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overburden containing 70 percent sandstone. Also, because of hardness, fractures do not ~. close as readily in brittle rocks as they do in soft rocks during recompression. Heights of 9 to 11 times the coal extraction thickness (9 to l lt) aze reported where all the rocks consist of soft, plastic shales and claystones, The fractures also commonly close again under lateral vertical compression associated with static condifions, and become impermeable again. Within the permit azea, fracturing will likely become discontinuous with increasing height because of the alternating sequence of harder and brittle and softer and yielding rocks. Steeply dipping fractures neaz 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 watenbeazing zones will tend to occur more in zones of convex upwazd curvature, along separated bedding planes toward the center of the panel, and along local cracks in zones of convex downward curvature (Figure 1, Exhibit 60. Fracturing within the expected zone of fracture may cease completely where soft shales and claystones occur as alternating sequences with sandstone. Mr. Dunrud has concluded that the maximum height of fracturingabove longwall panels in the B- Seam in the Apache Rocks mining area is estimated to range from about 15 to 20 times the extraction thickness (t} (for example, if t = 12 feet, the maximum fracture height would he 240 feet at 20t) near the mid-range of 9 to 30 times coal extraction thickness. This estimate is viewed as conservative by Mr. Dunrud because rocks above the B-Seam and below the Marine Sandstone, that • underlies the D-Seam, 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 the following azeas: (1) azeas of tension near areas of convex upward curvature above chain pillars; (2) along local bedding planes; and (3) areas of convex downwazd curvature above the longwall panels. Continuous Deformation Zone and Near-Surface Zone These two zones aze discussed together because the ground surface is where neazly all measurements are made that monitor subsidence processes active in the zone of continuous deformation. The neaz-surface zone, which typically consists of weathered bedrock, colluvium, and soil ranging in depth from a few feet to a few tens of feet, may deform differently than the underlying bedrock, especially on steep slopes. The zone of continuous deformation, which is transitional to the underlying zone of fracturing, consists of differential vertical lowering and flexure of the overburden rocks above the zone of caving and fracturing. • 2.05-114 MarcA 1005PR11 / ~~ ~-~