2008-01-16_APPLICATION CORRESPONDENCE - C2008086 (3)

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DRAFT 4.1 Structure The strike and dip of the bedding, the orientation of known faults, the direction of lineaments, the strike and dip of the bedding cross joints and the spacing and direction of the coal cleats (bedding cross joints in the coal seam) are important factors to consider in the design of longwall mining panels. Bedrock in the Proposed Coal Lease area for the Red Cliff Mine dips northeastward at approximately 3 degrees. The relatively flat dip is not expected to noticeably affect the angle of draw from that of flat-lying beds, based on NCB information (NCB, 1975). The relatively flat dip should not affect the panel orientation. The lineaments in the lease area are the deeply incised canyons indicated on Table 3. Slope Geometries Within Project Area. The perennial stream in Big Salt Wash canyon and the intermittent streams in the side canyons do not follow the normal dendritic (leaf-like) drainage pattern. The drainage pattern, shown on Figure 1. Red ClifiF Mine Project and Coal Lease Areas, roughly follows the orthogonal (right angle) trellis drainage pattern, also shown on the Garvey Canyon Quadrangle topographic map. The dominant Project Area linear feature is Big Salt Wash which enters the Coal Lease Application area bearing approximately N 22° E and continues for about 12,400 feet where it rotates further easterly, bearing approximately N 31 ° E for about 6,900 feet, then at N 45° E for 6,100 feet, then exits the Coal Lease Application area after bearing N 54° E for 3,600 feet. From the eastern boundary of the Coal Lease Application area to the eastern boundary of the Project Area, Big Salt Wash bears approximately N 69° E for 4,100 feet. The sub-parallel valley lineaments also follow the same directional rotation, from northeast on the west side of the proposed Lease Area, to a much more easterly direction on the east side of the Project Area. The secondary lineaments, that are side canyons entering Big Salt Wash from the northwest, bear northwest on the west side (lower Buniger Canyon bears roughly N 57° W) and bear more northerly from west to east across the lease area. The easternmost side canyon on the northwest side of Big Salt Wash, Lapham Canyon, bears approximately N 8° W. The less consistent secondary lineaments represented by side canyons entering Big Salt Wash from the southeast starting with Garvey Canyon that bears about S 82° E, past Hatchet Canyon that bears about S 65° E, to the last unnamed southeast side canyon before the Project Area eastern boundary which bears approximately S 57° E. The southeast side canyons seemingly bear less easterly and more southerly toward the east side of the Project Area. 4.2 Lithologic Factors Affecting Subsidence Different lithologies (rock types) have differing strengths and therefore differing swell potential when broken. As indicated on Table 4. Bank Density, Swell Factor and Percent Free Swell for Selected Rocks and Soils, there is considerable variation in the percent swell between rock types and within rock types. The height of caving above the mine workings is reduced where the roof rocks consist of strong (high percent swell) sandstones compared to weak (low percent swell) shales, mudstones or soft siltstones. However, the height of rock fracturing above mined openings is greater for strong, brittle sandstones compared to weak, more yietdable shales, mudstones and soft siltstones. The mean percent swell of the overburden rocks controls the potential maximum height of the collapse zone upward in the immediate roof above a longwall panel, an entry or an intersection between an entry and a crosscut. Figure 10. Potential Collapse Heights Above Different Mine Opening Geometries by Piggott and Eynon (1977) provides a percent swell based method for predicting the maximum collapse Page 14 of 57