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y 4.0 DATA ANALYSIS ' 4.1 Graphical Summary Monthly summaries of daily,air flow rates and other parameters for the quarter are included in Appendix A Because the unit operated only sporadically during the quarter, graphs of these ' paramaters were not prepared for this report However, in order to illustrate the overall long-term effects of remediation as indicated by vapor concentrations, plots of vapor concentration versus ' time since the initial start-up are shown as Figures 3 and 4 In both graphs, a single PID reading was selected as representative for each month Laboratory results for samples from the deep well are also shown in Figure 3, and for the shallow well in Figure 4 Both graphs illustrate that remediation became effective after the first three months, when equipment problems were finally solved and sustained air flow was established Over the next ' several months, marked reductions in vapor concentration were observed in both the shallow and deep zones as air flow rates were increased when the initial 4-cylinder engine was replaced by an 8- cylinder engine Vapor concentrations from the shallow zone increased and flow rates decreased ' after the 8-cylinder engine was replaced/with a new 4-cylinder engine in March 1995 Vapor concentrations from the deep zone stabilized during this period After May of 1995, vapor concentrations decreased markedly in both zones Decreased concentrations in the shallow zone ' were indicative of effective remediation, while decreases in the deep zone were attributed to a rise in the static water level above the opening of the well Vapor concentrations from the shallow zone decreased further in the third quarter of 1995, then stabilized between 500 and 1,000 ppm until early 1996 In contrast, concentrations from the deep zone began to increase in September, after the unit had been shut down for a month to allow the soil ' to relax Concentrations continued to increase until December, when the unit began to operate erratically Laboratory analysis of a sample collected in December 1995 suggested that abnormally high nitrogen concentrations were reducing the engine's efficiency during this period The deep well remained submerged below the water table in early 1996, and Apache began using it t as an air spargmg well in February Hence, concentrations from the deep zone remained near zero for most of the year Vapor concentrations measured by PID from the shallow zone rose abruptly and remained above 1,000 ppm through May, but it was unclear whether this increase was due to air sparging alone or was partly caused by cross-contamination from gasoline-saturated hoses ' and/or sample ports Therefore, new'hoses and ports were installed in May, but PID readings remained elevated, although laboratory analysis of the vapor sample collected in May showed a ' slight decline in concentrations from the previous sample in December 1995 The disparity between the PID and laboratory data was much larger than usual and could not be explained ' Figure 3 shows an abrupt increase in vapor concentrations in November 1996, after VE-2 was installed and VE-1 "deep"was disconnected VE-2 began extracting vapors from the silty or clayey zone between 35 and 50 feet, which previously had nbt been affected by extraction from either VE- 1 "shallow" or VE-1 "deep" Concentrations from this zone decreased in December 1996, but then 4 tr 1