2024-06-04 P & Z Packet - Laserfiche WebLink

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Stormwater volume management practices shall be the equivalent of infiltrating or retaining the first one and one-tenth (1.1) inches of precipitation over the impervious surface of the site. These practices should seek to utilize pervious areas for stormwater treatment and to infiltrate stormwater runoff from driveways, sidewalks, rooftops, parking lots and landscaped areas to the maximum extent practical to provide treatment for both water quantity and quality. A)New Development projects shall achieve no net increase from pre-project conditions (on an annual average basis) of stormwater discharge volume; discharges of total suspended solids (TSS); and discharge of total phosphorus (TP). B)Redevelopment projects shall achieve a net reduction from pre-project conditions (on an annual average basis) of stormwater discharge volume; discharges of total suspended solids (TSS); and discharge of total phosphorus (TP). The requirements of this section may be altered and alternative treatment BMPs approved under the following limitations: 1)Infiltration techniques shall be prohibited when the infiltration structural BMP will receive discharges from or be constructed in areas: (a)where industrial facilities are not authorized to infiltrate industrial stormwater under an NPDES/SDS Permit, (b)where vehicle fueling and maintenance occur (c)with less than 3 feet of separation from the bottom of the infiltration system to the elevation of the seasonally saturated soils or top of bedrock (d)where high levels of contaminants in soil or groundwater will be mobilized by the infiltration of stormwater. 2)Infiltration techniques will be restricted when the infiltration device will be constructed in areas: (a)with predominately Hydrologic Soil Group D soils (b)within 1,000 feet up-gradient or 100 feet down-gradient of active karst features (c)within a Drinking Water Source Management Area (DWSMA) as defined in the cities Wellhead Protection Plan (d)where soil infiltration rates are more than 8.3 inches per hour C)If volume and pollutant management controls cannot be constructed on-site, off-site locations where the controls can be met must be identified. Guidance for best management practices and standards for these mitigation processes should follow the Minimal Impact Design Standards (MIDS) Design Sequence Flowchart for flexible treatment options contained in the MN Stormwater Manual. 157.08. Impaired Waters and Total Maximum Daily Loads. If a site drains to a surface water that has been listed as impaired pursuant to section 303(d) of the federal Clean Water Act more stringent water quality measures will be required. If a Total Maximum Daily Load (TMDL) has been written for the impaired water then all best management practices deemed necessary to comply with the requirements of the TMDL must be implemented. 416 |Page