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i . rr L Geological Tecluucs W. Page 3 COE-Former Arco Site Monitoring Report-VETS _ Project No.: 750.2 January 21,2003 significant amounts of contamination are still sorbed to the soil at the site. If the sample collected immediately after startup showed much higher concentrations then the sample collected before the system was shutdown, then it would be apparent that significant contamination still exists in the soil. The sample collected one day after startup was to determine how quickly the concentrations decreased back to the levels observed before the test. Table 1 in Appendix A shows dates of operations and notes periods of downtime. 2.3 `'. Passive Air Recharge Due to the site showing good pneumatic conductivity, the other two vapor wells (VEW-1 and VEW-2) were operated as passive air recharge wells to introduce oxygen into the subsurface and to induce air flow across the site. 2.4 Treatment System Efficiency Testing r Monthly sampling is performed on the influent going into the IC and the effluent from the IC L treatment system to demonstrate that the required efficiencystandards are being met and to allow for the calculation of the mass of gasoline removed. SJVUAPCD required efficiency standards are: • The IC must destroy VOCs to a minimum of 95% efficiency or 0 The total VOC emission rate shall not exceed 2.0 pounds in any one day. The IC has met the 95% destruction efficiency standard every month. However, it was shut down at the end of February 2002 because the routine monitoring with an OVM showed that the IC would not meet efficiency standards. GTI uses an OVM for regular checking of the system so that changes can be made to allow for the highest removal rates possible. The OVM is a field portable photo ionization detector that uses a'10.0 eV lamp to detect compounds with ionization potential below 10.0 eV (hydrocarbon range). r Monthly reports showing the laboratory data and efficiency calculations have been submitted to L SCDER,RWQCB and SJVUAPCD. 2.5 Gallons of Gasoline Removed.to Date Table,1 shows OVM and.laboratory data and airflow rate data over the life of the project. From this data, removal rates were calculated and cumulative volumes were tracked. As of December r10, 2002, the IC had removed and destroyed approximately 67 gallons of gasoline from the u subsurface,which is near 50% of the estimatedmass of contaminants that was in the subsurface prior to start of the extraction system (refer to Table 3, Appendix A). . G67s ; 1f�2 IZ 3.0 DISCUSSION The influent vapor concentrations began to decrease significantly at the site starting in September of 2002. This is probably a result of the VETS having removed the large volume of gasoline vapors that were present in the soil,pore spaces. Gasoline that is currently being removed is probably coming from a small residual tightly sorbed to the soil particles.