SITE INFORMATION AND CORRESPONDENCE_FILE 2

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- - Iwo San Joaquin County DIRECTOR Pp Q!N Donna Heran, REHS Environmental Health Department ASSISTANT DIRECTOR 2.' ..'2 600 East Main Street Laurie Cotulla,REHS Stockton, California 95202-3029 PROGRAM COORDINATORS -- - Carl Borgman, REHS C9'••.. . AP Website: wwwsjgov org/ehd Mike Huggins,RENS,RDI �IFORl� rio,REHS Phone: (209) 468-3420 Robert M CeMargaret llon,REHS Fax: (209) 464-0138 Jeff Carruesco,REHS,RDI Kasey Foley,REHS March 9, 2009 Mr. Denis L. Brown Mr. Michael A. Dominquez Shell Oil Products 2494 E. Fremont Street 20945 S Wilmington Stockton, CA 95205 Carson, CA 90810-1039 Subject: Fremont Shell Station Site Code: RO#0251 2494 E. Fremont St. APN: 153-280-08 Stockton, CA 95205 The San Joaquin County Environmental Health Department (EHD) has recently reviewed Updated Corrective Action Plan dated October 10, 2008 submitted by your consultant, Conestoga Rovers &Associates (CRA) and has the following comments. The Corrective Action revision was required in EHD correspondence dated July 23, 2008. In this correspondence the EHD noted multiple concerns and required Shell to address these items in the revision. Of particular concern is the 1,2-dichloroethane (1,2-DCA) concentration in the ground water near the northern dispenser. CRA continues to maintain that the former ARCO site north of the Shell site is the source of this contamination. The EHD commented in the July 23, 2008 letter that the bulk of the 1,2-DCA on the Shell site appears to have originated onsite and is viewed by the EHD to be Shell's responsibility to remediate it or demonstrate convincingly that it is not. Such a demonstration was not included in the revised corrective action plan and no discussion was included that addressed how your chosen remedial alternative, insitu chemical oxidation (ISCO), would react to this contaminant. The EHD considers 1,2-DCA a constituent of concern (COC) for your site and it must be included in the evaluation of any remedial feasibility study. This evaluation must include a discussion of the reaction pathway and daughter products of 1,2-DCA, degradation under ISCO. The EHD did not concur with the technical justification for selecting ISCO over the other remedial alternative evaluated and requested a revision "to present the technical basis on which ISCO was selected with enough detail so that the EHD can properly consider and concur with the selected technology." The technical justification was not included in the revised corrective action plan and must be submitted before the EHD can complete its review. CRA concluded that no additional ground water assessment is necessary at this time: the EHD can agree with this if continued monitoring of the deeper zones during interim remediation indicates that only minor residual mass occurs at depth and can be reduced effectively, and if the ground water samples collected show a decreasing trend of concentrations of the COCs.