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Observed Ground Water Impacts <br />Mine Inflows and Discharges <br />Annual hydrology reports show the total dischazge for the 5 and 6 Mines was a <br />fairly constant 600 gpm during active mining in the early 1990s. After mining <br />ceased in 1995, Bumped water was pumped down. In 1997 and 1998 pumping <br />became intermittent, averaging less than I gpm. <br />Troert Creek Smidstone <br />Annu.sl hydrology reports as recent as 1998 indicate no continuing mining- <br />caused change in the Trout Creek Sandstone potentiometric surface or <br />water quality. The water level in the Trout Creek Sandstone monitoring <br />well (iVo. 5 Mine well) dropped 200 ft. during 1989 and 1990. The drop <br />probably was caused by pumping of the three mine water supply wells <br />completed in the Trout Creek, rather than by mining in the overlying E and <br />F coal seams. The water level fully recovered in 1991 and then tuctuated <br />200 ft. in 1998. The fluctuation is probably not related to dewatering in the <br />overlying E and F seams because the base of the E coal seam is above the <br />current water level in the No. 5 Mine well. Historical field conductivity <br />data for the Trout Creek Sandstone wells indicate no adverse water quality <br />impacts related to mining. <br />Middle Sandstone <br />The most significant hydrologic impact caused by Mines 5 and 6 appeazs to be an <br />approximate 60-foot drawdown of ground water in the Middle Sandstone as . <br />observed in well TR-4. This drawdown persisted as recently as 1998. This <br />drawdown was not predicted in the PHC of the permit, but is compazable to the <br />worst-case drawdown projected for the overlying Twentymile Sandstone at a one- <br />mile radius. <br />Monitoring wells near mine workings (TR-4, TR-7A, 81-01, 83-D1, 83-02). During <br />the years of active mining in Mines 5 and 6, water levels in Middle Sandstone <br />monitoring wells nearest the mine workings fluctuated in response to mine <br />dewatering and subsidence. Since mining ceased in 1995, water levels in these wells <br />appear to be gradually recovering to pre-mining levels. Since 1983, the Middle. <br />Sandstone's potentiometric surface has shifted from a westerly dip to a northward <br />dip as mine workings have been dewatered. The dip of the potentiometric surface <br />has steepened from 0.06 ft/ft in 1983 to 0.10 fUft in 1998 (see Annual Hydrology <br />Reports for those years). Water quality in the wells has shown no impact from <br />mining. The changes in the potentiometric surface and the water quality indicate <br />hydrologic impacts in the Middle Sandstone have been minimized within the permit <br />area. <br />24 <br />