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ENVIRONMENTAL INVESTIGATION REPORT Unocal Service Station No 5886 2761 West March Lane Stockton California ' Delta Project No D095-066 Page 13 ' 4 7 2 UST Removal On October 24, 1995, ballast water from the three tanks was pumped into two above ground Baker tanks ' for temporary storage Following removal of the tank ballast and the shoring of the tank area, the three USTs were excavated and removed from the site The tanks were transported to the ' H & H Environmental Services facility in San Francisco, California for disposal Work performed during the UST removal was performed according to Delta's Work Plan for Underground Storage Tank Removal dated October 16, 1995 After the tanks were removed, their outer surfaces were inspected for evidence of product leakage, holes, pitting or other areas of weakness Particular attention was paid to seams and points directly below the ' fill ports No holes or areas of weakness In either the diesel or gasoline tanks were observed Water was observed emanating from one rib on tank T2 (Figure 10, Tank Basin Soil Sample Locations) It 1s believed that the water from the rib was associated with a void between the tank and the overlying support rib rather than with a failure of the tank Because the tanks were partially submerged, ground ' water collected in voids between the tank and ribs After the water was drained, a fiberglass patch was placed over the void in the rib prior to transport The location of the tanks is shown on Figure 10 ' 4 7 3 Soil and Ground Water SMlllnl; After the tanks were removed, Tank Excavators collected soil samples from the sidewalis and base of the ' excavation using the excavator bucket Two soil samples were collected from each sidewall and from beneath each of the former tanks To collect soil samples from the sidewalls, one section of shoring was ' removed exposing approximately 18 inches of the sidewall The excavator bucket was used to collect soil from the sidewall at approximately eight feet bsg and approximately one to two feet above ground ' water The soil samples were collected using the methods described in Appendix B Following collection of the sidewall samples, each section of shoring was replaced by the excavator At the request of ' SJCEHD, two soil samples were also collected from beneath each of the 12,000 gallon USTs, one from each end These samples were collected below ground water in native material, approximately two feet below the base of each tank The location of the sidewall and tank samples are shown on Figure 10 ' RPT 160 SJS