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l ld). It should be noted TBA was detected in MW-DIS-11s with a concentration of 10 µg/1. This marks the second consecutive time and third time this year TBA has been detected in MW-DIS-1 Is and the first time TBA has been reported above the laboratory reporting limit in MW-DIS-11d, 12, 13, 14s, 14d, and 15. Further detailed review of past results have shown TBA present within the footprint of the Disco site in 1997, 1998, 1999, and 2000. The detections were sporadic and ranged from 21 µg/l to 140 µg/l. The laboratory detection limits during those years was 50 µg11 compared with the current detection limit of 5 µg/l. The laboratory chromatograms for the past four sampling events were reviewed to ascertain whether TBA was present yet below the laboratory reporting limits. It was found that small concentrations of TBA below the reporting limit of 5 µg11 were present in samples collected from within the Disco footprint and downgradient. From the chromatograms reviewed, it appeared that TBA was present in MW-1, MW-2, MW-9, NP1-70, 80, and 90, and MW-I Is and MW-15 for at least the past three events, and MW-11d, MW-13, and MW-14d for the past two events. TBA was present in MW-12 as shown during this past event only. TBA detections during the past three events ranged from 0.14 µgll to 3.93 µg/l. These are below the reporting limit of 5 1Lg11 and were therefore, not reported by the laboratory. As evidenced by the known presence.of TBA in wells MW-1, NPI-70, 80, and 90; concentrations may have been moving slowly across the site (gradient = 0.002 ft/ft) yet undetected in the past by the relatively low concentrations and high reporting limits previously employed. [Coupled with recent the start-up of the ozone/sparge system and lower laboratory reporting limits, TBA may have become mobilized and subsequently detectable.] The relative rise in concentrations noted in MW-I Is, l Id, 12, 13, 14s, 14d, and 15, may be directly related to the remediation activities. Subsequent monitoring will be needed to ascertain the dynamics at work for the remediation system and groundwater flow. 3. The supplemental groundwater samples collected from MW-DIS-I Is and MW-DIS- 14s on October 7, 2003 were analyzed for 1,2-DCA, TBA, and MTBE. The results showed concentrations of 1,2-DCA in both wells of 44 µg/1 and 1.9 µg11 respectively. The results also showed a concentration of MTBE in MW-DIS-14s of 0.65 µg/l. The chromatograms were reviewed for this event. TBA was not reported at or above the laboratory reporting limit and was not noted in the chromatograms. 4. Kleinfelder recommends that monitoring of the site should be continued in accordance with the "Groundwater Monitoring Frequency Decision Tree" at this time. { 5. A copy of this report should be submitted to the San Joaquin County Environmental Health Department and the Central Valley Office of the State of California Regional Water Quality Control Board by Del Monte, Inc. for their review and consideration. I This report is subject to the limitations found in Chapter 7 of this report. 12280.MON 1 ST03RI875 Page 12 of 13 ®2004,Kleinfelder,Inc February 9,2004 KLEINFELDER 2825 East Myrtle Street,Stockton,CA 95205-4794 (209)948-1345 (209)948-0621 fax