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DRAFT 12/2/14 <br /> 157.08. Calculations <br /> Hydrologic and hydraulic design calculations must be submitted for the pre-development and <br /> post-development conditions for the 2, 10, and 100 year events as well as the 10 day snow melt <br /> event. Such calculations shall include: (i) description of the design storm frequency, intensity <br /> and duration, (ii) time of concentration, (iii) Soil Curve Numbers or runoff coefficients, (iv)peak <br /> runoff rates and total runoff volumes for each watershed area, (v) infiltration rates, where <br /> applicable, (vi) culvert capacities, (vii) flow velocities, (viii) data on the increase in rate and <br /> volume of runoff for the design storms used, and (ix) documentation of sources for all <br /> computation methods and field test results. <br /> 157.07. Volume Control and Pollutant Management <br /> Stormwater volume management practices shall be the equivalent of infiltrating or retaining the <br /> first one and one-tenth (1.1) inches of precipitation over the impervious surface of the site. <br /> These practices should seek to utilize pervious areas for stormwater treatment and to infiltrate <br /> stormwater runoff from driveways, sidewalks, rooftops, parking lots and landscaped areas to the <br /> maximum extent practical to provide treatment for both water quantity and quality. <br /> A) New Development projects shall achieve no net increase from pre-project <br /> conditions (on an annual average basis) of stormwater discharge volume; <br /> discharges of total suspened solids (TSS); and discharge of total phosphorus (TP). <br /> B) Redevelopment projects shall achieve a net reduction from pre-project conditions <br /> (on an annual average basis) of stonnwater discharge volume; discharges of total <br /> suspened solids (TSS); and discharge of total phosphorus (TP). <br /> The requirements of this section may be altered and alternative treatment BMPs approved under <br /> the following limitations: <br /> 1) Infiltration techniques shall be prohibited when the infiltration structural <br /> BMP will receive discharges from or be constructed in areas: <br /> (a) where industrial facilities are not authorized to infiltrate industrial <br /> stormwater under an NPDES/SDS Permit, <br /> (b) where vehicle fueling and maintenance occur <br /> (c) with less than 3 feet of separation from the bottom of the <br /> infiltration system to the elevation of the seasonally saturated soils <br /> or top of bedrock <br /> (d) where high levels of contaminants in soil or groundwater wiil be <br /> mobilized by the infiltration of stormwater. <br /> 2) Infiltration techniques will be restricted when the infiltration device will <br /> be constructed in areas: <br /> (a) with predominately Hydrologic Soil Group D soils <br /> 31 <br />