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During second quarter 2003 (between March 24, 2003 and June 9, 2003), Stratus technician conducted seven site visits to troubleshoot the ozone injection system and collect field parameters and laboratory parameters. Field data sheets presenting field parameters collected between March 24, 2003 and June 9, 2003 are included in Appendix A, and certified analytical reports with chain-of-custody documentation are included in Appendix C. The C-SpargeTM system was non-operational between March 12, 2003 and April 3, 2003, and was restarted on April 3, 2003 after replacing a timer contact. In addition, other minor malfunctions (program controller) happened during second quarter 2003, resulting in relatively low uptime. Stratus also observed additional minor malfunctions during the second quarter 2003. Therefore the operational uptime period for C-SpargeTM system during second quarter 2003 was low. Stratus repaired the C-SpargeTM system program controller on June 26, 2003, and anticipates a higher operational uptime for the C-Sparge M system. Ozone infection Monitoring Plan Monitoring wells MW-3 through MW-10 are used as observation wells to monitor the performance of ozone injection system. Monitoring wells MW-1 and MW-2 are used as background wells to evaluate and monitor for natural geo-chemical changes in groundwater. The following field and laboratory parameters will be monitored periodically to evaluate and optimize the performance of the ozone injection system. Field Parameters (Bi-monthly): pH, Dissolved Oxygen (DO), and Specific Conductivity Laboratory Parameters (Quarterly): TPHG, BTEX, Chemical Oxygen Demand (COD), Ferrous Iron, Total Organic Carbon (TOC), DO, and Oxidation Reduction Potential (ORP) During second quarter 2003, field parameters were collected on a bi-monthly basis and laboratory parameters were collected on a quarterly basis. Table 3 presents the sampling frequency, field and laboratory parameters analyzed, and significance of both laboratory & field parameters. During the second quarter 2003 monitoring event, all samples were collected after purging three volumes of well casing. Results Results of field and analytical parameters collected to date to evaluate and optimize the performance of ozone injection system are presented in Tables 4 and 5. Due to low operational uptime of the C-SpargeTM system, no significant changes in DO levels and/or in petroleum hydrocarbon concentrations were observed during the second quarter 2003. The average DO levels at observation wells MW-7 and MW-9, both located approximately 15 feet from injection point IW-5, continue to be higher in comparison to the DO levels at background wells MW-1 and MW-2 (see Figure 4). Concentrations of petroleum hydrocarbons and/or fuel oxygenates appear to have increased at wells MW-4 through MW-8 in comparison to the concentrations observed during the previous quarter analytical data. The historical TPHG, benzene, and MTBE concentration variation over time for these monitoring wells are presented in Figures 5 through 9. This increasing trend or re-bounce in petroleum hydrocarbon concentrations in comparison to the first quarter 2002 can be attributed to low operational uptime of C-SpargeTM system and an increase in groundwater elevations. During the second quarter 2003, TPHG, benzene, and MTBE were detected in groundwater samples collected from wells MW-4, MW-8, and MW-10. The highest TPHG, benzene and MTBE concentrations • were observed in groundwater samples collected from MW-8 at 29,000 µg/L, 6,000 µg/L, and 33,000 µg/L. MTBE, was also detected in groundwater samples collected from wells MW-1, MW-3 through I P:IBp-Arco for URS154691Quarterly12003L9rco 5469_2QR3.doe Or;ZArU5