01/25/2011 Env Bd Packet - Laserfiche WebLink

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JIM ASKING RCWD FOR CLARIFICATION • DRAFT 01 -19 -2011 (a) Infiltration BMPs must be designed to provide: 1. Adequate pretreatment measures before discharge of runoff to the primary infiltration area; 2. Drawdown within 48 -hours or 72 -hours from the end of a storm event, for surface or sub - surface features, respectively. Soil infiltration rates shall be based on the appropriate HSG classification and associated infiltration rates (see Table 1 in Appendix A). Infiltration area will be limited to the horizontal areas subject to prolonged wetting; and 3. A minimum of three feet of separation from the seasonal high water table. 4. Design and placement in accordance with the Minnesota Department of Health guidance called "Evaluating Proposed Stormwater Infiltration Projects in Vulnerable Wellhead Protection Areas." (Final version to govern.) (b) Permanent sedimentation and water quality ponds must be designed to provide: 1. Water quality features consistent with NURP criteria and City wet pond criteria; • 2. A permanent wet pool with dead storage at least equal to the runoff from a 2.5- inch rainfall over the area tributary to the pond; and • 3. An outlet structure capable of preventing migration of floating debris and oils for at least the one -year storm. (c) Detention basins must be designed to provide: 1. An outlet structure to control the 2 -year & 100 -year frequency events to existing peak runoff sites; and 2. An identified overflow spillway sufficiently stabilized to convey flows greater than the 100 -year critical storm event. (d) An outfall structure discharging to a wetland, public water or public water wetland must incorporate a stilling- basin, surge- basin, energy dissipater, placement of ungrouted natural rock riprap or other feature to minimize disturbance and erosion of natural shoreline and bed resulting from stormwater discharges. (e) All new residential, commercial, industrial and other habitable or non - habitable structures, and all stormwater basins, must be constructed so that the lowest floor and lowest entry elevations of structures comply with the following table: Local Alternative Format 17