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f kNJ KLEINFELDER I As noted in the last quarterly report (Fourth Quarter 2003), review of past analytical I` 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 gg/1 to 140 gg/l. The laboratory detection limits during those previous years was 50 gg/l compared with the current detection limit of 5 µg/1. The laboratory chromatograms from 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 gg/1 were present in samples collected from within the Disco footprint as well as downgradient. From the chromatograms reviewed, it appeared that TBA was present in MW-1, MW-2, MW- 9, NPI-70, 80, and 90, and MW-IIs and MW-15 for at least the last three events of 2003, and MW-11d, MW-13, and MW-14d for the third and fourth quarters 2003. Although no detectable concentrations of TBA were noted at or above the laboratory reporting limits this quarter in the downgradient wells, the chromatograms were reviewed to ascertain the presence of TBA in low concentrations. Only MW-12 showed a very low concentration of TBA well below the. laboratory reporting limit. No other low level concentrations of TBA were noted. As evidenced by the known presence of TBA in wells MW-1, NP1-70, 80, and 90; concentrations may still be moving slowly across the site yet undetected in the past by the relatively low concentrations and high reporting limits previously employed. Coupled with the start-up of the ozone/sparge system and lower laboratory reporting limits, TBA may appear to have become mobilized and subsequently detectable. The relative rise in concentrations noted in MW-11s, I Id, 12, 13, 14s, 14d, and 15 I during the fourth quarter 2003 and drop during this quarter, may be directly related to the remediation activities as deeper contamination is lifted into the screened zones of the monitoring wells. The lifting effect and resonation of concentrations may continue until the deep contamination at the source area is significantly mitigated. 3. Kleinfelder recommends that monitoring of the site should be continued in accordance with the "Groundwater Monitoring Frequency Decision Tree" at this time. 4. 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. This report is subject to the limitations found in Chapter 7 of this report. f ; f 12280.MON/ST04R397 Page 12 of 13 ®2004,Kleinfelder,Inc May 11,2004