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SLOPE 1 SAE <br />During the construction of the Elk Creek Mine pad areas, slopes will be created which will grade down to <br />the Elk Creek. The slopes are labeled Slope 1 and Slope 2 and are shown on the Drainage and Sediment <br />Control Plan (Map 2.05-M4). Slopes 1 and 2 occupy 0.33 ac. and 0.14 ac., respectively. Due to the small <br />area affected by Slope 1, conventional drainage and sediment control measures are not necessary. <br />Oxbow proposes alternative sediment control measures to control erosion from the Slope 1 area. Final <br />grading will leave the slope in a roughened condition. As soon as final grading of the slopes is complete, <br />Slope 1 will be seeded with the previously approved interim seed mixture and covered with a straw mulch <br />at an application rate of 1 ton per acre. Therefore, the slope will be in a disturbed condition for a relatively <br />short time. A silt fence, constructed of hay bales instead of fencing, will be placed and anchored along the <br />contour at the bottom of the slope. The SEDCAD4 silt fence utility was used to model the water quality <br />from the runoff resulting from the 10-year, 24-hour storm. A flow rate of 5.6 gpm/sq. ft. was input to the <br />model to represent straw bales in lieu of a silt fence. The flow rate was obtained from Barfield (1978). The <br />use of straw mulch and straw bales is commonly used to control erosion on small out-slopes throughout the <br />United States. <br />The following calculations demonstrate that the straw bales will treat the runoff from the design storm. <br />Hvdrolo~y Inputs <br />The curve number (CN) assigned to the topsoil stockpile was indicative of a C subsoil (poor). A 60-day <br />period after seeding and mulching the slopes was assumed. <br /> Interim Reclaimed <br /> Watershed Area: 0.33 ac. <br /> Soil Type: C <br /> Ground Cover: 60-day interim reclamation straw mulch <br /> Cover Type: Poor <br /> CN: <br />K Factor: 8~_ <br />~~~ 0.037 • 3-7 .~+. S~DcA1~ <br /> C Factor: 0.26 (Slope roughened, Poor veg, tackifier-60 days) <br /> P Factor: 1.0 (No additional mechanical controls) <br />All other hydrology inputs are shown on the attached SEDCAD4 computer printouts. <br />Hydroloey Results <br />Runoff volume: 0.025 ac. ft. (1,089 cu. ft.) <br />Water Quality: 0.5 ml/1 <br />Based on the small size of the area, establishment of interim vegetation and mulching, and OMI's ability to <br />effectively meet water quality standards with straw bales, an SAE is requested for the Slope 1 area. <br />• <br />