SITE INFORMATION AND CORRESPONDENCE FILE 2

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C r 1� San Joaquin County DIRECTOR o u gni Donna Heran, REHS oP Environmental Health Department I ASSISTANT DIRECTOR 600 East Main Street Laurie Cotulla,REHS w Stockton, California 95202-3029 PROGRAM COORDINATORS Mike Huggins,REHS,RDI c' P Margaret Lagorio, REHS Website:4 www. jgov.orges / hd Robert McClellon, RENS Phone: (209)468-3420 Jeff Carruesco, REHS,RDI Fax: (209)464-0138 Kasey Foley,REHS July 13, 2009 Mr. Denis L. Brown Shell Oil Products US HSE _ Environmental Services 20945 South Wilmington Avenue Carson, California 90810-1039 Subject: Interstate Shell 620 West Charter Way Stockton, California 95206 The San Joaquin County Environmental Health Department (EHD) has reviewed analytical results from quarterly reports submitted by Conestoga-Rovers and Associates (CRA) on your behalf that included groundwater results from monitoring wells MW-11, MW-13-50, MW-13-77, MW-14-50, MW-14-77, and MW-15-77 installed off-site in February 2008. Although the petroleum hydrocarbon plume appears to be defined north/northeast of the Shell station by groundwater collected from MW-11 and MW-15-77, contaminants of concern have been detected east of the Shell station in groundwater collected from MW-13-50, MW-13-77, and MW-14-77. During the January 2009 sampling event, free product was reported in groundwater at fifty feet below surface grade (bsg) in MW-16-50, and high concentrations of total petroleum hydrocarbon quantified as gasoline (TPHG) and benzene, toluene, ethyl benzene, and total xylenes (BTEX) were reported in groundwater samples collected from MWA 6=90 at ninety feet bsg. The EHD believes a feasibility study/remedial action plan (RAP) is needed to identify a remedial technology, or a combination of technologies, capable of mitigating petroleum hydrocarbon contamination in: • Zone A at approximately twenty to forty feet bsg in MW-8 and MW-9; • Zone Bat approximately forty-five to fifty feet bsg in MW-13, MW-16, and MW-17; • Zone C at approximately seventy-two to seventy-seven feet bsg in MW-14 and MWA6, and at approximately ninety feet bsg in MWA6-90. The RAP should compare various remedial methods to determine the most cost-effective for removing contaminants based on site specific data. Locally, monitored natural attenuation (MNA) may be the preferred technology. Submit the RAP to the EHD by September 29, 2009, and include estimates and calculations for the contaminant masses in groundwater and soil as part of this study.