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. laboratory readings , a tedlar bag was attached to the sample pump and filled with influent vapor, and the PID readings were obtained from the bag. Until early November, influent readings were taken only at the individual well heads; thereafter, a third sampling port was added at the extraction unit and readings were also obtained from the combined vapor stream at the entry point to the destruction unit . Matching samples were collected in tedlar bags on November 10 and March 3, and delivered to Sequoia Analytical for analysis of TPH-g and BTEX concentrations in the vapor stream. 4 .0 DATA ANALYSTS 4 . 1 Graphical Summary Monthly summaries of daily air flow rates and other parameters are included in Appendix A. The data for air flow rate and total cubic feet of extracted vapor are plotted in Figures 3 and 4 to more graphically illustrate the operation of the system. In addition, vapor concentrations are graphed in Figure 5 . Following a 2-week start-up period, continuous operation was established in mid-October. Flow rates for the 4th quarter ranged from a low of approximately 100 cfm to a high of 160 cfm. More than 14, 000, 000 cubic feet of vapor were extracted. Hydrocarbon concentrations increased initially to more than 10 , 000 ppm in both wells, but then gradually decreased as flow rates were increased. This is particularly true of the shallow well, which had contributed the ma]ori.ty of the VOC' s during the first three months of system operation. In contrast, vapor concentrations in the deep well consistently exeeded those from the shallow well during the 4th quarter of 1994 and 1st quarter of 1995 . Comparison of laboratory results of samples collected on November 11 with PID readings on that date yields satisfactory agreement (the PID reading f rom the shallow well exceeded the lab result by 15%, whereas the lab result from the deep well exceeded the PID reading by 28% ) . However, the PID reading from the combined vapor stream on March 3 overestimated the laboratory result by nearly 80% . The laboratory result is probably too low ( such a low concentration would not sustain combustion without a greater consumption of natural gas) . The flow rate began to increase in late December, reaching a peak in mid-January. This increased rate was associated with increases in engine speed and temperature and auxiliary fuel consumption. Concurrently, vapor concentrations began to decline, which probably accounts for the increase in auxiliary fuel . The anomalously low vapor concentrations measured on Janaary 3 were due to malfunction of the PID, but a general trend toward decreasing concentrations in nonetheless evident. 4