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(I) Outfall structures within wetlands and public waters and public waters <br />wetlands must incorporate a stilling basin, surge basin, energy dissipater, <br />placement of ungrouted natural rock riprap or other devices to minimize <br />disturbance and erosion of natural shoreline and bed resulting from stormwater <br />discharges. <br />(j) All new residential, commercial, industrial and other habitable or <br />non habitable structures must be constructed so that the lowest floor elevations <br />are a minimum of two feet above the critical event 100 -year high water elevation <br />and are one foot above the overflow <br />elevation of nearby surface waterbodies wetlands and stormwater basins. Within <br />landlocked basins, lowest floor elevations must be at least one foot above the <br />surveyed basin overflow elevation. <br />(k) Development resulting in the creation of impervious <br />surfaces must explicitly address use of best management <br />practices (BMP's) to first limit the loss of pervious <br />area; and second, to infiltrate runoff which does occur <br />from impervious areas to the extent feasible considering <br />site©specific conditions. BMP's include the use of <br />vegetated swales, pond outlets perched above groundwater <br />levels, use of infiltration systems, roof drainage to <br />pervious areas, minimum of twenty percent pervious <br />surface, use of depressed/casual storage areas, and <br />minimization of the number and width of parking stalls <br />and use of deep-rooted native vegetation, and narrower <br />"rural section" roads. <br />The goal of these BMP's is to incorporate practices into <br />the design which are capable of infiltrating the <br />impervious surface runoff from the Mpls-St.Paul median <br />storm (0.34 inches) in seventy-two hours. Infiltration <br />volume will be calculated using the appropriate <br />hydrologic soil group classification and saturated <br />infiltration rate from the table below. <br />Hydrologic <br />Soil Group Infiltration Rate Soil Textures <br />A 0.50 in/hr sand, loamy sand, or sandy loam <br />B 0.25 in/hr silt loam or loam <br />C 0.10 in/hr sandy clay loam <br />D 0.03 in/hr clay loam, silty clay loam <br />silty clay, or clay <br />Source: Urban Hydrology for Small Watersheds, SCS, June 1986. <br />Infiltration area will be limited to the horizontal areas subject to prolonged <br />wetting. <br />Areas of permanent pools tend to lose infiltration capacity overtime and will <br />not be accepted as an infiltration practice. <br />(1) Landlocked basins may be provided with outlets only if they: <br />(1) Retain a hydrologic regime which complies with District Wetland Alteration <br />Rule F. <br />(2) Provide sufficient dead storage volume to <br />retain back to back 100 year, twenty four hour <br />rainfalls and runoff. <br />(3) Do not create adverse downstream flooding or water quality conditions as a <br />result of increased discharge rate or volume, or other factors. <br />(m) All stormwater management structures and facilities <br />must be properly maintained in perpetuity to assure that <br />they continue to function as originally designed. This <br />maintenance responsibility must be assumed either by the <br />