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Sunrise Over Gervais December 28, 2023 <br />Little Canada, Minnesota Page 2 of 3 <br />Plowe Engineering, Inc. <br />6776 Lake Drive, Suite 110, Lino Lakes, Minnesota 55014 <br />Office (651) 361-8210 • Fax (651) 361-8701 • Website: www.plowe.com <br />Wetlands <br />The site was inspected for wetlands, and Manage A wetland between the elevations of 868.0 <br />and 870.0 on the west side of the property was found. A buffer of more than 75 feet is <br />maintained per RWMWD requirements. No wetland impacts are proposed. <br />Floodplain <br />Per RWMWD, the site has a floodplain elevation of 867.40. <br />Run-off Volume Control <br />Stormwater runoff shall be retained onsite in the amount equivalent to 1.1 inches of runoff over <br />the new and reconstructed impervious surfaces of the development. <br /> Total Proposed New Impervious Area (sf) = 15,164 sf (new pads and driveways) <br />Required Stormwater Runoff Volume (cf) = 15,164 sf x 1.1 in x 1/12 ft/in <br /> = 1,390 cf <br /> Total Provided Treatment Volume (cf) = 3,523 cf (in basins P1 and P2) <br /> <br />A. INFILTRATION BASIN TREATMENT (P1) <br /> <br />The following calculations for the required water quality volume for an infiltration BMP: <br /> <br />New/Reconstructed Impervious Area in Drainage Area = 12,076 sq. ft. <br /> <br />12,076 sq. ft. Impervious x (1.1/12) = 1,107 ft3 required <br /> <br /> 3,341 ft3 provided (888.50 – 889.50) <br /> <br />DRAWDOWN TIME (P1): <br />The following is a summary of drawdown time for the infiltration basin, P1: <br /> <br />HWL = 890.5 <br />Surface Area of Infiltration = 4,384 ft2 <br />Equivalent Drawdown height = 3,341 ft3 / 4,384 ft2 = 0.37 ft <br />0.45 in/hr infiltration (media) = (0.45/12) = 0.0375 ft/hr infiltration <br />Total infiltration time = (0.76/0.0375) = 20.27 hr < 48 hr [OK] <br />_____________________________________________________________________________________ <br /> <br /> <br />