SITE INFORMATION AND CORRESPONDENCE 1995-2004

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+L HcAL111 �RIi(CE `Y'7 JUN 25 PM 1: 33 June 20, 1997 CaIUEPA Department of Mr. Robert Doss, P.E. Toxic Substancesproject Manager Pete Wilson Control Pacific Gas & Electric Company Governor 10151 Croydon Way Environmental Services Peter M.Rooney Suite 3 77 Beale Street, Room F-1636 Acting Secretary Sacramento, CA San Francisco, California 94106 for 95827-2106 Environmental DRAFT FEASIBILITY STUDY, PG&E STOCKTON PROJECT Protection Dear Mr. Doss: The Department of Toxic Substances Control (DISC) has received and evaluated the May 1997 revised Draft Feasibility Study (FS) prepared by CH2M-HILL for the PG&E Stockton remediation project. To expedite completion of the FS, submittal of the document was done in parts with part 1 (Chapters 1-5) submitted in early May and part 2 (Chapters 6-9 and Appendices) submitted in late May. DTSC comments concerning Chapters 1-5 were previously discussed with your office and CH2M-HILL by phone and are summarized below. The remaining comments listed below involve Chapters 6-9. A Draft FS was originally submitted November 1995 and DTSC comments were issued December 1995. Additional studies have been conducted to address DTSC comments on the 1995 FS and these results have been incorporated into the subject revised Draft FS. DTSC review of the revised Draft FS has resulted in additional comments to be addressed in the Final FS. The DTSC hereby approves the FS contingent on the following items being adequately addressed in the Final FS: I. The project summary presented in Section 3 should be expanded to discuss the basis for each of the subsequent phases o1 investigation completed rather than simply stating that DTSC required or requested the additional investigations. 2. Figure 3-9, depicts a misleading schematic cross section through source areas 1& 2. The scale provided on this figure seems to define two relatively small groundwater contaminant plumes in Zone A. 3. Several additional phases of investigation and groundwater monitoring events have been conducted since preparation of the Risk Assessment. Therefore, it would be important to update the risk characterization discussion presented in Section 3.2.2.4 to consider new data. Predictions made in Section 3.2.2.3 on the impacts of the new data should be quantified. 4. Specific depths for soil excavation have been determined by modeling to achieve water quality objectives. Concentration data points were extrapolated as shown on figure 6-3 to arrive at the final excavation intervals for each polygon. Although FA.Izw R,<ya d