SITE INFORMATION AND CORRESPONDENCE_FILE 2

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Former Exxon Service Station No. 73942 Page 3 of 4 4444 North Pershing Avenue December 23, 2014 Stockton, California 95207 3. The EHD and Regional Board conclusions that the lateral and vertical extents of impacted media were not fully assessed. EHD presented site cross sections that included soil lithology, well screen lengths and associated petroleum hydrocarbon contaminant concentrations to illustrate the current known vertical and lateral extent of highly-impacted petroleum hydrocarbon contamination at the source area and concluded that the groundwater contaminant plume has not been delineated vertically at the former underground storage tank (UST) area or laterally north of the source area; the EHD has suggested that a monitoring well be installed north of the site to complete the lateral assessment of impacted groundwater in that direction; 4. Steps to move the site to case closure. If active remediation is not an option, the most likely pathway to closure is to demonstrate that the site meets the criteria for the Low- threat Closure Policy (LTCP) enacted by the State Water Resources Control Board; one criterion of the LTCP is delineation of the soil and groundwater plume. Cardno stated that the plume is stable and the site is close to meeting the LTCP criteria; the EHD noted that the risk to exposure and direct contact still must be addressed; 5. Cardno discussed the technical challenges associated with mitigating the site that included: • Contaminated soil that lies beneath approximately twenty-five feet of groundwater; • Soil composition that is primarily fine-grained and tends to retain the contaminants of concern; and • Injection of any remedial compound will take the path of least resistance through the small sand units and not through the fine-grained soil. Cardno, ExxonMobil and the EHD generally agreed to the following action items: 1. Cardno and the EHD will try to meet with the Regional Board to discuss the NOI requirements for injecting PersulfOx; 2. A well will be installed north of the source area to define the soil and groundwater plume towards the north; 3. The vertical extent of petroleum hydrocarbon contamination in the source area will be assessed; and 4. The goal of all present was to move the site to closure as expeditiously as possible. The EHD preference is to implement an active remediation technology to reduce the contaminant mass and concentrations to reduce the time required for methods such as natural attenuation to achieve cleanup goals; but Cardno and ExxonMobil can try to make the case for site closure as a low-risk site or under the LTCP. The EHD notes at this time that if Cardno and ExxonMobil desire to purst case closure under the LTCP or as a low-risk site, then it must be shown that the site will achieve water quality goals