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Battle Mountain Resources <br />November 1, 2000 <br />Page 6 <br />the West Pit and the Pink Gneiss Pit using estimates of the areas of the backfilled surfaces and <br />estimates of the average depth in each pit. For the West Pit, the approximately surface area is <br />27.1 acres and the average depth was estimated to be 70 feet (based on consideration of the pit <br />geometry and borehole log information). The estimated surface area of the Pink Gneiss Pit was 5 <br />acres and the average depth ofbackfill was estimated to be 50 feet. The surface area and average <br />depth can be used to calculate the total volume (pore and solids) for both the West Pit and the <br />Pink Gneiss Pit. The resulting estimates of total volume were then used to calculate the <br />percentage of the total volume represented by each pit. The result is that approximately 88 <br />percent of the total amount ofbackfill material was placed in the West Pit, or 5,035,702 tons of <br />material. <br />A revised estimate of the saturated pore volume in the West Pit was made using thy; new estimate <br />of the total amount of material placed in the West Pit and applying the calculat on method as <br />presented in Section 3.1.2.2 of TR-26. The value of specific yield (0.22) as updated in the <br />January 2000 technical memorandum was used to calculate the revised total pore volume of <br />18,335,917 ft3. <br />The intent of TR-26 was to lower the groundwater level elevation in the West Pit suf£ciently to <br />reverse the hydraulic gradient between the pit and the Rito Seco alluvium. The field information <br />that has been gathered during the dewatering program allows a refinement in the recommended <br />groundwater table elevation required to reverse the hydraulic gradient in the West 1'it. Based on <br />more recent field survey information, the revised target groundwater table elevation in the West <br />Pit is 8582 feet amsl The dewatered backfill material in the West Pit is comprised predominately <br />of Santa Fe Formation material, which is not the backfill material that needs to be flushed of <br />secondary sulfate salts. Thus, the revised pore volume calculation should not account for the <br />volume of groundwater removed in conjunction with lowering the groundwater lev~:l elevation in <br />the West Pit. Therefore, the appropriate saturated pore volume for the West Pit c•~rresponds to <br />the saturated pore volume below a groundwater table elevation of 8582 ft. amsl elevation <br />2G3G Midpoinl Ur., Sni[e B, For[ Cu!(urs, Culorado 80525 <br />Telephone (J70) 484-7704 /FAX (970J 484-7789 <br />