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21 January 1993 <br /> (GeoAudit CV 42F4-1. 68) <br /> Page 2 of 4 <br /> 3.0 SOIL INVESTIGATION <br /> 3.1 Drilling and sampling <br /> ' Field work was performed on 20 and 23 November 1992 . Six oil <br /> borings were drilled with a truck-mounted drill rig equipped with <br /> 8-inch-diameter hollow-stem augers (Figure 3) . Great Sierra <br /> Exploration of Union City, California provided the 2-man drilling <br /> crew. Soil samples were collected at 5-foot intervals, usually <br /> starting at a depth of 5 feet, using a 140-pound hammer to advance <br /> a split-tube sampler loaded with three brass sleeves. The number of <br /> blows required to advance the sampler 18 inches was recorded on the <br /> boring log (see Appendix A) . <br /> ' After removal from the sampler, the bottom tube was screened for <br /> volatile organic vapors using a portable photo-ionization detector <br /> (PID model OVA-580A calibrated to isobutylene) and the reading was <br /> recorded on the boring log. The ends of the tube were then covered <br /> with sheets of aluminum foil, capped, and sealed with aluminum duct <br /> tape. Samples were labelled, logged on the boring log, and placed <br /> on ice until delivery to WEST Laboratories for analysis. Soil in <br /> the middle and upper tubes was extruded and described on the boring <br /> log. To, avoid contamination of subsequent samples, the tubes and <br /> sampler, were then triple-rinsed in a phosphate solution; the augers <br /> were steam-cleaned between borings. <br /> 3.2 Abandonment <br /> 1 { i <br /> Soil borings were grouted with a slurry of Portland cement from <br /> total depth to surface. <br /> 4. 0 SITE GEOLOGY <br /> Three stratigraphic horizons were penetrated in this investigation <br /> 1 (Figure 4) . From the surface to a depth of approximately 18 feet, <br /> all borings recovered slightly clayey to slightly sandy silt in <br /> various shades of brown. The color appeared to reflect different <br /> deg' r' ees of weathering. The' least-weathered samples were light gray <br /> i to tan; more strongly weathered samples were yellow-brown to <br /> reddish-brown. I <br /> I � , { <br /> i The „middle II layer , consists of quartz-rich dark-gray'' <br /> I sand i that <br /> generally medium tb coarse grainedE j The sand is well sorted and, <br /> loose,. and is moist to saturated. The Mower boundary of the sand, <br /> layer varies between 26 and 33 feet in depth, and is 'probablyll � f <br /> erosional (Figure 4) . Finer-grained sand or sandy silt is present k� <br /> , I i M beneath the coarse-grained sand bed. This lower bed is also gray in11 ; I, <br /> i, 'I col'ior, and is wet or saturated in most borings. <br /> 61 I , <br />