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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 gradually decreasing trend in 1996 for the two <br />20 Mile Sandstone wells. This deep aquifer would be expected to respond slowly to better <br />recharge years. Figure B-10 also presents the plot of U aquifer well GF-2, which shows a <br />significant increase in the 1996 sulfate concentration. A similar increase in TDS was not <br />observed and, therefore, this sulfate increase should not be given any significance until <br />additional monitoring data confirms the increase. <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. Additional <br />monitoring of this well is needed to determine whether a significant declining trend has <br />• begun in this backfill well, Concentrations in well GD-2 have been fairly steady with a slight <br />increase in average sulfate concentrations over the last few years versus concentrations <br />in 1987, 1988 and 1989. Sulfate concentrations, in general, seem to have increased during <br />the last few years in well GA-1. 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, declined significantly in 1996. Some decline in TDS did occur <br />in well GF-11 but additional monitoring of well GF-11 is needed to determine whether a <br />significant decline has occurred. The sulfate concentrations have been fairly steady over <br />the last several years in well GF-6, downgradient of well GF-11. Sulfate concentrations for <br />the last several years have also been relatively steady in QR wells GP-5 and GP-6. As <br />expected, the sulfate concentrations are greater in downgradient well GP-5. A significant <br />~1 <br />L_.I <br />3-5 <br />