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16 <br /> Margaret Lagorio <br /> ' July 19, 2004 <br /> Page 3 <br /> ' MtBE Concentration <br /> ' • MtBE was not detected in any of the samples above laboratory reporting limits. <br /> Ozone Microsparge System Description <br /> ' The Ozone system consists of groundwater treatment via C-SpargeTM panels installed at the <br /> site. Each C-SpargeTM system includes an ozone generator, air compressor, and a <br /> ' programmable timer/controller. The C-SpargeTM system utilizes ozone microsparging: a <br /> process where ozone is entrained in air and introduced into groundwater. The ozonelair <br /> mixture is injected at rates of 2 - 6 cubic feet per minute through specially designed sparge <br /> points to create "microbubbles." As these microbubbles rise within the column of water, <br /> ' dissolved volatile organic compounds (VOCs) including petroleum hydrocarbons are oxidized. <br /> The system cycles between 16 micro-sparge points and injects an ozone/air mixture into wells <br /> SP-1A&B, SP-1C, SP-2A, SP-213, SP-3A, SP-3B, SP-3C, SP-4A, SP-413, SP-5A, SP-513, SP-5C, <br /> ' SP-6A, SP-613 and SP-6C. Ozone sparge wells are located in the areas of highest dissolved <br /> VOC concentrations near the eastern property of the Unocal Site. Each sparge point has a <br /> dedicated line and is connected to the system by LDPE tubing. The tubing runs through <br /> Schedule 40 PVC. The system layout is shown in Figure 9. <br /> Ozone Microsparge System Operation <br /> The schedule was initially set to cycle through each point 18 times per day, for nine minutes per <br /> point per cycle. There is an eight-minute rest period between cycles. The programmable <br /> time rlcontrollers are varied during the quarter to provide more treatment to selected areas. <br /> Ozone Microsparge System Status <br /> System effectiveness is monitored by assessing groundwater analytical data and concentrations <br /> of dissolved oxygen (D.O.) from single-completion wells U-3 and U-10 and nested piezometers <br /> NP-1 and NP-2 (Figure 2). Wells U-3, U-10, and piezometers NP-1 and NP-2 are within the <br /> zone of influence of one or more sparge points. D.Q. readings are collected monthly, with <br /> groundwater samples, from wells U-3, U-10, and piezometers NP-1 and NP-2. A summary of <br /> D.O. concentration data is presented in Table 4. Well construction details and D.O. readings <br /> are summarized in Table 7 and Table 8, respectively. <br /> Concentrations of TPHg and benzene in wells U-3 and U-10 and piezometers NP-1 and NP-2 <br /> ' are depicted graphically in Attachment D. The ozone microsparge system was repaired and <br /> has been operating continuously during the second quarter 2004. <br /> Effectiveness of Ozone Microsparge System <br /> ' Monthly groundwater samples are collected from wells U-3, U-10 and peizometers NP-1 and <br /> • NP-2 to further assess the effectiveness of the Ozone Microsparge system. The monthly <br /> ' J:Projects10694010187-325\FinallReportsUnd Qtr04-QMR RSR10187 2nd Qtr 04-QMR RSR.doc <br /> Over 30 Years of Exceflence in Environmental Services <br />