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Review of the Draft Explanation of Significant Differences <br /> to the Site-Wide Comprehensive Record of Decision <br /> Defense Distribution Depot San Joaquin (DDJC) Tracy Site, <br /> Tracy, California <br /> October 2003 <br /> GENERAL COMMENTS <br /> 1. U.S. EPA concurs with the decision to document changes in cleanup levels and remedies <br /> at Solid Waste Management Units (SWMUs) 6, 8, and 20, and DSERTS 67 in this <br /> Explanation of Significant Differences (ESD) to the Site-Wide Comprehensive Record of <br /> Decision (ROD) for DDJC-Tracy. <br /> 2. The recommended revised cleanup standard for dieldrin at SWMU 6 is 161 micrograms <br /> per kilogram (ug/kg), but it is not clear that this cleanup level will be protective of human <br /> health and the environment. The ROD stated that the Baseline Risk Assessment (BRA) <br /> showed no potential human health or ecological risks for SWMU 6. However, the BRA <br /> was based on a maximum dieldrin concentration of 24.9 ug/kg, well below the 110 ug/kg <br /> industrial preliminary remediation goal (PRG). The new proposed cleanup standard is <br /> greater than the industrial PRG and greater than the maximum concentration used in the <br /> BRA for SWMU 6. Please explain how the new cleanup standard of 161 ug/kg is <br /> protective of human health and the environment. <br /> 3. The Response to Comments on the Draft DDJC-Tracy Post ROD Remedial Action Status <br /> Review for DSERTS 67 and SWMUs 6 and 8, dated August 15, 2003, stated that the <br /> validated data for SWMU 8 will be included as an appendix to this ESD, but there was no <br /> appendix of SWMU 8 data in the Draft ESD. It was agreed at the November 5, 2003 <br /> Remedial Project Managers meeting that the data would be provided as an Addendum to <br /> the ESD as soon as possible, since the data were used as the basis for modeling that <br /> supports the proposed cleanup levels. The validated data for SWMU 8 as Appendix E to <br /> this ESD was provided for review. The review comments on Appendix E were also <br /> included in this review. Please include the data in future versions of the ESD. <br /> 4. The recommendation that land use controls (LUCs) are not necessary for SWMU 8 seems <br /> premature at this time and requires further justification. Considering the size of the <br /> original source area and the wide range of contaminants of concern, it would seem more <br /> prudent to evaluate the groundwater monitoring data collected from wells around the site <br /> for a few more years prior to removing land use controls, especially considering that the <br /> Defense Logistics Agency (DLA) no longer proposes to perform any soil gas sampling <br /> and the extent of contamination was not fully defined during excavation. The maximum <br /> concentrations of DDT and dieldrin left in place were found in sample SS0146-SO-323, <br /> which was a sidewall sample at 7 feet below ground surface (bgs) from the northwestern <br /> portion of the excavation. This allows for considerable uncertainty in determining how <br /> much contamination was left in place. Therefore, LUCs should be recommended for <br /> 1 <br />