2018-09-04_PERMIT FILE - C1980007A (44)

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West Elk Mine There aze three lazge landslides that have occurred in the general azea of West Elk Mine. These are Minnesota Reservoir, Jumbo Mountain and Highway Slides neaz Box Canyon. Each is discussed below: Minnesota Reservoir This relatively lazge landslide bordering Minnesota Reservoir was caused by a series of unique geologic and climatic conditions (Map 9). Those conditions include: Initial down cutting by the Dry Fork of Minnesota Creek exposing the D Coal Seam and a relatively weak series of overlying shales and sands in the area. 2. Ancient burning of the coal seam reduced the volume and caused considerable fracturing of the overburden. A relatively wet north-facing slope contributed water to the weakened area. Currently, one north flowing perennial stream crosses the slope azea and a series of springs issue along the northern toe of the slide. During the spring of 1987, a lazge portion of the landslide slid into the Minnesota Creek drainage destroying the Dry Fork road access. Appazently, this also formed a mudflow or debris flow that went down the channel of the Dry Fork for some distance. Although the slide is now mazginally stable, it will ultimately move into and fill Minnesota Reservoir and may well seriously impact the dam structure. It should be noted that this slide occurred prior to any mining and related activities in the proposed permit azea. A minimum buffer zone of 500 feet for development and 700 feet for longwall mining has been and will 6e maintained to prevent potential mining-related impacts to the slide and reservoir. Jumbo Mountain This very lazge, old landslide on Jumbo Mountain was thoroughly investigated by Dames and Moore (1993) (Exhibit 14). Dames and Moore's reseazch indicated that this lazge, deep-seated landslide on its northern-most edge cut down into the top of the B Seam (Map 12). Dames & Moore assured MCC that the B Seam could be mined safely with the proposed mining plan and that it would be highly unlikely that the underground mining would adversely impact the landslide. Although photo evaluation and field glass study of the area by John Rold in 1994 indicated the old slide to be more active than stated by Dames and Moore, all agree that reactivation of the slide would probably not adversely affect planned B-Seam mining or cause new, serious or irreparable harm to future land use of the azea. A cazeful geomorphic review of the azea indicates a very old landslide with episodic periods of renewed movement and dormancy. • 2.04-39 Revised November 1004 PRIG