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Subsidence Evaluation for the <br />Exhibit 60E Southern Panels, Apache Rocks West, & Sunset Trail Mining Areas Page 36 <br />units, in the subsidence process. This same reasoning also applies to the colluvium in the area. <br />Although subsidence cracks were locally observed in colluvium less than one foot to a few feet <br />thick, no cracks were observed in colluvium more than about ten feet thick. No cracks have been <br />observed in alluvium above mined longwall panels in the Apache Rocks and Box Canyon mining <br />areas. <br />11.3.1 Potential for Hydraulic Connection between Mine Workings and Surface <br />Near the southwest corner of E -seam longwall panel E2, the Dry Fork channel encounters a short <br />reach 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 the <br />Dry Fork stream channel and the mine workings. To address this scenario, the maximum projected <br />height of fracturing and the maximum depth of surface cracks were considered. As discussed in <br />Section 5.2, the effective height of fracturing in the Southern Panels and Sunset Trail mining areas <br />is estimated to range from 9t to 18t, or a maximum fracture height of 252 feet for a mining height <br />of up to 14 feet. However, Peng (1992) states that the upper one-third of the fractured zone has <br />only minor fractures with little potential for water conductivity. Therefore, the height of the <br />fractured 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 5t, or 70 feet, for the Southern Panels <br />and Sunset Trail mining areas with a projected mining thickness of up to 14 feet. When added to <br />the effective fracture zone height of 252 feet, the combined heights of the caved and fracture zones <br />capable of transmitting water is projected to be a maximum of 322 feet. <br />As discussed in Section 5.3.2, the maximum crack depth in the Southern Panels and Sunset Trail <br />mining areas 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. Even <br />at the minimum overburden thickness of 375 feet, an estimated 122 feet of unfractured bedrock <br />will remain intact. In addition, the presence of soft shales and claystones in the E -seam overburden <br />will increase the probability that the strata will warp rather than fracture during the subsidence <br />process. The expected lack of hydraulic connection was confirmed as mining occurred in E -seam <br />panel E2 without any adverse impacts to Dry Fork or any anomalous water inflows observed in <br />the mine. With the proposed B -seam mining occurring below the E -seam, we do not foresee the <br />potential for hydraulic connection between Dry Fork and the mine workings. <br />11.4 Springs and Water -Bearing Zones <br />MCC has produced the Spring and Stock Pond Location Map that covers the Southern Panels, <br />Apache Rocks West, and Sunset Trail mining areas. Only a few springs in the West Elk Mine area <br />indicate a source from a local bedrock water -bearing zone. Most springs likely have sources from <br />local water -bearing zones in surficial material (debris flows, colluvium, and possibly alluvium). <br />In contrast to surface water containment structures, such as reservoirs, ponds, streams and ditches, <br />springs and water -bearing zones may have water sources that are either in bedrock beneath the <br />blanket of clay -rich surficial material (debris flows, alluvium, and colluvium), or have a source <br />831-032.816 Wright Water Engineers, Inc. <br />October 2018 <br />