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West Elk Mine <br />i 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 in the South of Divide mining area with <br />an estimated very high rockfall potential, longwall mining in this area will not affect the rock fall <br />potential. <br />Signs stating "Watch for Falling Rock" will be posted in strategic places along more well- <br />traveled roads, such as the roads along Minnesota Creek, Dry Fork and Lick Creek at least one <br />month prior to longwall mining and remain in place until approximately 18 months after mining <br />and initial subsidence is complete in the area. This procedure would be similar to signs posted <br />along such major interstate highways as I-70 in the Glenwood Canyon area, where the rockfall <br />potential and risk to travelers is high to very high compared to very low to risk to travelers in the <br />South of Divide and Dry Fork Lease mining areas). <br />Importance of Baseline Landslide and Rockfall Data <br />The most significant landslide in the South of Divide mining area, in terms of proximity to man- <br />made structures, is located above the northern part of longwall panel E9 (Exhibit 60B, Map 1). <br />Although there is a large landslide within the area of mining influence of the southeast corner of <br />longwall panel E8 (mostly in the NEl/4 of Section 8), the landslides located north and south of <br />Minnesota Reservoir are the most important in the mining area. It is important to monitor the <br />existing, natural (baseline) conditions before mining begins in order to document their natural <br />state. The cracks, bulges, and depressions observed in the landslide areas north and south of <br />Minnesota Reservoir are much more extensive and dramatic than those caused by subsidence. <br />The July 2004 aerial photographs obtained by MCC provides good baseline images of the <br />natural, pre-mining features in the South of Divide mining area. <br />Observations made by Mr. Dunrud in the West Elk mining area indicate that mining may <br />accelerate the natural landslide process, where there are landslides that have already become <br />unstable. However, annual observations of the surface cracks and depressions in the landslide <br />area on Jumbo Mountain above mined 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 />Baseline information has been gathered in the eight areas with low to moderate rockfall potential <br />that are listed above prior to any mining activities. Evidence of naturally-occurring rockfalls-such <br />as remnant boy elders at the base of steep slopes, or in the run-out zones of these areas with a rockfall <br />potential -\vill be documented prior to mining. <br />Effects Of Subsidence And lVine-Induced Seismic Activiiv On Mall-Made Structures And <br />Reneivable Resources <br />Man-made structures and renewable resources in the South of Divide mining area basically consist <br />of 1) A dam and reservoir (Monument Dam - Minnesota Reservoir), 2) stock watering ponds, 3) <br />streams (primarily Dry Fork and the upper part of Lick Creek), 4) roads, and 5) local cabins. <br />. Minnesota Reservoir, the ponds, and the Deep Creek Ditch diversion to Dry Fork serve the dual <br />purpose of being both man-made structures and containment structures for the valuable water <br />2.05-149 Revised June 200.1 PRIO. Rev. Vm-ch 2006; Mqv 2006 PRIG, Yov. 2006TR107.Apri12007TR108:Sep. 2007 PRl2; Feb. 2008 PR-12