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San Joaquin County <br /> Environmental Health Department DIRECTOR <br /> M Donna Heran,RENS <br /> 600 East Main Street <br /> PROGRAM COORDINATORS <br /> :X Stockton, California 95202-3029 Robert Mr-Clellon,REDS <br /> _ Jeff Carruesco,RENS, RDI <br /> - �• <br /> cQi ioR��P Website: www.sjgov.org/ehd Kasey Foley,REHS <br /> Phone: (209) 468-3420 <br /> Fax: (209) 464-0138 <br /> September 17, 2010 <br /> Mr. Denis L. Brown <br /> Shell Oil Products US <br /> 20945 South Wilmington Avenue <br /> Carson, CA 90810 <br /> Subject: Former Shell-branded Service Station <br /> 1160 West Yosemite Avenue <br /> Manteca, California 95337 <br /> Dear Mr. Brown: <br /> The San Joaquin County Environmental Health Department (EHD) has reviewed Case <br /> Closure Summary, dated 19 March 2010, prepared by Conestoga-Rovers & Associates (CRA) <br /> on your behalf for the above-referenced subject site, and has discussed the Case Closure <br /> Summary with the California Regional Water Quality Control Board Central Valley Region <br /> (CRWQCBCVR). Not addressed in the Case Closure Summary, is the potential risk posed by <br /> residual contamination by vapor entering nearby buildings. <br /> Although no soil sample data is available from the former underground storage tank (UST) pit, <br /> now under the east building, total petroleum hydrocarbons quantified as gasoline (TPH-g) <br /> were detected at 24 milligrams per kilogram (mg/kg), 290 mg/kg, and 340 mg/kg in soil <br /> samples collected from monitoring well MW-1 at 5.5 feet below surface grade (bsg), 10.5 feet <br /> bsg, and 15.5 feet bsg, respectively. This well is located within twenty-five feet of the west <br /> building. Soil boring GP-1, advanced approximately five feet from MW-1, had TPH-g detected <br /> at 150 mg/kg at 15.5 feet bsg; and soil borings B-2 and B-3, advanced within five feet of the <br /> same building, had TPH-g detected at 220 mg/kg at 15.5 feet bsg, and 1.21 mg/kg at 5.5 feet <br /> bsg, respectively; these data are probably associated with the former dispenser(s). Additional <br /> borings were not advanced west of borings B-2 and B-3 due to the structure of the building <br /> and the congested intersection beyond the building. <br /> In Agency Response and Site Investigation Work Plan, dated 26 October 2006, your <br /> consulting firm, then known as Cambria Environmental Technology, Inc., evaluated the <br /> potential health risk posed by vapor intrusion into buildings at this site. Soil and groundwater <br /> analytical data were compared to residential Environmental Screening Levels (ESLs), <br /> Appendix 1, Table E-1b "Soil Screening Levels for Evaluation of Potential Vapor Intrusion <br /> Concerns," published by the San Francisco Bay Regional Water Quality Control Board <br /> (SFBRWQCB). Although the soil and groundwater concentrations were below the ESLs for <br /> benzene, toluene, ethylbenzene, total xylenes, (BTEX), and methyl tertiary butyl ether (MTBE) <br />