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• <br />• <br />SPRING 2011 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 June 20 -21, 2011, Wright Water Engineers, Inc. (WWE) performed subsidence and geologic <br />field investigations of Box Canyon, Apache Rocks, and South of Divide (SOD) mining areas for <br />Mountain Coal Company, LLC (MCC). These observations have been made annually since 1996 <br />and semi - annually since 2007. <br />Based on field observations from 1996 to spring 2011, 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 was estimated to be 30 feet. The maximum depth of cracks near cliffs on West <br />Flatiron was estimated to be between 40 and 60 feet. <br />The range of maximum horizontal tensile strain values predicted for the Apache Rocks mining <br />area by Richard Dunrud in Exhibit 60 was 0.3 to 1.3 percent (0.003 to 0.013). The maximum <br />values of horizontal strain measured at Apache Rocks since 2000 (0.48 percent) was below the <br />median horizontal tensile strain values (0.65 percent) predicted in Exhibit 60. <br />During the spring 2011 field traverses, no subsidence tension cracks or compression bulges were <br />observed in the surficial deposits (colluvium and local alluvium) above mined B -seam Longwall <br />Panels 14 to 17 and 19 to 25 in the Apache Rocks, and Box Canyon mining areas. No cracks <br />were observed on the Dry Fork Road above mined E -seam Longwall Panels El and E2 and <br />cracks observed along Horse Gulch Road in spring 2010 are no longer discernable. Subsidence <br />tension cracks were noted above recently mined E -seam Longwall Panel E2 at drill pads for <br />methane drainage wells (MDWs) E2 -13 and E2 -9 as well as along the drill road between these <br />pads and also along Dry Fork Road downstream of Horse Gulch Road. Additional details <br />831 - 032.793 <br />September 2011 <br />Wright Water Engineers, Inc. Page 1 <br />