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EN Mt. • Ms. Margaret Lagorio ' October 14, 2004 Page 3 ' MtBE Concentration MtBE was not detected above laboratory reporting limits in any of the samples. ' Overall concentrations of TPHg and benzene are increasing in zone A and decreasing in zone C. ' Ozone Micros ar e System Description The Ozone system consists of groundwater treatment via C-SpargeTM panels installed at the site. Each C-SpargeTM system includes an ozone generator, air compressor, and a programmable timer/controller. The C-SpargeTm system utilizes ozone microsparging: a process where ozone is entrained in air and introduced into groundwater. The ozone/air mixture is injected at rates of 2-6 cubic feet per minute (cfm) through specially designed sparge points to create "microbubbles." As these microbubbles rise within the column of water, dissolved volatile organic compounds (VOCs) including petroleum hydrocarbons are oxidized. ' The system cycles between 16 micro-sparge points and injects an ozone/air mixture into wells SP-1 A&B, SP-1C, SP-2A, SP-213, SP-3A, SP-313, SP-3C, SP-4A, SP-413, SP-5A, SP-513, SP-5C, SP-6A, SP-613 and SP-6C. Ozone sparge wells are located in the areas of highest dissolved VOC concentrations near the eastern property of the Unocal Site. Each sparge point has a dedicated line and is connected to the system by LDPE tubing. The tubing runs through Schedule 40 polyvinyl chloride (PVC). The system layout is shown in Figure 9. ' Ozone Micros ar e System Operation The schedule is set to cycle through each point 18 times per day, for nine minutes per point per ' cycle. There is an eight-minute rest period between cycles. The programmable timer/controllers are varied during the quarter to provide more treatment to selected areas. ' Ozone Microsparcie System Status System effectiveness is monitored by assessing groundwater analytical data and concentrations of dissolved oxygen (D.O.) from single-completion wells U-3 and U-10 and nested piezometers NP-1 and NP-2 (Figure 2). Wells U-3, U-10, and piezometers NP-1 and NP-2 are within the zone of influence of one or more sparge points. D.O. readings are collected periodically, with ' groundwater samples, from wells U-3, U-10, and piezometers NP-1 and NP-2. Well construction details and D.O. readings are summarized in Table 7 and Table 8, respectively. The microsparge system was operated continuously during the third quarter 2004. ' Effectiveness of Ozone Micros ar e System Monthly groundwater samples are collected from wells U-3, U-10 and peizometers NP-1 and ' NP-2 to further assess the effectiveness of the Ozone Microsparge system. The monthly groundwater samples were submitted to CLS for analyses of BTEX by EPA Method 8021 and TPHg by EPA Method 8015 Modified. Laboratory analytical results with chain-of-custody ' J:lProjects10694o1o187-325TinaRReportsl3rd Qtr 04-QMR RSM0187 3rd Qtr 04-QMR RMA% ' Celebrating 35 Years of Excellence io Environmental Services