2018-09-04_PERMIT FILE - C1980007A (40)

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West Elk Mine resources in the area. Based on annual subsidence observations in the Jumbo Mountain, Apache Rocks, and Box Canyon mining areas during the last nine years, the following information is considered appropriate for the South of Divide mining area. Monument Dam -Minnesota Reservoir Monument Dam - Minnesota Reservoir, which provides storage water primarily for irrigation, is located between two landslides—one beginning at the north shore and the other beginning at the south shore. As explained above, landslide movement on Jumbo Mountain occurred during unusually wet periods before mining began, during mining, and after mining and subsidence was complete. The conclusions were that landslide movement occurs in response to ground saturation and is not noticeably affected by subsidence and seismic activity produced by longwall mining beneath, or near, landslide areas. Both the landslides on Jumbo Mountain and those north and south of Minnesota Reservoir occur in surficial material (loose rock, gravel, sand, silt, clay, and soil) and local bedrock outcrops. The author therefore expects that the mining of longwall panel E9 will not noticeably affect the large landslide south of Minnesota Reservoir. Mining of the nine longwall mining panels in the South of Divide mining area, as currently planned, will not affect Minnesota Reservoir. The reservoir is located outside the area of mining influence, using the most conservative 45 -degree angle of draw. Measured ground subsidence will not affect Monument Dam and Minnesota Reservoir, however, seismicity caused by longwall mining is possible and could affect the dam, reservoir and the landslide abutting the dam. Water Resources Stock Watering Ponds and U.S. Forest Service The stock watering ponds in the South of Divide mining area are located in debris flows or colluvium derived from the debris flows (Dunrud 1989). A total of 14 ponds have been mapped in the South of Divide mining area (for more information see Section 2.2 of Exhibit 71). Ten of these ponds are also classified as U.S. Forest Service water resources. The ponds in the permit area are photographed on the ground on an annual basis beginning in 2005. The debris flows consist of a heterogeneous mixture of clay derived from the Wasatch Formation and boulders and gravels derived primarily from the Mount Gunnison intrusive (granodiorites and quartz monzanites). Based on observations made during geologic mapping in the area, these debris flows are even less likely to be affected by longwall mining than the alluvium The debris flows have a very low permeability and, because the clay matrix is armored by the interstitial gravel and boulders, are resistant to erosion (the Deep Creek Ditch locally flows in this material at steep gradients). Based on the above-mentioned observations, no effects are expected when ponds in the South of Divide mining area are undermined. The clay -rich material that lines these ponds is expected to provide a seal against any subsidence effects. Stock watering ponds conditions will be surveyed before the ponds are within twice the angle of draw. A second survey will be conducted within three months after the ponds are no longer within the angle of draw. Stock ponds will be surveyed assuming climatic and ground conditions allow reasonable and safe access for such monitoring. 2.05-150 Rev. 06/05- PRIO, 03/06- PRIO, 05/06- PRIO, 11/060- 7RI07, 04/07- 7R108, 09/07- PR12, 02/08- PR12; 10/10- MR372