2010-12-17_REVISION - C1981019 (127)

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Site conditions DRAFT 41 The Williams Fork Formation consists of alternating beds of sandstone, sandy shale, mudstone and coal. Aquifers of regional extent do not occur within the Williams Fork Formation due to the discontinuous nature of its strata. A generalized stratigraphic column of the Williams Fork Formation in the vicinity of the Colowyo Mine is presented in Figure 2.1. Up to 22 individual coal seams have been documented in this sequence within in the area under consideration. Geologic structure around the proposed Collom pit is dominated by the Axial Basin Anticline which is asymmetrical and trends north 60 west. The south flank of the anticline has several secondary folds which trend sub - parallel and perpendicular to the main anticlinal axis. The Collom syncline is an asymmetrical secondary fold which strikes N 70 0 W. Bedding dips up to 20 degrees are measured on the north limb whereas dips range from 2 to 8 degrees on the southern limb where the proposed Collom Pit is to be located. Faulting in the area is not pervasive and there are very few mapped structures with vertical displacement. There are three major joint trends in the mine area. These are nearly vertical and strike N 70 °W, N 45 0 W and N 30 0 E. Jointing appears to be more pervasive in the sandstone units of the Williams Fork Formation than the other lithologic units. 2.4 Groundwater • Groundwater conditions on the Collom property are expected to be very similar to those on the existing Colowyo Mine. Generally, very little groundwater has been encountered by the existing operation. No aquifer of regional extent has been intercepted by the existing operation. Groundwater that has been encountered by the current operation occurred in perched lenticular sandstones. The upper -most regional aquifer that has been identified in the general area of the proposed activity is the Trout Creek sandstone (described above). A study conducted by Leonard Rice Consulting Water Engineers (LRCWE, 1979) documents this condition fully. Groundwater recharge areas appear to be located in the higher elevations to the south where sandstones and coal seams crop out. Flow proceeds down dip (northeastward) towards the axis of the syncline. Several small springs and seeps have been identified in the drainages of the property, however none of these represents a significant groundwater discharge area. The Trout Creek sandstone is considered the uppermost regional aquifer in the area. It is located some 400 to 450 ft below the bottom of the G coal seams. Preliminary estimates place the potentiometric surface of the Trout Creek at approximately 6,800 ft amsl in the vicinity of the Collom pit. Gradients are to the northeast. • 2572 -R1 Colowyo Coal Company, L.P. Water Management Consultants