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<br />increased in TDS, sulfate and other major constituents in 1983. This increase is <br />likely the result of water that has been in the Spoil aquifer for a longer period of <br />time before reaching this spring. The concentrations in 1983, 1984 and 1985 are <br />likely the maximum concentrations that this seep will yield. The 1986 <br />concentrations indicate that the levels in this seep are starting to decline. The <br />major constituent concentrations from the Cottonwood Spring, which has not existed <br />as long as the Colt Seep, contains concentrations that are much lower than those <br />from the Colt Seep, except for chloride and bicarbonate. The lower concentrations <br />from the Cottonwood Spring are probably representative of this portion of the Spoil <br />aquifer and, therefore, will never reach the levels observed from the Colt Seep. <br />The concentrations from backfill well GF5 are similar to those from the Cottonwood <br />Spring which indicate that these values may be more typical of the Spoil aquifer. <br />• The concentrations from the Cottonwood Spring are representative of the values <br />in the surface water during low flow conditions when all of the surface water is <br />derived from ground-water discharge. The concentrations from Colt Seep are higher <br />than the typical low flow concentrations, but the discharge from this seep is too <br />small to impact surface-water quality. The average ground-water quality being <br />discharged to the surface is expected to contain higher concentrations during the <br />initial several years after mining and, therefore, increase the concentrations <br />slightly. The discharge from the more permeable areas of the Spoil aquifer will <br />yield the majority of the input to surface water and monitoring indicates this <br />quality should be close to the natural ground water being discharged in this area. <br />Therefore, the impact to surface-water quality from Spoil aquifer discharge to the <br />surface is expected to be small. <br />r <br />LJ <br />4-227a REVISED JAN 7 '88