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Spring 2009 Subsidence and Geologic Field Observations <br />Box Canyon, Apache Rocks, and South of Divide Mining Areas <br />• <br />n <br />LJ <br />5.4.1 Location 2 <br />A previously- observed subsidence crack identified at this location is primarily in an exposed <br />sandstone outcrop above the roadcut (Figure 11). The crack (also previously observed in the soil <br />and colluvium over the sandstone outcrop) trends roughly parallel to the long direction of mined <br />Longwall Panel 14 near the headgate entries. Since its first observation in 2004, the exposed <br />crack in the sandstone bedrock has healed substantially to the point that any previous width on <br />the crack (as much as I inch in width at the top of the outcrop) has been filled with sediment <br />washed in from above (Figure 12). However, erosion has widened and scoured the original crack <br />in the overlying soil and colluviums (top of photograph). <br />Figure 11. Westward view of a subsidence <br />crack located on the uphill side of the main drill <br />road to West Flatiron taken in Summer 2005. <br />Note that the crack width decreased downward <br />from the 4 to fi inched in the soil and colluviums <br />above the bedrock a closed fracture at the base <br />of the sandstone outcrop. <br />Figure 12. Spring 2009 photograph of the <br />same subsidence crack. Complete filling of the <br />central crack along the sandstone face can be <br />discemed from comparing this image with <br />Figure 11, <br />831- 032.791 Wnght Water Engineers, Inc. Page 24 <br />November 2009 <br />