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• <br />TDS has been significantly less the last few years than it was in 1976 <br />through 1978. This could be due to the higher rates of ground-water <br />flow in this area from the increased gradient. Average TDS in these <br />two aquifers could be on a gradual increase. <br />Figure B-13 shows a steady TDS concentration plot for well GF1, a <br />20 Mile Sandstone well. TDS concentrations for this well have not <br />varied as the 20 Mile at well GD1 has. A fairly steady concentration <br />would be expected of a deep aquifer as the 20 Mile Sandstone. The <br />concentration plot from well GF1 is thought to be more typical of this <br />aquifer. The TDS for well GF2 has also been steady (see Figure B-14). <br />This well is completed in the U aquifer below the R coal seam. The <br />• 1987 value shows essentially no change from past values. The RLM <br />aquifer, which is above the QR aquifer, is monitored at well GF3. <br />Results from this well show steady concentrations with time. The H <br />and I coal seams have recently been mined uphill of well GF4. TDS <br />data from this well indicates that mining has not affected <br />concentrations in this area of the HI aquifer (see Figure B-16). <br />Backfill well, GF5, has been monitored the last four years. The <br />data for the last three years indicates that TDS in the backfill <br />aquifer has reached the maximum concentration (see Figure B-17). The <br />last three TDS values are greater than the HI aquifer would have <br />likely contained in this area prior to mining, as expected. The TDS <br />of the backfill aquifer in this area is probably only approximately ' <br />• 1.5 times the pre-mine value in the HI aquifer. TDS in backfill <br />3-4 <br />