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19449 Riverside Drive,Suite 230,Sonoma, California 95476 <br /> CONESTOGA-ROVERS Telephone: 707.935.4850 Facsimile: 707.9356649 <br /> &ASSOCIATES www.CRAworkd.com <br /> July 16,2010 Reference No. 240778 <br /> Ms.Vicki McCartney <br /> San <br /> San Joaquin County Environmental Health Department `�►^{u v <br /> 600 East Main Street <br /> Santa Rosa,California 95202 <br /> Dear Ms. McCartney: ENVIRONMENT <br /> HEALTH <br /> I <br /> �T/SERVICES <br /> jk <br /> Re: Shell-branded Service Station <br /> 620 West Charter Way �0 �•�'r;��tty� !" <br /> Stockton,California V l � :_f <br /> SAP Code 136147 <br /> Incident No. 98996187 <br /> Agency No. 1058124 <br /> Response to May 21,2010 Agency Correspondence-Vapor Intrusion <br /> Conestoga-Rovers&Associates (CRA) prepared this letter on behalf of Equilon Enterprises LLC <br /> dba Shell Oil Products US(Shell) pursuant to the San Joaquin County Environmental Health <br /> Department(SJCEHD) May 21,2010 letter to Shell,and subsequent discussions with SJCEHD <br /> staff. The SJCEHD letter requested that Shell evaluate site-specific data against the <br /> Environmental Screening Levels (ESLs) established by the San Francisco Bay (SFB) Regional <br /> Water Quality Control Board (RWQCB). In effect,Shell was asked to perform a Tier 1 Human <br /> Health Risk Assessment(HHRA),and if the Tier 1 HHRA indicated soil and groundwater <br /> concentrations exceeded the ESLs,Shell was to submit a work plan to evaluate potential vapor <br /> intrusion into onsite buildings. <br /> CRA compared current maximum concentrations of gasoline constituents in groundwater to <br /> ESLs as published in the SFB-RWQCB's Screening for Environmental Concerns at Sites with <br /> Contaminated Soil and Groundwater-Interim Final, November 2007-Revised May 2008 (ESL <br /> Document). CRA also evaluated historic soil concentrations at the site,although no current ESLs�? <br /> exist in the ESL Document for these data. <br /> The table below lists the historical and current maximum concentrations of gasoline <br /> constituents in groundwater beneath the site compared to the ESLs in Table E-1 (attached) of <br /> the ESL Document. Detections in groundwater that exceed these ESLs are in bold. The current <br /> constituents of potential concern (COPC) at this site are total petroleum hydrocarbons as <br /> gasoline (TPHg),benzene,toluene,ethylbenzene,and xylenes (BTEX),methyl tertiary butyl <br /> ether(MTBE),and tertiary butyl alcohol (TBA). <br /> Equal <br /> Employment <br /> Opportunity Employer <br /> Worldwide Engineering,Environmental,Construction,and IT Services <br />