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I.VT y _ _ Subsurface Investigation December 12, 1990 Former Unocal Station No. 2859, Stockton, California AGS 38012-5 Results indicated benzene, toluene, ethylbenzene, and total xylene isomers (BTEX) concentrations were below 1.0 ppro in soil samples collected from approximately 25 and 30 feet below grade in borings KBI,KB2. BTEX concentrations in soil samples collected from boring KB4 from approximately 15 and 21 feet below grade were also below 1.0 ppm except total xylene isomers in the soil sample collected from 21 feet below grade; the compound was detected at 2,0 ppm. Results of analyses of soil samples collected from borings KB3 and KB5 at approximately 15 feet indicated BTEX concentrations were below 1.0 ppm excep. toluene detected at 1.71 ppm in boring KB5. However, soil samples from approximately 20 feet below grade in those two borings contained BTEX concentrations ranging from 6.58 to 53.15 ppm. Tank Removal f vesti ation A geologist from Applied GeoSystems was at the site in March and April 1988, to observe removal of the underground storage tanks by Unocal's contractor and to collect soil samples from the gasoline and waste-oil tank cavities and product tranches for laboratory analysis (Applied GeoSystems,April 23. 1988). Three soil samples were collected from native soil below each former gasoline takzk at approximately 16 feet below grade(Plate P-2).Results (Table 2)indicated total petroleum hydrocarbons as gasoline(TPHg)concentrations ranged from below 2 to 38 ppm and the concentrations of BTEX compounds ranged from below detection limits to 0.60, 1.31,0.62, and 4.05 ppm,respectively,except in soil sample S-0329- ISTP. This soil sample was collected from the west end of tank T-1 at 16 feet below grade. Results indicated a TPHg concentration of 582 ppm and BTEX concentrations of 0.60,6.50, 10.40 and 39.10 respectively in sample S-0329-ISTP. 4 Ajojol ed IGe0S'VSA9MS