SITE INFORMATION AND CORRESPONDENCE 1995-2004

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James L. Tjosvold, P.E. April 22, 1997 Page 3 The Area I soil analytical results from the December, 1996 field work have been incorporated into the VLEACH model (creating additional polygons). Additional sensitivity analysis was performed on the VLEACH and groundwater mixing cell models in preparation of a meeting between PG&E and DTSC to discuss and agree on the final input parameters to be used in the VLEACH and groundwater mixing cell models (these models are being used to help evaluate remedial alternatives in the FS). On March 4, 1997, PG&E submitted a technical memorandum with proposed degradation rates for benzene, naphthalene and chrysene in soil and in groundwater(appropriate degradation rates are to be incorporated into the VLEACH and mixing cell models). The proposed degradation rates were derived from an extensive literature search. In the technical memorandum, it was suggested that two times the longest half-life found in the literature for these chemicals be used in the models (to be conservative). These proposed degradation rates were discussed during a March 7, 1997 telephone conference call between PG&E, DTSC and the RWQCB and during a March 24, 1997 meeting between PG&E and DTSC. At the March 24, 1997 meeting, it was agreed that the longest half-lives found in the literature will be used as the degradation rates for these chemicals. These degradation rates will be incorporated into the VLEACH and groundwater mixing cell models. On March 24, 1997, PG&E and DTSC met to: discuss and agree on the VLEACH model and groundwater mixing cell model input parameters (including chemical degradation rates); to present the results of the VLEACH model after incorporation of the December, 1996 Area I soil analytical results; and to briefly present the proposed soil and groundwater technologies and the remedial alternative selection criteria. At the meeting, DTSC discussed the RWQCB's future role in the project, namely that the RWQCB will not be actively participating in future project meetings and will rely on DTSC to represent its interests. The schedule for completing the FS was discussed, with an emphasis on the short time frame remaining to complete the FS tasks. Because of this, agreement on key items must be reached at every meeting to maintain the current schedule. The input parameters for the VLEACH and groundwater mixing cell models were agreed upon at the meeting, however, in the FS, DTSC wants to see a thorough discussion of these input parameters and the rationale for using them. The latest modeling results predicting the concentrations of benzene, naphthalene and chrysene beneath the site and at the site perimeter were presented at the meeting. Revised initial and secondary screening of soil and groundwater technologies and suggested preliminary remedial alternatives were presented at the meeting. The group was asked to think about their own preferred alternatives prior to the next meeting on April 24-25, 1997. On April 3, 1997, PG&E submitted minutes from the March 24, 1997 meeting and draft Chapters 1-5 for the FS (for DTSC and RWQCB advance review and comment).