SITE INFORMATION AND CORRESPONDENCE

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Mr. Maurice Benson • • February 23, 2010 Page 4 1/Building 237. Analytical soil results indicated that contaminant concentrations were above the hazardous disposal criteria and prompted DESJC to plan future fieldwork efforts to ascertain a better understanding of possible pesticide/herbicide distributions in soil. In October 2009 DESJC initiated additional fieldwork efforts at six locations and planned soil sampling at depths of one, three, and five ft. bgs. Analytical soil data from these six locations reported extremely high concentrations of heptachlor, dieldrin, dichlorodiphenyldichloroethylene (DDE), (-ethane)DDD, dichlorodiphenyltrichloroethane (DDT), a-Chlordane, and g-Chlordane. Sampling results show that at least three of the sampling locations represent areas with waste left in place above unrestricted use levels. The maximum concentration of DDT detected was 1,120 milligrams per kilogram (mg/kg), with dieldrin reporting 5.23 mg/kg. These concentrations represent over 650 and 170 times, respectively, the United States Environmental Protection Agency (U.S. EPA) Region IX residential preliminary remediation goals (PRG) for soil. The report should include a section for pesticide pontamination in soil at the Area 1/Building 237 "pesticide source area" and discuss the current known contaminant distribution with possible recommendations for future remedial efforts to delineate and possibly remove the contaminated soil. 10.) Page 4-5, section 4.4, Natural Attenuation Study: In order for monitored natural attenuation to be considered as a viable component of the pump and treat remedy for the DDJC-Tracy Record of Decision, specific criteria must be met as provided in the United States Air Force MNA Guidance, published in 1995. The first metric that must be met as part of monitored natural attenuation is the evidence that the plume is not migrating under normal conditions (i.e., no pumping conditions). Currently at DDJC-Tracy there are 19 operating extraction wells in optimization configurations to extract and treat contaminated groundwater, but also to create a hydraulic influence to help mitigate and ideally capture contaminant plumes migration due to off-site and normal regional hydraulic influences. The fact that operating extraction wells are responsible for creating a hydraulic influence to counter the regional groundwater flow is one aspect demonstrating why MNA may not be a viable remedy component at DDJC-Tracy. The report should clearly identify the criteria necessary for the demonstration of MNA and also be concise in identifying whether the DDJC- Tracy characteristics or data support MNA. DTSC recommends using the U.S. Air Force MNA guidance from 1995 to assist in identifying the required parameters. 11.) Page 4-9, section 4.5.3.1, COC Mass Removal: According to the report, approximately 1 .4 pounds of VOCs and dieldrin were removed from the liquid granularactivated carbon vessels. The report should present the specific mass removed for each compound, not just the composite total.