SITE INFORMATION AND CORRESPONDENCE

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. MEMORANDUMO CALIFORNIA REGIONAL WATER QUALITY CONTROL BOARD - CENTRAL VALLEY REGION 3443 Routier Road, Suite A Phone: (916) 361-5600 Sacramento, CA 95827-3098 ATSS Phone: 8-495-5600 TO: Wendy L. Cohen FROM: Philip S. Isorena Senior Engineer Associate Engineer DATE: 4 January 1993 SIGNATURE: SUBJECT: RESPONSE TO CO MENTS ON THE ADDITIONAL SITE ASSESSMENT WORK PLAN AND VERTICAL GROUND WATER GRADIENT EVALUATION: SANTA FE PACIFIC PIPELINE PARTNERS (SFPP), STOCKTON FACILITY, SAN JOAQUIN COUNTY I have reviewed SFPP's 17 December 1992 response to our 30 November 1992 comments on the subject documents. My comments follow. Additional Site Aassessment Work Plan My concerns regarding decontamination of the core sampler and duplicate samples have been adequately addressed. However, a revised work plan implementation schedule was not provided. Vertical Ground Water Gradient Evaluation I have attached sections of the two articles from Petroleum Contaminated Soils which I referenced in my 30 November 1992 comments. The correct author of the first article is Bauman instead of Preslo, et. al . This article partly discusses matrix interference in soil sampling. SFPP states that matrix interference does not appear to be evident within soil samples collected at the Stockton facility. As stated in the article, it is not always possible to eliminate matrix interferences, or even recognize when they may be present. The second article is by Preslo, et. al . which is the source of the table attached to my 30 November comments. My interpretation of the table is that it represents a general characterization of how petroleum constituents would behave in the subsur- face. Thus, the table indicates that benzene would be most amenable to a remedia- tion system that includes volatilization. As stated in the article, the results have significant impacts in determining human exposure pathways and remedial actions. I referenced the two articles to emphasize that the absence of contamina- tion in saturated soil samples does not necessarily mean the soil gas and ground water are clean. However, the real reasons for asking SFPP to install in a monitoring well in the next water bearing zone are the ground water monitoring results from ARCO and the wells recently installed by the EMCON Associates for the Stockton Terminals Technical Committee. Although I have not seen the results, which will be available on 10 February 1993, verbal accounts by EMCON indicate that the next water bearing zone has some contamination. Therefore, SFPP needs to ascertain whether there also is contamination in the next water bearing zone beneath SFPP through installation of a well screened in that zone.