2008-03-21_PERMIT FILE - C1980007A (5)

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West Elk Mine projected in the western panels of the Apache Rocks mining area, after E and B-Seam mining is completed, is projected to range-from 0.00026 to 0.001-32- rad/ft. Maximum negative curvature projected in the western panels for E and B-Seam mining ranges from approximately -0.00026 to -0.00132 rad/ft. Box Canyon Mining Area - Maximum positive curvature for the two northern panels, Panels 1 and. 2, is projected to be 0.000030 to 0.000410 rad/ft; for Panel 3, 0.000024 to 0.000202 rad/ft; for Panels 4 through 6, 0.000016 to 0.000239 rad/ft. Similarly, maximum negative curvature is projected at -0.000022 to -0.000410 rad/ft for Panels 1 and 2; -0.000024 to -0.000202 rad/ft for Panel 3; -0.000016 to -0.000239 rad/ft for Panels 4 through 6. Maximum Horizontal Strain Maximum positive horizontal strain (Em) measured in the West Elk Mine monitoring network ranges from 1.1 to 1.4-(Sm/d) (0.0058 to 0.0102, that is 0.58 and 1.0 percent); maximum negative strain between -0.20 and -4.0 times (S,,,/d) (or 0.0009 and 0.0307, that is 0.09 to 3.0 percent) (Table 1 of Exhibit 60B). The range of horizontal tensile strain in four different mine areas of the Western United States studied by Mr. Dunrud is 0.45 to 3-(S,,,/d). Maximum tensile and compressive strain is significantly greater above large barrier pillars and rigid chain pillars and mine boundaries than it is above longwall mining faces. This is because tensile strains caused by mining the two adjacent panels are additive above the common rigid chain pillars or unyielding mine panel boundary pillars. Cracks tend to be wider and deeper above barrier pillars or lease boundary barrier pillars than chain pillars because of their greater rigidity (for example, the large tension crack on the north side of Lone Pine Gulch). The tensile strains presented in Exhibit 60B (Figure 4) are believed to be conservative for the South of Divide mining area. Maximum horizontal tensile strains, measured by Mr. Dunrud in bedrock during annual observations in the Apache Rocks area (in hard brittle sandstone, where the only strain is revealed by cracks), were 0.0031 to 0.0062 (0.31 to 0.62 percent). The tensile strain is considered to be close to a maximum value for those observed by Mr. Dunrud in the. Apache rocks area because (1) the features are located above the area if influence of a large solid coal pillar and (2) no greater strain was observed in the Apache Rocks mining area. Apache Rocks 41ining Area - The horizontal tensile strain in the eastern panels after B Seam mining is projected to range from 0.003 on the south flank of West Flatiron (overburden depth is about 2,250 feet) to 0.013 (units are dimensionless [L/L]) near the head of Sylvester Gulch. Projected horizontal tensile strain for the western panels for E Seam mining are 0.008 above the thickest overburden on the ridves to 0.023 above the thinnest overburden hi Horse Gulch. Tensile strain after both E and B Seam mining is completed may range from about 0.016 to 0.041 above thickest and thinnest overburden, respectively. Projected horizontal compressive strain i,7ill be in the panel centers. In the eastern panel area. using an average value of 2.0 (S,,,; d) fl•om the West Elk Mine subsidence network, compressive strain is projected to range from -0.004 near the south flank of West Flatiron to -0.020 near the head of Sylvester Gulch. Compressive strain above the western panels after E Seam mining is estimated to range from -0.013 in areas of thickest overburden to -0.035 in areas of thinnest overburden. After 2.05-131 Revised June 2005 PRIG, Rev. March 2006: A1ay 2006 PR10, Nov. 2006TR107,.4pril2007TR108; Sep. 2007 PR12: Feb. 2008 PR-12