2008-07-11_PERMIT FILE - M2007044 (18)

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and potentially compromise the stability of the embankment. Exhibit U presents a slope stability analysis using commonly accepted basic equations and material parameters. The analysis indicates that the waste embankment has a calculated safety factor above 2, which is well above the minimum safety requirements for permanent slopes. Runoff from the waste rock pile and other disturbed areas will be collected in the sediment pond shown on Map C-2. The sediment pond will allow suspended solids to settle out of solution before the water enters the natural drainage. As an added precaution, the sediment pond water will be tested quarterly for radium-226 and uranium, as well as other parameters (see Exhibit T for monitoring details). The sediment pond is designed to fully contain the ten-year, twenty-four-hour precipitation event for the site. It is also designed to safely pass the 100-year, 24-hour storm event through the principal spillway pipe (see Section 18 below). 6.Ore Stockpile Area • Ore will be end dumped directly onto the ore stockpile pad located north of the Whirlwind portal by the buggies. The stockpile pad has been sized to contain up to 15,000 tons of ore, which represents three to four months of full production. As shown on Map C-2, the ore pad covers approximately 0.5 acre and drains to a collection sump. The ore pad will consist of a geosynthetic clay liner (GCL) covered by a 2.5-foot thick cushion layer of finer-grained material and 1 foot of compacted run-of- mine (ROM) waste rock. The lined pad will drain to a concrete sump. The ore stockpile area will be able to store the entire first year of ore production, which is estimated to be approximately 10,000 tons. The sump will be equipped with an overflow that drains directly to the lined tank that feeds into the water treatment plant. This overflow will utilize asix-inch diameter HDPE pipe that will be buried at least eighteen inches below the surface from the sump to the Untreated Water Tank. The entrance to the pipe will be screened to prevent large pieces of rock or debris from entering and clogging the pipe. The ore pad design is presented in detail in Appendix J The ore pad will be sloped toward the concrete sump described above. As shown on Map C-2, the ore pad area will be surrounded by a gradual sloping berm that will direct all runoff from the ore pad area • to the sump. These provisions are designed to capture and allow for treatment of surface water runoff Whirlwind Mine 07 (rev. April 08) D-14