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2.4 Recent Investigation During the fourth quarter of 1996,Emcon of Sacramento drilled two new soil borings to gather data ' for preparation of a Risk-based Corrective Action Plan One boring is located near MW-5, and one is located approximately 15 feet east of VE-1 (Figure 2) This boring was completed as a vapor ' extraction well and has replaced VE-1 "deep" The new well is screened from 35 to 55 feet and is referred to in this report as VE-2 1 3.0 VAPOR EXTRACTION SYSTEM OPERATION AND MONITORING t3.1 System Operation During the quarter, the system operated for a total of 1,071 hours (Appendix A) It operated for 24 ' days in July, 16 days in August, and 15 days in September During that penod, 2,090,340 cubic feet of vapor were extracted. This brings the total to approximately 68,650,000 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 spot stream (influent soil gas) and effluent (combustion products) were manually monitored 8 times during the quarter with a Microtip 2020 photo- ' ionization detector In addition, vapor samples were collected from the VE-1 "shallow" influent line, from the VE-2 influent line, and from the combined influent line on September 22 The samples were collected in tedlar bags and delivered to Sequoia Analytical for analysis of TPH-g and ' BTEX concentrations. The results, reported in parts per million by volume (milligrams per cubic liter),are shown in Appendix B ' PID readings at the exhaust port ranged between 0 and 36 ppm during the Quarter Effluent readings did not follow upward or downward trends in inlet concentrations PID readings from VE-2 were measured both at the well inlet and at the water dropout drum on most occasions PID readings at ' the drum were between 40% and 95% of those at the well head, which indicates that a significant proportion of the withdrawn vapors are not reaching the destruction unit for some reason Well- head concentrations ranged from 870 to 3,850 ppm Readings from VE-1 "shallow" ranged from ' 285 to 680 ppm Readings from the combined inlet consistently fell between those of VE-1 and VE-2, but were generally closer to the readings from VE-2, implying that most of the air flow was ' from the deep zone This inference is supported by the laboratory results of the vapor samples collected in September (800 ppmv from VE-1, 2,400 ppmv from VE-2, and 2,300 ppmv from the combined inlet). 3 1