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Updated Site Conceptual Model and Third Quarter 2003 Monitoring and Remediation Report Cleanu and Abatement Order No 5-00-707 EAI Pra ect No 1232 i 4.4 REMEDIATION SYSTEM STATUS REPORT Due to low concentrations of VOCs observed in the extracted soil vapor during the first and second quarters 2003 quarterly system testing, the oxidizer was operated only 173 hours during the third quarter 2003 However, the air spargmg compressor was operated for approximately 627 hours on a weekly on/off basis ' On September 8, 2003, the oxidizer was restarted to obtain VOC readings from individual vapor extraction wells (using an OVA calibrated to methane) and to collect soil vapor samples for quarterly monitoring The field measurement data are compiled in Tables 5 through 7 Soil vapor samples were obtained from the inlet of the oxidizer while being operated separately on both the Ward and Unocal sites The samples were analyzed for TPH-G using modified EPA Method 8015 and for BTEX and MTBE by EPA Method TO-3 which has a lower detection limit than EPA Method 8260B used in previous tests The TPH-G concentration of 18 ppmv, benzene of 0 016 ppmv, toluene of 0 26 ppmv, ethylbenzene of 0 088 ppmv, and total xylenes of 0 66 ppmv were detected in soil vapor extracted from the Wards site The TPH-G ' concentration of 4 4 ppmv, benzene of 0 014 ppmv, toluene of 0 13 ppmv, ethylbenzene of 0 032 ppmv, and total xylenes of 0 25 ppmv were detected in soil vapor extracted from the Unocal site To assess the effect of biodegradation of chemicals in the subsurface by indigenous microorganism, both samples were tested for the concentration of carbon dioxide The soil vapor samples obtained from the Wards and Unocal sites contained 0 23 % and 1 1 % carbon dioxide, respectively These data indicate biodegradation is still occurring in the subsurface To comply with the condition of the air quality district permit, a sample of combustion gases was obtained and analyzed for benzene by EPA Method TO-3, which resulted in a benzene concentration of 0 017 ppmv ' The analytical data and chain of custody are presented in Appendix C ' Since starting the remedial system, the thermal oxidizer has operated for a total of 6,410 hours and the sparging compressor for approximately 12,690 hours, removing approximately 8,462 pounds of petroleum hydrocarbons from impacted soil and ground water (see Table 7), ' including 6 pounds during the current quarter The amount of biodegraded hydrocarbons is not included in this total and is difficult to calculate eBased on the historical results of operational and analytical data, it appears that further use of vapor extraction is not practical and not economical EAI recommends continued use of the air spargmg system without vapor extraction ' SHM WORD 1232RO351 -6-