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• SPRING 2008 SUBSIDENCE AND GEOLOGIC FIELD OBSERVATIONS <br />BOX CANYON, APACHE ROCKS, <br />AND SOUTH OF DIVIDE MINING AREAS <br />r1 <br />U <br />r 1 <br />1.0 SUMMARY OF MAJOR FINDINGS <br />On June 4 and 5, 2008, Wright Water Engineers, Inc. (WWE) performed subsidence and <br />geologic field investigations of Box Canyon, Apache Rocks, and South of Divide (SOD) mining <br />areas for Mountain Coal Company. These observations have been made regularly for the past <br />twelve and one half years. <br />Based on field observations from 1996 to spring 2008, the effects of longwall mining in the <br />Apache Rocks and Box Canyon mining areas have been less than were initially projected as <br />reported in Exhibit 60 (Dunrud 1998 rev.). The maximum depth of tension cracks was projected <br />to be 50 to 100 feet on steep slopes and 75 to 200 feet near cliffs. The maximum depth of cracks <br />at Apache Rocks is estimated to be 30 feet. The maximum estimated depth of cracks near cliffs <br />(at Location 5 and 11 in this report) is 30 to 75 feet. <br />The range of maximum horizontal tensile strain values predicted for the Apache Rocks mining <br />area by the author in Exhibit 60 is 0.3 to 1.3 percent (0.003 to 0.013). The maximum values of <br />horizontal strain measured at Apache Rocks in 2000 and in the last three field visits (0.47 and <br />0.48 percent, respectively) are below the median horizontal tensile strain values (0.65 percent) <br />predicted in Exhibit 60. <br />During the spring 2008 field traverses, no subsidence tension cracks or compression bulges were <br />observed in the surficial deposits (colluvium and local alluvium) above mined Longwall Panels <br />14 to 17 and 19 to 24 in the Apache Rocks, and Box Canyon mining areas (Longwall Panel 18 is <br />currently being mined). During the past twelve and one-half years of field observations <br />(including spring 2008), no cracks were observed in the surficial deposits (colluvium and local <br />831-032.790 <br />August 2008 <br />Wright Water Engineers, Inc. <br />Page 1