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Fall 2007 Subsidence and Geologic Field Observations <br />Box Canyon, Apache Rocks, and South of Divide Mining Areas <br />• <br />• <br />Cracks caused by lateral spreading in the area were first observed by Dunrud in 2002. The <br />cracks, which began 50 to 75 feet south of crack number 4 (Figure 11 of this fall 2007 report) <br />were 150 feet long, as much as 3.5 inches wide, and trended southward along an old drill road. <br />The cracks were located in the approximate centerline of the ridge, where the West Flatiron ridge <br />narrows northward from about 2,000 feet wide to 200 feet wide in a lateral distance of about <br />2,500 feet. Large extension cracks were also observed on the cliffs at this time. <br />In addition, the following observations were made in the 2004 report based on the presence of <br />numerous cracks and the fact that no mining had occurred in the area. 1) the northward <br />convergence of West Flatiron may have caused increased lateral stresses, compared to other areas <br />on West Flatiron; 2) this lateral movement, as exhibited by the numerous cracks, may be the <br />initial stage of rockfall/landslide scarp development; and 3) the tension fractures on the road and <br />on the cliff outcrops in the area look like mining-induced features, but must be caused by <br />gravitationally-induced lateral movement towards the cliff faces on either side of the ridge. <br />The current cracks at Location 3, 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, maybe 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 were observed as <br />follows: <br />1) Crenulate, branching and diverging crack zone as much as 8 inches wide and an <br />estimated SO feet long that trends into the actively slabbing west cliff scarp (Figure 7). <br />831-032.780 <br />November 2007 <br />Wright Water Engineers, Inc. <br />Page 20 <br />