Ethanol effects on the fate and transport of gasoline constituents in the UK.

In the UK, use of ethanol in fuel as a fuel oxygenate/fuel supplement is currently limited but could rise in an effort to meet the requirements of the European "Biofuels" Directive. This Energy Institute study focussed on the risk that accidental releases of ethanol blended gasoline (EBG) (i.e. gasoline containing 10% or less of ethanol) could pose to UK groundwater resources. Ethanol is miscible and highly biodegradable. As a result it tends to be strongly attenuated in the unsaturated zone and in groundwater and so does not, in itself, pose a significant risk to groundwater resources. However, it may lead to increased persistence of other gasoline constituents, particularly through alteration of geochemical conditions as a result of intensive biodegradation activity. A semi-probabilistic modelling exercise was undertaken to better understand the risks that use of EBG could pose to UK groundwater resources. Site investigation information from over 500 filling stations was used in combination with GIS data to predict the proportion of potable water supply wells that could potentially be impacted by benzene and MtBE, and estimate the length of benzene and MtBE plumes with and without the use of ethanol in gasoline. The results show that the use of EBG is likely to have a negligible effect on MtBE plumes. Some increase in benzene plume length is predicted, most notably in fissured aquifers, but increases in plume length of greater than 30% are predicted to be rare. A corresponding slight increase in risk to licensed potable water supply wells from benzene was predicted with the use of EBG but the percentage of wells at risk was still predicted to be small (0.13%), and in the context of the conservatism within the modelling, it was concluded that widespread use of EBG is unlikely to cause an increased risk to UK water resources.