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S E C O R ranging from 20 to 21 feet bgs. Groundwater was encountered in the well borings during drilling at depths ranging from approximately 8 to 10 feet bgs. All soil samples analyzed were non-detect for all hydrocarbon constituents, except for soil sample MW-16-S9.5, which contained MtBE at a concentration of 0.040 ppm. MtBE was detected in all groundwater samples collected from the newly installed monitoring wells at concentrations ranging from 28 to 3,900 ppb. All other hydrocarbon constituents and fuel oxygenates were non-detect. An ozone sparge unit was placed into operation on December 20, 2002 and injects ozone in to sparge wells SP-1 through SP-15. SENSTIVE RECEPTORS A sensitive receptor survey and a'/-mile radius water well survey were performed by Alisto in 1999. No basements or subways were found within a 300-foot radius of the subject site. An offsite subsurface utility survey revealed the presence of a sanitary sewer trench adjacent to the subject site that may influence the transport of petroleum hydrocarbons in groundwater. A search of California Department of Water Resources (DWR) and Banks Information Solutions files indicated that seven water wells had been installed within a %-mile radius of the subject site, however, the wells could not be located based upon the information provided by DWR. A visual reconnaissance of the area did not identify the presence of any additional water wells(Alisto, 1999). MONITORING AND SAMPLING The site has been monitored and sampled since 4th quarter, 1992. From 1992 to the present the Site has been monitored/sampled quarterly. Currently, 20 wells (MW-1 through MW-6 and MW-8 through MW-21) are monitored and sampled quarterly each year. Samples are analyzed for TPHg, TPHd, BTEX, and fuel oxygenates. Maximum reported concentrations of TPHg and MtBE were 460 ppb and 550 ppb in well MW-14 during the third quarter 2004. Based on the third quarter data, TPHg and MtBE concentrations in groundwater continue to decline in on and off- site. REMEDATION STATUS The ozone injection system consists of a panel mounted KVA C-Sparge"', System that produces 4 grams per hour (0.009 pounds per hour) of ozone. The system injects ozone to fifteen ozone wells: SP-1 through SP-15. The system was placed into operation on December 20, 2002. During the current quarter the system ran for 1,094 hours. System operation data is presented in Table B-1 (Attachment B). The performance of the ozone injection system is evaluated by groundwater sampling. Monthly groundwater samples were collected from monitoring wells MW-3 and MW-10 on July 6, August 9, and September 23, 2004 and analyzed for total petroleum hydrocarbons as gasoline (TPHg), benzene, toluene, ethylbenzene, and total xylenes (BTEX compounds), and methyl tert-butyl ether (MtBE). TPHg and MtBE concentrations in wells MW-3 and MW-10 continue to decline indicating the effectiveness of ozone sparging. Results of monthly groundwater sampling events are summarized in Table B-2. Concentration versus time graphs for dissolved TPHg, benzene, and MtBE in monitoring wells MW-3 and MW-10 are provided in Figures B-1 and B-2. CHARACTERIZATION STATUS Contamination in soil has been adequately delineated. Contamination in groundwater has not been delineated south of well MW-19. }