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May 2013 Groundwater POC Memorandum ♦ 5 <br />areas where the Tt and Qd are absent (Figure 4). Xg forms the topographic bedrock ridge <br />that forms the eastern boundary of the Ute Creek subbasin. 3 -Dam is constructed along this <br />bedrock ridge, and outcrops of Xg buttress the north and south ends of the dam. <br />2.2 SITE HYDROGEOLOGY <br />2.2.1 Hydrostratigraphic Units <br />Hydrostratigraphic units are bodies of rocks or sediments that are hydraulically continuous, <br />mappable, and can be described as distinct hydrologic systems. The following <br />hydrostratigraphic units occur within the vicinity of the TSF: <br />• Quaternary sediments, including glacial drift (moraine and till deposits), outwash, and <br />alluvium <br />• Tertiary Troublesome Formation <br />• Precambrian bedrock <br />2.2.1.1 Quaternary Sediment Aquifer <br />Water - bearing Quaternary sediments, including glacial drift, glacial outwash, and recent <br />alluvial deposits, occur in the lower Ute Creek Basin and Williams Fork River valley and <br />comprise an aquifer system east of 1 -Dam. The depth to groundwater within the aquifer is <br />shallow, typically 10 to 30 feet below ground surface (bgs). Aquifer thickness varies <br />depending on the thickness of Qd. In the vicinity of 1 -Dam, the aquifer thickness ranges up <br />to 160 feet. From a hydrologic standpoint, the glacial and alluvial sediments in the vicinity <br />of 1 -Dam comprise a single shallow aquifer system, with flow within the sediments <br />controlled by the varying hydraulic characteristics (i.e., compaction, grain size and the degree <br />of sorting). In the vicinity of 3 -Dam, the Quaternary sediments are comprised of glacial <br />deposits. Groundwater occurs in isolated areas and does not appear to comprise a <br />continuous aquifer system and its thickness varies due to the isolated occurrences of <br />groundwater but appears to be up to 30 feet thick. <br />AJAX Ltd ♦ 28828 Cedar Circle ♦ Evergreen, CO 80439 ♦ (303) 241 -2057 <br />Clear Creek Associates* 6155 E. Indian School Rd. ♦ Scottsdale, AZ 85251 ♦ (480) 659 -7131 <br />