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0 <br /> 5.0 Stormwater Control Plan <br /> Existing Site Hydrology <br /> The stormwater on-site currently sheet flows southwest and flows into existing catch basins within <br /> the roadway which are tributary to the existing combined sewer system that runs through the site. <br /> This site has a small upstream drainage basin as it is located near a ridge line. The upstream <br /> drainage area is approximately 1.5 acres and sheet flows southwest toward the project site. Most <br /> upstream drainage is captured within the combined sewer system before reaching the project area. <br /> A topographic map of the vicinity can be seen in Figure 2 within Section 4.1 of this report. <br /> Additional information on existing site hydrology can be found in section 2.0 of this report. <br /> Developed Site Hydrology <br /> The stormwater from the proposed clubhouse building will be routed from downspouts to a rain <br /> garden located along the west side of the building. Stormwater from the proposed parking lot will <br /> sheet flow west to a drainage swale where the run-off will then be routed to the rain garden. <br /> Stormwater will be given the opportunity for treatment and infiltration within the rain garden. In <br /> the event that the rain garden soil media becomes oversaturated or the ponding depth exceeds 6 <br /> inches, stormwater will be routed to the existing combined sewer system through a catch basin <br /> with floatable material separator and gas trap.Additional Information can be found in section 3.0 <br /> of this report. <br /> Performance Standards and Goals <br /> The bioretention facility on site has been designed to match developed discharge durations to pre- <br /> developed durations for the range of pre-developed discharged rates from 50%of the 2-year peak <br /> flow to 50% of the 50-year peak flow. <br /> Low Impact Development Features <br /> This project proposes to use low impact development through use of a rain garden.The rain garden <br /> serves as a small detention/infiltration facility which will allow the stormwater the opportunity to <br /> evaporate or infiltrate before overflowing into the existing conveyance system on site. For more <br /> information, see Section 3.0 of this report. <br /> Flow Control System <br /> Flow control for this project will be provided by the proposed rain garden. Rather than routing the <br /> storm drainage directly into the combined sewer system, the rain garden shall act as a small <br /> detention/infiltration facility. This will allow the storm water to evaporate or infiltrate before <br /> overflowing into the combined sewer system on site. <br /> DAVID EVANS AND ASSOCIATES,INC. <br /> GRANDVIEW APARTMENTS CLUBHOUSE MARCH,2017 <br /> STORMWATER SITE PLAN PAGE 9 <br />