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First, the new roof area will be collected and conveyed to a 6,500-cubic-foot StormChamber detention system <br /> located east of the showroom under the central parking area. Tables 4-1 and 4-2 below detail the existing and <br /> proposed stormwater discharge rates based on the flow control performance standard above. <br /> Table 4-1: New Roof Existing Versus Proposed Site Areas <br /> Existing Site Areas Proposed Site Areas <br /> (SF) (SF) <br /> Impervious Surface(Roof) 3,130 8,346 <br /> Impervious Surface(Pavement) 5,216 0 <br /> Pervious Surface 0 0 <br /> Table 4-2: New Roof Existing Versus Proposed Peak Flows Rates <br /> Predevelopment Runoff Post-Development Runoff <br /> Tr (Years) Discharge Tr (Years) Discharge <br /> (cfs) (cfs) <br /> 2-Year 0.004 2-Year 0.002 <br /> 10-Year 0.008 10-Year 0.006 <br /> 25-Year 0.011 25-Year 0.008 <br /> 50-Year 0.012 50-Year 0.009 <br /> Second, the remaining on-site disturbed area will be treated for both water quality and flow control by <br /> capturing a sub-basin in-kind. The in-kind area will be routed through a Biopod water quality unit before <br /> conveyed to a 21,000-cubic-foot R-tank full-infiltration system. The Biopod system will provide required runoff <br /> treatment and pre-settling required before infiltration per DOE Manual Section V-5.3. <br /> See Figures 4-1 and 4-2 for the onsite disturbed area and the sub-basin captured in kind. The new roof area is <br /> treated by the StormChamber detention system, as noted above. <br /> If 7111111111 _ 1 1,1 111111'1111 1 11 11 <br /> __ ____ .1.1.111_ j <br /> y <br /> 44. <br /> , * / dP . <br /> EL, , , <br /> ...." '/ <br /> i - . - ' . ---.,-, .4- <br /> li, • <br /> / <br /> / <br /> sdi <br /> Figure 4-1: Disturbed Areas <br /> LMJ Hyundai—Showroom Remodel <br /> 7 <br />