Abstract
Lysimeter experiments were conducted to compare the vapour phase transport of 20 % ethanol- and butanol-blended gasoline (E20 and B20) compounds in soils using the unblended gasoline (UG) compounds as the standard. Sand containing approximately 0 and 5 % organic matter (0 %fom and 5 %fom) was used to simulate the vadose zone. The 5 %fom soil promoted higher vapour phase transport of compounds than the 0 %fom soil due to its higher porosity, hence, was used to compare the transport to the groundwater zone of the different gasoline blends. The addition of 20 % alcohol by volume to gasoline reduced the retentive capability of the soil for gasoline compound vapours and thus resulted in greater downward transport and higher accumulation of gasoline compounds in the groundwater zone. The transport of gasoline compounds from the vadose zone to the groundwater zone was found to be in the order of E20 > B20 > UG, indicating that the risk of groundwater contamination with gasoline compounds after a spill or leak is more likely to be greater for ethanol-blended gasoline compared with butanol-blended gasoline.
Highlights
Alcohol-blended gasoline is widely used as fuel and its release into the environment is likely
Soil gas samples were extracted from SP3–SP7 and SP8 and analysed for background concentrations of gasoline compounds
After contamination, the source zone (SP3) was sampled and analysed, and the concentration obtained was used as the initial concentration of gasoline compounds
Summary
Alcohol-blended gasoline is widely used as fuel and its release into the environment is likely. When released to the soil, either from leaks or spills, gasoline migrates downward in the vadose zone due to gravity. This is accompanied to some extent by lateral spreading due to the effect of capillary forces and medium spatial variability, with a fraction of it being retained in the pore spaces due to interfacial forces. This creates a residual saturation of gasoline that generally occupies 1–7 % of the pore space in the vadose zone [14, 19].
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