <br />Existing Site <br />On -Site Impervious area: <br />None <br />The entire project clearing area is to be modeled as existing forest. <br />Existing Site Area for Detention Sizing = 40,899 sf. (assume forested) <br />WESTERN ENGINEERS, INC. 15 PROJECT: 15-1415-A <br />