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TECHNICAL MEMORANDUM To: Bill Lyle Date: January 3, 2004 Page 10 ~ adequately manage the elevated copper concentrations. These elevated copper concentrations are a natural component of the original mineralization. The effect of this elevated copper zone was indicated by the measured copper concentrations observed in the pre-mining wells 87-13 and 87-9 that are located in the western portion of the West Pit ' associated with the elevated copper ore (Figure 5). The two pre-mining wells located in the approximate area of the elevated copper ore showed copper concentrations (range 0.007 to 0.068 mg/L, average 0.033 mg/L} similar to the current copper concentrations ' measured in western portion West Pit ground water wells (range 0.008 to 0.109 mg/1„ average 0.027 mg/L), The basis for the comparison with copper is that the one shallow pre-mining well (87-86) does not capture all of the detailed geochemistry associated with ' the naturally oxidizing ore body. Apre-mining ground water well located near 87-13 or 87-9 located at a shallow depth would be expected to record similar copper concentrations as in the mid-depth wells. Therefore, the fact that the western portion of the West Pit shows measurable copper is consistent with pre-mining conditions. The spatial variation in trace meta] concentrations (such as copper) associated with the naturally oxidizing pre- mining ore body is consistent with the mineralization processes associated with the San Luis deposit. Thus, there is a geological basis for considering greater local detail in evaluating copper concentrations while applying more general conditions for the other constituents evaluated. Overall, the water quality data shown in Figures 7 through 9 demonstrates that the West Pit ground water chemistry concentrations aze equal to or less than pre-mining conditions. 1 , ~r ~~ ~~ ii ~~ I ' y;Hrojens~21I-nenmanKmnlniiAsanL~idrr-1RxvglrJpremine cexgiblac