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<br />Battle Mountain Resources <br />November 1, 2000 <br />Page 10 <br />The form of Equation (2) implies that the long-term concentration of sulfate in the West Pit <br />backfill groundwater system will not fall below the concentration designated by C,„ <br />For purposes of the present evaluation, the average concentration of sulfate observed in BF-1 was <br />used to set the value of C,~. The West Pit backfill groundwater monitoring Nell BF-1 was <br />installed in the southeast corner of the West Pit in an area that had been flushed by inflowing Rito <br />Seco alluvial groundwater. Groundwater quality for BF-1 is reflective of backfill material that has <br />been flushed of secondary sulfate salts and is the best estimate at this time ~>f steady-state <br />conditions in the West Pit. Periodic sampling of groundwater from BF-1 would provide the <br />information necessary to revise the value of C,~.. <br />The cumulative pore volumes, from Table I, were combined with the corresponding monthly <br />concentration data for water quality samples collected at BF-2, BF-4, and BF-6 to evaluate the <br />flushing characteristics as exemplified by each backfill location. The water quality data for <br />backfill groundwater monitoring wells BF-4 and BF-6 were combined because the difTerences <br />between the observed flushing response for the two groundwater wells was less that the variation <br />of the data Figure I shows the relationships between the concentration of sulfate and pore <br />volume for backfill locations. Anon-linear least-squares numerical method wtis used to fit <br />Equation (2) to the data for each location. The resulting theoretical values for Co and ~, as <br />calculated for each set of data, were then used to calculate the number of predicted pore volumes <br />that would result in Flushing the backfill material to yield a sulfate concentration of 250 mg/L. <br />For the purpose of estimating the flushing characteristics of the West Pit backfill, the results front <br />the analysis of data from BF-2 and the combined data from BF-4 and BF-6 should ~e considered <br />as the range of representative response for backfill flushing. Table 2 presents a summary of the <br />pore volume analysis. As shown the Table 2, the results obtained using the two s~;t of data are <br />consistent and capture the reasonably capture the range of response for backfill flushing. The <br />values reported in the column entitled "Total Volume to Flush (gal.)" corresponds to the <br />predicted amount of groundwater that would need to be circulated through the West Pit backfill <br />2636 M[dpoin[ Dr., Sure B, For[ Collins, Colorado 80~2.i <br />"!'elephone (970) 484-7704 !FAX (970) 484-7789 <br />