2011-04-29_REPORT - C1981044 (2)

Home Browse Search

• and 83-03 show fluctuations which are apparently related to dewatering and subsidence associated with Mines 5 and 6. Wells TR-4 water levels appear to be slightly rising since 2008. Levels in TR-7A and 81-01 in 2010 are very consistent with that seen in 2006 through 2009. The water levels in 83-01 (Figure 7) have been on the rise since monitoring was reactivated in 2006. The water levels in well 83-02 (Figure 8) are consistent with those found since minotoring was reactivated in 2006. 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 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 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 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. Unusually large fluctuations for TR-4 for 1999 through 2000 have been attributed to a faulty pressurized line system. Well 83-03 (Figure 9) is the Middle Sandstone monitoring well located furthest (more than 1.5 miles) from is active underground operations for Mines 5 and 6. The overall trend from 1984 through 2000 and again in 2006 to date 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. The water levels in the Middle Sandstone wells had either recovered or stabilized in 1995. Note that there was a drop of about 13 feet in water level, followed by a subtle rise. Monitoring results through year 2001 and again in 2006 to date (Fig. 10) showed no apparent change in the water levels in the Twentymile Sandstone that could be attributable to mining activities. During 2010, 9 Mine well, and wells 259 and 84-01 remained stable as compared to 2006 through 2009. Note that in 2006 the first reading of the 9 mine well appeared elevated, and subsequently leveled off and has been stable through 2010. 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 2010 measurements. Water Ouality The 2010 field parameter data for No. 5 Mine well do not suggest any significant mining related water quality impacts to the Trout Creek Sandstone. The water quality data for this Trout Creek Sandstone well is summarized on Tables 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. Page 4 GAEnvironmentaAEMPMENAHM2010\Empire201 OAHR. doc