2007-12-19_REVISION - M1988112 (12)

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with a HDPE (or equivalent) synthetic geomembrane liner. Interior pond slopes will be graded at 3:1 (horizontal:vertical) and exterior embankment slopes will be graded at 2.5:1 (horizontal:vertical) or flatter. The East Pond will be constructed by excavating approximately 62,860 cubic yards of material, up to 14 feet deep into the existing pit backfill, and constructing a perimeter berm as shown in Figure G.2-8. Approximately 25,000 cubic yards of excavated material will be used in embankment construction and the remaining 37,869 cubic yards will be placed in a stockpile area adjacent to the southeast edge of the pond and reclaimed or may be used to regrade sections of the West Pit highwall. The East Pond will consist of 10 feet of above-grade storage impounded by the perimeter embankment, and 14 feet of below-grade storage created by excavation below the existing ground surface. The East Pond will have a crest elevation of 8613 ft-amsl with a statutory ground elevation at approximately 8603 ft-amsl, and a bottom sloping toward a sump area at elevation 8589 ft-amsl. Relevant East Pond cross sections are shown in Figures G.2-9 and G.2-10. Drainage from the East Pond will also be provided by a gravity-flow outlet pipe that ultimately leads to the center pivot irrigation system at the ranch. This outlet pipe will be located at or above the statutory ground elevation at 8603 ft-amsl. The outlet pipe will flow by gravity under positive-head conditions when the pond water level is above an elevation of 8603 ft-amsl and will operate as a gravity-siphon when water level is below this elevation. The East Pond will also be lined with a HDPE (or equivalent) synthetic geomembrane. Interior pond slopes will be graded at 3:1 (horizontal:vertical) and exterior embankment slopes will be graded at 2.5:1 (horizontal:vertical) or flatter. Analyses of the stage-area and stage-capacity characteristics demonstrate that the design configuration of the irrigation ponds meets the SEO criteria for non- jurisdictional reservoirs. The stage-capacity and stage-area characteristics for the West Pond are shown in Figures G.2-11 and G.2-12, respectively. The pond storage capacity of the West Pond at the maximum pool elevation (8615 ft-amsl) and at the statutory ground elevation (8605 ft-amsl) are 139.3 acre-ft and 51.3 acre-ft, Battle Mountain Resources, Inc. 27 P:\Pmimb\212-New ont(SmLLis)\SanLuis\Permit Amendment- West Pit MemgemenAVS Report &PDFs\TezdPvn itn^»nd=m_v5c.doc December 2007