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1 <br /> 4.0 DATA ANALYSIS <br /> 4.1 Graphical Summary <br /> 1 <br /> Monthly summaries of daily air flow rates and other parameters for the quarter are included in <br /> Appendix A In order to graphically illustrate the operation of the system, several graphs have been <br /> constructed Figure 3 shows representative monthly PID readings and laboratory results for the deep' <br /> zone (from well VE-1 "deep" pror to December 1996 and from VE-2 since then) Corresponding <br /> data from the shallow zone (VE-1 "shallow") are graphed in Figure 4 Data for air flow rate since <br /> September 1995 are plotted in Figure 5 <br /> ' As Figure 3 shows, concentrations from the deep zone increased steadily from approximately 900 <br /> ppm at the beginning of the quarter,to more than 1,500 ppm by mid-quarter and more than 2,500 <br /> ppm by the end of the quarter The laboratory result of 2,400 ppmv on September 18 is only about <br /> ' 60% of the value of 3,850 ppm measured by PID on that date, although PID and laboratory data <br /> have agreed well for the past several quarters The increase in concentrations from the deep zone <br /> may be partly due to the drop in the water table during the quarter, enlarging the thickness of the <br /> ' vadose zone and exposing the capillary fnnge to the effects of the unit Another contributing factor <br /> may be the fact that the extraction unit was shut down for extended periods in August and { <br /> September, providing time for hydrocarbon vapors to accumulate <br /> ' In contrast, concentrations measured by PID from the shallow zone fluctuated up and down but <br /> overall have continued to decrease (Figure 5) Laboratory results for samples from the shallow zone <br /> have shown a similar decrease, but, curiously, have consistently exceeded PID readings for the past <br /> several quarters The reason for this is not evident <br /> ' 4.2 Weight of VOC's Destroyed <br /> The weight of VOC's extracted during the quarter can be computed from the mean vapor <br /> ' concentration at the combined well inlet and the cumulative volume of extracted vapors The <br /> average concentration measured at the combined inlet on the 8 measurement days was 832 ppm, <br /> which is almost the same,as in the second quarter <br /> ' WEIGHT OF VOC'S =CF_x JVAPORJ x 10 6 x 100 mol/wt <br /> 379 cf/mole <br /> ' =2 090 x l 06 W x 832 x 10-6 x 100 mol/wt <br /> 379 cflmole <br /> ' = 1 739 x 105 lbs <br /> 3 79 x 102 =459 lbs <br /> 4 <br />