Laserfiche WebLink
Spring 2009 Subsidence and Geologic Field Observations <br />Box Canyon, Apache Rocks, and South of Divide Mining Areas <br />• and spring 2009 field visits found there to be virtually no evidence of these cracks due to the re- <br />grading and reclamation of the drill pad (Figures 15). Close observation of Figure 15 reveals that <br />many of the pine trees on the periphery of the pad are dead or dying which suggests that there has <br />been some disruption of the supporting root zone. <br />Previously observed and studied cracks at this location were at one of the two narrowest portions <br />• of the West Flatiron ridge where the overburden depth to the B -seam is about 2,150 feet. In June <br />2008, the cracks had transeeted the entire ridge with the most obvious representation of their <br />presence being the rockfall /landslide originating in the thick, massive sandstone outcrop on the <br />west side of West Flatiron located immediately west of the MD W drill pad. <br />Cracks caused by lateral spreading in the area were first observed by Dunrud in 2002, before <br />mining had occurred beneath the site. The cracks, which began near the south edge of the MDW <br />pad area were 150 feet long, as much as 3.5 inches wide, and trended southward along an old <br />drill road. The cracks were located in the approximate centerline of the ridge, where the West <br />Flatiron ridge narrows northward from about 2,000 feet wide to 200 feet wide in a lateral <br />distance of about 2,500 feet. Large extension cracks were also observed on the west - facing cliffs <br />at this time. In 2004, Durand reported that the tension fractures on the road and on the cliff <br />outcrops in the area looked like mining - induced features, but must have been caused by <br />gravitationally - induced lateral movement towards the cliff faces on either side of the ridge <br />because no mining had occurred in the area. <br />831- 032.791 Wright Water Engineers, Inc. Page 28 <br />November 2009 <br />rigure 15. Spring 2009 panorama from south to nosh of the drill pad for MDWs 21 -32, 21 -36, and 21 -38, <br />located above mined Longwall Panel 21. This reclaimed pad shows no evidence of the MDWs or the five <br />crack zones (except as shown in Figures 16 -18) previously observed at this location. <br />