Laserfiche WebLink
SLOPE 2 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 the Slope 2, conventional drainage and sediment control measures are not necessary. <br />Oxbow proposes alternative sediment control measures to control erosion from the Slope 2 area. Final <br />grading will leave the slopes in a roughened condition. As soon as final grading of the slopes is complete, <br />Slope 2 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 straw bales instead of fencing, will be placed and anchored along <br />the contour at the bottom of the slope. The SEDCAD4 silt fence utility was used to model 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. The flow rate was obtained from Barfield (1978). The use of straw mulch <br />tackifiers and straw bales is commonly used to control erosion on small out-slopes such as these throughout <br />the United States. <br />The following calculations demonstrate that the straw bales will treat the runoff from the design storm. <br />Hvdrology Inputs <br />• <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: 0.14 ac. <br />Soil Type: C <br />Ground Cover: 60-day interim reclamation straw mulch <br />Cover Type: Poor <br />CN: 87 <br />K Factor: 0.37 <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 />Hvdroloey Results <br />Runoff volume: 0.017 ac. ft. (751 cu. ft.) <br />Water Quality: 0.5 mUl <br />Based on the small size of the area, establishment of interim vegetation and mulching, and Oxbow's ability <br />to effectively meet water quality standards with straw bales, an SAE is requested for the Slope 2 area. <br />• <br />