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Subsidence Evaluation for the <br /> Exhibit 60E Southern Panels, Apache Rocks West, & Sunset Trail Mining Areas Page 27 <br /> 8.0 FRACTURE-CONTROLLED DRAINAGES <br /> Based on mapping in the Southern Panels mining area, Dunrud believes that there is reasonably <br /> good,but certainly not conclusive, evidence that some drainages are controlled by fractures and/or <br /> joints. The Dry Fork of Minnesota Creek and some of its tributaries exhibit linear trends on <br /> satellite images and on high-altitude photographs that indicate, or at least suggest, fracture control <br /> (Dunrud 1976, p. 14-15). These fractures may have been caused in part by stresses generated by <br /> the West Elk Mountain intrusive bodies—particularly Mt. Gunnison. <br /> The conservative approach may be to assume that the drainage system is fracture controlled. <br /> However, even if fractures control the present drainage system,they may not extend downward as <br /> continuous joints of fractures to the E-seam located several hundreds of feet below. Even if the <br /> fractures were present in the more brittle sandstone units, it would be very unlikely that these <br /> fractures would occur in the softer siltstone and shale units. Even under the conservative approach <br /> that the drainages in the Southern Panels, Apache Rocks West, and Sunset Trail mining areas are <br /> fracture controlled, it is extremely unlikely that they extend downward to the E-seam through <br /> multiple shale, claystone, and siltstone units. Using this conservative evaluation, it is now <br /> important to evaluate the potential impact that subsidence may have on any pre-mining fractures. <br /> Evaluation of subsidence due to downwarping of laterally constrained strata shows, as stated <br /> previously, that rock strata with different deformation and strength characteristics deform as <br /> discrete units. For example, strata of shale and siltstone behave as units discrete from sandstone. <br /> Above the fractured zone (Section 4.2) and within the continuous deformation zone (Section 4.3) <br /> these units undergo continuous flexure (Figure 2, enlargement 2). Above the neutral surfaces, in <br /> zones of convex-upward curvature, the material is in tension and below them, and the material is <br /> in compression. <br /> Consequently, stresses change across neutral surfaces from tension to compression across each <br /> successive rock unit that deforms as a plate. Fractures already present would thus tend to open <br /> more in the zones of tension, but would close more in the zones of compression, which would <br /> close these fractures more than they were prior to mining and subsidence. <br /> After longwall mining is completed in the area and static conditions are attained, the zones of <br /> tension and compression commonly cease, and any fractures present will likely resume the pre- <br /> mining condition. Therefore,the impacts on surface flow in the drainages of the Southern Panels, <br /> Apache Rocks West, and Sunset Trail mining areas are likely to be minimal or non-existent under <br /> even the most conservative assumptions. <br /> 831-032.912 Wright Water Engineers, Inc. <br /> December 2020 <br />