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v <br /> 'ENVIJOMEE7�1" EALTH D ISI304E. " tii Floor ENVIRONMENTAL RESOLUTIONi <br /> f Approve <br /> Denied 1] l� iFAxtD cOPq <br /> Conditions Dym cF [OM 2�zC.E,Je-D g.g." August 8,'1997 i <br /> ERI 205503.A02 <br /> Date ( � bq <br /> r. na ow , r. < <br /> Site Mitigation Unit - g��,, � <br /> San Joaquin County Public Health Services 1 ' IV" <br /> Environmental Health Division � o �7 glop nC <br /> 304 East Weber Avenue, Third Floor WWW ; 1F' <br /> Stockton, California 95202 <br /> Subject: Addendum to Work Plan for Supplemental Environmental Investigation at Unocal EJ <br /> Service Station 5886, 2701 March Lane, Stockton, California. <br /> Mr. Rowe: <br /> At the request of Tosco Marketing Company (Tosco), and pursuant to correspondence from San Afn <br /> Joaquin County Public Health Services, Environmental Health Division (PHS/EHD) dated July 24, <br /> 1997, Environmental Resolutions, Inc. (ERI) is submitting this addendum to our work plan (dated <br /> July 14, 1997) for the subject site. The addendum addresses the directive for a full dimensional W ; <br /> definition and investigation of soil and groundwater beneath and in the vicinity of the site and <br /> submittal of a Soil and Water Investigation report. The site is immediately west of Interstate I-5 on " WO, <br /> the northwestern corner of March Lane and the I-5 offramp in Stockton, California, as shown on the <br /> Site Vicinity Map (Plate 1). The locations of existing underground storage tanks (USTs), dispenser <br /> islands, and other selected site features are shown on the Generalized Site Plan (Plate 2). Properties <br /> in the vicinity of the site are generally occupied by commercial developments. <br /> Work outlined in ERI's(Work Plan included: 1) obtaining and reviewing available MTBE data from ,. <br /> previous,investigations; 2).performing two additional groundwater monitoring and sampling events <br /> and,interpreting the data to further evaluate the extent of dissolved MTBE in groundwater and'select <br /> ;additional well locations-(if necessary); 3) drilling three soil borings adjacent to former drains; 4) <br /> obtaining appropriate permit(s) and access agreement(s), drilling off-site soil boring(s); collecting soil <br /> samples; constructing groundwater monitoring well(s); developing and purging the new well(s); <br /> collecting groundwater samples; analyzing selected soil and groundwater samples; and 5) preparing a <br /> report. <br /> The San Joaquin County PHS/EHD response to the work plan requested Tosco complete the <br /> following; 1) perform a detailed site assessment to evaluate the lateral and vertical extent of.MTBE in <br /> groundwater and whether these compounds have migrated off-site and additionally analyze <br /> groundwater samples for the seven oxygenate compounds identified in the California Regional Water <br /> Quality Control Board Central Valley Region (CRWQCB) document dated July 18, 1997; 2) perform <br /> a conduit study and well survey to identify underground facilities that may provide potential <br /> preferential groundwater flow conduits; 3) characterize hydrogeology beneath and in the vicinity of <br /> the site; and 4) identify the source(s) of MTBE detected in groundwater beneath the site and the <br /> approximate timeframe of MTBE/additives release and history. <br /> 74 Digital Drive, Suite 6, Novato, California 94949 415.382-9105 (FAX 415-382-1856) <br /> Lake Forest- • Novato • Seattle <br />