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i Sinto carbon dioxide and water, and any un-reacted ozone will degrade to dissolved oxygen, which is likely to enhance natural biodegradation of residual petroleum hydrocarbons. System Operation Details The C-SpargeTM system was started on December 26, 2002. The C-SpargeTM control panel was programmed and scheduled to inject ozone cyclically into each injection point for 14 minutes. Based on this programming, each injection point will have ozone injection in 18 cycles for 4.2 hours every day. During the first quarter 2004 (between January 2, 2004 and March 24, 2004), a Stratus technician conducted six site visits to collect field parameters and laboratory parameters. The hour meter of the ozone injection system was observed as non-functional during the site visits and will be replaced during the second quarter 2004. Field data sheets presenting field parameters collected between January 2, 2004 and March 24, 2004 are included in Appendix A, and certified analytical reports with chain-of-custody documentation are included in Appendix C. Analytical data were submitted to the State Water Resources Control Board as required by AB2886. The electronic delivery receipt is attached in Appendix C. Ozone Infection Monitoring Plan Monitoring wells MW-3 through MW-10 are used as observation wells to monitor the performance of the 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 the groundwater. During the first quarter 2004, field parameters were collected on a monthly basis and select laboratory parameters were collected on a quarterly basis. During the first quarter 2004 monitoring event, all samples were collected after purging three volumes of well casing. The modified ozone injection monitoring plan is listed below and a summary of frequency and significance of field and laboratory parameters is presented in Table 3. Field Parameters (Monthly): pH, Dissolved Oxygen (DO), and Specific Conductivity Laboratory Parameters (Quarterly): GRO, BTEX, five oxygenates, Chemical Oxygen Demand (COD), Ferrous Iron, Total Iron, and Heterotrophic Plate Count. Laboratory Parameters (Annually): Total Organic Carbon (TOG), Nitrates, Sulfates, Phosphates, and Total Dissolved Solids. Results Results of field and analytical parameters collected to date to evaluate and optimize the performance of the ozone injection system are presented in Tables 4 and 5. The GRO, benzene, and MTBE concentrations observed in all the groundwater monitoring wells during the first quarter 2004 are presented in Figure 4. Change in DO concentrations for select observation and background monitoring wells are presented in Figure 5. The historical GRO, benzene, and MTBE concentration variation over time at select monitoring wells(MW-4 through MW-8) are illustrated graphically in f=igures 6 through 10. GRO concentrations have decreased in the groundwater samples collected from MW-4, MW-5, MW-6, and MW-8 since the previous sampling event (December 10, 2003). The greatest decrease of GRO (from 25,000 µg/L to 5,700 µg/L) was reported in the sample collected from MW-6. However, for analytical results of groundwater samples collected from wells MW-5 and MW-6, the laboratory noted these results were due to a discrete peak at C5, and hence may not be a representative of GRO. These results have been rejected, and the GRO concentrations continue to be lower than the historical high concentrations and appear to be decreasing. PADp-Arco for URS154691Quarter1y\20041Arco 5469rv1Q04.doc 57'RATU5 4