SITE INFORMATION AND CORRESPONDENCE

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MEMORANDUM To: Magaret Lagorio, Supervising REHS CC: NA From: Ron Rowe, Sr.REHS,Unit IV, LOP/Site Mitigation San Joaquin County Public Health Services Environmental Health Division (PHS/EHD) Date: Tuesday,November 24, 1998 Subject: Chevron Site#9-6258, 2409 Main St., Stockton Margaret, A review of the LOP files for the above referenced site has been completed in response to the attached letter from Chevron. I refer you and Chevron to OEHHA's PHG's (Public Health Goals) for MtBE in Drinking Water April 1998. In this document the use history of MtBE is revealed and known from 1970 to date in California. Other blending agents and additives were also common during this period (Pb, DCA, EDB, & many Alcohols). Two agencies including California's legislative body and our CVRWQCB require oxygenated fuel analyses at UST sites. Chevron's request is lacking sufficient justification as it relates to omitting the oxygenates required by these agencies and ours. Testing for MtBE by EPA Method 8020 will not suffice, presence or absence in preliminary assessments does not allow this agency to conclude that other components do not exist at this site, or off-site. It is my understanding that EPA Method 8260 is required to maintain consistency at all UST sites currently under investigation. As can be observed, preliminary assessment work at this site confirms the presence of significant vertical distribution of fuel hydrocarbons. Water is currently at 58' bgs and is impacted by fuel hydrocarbons (TPH-g 32,000 ug/1). I would suggest that the vertical distribution is likely to be greater than 58' bgs with the knowledge of Stocktons ever increasing rising groundwater phenomena. Mr. Hunter state's "The fate and transport characteristics of a weathered gasoline plume without oxygenates are well understood and a limited migration distance can be assumed." I could not disagree more. Generalization such as this clearly fails to consider the complexity of the site specific hydrogeologic setting, nearby pumping influences, depth to water fluctuations, the mass of the release and the like. I would suggest they evaluate the complexity and size of the 1970's Del Monte site which has reported detections of TBA and MtBE directly beneath the release and Benzene 700 feet down gradient and confirmed by several QME's at 153' bgs in a short screened well although water is currently 50' bgs. Cross sections are needed to visualize contaminant fate and transport regardless of the contaminants of concern (ie-benzene, MtBE). The efficient utilization of staff time is already strained by incomplete data set review. Spending considerable time to look at numerous non-continuous core borehole logs which at best represent only 30% of the subsurface to make in house conclusions regarding fate and transport conditions is in my opinion an unnecessary and hazardous activity which should be the responsibility of the RG/CEG/PE or ultimately the RP(three 6" sleeves at the bottom of any five foot section of borehole, 18" out of 60" = 30%). We are likely to make significant errors while simultaneously loosing valuable time needed for other sites. I believe that the better we define sites the more likely we are to close sites with greater confidence,particularly in an era of limited remediation efforts. Keep in mind that Chevron demolished this site in the 70's and has provided the owner with a written record of such including the off-haul of building materials as the service station building and contents. The reality of the matter is the demo report was falsified, we attempted to install boreholes at this site and several times met refusal with a hollow stem auger only to discover they had back filled the tank pit with