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documenting the effectiveness of this drainage configuration for the Storage and Training Area is provided in Exhibit
<br />8U.
<br />No. 7 North Escape Shaft -This SAE covers 1.82 acres of disturbance and is located in the SE1/4, Section 20, TSN,
<br />R86W, 6th P.M. on Cochetopa Loam (a C soil). SAE demonstrations have characterized four areas; the north outslope;
<br />the east and west outslopes; the south side of the topsoil pile and pad, which incorporates drainage from the north side of
<br />the topsoil pile; the cutslope, the berm, the pad, and road drainage. Sediment control will be achieved by seeding and
<br />mulching the pad outslopes, the cutslopes, and the topsoil pile, and by placing straw bale dikes or a silt fence below each
<br />of these locations to prevent off=site migration of sediment prior to vegetative stabilization. Vegetative filters will
<br />provide adequate sediment detention to achieve effluent limitations following a 10-year, 24-hour storm event for these
<br />locations. Rock check dams will be installed at the southeast corner of the topsoil pile and below a riprapped Swale
<br />descending the northeast corner of the outslope. Peak flows from a 10-year, 24-hour storm are 0.06 cfs, 0.03 cfs, 0.42
<br />cfs, and 1.59 cfs for the north outslope, east or west outslope, north side of the topsoil pile, and pad, respectively.
<br />EMD Ventilation Shaft -The SAE for the EMD Ventilation Shaft covers approximately 2.66 acres of disturbance and
<br />is located in the NWl/4SE1/4 Sec. 14, TSN, R86W, 6th P.M. on Routt loam (a C soil). SAE demonstrations have
<br />characterized three areas; the east side of the east topsoil pile; the south and west sides of the southwest topsoil pile; and
<br />other topsoil slopes and the benches and cut and fill slopes of the facility itself. Sediment control will be achieved
<br />through the installation of an upland clean water diversion ditch, seeding and mulching the topsoil piles and cut and fill
<br />slopes with 2 tons/acre straw; and graveling the pads and roads with gravel adequate to achieve at least 80 percent
<br />surface coverage. Vegetative filters will provide adequate sediment detention to achieve effluent limitations following a
<br />10-year, 24-hour storm event. Peak flows from the design storm are 0.05 cfs, 0.27 cfs, and 1.96 cfs for the east side of
<br />the east topsoil pile, the south and west sides of the southwest topsoil pile, other topsoil slopes, and the benches and cut
<br />and fill slopes of the facility, respectively.
<br />Pond T Topsoil Stockpile -This SAE covers about 0.5 acres between the Pond T embankment face and railroad
<br />spur. Runoff from this area flows downslope between the railroad embankment and Pond T embankment outslope to
<br />the Pond T weir, and is then conveyed under the track by means of a culvert to Foidel Creek. Vegetative filtering is
<br />provided by the establishment of good vegetation on the topsoil pile and in the conveyance ditch below the topsoil
<br />• stockpile. Additional filtering of sediment is provided by a rock filter between the stockpile and the culvert, benches,
<br />and cut and fill slopes of the facility itself.
<br />EMD - lORT Dewatering Installation -The SAE demonstrations for the TORT Dewatering installation located in the
<br />NWl/4SW1/4 Sec. 21, TSN, R86W, 6th P.M. on Binco silty clay (a D soil) cover approximately 3.6 acres of disturbance
<br />and 4.4 acres total. SAE demonstrations have characterized three areas; the west side of the topsoil pile, the east side of
<br />the topsoil pile, and the cut-slope west of the dewatering ponds. Sediment control will be achieved through gravel
<br />surfacing of the pad and road disturbance, and seeding and mulching the topsoil pile and cut-slope with 2 tons/acre straw.
<br />A combination of site ditches, berms, arock-lined sump and discharge channel, and a vegetative filter of unmanaged
<br />cropland vegetation provides adequate runoff control and sediment detention to achieve effluent limitations following a
<br />10-year, 24-hour storm event. Peak flows from this storm are 1.14 cfs, 0.64 cfs, and 0.38 cfs for the upland and west
<br />side of the topsoil pile, the east side of the topsoil pile, and the area downgradient, and the cut-slope, respectively.
<br />Rockfall Hazard Trenches -There are three rockfall hazard mitigation zones. The zones consist of various
<br />combinations of trenches and berms established between the Twentymile Road and the Twentyrnile sandstone cliffs
<br />north of the facilities area. Two to three SEDCAD+ demonstrations were developed for each trench; one addressing the
<br />overlying watershed with the accompanying trench, and the other addressing the outslope. The west rockfall hazard
<br />trench was divided into segment A through G, and segment G through L (Sheet 4, Exhibit 7F). For Segment A through
<br />G of the West Rockfall Hazard Trench, the SEDCAD+ demonstrations document attainment of water effluent limitations
<br />fora 10-year, 24-hour storm following treatment of 56.47 acres, of which 5.42 acres are disturbed. SEDCAD+ modeling
<br />anticipates a 10-year, 24-hour peak flow of 3.3 cfs. The trench will be mulched with 2 tons/acre of mulch, following
<br />seeding and prior to the development of a vegetated channel, and runoff will flow through a natural vegetative filter 100
<br />feet long at the outfall at point G. For Segment G through L of the West Rockfall Hazard Trench, the SEDCAD+
<br />demonstrations document the attainment of water effluent limitations fora 10-year, 24-hour storm following treatment of
<br />25.9 acres, of which 1.85 acres are disturbed. Segment G through I consists exclusively of a berm. SEDCAD+
<br />`modeling estimates a 10-year, 24-hour peak flow of 1.77 cfs. The trench will be mulched with 2
<br />MR08-228 2.05-82 03/06/08
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