SITE INFORMATION AND CORRESPONDENCE

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Site-Wide Comprehensive ROD -7- • 1 May 1997 DDRW Tracy beneficial uses or exceed background concentrations; however, Table 2-1 shows that SWMU l0A has SVOCs which pose a threat to groundwater quality and SWMUs 11, 25, 64, Area 1 Building 236, and the Day Care Center as not analyzed for threats to groundwater. These discrepencies should be clarified. 5. Section 2.3.1: This section should include a statement that all USTs except USTs 8, 21, and 31 are not subject to CERCLA. Text should be included to state that USTs 8, 21, and 31 were addressed under the CERCLA process as SWMUs 64, 6, and 4, respectively, because of the close proximity of these USTs to these SWMU sites where hydrocarbon compounds were identified in soil and/or ground water. USTs which were not maintained under CERCLA should be deleted from Table 2-2 and the others should include a footnote which indicates regulated under both CERCLA and Tri- Regional Guidelines. 6. Section 4.2: The term "potential' should be replaced by"soiUvadose zone." This section should also clarify that the ROD objectives include documenting the selected remedial actions which protect water quality and public health and the environment. 7. Section 4.4: Modify the text to state this ROD "identifies" the sites"selected" for no further action. The text should also clarify that only one additional action for groundwater to address one constituent is selected. Discussions which summarize the scope of problems addressed by each selected remedial action and to identify how each action will address principal threats should be added to the "scope and role" of the response action. 8. Section 5.2.2 (Site Characterization Summaries): The site characterization summaries are inclomplete and the presentation is too complex. All constituents of concern associated with past site activities, and detected at concentrations greater than background in site-soils, should be clearly identified. Text should be included to clarify that a water quality site assessment was conducted followed by a fate and transport analysis to determine which COCs posed a threat to background groundwater quality and beneficial uses. While the RI site diagrams included in the ROD illustrate CoCs and concentrations detected, this information is too complex, leaving the reader to compile information regarding impacts to soil and ground water from site contaminants. These figures can be referred to, if necessary, but for clarity these maps and data should be replaced by text and tables which summarize site-specific information regarding the types, characteristics, and volume of contamination present and impacts to ground water. In many cases, the summary tables present incomplete lists of the CoCs which pose a threat to ground water. Results of the DI-WET sampling and analysis, including general location and depth of samples collected, used as the basis for determining chemicals which pose a threat to water quality should be summarized. Also, more detailed text is necessary regarding VOC contamination for sites where both soil gas and soil samples were analyzed for VOCs. Specifically, the ROD should show VOC mass estimates and clarify that limited data was used in estimating VOC mass at some sites. Further text should describe how comparitive analysis conducted for SWMUI/Area 2 which resulted in similar VOC mass estimates using either soil data or soil-gas data is considered to support remedial alternative decisions. The ROD should clarify the limitations of using only soil data in calculating VOC mass present at the other VOC source areas at DDRW Tracy. Text should state that additional site- specific soil-gas data will be collected and the"trigger" (see general comments #7 & 8) will be