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FALL 2008 SUBSIDENCE AND GEOLOGIC FIELD OBSERVATIONS <br />BOX CANYON, APACHE ROCKS, <br />AND SOUTH OF DIVIDE MINING AREAS <br />1.0 SUMMARY OF MAJOR FINDINGS <br />On October 2 and 3, 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 annually for the past <br />thirteen years (semi-annually since 2007). <br />Based on field observations from 1996 to fall 2008, the effects of Longwall mining in the Apache <br />Rocks and Box Canyon mining areas have been less than were initially projected as reported in <br />Exhibit 60 (Dunrud 1998 rev.). The maximum depth of tension cracks was projected to be 50 to <br />100 feet on steep slopes and 75 to 200 feet near cliffs. The maximum depth of cracks at Apache <br />Rocks is estimated to be 30 feet. The maximum estimated depth of cracks near cliffs (at <br />Location 4, 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 four 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 fall 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 25 is <br />currently being mined). Cracking was observed along the Box Canyon access road beneath <br />Longwall Panel 18 but with no extension beyond the road surface into the cutbank or downslope <br />into the valley bottom. B-seam overburden thickness in this area is approximately 550 feet. <br /> <br />831-032.790 Wright Water Engineers, Inc. Page 1 <br />December 2008