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Chevron U.S.A. <br /> Page 18 <br /> indicated that benzene, toluene and xylenes are sporadically <br /> present in concentrations of 0. 05, 0. 03 and less than 0.01 <br /> ppm, respectively. The reported concentrations are only <br /> slightly over (0.005 to 0. 03 ppm) the minimum detection limit <br /> described for each analysis. It is Dames & Moore's opinion <br /> that these values are inappropriate for reporting on a soil <br /> matrix. Further, the reported concentrations probably <br /> represent vapor-phase product and not residual product. <br /> Total petroleum hydrocarbons referenced to gasoline were <br /> detected at the bottom of the excavation near the south west <br /> (by DI-3) . The absence of benzene, toluene, ethylbenzene and <br /> xylenes suggest that only low mobility, heavier hydrocarbons <br /> iremain. These types of hydrocarbons tend to remain in <br /> residence rather than migrate readily. Further, degradation <br /> of remaining minor concentrations of hydrocarbon may be <br /> anticipated to occur over time by natural biological <br /> processes. <br /> The replacement of the excavated soils as an engineered <br /> fill will likely have the effect of reducing permeabilities <br /> by destroying natural discontinuities (macro-pores) and by <br /> creating a dense (reduced pore-ration) , well graded (fines <br /> with sands) cap. As previously described, the net effect <br /> will be to reduce surface water infiltration; a potential <br /> transport mechanism. <br /> 16000-250-044 <br /> Corrected <br /> D\\IFS S, N100RE <br />