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2.3 Summary of Previous Investigations Previous investigations at the site were performed by ERM-West, Inc (ERM-West) of Sacramento, California (August, 1989, March, 1991, and July, 1991) and McLaren/Hart (December, 1992, April, 1993) The majority of this summary is based on information contained in ERM-West's March, 1991 and July, 1991 reports entitled Final Site Assessment Report of Former Underground Storage Tank Sites (ERM-West, Inc , 1991a) and Addendum to Final Site Assessment Report of Former Underground Storage Tank Sites (ERM-West, Inc, 1991b), respectively Section 2 3 1 discusses previous soil investigations at the site and previous groundwater investigations are discussed in Section 2 3 2 231 Soil Investigations In December, 1987 and January, 1988, the underground vault and the three underground storage tanks (Tanks #1, #2, and #3) were removed under the supervision of the Environmental Health Division of the San Joaquin County Public Health Services During the removal of the tanks, it was discovered that Tanks #1 and #2 had leaked to the surrounding soils Reportedly pooled product was discovered at the bottom of the excavation and was removed Approximately 102 cubic yards of fuel-impacted soil were reportedly removed and transported to a waste management facility by Erickson, Inc Soil samples were obtained from two feet below the base of the vault of Tanks #1 and #2, and one foot below the base of Tank #3 prior to backfilling the excavation FIGURE 2-2 presents the location of these soil samples The samples were analyzed for total petroleum hydrocarbons as diesel (TPHd) using EPA Method 8015 Modified (8015M), benzene, toluene, ethylbenzene, and xylene (BTEX) using EPA Method 8020, halogenated volatile organics using EPA Method 8010, and polychlorinated biphenyls (PCBs) using EPA Method 8080 Analytical results from the soil samples indicated TPHd concentrations in the soil up to 6,900 parts per million (ppm), however, halogenated volatile organics, PCBs, and BTEX were not detected in any of the samples A summary of analytical results from these soil samples are presented in TABLE 2-1 In August, 1989, ERM-West, conducted a soil investigation to obtain a preliminary assessment of the vertical and horizontal extent of any impacted soil that may have remained following the removal of the tanks Ten soil borings (13-1 through B-10) were drilled below and adjacent to the former tank/vault area Three borings (B-3, B-6, and B-9) G tiQM17tSANTAFE FNLmm&pW 26 93 2-3 Ch=%Ruk* 1993