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a i i Eraluation of Sail and Graund 11 attr l cbrucuy 19, 1991 Unocal Stati:)n No. 69Sl. Stock'on, California AGS 3SO32-3 ' R i " I approximately 26 feet below surf:�ce i rade r:ay b - laterally cantinuous across the site from borings 13-1 and B-2. The water-bcaring zone consists of a fine-grained,yellowish brown sand. Silt and/or clay was encountered bene;r!: the first encountered water zone,approximately 53 below surface grade. 11te silt and clan appears to extend laterally a,ross the site, forming a possible lower permeability layer beneath the first encountered water tune. This layer was interpreted to be an aqur lard, therefore, the soil borings were terminated before this layer tyas folly penetrated. LABORATORY ANALYSIS Soil samples r:.re submitted for lal�nruturc analysis io evaluate whether asokine h+'drocarbons detected in ,oil samples collected from the base of the tank cavity and product pipeline trenches (15 to 22 feet below grade) had migrated vertically and laterally (Applied Gec'�vstems. 1989). Therefore, to evaluate whedior gasoline hydrocarbons had effected the sol! beneath the base of the tank ca',ity and product pipeline trenches, we submitted the soil samples collected approximately 25 feet below surface grade from each boring for laboratory analysis. To evaluate whether gasoline htidrocarbom were near the top of the ground water, We submitted the soil samples collected ,approximately 45 feet below grade from each boring. :%aditionally, to evaluate the sample with 11he highest PID reading from boring B--t and the sample with the next to the highest PID reading from 13-2, we submitted Tile soil sample collected approxim-ately 35 feet below surface grade. The sample collected at 35 feet from boring B-5 was analyzed to evaluate whether the PID readings were indicating a decrease in hydrocarbons with depth. A,1,11112d 1980SYSZOMS — }Te