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Subsidence Evaluation for the <br />Exhibit 60E South of Divide and Dry Fork Mining Areas Page 6 <br />4.2 Construction Cracks <br />Cracks caused by construction activities are common on the banks of newly constructed roads <br />and drill pads. These cracks are caused by the bulldozer and related differential compaction <br />during construction activities. The cracks are most noticeable where fractured and weathered <br />bedrock is encountered. However, this type of cracking also occurs in soil and colluvium where <br />roots of brush and trees are pulled out of the road cut by the bulldozer. In contrast to subsidence <br />cracks, construction cracks occur in a continuous zone where weathered and/or fractured bedrock <br />is encountered during road construction. <br />Construction cracks may be confused with subsidence cracks, particularly where mining has <br />occurred in the area, and where local bedrock is weathered and fractured, or where brush and <br />trees have been ripped out of soil and/or colluvium during the construction process. The most <br />diagnostic features of construction cracks are that they 1) have a less regular pattern, 2) are <br />related to the material they occur in, and 3) they lack of any spatial relationship to the underlying <br />longwall mine geometry. <br />4.3 Desiccation Cracks <br />Desiccation cracks tend to occur in claystones and siltstones of the Mesaverde and Wasatch <br />Formations in the West Elk Mine area, particularly where the rocks are weathered to clays and <br />silts. The process of desiccation involves the shrinking of the clays and silts after a dry period <br />that follows a wet period, when the material swells (the shrink/swell process). <br />is Desiccation cracks can often be recognized by their irregular, branching and diverging pattern— <br />less regular than typical subsidence cracks. Some of the largest desiccation cracks in the West <br />Elk Mine area were observed in clays of the Barren Member of the Mesaverde Formation in the <br />Horse Gulch - Minnesota Reservoir area and in the weathered claystones of the Wasatch <br />Formation on West Flatiron, where there has been no mining. The larger, more regular <br />desiccation cracks and construction cracks may be confused with subsidence cracks in areas <br />where mining has occurred. However, transverse and longitudinal subsidence cracks have a <br />definite spatial relationship to the longwall mining panel causing the cracks. <br />4.4 Pseudo Subsidence Features (Gravity - induced Tension Cracks) <br />Cracks have been observed on high, steep ridges, near cliffs, and in landslides, in the Box <br />Canyon and Apache Rocks mining areas. These cracks look very much like subsidence cracks, <br />but cannot be, because no mining had been done when they were observed. A good example of a <br />gravity- induced crack is the extensive crack that Dunrud observed on the narrow ridge of West <br />Flatiron in August 2002. This crack was as much as 3.5 in wide and 150 feet long. This was not <br />a mining - related crack because no mining had occurred in the area The possibility of gravity - <br />induced cracking in the rugged country above planned mining activities at the West Elk mining <br />areas is a good reason to perform baseline studies of the area prior to mining so that these <br />features can be documented prior to any mining. <br />Cracks and bulges caused by landslides are other types of gravity - induced features that may <br />appear to be related to subsidence, particularly in areas that have been, or are being, undermined. <br />831 - 032.810 <br />Wright Water Engineers, Inc. <br />im <br />