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Subsidence Field Observations <br />West Elk Mine <br />August 28 and 29, 2001 <br />• This was a baseline traverse along a recently graded road above un-mined longwall panels <br />15, 14, 24, and 23, and above mined longwall panel 14 on the ridge to drill site RAV-10. <br />• No subsidence cracks were observed in the sandstone bedrock of the Ohio Creek Member <br />or undisturbed silty claystone of the overlying Wasatch Formation (see video for details). <br />The longwall face was located 100 feet west of drill site RAV-10 and, therefore, the area <br />had already been subjected to maximum tensile stress and strain. <br />• Two irregular, northward-trending cracks were observed on August 29, 2001 in the <br />graded and compacted silty clays of the Wasatch Formation (Figure 1). One crack is as <br />much as 3Y inches wide and 70 feet long. Another crack, 12 feet east of the 70-foot <br />crack, is 30 feet long and up to 2%: inches wide. Because no cracks were found in <br />undisturbed bedrock, these cracks are most likely the result of desiccation and differential <br />compaction rather than mine subsidence. <br />J <br />J <br />J <br />831-032.560 <br />September 2001 <br />Wright Water Engineers, Inc. <br />Page 3 <br />Figure 1. Irregular, north-trending crack located in graded and <br />compacted silty claystone of the Wasatch Formation. <br />