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Stillwater, MN <br />Design Criteria (for new construction): <br />Irregularly shaped with minimum length to <br />width ratio of 1.5:1 <br />Permanent pool volume of '1800 cubic feet per <br />acre draining to pond. <br />Permanent pool depth 3' minirnum, 10' <br />maximum at deepest points <br />Extended detention (ED) storage sufficient to <br />treat V,N, <br />Pre-treatment required (sediment forebay <br />sized at 10% of pond area recommended) <br />Stabilized emergency overflow and energy <br />dissipation at all outlets <br />Side slopes not to exceed 1 V:3H <br />Benefits: <br />► Able to effectively reduce many pollutant loads <br />and control runoff flow rates <br />► Relatively straightforward design procedure <br />► Potential wildlife habitat and aesthetic or <br />recreational enhancement <br />► May be used as temporary sedimentation <br />basin during construction <br />Limitations: <br />Relatively large space requirement <br />Tends to increase water temperature and may <br />cause downstream thermal impact <br />Potential for nuisance insects or odor <br />Problematic for areas of low relief, high water <br />table, or near -surface bedrock <br />> Possible safety concerns <br />1 <br />A constructed basin situated to receive local <br />stormwater runoff and hold designated <br />volumes of runoff for specified periods of <br />time. The objectives are to improve water <br />quality through settling and biological <br />uptake, and prevent downstream channel <br />degradation or flood damage through <br />storage and outflow rate reduction. <br />Water Quality (V,,,o) <br />Channel Protection (VCP) <br />Cverbank Flood Protection (V P o) <br />Extreme Flood Protection (V pioa) <br />Recharge Volume (VRE) <br />17- MECHANISMS <br />Infiltration <br />Screening/ Filtration <br />Temperature Control <br />Settling <br />Evaporation <br />Transpiration <br />Soil Adsorption a n<<P(n <br />Y<<' Biological/ Micro. Uptake <br />Total Suspended Solids <br />Nutrients - Total Phosphorus/ <br />Total Nitrogen <br />Metals - Cadmium, Copper, Lead, <br />and Zinc <br />R Pathogens - Coliform, Streptococci, <br />E. Coli <br />Toxins - Chloride, Hydrocarbon, <br />Pesticide <br />