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• 2.4 Recent Investigation • During the fourthuarter of 19§6 Emc q on of Sacramento dulled two new soil borings to gather data for preparation of a Risk-based Corrective Action Plan Emcon's report of the investigation is apparently stall in preparation One boring is located near MW-5, and one is located approximately 15 feet east of VE-1, This boring was completed as a vapor extraction well and was used for the remainder of the quarter in place of VE-1 "deep" The new well is screened from 35 to 55 feet and is referred to in this report as VE-2 3.0 VAPOR EXTRACTION SYSTEM OPERATION AND MONITORING 3.1 System Operation During the quarter, the system operated for a total of 1,945 hours (Appendix A) It operated for 29 days in October, 29 days in November, and 28 days in December During that period, 4,978,620 cubic feet of vapor were extracted This brings the total to over 60,000,000 cubic feet since July, 1994 The Air Quality Managment District operating permit was due to expire on January 1, 1997, and the unit was therefore shut down on December 31, 1996 Currently, the unit remains shut down pending a response from the San Joaquin County PHS/EHD to the Risk-based Corrective Action Report and Request for Closure that has been prepared by Emcon of Sacramento At this time, Apache has not applied for continuation of its operating permit • 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 NhmRae detector In addition, vapor samples were collected from the VE-1 "shallow" influent line and four the VE-2 influent line on December 4 The samples were collected in tedlax bags 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 15 ppm during the quarter Effluent readings did not follow upward or downward trends in inlet concentrations PID readings from VE-1 "deep" ranged from 0 to 40 ppm, but readings from VE-2 were consistently above 2,000 ppm PID readings from VE-1 "shallow"ranged from 440 to 800 ppm and averaged 637 ppm After the new - extraction well was installed on November 17, readings were also collected at the combined flow inlet port, as they had been earlier in the year These readings ranged between the deep and shallow well readings, averaging 1250 ppm 3