2008-04-01_REPORT - C1981044 (5)

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• 1990 is thought to be a drawdown response due to subsidence as it is located 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 1!94 when it recovered to the 1983 levels. Wells TR-4 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 dow-1 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 We1183- 02 although the magnitude of decline is considerably less. Unusually large fluctuations for TR-4 for 1999 through 2000 ha~re been attributed to a faulty pressurized line system. Well 83-03 (Fig~zre 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 2007 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 stability and a slow recovery. Monitoring results through year 2001 and again in 2007 (Fig. 10) showed no apparent change in the water levels in the Twe;ntymile Sandstone that could be attributable to mining activities. During 2007, 9 Mine well, and wells 259 and 84-01 remained stable as compared to 2006. Note in 2006 the first reading of the 9 mine • well appeared elevated, and subsequently leveled off and has been stable through 2007. The elevated reading may be attributed to an error in monitoring equipment, as a pressurized reading was first attempted, and subsequent readings have used a water level meter. The groundwater gradient in the Middle Sandstone in the vicinity of the mining operation generally decreases from the southeast to the northwest as reflected on Figure 11. The piezometric contour map of the Twentymile Sandstone is presented as Figure 12. This gradient remains generally consistent with previous years, according to 2007 measurements. Water Quality The 2007 field parameter data for No. 5 Mine well do not suggest any significant mining related water quality impacts to the "Grout Creek Sandstone. The water quality data for this Trout Creek Sandstone well is summarized on 'Cables 5 and 6. A plot of field conductivity measurements is presented in Figure 13. Note that conductivity values for the No, 5 Mine well appear elevated to levels seen in the early 1980's, but appear to be in the same range as the former Okie Plaza well. This may be related to consistent pumping at this site. BTU-EC will continue to monitor this site and to determine the reason for this effect. The field parameter data for the three Middle Sandstone wells (TR-4, TR-7A, 81-01), again, suggest no adverse impact or trend. Water quality data are summarized in Tables 7 through 12. Plots of field conductivity for these Middle Sandstone Wells are presented in Figure 14. The conductivity measurements recorded at well. TR-7A remain stabile as compared to historic values. However it has recently become evident that Middle Sandstone wells TR-4 and 81-01 continued to have elevated conductivity values since • Page 4 G:~EnvironmentaAEMPII2E~AHR~2007~Empire2007AHR.doc