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1 •M <br /> 4.2 Lateral Extent of Contamination 1 <br /> The lateral extent of contamination will be assessed bye drillifig three additional b3rings <br /> around the perimeter of the former tank cavity. Their exact,depths and locations may <br /> Amagnitude <br /> depend on the of contamination that is evident in the first boring, but tentative <br /> locations are shown in Figure 2. The estimated depth`; of these borings is 30 f,-et. If <br /> groundwater is reached before two consecutive uncontaminated soil samples have been <br /> collected, two of the three borings will be converted to monitoring wells. The elevation of <br /> the well casings will then be surveyed relative to a temporary benchmark and the depth to <br /> groundwater will be measured before purging and sampling. <br /> 5.0 PROCEDURES <br /> The procedures that will be used in this investigation are listed b low: <br /> 1)Notify San Joaquin EHD at least 48 hours prior to fieldwork. <br /> 2) Drill one vertical boring through the former tank cavity to an, <br /> estimated depth of 40 feet <br /> below grade using a hollow-stem auger drilling rig'. 'p <br /> 3) Collect discrete soil samples at 5-foot intervals, using a:Calif6hiia modified split-spoon <br /> q 11 <br /> sampler loaded with three 6-inch brass sample sleeves. <br /> 4) Preserve the bottom sleeve by covering the ends with aluminum foil or Teflon sheets, <br /> capping,and sealing with duct tape. Place samples: a cooled ice chest. <br /> 5 Screen the middle sample for the presence of organic vapors sing a portable <br /> } p <br /> photo-ionization detector(PID) and record the measurement on the boring log. <br /> II 1 <br /> 6)Extrude the middle and upper sleeves and record.the sample descriptions on the boring <br /> log in accordance with the Unified Soil Classification System. <br /> 7)Decontaminate the sampling equipment between sampl' s. <br /> 8) Steam clean the drilling equipment. ` <br /> 9)Place auger returns on visquine. p <br /> 1 Q s.Repeat steps 2-9 for three additional burin <br /> p p g <br /> 1 ,r <br /> h <br /> i 5 <br />