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West Elk Mine <br />The thalweg of the Dry Fork will be surveyed over panels E2 and E3 beginning at a point <br />downstream of the angle of draw of panel E2 and continue upstream to a point above the angle of <br />draw of panel E3. This survey will completed before subsidence mining commences in the SOD <br />and then remeasured upon completion of mining panel E2 and then again at the completion of <br />mining E3. A final survey will be conducted approximately one year after completion of mining <br />E3 and subsidence within the azea of both panels is essentially complete. <br />These flow and thalweg surveys will be used to determine if mitigation of the stream channel due <br />to significant changes in flow or the stream profile due to subsidence aze warranted. Mitigation <br />of mining impacts may be necessazy if loss or diversion of flow or a significant change in the <br />stream profile will significantly impact vegetation. Mitigation measures are discussed in more <br />detail in Section 2.05.6(6)(f)(iv)(A-D) -Detailed Description of Mitigation Measures. The <br />results of the flow measurements and stream channel surveys will be included the Semi-Annual <br />Subsidence Report. If significant changes in the stream flow related to mining activities are <br />noted, the CDMG will be notified within three days of observing the flow anomalies. <br />Potential for Hydrau[ic Connection Between Mine Workings and Surface <br />Near the southwest corner of longwall panel E2, the Dry Fork channel encounters a short reach <br />where the E Seam overburden is less than 400 feet, with a minimum of 375 feet. A prudent <br />concern is whether mining induced subsidence could establish a hydraulic connection between <br />the Dry Fork stream channel and the mine workings. To address this scenario, the maximum <br />projected height of fracturing and the maximum depth of surface cracks were considered. As <br />discussed in Section 5.2, the effective height of fracturing in the South of Divide mining area is <br />estimated to range from 9t to 18t, or a maximum fracture height of 252 feet for a mining height <br />of 14 feet. However, Peng (1992) states that the upper one-third of the fractured zone has only <br />minor fractures with little potential for water conductivity. Therefore, the height of the fractured <br />zone capable of transmitting water would be two-thirds of the 18t, or 168 feet. <br />The maximum height of the caved zone is projected to be St, or 70 feet, for the South of Divide <br />mining area. When added to the effective fracture zone height of 168 feet, the combined heights <br />of the caved and fracture zones capable of transmitting water is projected to be a maximum of <br />238 feet. <br />As discussed in Section 5.3.2 of Exhibit 60B, the maximum crack depth in the South of Divide <br />mining azea is estimated to be 15 feet in terrains with slopes less than 30 percent, with depths up <br />to 35 feet occurring locally in steep topography. For the Dry Fork channel near the western edge <br />of panel E2, the maximum projected crack depth is 15 feet. Consequently, the combined <br />maximum height of the caved and fractured zones and the maximum crack depth is 253 feet. <br />Even at the minimum overburden thickness of 375 feet, an estimated 122 feet of unfractured <br />bedrock will remain in tact. In addition, the presence of soft shales and claystones in the E Seam <br />overburden will increase the probability that the strata will warp rather than fracture during the <br />subsidence process. <br />Springs. Aquifers, and Ground Water Wells <br />Map 37 shows one decreed spring (Spring 21), three springs found flowing at every site visit (in <br />1975, 1977, 1979, and 1980), thirty-three internuttent springs, and two groundwater wells that aze <br />2.05-153 Revised Jwie 2005 PRIO, Rev. March 2006; May 1006 PRI G <br />