Laserfiche WebLink
2 <br />The Iles Formation consists of fine- to medium - grained, poorly sorted calcareous <br />sandstone interbedded with sandy and silty carbonaceous shale. The uppermost unit of <br />the Iles Formation is the Trout Creek member which is approximately 75 ft thick and <br />consists of white, fine - grained, well sorted, massive sandstone. The Trout Creek <br />sandstone is considered the upper -most regional aquifer in the area. <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. <br />Geologic structure around the proposed Collom pit is dominated by the Collom syncline <br />which is an asymmetrical fold that strikes N 70 0 W. The bedding dips up to 20 degrees <br />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 0 E. Jointing appears to be more <br />pervasive in the sandstone units of the Williams Fork Formation than the other lithologic <br />units. <br />1. 1.4 Groundwater <br />Groundwater conditions on the Collom property are expected to vary from south to north. <br />In the southern portion of the site, groundwater conditions may be similar to those on the <br />existing Colowyo Mine. Groundwater is present in perched zones which drain relatively <br />rapidly to the working mine face. In the northern portion of the Collom pit, the regional <br />groundwater table may be encountered and the deeper units are probably continuously <br />saturated from a depth of about 300 feet down the ultimate pit depth of about 650 ft. <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 />The Trout Creek sandstone is considered the uppermost regional aquifer in the area. It <br />is located some 400 to 450 ft below the bottom of the G coal seams. Preliminary <br />estimates place the potentiometric surface of the Trout Creek at approximately 6,800 ft <br />amsl in the vicinity of the Collom pit. Gradients are to the northeast. <br />Preliminary drilling suggests that the F ab 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 F ab 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 />• <br />2572 -R1 Colowyo Coal Company, L.P. <br />Water Management Consultants <br />