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Subsidence Evaluation For Exhibit 608 South of Divide Mining Ama Page 17 been caused in part by stresses generated by the West Elk Mountain intrusive bodies particulazly Mt. Gunnison The wnservative approach may be to assume that the drainage system is fiacture controlled. However, even if fractures control the present drainage system, they may not extend downward as continuous joints of fractures to the E Seam located several hundreds of feet below. Even if the fractures were present in the more brittle sandstone units, it would be very unlikely that these fractures would occur in the softer sdtstone and shale units- Even under the wnservative approach that the drainages in the South of Divide mining area are fiacture controlled, it is extremely unlikely that they extend downward to the E Seam through multiple shale, claystone, and siltstone units. Using this conservative evaluation, it is now important to evaluate the potential impact that subsidence may have on any pre-mining fractures. Evaluation of subsidence due to downwarping of laterally constrained strata shows, as stated previously, that rock strata with different deformation and strength characteristics deform as discrete units. For example, strata of shale and siltstone behave as units discrete from sandstone. Above the fractured zone (Section 42) and within the continuous deformation zone (Section 4.3) these units undergo continuous flexure (Figure 2, enlargement 2). Above the neutral surfaces, in zones of convex-upward curvature, the material is intension and below them, and the material is in compression. Consequently, stresses change across neutral surfaces from tension to compression across each successive rock unit that deforms as a plate. Fractures already present would thus tend to open more in the zones of tension, but would close more in the zones of wmpression, which would close these fractures more than they were prior to mining and subsidence. After longwall mining is completed in the area and static conditions are attained, the zones of tension and compression commonly cease, and any f'rectures present will likely resume the pre- mining condition. Therefore, the impacts on surface flow in the drainages of the South of Divide mining area are likely to be minimal or non-existent under even the most conservative assumptions. 9.0 WATER AND METHANE Observations of the north and west flanks of Mt. Gunnison during areal geologic mapping and an October 1996 field trip revealed numerous talus and rock glacier deposits that occur in the valleys and lower part of this intrusive body. Snowmelt and rain can easily infiltrate these deposits, which may eventually enter any permeable rocks, faults, fractures, and joints neaz the mountain. Coal beds and rocks in the deformed zone around Mt. Gunnison may also contain increased concentrations of methane where the coal is deformed and perhaps metamorphosed to a higher rank by the intrusive body. Greater quantities of water and methane may therefore be expected as coal is mined closer to MC. Gunnison. i 63f-032690 tNrightWaterErrgirreers, inc.