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RAG, Empire Corporation 1999 AHR <br />solids level of the discharge has increased from an average of approximately 900 mg/I <br />• <br />in 1982 and 1983 to almost 1,400 mg/I in 1986, and then decreased to approximately <br />1,100 mg/I since 1987. The decreasing trend was noted to continue in 1998. Figure <br />28 illustrates the variable nature of total recoverable iron concentrations in the Strip Pit <br />discharge. During 1998, these levels occurred within normal ranges established for <br />this site. <br />PONDS <br />There was no discharge from the sediment ponds in 1999. <br />HYDROLOGIC IMPACTS <br />No significant unpredicted adverse impacts were detected during 1999. The continued <br />• drawdown in the Middle Sandstone unit is determined to be the most significant <br />impact related to mining operations associated with Mines 5 and 6. Drawdown effects <br />in the Twentymile Sandstone unit were evident in the 1999 data as well. The Probable <br />Hydrologic Consequences section of the Permit predicted drawdown in the Middle <br />Sandstone unit associated with mining the F and E coal seams at Mines 5 and 6, <br />although the extent and magnitude of the drawdown were not quantified. Aworst-case <br />evaluation was, however, prepared for the overlying Twentymile Sandstone. The <br />drawdown in Middle Sandstone Well TR-4 attributable to the longwall mining in the E <br />and F seams at a distance of approximately one mile has historically been determined <br />to be between 50 and 60 feet. This is comparable to the 60-foot drawdowns projected <br />. Page 12 <br />