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Report on Additional Site Assessment and First Quarter 2000 Groundwater Monitoring 1 7-Eleven Inc Store#17647 1048 W Yosemite Avenue Manteca CA February 22 2000 1 0 INTRODUCTION ' This report is submitted by IT Corporation, Inc to summarize the results of additional site assessment conducted at 7-Eleven Store No 17647, 1048 West Yosemite Avenue, Manteca, California (Figures 1 ' and 2) The scope of work included installing three groundwater moitoring wells and collection of sod and groundwater samples The work was designed to fulfill the requirements of the San Joaquin County Public Health Services Environmental Health Division (SJCEHD) as requested and outlined in IT Corporation's Work Plan For Subsurface Investigation, dated October 26, 1999 The work scope described in this report was completed at the site on December 21, 1999 All work was ' performed in accordance with the work plan,which was approved by the SJCEHD prior to field activities 20 BACKGROUND ' On December 4 , 1998, two 10,000-gallon single-wall steel underground storage tanks (USTs) and one 6,000-gallon single-wall steel UST were removed from the site One soil sample was collected from beneath each end of each UST (for a total of six)from the base of the tank pit excavation at depths of 14 feet below grade Two tank pit sidewall samples were also collected from depths of 6 feet below grade All soil sampling was conducted at the direction of Mr Harlin Knoll of the SJCEHD (IT Corporation, January 1999) ' All soil samples collected during UST removal were analyzed for benzene, toluene, ethylbenzene, total xylenes (BTEX), methyl-tertiary butyl ether(MTBE), and total petroleum hydrocarbons as gasoline ' (TPH-G) by EPA Methods 8020/8015 modified, and for MTBE and other oxygenates by EPA Method 8260 Total lead was analyzed for using EPA method 6010 Benzene was not detected in the soil samples, TPH-G concentrations ranged up to 1,300 milligrams per kilogram (mg/kg) at the base of ' excavation (the sidewall samples were non-detectable) Soil MTBE levels were less than 0 02 mg/kg, and soil lead levels were up to 6 1 mg/kg The SJCEHD requested further assessment upon receipt of tank pit sampling findings Historical soil analytical data are included in Table 1 On June 18, 1999, Five push-probe drilling points were advanced to depths of about 15 feet below grade (IT Corporation, August 1999), at locations adjacent to and farther from the hydrocarbon source area (the USTs/pump islands) 1 Sod samples collected during drilling contained up to 0 026 mg/kg MTBE, and no other detectable constituents, grab groundwater samples contained up to 19,400 micrograms per liter ' (fig/L) TPH-G and 126 pg/L MTBE Historical soil analtyical data are included in Table 1 Site closure was requested in the report of findings submitted to the SJCEHD, subsequent discussions with the agency indicated that groundwater monitoring well installation would be required, and a workplan for Imonitoring well installation was submitted } f 17647SA2 RPT Ili it of I Illi 1 ' Ill II I ! it l Ill '—Ili V V „VI 'I, Il' ` If I Il � Illi I lj ilf IV 1 I`i 1 it II l' 4i I IIVIl