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Battle Mountain Resources <br />November 1, 2000 <br />Page 4 <br />concentration of sulfate as measured in West Pit backfill groundwater monitoring wells as of <br />November 1999. The average concentration of sulfate in West Pit groundwater in November <br />1999 was approximately 608 mg/L. This estimate of the initial concentration was applied using <br />Equation (1) to revise the estimate of flushing pore volumes required to lower Ih~: concentration <br />of sulfate in the West Pit to a value of 250 mg/L. Based on the re-evaluation the estimated <br />number of flushing pore volumes required for the West Pit backfill was revised to ;. value of 5.23. <br />This calculation was still based in part on the analysis of the experimental data :is presented in <br />Appendix B of the TR-I S Response Plan in that the parameter the shape of the jecay curve in <br />Equation (1) was based on laboratory experimental data [i.e., n = 0.17 in Equation ~,1)]. <br />An analysis of the West Pit hydraulics was also conducted using available West Pit drawdown <br />data. Direct groundwater pumping from the West Pit began in December 1999, which resulted in <br />a period of steady groundwater table decline in the backfill. The drawdown data were then <br />evaluated to revise if appropriate the value of the effective porosity, or specific yield, for use in <br />calculating the saturated West Pit backfill pore volume. Additionally, a hydrauli•; analysis was <br />conducted to estimate the specific yield of the West Pit backfill and to estimate :he number of <br />pore volumes of Flushing that had occurred in the southeast corner of the West Pit backfill (BF-1 <br />area) The area of the West Pit backfill that surrounds BF-1 has already been flushej based on the <br />available groundwater quality data. As a result of these hydrologic analyses, the val.te of effective <br />porosity used in the calculation of the saturated West Pit pore volume was revised from the value <br />used in TR-26 (0.30) [o a value of 0.22. <br />The analysis conducted in January 2000 resulted in revised estimates of total flushing pore <br />volumes (from l0 to 5.23) and total saturated pore volume of groundwater (from approximately <br />180 x 106 to 132 x 106 gallons). The revisions made to the pore volume and flushinl; requirement, <br />as presented in the January 2000 technical memorandum, were still based fundamentally on the <br />use of Equation (I) to describe the flushing process and on the value n, which was derived from <br />the analysis of experimental laboratory data. <br />2G3G Midpuin! Dr., S'urte B, For[ Collins, Colurndo 8052.1 <br />telephone (970) 484-7704 !FAX (970) 484-7789 <br />