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Subsidence Field Observations <br />West Elk Mine <br />August 27-29, 2002 <br />1.0 SUMMARY OF MAJOR RESULTS OF THE SUBSIDENCE STUDY <br />1. No subsidence cracks were observed in the Deep Creek traverse. A detailed inspection of <br />the deep alluvial and colluvial surfaces within the azea of influence of longwall mining <br />Panels 14 and 15, which is an estimated 50 to 150 ft thick, revealed no subsidence features. <br />2. Most of the subsidence cracks observed in surficial material (soil and weathered bedrock) <br />during the 2001 field study, especially above longwall mining Panels 13 and 13-A, aze less <br />visible or are healed completely, compazed with the 2001 observations. <br />3. Subsidence cracks in less durable to friable sandstones, such as above the midpoint of <br />longwall Panel 13, show more signs of sloughing, infilling, and sealing than they did in <br />2001. Some of these cracks that were observed last yeaz aze now completely healed by <br />weathering, infilling, and mass wasting. <br />4. Some of the major subsidence cracks in the durable sandstone of the Apache Rocks area aze <br />observed to be as much as 10 to 20 percent wider and 20 to 40 percent longer than were <br />observed in 2001. The wider cracks, which were bridged by weathered sandstone and soil, <br />aze now revealed as the material has fallen into them. Except for some further signs of <br />aging and extension of cracks in width and length, the crack occurrence and distribution is <br />the same as last year. <br />5. No positively identifiable subsidence cracks were observed on the southeast ridge azea of <br />West Flatiron in the azea of RAV-10 in either the sandstones of the Ohio Creek Member of <br />the Mesaverde Formation or in the overlying clays and silts of the Wasatch Formation, even <br />though the longwall mining face in Panel 14 had passed beneath the point. A compression <br />azch may have developed in the underlying 2,250 feet of Mesaverde sandstones and <br />siltstones, thus delaying crack formation until the azch finally reaches the surface. <br />831-032.570 Wright Water Engineers, Inc. Page 1 <br />October 2002 <br />