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PUBLIC HEALTH SERVICES OPO�Iry <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 f <br /> 209/468-3420 <br /> OCT 1011 <br /> BRETT HUNTER PEARL ELAINE MEYER <br /> CHEVRON PRODUCTS USA 1120 S HUNTER <br /> PO BOX 5004 STOCKTON CA 95206 <br /> SAN RAMON CA 94583-0804 <br /> RE: CHEVRON STATION#9-2033 SITE CODE: 1057 <br /> 508 W CHARTER WAY <br /> STOCKTON CA <br /> San Joaquin County Public Health Services Environmental Health Division (PHS/EHD) has reviewed the <br /> 311 Quarter 1997 Groundwater Sampling Report prepared by Blaine Tech Services (BTS) and provides the <br /> following comments and directives. <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. This letter presents a directive for an immediate full three dimensional definition and investigation <br /> of soil and groundwater contamination by fuel hydrocarbon constituents resulting from an unauthorized <br /> release documented at your site. <br /> The results of recent groundwater sampling indicate the presence of increasing concentrations of dissolved <br /> MTBE (MW-1: from 19 ug/I on 5/15/96 to 1300 ug/1 on 8/21/97). This increase in concentration <br /> continues with groundwater elevations rising from 33.60' bgs to 24.58' bgs. All monitor wells are <br /> screened from approximately 50' to 30' bgs. Groundwater has exceeded the screen intervals since 2/27/96. <br /> Given these conditions and potentials for increasing groundwater elevation in 1998 the installation of <br /> additional monitor wells on-site and off-site is necessary. <br /> Other fuel additives may also be present in the subsurface environment at this site. You are required to <br /> analyze all water and selected soil samples for Tertiary Butanol, MTBE, DIPE, ETRE, and TAME <br /> employing EPA 8260(see CVRWQCB attachment#1)for all samples until further written notice from this <br /> office. Selected soil samples shall include at a minimum the historic low and high groundwater elevation <br /> equivalent and the current capillary fringe. Traditional TPH as gasoline and diesel as well as BTEX <br /> analyses are also required. Given the confirmed presence of 1,2-DCA and naphthalene constituents the <br /> responsible party(s) shall continue to analyze samples by EPA Method 8270 and 8260 (both as full scan <br /> reports)on a quarterly basis until further written notice from this office. <br /> Conventional monitoring well networks existing and proposed for this Underground Fuel Tank(UST) leak <br /> site may be insufficient to properly locate and define the extent or existence of MTBE / Fuel Additive / <br /> Chlorinated Solvent plumes as evidenced by the vertical and horizontal variations of contamination <br /> observed at this site. For example, MTBE plumes can be non-elliptical, long, narrow and erratic <br /> (meandering), chlorinated solvent plumes can be unlimited in depth and length. Therefore, PHS/EHD <br /> directs you to perform a detailed,expedited site assessment using depth discrete and continuous core <br /> sampling to define and quantify the full three-dimensional extent of MTBE and other additives,Total <br /> I <br /> A Division of San Joaquin County Health Care Services <br />