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West Elk Mine <br />0 <br />Subsidence Survey - 2.05.6(6) (b) (iii) (A) & (6) (e) <br />The following information documents subsidence processes that have been observed from studies above <br />longwall mining panels in the current West Elk Mine pennit area. The subsidence data obtained in the current <br />West Elk Mine area have been used to project subsidence processes, amounts, and effects into the Apache <br />Rocks, as well as Box Canyon in the B Seam, and South of Divide mining areas where only the E Seam coal is <br />to be mined. These data have been used to calibrate the subsidence prediction models described above. <br />In addition to relying on actual subsidence data, WWE and TetraTech have concluded that many of the findings <br />pertaining to subsidence and probable hydrologic consequences from previous pen-nit revisions apply to the <br />South of Divide with the Dry Fork Lease pen-nit revision and mining area. The basis for this conclusion is as <br />follows: <br />Comparison of lithologic data from boreholes in the Jumbo Mountain, Apache Rocks and Box Canyon <br />mining areas show consistency in the B Seam overburden materials, including those units immediately <br />above and below the E Seam coal. While direct correlation of lithologic units, excluding coal beds, is <br />generally difficult, comparison of lithologic logs shows very similar alternating sequences of shales, <br />claystones, and sandstones. Based on the stratigraphic and lithologic information obtained from drill holes in <br />the South of Divide mining area, the rocks consist of a greater proportion of shales, siltstones, and claystones <br />than are present in the Apache Rocks and Box Canyon mining areas. <br />• The South of Divide and Dry Fork permit revision area is topographically similar to the Apache Rocks and <br />Box Canyon mining areas although with a less extreme range of topographic relief. The elevation range <br />• across the South of Divide permit revision area is from about 7,000 feet to approximately 8,400 feet with <br />fewer abrupt elevation changes than those seen in the Apache Rocks and Box Canyon permit areas, such as <br />between the Sylvester Gulch drainages and West Flatiron. Like these two previously permitted areas, the <br />South of Divide permit revision area contains gentle as well as steep slopes making it susceptible to rockfalls <br />and landslides. <br />• Expected subsidence characteristics of the South of Divide permit revision area, based on lithology and <br />topography, do not vary significantly from previous evaluations for B Seam mining according to Mr. <br />Dunrud, with the obvious exception of the reduced overburden thicknesses associated with mining of the E <br />Seam. Overburden thickness impacts will be discussed later in this section. <br />Based upon these similarities, much of the information contained within the documents pertaining to the <br />Apache Rocks and Box Canyon permit revision area is applicable to the South of Divide permit revision <br />area. Where differences occur, discussions of the resulting effects have been provided. <br />Inventory of Structures and Renercable Resource Lands - 2.05.6 (6)(a)(i & ii) <br />hi order to ascertain the impacts that subsidence will cause on structures and renewable resource lands, an <br />inventory of these features v,,as conducted. Projected impacts to surface and gr?)LII-Id water resources are <br />presented later in Section 2.05.6(3). These water resources are shov,7n on Map 37. MCC's hydrologic <br />monitoring stations are shown on Maps 1 of Exhibit 71, 34, and 37. The many trails and U.S. Forest Service <br />roads utilized to access these sites are she v- or. Maus 67 and 68. <br />2.05-107 Revised June 2005PRIO. Rev. ATarch 2006; Rest Apri( 2006 PRIO; Alai, 2006 PRIO, lov. 2006 TRI07, Sep. 2007 PR-12; Feb. 2008PR-12