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' May 2014 Groundwater POC Update Memorandum♦2 <br /> ' 2.0 SUMMARY OF GEOLOGY AND HYDROGEOLOGY <br /> 2.1 SITE GEOLOGY <br /> ' The Henderson Mill and TSF are located within the Ute Creek Basin of the Williams Fork <br /> River valley. The Ute Creek Basin drains through a gap in the bedrock ridge at Ute Park, <br /> just west of the confluence of Ute Creek and the Williams Fork River. The TSF is within a <br /> ' shallow sloping portion of the basin near its downstream outlet. <br /> Shallow geology beneath and downgradient of the TSF, including portions of 1-Dam and 3- <br /> Dam,is characterized by Quaternary glacial drift (moraine and till deposits undivided),glacial <br /> ' outwash, and alluvium (Qd). Pre-quaternary geologic units in the vicinity of the TSF include <br /> the Tertiary Troublesome Formation (Tt) and Precambrian bedrock (Xg). A more detailed <br /> ' description of the geology is provided in the POC Memorandum (AJAX and Clear Creek, <br /> 2013). <br /> t2.2 SITE HYDROGEOLOGY <br /> Hydrostratigraphic units are bodies of rocks or sediments that are hydraulically continuous, <br /> mappable, and can be described as distinct hydrologic systems. Water-bearing Quaternary <br /> sediments, including glacial drift, glacial outwash, and recent alluvial deposits, occur in the <br /> lower Ute Creek Basin and Williams Fork River valley and comprise an aquifer system east <br /> ' of 1-Dam. The depth to groundwater within the aquifer is shallow, typically 10 to 30 feet <br /> below ground surface (bgs). Aquifer thickness varies depending on the thickness of Qd. In <br /> ' the vicinity of 1-Dam, the aquifer thickness ranges up to 160 feet. From a hydrologic <br /> standpoint, the glacial and alluvial sediments in the vicinity of 1-Dam comprise a single <br /> shallow aquifer system. Groundwater in the shallow aquifer flows beneath the dam east- <br /> northeast, towards the Williams Fork River. As discussed in the POC Memorandum (AJAX <br /> and Clear Creek, 2013), both the Tt and Xg were observed to be non-water bearing east of <br /> 1-Dam. At 3-Dam, there is not a continuous aquifer system from which to directly interpret <br /> the direction of groundwater flow. Only one of the five monitor wells consistently yields <br /> ' groundwater. Consideration of the geology and watershed boundary suggests that only a <br /> small amount of groundwater flows through the glacial deposits in this area. <br />