SITE INFORMATION AND CORRESPONDENCE

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a Overview of Three Sites and Summary of the Basis for Change SWMU 4 The recent investigations identified three sites at DDJC-Tracy It is believed that in the past,rinse water from former depot where more applicable cleanup strategies require changes to operations was discharged to the unlined stormwater the cleanup remedies agreed to in the original ROD: detention pond now known as SWMU 4. These former operations included paint-stripping, degreasing,and steam- 1)Solid Waste Management Unit(SWMU)4 is an unlined cleaning. Chemical contaminants of concern found in the stormwater detention pond. ABaseline Ecological Risk pond sediment include residues from PCBs,pesticides, Assessment(BERA)of conditions at SWMU 4 was conducted selenium, and lead. The pesticides of concern are primarily after the original ROD was published. The BERA provides a from a trio of similarly named compounds called DDD, better understanding of the potential effects of contamination DDE and DDT,and are referred to collectively as DDX. on ecological receptors(such as waterfowl). The ROD amendment proposes that it is not necessary to excavate The original ROD identified the following remedies soil from SWMU 4,because the soils are not as hazardous for SWMU 4: to wildlife as was previously believed. •Continued groundwater monitoring; •Installation of an overflow weir to prevent contaminated 2)The contaminated groundwater beneath DDJC-Tracy is known sediment from being discharged into the pond; as Operable Unit 1 (OU 1). OU 1 also includes groundwater •Excavation of contaminated sediments that pose a risk that is moving in a northeasterly direction away from the depot. to ecological receptors; The cleanup remedy proposed in the original ROD has not •Installation of a sediment trap; and been as effective as anticipated. Although the groundwater • Stormwater monitoring to ensure the overflow weir and treatment plants have been effective in removing hazardous sediment trap are effective. chemicals from the groundwater,the treated(cleaned)ground- water is not being reinjected into the ground as quickly as The sediment excavation portion of the remedy was was expected. The ROD Amendment proposes discharging developed to address concerns about PCBs and DDX, some of the treated groundwater to overland flow disposal which pose a potential threat to ecological receptors plots on the DDJC-Tracy Annex property and,as necessary, (including waterfowl). Excavation was not believed to be to the West Side Irrigation Ditch. necessary to protect human health or water quality. 3)In 1998 and 1999,a new storm drain and catch basin were Sediment excavation standards presented in the ROD were constructed in an area known as Defense Site Environmental developed based on a"screening-level"literature-based Reporting and Tracking System(DSERTS)72. Soil was ecological assessment. This means that the ROD used removed during construction. Analysis of the excavated soil generally available information about the impacts of the showed that chemical contaminants were present in this soil. chemicals of concern,but detailed studies related to specific The soil has since been removed. The ROD amendment conditions at SWMU 4 were not performed. proposes that DSERTS 72 should be added to the list of remedial action sites at DDJC-Tracy,and that institutional After the ROD was published, a more comprehensive and controls should be implemented at DSERTS 72.The site-specific Baseline Ecological Risk Assessment was institutional controls consist of an aggregate cover,and conducted. The BERA evaluated risks to mallard ducks a requirement that the land remain in industrial use.If, and great blue herons potentially exposed to PCBs,DDX, in the future,the site is proposed for non-industrial use, lead,and selenium at SWMU 4. Risks were evaluated using ftuther investigations will be required. In addition,the concentrations that represented central-tendency"average" site will be monitored. exposures as well as maximum concentrations. The BERA found that mallard ducks and great blue herons are not at a The ROD amendment evaluated remedial alternatives that significant risk from exposure to soil sediments. To protect could be used at each of the three sites. These alternatives ecological receptors,it is not necessary to excavate sediment were evaluated against the NCP criteria. Following are to meet lead,selenium,PCB,and DDX standards. details about the evaluation process and the cleanup alternatives recommended at each site. continued on page 7 6