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. 10969 Trade Center Drive, Suite 107 <br /> - Rancho Cordova, California 95670 <br /> CORIESTOGA-ROVERS Telephone: (916) 889-8900 Fax: (916) 889-8999 <br /> & ASSOCIATES www. CRAworld .com <br /> April 21, 2015 Reference No. 632277D <br /> Ms. Victoria McCartney, REHS � �� � I � (Cl1 <br /> San Joaquin County Environmental Health Department RECEIVED <br /> 1868 East Hazelton Avenue APR 2 7 2015 <br /> Stockton, California 95205 <br /> ENVIRONMENTAL HEALTH <br />� Re : Site Assessment Work Plan Addendum PERMIT/SERVICES <br /> Former Chevron Service Station 98632 <br /> 575 West Grant Line Road <br /> Tracy, California <br /> LOP Case No . 1408 <br /> Dear Ms, McCartney: <br /> Conestoga-Rovers & Associates (CRA) is submitting this Site Assessment Work Plan Addendum on behalf <br /> of Chevron Environmental Management Company (Chevron) for the site referenced abov Figure 1) . <br /> This work plan was prepared in response to the San Joaquin County Environmental Mai <br /> Department (SJCEHD) letter dated February 19, 2015 (Attachment A), responding to the CRA's Site <br /> Assessment Work Plan dated December 22, 2014. The SJCEHD did not consider the proposed scope of <br /> work (2 soil borings) adequate to characterize the current distribution and concentrations of petroleum <br /> hydrocarbons in shallow soil in orderto meet the State Water Resources Control Board's Low-Threat <br /> Closure Policy ( LTCP) . The SJCEHD indicated that the proposed scope of work should be adequate to <br /> address their following concerns. <br /> 1. - What are the current distribution and representative concentrations of the petroleum <br /> hydrocarbons in shallow soil at this time and can the concentrations pass the LTCP <br /> criterion for direct contact and exposure to outdoor air? <br /> 2. What are the effects and rate of natural attenuation on the concentrations of petroleum <br /> hydrocarbons in shallow soil? <br /> 3. Is there a systematic distribution of contaminants of concern in shallow soil, particularly <br /> along a possible preferential pathway between boring PP-3 and well MW-4, which is <br /> represented by a linear high benzene concentration fairway' trending northeast-southwest <br /> across the site? <br /> CRA has considered SJCEHD's comments, as well as the State Regional Water Quality Board's Five Year <br /> UST Cleanup Fund Summary Report (Attachment A) and proposes to advance three shallow soil borings <br /> ( B-11 B-2 and B-3 ) at the locations shown on Figure 2. The locations of these borings follow the <br /> recommendations presented in February 19, 2015 SJCEHD letter (Attachment A) in order to further <br /> evaluate petroleum hydrocarbons in shallow soil, address the concerns listed above as questions one <br /> and two, and meet the criteria of the LTCP . It is CRA's opinion that if impacted shallow soil immediately <br /> Equal <br /> Employment Opportunity <br /> Employer <br /> Worldwide Engineering, Environmental, Construction, and IT Services <br /> K <br />