2015-03-18_REPORT - C1982056 (4)

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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 was not apparent, although many historical boreholes and some faulting exists in this general vicinity. Water levels in 2014 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 2014. 2011 exhibited an historic low TDS of 380 mg/1. The exact reason for this decline is unknown, and does not appear to correspond with stable water levels. The TDS value rebounded significantly in 2014 (Figure 23) but is still within historic values. The reason for this jump is unknown, but TC will continue to monitor and assess it. Well 97013TC (Figure 24) water levels remained consistent from 2004 through 2010. A drop in water level occurred in mid 2010, which is the result of being mined through. The water level continued to drop during 2014. Water quality values for well 97013TC (Figure 25) appear consistent with historical values. Fish Creek Sandstone: Two Fish Creek Sandstone wells (91 M001 and 91 M004) require monitoring on a semiannual basis for water level only. An additional well (Ashley) requires semi - annual monitoring for water levels and field parameters, and annual water quality sampling. Tables 15 through 17 provide summaries of the 2006 Water Year data collected at each site. Tables 15a through 17a provide historical statistical summaries of collected data at each site. Figure 26 provides graphical representation of the period of record water levels measured at sites 91 M001 and 91 M004. 91 M004 has been dry the last two years. Water levels at the Ashley well (Figure 27) dropped appreciably after subsidence in 1998, but afterward began to recover in 1999. Seasonal changes in water levels have been evident, although water levels have appeared close to the same levels from 2005 through 2014. TDS values at the Ashley well (Figure 28) have exhibited a general decline since 1996, rose somewhat in 2011, and dropped again in 2011 through 2014. Field measurements and water quality parameters for the Ashley well are provided on Table 17. Water quality values were within the typical historical range of other wells in this aquifer. 3.2 Alluvial Groundwater Monitoring Table 18 presents a summary of alluvial well monitoring frequencies, which was last updated for Permit Revision 6 (PR 03 -06) in March of 2004. Alluvial ground water in the Twentymile Park Basin exists under unconfined conditions within the alluvial materials underlying the major surface drainages of the area and backfilled areas of adjacent surface mined areas. Stream flows are the primary source of recharge to the alluvial aquifers. Alluvial deposition is limited in areas where stream gradients are relatively steep and in areas where the stream channel has eroded to or intersects resistant bedrock. Consequently, the alluvial deposits do not tend to be continuous. Shallow wells completed in these deposits indicate that they are usually less than 20 feet thick and the depth to ground water is typically less 7