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TECHNICAL MEMORANDUM <br />To: Bill Lyle <br />Date: January 3, 2004 <br />Page 9 <br />to the 25th and 75th percentile, (4) the solid black vertical bar is the median value, and (5) <br />the solid red vertical bar is the mean value. Bedrock water chemistry for the pre-mining <br />condition is shown in gray. For comparison purposes, water chemistry data were compiled <br />for current conditions (2004 data) observed in the West Pit backfill (Wells BF-1, BF-2, <br />BF-3, BF-5 [BF-5R], BF-4 and BF-6). The current West Pit backfill chemistries are <br />shown in blue. <br />Total dissolved solids (TDS) and fluoride are shown in Figure 7. As predicted for the <br />bedrock ground water system, concentrations from the shallow portion of the aquifer are <br />greater than concentrations measured in deeper portions of the aquifer (Table 2). Fluoride <br />shows greater relative variability than TDS, but the basic geochemical model still holds. <br />Current backfill TDS concentrations are lower than the concentrations measured in the pre- <br />mining shallow bedrock aquifer (Figure 7). Fluoride as measured currently in the West Pit <br />backfill shows a statistical distribution similar to the range of values recorded in the <br />shallow bedrock aquifer pre-mining. A t-test was conducted to evaluate if the two mean <br />values of fluoride concentration are statistically different and the statistical test <br />demonstrated that the mean fluoride values of current West Pit backfill and pre-mining are <br />statistically indistinguishable (Table 3) <br />West Pit backfill concentrations of sulfate are currently less than the values recorded for <br />the shallow pre-mining bedrock aquifer (Figure 8). A t-test was conducted to evaluate if <br />the current mean concentration of manganese in the West Pit backfill is less than the mean <br />shallow pre-mining concentration. The results of the t-test indicate that the current mean <br />concentration of manganese in the West Pit backfill is less than the mean value of <br />manganese measured in the pre-mining shallow bedrock aquifer (Figure 8; Table 3). <br />Figure 9 shows the box plot results for iron. The observed iron concentrations support a <br />similar conclusion as was drawn from analysis of Figures 7 and 8. That is, current West <br />Pit backfill ground water concentrations of iron are less than the iron concentration <br />measured in the shallow, pre-mining bedrock aquifer (Table 3). <br />Copper concentrations in well 87-86 were less than the detection limit (0.005 mg/L) in the <br />pre-mining shallow bedrock aquifer data set. Current copper concentrations vary with <br />location in the West Pit. For example, on the eastern portion of the West Pit (i.e., east of <br />BF-4; Figure 5), the average measured copper concentrations is equal to (2002 to present) <br />0.0049 mg/L, which is less than the pre-mining detection limit. This is comparable to the <br />pre-mining water quality data from well 87-86, which was also located in the eastern <br />portion of the West Pit. Current copper concentrations measured in ground water <br />monitoring wells on the western portion of the West Pit are higher than the shallow pre- <br />mining concentrations from well 87-86. This is consistent with the existence of a remnant <br />portion of the San Luis ore body located immediately west of the West Pit that contains <br />elevated copper concentrations. The remnant portion of the ore body was identified during <br />mining operations and was left in place due to the inability of the milling process to <br />p:(projectsl2l2-newmont(s lnis)lsmlvisltr-18wtrglrylpmmine westpit.doc