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• minor aquifer unit, known as the Fish Creek Sandstone. All these geologic units are monitored within the Foidel <br />Creek Mine permit area. <br />The Wadge Overburden is directly affected by the mining operation. Dewatering of this zone in the area of mine <br />operations is currently being conducted. The Wadge Overburden lies approximately 1100 feet below the ground <br />surface. The Wadge Overburden sequence varies in thickness from 50 to 100 feet, averaging approximately 75 <br />feet, and is characterized by low permeability (0.01 to 0.1 fbday), limited continuity, low yield and relatively <br />poor water quality. <br />Above the Wadge Overburden is the first major regional aquifer, known as the Twentymile Sandstone. The <br />Twentymile Sandstone aquifer is confined above and below by low permeability shale and interbedded <br />siltstone/shale units. The unit varies in thickness from 100 to 200 feet and is hydrologically isolated from the <br />underlying Wadge Overburden sequence by a low permeability marine shale, which has a thickness of up to 700 <br />feet. Approximately 125 feet above the Twentymile Sandstone is the 35-foot thick Fish Creek Sandstone. The <br />Fish Creek Sandstone is a discontinuous minor unit in the area that was the contact for a small coal seam that had <br />been surface mined. <br />Beneath the Wadge Overburden is a sequence of low 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 2007 Water Year data. Tables 2a <br />through 6a provide some historical statistical summaries of collected data at each site through 2007. Figures 3 <br />through 11 provide graphical representations of water levels and selected water quality parameters recorded at <br />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 />2007, the water levels in well 009-79-4 (Figure 3) continue to be comparable to previous years going back to <br />1984. Well 009-79-4 (Figure 4) has exhibited a general decline in total dissolved solids since 1995. We11006- <br />82-74C (Figures 5 and 6) water levels have been very stable since 1999. TDS measurement for 2005 was a new <br />high, however the levels seen in 2006 and 2007 are within historic ranges. Well 91M006 (Figure 7) had <br />exhibited a steady decline in water level beginning in 1992, however levels have shown a slight rise beginning in <br />• 2004. <br />4 <br />