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• 3.1 Groundwater Monitoring <br />3.1.1 Bedrock Wells <br />Three sandstone aquifers aze monitored at the subject site. In ascending order, they are: Trout Creek <br />Sandstone (1 monitoring well), Middle Sandstone (6 monitoring wells), and Twentymile Sandstone (3 <br />monitoring wells). The Eagle No. 5 and Eagle No. 6 Mines are located between the Trout Creek Sandstone <br />and the Middle Sandstone. <br />Trout Creek Sandstone: The potentiometric surface represented by water level measurements in the Trout <br />Creek Sandstone No. 5 Mine well (Fig. 3), has recovered to the levels measured in 1986 through 1988. This <br />recovery is appazently from a reduction in pumping for use by the mining operation. The well is used for <br />water supply as well as monitoring. Historical water level fluctuations of 20 to 200 feet have been observed <br />at this well but no seasonal pattern is evident. The Okie Plaza Trout Creek well was abandoned in June 1994 <br />as mining advanced through its location. See the 1994 Annual Hydrology Report for data on this well. <br />The 2001 field parameter data for the No. 5 Mine well does not suggest any significant water quality impacts <br />to the Trout Creek Sandstone. The water quality data for this Trout Creek Sandstone well is summarized on <br />Tables 5 and 6. A plot of field conductivity measurements is presented in Figure 13. <br />Middle Sandstone: The water levels as measured in wells TR-4, TR-7A, and 81-01, show fluctuations <br />which aze apparently related to dewatering and subsidence associated with Mines 5 and 6. Wells TR-7A, and <br />81-O1 displayed large fluctuations during 2001. Well TR-4, which displayed lazge fluctuations in 2000, <br />appears to have returned to historical levels in 2001. <br />Wells 83-02, and 83-03 did not indicate any significant changes from historic values in 2001. A water level <br />was no[ obtained for 83-O1 during the first quarter of 2001. This omission is discussed in the Summary and <br />Conclusions section of this AHR. Note, as a result of the temporary cessation monitoring plan, subsequent <br />quarterly water level monitoring for 83-01 was not required. Historically, the water levels in Wells 83-O1 <br />(Figure 7) and 83-03 (Figure 9) have exhibited consistent water levels, without significant declines or <br />increases. Historically, Well 83-02 (Figure 8) indicated a water level decline of about 150 feet from 1987 to <br />mid 1989, which was related to mine dewatering as Mine 5 workings approached the location of the well. <br />The more abmpt 200-foot decline in water levels observed near [he end of 1989 and beginning of 1990 was <br />thought to be a drawdown response due to subsidence as it is located on only a few hundred feet horizoutally <br />from an F seam longwall panel, which was mined in a similaz time frame. The water level stabilized until <br />1994 when it recovered to the 1983 levels. <br />Wells TR-4 and 83-03 aze located at greater distance horizontally from the active operations for mines 5 and <br />6. Water levels in Well TR-4 (Figure 4) historically appear to be related to the fluctuations observed on all <br />three of the down gradient Middle Sandstone Wells: 81-01, 83-01 and 83-02. The water level decline in TR-4 <br />prior to 1984 and the subsequent recovery up to 1988 closely parallels the trends observed in Wells 81-O1 and <br />3 <br />I:\Env\Empire\AHR\2001 \Text\Em pire2001 AH R.d oc <br />