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(b) Better Site Design principles will be incorporated and water quantity <br />BMPs (as defined in this ordinance) must be incorporated to the following standards: <br />1. BMP volume must retain the one -year event by providing at least the <br />volume equal to the runoff from a 2.3 -inch, 24 -hour storm over the tributary area within <br />the site under proposed conditions. <br />a. Infiltration BMPs (see City BMP standard plates and design <br />criteria) are to be incorporated in areas with A & B hydrologic soil groups. Stormwater <br />from impervious surfaces other than rooftops must be pretreated before discharge to <br />infiltration BMPs, to remove sediment and floatables, or other materials that would <br />restrict the BMP's capacity or contaminate ground water. <br />b. In the following areas, the volume requirements shall be provided <br />by bio- filtration features or two -cell wetland treatment systems (see City standard plates <br />and design standards): <br />(i) Areas of C or D hydrologic soil groups that cannot be routed by a <br />gravity system to onsite A or B hydrologic soil groups; Areas with a groundwater table <br />within three (3) feet of surface, or otherwise at an elevation that poses a threat of <br />groundwater contamination or renders the infiltration BMP ineffective; <br />(ii) Areas where soil contamination is present or land use history <br />indicates a likely threat of soil contamination. <br />(c) In addition to the BMPs required under (6)(b), volume control measures <br />are required reducing runoff by at least the volume from 0.5- inches of rainfall over <br />impervious surfaces on the site (0.5 -inch multiplied by impervious area). Volume <br />reduction required under this paragraph may be achieved only by the following measures: <br />Reestablishment of Effectively Drained Wetlands and Floodplain Meadows Upland <br />Restoration/Conservation, Restoration of Degraded Wetlands, Impervious Disconnection, <br />Soil Amendments /Tilling. <br />Volume Reduction Measures <br />Volume Calculation <br />Reestablishment of Effectively <br />Drained Wetlands and Floodplain <br />Meadows <br />1.0" x surface area (ac) for <br />floodplain meadows and seasonally <br />flooded, scrub shrub, and forested <br />wetlands <br />0.5" x surface area (ac) for fully <br />vegetated Type 2 and 3 wetlands <br />Upland <br />Restoration/Conservation <br />0.85" x surface area (ac) <br />Restoration of Degraded Wetlands <br />0.25" x surface area (ac) <br />Impervious Disconnection <br />Up to 0.5" x disconnected <br />P101 <br />• <br />