2010-05-03_REPORT - C1980007 (9)

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Fall 2009 Subsidence and Geologic Field Observations Box Canyon, Apache Rocks, and South of Divide Mining Areas • 5.8.1 Location 7 This is a rockfall/landslide area located above the rigid three-pillar entry system that separates Panels 18, 19, 20 and 21 (to the north) from Panels 22, 23, and 24 (to the south). The rockfall/landslide is therefore located in an area of maximum tensile strain, both due to mine geometry and topography. It is also in an area of high to very high natural rockfall potential (Map 3). A July 2005 photograph of this location, as observed from Photographic Observation Point 2, can be found on page 16 of the July 2005 report (Figure 16). With the exception of being more weathered in appearance, the rockfall/landslide area has not changed appreciably since July 2005. Observations from multiple directions suggest that there has been little change over the past several years. The only changes appear to be the result of seasonal differences (i.e., no leaves on the aspen trees, snow, sun location, etc.). 5.8.2 Photographic Observation Point 3 This observation point is located on the northern edge of the well site pad for MDWs 22-05 and 22-06. It was established to make continued observations of the areas on the east side of Box Canyon above mined Longwall Panels 19 and 20, and to observe and document the new active rockfall/landslide area above the eastern part of mined Longwall Panel 21 (Location 4 of this report). Figure 27 shows the area over mined Longwall Panels 19 and 20 as observed in October 2009. A comparison to a photograph from the same location in June 2008 (Figure 28) shows little change other than seasonal vegetation. This area is considered to have a medium to very high rockfall potential as is typical for the steeper slopes and canyons around West Flatiron (Map 3). • 831-032.791 April 2010 Wright Water Engineers, Inc. Page 39