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velocity and peak volumetric flow rate of stormwater runoff from the project • <br />site, as required by local plan approval authority. <br />b. Where necessary to comply with Special Condition S9.D.3.a, construct <br />stormwater retention or detention facilities as one of the first steps in grading. <br />Assure that detention facilities function properly before constructing site <br />improvements (for example, impervious surfaces). <br />c. If permanent infiltration ponds are used for flow control during construction, <br />protect these facilities from siltation during the construction phase. <br />4. Install Sediment Controls <br />The Permittee must design, install and maintain effective erosion controls and <br />sediment controls to minimize the discharge of pollutants. At a minimum, the <br />Permittee must design, install and maintain such controls to: <br />a. Construct sediment control BMPs (sediment ponds, traps, filters, infiltration <br />facilities, etc.) as one of the first steps in grading. These BMPs must be <br />functional before other land disturbing activities take place. <br />b. Minimize sediment discharges from the site. The design, installation and <br />maintenance of erosion and sediment controls must address factors such as the <br />amount, frequency, intensity and duration of precipitation, the nature of <br />resulting stormwater runoff, and soil characteristics, including the range of soil <br />particle sizes expected to be present on the site. <br />c. Direct stormwater runoff from disturbed areas through a sediment pond or other <br />appropriate sediment removal BMP, before the runoff leaves a construction site <br />or before discharge to an infiltration facility. Runoff from fully stabilized areas <br />may be discharged without a sediment removal BMP, but must meet the flow <br />control performance standard of Special Condition S9.D.3.a. <br />d. Locate BMPs intended to trap sediment on site in a manner to avoid interference <br />with the movement of juvenile salmonids attempting to enter off -channel areas <br />or drainages. <br />e. Provide and maintain natural buffers around surface waters, direct stormwater to <br />vegetated areas to increase sediment removal and maximize stormwater <br />infiltration, unless infeasible. <br />f. Where feasible, design outlet structures that withdraw impounded stormwater <br />from the surface to avoid discharging sediment that is still suspended lower in <br />the water column. <br />5. Stabilize Soils <br />a. The Permittee must stabilize exposed and unworked soils by application of <br />effective BMPs that prevent erosion. Applicable BMPs include, but are not <br />limited to: temporary and permanent seeding, sodding, mulching, plastic <br />covering, erosion control fabrics and matting, soil application of polyacrylamide <br />onstr uciion AStor inivaf er• General 1'ermit <br />Page 30 <br />