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EPA Comments on the <br /> Draft Engineering Technical Memorandum: <br /> Post-ROD Remedial Action Status Review for DSERTS 67 and SWMUs 6 and 8, <br /> Defense Distribution Depot San Joaquin (DDJC) Tracy Site, <br /> Tracy, California,June 2003 <br /> GENERAL COMMENTS <br /> 1. Most of the revised cleanup goals for Solid Waste Management Units (SWMUs)6 and 8 are the <br /> necessity for institutional controls (ICs) such as maintenance of asphalt cover at SWMU 6 depends <br /> on Vadose Zone Modeling performed for the two sites. It was not possible to review the modeling <br /> in detail because only summaries of the modeling have been provided. Please provide full <br /> documentation of the Vadose Zone Modeling, including raw data inputs and model outputs, so that <br /> a more detailed review of the Vadose Zone Modeling can be performed. <br /> 2. Two Vadose Zone Models were used to evaluate the threat to groundwater of residual <br /> contamination at SWMU 6,but only SESOIL was used at SWMU 8. Please explain why <br /> VLEACH was not used to model SWMU 8. <br /> SPECIFIC COMMENTS <br /> 1. DSERTS 67,Action Taken in Response to ROD Requirements,Page 6: The text in the last <br /> paragraph states that the gravel previously installed at DSERTS 67 meets the ESD requirements, <br /> but the basis for this statement is not provided. The aggregate base (AB)cover described in the <br /> ESD and Remedial Action Report includes a geotextile layer, a stabilizing compound("Soil <br /> Sement") and six inches of compacted aggregate. Please describe how the previously installed <br /> layer of gravel is equivalent to the AB cover, including thickness, compaction, and details of the <br /> final construction inspection, if available. <br /> 2. Figure 2,DSERTS 67,DDJC-Tracy: The legend note shows that concentrations in bold exceed <br /> ROD cleanup standards for soil, but the ROD cleanup standards were corrected in the ESD for <br /> DSERTS 67. Please revise the note to state that concentrations in bold exceed ROD Cleanup <br /> Standards for soil as revised in the ESD. <br /> 3. DSERTS 67, Conclusions and Recommendations,Pages 8-9: The recommended ESD <br /> documentation of reduced area covered by material considered protective of human health and the <br /> supplemental institutional controls appear to be appropriate for inclusion in <br />