2022-02-22_PERMIT FILE - C1980007 (5)

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West Elk Mine 2.04-39 Rev. 11/04- PR10, 04/06- PR10, 09/07- PR12, 10/08- PR14; 01/22- MR459 There are three large landslides that have occurred in the general area of West Elk Mine. These are Minnesota Reservoir, Jumbo Mountain and Highway Slides near Box Canyon. Each is discussed below: Minnesota Reservoir This relatively large landslide bordering Minnesota Reservoir was caused by a series of unique geologic and climatic conditions (Map 9). Those conditions include: 1. 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. 3. A relatively wet north-facing slope contributed water to the weakened area. Currently, one north flowing perennial stream crosses the slope area and a series of springs issue along the northern toe of the slide. During the spring of 1987, a large portion of the landslide slid into the Minnesota Creek drainage destroying the Dry Fork road access. Apparently, this also formed a mudflow or debris flow that went down the channel of the Dry Fork for some distance. Although the sli de is now marginally stable, it will ultimately move into and fill Minnesota Reservoir and could seriously impact the dam structure. It should be noted that this slide occurred prior to any mining and related activities in the permit area. A minimum buffer zone of 500 feet for development and 700 feet for longwall mining has been and will be maintained to prevent potential mining-related impacts to the slide and reservoir. Jumbo Mountain This very large, old landslide on Jumbo Mountain was thoroughly investigated by Dames and Moore (1993) (Exhibit 14). Dames and Moore’s research indicated that this large, 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 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 not adversely affect B-Seam mining or cause new, serious or irreparable harm to future land use of the area. A careful geomorphic review of the area indicates a very old landslide with episodic periods of renewed movement and dormancy. This landslide reactivated in the spring and summer of 1996. CDRMS and MCC personnel inspected the area at that time, with the landowner’s approval. Written comments by CDRMS provided an excellent description of the rejuvenation of a typical large landslide which had experienced numerous episodic periods of movement in historic and probably prehistoric time.