11/28/2001 Env Bd Packet - Laserfiche WebLink

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Within landlocked basins, lowest floor elevations must be at least one foot above the surveyed basin overflow elevation. (k) Development resulting in the creation of impervious surfaces must explicitly address use of best management practices ( BMP's) to first limit the loss of pervious area; and second, to infiltrate runoff which does occur from impervious areas to the extent feasible considering site- specific conditions. BMP's include the use of vegetated swales, pond outlets perched above groundwater levels, use of infiltration systems, roof drainage to pervious areas, minimum of twenty percent pervious surface, use of depressed /casual storage areas, and minimization of the number and width of parking stalls and use of deep - rooted native vegetation, and narrower "rural section" roads. The goal of these BMP's is to incorporate practices into €he design which are capable of infiltrating the impervious surface runoff from the Mpls - St.Paul median storm (0.34 inches) in seventy -two hours. Infiltration volume will be calculated using the appropriate hydrologic soil group classification and saturated infiltration rate from the table below. Hydrologic Infiltration Soil Group Rate Soil Textures A 0.50 in /hr sand, loamy sand, or sandy loam B 0.25 in /hr silt loam or loam C 0.10 in /hr sandy clay loam D 0.03 in /hr clay loam, silty clay loam, silty clay, or clay Source: Urban Hydrology for Small Watersheds, SCS, June 1986. Infiltration area will be limited to the horizontal areas subject to prolonged wetting. Areas of permanent pools tend to lose infiltration capacity overtime and will not be accepted as an infiltration practice. (1) Landlocked basins may be provided with outlets only if they: (1) Retain a hydrologic regime which complies with District Wetland Alteration Rule F. 13