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2004 Geologic Hazard Field Observations <br />South of Divide Mining Area <br />aeeas above gate roads with arigid-pillaz configuration. The cracks may stay open or close in <br />aeeas above gate roads with a combination rigid-pillar/yield pillar 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 towazd the center of the mining panel in zones of maximum compression, <br />are usually more difficult to recognize. They often ace masked, or absorbed, by soil and <br />colluvium, or are hidden in the brash 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 are common on the banks of newly constructed roads <br />and drill pads. The bulldozer often causes these cracks during construction activities. The cracks <br />are most noticeable where fiactured and weathered bedrock is encountered. However, this type <br />of cracking also occrus in soil and colluvium where roots of brush and trees are pulled out of the <br />road cut by the bulldozes. In contrast to subsidence cracks, construction cracks occur in a rather <br />continuous zone where weathered and/or fiactured bedrock has been cut through, or where brush <br />and trees have been pulled out of soil and/or colluvium. <br />The mast diagnostic differences between subsidence cracks and construction cracks is that the <br />construction cracks: 1) have a less regtilaz pattern, 2) are 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 lvlesaverde and Wasatch <br />Formations in the West Elk mining area where the rocks are 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 />• <br />831-032.621 Wright Water Engineers, Inc. Page 10 <br />November 2~4 <br />