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Site conditions DRAFT 3 <br />The Williams Fork Formation consists of alternating beds of sandstone, sandy shale, <br />mudstone, and coal. Aquifers of regional extent do not occur within the Williams Fork <br />Formation due to the discontinuous nature of its strata. A generalized stratigraphic <br />column of the Williams Fork Formation in the vicinity of the Colowyo Mine is presented <br />in Figure 2.1. Up to 22 individual coal seams have been documented in this sequence <br />within in the area under consideration. <br />Geologic structure around the proposed Collom Pit is dominated by the Collom syncline <br />which is an asymmetrical fold that strikes N 70°W. The bedding dips up to 20 degrees <br />5 ~ ~ on the north limb of the syncline whereas dips range from 2 to 8 degrees on the <br />southern limb where the proposed Collom Pit is to be located. <br />Faulting in the area is not pervasive and there are very few mapped structures with <br />vertical displacement. There are three major joint trends in the mine area. These are <br />nearly vertical and strike N 70°W, N 45°W, and N 30°E. <br />2.4 Groundwater <br />Groundwater conditions on the Collom property are expected to be very similar to those <br />within the existing Colowyo Mine. Very little groundwater has been encountered by the <br />existing operation. No aquifer of regional extent has been intercepted by the existing <br />operation. Groundwater that has been encountered by the current operation occurred in <br />perched lenticular sandstones. A study conducted by Leonard Rice Consulting Water <br />Engineers (LRCWE, 1979) found in the Colowyo permit, Volume 26, Exhibit 7, <br />documents this condition fully. <br />Groundwater recharge areas appear to be located in the higher elevations to the south <br />where sandstones and coal seams crop out. Flow proceeds down dip (northeastward) <br />towards the axis of the syncline. Several small springs and seeps have been identified <br />in the drainages of the property; however, none of these represents a significant <br />groundwater discharge area. <br />ask'1 The Trout Creek sandstone is considered the uppermost regional aquifer in the area. It is <br />I~ located some 400 to 450 ft below the bottom of the G coal seams. Preliminary estimates <br />~lh place the potentiometric surface of the Trout Creek at approximately 6,800 ft amsl in the <br />vicinity of the Collom Pit. Gradients are to the northeast. <br />Preliminary drilling suggests that the Fa° and G coal sequences may produce water <br />where they are saturated. These two sequences are currently thought to be <br />hydraulically connected by jointing and cleating. Estimates of potentiometric surface <br />elevations for the Fa° coal place it about 200 ft above the Trout Creek potentiometric <br />surface. A downward vertical gradient of 35% or higher indicates very little potential for <br />hydraulic communications. <br />The F and G coal seams and sandstone beds that occur above the G coal seams have <br />been initially identified as the most likely units that will produce water during mining. <br />Therefore, these units are considered as potential monitoring targets in this work plan. <br />2572-R1 Colowyo Coal Company, L. P. <br />Water Management Consultants <br />