SITE INFORMATION AND CORRESPONDENCE

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Np( San Joaquin County DIRECTOR PQu.±M S REH , Environmental Health Department ASSISTANT Donna Herann, REHS )., —•+ •O ' _ 600 East Main Street Laurie Cotulla,REHS to. Y :� Stockton, California 95202-3029 PROGRAM COORDINATORS Mike Huggins,REHS, RDI Website: www.s ov.or /ehd Margaret Lagorio, REHS �i FORS Robert McClellon, REHS Phone: (209) 468-3420 Jeff Carruesco, REHS, RDI Fax: (209) 464-0138 Kasey Foley, REHS April 28, 2009 Denis Brown Shell Oil Products 20945 South Wilmington Carson, CA 90810-1039 Subject: Shell Service Station Site Code: 1473 2375 Grant Line Road Tracy, CA 95376 The San Joaquin County Environmental Health Department (EHD) has reviewed Subsurface Investigation and Fourth Quarter 2008 Groundwater Monitoring and Remediation Report (Report) dated January 23, 2009, submitted on your behalf by Conestoga Rovers (CRA) and has the following comments. The Report documents installation of two shallow groundwater monitoring wells, MW-9 and MW-10, and one soil boring, SB-2 advanced to investigate the lateral extent of the petroleum hydrocarbon plume in the groundwater at this site. The boring was located just offsite to the northeast; the wells were installed north of the freeway which abuts the northern property boundary of the site. In the Report CRA recommends further assessment of the fuel oxygenate contaminant impact reported in MW-10. In a phone conversation with CRA the EHD discussed the reported findings and recommendations. CRA clarified that it is their intent to conduct the equivalent of a Phase 1 Environmental Investigation to rule out other potential sources for the contamination reported in MW-10. The EHD notes that with methyl tertiary butyl ether (MtBE) concentrations reported in all soil samples collected from the MW-10 boring, and groundwater concentrations higher than they have been onsite for two years, this recommendation is reasonable. Please proceed with conducting the assessment and evaluating the probability that the contamination reported in MW-10 is from this site. CRA also recommended discontinuing monthly batch extraction of groundwater from onsite wells MW-6 and MW-1. These extractions began in the third quarter of 2005 as both a means for remediation and as a mechanism for plume control. Since implementation of the batch extraction, the reported contaminant concentration in the affected wells have decreased to non-detect or below maximum contaminant levels (mcl's). The EHD agrees to cessation of the batch extraction at this time to conduct a rebound analysis. The EHD has discussed the status of this site with a representative of the Regional Water Quality Control Board, Central Valley Region (CVRWQCB) and they agreed that the site may be a candidate for closure, pending evaluation of the analytical results of the new wells and modeling that predicts continued decline in the onsite contaminant concentrations to show that maximum contaminant levels (MCL's) will be obtained in a reasonable time frame.