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• Flume Gulch has two alluvial monitoring wells, GC-3 and COY. TDS <br />concentrations have been fairly steady in well GC-3 with a minor decrease in 1996 and <br />1997 which is likely due to an increased rate of recharge. The TDS concentrations in the <br />COY well show that the Johnson alluvial TDS concentrations are within natural alluvial <br />concentrations in this area. <br />3.2 SULFATE <br />Sulfate concentrations for the 20 Mile Sandstone aquifer and the U aquifer are <br />presented in Figure B-10. This plot shows a significant amount of variation in the sulfate <br />concentrations in 20 Mile Sandstone wells with no long-term trend. This deep aquifer would <br />be expected to respond slowly to better recharge years. Figure B-10 also presents the plot <br />of U aquifer well GF-2. The 1996 value for well GF-2 is an outlier. <br />Figure B-11 presents the sulfate concentrations for QR wells GA-1, GD-2, GD-3 <br />and GE-1. Sulfate in backfill well GD-3 decreased significantly in 1996 and increased some <br />in 1997, but shows an overall decline during the last three years. Future monitoring of this <br />well will determine whether a significant declining trend is continuing in this backfill well. <br />Concentrations in well GD-2 have been fairly steady with a slight increase in average <br />sulfate concentrations over the last few years versus concentrations in 1987, 1988 and <br />1989. Sulfate concentrations have been fairly stable in the last few years after a gradual <br />rising trend for several years. Figure B-12 also presents sulfate concentrations for QR <br />wells. This figure shows that sulfate concentrations in backfill well GF-11, which is <br />upgradient of QR well GF-6, increased after the large decline in 1996. The 1997 value is <br />. below the earlier peak values. The sulfate concentrations have gradually declined in the <br />3-5 <br />