SITE INFORMATION AND CORRESPONDENCE_1993-2003

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Draft Soils FS Memorandum -4- 14 September 1993 - DDRW, Sharpe pesticides, PCBs, and total petroleum hydrocarbons (TPHs). General and specific guidance on the DLM in addition to detailed comments (21 September 1992) were presented in our review of the July 1992 Work Plan Addendum. Except for trichloroethene (TCE), the Draft FS does not address cleanup levels in relation to the DLM. An environmental fate (Water Quality Site Assessment) analysis for each contaminant of concern must be performed to determine whether a waste will impact ground water, the DLM may be used if appropriate. In addition, our 21 September 1992 review of the July 1992 Work Plan raises many of the same issues expressed in our Comments on the February 1992 Draft Soils FS. Despite a commitment to do so, the FS fails to use the existing data to its fullest capacity to address our previous comments. lc. Comment 8 refers to the cleanup level for TCE. This cleanup level was reevaluated and has been proposed to be set at 50 µg/kg. Lower cleanup levels (5 µg/kg) have been established at Sacramento Army Depot. The cleanup levels for TCE remediation in the vadose zone should consider the performance of the remedial action (i.e.. vapor extraction system - VES) and the remediation goal should be non-detect. The cleanup levels should be evaluated at an appropriate time, such as when consideration is being given to shutting down the VES system. The Draft Soils FS expresses reservations about the performance of in-situ vapor extraction at low concentrations and that such performance is being evaluated. These issues must be resolved in the Draft Final FS. 1d. Comment 9 refers to the areas of TCE contaminated soil identified for remedial action. Figure 4. 1-1 identifies the areas of TCE contaminated soil that require remediation. The Draft FS does not adequately identify the criteria for requiring soil remediation, and the technical basis for selecting only four areas for soil remediation. In addition, Figures 1.3-15 and Figure 1.3-16 show high concentrations of TCE (3,191 parts per billion or ppb) in soil gas samples along Columns Q and U in the Central Area. The Draft Soils FS does not indicate why this area is not recommended for remediation. The soil gas data suggests that a source area for ground water Plumes 4 and 5 originates in this area. The Draft Soils FS does not identify sites recommended for remediation as source areas for ground water contamination. The FS should identify source areas for each TCE ground water plume at Sharpe, and propose appropriate remediation. Without source removal, the ground water cannot be effectively cleaned up since source removal also prevents further impacts and degradation to ground water quality. te. Comment I I refers to Federal and State ARARs. A table identifying ARARs for each remedial alternative should be prepared. The latest format for presenting ARARs was developed for the DDRW, Tracy Operable Unit No. I (OU-1) Record of Decision (ROD), August 1993. The OU-1 ROD ARAR table prepared for DDRW. Tracy is provided as an attachment. Preparation of an ARAR table is necessary for the ROD to identify all ARARs. It appears that several State ARARs identified in Comment 11 still have not been identified (TPCA for sump at Bldg. S-119, and Chapter 16 of the CCR).