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EMD Dewaterin¢ Treatment Faciliri <br />The SAE demonstrations for the EMD dewatering ponds located in the NW%SW% Sec. 21, TSN, R86W, 6th P.M. on <br />• Binco silty clay (a D soil) cover approximately 3.12 acres of disturbance and 4.4 acres total. SAE demonstrations have <br />characterized three areas: the west side of the topsoil pile, the east side of the topsoil pile, and the cut slope west of the <br />dewatering ponds. Sediment control will be achieved by seeding and mulching the topsoil pile and cut slope with 2 <br />tons/acre straw. Vegetative filters of unmanaged cropland vegetation will provide adequate sediment detention to <br />achieve effluent limitations following a l0-year 24-hour storm event. Peak flows from this storm are 1.14 cfs, 0.64 cfs, <br />and 0.38 cfs for the upland and west side of the topsoil pile, the east side of the topsoil pile and the area down grade, <br />and the cut slope. <br />Rockfall Hazard Trenches <br />There are three rockfall hazard mitigation zones. The zones consist of various combinations of trenches and berms <br />established between the Twentymile Road and the Twentymile sandstone cliffs north of the facilities area. Two to three <br />SEDCAD+ demonstrations were designed for each trench: one treating the overlying watershed with the <br />• <br />APpgpVED auN z a 2000 <br />PR 99-OS 2.05-82.1 2/24/99 <br />