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• i <br />sedimentation ponds are expected to be used for erosion and sediment control and for <br />water treatment. <br />2.1.3.1 Vegetative Filters <br />Vegetative filters are dense strips of close-growing vegetation located to receive runoff <br />from diffuse sources, waterways, small drains, or intermittent streams. The vegetative <br />filter is used to reduce flow velocities and to trap sediment before the runoff leaves a <br />disturbed area. Vegetative filters are normally composed of perennial fast growing <br />rhizomatous grasses. Filters may be used where soils and moisture support the <br />necessary growth to provide an adequate filtering capability. Where water enters the <br />vegetative filter it should be spread by natural topography or by installation of a level <br />spreader ditch. Existing vegetation often makes excellent vegetative filter strips and <br />should be used when available. The width of the strip should be adequate to filter and <br />allow settlement of sediments. Slope, type of vegetation, and quantity of anticipated <br />runoff water will dictate the minimum width required for a vegetative filter to be <br />effective. A minimum width of 10 feet is recommended on relatively level ground, with <br />additional width being planted as conditions dictate. <br />2.1.3.2 Silt Fences <br />Silt fence may be used for areas where sediment control is needed for intermediate <br />periods of time (i.e., more than a year but not permanently). Silt fences will be placed on <br />the down gradient side of the disturbed area (Figure D-1 and Figure D-2). To the extent <br />possible, silt fence will be installed on the contour. However, silt fences are ideal for <br />installation along perimeters that vary in contour when flow and sediment volumes are <br />low. Care must be taken to avoid directing any excessive amounts of flow to low <br />points, which may overload fence capacity and result in fence failure. Support systems <br />for silt fence will be adequate to withstand the anticipated flow volumes and sediment <br />loads anticipated for the installation area. Sediment fence will be UV resistant with <br />fabric-tensioning strips. The bottom of the fabric will be keyed into the ground <br />according to standard installation procedures. Silt fences will not be used where <br />excessively rocky soils prevent their proper installation. Silt fences will be routinely <br />inspected and maintained following significant runoff events. The cost of maintaining <br />silt fence vs. the cost of implementing more costly control measures will be taken into <br />consideration when determining which control measure to use. Silt fence may also be <br />used as a substitute for straw or hay bale check dams, since its effective life is usually <br />longer. <br />2.1.3.3 Sediment Traps <br />Sediment traps are small incised dugouts or depressions that may be placed <br />intermittently along or at the outlet of a water course or erosion feature (Figure D-3). <br />They are effective in ponding surface water, increasing the time of concentration, <br />f reliminary Response Plan A_12 <br />Yankee Gulch Sodium Minerals Project <br />Amencan Soda, L.L.P. <br />