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i <br /> 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 /> { <br /> represent vapor-phase product and not residual product. <br /> Total petroleum hydrocarbons referenced to gasoline were <br /> �Y <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 /> remain. These types of hydrocarbons tend to remain in <br /> iE 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 /> VP7 <br /> The replacement of the excavated soils as an engineered <br /> A fill will likely have the effect of reducing permeabilities <br /> by destroying natural discontinuities (macro-pores) and by <br /> iTs <br /> creating a dense (reduced pore-ration) , well graded (fines <br /> with sands) cap. As <br /> previously described, the net effect <br /> eb <br /> Will be to reduce surface water infiltration; a potential <br /> transport mechanism. <br /> 16000-250-044 <br /> Corrected <br />