2011-03-14_REPORT - C1982056 (3)

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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 2010 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 2010. 2009 exhibited an historic low TDS of 675 mg/1. The exact reason for this decline is unknown, and does not appear to correspond with stable water levels. Well 97013TC (Figure 24) water levels remain consistent with that of the last two years. Water quality values for well 97013TC (Figure 25) appear consistent with historical values. Fish Creek Sandstone: Two Fish Creek Sandstone wells (91M001 and 91M004) 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 91M001 and 91M004. A rise in water level for 91M001 was observed in 2009, but has dropped back to historical values in 2010. The reason for the rise in 2009 is unclear, and this anomaly will be checked in 2011. Water levels at the Ashley well (Figure 27) dropped appreciably after subsidence, but afterward began to recover in 1998. Seasonal changes in water levels have been evident, although water levels have appeared close to the same levels from 2005 through 2010. TDS values at the Ashley well (Figure 28) have exhibited a general decline since 1996. 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 than 10 feet. The limited extent of the Foidel Creek alluvial deposits, and the lack of base flow in the creek indicates that these deposits are relatively insignificant to the area ground water hydrologic system. Alluvial deposits containing groundwater are monitored in the Foidel Creek, Fish Creek, Trout Creek and Middle Creek drainages. In the Foidel Creek drainage, sites both upstream and downstream of the TCC portals and support facilities are monitored. In the Fish Creek Drainage, sites upstream and downstream of the Mine 2 area and the Fish Creek Borehole mine dewatering facilities are monitored. 7