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J. H. KLEINFELDER &ASSOCIATES <br /> Point sources have been identified as the cause for contamination of soil <br /> at this site. One point source would be situated approximately Pproximately where <br /> g B-8 is located and the other point source in the vicinity of bgring <br /> B-15. These two point sources were derived after overlaying a plot of <br /> the boring locations (Figure 2) with the site play; for the layout of the <br /> Unocal Service Station previously located at this site (Figure 3), <br /> Correlation of the service station plan with the boring locations places <br /> boring B-8 in the approximate center of the underground fuel storage <br /> tanks, and boring B-15 near the product pump islands. Migration of the <br /> contamination from boring B-8 will be described first, then the migration <br /> from boring B-15, followad by a correlation of the migration from both <br /> sources. <br /> r A liquid phase leak occurring I+ <br /> in the bottom of the fuel storage tank(s) <br /> near boring B-8 would . cause the highest concentration of contamination <br /> near this position. The highest concentration in boring B-8 corresponds, <br /> given the observed migration pattern, to the approximate depth of the <br /> bottom of fuel storage tank(s). Migration of a liquid under the influence' <br /> r; <br /> of gravity to follow the path of least resistance downward, then lateral <br /> migration should be dependent to some degree on the resistance of flow in <br /> i <br /> a vertical direction. Examination of the litholagy in ;:tiring B-8 (Figure <br /> 6, Appendix C) indicates higher. clay content at a depth of 7-20 feet in <br /> boring B-8 and less clay at the same interval in nearby B-lo for the same <br /> i <br /> interval. This decrease in clay content near B--10 may have impeded <br /> movement downward at B-8 allowing the fluid to migrate laterally towardo <br /> B-10. A pattern for the movement of the contamination through the soil <br /> between 7 and 20 feet between B-8 and B-20 is similar to the iso-chem <br /> pattern for. TPli depicted in Figure 36, <br /> Followingthe <br /> path of ,east resistance the contamination would flow <br /> downward. Below the 20 foot interval at B-10, the sediments at this depth <br /> i <br /> are homogeneous and gravity the most influential factor of movement. A <br /> comparison of the lithology (boring logs, Appendix C) below 20 feet (20-30 <br /> foot interval) indicates a similai�ty between B-8 and B-10. Therefore the <br /> movement of the fluid below 20 feet should preferentially be downward. <br /> The 25-30 foot interval is similar in B-8, B-10 and B-11 (boring lora, <br /> 53-87-443 .. 21 <br />