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CTL\Thompson has performed augering web thickness design analyses to determine appropriate web sizing between auger holes to prevent web failures. These analyses focus on the prevention of web failure and subsidence adjacent to the high wall. Failure of the ground immediately adjacent to the high wall will subject the auger mining personnel and equipment to undue risk from rock fall and landslides. Because of the proposed 300 to 500 foot auger length, the Division is concerned that misalignment or deflection of the auger bores could result in deviation from design web thickness. Subsidence triggered by auger bores coalescing at depth from the high wall might result in subsidence of the reclaimed West Pit Excess Overburden Pile. Colowyo Coal suggests that visual inspection should suffice to determine whether surficial impacts requiring mitigation have occurred. The Division believes that a few monuments should be installed to verify whether the webs have remained stable. Colowyo should install a few monuments in a representative area to be angered at the beginning of the project. For documentation purposes, a map indicating the proposed location and a description of monument construction needs to be submitted. Slope Stability of the West Pit Fill Colowyo states; "Groundwater in the pit or from within the auger holes will not pose a problem as the Colowyo pit is essentially dry... No special plugging of the auger holes will be necessary." Areas immediately adjacent to the West Pit Fill have experienced slope stability problems. Field investigations and modeling have suggested that the problems are related to ground water, possibly seeping from the in-Pit pond within the West Pit, through the undisturbed rock of the outcrop barrier and into the slope adjacent to the 'toe of the West Pit Fill. Damp spots have also occurred in adjacent portions of the West Pit Fill. Because of the local dip of the bedrock section, the X-Seam level bench dips approximately 5 degrees into the low wall of the pit. Prior to the backfilling of the X-Seam bench, precipitation waters could flow from the bench into the open auger holes. Following backfilling of the X-Seam bench, auger holes could receive flow of waters which infiltrate the backfilled and reclaimed spoil and migrate vertically to the bench surface. In completing its original evaluation of the West Pit Fill CTL\Thompson stated; "An existing landslide was observed on the slope west of the spoil disposal site, adjacent to Taylor Creek. We believe precautions should be taken during backfilling of the pit upslope of Taylor Creek to limit risk of water from the pit "charging" the existing slope. We recommend placing a layer of claystone/shale fill on each bench where coal is exposed to 'seal' the coal layer and direct free water to the south." With the occurrence of the slope stability problems near the toe of the West Pit Fill, this unheeded statement has proven to be appropriate. Colowyo Coal should address the apparent incongruity of the above statements. It appears that the infiltration of waters into the undisturbed country rock adjacent to the West Pit low wall may have exacerbated a preexisting slope stability problem. If so, the presence of the auger holes may increase infiltration and worsen the problem. The Division believes that Colowyo should implement its consultant's original mitigative suggestion,'by sloping benches