2010-12-17_REVISION - C1981019 (153)

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Introduction 1. 3.3 Ecology The Collom study area contains four ecosystems: sagebrush /grassland, aspen woodland, mountain shrub, and riparian. The sagebrush /grassland and mountain shrub types cover more than 80 percent of the proposed mine area. The aspen woodland ecosystem is located south of the proposed mining area near the top of the Danforth Hills. Riparian ecosystems develop along creek bottoms and where drainage is poor. At lower elevations, the east - facing slopes of the ridges contain isolated cedar stands mixed with mountain shrub (VTN Colorado, 1976). 1.3.4 Geology The Collom study area is located north of the Danforth Hills on the south margin of the Axial Basin Anticline. The principal geologic units in the area include the upper Cretaceous Iles and Williams Fork Formations. Both are part of the Mesaverde Group. The Iles Formation consists of fine- to medium - grained, poorly sorted calcareous sandstone interbedded with sandy and silty carbonaceous shale. The uppermost unit of the Iles Formation is the Trout Creek Sandstone member, which is up to 75 ft thick and consists of white, fine - grained, well - sorted, massive sandstone. The Williams Fork Formation consists of alternating beds of sandstone, sandy shale, C mudstone, and coal. At the Collom site, the Williams Fork Formation contains 18 different coal groups (A through O, TC, X, and Y). Coal beds are separated by a combination of lenticular deposits of sandstone, siltstone, and mudstones. Geologic structure north of the Collom study area is dominated by the Collom Syncline, which is an asymmetric fold that strikes N 70 0 W. The bedding dips up to 40 degrees on the north limb of the syncline, whereas dips range from 2 to 8 degrees on the southern limb where the proposed Collom Mine is to be located. Faulting in the area is not pervasive and there are very few mapped structures with vertical displacement. There are two major joint trends in the mine area. These are nearly vertical and strike N 66 0 W and N 19 0 E. Jointing appears to be more pervasive in the sandstone units of the Williams Fork Formation than the other lithologic units. 1.3.5 Groundwater Groundwater conditions in the Collom study area are controlled by a combination of geology and topography. In the southern portion of the site, groundwater conditions are similar to those at the existing Colowyo Mine. Groundwater is present as perched zones in the coal seams and sandstone units. Within the pit of the existing coal mine, seeps are typically associated with perched water tables in the upper -most coal seams. These seeps normally drain within a few weeks, although sustained seeps recharged by upgradient drainages also occur, with a total discharge of approximately 15 -25 gallons per minute (gpm). In the northern portion of the proposed Collom Pit, the units are continuously saturated below a depth of approximately 300 ft below ground surface (ft bgs). 2572 -R2 Colowyo Coal Company Water Management Consultants