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West Etk Mine '~ well as the B-Seam, will be mined. However, less than one percent of the mining area has an overburden depth of less than 500 feet. Overburden thicknesses between 800 and 2,250 feet exist over the four eastern B-Seam panels (i.e., the 14SE through 17SE longwall panels). Minimum overburden thickness above the NE longwall panels is 600 feet. Within the Box Canyon permit revision azea, the overburden thickness is between 500 and 2,200 feet. No portion of the proposed mining azea has an overburden depth of less than 500 feet. Minimum overburden thickness above the NE longwall panels is 600 feet. These considerable overburden thicknesses greatly reduce the potential of connection between subsidence-induced surface cracks and the mine workings. As indicated in Section 2.05.6 (6) (e) (i) (C&D), Depth of Surface,' (Tension) Cracks, subsidence- induced surface cracks, to the degree they develop, will generally extend no deeper than 50 to 100 feet. Combining the maximum expected surface crack depth (100 feet) with the maximum predicted caved and fracture zone height (270 feet combined), reveals that a minimum overburden depth of 370 feet should be sufficient to ensure that surface vYater does not reach the mine workings. Map 14 and Map 19 show the B and E-Seam overburden thicknesses for the West Elk Mine coal lease area. To establish a connection between the neaz surface zone and the caved zone, the overburden in the proposed permit revision azea needs to be less than 470 feet thick under the worst conditions and less than 370 feet thick under "typical" conditions (270 feet to account for the caved and fractured zone and 100 to 200 feet for surface crack depth, according to Mr. Dunrud). When looking at a plan view of the Apache Rocks and Box Canyons permit revision areas, it is clear that less than 6 percent of the total surface area has overburden thicknesses of less than 470 feet and less than 3 percent has overburden thicknesses of less than 370 feet. Within the vicinity of the . IONE and 11NE longwall panels, overburden ranges from 600 to 1,200 feet; therefore, there is no ~ area with less than 470 feet of overburden thickness. It should be noted that these percentages drop to zero relative to the azeas influenced by longwall mining in the Boz Canyon permit revision azea. For a connection to be established, a surface crack will actually need to occur. As discussed in 2.05-137 and 2.05-138, the probability of a surface crack at any given location over a pillar is only 0.2 percent (0.002) and there is no measurable risk of long-term surface cracks in the internal portions of panels, based on MCC's mining experience to date. Given that there is less than a 6 percent chance of encountering overburden within the permit area, that is shallower than 470 feet and a 0.2 percent chance of encountering a surface crack at any given location over a pillar, the combined risk of having both shallow overburden and a surface crack is extremely small. (This risk is even smaller if a 370 foot overburden thickness is utilized, and only the mining area of influence is considered). Furthermore, the crack connection would need to stay open and clear for long enough to impose a measurable hydrologic change, and this is highly unlikely given the subsurface changes that will be occurring in the aftermath of longwall mining. In the isolated locations where a connection could be established, ithe stream channels in question have small drainage basins with average annual surface flows of approximately 200 acre-feet per square mile per yeaz. Cracks will close via "healing" and "sealing," as discussed in response to other questions. . These calculations are substantiated by the actual mining experience at the West Elk Mine. For example, during the unusually wet Iate spring and summer of 1995; there were no increased inflows 2.05-I55 November 2004 PRII