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2.4 Recent Investigation <br /> During the fourth quarter of 1996, Emcon of Sacramento drilled two new soil borings to gather data <br /> ' for preparation of a Risk-based Corrective Action Plan One boring is located near MW-5, and one <br /> is located approximately 15 feet east of VE-1 This boring was completed as a vapor extraction well <br /> and has replaced VE-I "deep" The new,well is screened from 35 to 55 feet and is referred to in this <br /> ' report as VE-2 <br /> ' 3.0 VAPOR EXTRACTION SYSTEM OPERATION AND MONITORING <br /> ' 3.1 System Operation <br /> During the quarter, the system operated for a total of 585 hours (Appendix A) It operated for part <br /> ' or all of 9 days in January, 10 days in February, and 17 days in March During that period, <br /> 1,175,720 cubic feet of vapor were extracted This brings the total to approximately 62,000,000 <br /> cubic feet since July 1994 The Air Quality Managment Distract operating permit expired in <br /> ' January, and the unit was therefore shut down on January 10, 1997 The Permit to Operate was <br /> extended and the unit was restarted on February 6, but combustion could not be maintained and for <br /> the next 9 days the unit operatbd for only a few hours Apache maintainence personnel located a <br /> ' malfunction in late February and repaired the unit in early March Since the;middle of March, it has <br /> performed normally <br /> 3.2 Monitoring Summary <br /> The extraction unit's on-board computer monitors several important parameters of engine <br /> ' performance, including air flow rates, well vacuum, and volume of extracted vapor These data are <br /> recorded hourly and averaged over the 24-hour day The daily averages are shown in Appendix A <br /> ' Hydrocarbon concentra#ions in the vapor stream (influent soil gas) and effluent (combustion <br /> products) were manually monitored 4 times during the quarter with a Microtip 2020 photo- <br /> ionization detector In addition,vapor samples were collected from the VE-1 "shallow" influent line <br /> and four the VE-2 influent line on March 26 The samples were collected in tedlar bags and <br /> delivered to Sequoia Analytical for analysis of TPH-g and BTEX concentrations The results, <br /> ' reported in milligrams per cubic meter, are shown in Appendix B <br /> PID readings at the exhaust port ranged between 5 and 12 ppm during the quarter Effluent readings <br /> ' did not follow upward or downward trends in inlet concentrations PID readings from VE-2 ranged <br /> between 1,000 and 2,000 ppm, and readings from VE-1 "shallow"ranged from 700 to 1200 ppm <br /> i <br /> 3 <br /> 1 , <br /> 1 <br />