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1 Fourth Quarter 2002 Monitoring and Sampling Report 2 7-Eleven, Inc Store#21756, 853 E Yosemite Avenue, Manteca, CA December 10, 2002 ' All soil samples were analyzed for BTEX, TPH-G, and total petroleum hydrocarbons as diesel (TPH-D) by EPA Methods 8015/8020 The samples were also analyzed for MTBE and other oxygenates using EPA ' Method 8260 None of the soil samples contained detectable levels of BTEX, TPH-G, or TPH-D, soil MTBE levels ranged up to 0 18 milligrams per kilogram (mglkg), with highest levels found in the northwest corner of the UST pit at a depth of about 14 feet bg Initial site assessment was conducted in June 1999 (IT Corporation, 1999) and consisted of the installation of five push-probe borings to total depths of up to 25 feet bg Soil samples collected during drilling contained up to 0 167 mg/kg MTBE, and no detectable benzene or TPH-G Grab groundwater samples collected at the base of the borings contained up to 607 micrograms per liter(ug/L) benzene, 32,200 ug/L TPH-G, and 46,300 ug/L MTBE The highest dissolved concentrations in the grab water ' samples were observed in boring GP-3, located near the western end of the former dispenser island location ' On December 20, 1999, three groundwater monitoring wells (MW-1 to MW-3)were installed to depths of 25 feet bg, and screened from 10 to 25 feet bg (IT Corporation, February 2000) Soil samples were collected from each borehole from depths of 5 feet bg to total depth Soil benzene and TPH-G were not detected Soil MTBE was found only in one location (GP-4) at a concentration of 0 167 mg/kg Groundwater analytical data indicated dissolved concentrations ranged up to 0 32 ug/L benzene, 55 ug/L ' TPH-G, 230 ug1L MTBE, and 3,710 ug/L TBA The reported TBA detection in well MW-1 may be anomalous, as TBA has not been detected during subsequent quarterly sampling events ' A workplan for additional site assessment and feasibility testing (IT Corporation, October 2001)was reviewed and approved by the San Joaquin County Public Health Services/Environmental Health ' Department(SJCEHD) On April 1-3, 2002, monitoring well MW-4 was installed to 30 feet bg and screened from 15 to 30 feet bg (Shaw, August 2002) Dual-nested sparge/vent wells (SPV-1 and SPV-2) were also installed during the same field event to 29 feet bg The wells are screened from 24 to 29 feet bg ' (sparge segment) and 12 to 22 feet bg (vent segment) A Geoprobe soil boring (GP-6)was also advanced to a depth of 40 feet bg to obtain vertical plume delineation data Soil samples collected from GP-6 and MW-4 were non-detectable for BTEX, TPH-G, and MTBE/oxygenates A Simulprobe grab ' groundwater sample from GP-6 was also non-detectable for all analytes ,1