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i S E C O R into the 15 ozone wells (SP-1 through SP-15). During the current quarter (December 2, 2004 to March 29, 2005), the OS system was non-operational due to the circuit breaker ripping. On March 29, 2005 it was determined that the breaker was faulty; a new one has been ordered and will be installed during the second quarter 2005. Cumulatively, the OS system has operated for 9,108 hours, and has injected a total of approximately 82 pounds of ozone into the subsurface. Table 1 presents the operating data for the OS system, and includes operating hours and pressure readings. Remediation system field data sheets are included in Attachment 2. Monthly Groundwater Sampling During the first quarter 2005, groundwater samples were collected monthly from wells MW-3 and MW-10 on January 10, February 28, and March 29, 2005, and were analyzed for GRO, BTEX, and MtBE by EPA Method 8260B. Results of monthly groundwater sampling events are summarized in Table 2. Remediation system certified laboratory analytical reports and chain-of-custody documentation for the monthly groundwater monitoring events conducted during the current quarter are provided in Attachment 3. OS System Effectiveness The existing OS well network appears to be successfully remediating hydrocarbons dissolved in the groundwater downgradient of the USTs in the area of well RW-1. Although the system had a low run time this quarter due to pending parts, concentrations ?' of GRO and BTEX have continued to be reported as non-detectable above the laboratory reporting limits in wells MW-3 and MW-10. MtBE concentrations were not detected at or above laboratory reporting limits this quarter in well MW-10, and have decreased from the previous quarter in MW-3 from 9.8 pg/L to 3.2 pg/L. Concentration versus time graphs for dissolved GRO, benzene, and MtBE in wells MW-3 and MW-10 are provided in Figures 2 and 3. SECOR will continue to operate and evaluate the s effectiveness of the OS system during the second quarter 2005. CHARACTERIZATION STATUS Contamination in soil beneath and downgradient of the site has been adequately delineated. Contamination in groundwater, specifically MtBE, has not been delineated to non-detectable concentrations southeast (downgradient) and south (cross- s gradientldowngradient) of wells MW-17 through MWA 9. r WASTE DISPOSAL The volume of purged groundwater generated during the first quarter 2005, and the method of disposal are documented in TRC's Quarterly Monitoring Report, January through March 2005 dated April 15, 2005 (Attachment 1). 1 RECENT SUBMITTALS 1 CORRESPONDENCE The City of Lathrop issued an encroachment permit for the installation of off-site well a MW-23 on February 4, 2005. hConocoPhillipslRetail Sites1111951QSR&QRPS 2005/11195 QSR&QRPS 1 Q05.doc