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Subsidence Evaluation For <br />Exhibit 60 The Apache Rocks And The Box Canyon Mining Areas Page 10 <br />Apache Rocks Mining Area. Based on analyses of the current West Elk Mine subsidence <br />monitoring network, and using an average value of 2.7•(Sm/d), tilt above the eastern panels is <br />projected to range from about 0.006 in the southern flank of West Flatiron to about 0.027 neaz <br />the head of Sylvester Gulch (Table 2). <br />Tilt above the western panels, for E-Seam mining only, is projected to range from 0.017 on the <br />higher ridge areas to about 0.048 in the lower areas of Horse Gulch. Following completion of E- <br />and B-Seam mining, tilt is projected to range from about 0.033 on the higher ridges to 0.085 in <br />Horse Gulch. <br />Box Canvon Minin¢ Area. Maximum' tilt, based on analyses of West Elk Mine subsidence <br />measurements, is projected to range from 0.004 beneath West Flatiron to 0.035 above the <br />northernmost panel beneath Box Canyon (see Table 3 for estimated values for various <br />overburden depths in the Box Canyon mining area). <br />4.3.1.4 Maximum Curvature <br />Curvature, i.e., subscript (Cm), which is the reciprocal of radius of curvature (and thus expressed <br />in radians/foot [rad/ft]), is calculated from differential tilt. Maximum positive (convex upward) <br />curvature in the West Elk Mine monitoring network is as much as 50 percent more over chain <br />• pillars than it is above longwall panel boundaries. Maximum positive curvature at the current <br />West Elk Mine ranges from 14.4 to 18~(Sm/d') with a numeric range of 0.000060 to 0.000065 <br />rad/ft above longwall panel boundaries to an average of 24~(Sm/d'') with a numeric range of <br />0.000144 to 0.00022 rad/ft above the chain pillazs (see Table I ). <br />Maximum negative (concave upwazd) curvature averaged about the same when measured above <br />the chain pillars as it did above the panel boundaries. Maximum negative curvature ranges from <br />about -20 to -25•(Sm/d2) (-0.000111 to -0.000066 rad/ft) above longwall panel boundaries and has <br />an average value of -24~(Sm/d') (-0.00012 to -0.00025 rad/ft) in the panel centers between the <br />chain pillars. Maximum positive and negative curvature in four different areas of the Western <br />United States ranges from 9 to 45 (Sm/d-). Maximum curvature ranges are given below for the <br />eastern and western panels of the Apache Rocks and the Box Canyon mining areas (Tables 2 and <br />3). <br />Apache Rocks Mininu Area. Maximum positive curvature projected for B-Seam mining in the <br />eastern panels of the Apache Rocks mining area (using an average West Elk Mine value of <br />24•(S,,,/dz)), ranges from 0.000023 to 0.0002 rad/ft; maximum negative curvature (using a <br />similar average of -24~(Sm/d')) ranges from -0.000033 to -0.00069 rad/ft. Maximum positive <br />curvature projected in the western panels of the Apache Rocks mining area, after E- and B-Seam <br />mining is completed, is projected to range from 0.00026 to 0.00132 rad/ft. Maximum negative <br /> <br />831-032.181 Wnght Water Engineers, inc. <br />