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West Elk Mine Peng (1992) reports that the combined height of the zone of caving and fracturing ranges • from 20 to 30 extraction thicknesses (20 to 30t), and that the height of the fractured zone is greater for hard, strong rocks than it is for soft, weak rocks. As discussed in more detail in Exhibit 60, Richard Dunrud has concluded that within the Apache Rocks and Box Canyon mining areas, a more appropriate range is 15 to 20t. The height of the zone of fracturing is a function of lithology and layer thickness, according to Peng (1992}. For example, the zone of fracturing commonly is higher for strong, thickly-bedded, brittle sandstones than it is for thinly layered, soft, plastic shales and claystones. Liu (1981), reports ranges of heights of the zone of fracturing for various rock types as follows: • Heights of 20 to 30 times coal extraction thickness (20 to 30t) are reported in strong brittle rocks, such as siliceous sandstones and limestones; a value of 28t was reported for 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 conditions, and become impermeable again. Within the South of Divide mining area, fracturing will likely become discontinuous with increasing height because of the alternating sequence of harder and brittle and softer and yielding rocks Due . to the stratigraphic position of the E Seam, above the 170' to 250' thick Bowie Sandstone, the proportion of soft yielding strata as compared to the hard brittle strata in the fractured zone is higher than for the B Seam mining. The absence of the Bowie Sandstone in the fractured stratum and the high percentage of softer rocks is best illustrated in the Cross-Sections A-A' through F-F'. The height of the fracture zone, therefore, will likely be less, by possibly 10 to 20 percent, than the height predicted for the Apache Rocks and Box Canyon mining areas because of the presence of more shale. 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 water-bearing zones will tend to occur more in zones of convex upwazd curvature, along sepazated bedding planes towazd the center of the panel, and along local cracks in zones of convex downward curvature (Figure 2, Exhibit 60B). Fracturing within the expected zone of fracture may cease completely where soft shales and claystones occur as alternating sequences with sandstones. Mr. Dunrud has concluded that the maximum height of fracturing above longwall panels in the B- Seam in the Apache Rocks mining azea 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 be 240 feet at 20t) neaz the mid-range of 9 to 30 times coal extraction thickness. This estimate is viewed as conservative by Mr. Dunntd 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. 1.05-111 Revised November 2004 PRIG