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2005 Subsidence and Geologic Field Observat(ons <br />Box Canyon, West Flatiron, Apache Rocks, <br />and South of Divide Mining Areas <br />mined beneath in 2004. Based on observations made in July 2005 of fresh-looking cracks in the <br />cliffs, more rockfall activity is predicted. The already very high natural rockfall activity was <br />likely accelerated by mining. Though the rockfall potential is very high, the risk to life and <br />property is low because the location is remote to human activities. <br />The landslides on the north and south sides of Minnesota Reservoir appear similar to their <br />appearance during the period 2001 through 2004. The slides are expected to be stable until <br />another unusually wet year occurs. The landslides on the north side of the reservoir are out of the <br />area of all planned coal-mining activities. The upper, less active landslide on the south side of <br />[he reservoir is not expected to be affected by the mining of longwall panel 9 in its current <br />projection during a yeaz of average precipitation for the following reasons: <br />1. The upper, more stable part, of the landslide is on a gentle slope (one of the most gentle <br />of all landslide slopes in the West Elk Mine area) that averages 20 degrees. <br />' 2. As the panel is mined northward beneath the upper part of the landslide, the tilt caused by <br />the moving longwall face will continually reduce the slope. <br />' 3. Longwall coal extraction is not planned within the area of mining influence of the more <br />' active part of the landslide (only the remaining pillars of the three-entry system north of <br />the extraction part of the panel are located within the area of mining influence of the <br />~ active part of the landslide}. <br />4. Over the last decade of annual observations, no mining effects were observed on the <br />landslides that were located on slopes steeper than this slide area in the Jumbo Mountain, <br />Apache Rocks, and Box Canyon mining areas. <br />Renewed landslide activity, however, may occur during times of unusually high precipitation, <br />such as occurred in the mid 1980s and mid 1990s. Should longwall pane] 9 be mined during a <br />period of unusually high precipitation, landslide activity would likely only be a function of <br />ground saturation rather than mining activity. <br />831-032.710 Wright Water Engineers, Inc. Page 3 <br />November 2005 <br />