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While many faults and folds locally modify the synclinal structure, no significant faults or folds have been identified in the permit area. The local stratigraphic sequence, in ascending order, is the Mancos Shale; the Mesaverde Group, which may be subdivided into the Iles and Williams Fork Formations; the Lewis Shale; and the Lance Formation, all of which are upper Cretaceous in age. Overlying the Lance Formation are the Tertiary Fort Union and Wasatch Formations. Quaternary alluvial deposits, generally derived from the Mesaverde Group, are locally present in stream valleys. Recent colluvial slides and slumps may also be present in canyons and gulches throughout the area. The Seneca II Mine extracts coal from the Middle Coal Group of the Williams Fork Formation, a member of the Mesaverde Group. The Williams Fork Formation, which conformably overlies the 1550 foot thick Iles Formation, is a 1100 to 2000 foot thick sequence of interbedded shales, sandstones, sandy shales and coal. The lower-most economically recoverable coal member of the Middle Coal Group is the Wolf Creek Coal, which averages 15 feet thick at the Seneca II Mine site. The underlying Trout Creek sandstone, considered to be a regional aquifer, is separated from the Wolf Creek Coal by about 70 feet of carbonaceous shale, sandstone, siltstone, and clean shale. Overlying the Wolf Creek Coal is about 150 feet (stratigraphically) of lenticular sandstone, siltstone, shale and thin coal seams. This interburden is overlain by the Wadge Coal, a 9 to 10 foot thick coal seam. The Wadge overburden is a moderately thick sequence of sandstone, siltstone and shale. About 50 feet above the Wadge Coal is the 2.5 to 5.5 foot thick Lennox Coal. This poor quality coal is recovered in the southern portion of the permit area. Overlying the Lennox Coal is a thin sandstone cap which is overlain by a thick shale unit. Mining at the Seneca II site began along the western limb of the Tow Creek anticline and has progressed toward the south, around the toe of the anticline. The coal seams generally strike to the south, while the dip varies from 6° to 9° to the west. The permittee conducted an extensive geochemical sampling program at the time of permit issuance. Areas where the sampling program indicated toxic conditions or acid-forming potential were mitigated by either avoidance or mixing of the overburden material when it was replaced by dragline and through final dozer grading. During the permit renewal process, the Division identified a number of parameters which were considered to have the potential to create toxicity problems upon reclamation of the mine site. In order to alleviate potential problems, Peabody Coal Company has committed to various mitigation techniques and analyses. Peabody Coal Company anticipates that sodic overburden may be encountered where the Lennox Coal seam is intercepted upon final Lennox highwall reduction (near core hole 2614E, Exhibit 6-1 ). Regraded spoil in this area will be -g-