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PUBLIC I'-rEALTH SERVICES <br /> OPO.U,Iry. C <br /> SAN JOAQUIN COUNTY <br /> ENVIRONMENTAL HEALTH DIVISION <br /> Karen Furst, M.D., M.P.H., Health Officer <br /> 304 East Weber Avenue, Third Floor • Stockton, CA 95202 <br /> 209/468-3420 COPY <br /> ED RALSTON <br /> UNOCAL CORPORATION JUL 2 41997 <br /> 2000 CROW CANYON PLACE STE 400 <br /> SAN RAMON CA 94583 <br /> RE: UNOCAL STATION#5886 SITE CODE: 1176 <br /> 2701 MARCH LANE <br /> STOCKTON CA <br /> As a result of reviewing the workplan dated July 14, 1997 submitted by Environmental Resolutions <br /> Incorporated (ERI) on behalf of Tosco Marketing Company (Tosco) San Joaquin County Public Health <br /> Services Environmental Health Division(PHS/EHD)provides the following comments and directives. <br /> PHS/EHD does not concur with several ERI background statements and the workplan submitted fails to <br /> address critical aspects related to current regulations. Groundwater contamination of variable concentration <br /> at different elevations (in shallow and deep wells) at this site suggests hydraulic communication between <br /> the two depths and therefore possible contamination at other intervals. The vertical and lateral extent <br /> (three-dimensional)of hydrocarbon distribution in both soil and groundwater must be addressed in the next <br /> scope of work adhering to the directives provided below. <br /> This letter presents a directive for an immediate full three dimensional definition and investigation of soil <br /> and groundwater contamination of fuel hydrocarbon constituents resulting from the unauthorized release <br /> documented at your site. You are hereby required to complete a Soil and Water Investigation (SWI). This <br /> directive is issued in accordance with California Code of Regulations(CCR), Title 23, Division 3, Chapter <br /> 16, Article 11, Corrective Action Regulations, Chapter 6.7 & 6.75, Article 4, Section 2529937, California <br /> Health and Safety Code, and the Central Valley Regional Water Quality Control Board (CVRWQCB) <br /> Basin Plan. <br /> The results of recent groundwater monitoring indicate the presence of high levels of dissolved MTBE <br /> (20,000 ug/I in MW-3 confirmed by EPA Method 8240). Other fuel additives may also be present in the <br /> subsurface environment at this site. You are requested to analyze all water samples for Methanol, Ethanol, <br /> Tertiary Butanol,MTBE, DIPE, ETBE, and TAME (see CVRWQCB attachment#1)during each sampling <br /> event. <br /> Conventional monitoring well networks currently installed at this.fuel leak site are insufficient to properly <br /> locate and define the extent or existence of MTBE/Additive plumes as evidenced by the vertical and <br /> horizontal variations of contamination observed at this site. MTBE plumes can be non-elliptical., long, <br /> narrow and erratic (meandering). Therefore, PHS/EHD directs you to perform a detailed, expedited <br /> site assessment using depth discrete and continuous core sampling to define and quantify the full <br /> three-dimensional extent of MTBE and other additives,Total Petroleum Hydrocarbons,Benzene and <br /> other contaminants in groundwater. <br /> A Division of San Joaquin County Health Care Services <br />