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Report on Additional Site Assessment 1 7-Eleven Inc Store#19976,1399 N Main St Manteca,California March 5,2001 10 INTRODUCTION This report is submitted by IT Corporation to summarize the results of site assessment conducted at the 7-Eleven Inc , Store No 19976, located at 1399 N Main Street,in Manteca, California (Figures 1 through 3/3A) The scope of work for the site assessment included the Installation of eleven soil gas survey points, one vertical delineation boring, and one additional (offsite) groundwater monitoring well, Including soil vapor,soil, and groundwater sample collection The work was completed as outlined in IT Corporation's August 1,2000,workplan prepared as requested and approved by the San Joaquin County Public Health Semces(SJCPHS) The work scope described in this report was completed at the site between September 18, 2000 and January 5,2001 Results indicate that the sod source area is defined at depths of less than 40 feet below grade, and is localized to the immediate tank pit area 20 BACKGROUND Underground storage tank replacement and associated sod sampling activities were conducted in September 1996 Fare underground storage tank pit samples were collected on September 19, 1999, one from beneath each end of the three USTs at 15 feet below grade (except for the north end of the central tank,which was under an excavation stockpile) Sample analysis for benzene,toluene, ethylbenzene, and total xylenes (BTEX), methyl-tert-butyl-ether(MTBE), total petroleum hydrocarbons as gasoline(TPH-G) (EPA methods 8020/modified 8015),total lead (EPA method 6010), and confirmatton sampling for MTBE by EPA method 8260 Indicated the presence of hydrocarbons in levels of up to 0 93 milligrams per kilogram (mglkg) benzene,220 mg/kg TPH-G, and 0 35 mg/kg MTBE(EPA Method 8260) (Table 2) The tank pit was overexcavated slightly to accomodate the new underground storage tanks,which were Installed to the existing tank pit(Figure 2), and samples collected on September 20, 1999, at the lateral and vertical edges of the over-excavation were largely non-detectable (Table 2) 19976 4SA