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West Elk Mine <br />Based on a stereographic review of July 2004 vertical aerial photographs, renewed activity <br />occurred locally in western part of the landslide aeeas north and south of Dry Fork during wet <br />periods in the 1980s (1984 to 1987) and the mid 1990s (1994 to 1996). The Dry Fork road was <br />taken out one half-mile west of the Minnesota Reservoir dam by this renewed movement in 1987 <br />(Map 1 of Exhibit 60). <br />Landslide located neaz the north shore of Minnesota Reservoir in the SWY. of Sec 29. This slide <br />is located on the border between the Apache Rocks and South of Divide mining aeeas. <br />Landslide area located on the Dry Fork road in the approximate center of Sec 31, T 13 S, R 90 <br />W. Two small landslides aze located to the southeast in the SE'/, of Sec 31 and the S W'/. of Sec <br />32. <br />Landslide located near the southwest corner of un-mined longwall panel 8 in the N%z of Sec 8 <br />and the S%z of Sec 5, T 14 S, R 90 W. <br />Some of the most important information regazding mine subsidence and mine-induced seismicity <br />was obtained from observations of active landslides on Jumbo Mountain above longwall panels 8 <br />and 9, which were mined during the mid 1990s. Landslide movement occurred during unusually <br />wet periods before mining, during mining, and after mining and subsidence was complete. The <br />landslides located north and south of Minnesota Reservoir are similaz to those on Jumbo Mountain. <br />Both occur in surficial material (rocks, gravel, sand, silt, clay, and soil) and local outcrops of <br />bedrock that have slumped and flowed downhill during periods of increased saturation. Cracks, <br />bulges, and depressions or troughs, and springs were locally observed in both landslide areas. <br />It is important to note that no earth tremors (seismic activity) were felt by Mr. Dunrud in all the <br />annual traverses and observations made above the longwall mining areas in the Jumbo Mountain, <br />Apache Rocks, and Box Canyon mining areas during the last 9 yeazs (1996 through 2004). For <br />example, no tremors were felt during the annual traverse above longwall panel 13 in 1999, when <br />the mining face was located directly beneath one of the subsidence observation points. This <br />point was located approximately 1,200 feet vertically above the active mining face, and 2,800 <br />feet north of Minnesota Reservoir. <br />In contrast to room-and-pillar mining, longwall mining is a uniform extraction procedure that <br />basically involves 1) the uniform cutting of a coal face, 2) the caving of the roof behind the <br />moving coal face, and 3) the recompression of the caved material behind the support system. <br />This system therefore causes only a minimum amount of very low magnitude seismic activity <br />(below the threshold of feeling at the ground surface), particulazly where the overburden depth to <br />the coal being mined is less than about 1,500 feet. <br />Based on field observations during the past nine yeazs (1996 through 2004), the major fmding is <br />that landslide movement occurs in response to moisture and ground saturation, and is not <br />noticeably affected by subsidence or any mine-related seismic activity caused by longwall <br />mining beneath or neaz the landslides. <br />Records of seismic events in the immediate azea of the West Elk Mine provided by the NEIC <br />i indicate that since 1983, the lazgest event registered 3.60 on the Richter scale and occurred on <br />1.05-l3! Revised November 2004 PRIG <br />