Oxygenated gasoline release in the unsaturated zone - Part 1: Source zone behavior
Juliana G Freitas1, James F Barker
1Department of Earth and Environmental Sciences, University of Waterloo, 200 University Ave. W., Waterloo, Ontario, Canada. jgfreitas@unifesp.br
Journal of Contaminant Hydrology
|November 26, 2011
Summary
Ethanol in gasoline, a common fuel additive, is retained in the unsaturated zone soil, unlike more volatile components. This finding is crucial for understanding subsurface contamination from fuel spills.
Area of Science:
- Environmental Science
- Geochemistry
- Hydrogeology
Background:
- Oxygenates like ethanol and MTBE in gasoline pose subsurface contamination risks due to their solubility.
- Their behavior differs from low-solubility gasoline hydrocarbons, necessitating specific fate studies.
- Understanding their subsurface fate is critical for effective environmental remediation strategies.
Purpose of the Study:
- To evaluate the fate of gasoline containing ethanol and MTBE in the unsaturated zone.
- To assess the retention capacity of the unsaturated zone for ethanol following a spill.
- To inform conceptual models for sites contaminated with ethanol-blended fuels.
Main Methods:
- A controlled field test involving the release of 200L of gasoline with 10% ethanol and 4.5% MTBE.
- Release conducted in the unsaturated zone of a field site at Canadian Forces Base Borden, Ontario.
- Analysis of soil cores to determine the distribution and retention of oxygenates over time.
Main Results:
- Most ethanol was retained in the source zone within the unsaturated soil for over 100 days.
- Ethanol partitioned into pore-water and was retained despite a shallow unsaturated zone.
- MTBE, due to lower solubility, remained primarily within the NAPL as it moved deeper.
Conclusions:
- The unsaturated zone plays a significant role in retaining ethanol from fuel spills.
- Conceptual site models for ethanol-contaminated sites must incorporate unsaturated zone processes.
- Ethanol's retention behavior differs markedly from MTBE and gasoline hydrocarbons.
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