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25 <br /> CUMIN I <br /> J. H. KLEINFELDER &ASSOCIATES <br /> Appendix C). Relatively high permeability coefficients were measured from <br /> the 30 foot interval for B-11, suggesting fluid migration under the <br /> influence of gravity should be greatest downward rather than laterally. <br /> After the supply of contamination was terminated (tank removed), movement <br /> of the liquid phase of the contamination would be vertical, towards the <br /> water table. rockets of gasoline may form as resistance to fluid flow <br /> through the soil increases (clay layers). Migration of tha gas phase also <br /> may encounter resistance formed by lithological or structural traps. <br /> Examination of Figures 36 through 38 indicate two areas of high <br /> concentration of contaminates: the 10-20 foot zone in 2-8, and the 20-30 <br /> foot zone in B-1+1. The iso-chem drawings (Figures 36 through 38) and the <br /> chemical analyses results (Table 2) show higher concentration of the more <br /> volatile components situated at the highest g positions in these two <br /> intervals. This suggests a movement of the lighter gas phase upwards. f <br /> The 10-20 foot contamination zone in B--B appears to be capped by a clayey t <br /> i <br /> silt layer from 4 to 10 feet. This layer would constitute a stratigraphic <br /> 17 trap holding the gas phase of this contamination at 10 feet. Another <br /> explanation for a relatively low concentration of contamination above 10 t . <br /> feet in 2-8 could be due to removal of the contamination.between 0 and 10 ! <br /> j <br /> feet when the tanks were removed. Backfilling with permeable clean soil . <br /> could account for the relatively low levels of contamination between 0 and <br /> 10 feet at B-8. <br /> i <br /> An examination of the iso-chem drawings (Figures 36 through 38) and the <br /> chemical analyses (Table 2) shows differentiation of Lighter.fractions <br /> upward in B-10 for the 20-30 foot:zone similar to the 10-20 foot zone in <br /> fl B-8. Migration of the gas phase in B-10 appears to be impeded by the <br /> decrease in permeability above 25 feet in 8-10. The permeability of the <br /> strata at i0 feet was 1.2 x 10 5 cps and 4.9 x 10-6 cps at 25 feet in <br /> B-11 (Table 8, Appendix B). A comparison of the lithologies between B-10 <br /> and B-11 indicates a similarity in the strata of these two borings. This <br /> would suggest that a decrease in permeability from the 30 foot depth to <br /> the 20 foot depth should be expected in B-10, thus impeding the upward <br /> movement of the phase contamination in B-10. <br /> 53-87-443 �2 <br />