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<br />SOUTHWEST MINING DISTRICT <br />• One oil and gas well exists within the permit boundary for the Southwest Mining District. The well was drilled <br />during 1975 and originally was completed as an oil well. However, the yield was insufficient and the well was <br />converted to a gas well. The well is approximately 7,500 feet in depth and its location is shown on Map 23. <br />Twentymile Coal Company acquired ownership of the well in 1993. The well was plugged by placing a cement <br />plug in the well. - <br />EASTERN MINING DISTRICT <br />RESPONSE <br />The Eastern Mining District is located at the southern end of the Eckman Park sub-basin on the flank of a locally <br />significant syncline in the Twentymile Park Basin. This geological basin forms an enclosed ground water basin, <br />which is rimmed by outcrops of the major water-bearing units described in Section 2.04.6, Geology Description. <br />The limits of potential mining-related impacts on the ground water hydrologic system aze shown on Map 4, <br />Proposed Hydrologic Area Boundaries. <br />BEDROCK AQUIFER SYSTEM <br />Twentvmile Sandstone Aquifer <br />Aquifer characteristics of the Twentymile Sandstone have been measured within the permit area in six wells and the <br />results for transmissivity are reported in a range of 0.25 to 32 ft /day (Applied Hydrology Associates, ]984). Water <br />levels of the Twentymile Sandstone have been monitored in the mine plan area in wells 006-BRDH-7, 006-82-48A, <br />• FBR-11-B, FBR-12-A, FBR-9 & 10, and FBR-2. Recharge, discharge, ground water movement, and water quality <br />in the Twentymile Sandstone aze discussed later in this section. The potentiometric surface map for the <br />Twentymile Sandstone is presented in Figure 6R. <br />Trout Creek Sandstone Aquifer <br />Recharge to the Trout Creek Sandstone occurs along the unit outcrop, as shown on the Twentymile Sandstone <br />Potentiometric Surface Map (Figure 6R). There is very limited hydrologic connection between the Trout Creek <br />Sandstone and the Wadge Coal Seam that could change the proposed mining operation. Results of monitoring in <br />the current mining azea indicated that the hydraulic communication between major aquifers along the fault zones is <br />non-existent or very limited. <br />Wadee Overburden Aquifer <br />Field data from ground water monitoring wells was used to construct a potentiometric contour map for the Wadge <br />Overburden aquifer in the permit area. This was developed by using water level data from yeaz 1983 prior to the <br />start of underground mining in the eastern portion of the study area and recent data (1993) from the western sector, <br />and is presented in Figure 6S. This figure will be upgraded after completion of the proposed installation of <br />additional monitoring wells. The potentiometric map for the Wadge Overburden aquifer was constructed using <br />only water level data, which were deemed to be reliable. The data from the new well has been used to update the <br />above figures. Additionally, TDS contours have been placed on the figures; therefore, the upgraded figure has been <br />placed in Exhibit 11D. Figure 6S will remain to provide historic perspective. Exhibit 1 lD does show a TDS plume <br />extending into the Eastern Mining District. The highest TDS concentration is to the southwest in the vicinity of the <br />adjacent surface mine and diminishes as it goes to the northeast. <br />• <br />A~~~4'D~'~!3 APR 2 4 2000 <br />Permit Renewal No. 3 2.04-41 (1/1/99 <br />