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owned by Elk River Landfill will be utilized as the outlet channel for the southwest storm water <br />• pond. The channel outlet will be re-excavated to match the elevation of the more southerly <br />outlet to ensure that flows through the south outlet onto the adjoining property are not <br />significantly increased from the exiting condition. The following table summarizes the existing <br />and proposed 25-year flood conditions for the northwest wetland: <br /> Normal Water Elevation <br />(ft 25-year Flood Elevation <br />(ft) 25-Year Outlet Channel Flows <br />(cfs) <br />Existin 955.76 956.00 1.3 0.0 <br />Pro osed 955.76 956.27 3.9 3.9 <br />The General Permit for Construction requires wet sedimentation ponds discharge at no greater <br />than 5.66 cfs/surface acre of pond for the water quality volume event (2.5-inches over 24-hours). <br />The Pond 1 outlet limits discharge out of P-1 to 2.4 cfs for the 2.5" rainfall event. The surface <br />area of the P-1 at the invert elevation (989.0') is 43,473 ft2. The resulting ratio is 2.4 cfs/surface <br />acre of pond which is less than the requirement of 5.66 cfs/surface acre of pond and is in <br />accordance with Part IILC. l .c of the General Permit for construction activity. <br />• <br />I:\3230\323008001\Itepor[s\Application\Drainage Calculations -Surface Water Management.doc <br />