SITE INFORMATION AND CORRESPONDENCE_FILE 1

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Chevron Chevron .rr t , X„ f n r” I1 34 January 8, 1996 Chevron Pipe Line Company 4000 Executive Parkway,Suite 400 San Ramon,CA 94583 Ms. Karen W. DiBiasio, Ph.D. P.O.Box 5059 Staff Toxicologist San Ramon,CA 94583-0959 Office of Scientific Affairs D.O.Culbertson California Environmental Protection Agency Site Remediation Specialist Department of Toxic Substances Control (510)842-6930 P.O. Box 806 Sacramento, California 95812-0806 Revised Screening Health Risk Assessment Dividend Property Tracy, California Dear Ms. DiBiasio: Thank you for your November 3, 1995 memorandum (attached) outlining your comments on the September 28, 1995 Revised Screening Health Risk Assessment, Dividend Property, Tracy, California. The revised Screening Health Risk Assessment(HRA) was prepared on behalf of Chevron Pipe Line Company (CPL) and Texaco Trading and Transportation Inc. by Geomatrix Consultants, Inc. The conclusions of your memorandum stated that"the exposures by potential future on-site residents to levels of chemicals currently in soil or groundwater result in risks and hazards less than the acceptable benchmark levels of 1 x 106 and 1 respectively." It was also stated in Comment 2 of your memorandum that the chromatograms presented in the revised Screening HRA should be interpreted "with respect to potential chemicals being detected by the PID in the soil gas survey." For clarification, a formal soil gas survey was not performed. Soil vapor readings were obtained with a photoionization detector(PID) to screen soil samples prior to laboratory analysis. Additionally, the screening of soil with a PID is done as part of general health and safety procedures. In order to interpret chromatograms for specific chemicals, a standard of the compound of interest must be analyzed for comparison. The chromatograms presented in the Screening HRA were of total extractable petroleum hydrocarbons (TEPH as analyzed by EPA Method 8015) quantified against a crude oil standard. However, no specific information on the chemicals present, beyond the general carbon range of compounds, is obtained. As discussed in the revised Screening HRA, there are a number of volatile petroleum and non-petroleum(i.e. degradation products) compounds that could be detected with a PID and show up in the low boiling point range (>C12) of the chromatograms. Thus, any interpretation of the PID readings with respect to the chromatograms and specific constituents is not possible.