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' 3.0 VAPOR EXTRACTION SYSTEM OPERATION AND MONITORING '• 3.1 System Operation Y P During the quarter, the system operated for a total of 1,596 hours (Appendix A) It operated for 27 days in July, 27 days in August, and 27 days in September During that period, 3,852,360 cubic feet of vapor were extracted This brings the total to over 55,000,000 cubic feet since July 1994 3.2 Monitoring Summary The extraction unit's on-board computer monitors several important parameters of engine performance, including air flow rates, well vacuum, and volume of extracted vapor These data are recorded hourly and averaged over the 24-hour day The daily averages are shown in Appendix A ' Hydrocarbon concentrations in the vapor stream (influent soil gas) and effluent (combustion products) were manually monitored on a weekly basis with a Microtip HL2000 photo-ionization detector until it was stolen in mid-August Thereafter, concentrations were measured with a Microtip 2020 and/or a ' MiniRae detector In addition, a vapor sample was collected from the shallow well influent line on August 28 The sample was collected in a tedlar bag and delivered to Sequoia Analytical for analysis of ' TPH-g and BTEX concentrations The results, reported in milligrams per cubic meter, are shown in Appendix B PID readings at the exhaust port ranged between 0 and 23 ppm during the quarter Effluent readings did not follow upward or downward trends in inlet concentrations PID readings from the deep well ranged from 6 to 45 ppm PID readings from the shallow well ranged from 550 to 950 ppm and ' averaged 680 ppm ' 4.0 DATA ANALYSIS 4.1 Graphical Summary ' Monthly summaries of daily air flow rates and other parameters for the third quarter are included in Appendix A In order to graphically illustrate the operation of the system, data for air flow rate since ' January 1996 and total cubic feet of extracted vapor since September 1995 are plotted in Figures 3 and 4 PID readings are graphed in Figure 5 to illustrate the effect of the system on soil vapor concentrations Flow rates on operating days ranged from a low of 32 cfm to a high of 56 cfrn For most of the quarter, the unit operated at somewhat higher rates than in the previous quarter_ 1 As discussed in the seconduarter 1996 report, there qere wad a marked increase in vapor concentrations in ' the shallow-well inlet stream in the first half of this year Concentrations rose from 500 ppm to more than 1,000 ppm, and exceeded 1,500 ppm on several occasions The concentration declined abruptly at 3