SITE INFORMATION AND CORRESPONDENCE

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Ms. Mary Meays January 29, 1992 Page 2 • Item 4. The constituent concentration map (Figure 2) in the Third Quarterly Report for 1991 erroneously reported the hydrocarbon concentrations for well E-10. As stated in your January 9 letter, these concentrations should have been 9,400 parts per billion (ppb) TPH-G, 850 ppb benzene, 210 ppb ethylbenzene, 230 ppb toluene, and 1,100 ppb xylenes. • Item 5. As requested, the total depth of the monitoring wells will be included in future quarterly reports. • Item 6. The hydrocarbon concentrations in the indicated wells (E-2, E-10, E-11, E-12, and BHD-1) did indeed increase in the third quarter of 1991, however, the increase was significant only in well E-11. The hydrocarbon concentration in groundwater from three of these five wells has decreased in the fourth quarter of 1991. This indicates that the concentrations are relatively stable and, in general, vary only slightly on a quarter-to-quarter basis. Although the hydrocarbon concentrations vary from quarter to quarter,the long-term beneficial effects of the groundwater extraction system have not yet been determined. At least two more quarters of sampling should be accomplished before trends in the hydrocarbon concentrations can be established. Information on the volume of extracted groundwater discharged to the sanitary sewer is currently included in the monthly status reports for the groundwater extraction system. You receive a copy of this report, therefore, this information will not be included in quarterly reports. • Item 7. Currently, ARCO and Brown and Caldwell receive copies of Chevron's quarterly reports. Chevron continues to receive copies of ARCO quarterly reports. ARCO and Brown and Caldwell plan on attending the January 28, 1992, meeting at the Regional Water Quality Control Board, Central Valley Region. • Item 8. We disagree with the need to install additional monitoring wells at this time for the purpose of resolving the exact location of a "zero" line. We are confident that the "zero" line, as shown on the Fourth Quarter 1991 Report, lies within the capture zone of the pumping well. As stated in Item 6, the hydrocarbon concentrations in the groundwater are relatively stable. Because groundwater remediation is a long-term process, the effect of the groundwater extraction system on the hydrocarbon plume will take several more quarters to assess. We feel confident that the extraction system is having a beneficial effect on the groundwater at this site. • Item 9. An addendum to the Draft Final Remediation Plan (FRP) addressing soil will be submitted by the March 31, 1992, County imposed deadline. If, for any reason, this deadline cannot be met (e.g., if insufficient data has been collected), Brown and Caldwell Consultants 569000RRESA5690-02.Lr1