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2004 Geologic Hazard Field Observations <br />South of Divide Mining Area <br />• areas above gate roads with arigid-pillar configuration. The cracks may stay open or close in <br />areas above gate roads with a combination rigid-pillaz/yield-pillaz configuration. <br />Compression features (bulges and warps) also occur above the longwall mining panels in areas <br />where the ground surface undergoes compression in the subsidence process. The compression <br />features, which occur toward the center of the mining panel in zones of maximum compression, <br />aze usually more difficult to recognize. They often aze masked, or absorbed, by soil and <br />colluvium, or aze hidden in the brush and grass. They also maybe indistinguishable from natural <br />humps and mounds in the soil and colluvium. <br />6.2 Construction Cracks <br />Cracks caused by construction activities aze common on the banks of newly constructed roads <br />and drill pads. The bulldozer often causes these cracks during construction activities. The cracks <br />aze most noficeable where fractured and weathered bedrock is encountered. However, this type <br />_ of cracking also occurs in soil and colluvium where roots of brush and trees are pulled out of the <br />road cut by the bulldozer. In contrast to subsidence cracks, construction cracks occur in a rather <br />continuous zone where weathered and/or fractured bedrock has been cut through, or where brush <br />and trees have been pulled out of soil and/or colluvium. <br /> <br />The most diagnostic differences between subsidence cracks and construction cracks is that the <br />construction cracks: 1) have a less regulaz pattern, 2) aze related to the material they occur in, and <br />3) lack any spatial crack relationship to the longwall mining geometry. <br />6.3 Desiccation Cracks <br />Desiccation cracks tend to occur in claystones and siltstones of the Mesaverde and Wasatch <br />Formations in the West Elk mining area where the rocks aze weathered to clays and silts. The <br />process of desiccation involves the shrinking of the clays and silts after a dry period that follows <br />a wet period, when the material swells (i.e. the shrink/swell process). <br />831-032.621 Wright Water Engineers, Inc. Page 10 <br />November 2004 <br />