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1 <br /> Report on Additional Site Assessment and First Quarter 2000 Monitoring 1 <br /> 7-Eleven, Inc Store#21756,853 E Yosemite Avenue Manteca CA Februiary 21 2000 <br /> 1 0 INTRODUCTION <br /> 1 This report is submitted by IT Corporation, Inc to summarize the results of site assessment conducted at <br /> 7-Eleven Store No 21756, 853 E Yosemite Avenue, Manteca, California (Figures 1 and 2) The scope <br /> 1 of work Included Installation of three groundwater monitoring wells and collection of soil and groundwater <br /> samples The work was designed to fulfill the requirements of the San Joaquin County Environmental <br /> Health Department (SJCEHD) as outlined in IT Corporation's October 27, 1999, Workplan for Additional <br /> Site Assessment <br /> 1 <br /> 20 BACKGROUND <br /> On December 9, 1998, three 10,000-gallon steel single-wall underground storage tanks (USTs) were <br /> removed from the site (IT Corporation, January 1999) Six soil samples were obtained from the base of <br /> ' the UST pit, and two soil samples were obtained from beneath the pump islands and associated fuel <br /> dispensing piping Tank pit soil samples were collected from about 14 feet below grade, pump-island- <br /> area samples were obtained from depths of about 4 feet below grade <br /> All soil samples were analyzed for benzene, toluene, ethyl-benzene, xylenes (BTEX), total petroleum <br /> ' hydrocarbons as gasoline (TPH-G), and total petroleum hydrocarbons as diesel (TPH-D) by EPA <br /> Methods 8015/8020 Methyl-tert-butyl ether(MTBE) and other oxygenates were analyzed for using EPA <br /> 1 Method 8260 <br /> None of the soil samples contained detectable levels of BTEX, TPH-G or TPH-D, soil MTBE levels <br /> ' ranged up to 0 18 milligrams per kilogram (mglkg), in the northwest comer of the UST pit at a depth of <br /> i <br /> about 14 feet below grade <br /> Initial site assessment was conducted in June 1999 (IT Corporation, 1999) and consisted of the <br /> installation of five push-probe borings to total depths of up to 25 feet below grade (Figure 2) Soil <br /> 1 samples collected during drilling contained up to 0 167 mg/kg MTBE, and no detectable benzene or <br /> TPH-G Grab groundwater samples collected at the base of the borings contained up to 607 <br /> ' micrograms per liter(Ng/L) benzene, 32,300 pg/L TPH-G, and 46,300 pg1L MTBE (the highest <br /> concentrations were observed in boring GP-3, located near the western end of the former dispenser <br /> ' island location) <br /> i <br /> f <br /> 1 <br />