PERMFILE128862 - Laserfiche WebLink

Home Browse Search

~OOMPIHyn'COAL C AI11 LLC. A Subsidiary of Arch Western Resources, LLC West Elk Mine P O Box 591 5174 Highway 133 Somerset, CO 81434 (970)929-5015 Faz (970) 929-5595 MCC Response: Please refer to Sections 5.2 and 11.3 (Streams and Ditches, particularly paragraphs 2 and 3). Based on periodic observations in the West Elk longwall mining area and the U. S. Steel room-and-pillar mine extraction area beneath Bear Creek, no cracks are expected in the South of Divide mining area for the following reasons: 1) No cracks, or effects on stream flow, were observed in the stream alluvium that is located 220 to 300 feet above groom-and~il[ar extraction area. The minimum overburden thickness above the western end of projected longwall mining panels rs 375 to 400 feet-50 to 180 feet greater than in the Bear Creek area. 2) As explained Section 3.0 (Geologic Factors Influencing Subsidence), Item 3, and the 4th from last paragraph of Section 5.2, the first 200 to 300 feet of rocks above the E Seam contain more siltstone, shale, clay stones, lenticular sandstones, and coal seams than do the rocks (of similar vertical distance) above the B Seam. The height ojthe fracture zone, and consequently the vertical fracture distance above the E Seam, is therefore expected to be less than the vertical fracture distance in the stronger, more brittle rocks above the B Seam. • 3) However, a greater potential exists for subsidence to impact streams in the South of Divide mining area than in the Apache Rocks and Box Canyon mining areas. This isprimarily because: a) the overburden depth is less than in the Apache Rocks and Box Canyon mining areas, particularly in the northwestern part of the area, and b) the coal extraction thickness is projected to be greater for the E Seam than was mined in the B Seam (14 feet versus 12 feet). Although no subsidence cracks are expected to affect streamflow in the South of Divide mining area, based on prior observations in the West Elk and Somerset Mine areas, it is recommended that detailed subsidence and surface Jlow measurements be done in order to verify this concept The measurements should be conducted particularly in the northwestern part of the mine area where coal extraction thickness is projected to be a maximum of 14 feet and overburden depth ranges from 375 to 400 feet (Note: this statement will be added as the first paragraph of Section 11.3). ~`~`~95. Response accepted. 1~~ 96. Original Comment: Exhibit SSA states "Monitoring of any channel morphology and geometry changes V' will allow for site-specific prescriptive mitigation as deemed necessary" What are these prescriptive mitigation measures? MCC Response: This relates to comments 56 and 89. MCC has established study transects in the SOD drainages and proposed mitigation measures and monitoring. New Comment: The original question remains. (What aze the prescriptive mitigation measures for site-specific stream channel morphology and geometry changes?") n U 12