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MINNEHAHA CREEK <br />QUALITY OF WATER <br />June 18, 2018 <br />Proposed Subdivision: 387 Orono Orchard, Orono <br />Rules Triggered: <br />WATERSHED DISTRICT <br />QUALITY OF LIFE <br />Erosion Control, Wetland Protection and Stormwater Management Rules <br />Stormwater Management: <br />MCWD Stormwater Management Rule is triggered for land disturbance that creates new or replaces <br />existing impervious surface and/or subdivides a parcel greater than one acre in size into three or more <br />lots. <br />For the purposes of determining treatment scope, the project is considered redevelopment. <br />The project as proposed shows an increase in impervious surface greater than 50%. Therefore <br />phosphorus, rate, and volume control is required for the entire site's impervious surface. <br />Table 4: Stormwater management requirements for redevelopment resulting in an increase in impervious <br />surface <br />Site Size <br />Site Disturbance <br />Impervious Surface Increase <br />Requirements <br />Treatment Scope <br /><_ 1 acre <br />N/A <br />N/A <br />Incorporate 13MPs <br />N/A <br />< 50% increase in <br />Additional impervious <br />< 40% site <br />impervious surface <br />Phosphorus Control, <br />surface <br />Rate Control, and <br />o <br />>_ 50/ increase in <br />Entire site's impervious <br />disturbance <br />Volume Control <br />> 1 <br />impervious surface <br />surface <br />acre <br />Phosphorus Control, <br />>_ 40% site <br />Rate Control, and <br />Entire site's impervious <br />disturbance <br />N/A <br />Volume Control <br />surface <br />Volume control is achieved by abstraction of the first 1" of rainfall off the site's impervious surface. <br />Phosphorous control is assumed to be achieved through the volume control. If abstraction of one 1" is <br />not feasible an abstraction analysis must be provided that lists the variables limiting the feasibility of <br />providing the required abstraction and the efforts undertaken to improve the feasibility of abstraction. If <br />abstraction of 1 inch is not feasible, a half inch of abstraction shall be provided and phosphorus control <br />should be provided as though an inch was abstracted. In that case, water quality modeling, such as P8 or <br />MIDS should be submitted with a dummy model showing the phosphorus removal from infiltrating a 1 <br />inch event over all of the impervious surface. <br />We collaborate with public and private partners to protect and improve land and water for current and future generations. <br />........................................................................................................................................................................................ <br />15320 Minnetonka Boulevard, Minnetonka, MN 55345 • (952) 471-0590 • Fax: (952) 471-0682 • www.minnehahacreek.org <br />