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I PROJECT 02510.01 January 31, 1991 sampled through a 1/4-inch Teflon sample line that was connected to a stainless steel , air tight, 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 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. Depth to groundwater was measured at monitoring wells tested during the Soil Gas Survey using an electronic water level indicator. Performance Test . The Performance Test was conducted January '30, 1991. A portable skid containing a vacuum pump, flow meters, and vacuum gauges was used on site. A vacuum line was connected to an existing ground water monitoring well to create an extraction point. Five monitoring wells (MW-5, MW-7, MW-10, MW-13, and MW-19) were used as extraction points (Figure 1) . Each extraction point was 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 and vertical planes. The capture radius was noted by recording the vacuum gradient in neighboring wells in inches of water ("H 0) . This procedure was- performed at various flow rates at several of the 2wells. The detection limit for the vacuum gradient was 0.00511 -H 0. The effluent from the extraction points was routed through two cy?inders 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. RESULTS Soil Gas Survey TVH concentrations recorded at the wells tested are given in Table 1 . • The highest TVH concentration, 11 ,550 parts per million (ppm) , was recorded at monitoring well MW-2 located east of the existing underground fuel storage tanks and south of the station building. The next highest I 2 �