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Beneath the Wadge Overburden is a sequence of ]ow permeability siltstones, shales, and coals, approximately <br />200 feet thick. This is followed by afine-grained massive sandstone, approximately 250 feet thick, known as the <br />Trout Creek Sandstone. The Trout Creek sandstone is the second major regional aquifer, which exists in the <br />Twentymile Park Basin. There is very little hydrologic connection between the Trout Creek sandstone and the <br />overlying Wadge Overburden. <br />Table 1 presents a summary of bedrock well monitoring frequencies, which was last updated for Permit Revision <br />6 (PR 03-06) in March of 2004. <br />Wade Overburden: Five Wadge Overburden wells (009-79-4, 006-82-74C, 91M006, 008-77-58, and <br />93M001) are currently monitored. Water quality sampling is required annually. All monitoring requirements <br />were completed at these sites. Tables 2 through 6 provide summaries of the 2005 Water Year data. Tables 2a <br />through ba provide some historical statistical summaries of collected data at each site through 2005. Tables 2b <br />through 6b provide period of record water level summaries for each site. Figures 3 through 11 provide graphical <br />representations of water levels and selected water quality parameters recorded at each site. <br />The potentiometric surface in the Wadge Overburden generally slopes from south to north in monitored wells in <br />the vicinity of the TCC facilities, as shown by water levels in wells 009-79-4, 006-82-74C, and 91M006. During <br />2005, the water levels in well 009-79-4 (Figure 3) continue [o be comparable to previous years going back to <br />1984. Well 009-79-4 (Figure 4) has exhibited a general decline in Iota] dissolved solids since 1995, although <br />• concentrations were up slightly in 2005. Well 006-82-74C (Figures 5 and 6) has returned to water levels and <br />TDS concentrations typical of the early 1990s, although the final TDS measurement for 2005 was a new high <br />(see Table 2). Well 91M006 (Figure 7) continues to show a steady decline in water level. <br />Well008-77-58 (Figure 8) has been unaffected by mining and exhibits seasonal water level fluctuations. During <br />1998, this well experienced an unusually long seasonal decline, and subsequently an established recovering water <br />level trend resumed. In 2005 TDS concentrations (Figure 9) remain at consistent levels seen since 1980s. <br />The potentiometric surface reflected by well 93M001, has generally been observed [o slope from southwest to <br />northeast. Well 93M001 (Figure 10) had indicated declines in water level since the 1999 water year through <br />2002, and has since stabilized. These earlier declines were associated with underground mining of the Eastern <br />Mining District (EMD). TDS concentrations (Figure 11) in this well remain stable. <br />No anomalous water quality impacts attributable to mining were evident in data collected from Wadge <br />Overburden wells during 2005. <br />TwentVmile Sandstone: During 2005, one well, 006-BRDH-7, required monitoring for water levels and field <br />parameters on asemi-annual basis, and two wells, FBR-2, and 97013TM, required monitoring for water levels, <br />field parameters, on asemi-annual basis, and water quality parameters on an annual basis. Water quality <br />. frequency is annual. Al] monitoring requirements were completed at these sites during 2005. Tables 7 through 9 <br />provide summaries of the 2005 Water Year data collected at each site. Tables 7a through 9a provide historical <br />statistical summaries of collected data at each site through 2003. Tables 7b through 9b provide period of record <br />4 <br />