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• SLOPE 1 SAE <br />During the construction of [he Elk Creek Mine pad areas, slopes will be created which will grade down [o <br />the Elk Creek. The slopes are labeled Slope I and Slope 2 and are shown on the Drainage and Sediment <br />Control Plan (Map 2.05-M4). Slopes I and 2 occupy 0.33 ac. and 0.14 ac., respectively. Due [o [he small <br />area affected by Slope 1, conventional drainage and sediment control measures are not necessary. <br />Oxbow proposes alternative sediment conVOl 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 [he previously approved interim seed mixture and covered with a sVaw mulch <br />at an application rate of 1 [on per acre. Therefore, the slope will be in a disturbed condition for a relatively <br />short time. A silt fence, consVUC[ed of hay bales instead of fencing, will be placed and anchored along the <br />contour a[ the bottom of [he slope. The SEDCAD4 silt fence utility was used to mode[ the water quality <br />from [he runoff resulting from the 10-year, 24-hour storm. A flow rate of 5.6 gpm/sq. ft, was input to the <br />model [o represent straw bales in lieu of a silt fence. The flow rate was obtained from Bartield (1978). The <br />use of straw mulch and sVaw bales is commonly used to control erosion on small out-slopes throughout the <br />United States. <br />The following calculations demonstrate that [he straw bales will treat the runoff from the design storm. <br />Hvdroloev 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: 87 <br />KFactor. AFC 0.037 . 3~ .~., sGdcA~ <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 [he attached SEDCAD4 computer printouts. <br />Hvdrolo¢v Results <br />Runoff volume: 0.025 ac. ft. (1,089 cu. ft.) <br />Water Quality: 0.5 nd/I <br />Based on the small size of [he area, establishment of interim vegetation and mulching, and OMI's ability [o <br />effectively meet water quality standards with straw bales, an SAE is requested for the Slope 1 area. <br />• <br />