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2005 SUBSIDENCE AND GEOLOGIC FIELD OBSERVATIONS <br />BOX CANYON, WEST FLATIRON, APACHE ROCKS, <br />AND SOUTH OF DIVIDE MINING AREAS <br />1.0 SUMMARY OF MAJOR FINDINGS <br />During the past decade of annual subsidence observations and evaluations (1996 to 2005 <br />inclusive), the effects of longwall mining beneath cliffs and steep slopes has been less than <br />initially projected. The maximum depth of tension cracks on steep slopes and cliffs in the <br />Apache Rocks and Box Canyon mining areas was projected to be 50 to 100 feet and 75 to 200 <br />feet, respectively in Exhibit 60 (Duntud, et al. 1998 rev). The maximum estimated depth of <br />cracks observed to date ranges from about 5 feet at Location 10 (of this report} to 10 feet near the <br />west boundary of mined longwall panel 14, and 30 feet at the Apache Rocks subsidence area. <br />The range of tensile strain measured and calculated in August 2000 at Apache Rocks was 0.23 to <br />0.47 percent (Dunrud 2000) (using values of 0.75 to 1.5 feet across the crack area that measured <br />320 feet wide). The tensile strain is still within this range, as observed in July 2005. This range <br />is considerably less than the values of 0.3 to 1.3 percent that are projected for the Apache Rocks <br />mining area, or 0.2 to 1.7 percent for Box Canyon mining area in Exhibit 60, particularly at the <br />upper end of the ranges. <br />No subsidence features (cracks or bulges) were observed in the alluvium above mined longwall <br />pane122 (Box Canyon) and mined longwall panels 14, 15, 16, and 17 during the past seven years <br />of observations in the Box Canyon and Apache Rocks mining areas. Observations over six years <br />(three years of pre-mining traverses and three years of post-mining traverses) in the alluvium, <br />mixed alluvium, and colluvium in Deep Creek revealed no noticeable subsidence effects as <br />longwall panels 14 through 17 were mined beneath overburden 1,050 to 1,100 feet thick. No <br />subsidence features were observed on traverses in Sylvester Gulch above mined longwall panels <br />14 through 16 over the last seven years, where the overburden depth to the B-Seam ranges from <br />900 to 1,600 feet. <br />831-032.710 Wright Water Engineers, Inc. Page 1 <br />November 2005 <br />