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2006 Subsidence and Geologic Field Observations <br />Box Canyon, West Flatiron, Apache Rocks, and South of Divide Mining Areas <br />influence. Crack duration, in areas of permanent tension-such as above solid coal boundaries <br />or rigid chain pillazs, is summarized (from eazlier annual observation reports) as follows: <br />1. Cracks in colluvium commonly heal and re-vegetate in about one to three years. <br />2. Cracks in soft, friable bedrock, such as the soft sandstone above mined longwall panel 13 <br />(Apache Rocks Mining azea), are no longer visible in roughly three to six years. <br />3. Cracks in hard, durable bedrock, such as the sandstone outcrop at Apache Rocks, will <br />likely be visible for many decades. <br />No mining effects on rockfalls or landslides were observed in the Apache Rocks mining area. <br />However, fresh-looking cracks and scarps have been recently observed, suggesting that local, <br />sporadic falls and slides continue in the rockfall/landslide area near the head scarp of the first <br />east drainage of Sylvester Gulch. Rockfalls and landslides in this area located above mined <br />longwall panel 22, are categorized as having a very high rockfall potential. Rockfall and <br />landslide activity was notably accelerated during the mining of longwall pane122. <br />Field observations, and a review of aerial photographs, indicate the excavation azea for the Deer <br />Creek ventilation shaft and escapeway for the South of Divide mining area is at least partially <br />constructed in the lower part (toe area) of a landslide slump block (Maps 1 and 2). Lateral <br />support of the slump block in the western part of the excavation area has subsequently been <br />reduced. Although the landslide appears to have been stable over the last 43 years, based on the <br />U.S. Geological Survey (USGS) aerial photos dated 1963, continued stability will likely depend <br />on adequate dewatering of the landslide material in the excavation azea. <br />It is the author's opinion that annual field observations are adequate to evaluate the effects of <br />longwall mining in the West Elk Mine area. This opinion is based on the following: <br />1. The duration of subsidence effects is considerably longer than one yeaz. <br />831-032.750 Wright Water Engineers, Inc. Page 2 <br />December 2006 <br />