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provides a historical summary of flow rate data for the surface water monitoring sites. Figures 3 through 133 <br />provide graphical representations of selected data. Figure 121 presents data documented during the 2003 Mine <br />Inflow Study. Statistical summaries of the historical data base are provided after presentation of the 2003 data. <br />Statistical summaries of water levels or flows are presented as well. <br />Note that in 2A03, DMG approved TR03-42 (See Exhibits 14-5, 14-6, and 14-10), and PR 03-06 (See Exhibits <br />14-7 through 14-9), which eliminated some surface, alluvial, and bedrock well monitoring sites, and reduced [he <br />monitoring frequency of other sites, while adding additional monitoring requirements to existing surface site 305. <br />Specific changes resulting from TR03-42 and PR03-06 are discussed in the following sections. <br />3.1 Bedrock Groundwater Monitoring <br />Hvdro¢eoloev: TCC's underground mining operations are located on the southwest flank of the Twentymile <br />Park Basin. This is an enclosed synclinal ground water basin, rimmed by outcrops of major lithologic units. <br />Ground water in the Twentymile Park Basin exists primarily under confined conditions within the bedrock units. <br />All ground water aquifers in the general area, except the alluvial aquifers, are recharged by infiltration in outcrop <br />areas, located primarily in the southern and western margins of the Twentymile Park Basin. Recharge is limited, <br />due to low average annual precipitation and the loss of moisture through evapotranspiration and sublimation in <br />this semi-arid climatic zone. Ground water occurrence and movement within the bedrock aquifer system is <br />controlled by geologic structure and lithology. Ground water movement tends to follow the structural dip of the <br />• lithologic units toward the basin axis. The general trend of movement in the permit area is to the north and <br />northwest. This results in confined aquifer conditions down gradient from the outcrop area. A detailed <br />discussion of the geologylhydrology for the site is available in the Twentymile Coal Company, Foidel Creek Mine <br />Permit C-82-056, Volume 1, Rules 2.04.6 and 2.04.7. <br />The Twentymile Park Basin is underlain by a large, high quality coal reserve. This reserve, mined by <br />underground operations, is known as the Wadge Seam. The Wadge Seam lies within a sequence of sedimentary <br />rocks characterized by shales, claystones, mudstones, siltstones, sandstones, and minor coal stringers referred to <br />as the Wadge Overburden. The Wadge Overburden is hydrologically isolated from the two major bedrock aquifer <br />units in the Twentymile Park Basin, the Twentymile Sandstone aquifer and the Trout Creek Sandstone aquifer, <br />which lie above and below the Wadge Overburden, respectively. Lying above the Twentymile Sandstone is a <br />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 fUday), 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 />3 <br />