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Subsidence Evaluation For Exhibit 808 South of Divide Mining Area Page 18 • 9.1 Potentfal Impact of Water on Subsidence in Wet Mining Areas As discussed in Section 3.0, the moisture content of the caved and downwarped rocks controls the amount of subsidence that can be expected. In the South of Divide mining azea where water might be encountered in an azea equal to, or greater than, the width of the proposed longwail panels, maximum vertical displacement maybe expected to approach 0.8t. 10.0 POTENTIAL IMPACTS OF SUBSIDENCE AND MINE-INDUCED SEISMIC ACTIVITY ON LANDSLIDES AND ROCKFALLS 10.1 Landslides The landslides listed below are all naturally occurring features, which become less stable, or become unstable and slide, during periods of increased precipitation. A review of aerial photographs of the Apache Rocks, Box Canyon, and South of Divide mining areas, which were taken in 1963 and 2004, show that the slides listed below appeared to be more stable in 1963 than they aze now. Dunnxd observed that many of the existing landslides during periods of high precipitation were less stable, or became unstable and moved in the mid 1980s and mid 1990s. The landslides in the southeast side of West Flatiron and on the west side of Deep Creek in the • Apache Rocks mining azea showed no visual effects when longwall mining occurred beneath the azeas. It therefore seems appazent that wet seasons affect landslides more than does longwall mining. During very wet periods, however, landslides that aze already unstable may locally be triggered by mine subsidence. A total of twelve landslides, landslide areas, or landslide and rockfall azeas, have been mapped in the Apache Rocks, Box Canyon, and South of Divide mining azeas during field mapping with the U.S. Geological Survey (USGS) in the 1980s and also during the annual subsidence observations in these azeas (all the IandsIides listed in the Apache Rocks and Box Canyon mining azeas occur in Township 13 South, Range 90 West). 1. Apache Rocks mining azea a. Landslide located just north of Minnesota Reservoir in SW'/+ of Section 29. No mining has occurred in the azea. b. Landslide azea located above mined longwall panels 14 and 15 in NW'/a of Section 26. These landslides appeared to be unaffected by longwall mining beneath them. c. Landslide area located on the west side of Deep Creek, located above the southeastern part of miffed longwall panel 17 in the NWl/+ of Section 35. This landslide also appeazed to be unaffected by mining below when observed in July 2003. • 831-032.620 Wright Water Engineers, Inc.