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decease. These small variations are well within the natural variation of sulfate conc~trations in the HI aquifer but could be defining the very small effects of the backfill aquifer upgradient Sulfate concentrations in bacldill well GF7 significantly decreased during the period of 1995 through 1997 and has overall increased in the last few years. The water levels for the last few years have been fairly similar in well GF7, indicating that these changes are not due to new backfill being saturated. Sulfate concentrations have stayed low and steady in badcfill well GF5 and downgradient well G&5. Concentrations in HI well GE2 have gradually decreased the last five years after a very gradual previous increase. This small change may be defining the very small effects of upgradient mining but the changes are well within natural ranges. This monitoring indicates that if the HI aquifer has been affected by upgradient mining it has been very small. • Sulfate concenU-ations in well GMP-1 have been highly variable but showing no long- term trend. The water level in well GMP-1 had been steadily increasing for several years prior to becoming fairly steady in 2002, which is likely due to increase in water levels in the badcfill aquifer to the south of this well. Sulfate concentrations in this well should be influenced by the sulfate concentrations in the bacidiil aquifer upgradient of GMP-1 and have overall increased during the last two years. The sulfate concentrations in welt GP-3 show a gradual increasing trend but these variations are within natural observed variations. Overall steady sulfate concentrations have been observed in well GP-7. Sulfate concentrations in eastern HI aquifer well GC-1 have been similar to the higher values in well GMP-1 and had to be natural unto the last few years. Therefore, a sulfate concentration of at least greater than 600 mg/1 is r-eeded to indicate that the increases may be due to the • mining operation. 3-7