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• Flume Gulch has two alluvial monitoring wells, GC-3 and COY. TDS concentrations <br />have been fairly steady in well GC-3. The TDS concentrations in the COY well and <br />historical variations in well P-i show that the Johnson alluvial TDS concentrations are <br />within natural alluvial concentrations in the alluvial aquifer in this area. <br />3.2 SULFATE <br />Sulfate concentrations for the Twenty Mile Sandstone aquifer and the U aquifer are <br />presented in Figure &10. This plot shows steady sulfate concentrations for the last three <br />years in Twenty Mile Sandstone well, GF-1, with no tong-term trend. This deep aquifer <br />would be expected to respond slowly to better recharge years. Figure B-10 also presents <br />the plot of U aquifer well GF-2. Sulfate concentrations in well GF-2 have been steady in <br />• recent years. <br />Figure B-11 presents the sulfate concentrations for QR wells GD-2, GD-3 and GE-1. <br />Sulfate in bacidll well GD-3 decreased significantly in 1996 and have increased since that <br />decrease to a level similar to the maximum value previously observed. This indicates that <br />the sulfate fluctuations in the bacldill aquifer may be larger than the native QR aquifer. <br />Future monitoring of this well will define whether the present trend continues in this <br />backfill aquifer. Concentrations in well GD-2 have been fairly steady with a slight increase <br />in average sulfate concentrations over the last few years versus concentrations in the late <br />1980's. The sulfate concentrations in well GD-2 show that the QR aquifer near well GD-2 <br />has not been significantly affected by the upgradient backfill aquifer water quality. Sulfate <br />concentrations had been fairly stable in the last few years in weft GE-i after a gradual <br />rising trend for several years. The 1999 and 2000 values show a large decline. Figure B- <br />3-5 <br />