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Report on Soil and Ground-Water Evaluation September 11, 1989 <br /> Proposed ARCO Station, Woodbridge, California AGS 39044-1 <br /> constructing monitoring wells (boring B-1, B-2, and B=3) were drilled to total depths of <br /> approximately 31 feet below the surface. Soil boring B-4 was drilled to a total depth of <br /> approximately 15 feet below grade. This boring was .used to evaluate soil contamination <br /> in the area where the previous underground tanks were thought to have been located. <br /> Ground water was encountered at approximately 14-1/2 feet below the ground surface in <br /> each boring. During drilling, soil samples were typically collected at 5-foot intervals or at <br /> obvious changes in sediments using a 2-1/2-inch-diameter California-modified, split-spoon <br /> sampler equipped with clean brass sleeves. The samples were collected by advancing the <br /> boring to a point immediately above the sampling-depth and then driving the sampler into <br /> the undisturbed native soil through the hollow stem of the auger. The sampler was driven <br /> 18 inches with a standard 140-pound hammer dropped 30_inches. The number of,blows <br /> required to drive the sampler each successive 6-inch interval was counted and recorded to <br /> give an indication of soil consistency. <br /> During sampling, a. field photoionizing organic vapor meter (OVM) was used to <br /> characterize the relative levels of hydrocarbon contamination by placing the intake tube of _ <br /> the instrument into freshly sampled soil. Field instruments such as the OVM can measure <br /> relative concentrations of vapor but not with the level of confidence of laboratory analyses. <br /> The soil samples collected above the ground-water surface produced no readings on the <br /> OVM. The samples collected below the ground-water surface in the boring. .MW-1 <br /> 1r � rt <br /> 12 <br /> APP1490' GeoSyste1ns <br />