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i <br />=Walsh <br />Environmental Scientists and Engineers. LLC <br />Although the spring exits from shallow valley fill, the source is most likely from bedrock <br />outcrop upgradient and on the eastern slope of valley. <br />Straight Gulch Spring <br />One spring was sampled in Straight Gulch, SPRS -01, at the base of the eastern slope of <br />Straight Gulch. On December 2, 2004, discharge was visually estimated at less than 10 <br />gpm. The spring is undeveloped. The spring emerges from shallow valley fill, although <br />the source is likely from bedrock outcrops up gradient of the location. This spring is <br />considered to be perennial. <br />3.6.2 Groundwater <br />Regional Conditions <br />Regional Hydrogeology <br />The proposed Collom Mine is located in a groundwater basin bounded in most areas by <br />the outcrop of the Trout Creek Sandstone (WMC 2005). The boundaries of the basin are <br />the north limb of the Collom Syncline, the west edge of the Morgan Syncline, the crest of <br />the Danforth Anticline to the south, and to the east (Figure 4). Elevations of the base of <br />the Trout Creek Sandstone range from about 8,000 to 7,200 feet amsl on the south limb <br />of the syncline, to approximately 6,500 feet on the north limb of the syncline in the <br />valleys. The Trout Creek Sandstone yields moderate quantities of water to wells on a <br />local basis and is generally considered the upper -most aquifer of regional extent in the <br />area. However, since the Trout Creek Sandstone outcrops around the periphery of the <br />synclinal basin containing the Collom Mine, it is not in direct hydraulic connection with <br />the Trout Creek Sandstone outside the Collom synclinal basin. <br />The Williams Fork Formation, which overlies the Trout Creek Sandstone, includes a <br />sequence of sandstone, siltstone, mudstone, and coal units approximately 1,000 feet thick. <br />Groundwater is primarily stored and transported in the coal and sandstone units. The coal <br />seams are relatively continuous over large areas. The sandstone units tend to be less <br />continuous as a result of the depositional environment. Low - permeability siltstone and <br />mudstone beds form the confining units of the groundwater system. The upper water - <br />bearing units tend to be somewhat localized due to dissection by streams. <br />Regional Groundwater Flow <br />The overall direction of groundwater flow in the Collom synclinal basin is from south to <br />north down the dip of the south limb of the syncline (WMC 2005). Lateral flow (east or <br />west) occurs locally where units drain into the adjacent stream drainages. The water table <br />in the basin varies from about 7,800 feet amsl on the south to about 6,500 feet amsl on <br />the north. <br />P PROW( is Cokre)o 5158 1 \ Fm.I 144 -I, \t olk,m .n, Jc <br />31 <br />