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Project 06020.01 June 11, 1991 perforations were drilled into each probe beginning at three inches from the point (Figure A) . The vapor probes were driven pneumatically into the soil to a depth of 8 to 11 feet below grade (Table 1) . L After installation, a vacuum was applied to each probe to extract soil gas. One psi sample pressure was maintained during the analysis. Sample flow rate and instrument pressures were checked before each test. The soil gas was sampled through a 1/4-inch Teflon sample line that was connected to a stainless steel well head fitting. Use of Teflon tubing �► minimizes sample loss through adsorption and the possibility of distorted results from a sample line contaminated by a previous analysis. Leak checks were performed on the sample line before the analysis. Filters were used extensively throughout the system to remove foreign material from the sample pathway. The sample line was connected to a w. diaphragm pump located in a mobile laboratory. The extracted soil gas was analyzed using a Beckman Model 400 Total Hydrocarbon Analyzer equipped with a Flame Ionization Detector (FID) . The Beckman Model 400 was calibrated using certified standards of propane in nitrogen. The instrument was recalibrated periodically throughout the day using certified standards. v Limited Performance Test A limited Performance Test was conducted on June 4, 1991 at the subject site. A portable skid containing a vacuum pump, flow meters, and vacuum gauges was used on site. One of the temporary vapor probes was used as an extraction point. A rigid vacuum line was connected to the vapor probe to create an extraction point. A set volume of air was pumped from the extraction point. Extraction points are tested for a period of 20 minutes. The information from the Performance Test was used to determine the +� capture radius, the distance at which the pressure differential created by a vacuum pump is measured in the lateral plane. The capture radius was noted by recording the vacuum gradient in neighboring probes and wells in inches of water ("H 0) . The detection limit for the vacuum gradient was 0.005" H 0. Th9 effluent from the extraction point was routed through two cyNders in series, each containing 200 pounds of +� vapor phase activated carbon. The carbon adsorbs organic vapors from the extraction air stream, preventing discharge of contaminants into the atmosphere. After the investigation was completed, the temporary vapor probes were removed. Upon removal of the probes, all locations were sealed with ,60 bentonite and Portland cement - 2 -