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KEI-P89-1104 .R9 December 17 , 1992 Page 9 The unsaturated zone beneath the site as approximately 58 feet thick and consists predominantly of clayey silt and/or silt, silty clay, sand, salty sand and sandy gravel, in order of decreasing abundance . Mostly silt and sand units characterize the base of the unsaturated zone. The first water bearing unit beneath the site (first aquifer) consists largely of silty sand and sand with slightly lesser amounts of clayey silt and salt. Salty clay, clayey silt and silty sand characterize the units immediately below the water table. DISCUSSION AND RECOMMENDATIONS KEI ' s work plan/proposal (KEI--P89-1104 . P7R) dated October 16 , 1992 , originally contained recommendations for the installation of six on-site exploratory borings (EBI through EB6) However, an additional boring was also installed on the western boundary of the Unocal site (adjacent to the pit excavated for the removal of a concrete underground septic tank that was previously situated in the southwestern corner of the subject site) . EB7 was drilled at an angle of 10 degrees to the vertical , starting on the western boundary of the Unocal site and extending under the adjacent property. The total drilled depth of EB7 was 37 feet below grade, and the true vertical depth of EB7 was 36 . 4 feet below grade. EB7 was drilled to determine whether any contamination from the septic tank located at the Unocal site had impacted the adjacent property. Ground water was not encountered in EB7 The analytical results of the soil samples from the boring of EB7 indicated non-detectable concentrations of TPH as gasoline, TPH as diesel , BTX&E, TOG, and all EPA method 8240 constituents . It therefore appears that the adjacent parcel has not been impacted by contamination from the former septic tank at the Unocal site. The analytical results of the ground water samples collected from the four borings (EB1 through EB4) indicated non-detectable to very low concentrations of TPH as gasoline, TPH as diesel , and benzene, except for the water sample collected from EB1, where TPH as gasoline and benzene were detected at concentrations of 260 ppb and 87 ppb, respectively In the water samples collected from the borings of EB3 and EB4 , the analytical results indicated non- detectable concentrations of TOG and EPA method 8010 constituents, except for the sample collected from EB4 , where relatively minor concentrations of chlorobenzene, 1, 2-dichlorobenzene, and 1 , 2- dachloroethane were detected. It should be noted that these water samples were grab samples that were collected during drilling, and that the analytical results of these samples may not be representa- tive of formation water . In addition, ground water samples collected from the four existing monitoring wells at the site have