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r 2 r • r The temporary vapor probes installed for the investigation ' were constructed of 1/2-inch diameter Schedule 40 steel pipe. A point was forged on one end. A 24-inch range of 3/16-inch perforations were drilled into the probe beginning ' at 3 inches from the point (Figure A) . The vapor probes were driven pneumatically into the soil at various depth intervals. The depth intervals include 8 to 10 feet, 14 to 16 feet, 19 to 21 feet, 28 to 30 feet, and 32 to 34 feet below grade. In locations where the soil was covered by concrete or asphalt, a 1-inch diameter hole was drilled through the surface material with an electric roto-hammer. I The existing groundwater monitoring wells were screened at a depth interval of 28 to 58 feet below grade. 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 and during the analysis. I Filters were used extensively throughout the system to remove foreign material from the sample pathway. The sample line was connected to a 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) and the results recorded on a Houston Instruments chart recorder. The Beckman Model 400 was calibrated using certified standards of propane in nitrogen. The instrument was recalibrated periodically throughout the day using certified standards. Performance Test A portable skid containing a vacuum pump, flow meters, and vacuum gauges was used on site. A rigid vacuum line was connected to a probe or monitoring well to create an extraction point. Three of the temporary vapor probes r installed for the Soil Gas Survey and three existing i monitoring wells were used as extraction points. A set volume of air was pumped from the extraction point. Each Iextraction point was tested for a maximum of 15 minutes. . The information from the Performance Test was used to determine the capture radius, the distance at which the i