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May 2013 Groundwater POC Memorandum ♦ 4 <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. Figure 4 presents a geologic <br />map of the TSF area and Figures 5 and 6 present two cross - sections through the area. The <br />geologic map and cross - sections are based on reconnaissance mapping, pre - tailings <br />topography, drill-hole data, and air photo interpretation. The locations of the two cross - <br />sections are shown on Figure 4. Cross Section A -A' (Figure 5) is oriented northwest to <br />southeast and extends from north of 1 -Dam, through internal monitor well pairs, and <br />through the existing 1 -Dam extraction wellfield. Cross Section B -B' (Figure 6) is oriented <br />southwest to northeast from 1 -Dam through the extraction wellfield, through internal <br />monitor well pair and potential POC locations MLGW -7/15, and to the Williams Fork <br />River. Both sections use a vertical exaggeration of 5:1. <br />As shown on the geologic map and cross - sections, shallow geology beneath and <br />downgradient of the TSF, including portions of 1 -Dam and 3 -Dam, is characterized by <br />Quaternary glacial drift (moraine and till deposits undivided), glacial outwash, and alluvium <br />(Qd). The thickness of alluvium /glacial drift deposits ranges between 60 and 180 feet in the <br />areas of 1 -Dam and 3 -Dam. Pre - quaternary geologic units in the vicinity of the TSF include <br />the Tertiary Troublesome Formation (Tt) and Precambrian bedrock (Xg). These units occur <br />beneath the Qd or are exposed at the surface at topographic highs, such as ridges adjacent to <br />the TSF. Tt in the vicinity of the TSF consists of reddish -brown weathered to highly <br />weathered clay, claystones and siltstones with some thin limestone beds based on well <br />borings and observed outcrops of Tt located north of 1 -Dam. The thickness of the Tt is <br />defined in boreholes located east and north of 1 -Dam to be between 40 to 120 feet. <br />Bedrock in the vicinity of the TSF is comprised of metamorphic gneiss and migmatites of <br />the Precambrian Idaho Springs Formation. Xg underlies the Qd and Tt, and crops out in <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 />