2009-03-03_REPORT - C1982056 (2)

Home Browse Search

Trout Creek Sandstone: During 2008, five Trout Creek Sandstone wells, 001-83-106, 001-83-107, 95M001, FBR-2-E, and 97013TC. Note that per TR03-42, monitoring frequency for water levels and field parameters were reduced to an annual basis, and water quality sampling to a bi-annual (every other year) basis. Also per TR03-42, Trout Creek Sandstone wells 008-75-EFC and 97012TC were deactivated. All monitoring requirements were completed at these sites. 2008 data is presented in Tables 10 through 14. Well FCM#2 was replaced in the fall of 1995 by monitoring well 95M001, with semi-annual monitoring during 2008 occurring at well 95M00l in lieu of FCM #2. Summaries of the Water Year data collected at each site can be found in previous AHRs. Tables 10a through 14a provide the historical statistical summaries of collected data at wells 001-83-106, 001-83-107, 95M001, FBR-2-E, and 97013TC, respectively. Figures 18 through 25 provide graphical representations of water levels and selected water quality parameters recorded at active sites. The pumping of TCC domestic water well 001-83-106 (Figure 18) complicates the potentiometric surface in the Trout Creek Sandstone. Water levels in well 001-83-106 were showing a slight increase since 1998, which appears to have stabilized back in 2003. The potentiometric surface trends prevalent in the Twentymile Sandstone and Wadge Overburden aquifers are not evident in the monitored Trout Creek wells. The previously monitored well 006-83-48C routinely exhibited water levels in the 7100 ft elevation range while replacement well FCM#2 exhibited levels around the 6520 ft elevation during 1995. In the fall of 1995, well 95M00l was established in part to address the apparent discrepancy in water levels between wells 006-83-48C and FCM#2. Water levels from well 95M00l confirm that levels recorded from well FCM #2 were accurate (Figure 20). Mining in the northern mining district began in 1995, which is down dip of this well. Water levels in well 95M00l declined since 1994, appeared to stabilize since 2002, and again declined in 2008 (Figure 20). The declines may have been influenced by the mining operation. Significant inflows from the Trout Creek Sandstone into the mine workings have not been encountered to date to account for the apparent lowering of the potentiometric surface in the Trout Creek formation, as indicated by the water level data previously recorded for well 006-83-48C. Some dewatering of the aquifer does occur from the pumping of well 001-83-106 to supply the mine with domestic water. The southernmost Trout Creek well, 001-83-107 (Figure 19), water levels continue to decline. Located down dip of the TCC facility water well (001-83-106), steady declines in water level since the early 1990 may reflect effects from longwall mining that began in the western mining district in 1990, in addition to water well use (Figure 21). Well FBR-2-E (Figure 22), located along the eastern permit boundary exhibited consistent water levels until early 1999, then dropped about 50 feet and immediately stabilized with consistent water levels at the lower depth to date. The specific reason for this drop is not apparent, although many historical boreholes and some faulting exists in this general vicinity. Water levels in 2008 were similar to the previous water years. TDS values for FBR-2-E (Figure 23) dropped in 2001, rebounded back to historical values, and began dropping again in 2003 . through 2008. Although close to historic values, 2008 exhibited an historic low TDS of 730 mg/l. The exact reason for this decline is unknown, and does not appear to correspond with stable water levels. 6