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San Joaquin County <br /> Environmental Health Department DIRECTOR <br /> M Donna Heran,REHS <br /> 2 600 East Main Street <br /> c A PROGRAM COORDINATORS <br /> < Stockton, California 95202-3029 Margaret Lagorio, REHS <br /> s -�= Robert McClellon, REHS <br /> !' Jeff Carruesco, REHS,RDI <br /> 0.. FORcj`P Website: www.sjgov.org/ehd Kasey Foley, REHS <br /> Phone: (209) 468-3420 <br /> Fax: (209)464-0138 <br /> 10 December 2009 <br /> Denis L Brown <br /> Shell Oil Products US <br /> 20945 S Wilmington Avenue <br /> Carson, CA 90810 <br /> Subject: Shell Service Station <br /> 2320 N. EI Dorado Street <br /> Stockton, CA 95204 <br /> The San Joaquin County Environmental Health Department (EHD) has received and reviewed <br /> Subsurface Investigation Report, Updated Site Conceptual Model, and First Quarter 2009 <br /> Groundwater Monitoring Report, dated 28 August 2009, prepared by your consultant <br /> Conestoga-Rovers & Associates, Inc. (CRA). For brevity, the whole report will be referred to <br /> herein as the SCM. <br /> Three underground storage tanks (USTs) were removed from the site on July 10, 1990; new <br /> USTs were later installed in a new location. Soil samples collected at the time from the former <br /> UST excavation contained total petroleum hydrocarbons quantified as gasoline (TPHg), <br /> benzene, toluene, ethylbenzene and total xylenes (BTEX) at concentrations as high as 160 <br /> milligrams per Kilogram (mg/Kg) TPHg, 0.013 mg/Kg benzene, 0.432 mg/Kg toluene, 0.735 <br /> mg/Kg ethylbenzene and 6.502 mg/Kg total xylenes. Soil samples collected in the dispenser <br /> island area contained as much as 1,200 mg/Kg TPHg, 0.86 mg/Kg benzene, 27 mg/Kg toluene, <br /> 45 mg/Kg ethylbenzene and 270 mg/Kg total xylenes. It was reported that over-excavation of <br /> the former UST pit removed the known impacted soil in the former UST pit. <br /> Four of eleven shallow soil samples collected along removed piping runs and dispensers were <br /> found to be variously impacted by tetrachloroethane (PCE), 1,1,1-trichlorethene (TCE), and <br /> methylene chloride at concentrations as high as 12 micrograms per Kilogram (Ng/Kg), 13 pg/Kg <br /> and 16 pg/Kg, respectively. <br /> According to the history section in the SCM, Shell installed monitoring wells MW-1, MW-2, <br /> MW-3 and MW-4 in 2003 as part of their voluntary groundwater assessment program; <br /> groundwater impacted by moderate to low concentration of total petroleum hydrocarbons <br /> quantified as gasoline (TPHg), benzene, toluene, ethylbenzene and total xylenes (BTEX) and/or <br /> methyl tert-butyl ether (MTBE) was collected from the wells, although no contaminants were <br /> detected in soil samples collected from the boring for MW-1, the only boring for the first four <br /> monitoring wells so sampled. The site was entered into the Local Oversight Program (LOP) <br /> through the EHD. <br /> As part of ongoing site assessment investigations, an additional four groundwater monitoring <br /> wells were installed on the site up through November 2008; soil samples collected from the <br /> borings for the wells were not found to be impacted by any contaminants of concern (COCs) <br /> except for low concentrations of 1,2-dichloroethane (1,2-DCA), PCE and TCE in the 40-foot soil <br /> SCM, QM, NFAR Comment Letter 1210 <br />