2011-09-27_REVISION - M1990057 (10)

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tailings disposal capacity for a more efficient concentrating system and increased tails reporting to the TSF. The historical Phase 1 TSF embankment compaction is inadequate for current production requiring complete removal of the existing embankment and reconstruction of the TSF facility with a lined facility. The reconstruction honors the original permit parameters as follows: • The same 4.6 acre tailings disposal facility (TSF) is utilized. • The pond excavation at a maximum 21 ft depth does not impact the known aquifers at 80- 100ft below the surface. • The tailings impoundment dam will be constructed from available onsite soils borrowed from the tailings disposal area as outlined in the recommendation of CTL /Thompson, Inc., Consulting Geotechnical and Materials Engineers, Permeability Study Tailing Pond Area, April 10, 1990, presented as Appendix A, Slope Stability Evaluation Tailings Pond Embankment and Future Tailing Slope, July 8, 2011. • The TSF will be constructed as a zero discharge facility with aft of freeboard in accordance with the Probable Maximum Precipitation Estimates — United States Between the Continental Divide and the 103" Meridian. • Non disturbed drainage is diverted around the TSF while disturbed area drainage from the mill area disturbance reports to the TSF. • The observation well down gradient from the 4.6 acre TSF area will be maintained in its current location and monitored. • Topsoil, in accordance with the topsoil plan will be removed and stockpiled. Additionally, the proposed TSF facility further commits to: • Stability analysis initiated by CTL Thompson, Inc. May 12, 2011, on samples collected from the existing compacted fill embankment, 2 additional holes drilled to compliment and confirm the 1990 permeability test hole data, and the CTL Thompson Letter Report of July 8, 2011, presented as Appendix A, Slope Stability Evaluation Tailings Pond Embankment and Future Tailing Slope, July 8, 2011. Subsequently, CTL Thompson issued an update to the July 8, 2011 Report, presented as Appendix B, Slope Stability Evaluation Tailings Pond Embankment and Future Tailing Slope, August 17, 2011. • A 2.5:1 (horizontal to vertical) outside face, and a 2:1 interior face embankment dam with a 12 ft wide crest berm. • A 12in minimum clay under liner of 1 x 10 cm/sec from available onsite selective impermeable soils borrowed from the tailings disposal area, placed and compacted in two lifts, 6in each, with a sheepsfoot roller. • A seepage /leak detection system between the clay layer and the synthetic liner with the collection system located in the northwest corner of the impoundment, and the pond impoundment sloping at 0.5% slope to the northwest. • A synthetic pond liner of 45 -mil Polypropylene Geomembrane or equivalent. • Compaction testing during construction. M1990 -057 September 27, 2011