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Fall 2008 Subsidence and Geologic Field Observations <br />Box Canyon, Apache Rocks, and South of Divide Mining Areas <br />much as 5 inches wide, are located in the tension zone above the southern edge of gate road <br />pillars between mined Longwall Panels 12 and 13 in the B-seam. The area is therefore in a <br />double extension zone produced by the mining of Panels 12 and 13. <br />The cracks trend primarily N65-75°E, but locally diverge to N40°E, N80°E, and E-W. The <br />overburden depth to the B-seam is about 1,350 feet. More cracks were observed soon after <br />mining than are now present. Some of the smaller cracks in the northernmost part of the initial <br />crack area have closed, or healed and sealed, a year or two after they formed. There currently are <br />essentially five individual cracks or crack zones over a lateral distance of approximately 280 feet. <br />From north to south, the maximum widths of the individual cracks or crack zones, the centers of <br />which average 70 feet apart, are as follows: <br />Crack 1 zone. <br />Crack 2 zone. <br />Crack 3 zone. <br />Crack 4 zone. <br />Crack 5 zone. <br />1.5 inches (Figure 38) <br />2.5 inches (Figure 39) <br />4.0 inches (total width of several branching cracks) (Figure 40) <br />5.0 inches (two cracks with widths of 3.0 and 2.0 inches) (Figure 41) <br />3.0 inches (Figure 42) <br />831-032.790 <br />December 2008 <br />Wright Water Engineers, Inc. <br />Page 53