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EbWt. �� Margaret Lagorio February 17, 2004 Page 2 ' as Figure 4. The groundwater flow direction for zone B was generally northwest with an average hydraulic gradient of approximately 0.001. Groundwater measurements from wells screened in zone C (U-10, U-12, U-15, U-17, U-19, U-21, ' U-23, U-25, U-26, NP-1-111 and NP-2-116) were used to construct the groundwater elevation contour map included as Figure 5. The groundwater flow direction for zone C was generally southwest with an average hydraulic gradient of approximately 0.016. Copies of the groundwater ' sampling information sheets are included as Attachment B. Groundwater Sampling and Analytical Results ' Groundwater samples were collected from site wells between November 25, 2003 through December 21, 2003. Samples were not collected from wells U-20 and U-21 due to cars parked ' over the wells. The groundwater samples were submitted to California Laboratory Services (CLS) in Rancho Cordova, California for analyses of benzene, toluene, ethylbenzene and total xylenes (BTEX) by EPA Method 8021, total petroleum hydrocarbons (TPH) as gasoline by EPA Method 8015 Modified, and fuel oxygenate compounds: methyl tertiary butyl ether (MTBE), tertiary-amyl methyl ether (TAME), tert butanol (TBA), diisopropyl ether (DIPE), and ethyl tertiary butyl ether (ETRE) using EPA Method 8260B. Cumulative groundwater sampling analytical results are summarized in Tables 1 through 6. Dissolved concentrations of benzene, TPHg, and MTBE in groundwater for Fourth Quarter 2003 are presented in Figures 6 through 8. Copies of the groundwater sampling information sheets are included in Attachment B. Laboratory analytical results with chain-of-custody documentation are included in Attachment C. Ozone Micros ar e System Description The Ozone system consists of groundwater treatment via C-SpargeTM panels installed at the i, 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 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-1A, SP-113, SP-2A, SP-213, SP-3A, SP-36, SP-4A, and SP-413). 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 though Schedule 40 PVC. J:1Projects1069401325-01871Final\Reportsl4th Qtr 2003-QMR RSR.doc 35 Years of Excellence in Environmental Services