Transport of mineral oil components to groundwater—I: Model experiments on the transfer of hydrocarbons from a residual oil zone to trickling water

Abstract

It is well-known that oil spills in soils after some time become immobile. Subsequent rainfall may then leach out water-soluble components, which are carried downward by the rainwater. In laboratory experiments a pack of non-adsorbing glass particles has been used as a soil model to study the transfer of oil components to ground water. Oil was injected into a zone with residual water saturation of this model and allowed to disperse freely. Subsequently water was allowed to trickle through the pack and the drain water, not containing any free oil, analysed for contaminants. Experiments were carried out with a gas oil raffinate containing very small amounts of 2-isopropylphenol as a model for transferable components and with actual mineral oil products: gasoline, kerosine and gas oil. In all the experiments we found evidence that waterextractable components are leached out from an oil zone by trickling water at a rate which is determined by the partition coefficient of the components and by the water/oil ratio. When the glass particles were replaced by natural dune sand the transfer of oil components was delayed by adsorption and their concentration in the drain water decreased correspondingly. Under conditions prevailing in practice these effects of adsorption might be much stronger; in addition, chemical or biological oxidation and evaporation may also to some extent determine the fate of oil in soil. Further work is in progress to assess the effect of adsorption on the transport of watersoluble oil components in packs with compositions closer to those of natural soils.