title: Small-volume releases of gasoline in the vadose zone: impact of the additives MTBE and ethanol on groundwater quality.
abstract: A controlled gasoline spill experiment was performed under outdoor conditions typical for winter in temperate regions to study the fate of methyl tert-butyl ether (MTBE), ethanol, benzene, and selected other petroleum hydrocarbons. Artificial gasoline containing MTBE and ethanol (5% w/w of each) was placed at a defined depth into a 2.3 m thick unsaturated zone of alluvial sand overlying a gravel aquifer in a lysimeter. During an initial period of 41 days without recharge, MTBE and hydrocarbon vapors migrated by vapor-phase diffusion to groundwater, while ethanol vapors were naturally attenuated. In a subsequent period of 30 days with 5-mm daily recharge, all soluble compounds including ethanol were transported to the groundwater. Ethanol disappeared concomitantly with benzene and all other petroleum hydrocarbons except isooctane from the aerobic groundwater due to biodegradation. MTBE persisted for longer than 6 months at concentrations larger than 125000 microg L(-1). No evidence for MTBE biodegradation was found, whereas > 99.6% of ethanol removal from the lysimeter was due to biodegradation. It is concluded that MTBE-free gasoline would be less harmful for groundwater resources and that ethanol is an acceptable substitute.
authors.affiliation: Swiss Federal Institute of Technology Lausanne (EPFL), ENAC-ISTE-LPE, CH-1015 Lausanne, Switzerland.
authors.forename: Nathalie
authors.initials: N
authors.lastname: Dakhel
authors.forename: Gabriele
authors.initials: G
authors.lastname: Pasteris
authors.forename: David
authors.initials: D
authors.lastname: Werner
authors.forename: Patrick
authors.initials: P
authors.lastname: Höhener
mesh_terms: D001673:Biodegradation, Environmental; D000431:Ethanol / Q000032:analysis*; D005618:Fresh Water / Q000737:chemistry*; D005742:Gasoline / Q000032:analysis*; D008738:Methyl Ethers / Q000032:analysis*; D008962:Models, Theoretical; D012621:Seasons; D013696:Temperature; D014835:Volatilization; D014874:Water Pollutants, Chemical / Q000032:analysis*; D014881:Water Supply / Q000592:standards
chemical_list: D005742:Gasoline; D008738:Methyl Ethers; D014874:Water Pollutants, Chemical; C043243:methyl tert-butyl ether; D000431:Ethanol