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r <br />.777 <br /> a <br /> FUEL alis 66-11 <br /> 66.2 ENVIRONMENTAL FATE APIA LUOSURE—rAT?UA`_5 <br /> A discussion of the environmental behavior of fuel oil is limited <br /> by cha lack or data defining its maiar components. The environmental <br /> behavior of hydrocarbons selected from the major classes will be <br /> addressed: however. trace elements and the many diverse additives Will <br /> not be specifically addressed. Kany of the hydrocarbons characteristic <br /> of diesel fuel have been addressed previously in the more extensive <br /> environmental fate section of the .!P-4 chanter since these hvdrocarbons <br /> are common to both petroleum :uels. The general discussions of <br /> aliphatic and aromatic hydrocarbons and their behavior in <br /> sail/ground-water systems will not be repeated here; the reader is <br /> referred to the relevcnc sections of Chapter 64. <br /> 66.1.1 Equilibrium Pareitio'_?ng Model <br /> In general. soil/ground-water transport pathways for Lou <br /> concentraeiens of poLlucancs in soil can be assessed by using an <br /> equilibrium oartitioning model. For the purposes of assessing ,he <br /> environmental transport of diesel fuel. a group of specific <br /> hvdrocarbons was selected from the dominant hydrocarbon classes, i.e., <br /> alkanes, cycloaLkanes. and aromatics. there were no available data co <br /> confirm the presence of the selected compounds in a typical diesel fuel <br /> sample. Table 66-3 identifies the selected hydrocarbons and presents <br /> the predicted partitioning of low soil concentrations of those <br /> hydrocarbons among soil particles. soil water. and soil air. The <br /> portions associated with the water and air phases of the sail are <br /> expected co have higher mobility than the adsorbed portion. <br /> Estimates frz the unsaturated topsoil indicate char sorption is <br /> expected to be'.an important process for all the dominant hydrocarbon <br /> czcegor3.;--s. Partitioning co the soil-vapor phase is much less <br /> Cmport'tnc than for ocher petroleum distillates since many oc the Loser <br /> molecular weight aliphac,e hydrocarbons (C,,-C,) characcerired by high <br /> vapor pressure and low water solubility are not expected to be major <br /> components of diesel fuel. The aromatics have slightly higher -water <br /> solubilities and transport with Lnfilcrating water may be more <br /> important for these compounds; volatilisation, on the other hand, is <br /> not expected to be important. In saturated. deep soils (containing no <br /> - soil air and negligible soil organic carbon). a significant wercent of <br /> the aromatic hvdrocarbons is predicted co be present in the soil-water <br /> phase and available for transport 'rich flowing ground water. <br /> Partitioning to Che air and water phases is expected ca be even less <br /> important for the organic components of residual fuel oils compared to <br /> components of dleneL oil; sorption to soil particles is expected to be <br /> significant. <br /> In interpreting these results, is must be remembered that this <br /> model is valid only for low soil concentrations (below aqueous <br /> solubility) of the components. Large releases of diesel fuel (spills, <br /> i leaking underground storage tanks) may exceed the sorpc_re caoacir'r of <br /> the soil. thereby Eilling the pore spy ces of the soil vich the fuel. <br /> E ' <br /> k,+ 6/87 <br />