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Supplemental Geotechnical Engineering Report Proposed Slurry Cut-off Walls @ St. Vrain Development Weld County, Colorado Terracon Project No. 25045300 Terracon were also encountered, predominantly on the eastern portion of the site. Claystone and/or sandstone bedrock were encountered beneath the native soils in the majority of the borings at depths ranging from about 7 to 30 feet below existing site grade and extended to the full depth of exploration. Bedrock was not encountered to the full depth of exploration in Boring Nos.1 and 8. Auger refusal was encountered in these borings at depths ranging from about 5 to 18 feet below existing site grade and appears to be in gravel and/or cobble sized materials. in addition, auger refusal was encountered in very hard and strongly cemented sandstone bedrock materials at depths ranging from about 13 to 20 feet below existing site grade in Boring Nos. 45, 47 and 48. Field and Laboratory Test Results: The predominant sand materials overlying the bedrock generally classify as silty sand (SM) per the Unified Soil Classification System (USCS) and have varying amounts of clay, silt, and gravel. The amount of fines (predominantly silt) within the overburden materials encountered in the packer testing locations varied from about 24 to 28 percent. Laboratory test results are included in Appendix B. Field test results from the current and previous studies indicate that the claystone bedrock materials vary from medium hard to very hard in hardness. The claystone bedrock materials appear to be generally intact to moderately fractured in terms structure. The sandstone bedrock materials within the western portion of the site are very hard in hardness and strongly cemented but have a higher degree of fractures within the upper approximate 5 to 10 feet. Auger refusal on the sandstone bedrock was generally encountered ih these areas. Results of the packer permeability testing are as follows: Table No. 1 Depth of Test Bedrock Total Head RQD Average (%) Permeability Location Interval(ft) Description (ft) (in/sec) Packer 1 7' 2" to 12' 2" a w/ San 38.75 82 7.24 x 10'5 Clay Packer 1 12' 5" to 17' 3" San C ay e.wl 43.6 55 8.5 x 10~ l Packer 2 27' %" to 32' Sandy 69.3 86 'Less than 10"' Claystone Packer 3 11' 10" to 16' 7" l 33.7 80 9.8 x 10"~ dstone San Packer 4 27' to 32' Claystone 92.4 86 'Less than 10- 'accepteq no water under the specitieq neap pressure Groundwater Conditions: Groundwater was encountered in the majority of the borings at depths ranging from about 3 to 19 feet below existing site grade at the time of field exploration from the previous study. When checked a minimum of one day after drilling, groundwater was measured at depths of about Z fo 25 feet below existing site grade in some of the borings. However, some of the borings caved-in under wet conditions at depths 5