2014-06-06_REPORT - C1981044 (7)

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Three sandstone aquifers are found beneath the subject site. In ascending order, they are: Trout Creek Sandstone, Middle Sandstone, and Twentymile Sandstone. The Eagle No. 5 and Eagle No. 6 Mines are located between the Trout Creek Sandstone and the Middle Sandstone. Water Levels The potentiometric surface represented by water level measurements in the Trout Creek Sandstone 5 Mine well (Fig. 3), has dropped from levels measured prior to TC. This drop is apparently from a consistent subsurface dewatering pumping. Historical annual water level fluctuations of 20 to 200 feet have been observed at this well but no seasonal pattern is evident. The former Okie Plaza Trout Creek well was abandoned in June 1994 as mining advanced through its location. The water levels in the Middle Sandstone formation as measured in wells TR -4, TR -7a, 81 -01, 83 -01, 83 -02, and 83 -03 show fluctuations which are apparently related to dewatering and subsidence associated with Mines 5 and 6. Wells TR-4, TR -7A, and 8 1 -01 displayed unusually large fluctuations during 2013. BTU EC will continue to monitor this trend toward large fluctuations in water level. The water levels in well 83 -02 (Figure 8) show a different pattern. The water level decline of about 150 feet from 1987 to mid 1990 in well 83 -02 was determined to be related to mine dewatering as Mine 5 workings approached the location of the well. The more abrupt 200 foot decline in water levels observed in 1990 is thought to be a drawdown response due to subsidence as it is located on only a few hundred feet horizontally from an F seam longwall panel which was mined in a similar time frame. The water level stabilized until 1994 when it recovered to the 1983 levels. Wells TR4 and 83 -03 are located at greater distance horizontally from the active operations for mines 5 and 6. Water levels in Well TR -4 (Figure 4) historically appear to be related to the fluctuations observed on all three of the down gradient Middle Sandstone Wells: 81 -01, 83 -01 and 83 -02. The water level decline in TR-4 prior to 1984 and the subsequent recovery up to 1988 closely parallels the trends observed in Wells 81 -01 and 83 -01. The decline during the first part of 1991 also parallels the trend in these two wells. However, the rapid decline during the last part of 1989 and the first part of 1990 appears to follow the trend observed in Well 83- 02 although the magnitude of decline is considerably less. Well 83 -03 (Figure 9) is the Middle Sandstone monitoring well located furthest (more than 1.5 miles) from active underground operations for Mines 5 and 6. The overall trend from 1984 through 2000 and again in 2013 suggests a similar trend to the other Middle Sandstone wells. The long term decline could be a pressure response due to the overall drop in potentiometric levels in the Middle Sandstone in the vicinity of Mines 5 and 6. Except for Well 83 -03, the water levels in the Middle Sandstone wells had either recovered or stabilized in 1995. The water level data collected for the other Middle Sandstone wells continue to display increased stability and a slow recovery. Monitoring results through year 2001 and again in 2013 (Fig. 10) showed no apparent change in the water levels in the Twentymile Sandstone that could be attributable to mining activities. During 2011, 9 Mine well displayed some fluctuations, while wells 259 and 84 -01 remained stable. These responses were not believed to be mine - related as no mining occurred in the vicinity of these wells during 2011. 9 Mine well has been stable since 2011. WFM will continue to monitor these sites. The groundwater gradient in the Middle Sandstone in the vicinity of the mining operation generally decreases Page 4 1:\ Env \Empire\AHR\2013 \Test \Empire2013 AHR.doc