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West Elk Mrne <br />. Eight crack locations were visited during the CDMG inspection. While most of the <br />surface cracks were attributable to rejuvenated landslide movement, three minor cracks <br />were reported to be the result of mining subsidence (Nos. 2, 3, and 8 on Figure 19A). <br />These cracks were three to four inches wide and less than one foot deep. Field <br />observations by MCC personnel indicated that these cracks were already healing, shortly <br />after mining had occurred. Two of these cracks (Nos. 3 and 8) are typical of the <br />dynamic subsidence process. As minutg occurs, the overburden above the mined <br />portion subsides and differential movement results between the mined and unmined <br />areas. Surface cracking can occur at the locafion of the differential subsidence. As <br />mining continues, the adjacent overburden subsides and the surface cracks will usually <br />close completely (DeGraff and Romesburg 1981). These cracks healed significantly as <br />evident in the late summer of 1997. Additionally, the overburden thickness under the <br />azeas where the cracks occurred was less than 500 feet-one of the few locations within <br />the permit area where the overburden is this shallow. <br />~~ <br />I": <br />Given the long and extensive history of mining in the azea, it is surprising that only four areas of <br />subsidence related features have been identified. It cannot be proved that these represent the only <br />cracks associated with the mine, but given the regular survey activity, inspection of the <br />subsidence profiles, and seasonal landowner, hunter, and U. S. Forest Service (USFS) personnel <br />activity, additional cracks would have been noted if they existed. This lack of evidence of surface <br />cracking would lend strong validation to the premise that longwall mining has had m;n;mal <br />surface impacts at the West Elk Mine. <br />Landslides - It could be expected that the changes in stress and strain of the near-surface strata <br />and possible neaz-surface fractures associated with the predicted subsidence could reactivate or <br />initiate landslides. Presently, there aze four known locations within the permit area where the <br />reactivation of a landslide could be potentially linked to past or current mining. The first azea, in <br />Lone Pine Gulch (Section 20, T13S, R90W, 6`" P.M.), contains numerous old landslide features, <br />including steep, hummocky topography with many smaller surfiicial slumps. Cracking and <br />shmtping occurred on one section of a jeep trail in this azea in early October 1994. The cracks <br />appeazed during mining of the SNW longwall panel in the B-Seam. Location of the cracks <br />coincides with the boundary of earlier F-Seam room-and-pillaz panels. The second area, <br />discussed previously, is above the 8NW longwall panel. This landslide activity, which could not <br />be definitively linked to longwall mining, is described in considerable detail in CDMG's <br />inspection report (CDMG 1996). The third area is above the 9NW longwall panel. Another <br />known landslide area is south of Highway 133 near Box Canyon within the Box Canyon Permit <br />revision area. These landslides are outside the projected longwall mining subsidence effects (i.e., <br />16 degree angle of draw) by more than 600 feet. Amore thorough description of these slides can <br />be found in Section 2.04.6, Geology Description. <br />2.05-104 Revised Jun. l995PR06; lN6 RN03; Revised May l9997R89; RevisedJan 1998PR08 <br />