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6 <br /> 1 <br /> Chevron U.S.A. - Page 6 <br /> r <br /> 5.0 METHODOLOGY", <br /> Drilling was performed utilizing a truck: mounted drill rig equipped with <br /> flight hollow-stem auger. A Dames & Moore geologist was present during drilling <br /> to assist in obtaining relatively undisturbed samples of the subsurface <br /> materials, to maintain a log of borings, to field screen samples with a device <br /> i; <br /> capable of detecting volatile organic hydrocarbons as a trace gas, and to make <br /> observations of the site conditions. <br /> Subsoils were sampled at approximate 5 foot intervals, commencing at an <br /> w� approximate depth of five feet below the existing grade. Samples were obtained by <br /> "- means of a California Modified sampler which was li*:ed with brass sleeves. The <br /> } . <br /> sampler was advanced by blows from a 140 pound hammer failing 30 inches. upon <br /> retrieval, samples were retained for visual observation and iaterpretation. Those <br /> samples retained for chemical analysis were capped with a plastic cap over a <br /> teflajr =pal. and taped at each end. The samples were placed into a cooler chest <br /> y <br /> under proper chain of custody protocol for shipment to the analytical laboratory. <br /> Between sampling attempts, the sampler was dissassembled and washed in a <br /> trisodium phosphate (TSP) solution, rinsed twice with purified water, and <br /> reassembled with brass rings to minimize the potential of spreading contaminants <br /> among samples, if any were present. Soils were classified according to the . <br /> Unified Soil Classification System (Plate 5) , <br /> w.: <br /> The ground water monitoring wells were installed in each soil boring through <br /> the center of the hollow- ' <br /> stem auger. Each monitoring well was constructed using <br /> 4-inch diameter flush-thread pvc schedule 40 well <br /> pipe. screened intervals were <br /> ive <br /> DA\1ES 6 MOORE <br />