SITE INFORMATION AND CORRESPONDENCE

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• Lopez Property Page 2 1601 Turnpike Road April 2,2009 Stockton, California 95206 • The 1,2-dichloroethane (1,2-DCA) plume from the Lopez site appears to be commingling with the 1,2-DCA plume from the Comfort Air site at depths of approximately fifty to sixty-five feet bsg. • For the third consecutive quarter, contaminants of concern were not detected in groundwater collected from MW-9, the deepest on-site monitoring well screened between 110 and 120 feet bsg. The EHD concurs that the vertical and lateral extent of petroleum-hydrocarbon-impacted groundwater appears to be defined, except east to southeast of the former USTs at depths of approximately fifty to sixty-five feet bsg. This is evident by the detection of 1,2-DCA at sixty-three to sixty-six feet bsg in soil boring B6; therefore, the EHD recommends that additional monitoring wells be installed east to southeast of B6 and Comfort Air monitoring well MW-5. The wells should be screened within the hydrological unit identified by AGE as HU2 (approximately forty-eight to sixty-eight feet bsg). The EHD will not comment concerning the recommended transfer of Comfort Air monitoring well MW-813 to the responsible party of the Lopez property until information is available from these newly-installed wells. The Central Valley Regional Water Quality Control Board (CVRWQCB) is requiring evaluation of Environmental Screening Levels (ESLs) and California Human Health Screening Levels (CHHSLs) for soil gas published by San Francisco Bay Regional Water Quality Control Board and the potential for vapor intrusion into buildings for closure consideration of sites having residual contamination left in place. Therefore, you are directed to evaluate the potential for vapor intrusion inside the buildings located onsite. Please submit either a work plan to EHD by July 15, 2009, to assess the potential for vapor intrusion into the existing onsite buildings, or a rational, with technical support, for discounting vapor intrusion into the buildings as a potential hazard for this site. AGE has recommended the preparation of a work plan for an ozone bench-scale pilot test to determine if this remedial method is appropriate at this site. The EHD approves the proposal to conduct an ozone bench-scale test to identify and evaluate generation, mobilization, or precipitation of harmful chemical species that could degrade groundwater or aquifer quality as a result of injecting oxidizers into the subsurface. Please submit the work plan to the EHD by June 15, 2009. The EHD believes a feasibility study/remedial action plan (RAP) is needed to identify a remedial technology, or a combination of technologies, capable of mitigating petroleum hydrocarbon contamination beneath the site. The RAP should compare various remedial methods to determine the most cost-effective for removing contaminants based on site specific data. Provide estimates and calculations for the contaminant masses in groundwater and soil as part of this study.