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Figure B-18 presents the sulfate concentrations for wells GC-3, P-1, P-3, J-1 and • <br />COY. The sulfate concentrations in alluvial well P-1 increased over the last two years but <br />the increase is within historical natural values for this well. The sulfate concentration in the <br />Lewis Shale near this well has been wnsistentiy higher with an increase in 2000. The <br />recent sulfate concentrations for Johnson Gulch well J-1 are essentially equal to the natural <br />level in the Flume Gulch alluvium at well COY. Sulfate concentrations in the Flume Gulch <br />wells (GC-3 and COY) have fluctuated from approximately 400 to 1100 mg/I. <br />3.3 pH <br />Field pH is an important parameter to monitor because some coal spoils have the <br />potential to increase acidity of the ground water, which increases the mobility of most <br />heavy metals. A pH of less than 5 would generally be needed to greatly increase the ~ ••• <br />mobility of most heavy metals. <br />Available pH data is tabulated in Table B-1 of Appendix B. The pH of water from <br />well GB-2 was near neutral in 2000. The pH value from well GB-5 in 2000 was near 8.3, <br />which is similar to historical values from this well. <br />The field pH of water from the GC wells has generally been slightly above 7.0 and <br />has been at similar values since the initiation of disturbance in this area. <br />Field pH from well GD-2 does not demonstrate a trend and is at neutral. The <br />upgradient mining in the QR seams has not significantly affected the pH in this area of the <br />aquifer. The pH values from backfill well GD-3 are at 6.5 for 2000, which is near the <br />values in the native aquifer at well GD-2. The QR aquifer at GE-1 has values above neutral <br />for 2000. The pH of water from well GE-2 in 2000 were similar to values observed during • <br />3-8 <br />