SITE INFORMATION AND CORRESPONDENCE

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Shell Oil Products USA Former Station, 1267Country Club Blvd, Stockton. Page 2 of 2 The ground water samples from CPT-1 also had similar concentration trends as the nearby CPT-3; neither had BTEX, both had TPH-d. The main difference is that the 40-foot and 50-foot samples from CPT-3 did not contain detectable concentrations of TPH-g; which may be due to the samples being taken from silt, silty clay and clayey silt lithologies, which are not as likely to be contaminant migration pathways as the sand lithologies sampled in CPT-3. The similarity of the CPT-2 data to the recent data indicates that either the same cross-contamination mechanisms occurred five years apart or that the data is reasonably good. The consistency of the data locally over time and the variations in the data areally indicate to EHD that the data is probably valid. With no appropriate sample blanks to demonstrate problems with the data collected, EHD accepts the data as valid. The data indicates to EHD that the contaminants of concern are most likely present in the three sand intervals and justify requiring further characterization of the ground water potentially migrating in these permeable zones. With significant contaminant concentrations detected in intervals identified as sand by the CPT data from as deep as 95' bsg and at all perimeter points, EHD considers the lateral and vertical extent of petroleum undefined. Therefore in addition to approving installation of a monitoring well in the area of CPT-4 to monitor the sand interval at 40' to 45' bsg, EHD directs you to also monitor the sand intervals generally occurring at 68' to 75' bsg and 91.5' to 97' bsg in the same area (the deepest sand unit appears to be thinner in the CPT-4 area and an intermediate sand interval occurs between 84.5' and 88.5' bsg). Also, EHD commented by letter dated 08 January 2003 on the work plan that provided for these five CPT installations, that EHD had concerns with dissolved metals in the ground water at the area of the former waste oil tank. EHD requested a ground water sample from this area and analyses for nickel, chromium, cadmium, and lead, as well as naphthalene. CPT-6 was installed approximately 40 feet down gradient of the former waste oil tank yet the collected ground water samples were not analyzed for the constituents requested by EHD. This is still an issue that must be addressed before site closure will be considered. Shell is hereby directed to submit a work plan that either proposes installation of multiple- screened or clustered monitoring wells that addresses the three major sand intervals where contamination has been detected. The submitted proposal is to include ground water sampling proposals. The work plan is due by April 30, 2004. Donna Heran, RENS, Director Environmental Hea Division Michael J. Infurna J ., Senior REHS Nuel C. Henderson Jr., RG LOP / Site Mitigation Unit IV LOP / Site Mitigation Unit IV MI/ c: CVRWQCB —James Barton, Sacramento. c: Cambria — Joe Neely, PO Box 259, Sonoma, CA., 95476.