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j. H, KLEINFELDER & ASSOCIATES Liquid phase movement of the contamination laterally toward B-8 from B--10 below the 30 ft interval appears to have occurred. The lithology of B-10 below 30 feet appears to have changed from a sand at 30 feet to silty sand at 35 feet (boring lags, Appendix C) suggesting the movement of the gasoline's liquid phase may have been impeded downward, allowing it to move laterally back to 3-8. Iso-chem drawings tend to support this interpretation showing a spread of contamination between B--B and B-10 below 30 feet. Migration upwards of the gas phase or lighter constituents can be seen in the iso-chem drawings (Figures 36 through 39) depicting the higher concentration of the lighter constituents (xylene) at the 25 to 30 foot interval while the higher concentration of the heavier fraction (TPH) is situated below 30 feet. A higher concentration of contamination between 5 and 10 feet exists at 8-10 than at B-8, as previously stated. This higher concentration of s contaminant,i may be residual contamination from the point source leak at B-8. j kn overlay of the service station map (Figure 3) with the boring locations y (Figure 2) places B-10 on the edge of the area previously occupied by the underground tanks. A leak from the tanks in the vicinity of B-8 should y largely move downward. due to the high permeability of typical backfill materia]. used around underground storage tanks. while most of the fluids should move downward, some of the fluids leaking, from the tank would t eventually move laterally under capillary forces. This lateral movement ? in the backfill could account for the relatively low concentration of F contamination found between 7 and 10 feet in B-10. As no contamination was found between 10 and 20 feet in B-10, it is assumed that the i f 53-87-443 23 L_�_U