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Observed Imoacte on Aquifers <br />Mining activities at the No. 5 and No. 6 Mines are affEacting piezometric <br />levels in at least two sandstone aquifers as well as the coal beds (s and F <br />coal seams). Declines in piezometric levels have been recorded in <br />observation wells in the Middle Sandstone and the Trout: Creek Sandstone. <br />No declines in piezometric levels have been observed irc the Twentymile <br />Sandstone. The water quality of all three sandstone ac~uifera does not <br />indicate significant trends or adverse impacts related to mining at Mines 5 <br />and 6. <br />Trout Creek Sandstone <br />The piezometric declines in the Trout Creek Sandstone are thought to be <br />related primarily to pumping of the three mine water supply wells completed <br />in this unit and not from mining the overlying S and F coal seams. The <br />piezometric levels, represented by water levels in the No. 5 Mine We11 and <br />the Okie Plaza well, recovered to the levels measured in 1986 through 1988. <br />The recovery of the two wells is apparently from reduction in pumping for <br />use, since both wells are used for water supply as well as monitoring. The <br />recovery would not have occurred if the declines observed in 1988 and 1989 <br />were due to dewatering of the S and F coal seams because mine dewatering <br />has continued. <br />Water levels in the No. 5 Mine Well and the Okie Plaza hell in 1991 appear <br />to be 25 to 50 feet lower than the levels measured when monitoring was <br />initiated in 1985 and 1987, respectively. Water level fluctuations of up <br />to 250 feet have been observed, which are likely related to pumping for <br />use, but no seasonal pattern ie evident or expected. Since the base of the <br />S coal seam in the vicinity of both Trout Creek Sandstone wells is above <br />the current piezometric level in these two wells, it ie not likely that the <br />recent fluctuations in piezometric levels in the Trout Creek Sandstone are <br />related to mine dewatering in the overlying s and F coal. seams. <br />A plot of field conductivity measurements for the Trout Creek Sandstone <br />wells is presented in Permit Figure 58A. This plot and the water quality <br />data for the Trout Creek Sandstone wells do not indicate any trend which <br />could be indicative of water quality impacts related to mining. <br />Middle Sandstone <br />The declines in the piezometric levels in the Middle Sandstone observed in <br />Figures 12 through 17, in Section 2.04.7 of the permit application package, <br />are apparently related to dewatering and subsidence associated with Mines 5 <br />and 6. The declines in the downgradient water levels between 1988 and 1990 <br />appear to have leveled off since the middle of 1990. The water levels <br />measured during 1991 are similar to the levels measured in 1983 and 1984. <br />A slight recovery from 1984 through 1988 is apparently the result of a <br />shift in the location of mining to an area further updip. Greater water <br />level fluctuations have been observed in areas closer to the location of <br />mine dewatering. <br />The water levels on the southeast side of the permit area (also down- <br />gradient) show a different pattern. A water level decline of about 150 <br />feet from 1987 to mid-1989 has been determined to be related to mine <br />dewatering which followed the progression of mine workings. Amore abrupt <br />200-foot decline in water levels observed near the end of 1989 and <br />beginning of 1990 is thought to be a drawdown response due to subsidence <br />over an F-seam longwall panel which was mined in a similar time frame. <br />The upgradient monitoring wells are located north of the mine workings at <br />greater distance horizontally from the active operations for Mines 5 and 6 <br />22 <br />