SITE INFORMATION AND CORRESPONDENCE FILE 1

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Mr. Paul Supple ARCO Station #2130 - 7906 N . 0 Dorado St., Stockton Page 2 of 2 Missing from the SCM were contaminant mass calculations , cross sections showing well screen intervals and soil and groundwater data, soil lithology, and recommendations for future action . The SCM should provide EHD and your consultant with an overall view of the site to date and should highlight areas where additional work is needed if the model does not support a recommendation for a " No Further Action' (NFA) status. Without recommendations, EHD is unsure of your plans for continuing or modifying the SVE portion of your approved remedial action plan or regarding NFA. With residual contamination above allowable limits in VW-10 area , additional remediation appears to be needed . The only cross section , actually a block diagram (Figure 3), included in the report was too small scale to be helpful . Please provide cross sections at a larger scale , that clearly show areas of petroleum contamination known from all the soil boring data and the soil type and suspected contaminant migration pathways. Also missing from both the SCM and the most recent quarterly report were groundwater analyses for 1 ,2-DCA and methanol and a complete table of soil data from all borings related to this site investigation . Please include the1 , 2-DCA and methanol analyses of all ground water samples in all subsequent quarterly monitoring reports. TPHg , benzene , MtBE, and 1 ,2-DCA soil and groundwater data should be on both iso- concentration maps and cross sections . Enclosed for your reference are the SCM components currently recommended by EHD that the CVRWCB has found to be adequate. After reviewing the document you should forward the missing items to EHD as they are compiled or you may modify your SCM to include the requested information noted in the document. As significant changes in site conditions or remedial actions occur, the SCM should be updated to include these changes . The site conceptual model as presented shows the plume of MtBE-impacted ground water to be distinct from the plume of hydrocarbon- impacted ground water. EHD would like to know your thought on this observation and what the implications are regarding source(s) and future corrective actions. EHD has discussed some minor errors noted in the SCM and quarterly reports with Vern Elarth of URS . Mr. Elarth has assured EHD that the corrected pages will be resubmitted as soon as possible. Thank you for your attention and you may contact Michael Infurna at (209) 468-3454 if you have any questions or wish to discuss the site. Donna Heran, REHS , Director Environmental Health Di ' 'on Michael J . Infurna Jr. , 0enior REMO Nuel C. Henderson Jr. RG LOP / Site Mitigation Unit IV LOP / Site Mitigation Unit IV MI/nh attachment (to URS only) c: CVRWQCB — J. L. Barton , Sacramento. c: SWRCB—CUF — Mark Owens , Sacramento. C: URS Corp. — Vern Elarth 2870 Gateway Oaks Dr, #300, Sacramento, 95833