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Spring 2008 Subsidence and Geologic Field Observations <br />Box Canyon, Apache Rocks, and South of Divide Mining Areas <br />• The cracks now transect the entire ridge. Initial cracks observed in spring 2007 at this location <br />were most likely caused by lateral spreading due to gravitational forces. <br />Cracks caused by lateral spreading in the area were first observed by Dunrud in 2002. The <br />cracks, which began near the south edge of the MDW pad area were 150 feet long, as much as <br />3.5 inches wide, and trended southward along an old drill road. The cracks were located in the <br />approximate centerline of the ridge, where the West Flatiron ridge narrows northward from about <br />2,000 feet wide to 200 feet wide in a lateral distance of about 2,500 feet. Large extension cracks <br />were also observed on the cliffs at this time. <br />In addition, the following observations were made by Richard Dunrud in the 2004 report based <br />on the presence of numerous cracks and the fact that no mining had occurred in the area: 1) the <br />northward convergence of West Flatiron may have caused increased lateral stresses, compared to <br />other areas on West Flatiron; 2) this lateral movement, as exhibited by the numerous cracks, may <br />be the initial stage of rockfall/landslide scarp development; and 3) the tension fractures on the <br />road and on the cliff outcrops in the area look like mining-induced features, but must be caused <br />by gravitationally-induced lateral movement towards the cliff faces on either side of the ridge. <br />The current cracks at Location 5, which greatly increased in size and number when longwall <br />mining occurred beneath the area, are individually as much as 12 inches wide and generally trend <br />N30-40°E in an en echelon, or stair-stepping, pattern northward from west to east. The depth of <br />some of these cracks, prior to sloughing, may be as deep as the massive sandstone cliff, which is <br />estimated to be about 50 feet. The two cracks on the western side of the crack area locally are <br />offset downward to the west, suggesting a downward movement along fractures in the massive <br />sandstone of the Ohio Creek Member of the Mesaverde Formation that underlies the methane <br />drainage well site. <br />Beginning near the actively slabbing west cliff edge and moving eastward to the east cliff edge, a <br />map distance of approximately 200 feet, five individual cracks or crack zones have been <br />observed and previously described in the fall 2007 report. Observations from the spring 2008 <br />field visit are as follows: <br />• 831-032.790 Wright Water Engineers, Inc. Page 25 <br />August 2008