2010-12-17_REVISION - C1981019 (153)

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43 ip 5 GROUNDWATER 5.1 Regional conditions 5.9.9 Regional hydrogeologic units The proposed Collom Mine is located in a groundwater basin bounded in most areas by the outcrop of the Trout Creek Sandstone. The boundaries of the basin are the north limb of the Collom Syncline, the west edge of the Morgan Syncline, the crest of the Danforth Anticline to the south, and to the east (Figure 2.2). Elevations of the base of the Trout Creek Sandstone range from about 8,000 to 7,200 ft amsl on the south limb of the syncline, to approximately 6,500 ft on the north limb of the syncline in the valleys. The Trout Creek Sandstone yields moderate quantities of water to wells on a local basis (Utah International, 1982) and is generally considered the upper -most aquifer of regional C extent in the area. However, since the Trout Creek Sandstone outcrops around the periphery of the synclinal basin containing the Collom Mine, it is not in direct hydraulic connection with the Trout Creek Sandstone outside the Collom synclinal basin. The Williams Fork Formation, which overlies the Trout Creek Sandstone, includes a sequence of sandstone, siltstone, mudstone, and coal units approximately 1,000 ft thick. Groundwater is primarily stored and transported in the coal and sandstone units. The coal seams are relatively continuous over large areas. The sandstone units tend to be less continuous as a result of the depositional environment. Low - permeability siltstone and mudstone beds form the confining units of the groundwater system. The upper water - bearing units tend to be somewhat localized due to dissection by streams. The local stratigraphy and the proposed pit are shown on three detailed hydrogeological cross sections through the proposed Collom Mine located as shown on Figure 5.1. Figures 5.2 and 5.3 show the stratigraphy through proposed Phases I and II of the mine, respectively, parallel to dip. Figure 5.4 shows a northwest- southeast cross section through the initial box subparallel to the strike of the strata. The cross sections shown on Figures 5.2 through 5.4 also show the groundwater data from wells and piezometers completed as part of this investigation. The stratigraphy shown in the cross sections was derived from the exploration borings and was provided by KEC from the detailed geological model. .A conceptual north -south cross section showing water levels b-the principal water - bearing sequences is presented in Figure 5.5. The profile of the proposed Collom Mine pit is also shown on Figure 5.5. 2572 -R2 Colowyo Coal Company Water Management Consultants