09/08/2021 P&Z Packet - Laserfiche WebLink

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Per the Storm Water Management Plan prepared by Civil Methods, Inc. dated June 18, 2020, the project is expected to disturb approximately 5 acres and add 2.22 acres of new impervious area to the site. Runoff from the site enters Lake Amelia at 4 general locations. Drainage patterns will be maintained from existing to proposed conditions. No other properties will be impacted by runoff from the project. Drainage from the proposed impervious area will be conveyed to stormwater treatment basins and ultimately to Lake Amelia as it does under existing conditions. oo Water Quality Treatment Volume The City requires treatment of runoff based on 1.1" over the new impervious surface. Eight(8) biofiltration basins with native vegetation are proposed for water quality treatment. Infiltration is not feasible due to presence of clay and the site is within the Drinking Water Supply Management Area(DWSMA). oo Runoff Rate Control The City requires no increase in peak flow rates for the 2, 10 and 100 yr. frequency events. With the proposed basins, runoff rates are held or reduced for the overall project. oo Water Quality Control Water quality control is being provided through a series of biofiltration basins (raingardens). A minimum 75 foot wide vegetated wetland buffer along Wetland A(lake) equivalent to the shore impact zone area shall be required as a stormwater management best management practice (BMP) to minimize runoff pollutants from entering the lake. This is supported by City Code Section 1102.07(1)(c)3c. The City Engineer comments that more information is needed to determine low floor separation, basins shall be on the same lot as they are treating, and filtration basins are not allowed in the Drinking Water Supply Management Area. Per City Code Section I IO2.07(2)(a), structures and facilities must be located to meet all setbacks. Stormwater facilities are not allowed within the 150ft OHWL setback, 40 ft CSAH 54 setback or 10 ft side yard building setbacks. The plans shall be revised. Utilities Sanitary Sewer Public sanitary sewer is not available to the site. Private septic systems will be required for each parcel. The plans show a primary and alternate site location per lot and corresponding soil boring data was provided. Standard mound systems are proposed for Lot 1 and Lot 2. Type 3 septic systems are proposed for Lot and Lot 4. Per City Code 6