SITE INFORMATION AND CORRESPONDENCE

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Site-Wide Comprehensive ROD -3- 1 May 1997 DDRW Tracy 5. Incomplete Ground Water Scope: The scope of the ROD is incomplete and unclear with respect to ground water remedial action decisions. The ROD focuses on "dieldrin in ground water" and is inadequate with respect to "all"ground water constituents of concern. The ROD should be modified to include an Operable Unit-1 (OU-1) ground water section (see general comment 41) which identifies all the groundwater CoCs (OU-1 CoCs and the remaining CoCs), including the basis for their identification (e.g., CoCs which have been detected above background concentrations in groundwater) (also see general comment !t6). This part of the ROD should also describe how these CoCs were evaluated for remedial action and present the basis for no further action determinations (e.g., based on infrequent detections, or the technical and economic feasibility to achieve background concentrations and/or protect beneficial uses). The ROD should also clarify whether or not the OU-1 groundwater treatment system will address the groundwater contamination associated with the CoCs. In addition, the remedial decisions of the Operable Unit-I ROD and ESD should be re-affirmed or modified, as appropriate. 6. Chloroform Contamination in Groundwater: As discussed above, the ROD should identify all the groundwater CoCs (OU-1 CoCs and the remaining CoCs) and describe how each was evaluated. Chloroform should be identified as a groundwater CoC. Groundwater data presented in the Annual Groundwater Monitoring Reports for 1994, 1995, and 1996, show that chloroform detected in monitoring wells LM03A and LM30AA is potentially related to SWMU 1 Area 2. Chloroform concentrations in these downgradient two monitoring wells ranged from 2 to 19 ug/1 during 1994 through 1996. The frequency of detections and distribution of chloroform in groundwater suggest that an onsite source area exists which has contaminated a small localized area downgradient of S WMU I Area 2. The ROD should acknowledge the presence of choroform in groundwater and the potential source area(s) for chloroform contamination. The data supports that chloroform contamination in groundwater is limited in nature and extent. Active groundwater remediation for chloroform does not appear to be warranted as long as the suspected source area(s) is investigated and remediated, as necessary. No further action to address chloroform in groundwater should be justified in the ROD. Text should be added to clarify that DDRW Tracy will continue to evaluate chloroform groundwater contamination as part of the Well Monitoring Program. DDRW Tracy should provide concentration trend plots for monitoring wells downgradient of SWMU I Area 2 and plume maps (if additional monitoring wells detect chloroform at similarly elevated concentrations) in future groundwater monitoring reports and also evaluate if chloroform groundwater contamination is remediated by the OU-1 Groundwater Treatment System. In addition, the ROD should clarify that DDRW Tracy will evaluate the presence of chloroform in soil and the potential need for SVE (see general comments # 7 & 8) as part of the remedial design/remedial action for the VOC soil remediation sites, including SWMU 1 Area 2. 7. Narrative Vadose Zone Soil Cleanup Standards: In cases where the selected remedy includes soil vapor extraction, the ROD indicates the selected remedy will continue until the requirements of the narrative cleanup standards are met in the vadose zone. However, the ROD presents inclomplete narrative cleanup standards for these sites. These narrative cleanup standards should be revised to specify the "standard," and how compliance with the standard will be evaluated, using the entire text presented in Section 8.3.0.5 of the RI/FS Report. In cases where the selected remedies include the