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San Joaquin.County <br /> Environmental Health Department <br /> DIRECTOR <br /> Q••"'• •"• C` <br /> GOQ East Main Street Donna Heran, REHS <br /> Stockton, California 95202-3029 .PROGRAM COORDINATORS <br /> + ' s Robert McClellon, REHS <br /> :�. Jeff Carruesco,REHS, RDI <br /> �;F Q• �,� Website: www-sjgov org/ehd Kasey Foley,REHS <br /> Phone: f209) 468-3420 Linda Turkafte,REHS <br /> Fax: (209) 464-0138 . <br /> February 16;2011. <br /> Mr. Sergio Morescalchi Ms. Shelby Lathop <br /> Atlantic Richfield Company ConocoPhillips Company <br /> Post Office Box 1257 .76 Broadway <br /> San Ramon, California 94583 Sacramento, California 95818 <br /> Subject: 76 Service Station No. 11193 <br /> 3202 West Hammer Lane <br /> Stockton, California <br /> The San Joaquin County Environmental'Health Department (EHD)'has received and reviewed <br /> Semiannual Groundwater Monitoring and Quarterly Remediation Progress Report, Fourth <br /> Quarter 2090 (report), dated27 January 2011, prepared and submitted by your consultant, <br /> Stantec Consulting Corporation (Stantec), on your behalf for the above-referenced site. In the <br /> report, Stantec stated that the ozone sparge (OS) system had been shutdown on 25 October <br /> 2010 in response to the letter dated 15 October 2010 from the EHD recommending the <br /> suspension of the ozone injection system followed by rebound testing. Stantec. also <br /> recommended that the groundwater be'sampled quarterly through the.'fourth quarter 2011, <br /> ;f noting that if there were no substantial rebound of concentrations of petroleum hydrocarbon <br /> contaminants in groundwater, that Stantec would then request site closure. <br /> The EHD concurs with Stantec's recommendation to sample the groundwater quarterly <br /> f through the fourth quarter 2011; however, instead of sampling all of the Wells quarterly, the <br /> EHD recommends that only wells MW-1R, MW-2R, MW-3, MW-5 through MW77, MW-9, <br /> MW-11, MW-13, and VW-1 be sampled quarterly and the sampling of MW-4, MW-8; and <br /> MW-10 be suspended based on historical groundwater analytical data. The EHD also <br /> recommends that groundwater samples be analyzed only for gasoline range organics (GRO); <br /> " diesel range organics (DRO); benzene, toluene, ethylbenzene, and total xylenes (BTEX); <br /> 3 <br /> methyl tertiary-butyl ether (MTBE); and tertiary butyl alcohol (TBA). Historical groundwater. <br /> i analytical data indicate that the other petroleum hydrocarbon constituents [di-isopropyl ether <br /> (DIPE), ethyl tertiary-butyl ether (ETBE), tertiary-amyl methyl ether (TAME), ethanol, 1,2- <br /> dichloroethane (1,2-DCA), and 1,2-dibromoethan (EDB)] either have not been detected or <br /> have been detected at.such very low concentrations in groundwater-as to warrant omission <br /> from the analytical list of compounds. <br /> 4 . <br /> If groundwater analytical results indicate that there is minimal .rebound following the <br /> termination of the ozone system, prior to submitting a closure summary report, the EHD" <br /> directs that a human health risk assessment. be performed. Residual contaminant <br /> concentrations should be compared.to Environmental Screening Levels (ESLs) established by <br /> �l <br />