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Spring 2008 Subsidence and Geologic Field Observations <br />Box Canyon, Apache Rocks, and South of Divide Mining Areas <br />• <br />• <br />.7 <br />overburden depth to the B-seam ranges from 2,200 to 2,250 feet. No subsidence features were <br />observed along this route. <br />This traverse includes Location 10 (photographed from Photographic Observation Point 2) which <br />cannot be viewed along this route but is located topographically lower and to the north of the <br />drill pad for MDWs 22-05 and 22-06 (Map 1). <br />This traverse also includes two annual observation locations: 1) to view and document the upper <br />part of the rockfall/landslide areas on the east side of Box Canyon above Longwall Panels 19, 20 <br />and 21 (now established as Photographic Observation Point 3), and 2) to observe the headscarp <br />of an eastern side drainage in Sylvester Gulch (Location 11). <br />5.8.1 Location 10 <br />This is a rockfall/landslide area located above the rigid chain pillars (three-pillar entry system) <br />that separate Panels 18, 19, 20 and 21 (to the north) from Panels 22, 23, and 24 (to the south). <br />The rockfall/landslide is therefore located in an area of maximum tensile strain, both due to mine <br />geometry and topography. It is also in an area of high to very high natural rockfall potential <br />(Map 3). <br />With the exception of being more weathered in appearance, the rockfall/landslide area has not <br />changed appreciably since July 2005. Observations from other directions suggest that there has <br />been little change over the past several years. Other apparent changes appear to be the result of <br />seasonal differences (i.e., no leaves on the aspen trees, snow, etc.) as opposed to additional <br />rockfall/landslide occurrences. The spring 2008 image of this area (Figure 25) was obtained <br />from Photographic Observation Point 2 and provided under that section heading (Section 5.6.2). <br />5.8.2 Photographic Observation Point 3 <br />This observation point is located on the northern edge of the well site pad for MDWs 22-05 and <br />22-06. It was established to observe and document the new active rockfall/landslide area above <br />831-032.790 <br />August 2008 <br />Wright Water Engineers, Inc. <br />Page 38