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Subsidence Evaluation for the <br /> Exhibit 60E Southern Panels, Apache Rocks West, & Sunset Trail Mining Areas Page 7 <br /> 4.2 Construction Cracks <br /> Cracks caused by construction activities are common on the banks of newly constructed roads and <br /> drill pads. These cracks are caused by the bulldozer and related differential compaction during <br /> construction activities. The cracks are most noticeable where fractured and weathered bedrock is <br /> encountered. However, this type of cracking also occurs in soil and colluvium where roots of <br /> brush and trees are pulled out of the road cut by the bulldozer. In contrast to subsidence cracks, <br /> construction cracks occur in a continuous zone where weathered and/or fractured bedrock is <br /> 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 trees <br /> have been ripped out of soil and/or colluvium during the construction process. The most diagnostic <br /> features of construction cracks are that they 1) have a less regular pattern, 2) are related to the <br /> material they occur in, and 3)they lack of any spatial relationship to the underlying longwall mine <br /> 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 area above the West Elk Mine, particularly where the rocks are weathered to <br /> clays and silts. The process of desiccation involves the shrinking of the clays and silts after a dry <br /> period that follows a wet period, when the material swells (the shrink/swell process). <br /> 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 area <br /> above the West Elk Mine were observed in clays of the Barren Member of the Mesaverde <br /> Formation in the Horse Gulch-Minnesota Reservoir area and in the weathered claystones of the <br /> Wasatch Formation on West Flatiron,before there had been any mining. The larger,more regular <br /> desiccation cracks and construction cracks may be confused with subsidence cracks in areas where <br /> mining has occurred. However, transverse and longitudinal subsidence cracks have a definite <br /> spatial relationship to the longwall mining panel causing the cracks. <br /> 4.4 Pseudo Subsidence Features (Gravity4nduced Tension Cracks) <br /> Cracks have been observed on high, steep ridges,near cliffs, and in landslides, in the Box Canyon <br /> and Apache Rocks mining areas. These cracks looked very much like subsidence cracks,but could <br /> not have been,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 in the West Elk Mine is a <br /> good reason to perform baseline studies of the area prior to any mining so that these features can <br /> be documented. <br /> Cracks and bulges caused by landslides are other types of gravity-induced features that may appear <br /> to be related to subsidence, particularly in areas that have been, or are being, undermined. <br /> 831-032.912 Wright Water Engineers, Inc. <br /> December 2020 <br />