Seeking the Impact of Ethanol in Gasoline on BTEX Plumes In Brazilian Ground Water

摘要

It has been suggested that the presence of ethanol in gasoline spills will produce more persistent and longer BTEX plumes in ground water. The expectation from simple modeling is that there would be a "shadow" of depressed electron acceptors in front of the ethanol-hydrocarbon plume. Ethanol would enhance this shadow. Thus, if ethanol has had a significant impact on BTEX persistence, a greater electron acceptor shadow is anticipated that for a typical gasoline-only spill. Ethanol, typically at 22%, has been blended into gasoline in Brazil for about 20 years, so evidence for significant impact on BTEX plume length is being sought there. A ground water plume in a shallow fine sand aquifer at an E22 spill in the Municipality of Itaguai, near Rio de Janeiro, Brazil has been instrumented. BTEX, ethanol, degradation products and electron acceptors are being monitored. Most free phase was removed in 1996 and local ground water sources have been replaced. Initial investigation in 1999 using transects of 15, 5-point multilevel wells found no ethanol and a >150 m (>500 ft) long BTEX plume. The aromatic hydrocarbons in ground water were dominated by the less-mobile xylenes and trimethylbenzenes. This could be due to significant bioattenuation of the more-mobile "front" of the BTEX plume where benzene and toluene are expected to dominate the aromatics. Monitoring suggests the dominant electron acceptors used by hydrocarbon degraders are oxygen, nitrate, and Fe(Ⅲ). No evidence of an enhanced electron shadow has been found to date. There is no obvious impact of the 22% ethanol in the spilled gasoline on the BTEX plume, but more quantitative assessment is underway.