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Battle Mountain Resourc~ <br />January 31, 2000 <br />Page 3 <br />Measured Baclaill Geochemistry <br />Subsequent to the development of the TR-26 water management plan, extensive additional <br />hydrologic and geochemical data have been generated as a consequence of the expanded <br />monitoring program. These data are more representative of current site conditions and can be <br />used to reasonably modify the initial estimates of pore volumes required to flush the West Pit <br />backfill. <br />Review of the water quality results obtained from the six groundwater mcnitoring wells <br />completed in the West Pit backfill serves as the basis for revising the concentration of sulfate <br />used as representative of the initial concentration (C~) in Equation (1). As of November 1999. <br />the average concentration of sulfate in the West Pit backfill was 608 mg/L. The average <br />concentration of sulfate was calculated using water quality results from BF-2, BF-3, BF-4, BF-5. <br />and BF-6. The water quality data from BF-1 were not used because the portion of the West Pit <br />immediately surrounding BF-I has already been flushed by the inflow of Ritc Seco alluvial <br />groundwater. Inserting the revised value of Co into Equation (1) and using the values for the <br />other parameters of Equation (1) as presented in the Response Plan yields a revised value for p of <br />5.229. That is, the number of pore volumes required to flush the secondary sulfatf• salts from the <br />backfill materials has been reduced from an initial estimate of 10 pore volume. to a value of <br />5.229 pore volumes based upon actual site specific data.. <br />Measured West Pit Hydrology <br />Corollary' to the issue of representative backfill chemistry was a consideration as [o why the <br />chemistry of groundwater in the vicinity of BF-I consistently reflects better qual ty water, even <br />during the early phases of data gathering. In addition, the automated water level measurements <br />that have been made in selected backfill groundwater monitoring wells since approximately mid- <br />July can be used to revise the pore volume Bushing calculations for the West Pit. <br />3801 Automation Wnv, Suite 100, Furt Collins, Colorado 80.5Z.i <br />Telephone (970) 2Z3-9h00 / F`LY(9i0) 2'3-'!71 <br />