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<br />infiltrate stormwater runoff from driveways, sidewalks, rooftops, parking lots, and landscaped areas to the <br />maximum extent practical to provide treatment for both water quality and quantity. The Minnesota Stormwater <br />Manual (MN Pollution Control Agency), the Minnesota Urban Small Sites BMP Manual (Metropolitan Council), <br />Local Road Research Board BMP Maintenance Guide, and Protecting Water Quality in Urban Areas (MPCA) <br />are resources that provide guidance in achieving these goals. <br />(A) Implementation. Low Impact Development, Better Site Design, or Green Infrastructure design <br />techniques are the preferred methods of achieving stormwater management. Mimicking the natural topography <br />and land cover as they exist in the pre-developed condition to meet the standards and requirements of the City <br />and other regulatory agencies shall be the first consideration. <br />(B) Recommended Practices. Practices and methods used to achieve the intent of the above paragraph <br />shall include, but not be limited to, the following: <br />(1) rain gardens <br />(2) green roofs <br />(3) bio-retention practices <br />(4) pervious pavements or pavers <br />(5) plots of native vegetation and/or buffers in place of sod <br />(6) reforestation and revegetation <br />(7) trees and tree box filters <br />(8) reduction of impervious area <br />(9) rain water harvesting <br />(C) Other Practices. Other traditional stormwater BMPs may be approved on a site <br />by site basis to achieve the goals of water quality and quantity, and rate control. These practices shall conform <br />to the standards outlined in the resources referenced above. <br />(D) All stormwater runoff shall be pre-treated prior to discharge to any surface water. <br />(E) Maintenance Plan. A plan shall be established to maintain all temporary and permanent BMPs in a <br />working and efficient condition. This may include removal of invasive species, sediment, debris, or any other <br />foreign or obstructive object or condition that prevents the BMPs from performing as designed. <br />(F) Exemption. The mill and overlay or rehabilitation of a public roadway that does not create additional <br />impervious surfaces; and sidewalk or trail projects are exempt from these stormwater requirements. These <br />projects may be subject to other regulations. <br /> <br />157.06157.22. Drainage. <br />Site alteration, grading, placement and installation of BMPs and other related activities shall be implemented in <br />such a way that drainage from the site shall not exceed the pre-developed rates and will not adversely affect <br />neighboring properties. <br /> <br />157.08. 157.23 Calculations. <br />Hydrologic and hydraulic design calculations must be submitted for the pre-development and post-development <br />conditions for the 2, 10, and 100 year events as well as the 10 day snow melt event. Such calculations shall <br />include: (i) description of the design storm frequency, intensity and duration, (ii) time of concentration, (iii) Soil <br />Curve Numbers or runoff coefficients, (iv) peak runoff rates and total runoff volumes for each watershed area, <br />(v) infiltration rates, where applicable, (vi) culvert capacities, (vii) flow velocities, (viii) data on the increase in <br />rate and volume of runoff for the design storms used, and (ix) documentation of sources for all computation <br />methods and field test results. <br /> <br />418 |Page <br /> <br /> <br />