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Spring 2009 Subsidence and Geologic Field Observations <br />Box Canyon, Apache Rocks, and South of Divide Mining Areas <br />C <br />• <br />the Sylvester Gulch road for comparison to images taken during our fall 2008 field visit. These <br />photographs and comparisons are discussed below. <br />No cracks were noted in the road along this traverse even though the latter half is mostly over the <br />central portion of mined Longwall Panels 19, 20 and 21. Because of our access to the entire <br />traverse, WWE was able to visit Photographic Observation Point 8. <br />5.1.1 Location 1 <br />Location 1 is the fall 2008 rockfall /landslide area located over mined Longwall Panel 25 above <br />cross cut 12. The B -seam overburden thickness at this location is about 650 feet. This is one of <br />two locations along the east side of Sylvester Gulch previously identified as a high rockfall <br />hazard area due to the presence of over - steepened slopes 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 laterally 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 May 2009. It is apparent from this comparison that the <br />clearing of the road pushed additional slide material (including several large bounders) below the <br />road cut. Close comparison of the sandstone ledge reveals that additional rockfalls occurred <br />between the two observations. <br />831- 032.791 <br />November 2009 <br />Wright Water Engineers, Inc. <br />Page 18 <br />