Fate and transport of dissolved monoaromatic hydrocarbons during steady infiltration through unsaturated soil

The concept of biological remediation of gasoline-contaminated groundwater by application to natural soil was investigated in laboratory and field experiments. The purposes were to quantify the processes governing the fate of the aromatic components of gasoline-contaminated groundwater during steady infiltration through natural soil and to identify factors controlling transformation.;Biotransformation of toluene was adequately described by zero order kinetics with respect to toluene concentration and was controlled by oxygen-, nitrogen- or substrate-limited growth. In the A-horizon, total BTEX transformation rates were 6-37 ;A volatile, sorptive and recalcitrant tracer compound (chloroform) was used to differentiate biotransformation from other attenuation mechanisms in the soil. Volatile removal by diffusion out of the soil and into the headspace above the soil column contributed insignificantly to the total mass removal in the laboratory column experiments. In the field experiments, calculations suggested that, volatile removal attributable to this process was responsible for less than 17% of the total mass removal.;When gasoline-contracted water, containing dissolved aromatic hydrocarbons such as benzene, toluene, ethylbenzene and xylenes (BTEX) was applied to soil, a brief adaptation period was observed prior to the onset of measurable BTEX removal. Following the adaptation period, biological oxidation by native microorganisms was found to be rapid and was the primary attenuation mechanism for the aromatic hydrocarbons in the soil. The number and activity of toluene-degrading organisms, and the non-toluene specific viable cell numbers all increased with exposure to toluene.