2008-03-21_PERMIT FILE - C1980007A (5)

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West Elk Mine • Location 12 - located on friable sandstones of the Barren Member of the Mesaverde Formation above the middle part of longwall panel 13, in NE 1/4, Section 29. • Location 10 -located in sandstones of the Barren Member above longwall panel 13, about 2,000 feet east of location 12 in El/z, Section 27. 7. Within the Box Canyon mining area all cracks observed were deemed to have been caused by mass-gravity movement (lateral spreading along ridges) or by the desiccation process (no longwall mining had occurred in this area at the last time the area was visited). These features were observed above projected longwall mining panels 18-22 in Section 14 and 23, T 13 S, R 90 W, (See Map 67 and Annual Subsidence Reports for general locations of historical subsidence cracks). Given the long and extensive history of mining in the area, it is surprising the small number of subsidence related features that have been identified. It cannot be proved that these represent the only cracks associated with the mine, but given the regular survey activity, inspection of the subsidence profiles, and seasonal landowner, hunter, and U.S. Forest Service (USFS) personnel activity, additional cracks would have been noted if they existed. This lack of evidence of surface cracking would lend strong validation to the premise that longwall muting in the B-Seam has had minimal surface impacts at West Elk Mine. Landslides It could be expected that the changes in stress and strain of the near-surface strata and possible near-surface fractures associated with the predicted subsidence could reactivate or initiate landslides. The landslides listed below are all naturally occurring features, which become unstable during periods of increase precipitation. A review of aerial photographs that were taken in 1963 show that the slides listed below were more stable at that time than they are now. Mr. Dunrud observed that many of the existing landslides, including the landslides north and south of Minnesota Reservoir became unstable and moved during the period of high precipitation in the mid 1980s. The landslides on the southeast side of West Flatiron and on the west side of Deep Creek in the Apache Rocks area appear-to have been unaffected by longwall mining beneath the areas. It therefore appears apparent that wet seasons affect landslides more than does longwall mining. During very wet periods, however, landslides that are already unstable may locally be triggered by mine subsidence. Panel 25 in Sylvester Gulch is not expected to increase the potential of landslides in that area, as the east side of Sylvester Gulch is in an up-dip area not prone to landsliding. Presently, there are four known locations within the pen-nit area where the reactivation of a landslide could be potentially linked to past or current mining. The first area, in Lone Pine Gulch (Section 20, T13S, R90W, 6?1 P.M.), contains numerous old landslide features, including steep, huinnocky topography with many smaller surficial slumps. Cracldng and slumping occurred on one section of a jeep trail in this area in early October 1994. The cracks appeared during mining of the 5NW longwall panel in the B-Seam. Location of the crocks coincides with the boundary of earlier F-Seam room-and- pillar panels. The second area, discussed previously. is above the 8NW longwall panel. This landslide activity, which could not be definitively linked to longwall mining, is described in considerable detail in CDMG's inspection report (CDIviG 1995). The third area is above the 9N W lon-, all panel. Another known landslide area is south of High',Ntay 133 near Box Canyon Nvitiun the Box Canyon Permit revision area. These landslides are outside the projected longwall mining subsidence effects (i.e., 16 degree angle of draw) by more than 600 feet as described in Exhibit 60C, 60D and 60E. 2.05-112 Revised June 2005 PRIO, Rev. 11arch 2006: Rev. April 2006 PRIO: Hqi, 2006 PRIO, Alov. 2006 TR107, Sep. 2007 PR-12; Feb. 2008PR-12