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The wetland receiving discharge from the site currently has two existing channel outlets, both of <br />which eventually drain into Rice Lake. The north channel outlet, currently located on property <br />owned by Elk River Landfill will be utilized as the outlet channel for the storm water ponds. <br />The channel outlet will be re-excavated to match the elevation of the more southerly outlet to <br />ensure that flows through the south outlet onto the adjoining property are not significantly <br />increased from the existing condition. The following table summarizes the existing and <br />proposed 25-year flood conditions for the northwest wetland: <br /> Normal Water <br />Elevation (ft) 25-year Flood <br />Elevation ft 25-Year Outlet Channel Flows (cfs) <br />South North <br />Existin 955.8 956.0 1.3 0.0 <br />Pro osed 955.8 956.3 4.6 4.6 <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 2.9 cfs for the 2.5" rainfall event. The surface <br />area of the P-1 at the invert elevation (993') is 0.74 acres. The resulting ratio is 3.9 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 III.C.I.c of the General Permit for construction activity. <br />T:\07420 406Uune11 CityApp\Comment raponse\Response_081811 \Attachment t VSurface Water Management Memo 08101 I .doc <br />