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(iii) Peak Stormwater Runoff Control. Stormwater runoff rates for the proposed <br />project must not exceed runoff rates for the critical two-year and 100 -year frequency <br />events. For those site areas not covered by hard surface in the pre - existing <br />condition, runoff rates are to be determined for the pre - settlement condition. The <br />following curve numbers shall be utilized for pre - settlement condition modeling: <br />Hydrologic Soil Group <br />Runoff <br />Nam <br />A <br />30 <br />B <br />58 <br />C <br />71 <br />D <br />78 <br />* Curve numbers from USDA -NRCS, Technical Release 55 <br />(iv) Bounce and Inundation Period. The project must meet hydroperiod <br />standards adapted from "Stormwater and Wetlands Planning and Evaluation <br />Guidelines for Addressing Potential Impacts of Urban Stormwater and Snowmelt <br />Runoff on Wetlands," (Minnesota Stormwater Advisory Group, June 1997), as <br />follows: <br />Highly <br />susceptible <br />wetland <br />Pre - development <br />Existing <br />Existing <br />Moderately <br />susceptible <br />Pre - development <br />+ 0.5 feet <br />Existing plus 1 Existing plus 2 <br />day days <br />Slightly <br />susceptible <br />wetland <br />Pre - development <br />+ 1.0 feet <br />Existing plus 2 Existing plus 14 <br />days days <br />Least - susceptible <br />wetland /Lake <br />No limit <br />Existing plus 7 Existing plus 21 <br />days days <br />(c) Design Criteria. <br />(i) Infiltration BMPs must be designed to provide: <br />(a) Adequate pretreatment measures before discharge of runoff to the <br />primary infiltration area; <br />(b) Drawdown within 48 -hours from the end of a storm event Soil <br />infiltration rates shall be based on the appropriate HSG classification and <br />associated infiltration rates (see Table 1 in Appendix C). Infiltration area will <br />DRAFT DOCUMENT <br />12 <br />• <br />• <br />