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Subsidence Evaluation for the <br />Exhibit 60E Southern Panels, Apache Rocks West, & Sunset Trail Mining Areas Page 43 <br /> <br />831-032.923 Wright Water Engineers, Inc. <br />December 2021 <br />4. The South Prong channel in the Sunset Trail mining area overlays panel SS4, where the <br />overburden is projected to be roughly 300 feet at the western end of the panel. The potential <br />for hydraulic connection between a surface crack and fractures from the mine are negligible <br />when overburden is 300 feet or more. If actual conditions show the overburden to be less <br />than 300 feet, then the mining height should be reduced to continue to minimize the risk of <br />a hydraulic connection forming. <br />5. Mining impacts on rockfalls were not observed during annual subsidence observations in <br />the Apache Rocks and Box Canyon mining areas over six years (1999 to 2004 inclusive), <br />in areas where the estimated rockfall potential was moderate to high. The highest estimated <br />rockfall potential is classified as moderate to high in the Southern Panels mining area, and <br />many of these are located in areas where no mining is currently planned. Consequently, <br />the natural rockfall process is not expected to be significantly accelerated by longwall <br />mining. <br />6. The landslides that are located north and south of Minnesota Reservoir and above the <br />northern part of E-seam longwall Panels E16 and E17, are not expected to be noticeably <br />impacted by subsidence or seismic activity caused by longwall mining. Based on field <br />observations, the major finding is that landslide movement occurs in response to moisture <br />and ground saturation and is not noticeably affected by subsidence or any mine-related <br />seismic activity caused by longwall mining beneath or near the landslides. <br />7. There is no historical record from annual observations in the West Elk Mine area regarding <br />effects of mining on springs and local water-bearing zones, with sources in either surficial <br />material or bedrock. These observations are documented in the Annual Hydrology <br />Reports. <br />8. Small cracks have occurred on the hard, compacted access roads following longwall <br />mining. However, these cracks have never affected use of the roads. <br />