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Fall 2009 Subsidence and Geologic Field Observations <br />Box Canyon, Apache Rocks, and South of Divide Mining Areas <br />Because of the roadway location relative to the source area of the October 2008 rockfall, WWE <br />has chosen not to make a close inspection of the site. However, photographs have been taken <br />from along the Sylvester Gulch road for comparison to images taken during our original <br />observation of the rockfall during the fall 2008 field visit. These photographs and comparisons <br />are discussed below. <br />5.1.1 Location 1 <br />Location 1 is the rockfall/landslide area (first observed during the fall 2008 field visit) located <br />over mined Longwall Panel 25 above cross cut 12. The B-seam overburden thickness at this <br />location is about 650 feet. This is one of two locations along the east side of Sylvester Gulch <br />previously identified as a high rockfall hazard area due to the presence of over-steepened slopes <br />and exposed sandstone ledges. <br />The source area for the rockfall is approximately 100 feet above the upper drill road (Figure 5). <br />Although difficult to assess without direct observation and measurements, it appears that the <br />failure area is about 100 feet in lateral extent and approximately 200 feet from top of outcrop <br />failure area to the bottom of the landslide. Much of the failed sandstone ledge above the road <br />was originally retained (or captured) by the drill road. These sandstone blocks have now been <br />moved to below the road cut as a result of clearing the road. Observations made while driving <br />through this area indicate that our original estimate of approximately 15 feet by 20 feet in <br />maximum dimension for the largest sandstone blocks is accurate. <br />Several photographs were taken of the rockfall/landslide area from the Sylvester Gulch Road for <br />comparison to photographs taken during the fall 2008 field visit. Figure 5 shows the slide <br />looking east/southeast from the Sylvester Gulch Road as it appeared in October 2008. Figure 6 is <br />the slide as it appeared during our visit in October 2009. It is apparent from this comparison that <br />the clearing of the road pushed additional slide material (including several large boulders) below <br />the road cut. Close comparison of the sandstone ledge reveals that additional rockfalls occurred <br />between the two observations. <br />831-032.791 Wright Water Engineers, Inc. Page 18 <br />April 2010