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Supplemental Geotechnlcal Engineering Report <br />Proposed Slurry Cut-off Walls @ St. Vrain Development <br />Weld County, Colorado <br />Terracon Project No. 25045300 <br />Terracon <br />boring locations and elevations should only be assumed to the level implied by the methods <br />used. <br />Lithologic logs of each boring were recorded by the field engineer during the drilling <br />operations. At selected intervals, samples of the subsurface bedrock materials were taken <br />by driving split-spoon and/or ring barrel samplers. NX rotary drilling methods were used to <br />advance borings within the bedrock material for this current study. Rock Quality Designation <br />(RQD) was recorded for each run and core samples were obtained for inspection by the <br />project engineer. <br />Penetration resistance measurements were obtained (excluding the packer borings) by <br />driving the split-spoon and ring bairet into the subsurface materials with a 140-pound <br />hammer falling 30 inches. The penetration resistance value is a useful index to the <br />consistency, relafive density or hardness of the materials encountered. <br />Groundwater measurements were made in each boring at the time of site exploration and a <br />minimum of one day after drilling for the previous study. Groundwater measurements were <br />obtained within the borings during drilling for the current study and were backfilled <br />subsequent to packer testing. <br />Samples retrieved during the field exploration were returned to the laboratory for <br />observation by the project geotechnical engineer, and were classified in general accordance <br />with the general notes for Rock Classification presented in Appendix C. At that time, the <br />Logs of Borings were confirmed and/or modified and are presented in Appendix A. <br />SITE CONDITIONS <br />Three lakes with varying capacities currently occupy the site. Access gravel surfaced roads <br />are located within the southern and eastern boundaries of the site and between the lakes. <br />The St. Vrain River is located to the south of the lakes. It is our understanding that gravel <br />mining operations were performed at the location of these lakes in the recent past. The <br />water surface of the lakes was observed to be about 10 to 20 feet below existing adjacent <br />site grade. The site was relatively flat with an estimated elevation differential of about 10 to <br />25 feet across the area around the lakes. Vegetation consisted of a moderate growth of <br />native grass, brush cover and trees. Evidence of potential underground utilities was <br />observed within the southern and western portions of the site. <br />3 <br />