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YENP .. r n 1_3tOBLEM ASS_PSSMENT REPORT Shoil Service Station 7910 Lower Sacramento Road,Stockton,Callrornin i Shell WIC No.2U.7524-08M Delta ProPet Na 40.88-147 Page I1 Laboratory analysis of soil sarnple T-1, collected from 4 feet beneath the south pump island on January 7, 1989,indicated that the TPH concentration was IS ppm, In order to evaluate the vertical extent I'F Of petroleum hydrocarbons at this location, soil boring SB-2 was advanc^•f on August 10, 1989. {" Concentrations of benzene,ethylbenzene,and TPH detected in soil samples collected from SB-2 at depths of I1.5 and 41.5 feet below the surface were below the laboratory analytical method detection limits. Concentrations of toluene and rylenes ranged from less than 0,002 to 0.006 ppm, a Laboratory analyses of soil samples T-5 through T-8, collected from 15 feet beneath the surface in the t bottom of the old storage tank excavation on December 20,1988,indicated that TPH concentrations ranged from 120 to 4,880 ppm, In order to evaluate the vertical CMWlt of petroleum hydrocarbons at this location, I;;+ sail boring SB-3 was advanced on August I.0,1989. Concentrations of BTEX in soil samples collected from SB-3 at depths of 16.5 and 26.5 feet below the surface ranged from 0.003 to 0.047 ppm,and concentrations of TPH ranged from 0.2 to 0.3 $ ppm.. Concentrations of BTF.X and TPF!in soilsamples collected rfrom SB-3 ' at depths of 365,465,and 56.0 feet below the surface were below the laboratory analyticsl method detection 3t !its- Concentrations of total lead in all of the samples collected from SB-3 ranged from,Iess t<'tan 1.0 to r' 1.A 4.0 ppm.. 4.2 accent or Dissolved Constituents In Ground 7Vater In order to determine whether petroleum hydrocarbons were present in ground water beneath the site,three monitoring wells were Listalied on August 11 through 13,1989. Chemical anal yeas of ground water samples �? collected on August 15, I989(Table 5),indicated that benzene concentrations in monitoring wells MW-I; g d 0 03 MW-2 -3 were 0,and MW .6, , and ppb, respectively, Chemical analyses a t-ground water samples collected on.May lI, 1990(Table 5), indicated that benzene concentrations in MW-I,MW-2,and MW-3 were I.1, t03, and 038 ppb, respectively. Monitoring well MW 1 is Iacated upgradient of the farmer ` underground gro gasoline storage tanks. E: f S.0 CG C IJ Q IS - - -'On-October 20;-1990:Delta submitted a-Phase 1 Hydtngeologre Assessment Report That report concluded f that no.furt-iter action was necessary at the site. However, in a letter dated April 10, 1990, the County € responded to the report requiring Shell to prepare and submit a problem assessment report addressing remediation of the soil from the original tank excavation that was placed back into the excavation. -The r following sections address soil remedial action alternatives. ' 1