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2 <br /> probes was determined in the field by the site investigator <br /> as the survey progressed (Figure 1) . Soil gases were <br /> analyzed for total hydrocarbon concentration as vapor (TVH) <br /> during the Soil Gas Survey to delineate the lateral and <br /> vertical extent of hydrocarbon vapor. <br /> The temporary vapor probes installed for the investigation <br /> were constructed of 1/2-inch diameter Schedule 40 steel <br /> pipe. A point was forged on one end. A 24-inch range of <br /> 3/16-inch perforations were drilled into the probe beginning <br /> at 3 inches from the point (Figure A) . The vapor probes <br /> were driven pneumatically into the soil to depth intervals <br /> of 12 to 14 feet and 17 to 19 feet below grade. Probes B, <br /> E, and H were driven to a depth of 8 to 10 feet, also. <br /> After installation, a vacuum was applied to each prole to <br /> extract soil gas. One psi sample pressure was maintained <br /> during the analysis. Sample flow rate and instrument <br /> pressures were checked before each test. The soil gas was <br /> sampled through a 1/4-inch Teflon sample line that was <br /> connected to a stainless steel well head fitting. Use of <br /> Teflon tubing minimizes sample loss through adsorption and <br /> the possibility of distorted results from sample lines <br /> contaminated by a previous analysis. heak checks were <br /> performed on the sample line before and during the analysis. <br /> Filters were used extensively throughout the system to <br /> remove foreign material from the sample pathway. The sample <br /> line was connected to a diaphragm pump located in a mobile <br /> laboratory. The extracted soil gas was analyzed using a <br /> Beckman Model 400 Total Hydrocarbon Analyzer equipped with a <br /> Flame Ionization Detector (FID) and the results recorded on <br /> a Houston Instruments chart recorder. The Beckman Model 400 <br /> was calibrated using certified standards of propane in <br /> nitrogen. The instrument was recalibrated periodically <br /> throughout the day using certified standards. <br /> After the investigation was completed, the temporary vapor <br /> probes were removed. Upon removal of the probes, the holes <br /> created by the probes were sealed with bentonite and <br /> Portland cement (Figure B) This prevents the possibility <br /> of contaminants reaching the aquifer through the holes. The <br /> holes were sealed in the presence of San Joaquin County <br /> Department of Environmental Health personne? . <br />