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impact related to mining operations associated with Mines 5 and 6. Drawdown effects <br />in the Twentymile Sandstone unit were evident in the 1996 data as well. The <br />Probable Hydrologic Consequences section of the Permit predicted drawdown in the <br />Middle Sandstone unit associated with mining the F and E coal seams at Mines 5 and <br />6, although the extent and magnitude of the drawdown were not quantified. A worst <br />case evaluation was, however, prepared for the overlying Twentymile Sandstone. <br />The drawdown in Middle Sandstone Well TR-4 attributable to the longwall mining in <br />the E and F seams at a distance of approximately one mile has historically been <br />determined to be between 50 and 60 feet. This is comparable to the 60 foot <br />drawdowns projected in the PHC for the overlying Twentymile Sandstone at a <br />distance of one mile from the location of mine subsidence. The impacts observed in <br />the Middle Sandstone are comparable to the worst case projections developed for the <br />Twentymile Sandstone. A small increase in the dissolved solids in Williams Fork <br />Alluvium Well AVF-3 appears to be fluctuating around 2100 mg/L. The cause of this <br />recent relative increase is unknown; however, the data indicates that it is not from the <br />mine discharge or from the waste water lagoon. In addition, these levels are <br />consistent with measurements recorded earlier in the well's data set. The increased <br />TDS in the 7 North Angle Discharge seen in 1991 has decreased to approximately <br />850 mg/L. The increase in TDS was due to the accumulation of water in the North <br />Angle Sump location which was able to equilibrate with oxidized rock within old <br />workings and rubbelized rock within subsidence panels. The maximum concentrations <br />. of 1474 mg/I probably represents this equilibrium concentration. Flow from the #1 <br />C-61-044 199fi AHR. I:\EMPIREWHR\96AHR\EMPAHR96 DOC Page 14 <br />