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Clv it Sit le <br /> CMR O U P <br /> 2.4 Stormwater Requirements City(Mounds View): <br /> The City of Mounds View defers to the Rice Creek Watershed District requirements. <br /> 2.5 Stormwater Requirements Watershed (Rice Creek Watershed District): <br /> Requirement threshold -A permit is required for subdivision of an area exceeding one acre. <br /> Rate Control— Peak stormwater runoff rates for the proposed project at the project site boundary, in <br /> aggregate, must not exceed existing peak runoff rates for the 2-year, 10-year and 100-year, 24-hour rainfall <br /> events. <br /> Water Quality Volume—The required water quality treatment volume is determined using the calculation <br /> below. For filtration basins a TP removal factor of 0.50 is required. <br /> Area of New or Reconstructed Impervious Surface(ft2)x 1.1(in) <br /> Required Water Quality Treatment Volume= TP Removal Factor x 12( n) <br /> ft <br /> 2.6 Stormwater Requirements - Minnesota Pollution Control Agency—NPDES permit(MPCA): <br /> Requirement threshold -A permit is required for projects with a disturbed area over 1 acre in size, <br /> Stormwater management is required for a project adding 1-acre of more of NEW impervious surface <br /> (reconstructed impervious is not included). <br /> Rate Control— No specific regulation, may not degrade downstream facilities. <br /> Water Quality—Stormwater water quality treatment volume must be provided equal to 1.0" over all new <br /> impervious surfaces (includes all newly constructed impervious surfaces only, re-constructed impervious <br /> surfaces are not included). <br /> Volume Control— Must consider volume reduction if feasible and not prohibited on site. The required <br /> infiltration volume is equal to the water quality volume described above. <br /> 3.0 Stormwater Calculations: <br /> 3.1 Proposed Stormwater Management Strategy& Facilities Description <br /> This project is disturbing approximately 2.14 acres of land. The project will be constructing 1.1 acres of <br /> new/reconstructed impervious surfaces. This land disturbance and creation of impervious surfaces will trigger <br /> stormwater management requirements from the Rice Creek Watershed District and the MPCA NPDES permit. <br /> The proposed stormwater strategy for this project is directing the site's stormwater runoff via surface drainage <br /> and storm sewer piping to two aboveground filtration basins. Each basin will outlet to the existing wetland. <br /> Drainage patter's will not be changed due to the project. Each filtration system has been designed to provide <br /> filtration for the volume requirement and the required water quality and rate control. The outlet for each basin <br /> is control by an Outlet Control Structure, each with a custom weir wall. <br /> 3.2 Rate Control <br /> Rate control is provided by live storage within the proposed filtration basin. This information was derived using <br /> HydroCAD stormwater modeling software. A significant portion of the adjacent church property currently <br /> drains into the exiting wetland on site. The proposed utility/grading/stormwater design anticipates collecting <br /> this runoff and managing it in the north filtration basin for Rate Control purposes only. The proposed runoff <br /> rates into the existing wetland are less than the existing conditions. <br /> The existing and proposed runoff rates are shown in the summary table below. <br /> Civil Site Group, PC• 5000 Glenwood Avenue• Golden Valley Minnesota 55422 <br /> www.CivilSiteGroup.com•(612)615-0060 <br />