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Evil! MMI- <br /> EL <br /> "l .4TLS 66-13 <br /> In chis situation, the hvdrocarbon m:xcur_ would move as a bulk fluid <br /> and the equilibrium partitioning model would not be applicable. <br /> 66.2.2 Transnorr and Transformation P_acesses <br /> Transport and transformation of individual fuel oil constituents <br /> will depend on the physicochemical (and biological) properties of thm <br /> consticuancs. Some constituents will dissolve more quickly in the <br /> percolating ground waters, be sorbed less strongly on the soils thus <br /> being transported more rapidly, and may be more or less susceptible to <br /> degradation by chemi.:al or biological action. Thus, as was shown in <br /> Figura 65-1, the relative concentrations of the constituents of the <br /> fuel will vary with time and distance from the site of contamination, <br /> This effect is called "Weathering'. (This term is also used to <br /> describes rho changes to oil following spills into surface waters whare <br /> fila spreading and breakup, and differential volatilisation, <br /> dissolution and degradation are all involved.) <br /> Transport processes have been shown to be more significant than <br /> transformation processes in determining the initial face of lower <br /> molecular weight petroleum hydrocarbons released to soil/ground-Vater <br /> systems. However, due to the lower wacer solubilities and lower vapor <br /> pressures of the higher molecular weight hydrocarbons, environmental <br /> transformation processes may be increasingly significant for <br /> hydrocarbons in the Cto-C19 range characteristic of diesel fuel and in <br /> the > Ct9 range expected in residual fuel ails. Spain er al. (184-6) <br /> demonstrated that compounds having up to nine carbons are weathered <br /> almost exclusively by evaporation; larger compounds were weathered by <br /> evapocation and biodegradaticn. <br /> !Under conditions Of limited volatilization (low temperatures, <br /> subsurface release or concentrated spill) ocher transport processes <br /> including downward migration into the soil, sorption to soils, and <br /> transport co ground water may be important. Several authors (1811, <br /> 2243,2252,2329) have reported that oil substances released in <br /> significant quantities to soils result in a separate organic phase <br /> which moves downward through the unsaturated zotiie to the less permeable <br /> layer• the soil/ground-waLz r boundary, where they rend to accu;Mulate <br /> and spread hori=oncally <br /> The organic layer floating an the ground water is carried in the <br /> general direction of ground water flow. At the oil-water interface, <br /> some hydrocarbons are Leached according to their aqueous solubility. <br /> 3s discussed in Chapter 64, the poV.ucion caused by the hvdrocarbon <br /> phase is Bauch less extensive (LOS-LOOS of meters) than pollution caused <br /> by hydrocarbons dissolved in grounri water (100s-LOOOs of meters) <br /> (1811) . Furthermore, the pattern of rtigracion of the hvdrocarbon phase <br /> may be very different From chat ,of the ground water. Due to <br /> fluctuations in ground-wacer elevation over time, the organic Laver cn <br /> top of the aquifer may be transported into several =ones -Here the <br /> components occur in the gaseous phase (able co diffuse in all <br /> directions, including upward), liquid phase (adsorbed onto rock <br /> particles or sealed under lacer) or dissolved/ emulsified in water <br /> (1811.2329). <br /> — 6/67 <br />