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Subsidence Evaluation For Exhibit 60 The Apache Rocks And The Box Canyon Mining Areas Page 5 • under lateral vertical compression associated with static conditions, and become impermeable again. Within the Apache Rocks the Box Canyon mining azeas, fracturing may become discontinuous in the caved zone with increasing height because of the alternating sequence of harder and brittle and softer and yielding rocks. Steeply dipping fractures near the top of the caved zone, therefore, will likely become less continuous with increasing height in the zone of fracturing. Also, with increasing height in this zone, and as lateral and vertical constraints increase, fracturing that could impact water bearing zones will tend to occur more in zones of convex upward curvature, along separated bedding planes toward the center of the panel, and along local cracks in zones of convex downward curvature (Figure 1). Fracturing within the expected zone of fracture may cease completely where soft shales and claystones occur as alternating sequences with sandstone. The maximum height of fracturing above longwall panels in the B-Seam in the Apache Rocks and the Box Canyon mining azeas is estimated to range from about IS to 20 times the extraction thickness, which is neaz the mid-range of 9 to 30 times coal extraction thickness as reported by Peng (1992, p. 7). This estimate may be conservative for rocks above the B-Seam and below the Marine Sandstone that underlies the D-Seam, because these rocks consist of about 150 to 200 feet of laminated sandstone and shale and sandy shale and sandstone. Most fractures will likely • become discontinuous at the base of the Marine Sandstone, and may be located only in azeas of tension near azeas of convex upward curvature above chain pillars, along local bedding planes, and in azeas of convex downward curvature above the longwall panels. In the western panels of the Apache Rocks mining area, where both the E- and B-Seams are to be mined, fracture heights may locally be as much as 220 feet above the E-Seam and 240 feet above the B-Seam. This may locally produce a fracture zone as much as 460 feet thick after E- and B- Seam mining is complete. Drainage, however, may cease after mining is complete and any water bearing zones present may be restored. This is particularly likely in the upper part of the fractured zone in shale sequences between sandstone layers, once subsidence is completed and the separated beds re-compress and close in response to overburden load (Figure 1). Evidence of restored water levels has been measured and reported in some wells in the West Elk Mine azea after mining and subsidence were complete. 4.3 Continuous Deformation Zone and Near Surface Zone These two zones aze discussed together because the ground surface is where nearly all measurements are made that monitor subsidence processes active in the zone of continuous deformation. 831-032.181 Wright Water Engineers, lnc.