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HYDROLOGIC IMPACTS <br />No significant unpredicted adverse impacts were detected during 1994. The continued <br />drawdown in the Middle Sandstone unit is determined to be the most significant impact <br />related to mining operations associated with Mines 5 and 6. The Probable Hydrologic <br />Consequences section of the Permit predicted drawdown in the Middle Sandstone unit <br />associated with mining the F and E coal seams at Mines 5 and 6, although the extent <br />and magnitude of the drawdown were not quantified. A worst case evaluation was, <br />however, prepared for the overlying Twentymile Sandstone. The drawdown in Middle <br />Sandstone Well TRH attributable to the longwall mining in the E and F seams at a <br />distance of approximately one mile is determined to be between 50 and 60 feet. This is <br />comparable to the 60 foot drawdowns projected in the PHC for the overlying Twentymile <br />Sandstone at a distance of one mile from the location of mine subsidence. No <br />measurable drawdown has been observed in the Twentymile Sandstone. The impacts <br />observed in the Middle Sandstone are comparable to the worst case projections <br />developed for the Twentymile Sandstone. A small increase in the dissolved solids in <br />Williams Fork Alluvium Well AVF-3 appears to have stopped and the concentrations are <br />now below 2000 mg/L. The cause of this increase is unknown; however, the data <br />indicates that it is not from the mine discharge or from the waste water lagoon. The <br />increased TDS in the 7 North Angle Discharge seen in 1991 decreased a little in 1994 to <br />approximately 1050 mg/I. This increase in TDS was due to the accumulation of water in <br />the North Angle Sump location which was able to equilibrate with oxidized rock within <br />old workings and rubbelized rock within subsidence panels. The maximum <br />concentrations of 1474 mgll represenls this equilibrium concentration. Concentrations <br />C-81-044 7994 AHR Page 11 <br />