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2) Low permeability soils (i.e., Hydrologic Soil Group C& D soils) or where a confining layer exists <br /> below the proposed basin; <br /> 3) Within fifty (50) feet of a public or private water supply well (Minn. Rules, Chapter 4725); <br /> 4) Potential storm water hot spots or contaminated soils (filling stations, industrial, etc.); <br /> 5) Within ten (10) feet of a property line or building foundation; and <br /> 6) Within thirty-five (35) feet of a septic system tank or drain field. <br /> 7) Within a Drinking Water Supply Management Area(DWSMA) <br /> 8) Where soil infiltration rates are greater than 8.3"/hr. <br /> b) Infiltration practices must be designed to draw down to the bottom elevation of the practice within forty- <br /> eight (48) hours. The pond depth shall be based on the soil infiltration rate determined from site-specific <br /> soils investigation data taken from the location of proposed infiltration practices on the site (e.g., double <br /> ring infiltrometer test). The maximum pond depth, regardless of infiltration rate shall be two (2) feet <br /> unless otherwise approved by the City Engineer. The soils investigation requirement may be waived for <br /> residential property practices where the maximum pond depth is one (1) foot or less. The following <br /> infiltration rates shall be used for the most restrictive underlying soil unless otherwise supported by an <br /> in-situ infiltration test: <br /> ASTM Unified <br /> Soil Group Rate Soil Textures Soil Class <br /> Symbols <br /> A 1.63 in/hr Gravel, sand, sandy gravel, silty GW, GP <br /> 0.80 in/hr gravel, loamy sand, sandy loam GM SW SP <br /> 0.45 in/hr SM <br /> B Loam, silt loam <br /> 0.30 in/hr ML, OL <br /> C 0.20 in/hr Sandy clay loam GC, SC <br /> D 0.06 in/hr Clay loam, silty clay loam, sandy CL, CH, OH, <br /> clay, silty clay, or clay MH <br /> Source: Minnesota Storm water Manual, January 2014.1 <br /> c) Infiltration practices shall have provisions for pretreatment of the runoff. Examples of pretreatment <br /> include: a mowed grass strip between a curb-cut and a small rain garden, a sump manhole or <br /> manufactured sediment trap prior to an infiltration basin, and a sediment forebay as the first cell of a <br /> two-cell treatment system. Where the infiltration system captures only clean runoff(e.g., from a rooftop) <br /> pretreatment may not be required. <br /> d) The design shall incorporate a diversion or other method to keep construction site sediment from <br /> entering the infiltration system prior to final stabilization of the entire contributing drainage area. <br /> e) The design shall incorporate provisions, where infiltration practices are proposed, that will prohibit the <br /> compaction of soils by construction equipment. <br /> Page 5 of 8 DRAFT <br />