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PUBLIC HIALTH SERVICIS <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 9Cr Qpm <br /> 209/468-3420 JUL 2 3 1999 <br /> KYLE CHRISTIE DON RODGERS <br /> ARCO PRODUCTS COMPANY ROSE V RODGERS CO TR ETAL <br /> PO BOX 5077 1321 S LINCOLN ST <br /> BUENA PARK CA 90662-5077 STOCKTON CA 95206 <br /> RE: ARCO STATION 42168 SITE CODE: 10-46 <br /> 441 W CHARTER WAY <br /> STOCKTON CA <br /> San Joaquin County Public Health Services Environmental Health Division (PHS/EHD) has reviewed the <br /> files including the most recent Quarterly Groundwater Monitoring Report by Emcon for the above <br /> referenced site and provides the following comments and directives. <br /> It is important to note that this site is one of seven sites in the immediate vicinity considered to be <br /> significant contributors to a large undefined commingled soil and groundwater plume. Data from <br /> adjacent sites confirms the presence of fuel hydrocarbon contaminants at depths in excess of 100 feet <br /> below grade surface. <br /> The vertical and lateral extent(three-dimensional)of contaminant distribution in both soil and groundwater <br /> is currently undefined and must be addressed in the next scope of work adhering to the directives provided <br /> below. Reviews of data from early to recent investigations indicate the lack of vertical definition beneath <br /> 40 feet below grade surface (bgs). Borehole and monitor well soil and groundwater dam support the <br /> absence of lateral definition. This letter presents a directive for an immediate full three-dimensional <br /> definition and investigation of soil and groundwater contamination by fuel hydrocarbon constituents <br /> resulting from an unauthorized release documented at your site. <br /> The results of recent groundwater sampling indicate the presence of significant concentrations of dissolved <br /> hydrocarbons (MW-1, 2, 3, 4 and 5 - Benzene; 834, 1,790, 9,820, 6,970 and 438 ugd respectively on <br /> 2/17/99). This observation is made recognizing all monitoring wells screen intervals are now drown by <br /> rising ground water. Groundwater elevations have risen trom approximately 37' to 20' below grade <br /> surface(bgs)since 1995. All monitor wells are screened from approximately 30' to 57' bgs. Proximal and <br /> distal monitor wells clearly indicate the lack of both vertical and lateral contaminant definition.Given these <br /> conditions the installation of additional boreholes and monitor wells on-site and off-site is necessary. <br /> MTBE has been analyzed by EPA Methods 5030/8020 modified and 3260 to date. Both MTBE and DIPE <br /> have been confirmed in groundwater. Raised method reporting limits due to high analyte concentrations <br /> have resulted in sample dilutions for all analyses performed. You are required to analyze all water and <br /> selected soil samples for Tertiary Butanol, MTBE, DIPE. ETBE, and TAME employing EPA Method 31_60 <br /> for all samples until further written notice from this office. <br /> PHS/EHD directs you to perform a detailed, expedited site assessment using depth discrete and <br /> continuous core sampling to define and quantify the full three-dimensional extent of fuel additives, <br /> DMilon of San wqum Counv- ealtb Cam <br />