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SUBSIDENCE FIELD OBSERVATIONS WEST ELK MINE AUGUST 28 AND 29, 2001 1.0 SUMMARY OF MAJOR RESULTS OF THE SUBSIDENCE STUDY 1. Subsidence cracks in the durable sandstone of the Apache Rocks area look similar to their appearance on August 28, 2000. Except for some signs of aging, the crack occurrence and distribution remain the same. 2. Subsidence cracks observed in surficial material (soil and weathered bedrock) during last year's field study are much less visible, or are obliterated completely, when compared with the previous visit. 3. Subsidence feature cracks in less durable to friable sandstones at certain other sites show significantly more signs of sloughing, infilling, and sealing. Some cracks, which were readily observed last year, are now nearly obscured by weathering, infilling and mass wasting. 4. No positively identifiable subsidence cracks were observed on the southeast ridge area of West Flatiron in the area of RAV-10 in either the sandstones of the Ohio Creek Member of the Mesaverde Formation or in the overlying clays and silts of the Wasatch Formation, even though the longwall mining face in panel 14 had passed beneath the location, and was now 100 feet west of the ridge area. A compression arch may have developed in the underlying 2,250 feet of Mesaverde sandstones and siltstones, thus delaying crack formation until the arch finally reaches [he surface. The area should continue to be observed to determine whether or not cracks eventually develop. 5. Hummocky topography and signs of mass-gravity movements on the north and south sides of Minnesota Reservoir reveal landslides that range in age from only a few years to many hundreds, or perhaps thousands, of years. These unstable slopes occur prior to any mining influence and, therefore, are not related [o mining activities. 831-032.560 Wright Water Engineers, Inc. Page 1 September 2001