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Flume Gulch has two alluvial monitoring wells, GC-3 and COY. TDS comm~trations <br />have been fairly steady in well GC-3. The TDS concentrations in the COY well and historical <br />variations in well P-1 show that the Johnson alluvial TDS concentrations are witliin natural <br />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 &S0. This plot shows steady sulfate concentrations for the last six <br />years in Twenty Mile Sandstone well, GFi, with no long-term trend. This deep aquifer <br />would be expected to respond slowly to better recharge years. Figure &SO also presents <br />the pkrt of U aquifer welt GF2. Sulfate concentrations in well GF-2 had been steady in <br />recent years but the 2003 value indicates a small ina~ease. <br />Fgure 8-11 pn~ents the sulfate concentrations for QR welts GD-2, GD-3 and GE-i. <br />Sulfate in backfill well GD-3 decreased signifipntly in 1996 and then increased to a similar <br />peak level by 2000. Sulfate concentrations in well GD-3 have been fairly steady at this peak <br />concentration for the last four years. This indicates that the sulfate fluctuations in the <br />backfill aquifer may be larger than the native QR aquifer. Future monitoring of this well will <br />define whether sulfate concenbations will decrease in the bacldill aquifer during wet cycles <br />and increase to a maximum during a dry cycle. Concentrations in well GD-2 have been <br />steady the last two years after a slight increase in average sulfate concentrations over the <br />previous few years versus wncentrations in the late 1980's. The sulfate concentrations in <br />well GD-2 show that the QR aquifer near well GD-2 has not been significantly affected by <br />• the upgradient backfill aquifer water quality. Sulfate concentrations had declined the lad <br />3-S <br />