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No. 7 North Escape Shaft -This SAE covers 1.82 acres of disturbance and is located in the SEl/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
<br />of 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
<br />each 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-yeaz, 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
<br />a 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
<br />to the Pond T weir, and is then conveyed under the track by means of a culvert to Foidel Creek. Vegetative
<br />filtering is provided by the establishment of good vegetation on the topsoil pile and in the conveyance ditch below
<br />the topsoil stockpile. Additional filtering of sediment is provided by a rock filter between the stockpile and the
<br />culvert, benches, and cut and fill slopes of the facility itself.
<br />EMD Dewaterin~ Treatment Facility -The SAE demonstrations for the EMD dewatering ponds located in the
<br />NW1/4SWl/4 Sec. 21, TSN, R86W, 6th P.M. on Binco silty clay (a D soil) cover approximately 3.12 acres of
<br />disturbance and 4.4 acres total. SAE demonstrations have characterized three areas; the west side of the topsoil pile, the
<br />east side of the topsoil pile, and the cut-slope west of the dewatering ponds. Sediment control will be achieved by
<br />seeding and mulching the topsoil pile and cut-slope with 2 tons/acre straw. Vegetative filters of unmanaged cropland
<br />vegetation will provide adequate sediment detention to achieve effluent limitations following a 10-year, 24-hour storm
<br />event. Peak flows from this storm aze 1.14 cfs, 0.64 cfs, and 0.38 cfs for the upland and west side of the topsoil pile, the
<br />east side of the topsoil pile and the azea downgradient, and the cut-slope.
<br />Rockfall Hazard Trenches -There aze three rockfall hazazd mitigation zones. The zones consist of various
<br />combinations of trenches and berms established between the Twentymile Road and the Twentymile sandstone cliffs
<br />north of the facilities area. Two to three SEDCAD+ demonstrations were developed for each trench; one addressing
<br />the 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 hazazd 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 aze disturbed. SEDCAD+
<br />modeling anticipates a 10-year, 24-hour peak flow of 3.3 cfs. The trench will be mulched with 2 tons/acre of mulch,
<br />following seeding and prior to the development of a vegetated channel, and runoff will flow through a natural
<br />vegetative filter 100 feet long at the outfall at point G. For segment G through L of the west rockfall hazard trench, the
<br />SEDCAD+ demonstrations document the attainment of water effluent limitations fora 10-year, 24-hour storm
<br />following treatment of 25.9 acres, of which 1.85 acres are disturbed. Segment G through I consists exclusively of a
<br />berm. SEDCAD+ modeling estimates a 10-year, 24-hour peak flow of 1.77 cfs. The trench will be mulched with 2
<br />tons/acre of mulch, following seeding and prior to the development of a vegetated channel, with discharge at point J.
<br />The three west rockfall hazard trench outslope demonstrations (A-G, G-J, and J-L) document the adequate treatment of
<br />4.93 disturbed acres using mulched disturbance areas and 5-foot long vegetative filters. The SEDCAD+
<br />demonstrations are provided in Exhibit 8.
<br />TR09-66 2.05-84.2 04/11/09
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