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Subsidence Evaluation for the <br />Exhibit 60E Southern Panels, Apache Rocks West, & Sunset Trail Mining Areas Page 11 <br /> <br />831-032.923 Wright Water Engineers, Inc. <br />December 2021 <br />In areas of two-seam mining, it is possible for the heights of the fractured zones to become <br />cumulative as the height of fracturing from the underlying B-seam could extend up to the E-seam. <br />This potential exists in the Apache Rocks West and Southern Panels mining areas. However, this <br />phenomenon would not increase the height of fracturing above the E-seam, which would govern <br />the potential for near-surface impacts. <br />Also, with increasing height in this zone, and as lateral and vertical constraints increase, fracturing <br />that could impact water bearing zones will tend to occur more in zones of convex upward <br />curvature, along separated bedding planes toward the center of the panel, and along local cracks <br />in zones of convex downward curvature (Figure 2). Fracturing within the expected zone of fracture <br />may cease completely where soft shales and claystones occur as alternating sequences with <br />sandstones. <br />Drainage into the fractured formations, however, may cease after mining is complete and any water <br />bearing zones present may be restored. This is particularly likely in the upper part of the fractured <br />zone in shale sequences between sandstone layers, once subsidence is completed and the separated <br />beds re-compress and close in response to overburden load (Figure 2). Although very few water <br />bearing zones have been encountered, evidence of restored water levels has been measured and <br />reported in some wells in the West Elk Mine subsidence monitoring area after B-seam mining and <br />subsidence were complete. <br />5.3 Continuous Deformation Zone and Near Surface Zone <br />These two zones are discussed together because the ground surface is where nearly all <br />measurements are made that monitor subsidence processes active in the zone of continuous <br />deformation. <br />The near surface zone, which typically consists of weathered bedrock, colluvium, alluvium, and <br />soil a few feet to a few tens of feet thick, may deform differently than the underlying bedrock <br />(Figure 2). Field studies by Dunrud indicate that near-surface colluvium and alluvium, which <br />consist of predominantly clay and silt, can undergo significantly more extension without rupturing <br />than can the underlying material. In both the Somerset, Colorado and Sheridan, Wyoming field <br />study areas, colluvium and alluvium 5 to 10 feet thick were observed to cover cracks as much as <br />10 to 14 inches wide so that there was no indication of the underlying fractures. <br />The zone of continuous deformation, which is transitional to the overlying near-surface zone and <br />also to the underlying zone of fracturing, undergoes differential vertical lowering and flexure as <br />laterally-constrained plates (in three dimensions) or beams (in two dimensions). With flexure, <br />shear occurs at the boundaries of rock units with different strength and stiffness, characteristics, <br />such as sandstones and shales. Zones of tension above the neutral surfaces of a rock unit, for <br />example, become compressive above the boundary with another rock unit and below its neutral <br />surface (Figure 2, Enlargement 2). Any cracks, therefore, which occur in the tension zone of a <br />rock unit, terminate at the neutral surface, because the unit is in compression below this point.