2008-04-25_PERMIT FILE - M2008010

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Letter: Response to adequacy review, Permit Application M-2008-010 4/2512008 page 11 i. The three ponds on the Neva Property, located near the northeast corner of the permit area, are partially incised and partially retained by dams of up to 8 feet crest height, constructed on the surface of the Mancos shale. The dams, were clearly constructed using alluvium from above the Mancos shale, and used some excavated shale as a core and/or liner. (The shale also allowed the ponds to be deeper, and larger capacity as originally built.) There are no known geologic structures within the alluvium above the Mancos shale which could be damaged by the mining as proposed, or which would create planes for potential failure of a cutbank. These ponds have silted in to a large degree, and are approximately seven feet in depth. They are NOT on the state's dam safety inventory. ii. As proposed in Exhibit D, along this portion of the perimeter the limits of excavation would approximate the final reclaimed slope rather than creating a 20- or 30-foot highwall to be backfilled. However, excavation will not extend into the Mancos shale, and data on the exact contact between the Mancos shale and the surface alluvium is not plentiful, but indicates that the depth to the shale may be significantly less than the 30-foot depth of mining proposed. iii. The lowest earthen dam is located, as shown in Cross- Section C-C', Figure E-4-1, page 24, 100 feet from the top of the final reclaimed slope at the nearest point, and 200 feet from the toe of that slope. The final reclaimed slope at this point is 3.3:1. iv. The middle earthen "dam" separating the two lower ponds is located approximately 100 feet from the top of the final reclaimed slope, which is actually at or above the elevation of the crest of the "dam." The toe of the final reclaimed slope is approximately 250 feet from the dam. The final reclaimed slope at this location is 4:1, 30 feet in 120 feet. v. The upper earthen dam holding the uppermost pond is located approximately 50 feet from the top of the final reclaimed slope, but that top is slightly higher than the elevation of the crest of the dam. The toe of the final reclaimed slope (still 4:1 at this point) is approximately 170 feet from the dam. vi. Based on the above information, there is no indication that mining as proposed would have any potential to damage these structures. There is no blasting proposed for either mining or reclamation. Therefore, there is no need for analysis by the Applicant to demonstrate that off-site areas will not be adversely affected by