SITE INFORMATION AND CORRESPONDENCE

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Mr. Marshall Cloud August 6, 2004 Page 2 extent necessary for the AB cover. The results from the data collection effort indicated that a smaller area, approximately 63,500 square feet of AB cap, would be required to protect human health and the environment. The approximate size of the DSERTS 67 was estimated to be 138,000 square feet in the ROD without any survey data. The site was professionally surveyed on May 24, 2003, and indicated a smaller area of 101,200 square feet for DSERTS 67. The survey also showed that 88% of the DSERTS 67 area is covered by structures related to the Operable Unit 1 ground water treatment system, existing asphalt pavement, railroad lines, and by a layer of AB. The remaining 12% of DSERTS 67 is covered by grass and provides protection from dust generation. Revised DSERTS 67 Cleanup Standards The ROD listed the cleanup standards of arsenic and manganese at 48 pg/kg and 1,000 pg/kg, respectively. A check of the data and calculations used to derive the DSERTS 67 ROD cleanup standards showed the exposure point concentrations in mg/kg, not pg/kg as they were intended to be. This oversight resulted in a less conservative cleanup standard for manganese to protect onsite workers. The revised cleanup level for manganese at DSERTS 67 is now documented as 812 mg/kg in both of DDJC- Tracy's Explanation of Significant Differences (ESD). Institutional Controls Institutional Controls that are currently in place at DSERTS 67 are documented in both of the DDJC-Tracy's ESDs, and include the following controls to protect grader operators, onsite workers, and human health and the environment: • Signs to warn grader operators or construction workers that all excavation and construction projects require the approval of the DDJC-Tracy Facilities Engineer and Environmental Management; • Notifications to the regulatory agencies prior to the removal and or modification of the cover, which constitutes disruption of the selected remedy, and follow-up activities to ensure that the controls are fully restored; • Annual Inspections and maintenance of the cover (ESD), to prevent the potential exposure of grader operators or construction workers to elevated concentrations of arsenic and manganese in surface and near-surface soils; and • Land use restrictions to prevent schools, playgrounds, hospitals, or housing from being built until the contaminants of concern are below levels of unrestricted land use.