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Subsidence Evaluation for the <br />Exhibit 60E South. of Divide and Dry Fork Mining Areas Page 28 <br />7. This area contains three rockfall areas that have an estimated low to high rockfall <br />potential. It is located in the Lick Creek area south of any currently planned mining <br />(located in parts of Sections 8, 9, and 16, Township 14 South, Range 90 West). <br />Of the seven areas listed above, six occur near local drill roads or agricultural access roads, <br />which have only local, limited traffic on them Any rocks that may fall in these areas could be <br />readily removed before local traffic is impacted, should rockfalls occur on these remote roads. <br />Evidence of naturally occurring rockfalls, such as remnant boulders located at the base of steep <br />slopes, or in the run -out zones of these areas, and documentation of these areas prior to mining is <br />recommended. <br />Two potential rockfall areas were identified in the Dry Fork mining area. The first area is located <br />on the east side of the main Deep Creek channel above longwall panel E3. This area is identified <br />as having low to moderate potential. It is located on an area remote for any access roads or <br />manmade features. The second area is located on the eastern boundary of the Deep Creek <br />watershed. This rockfall area is over the eastern ends of panels E3, E4, and E5 if mined to the <br />maximum projected potential extent. <br />Based on annual observations in the Apache Rocks and Box Canyon mining areas during the last <br />six years (1999 -2004 inclusive), subsidence and any seismic activity caused by longwall mining <br />is not expected to significantly affect rockfall areas with an estimated high ' to low rockfall <br />potential. Only rockfall areas with an estimated very high rockfall potential were noticeably <br />affected. However, because there are no rockfall areas with an estimated very high rockfall <br />potential in the South of Divide and Dry Fork mining areas, the planned longwall panels in these <br />mining areas will most likely not affect rockfall areas. <br />10.3 Importance of Baseline Landslide and Rockfall Data <br />The most significant landslide in the South of Divide area, in terms of proximity to man-made <br />structures, is located above the northern part of E -seam longwall panel E9 (Map 1). Although <br />there is a large landslide within the area of mining influence of the southeast corner of un -mined <br />E -seam longwall panel E8 (mostly in the NE' /, of Section 8), the landslides located north and <br />south of Minnesota Reservoir are the most important in the mining area. It is important to <br />monitor the existing, natural (baseline) conditions before mining begins in order to document <br />their natural state. The cracks, bulges, and depressions observed in the landslide areas north and <br />south of Minnesota Reservoir are much more extensive and dramatic than those caused by <br />subsidence. The vertical aerial photographs obtained by the West Elk Mine (dated July 2, 2004) <br />will provide good baseline images of all the natural, pre -mine features in the South of Divide <br />mining area. <br />Observations made by Dunrud in the West Elk mining area indicate that mining may accelerate <br />the natural landslide process, where there are landslides that have already become unstable. <br />However, annual observations of the surface cracks and depressions in the landslide area on <br />Jumbo Mountain above mined B -Seam longwall panels 8 and 9 determined that landslides are <br />very likely only related to natural mass- gravity movements and not related to mining. <br />• <br />831 - 032.810 Wright Water Engineers, Inc. <br />