2009-05-22_GENERAL DOCUMENTS - C1981044

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Middle Sandstone - Outlying Wells The most significant hydrologic impact caused by Mines 5 and 6 may be an approximate 60-foot drawdown of ground water in the Middle Sandstone as observed in well TR-4. This drawdown persisted as recently as 2008, which is the most recent reporting year, although the water levels have stabilized.. This drawdown was not predicted in the PHC of the permit, but is comparable to the worst-case drawdown projected for the overlying Twentymile Sandstone at a one- mile radius. The water level in the Middle Sandstone well farthest from the mine workings, 83-03, dropped 50 ft. from 1985 to 1997 and then began a gradual recovery until 2001 and has since stabilized. Water quality had shown no impact from mining. The trends in water levels and the stable water quality indicate mining has not adversely impacted the Middle Sandstone aquifer outside the permit boundary. Middle Sandstone- wells near mine workings (TR-4, TR-7A, 81-01, 83-01, 83-02). During the years of active mining in Mines 5 and 6, water levels in the Middle Sandstone monitoring wells nearest the mine workings fluctuated in response to mine dewatering and subsidence. Between 1995, when mining ceased, and 2001, when the temporary cessation monitoring plan became effective, the water levels in these wells recovered to pre-mining levels and have since stabilized. The Middle Sandstone was monitored in well TR-7a as part of the temporary cessation plan. This well showed continued recovery of the Middle Sandstone's potentiometric surface in 2001 and 2002 and a stabilization since 2006. Water quality in the Middle Sandstone wells has shown no impact from mining. The changes in the potentiometric surface and the water quality indicate hydrologic impacts in the Middle Sandstone have been minimized within the permit area. Twentymile Sandstone Water level monitoring data reported through the 2008 annual hydrology report had shown no change in the piezometric levels in the Twentymile Sandstone that could be attributable to mining activities. The water quality data for the two Twentymile Sandstone wells, No. 9 Mine Well and Well 259, showed no adverse impact or trend. Williams Fork Alluvium Ground water levels in the alluvium have remained fairly regular, with normal seasonal fluctuations apparently related to changes in river levels. Ground water levels in the alluvium are plotted in Figure 22 in Section 2.04.7 of the permit application package. Annual hydrology reports through 2008 indicate no depletion has occurred and suggest that mining appears to not have affected Williams Fork River alluvial water quality. In 2002, Colorado experienced a significant drought. Low water elevation in the Williams Fork River is recorded in the lower water Eagle Mine Complex 25 Permit Renewal 05 C-1981-044 May 22, 2009