Impacts of an ethanol‐blended fuel release on groundwater and fate of produced methane: Simulation of field observations

Abstract

In a field experiment at Vandenberg Air Force Base (VAFB) designed to mimic the impact of a small-volume release of E10 (10% ethanol and 90% conventional gasoline), two plumes were created by injecting extracted groundwater spiked with benzene, toluene, and o-xylene, abbreviated BToX (No-Ethanol Lane) and BToX plus ethanol (With-Ethanol Lane) for 283 days. We developed a reactive transport model to understand processes controlling the fate of ethanol and BToX. The model was calibrated to the extensive field dataset and accounted for concentrations of sulfate, iron, acetate, and methane along with iron-reducing bacteria, sulfate-reducing bacteria, fermentative bacteria, and methanogenic archaea. The benzene plume was about 4.5 times longer in the With-Ethanol Lane than in the No-Ethanol Lane. Matching this different behavior in the two lanes required inhibiting benzene degradation in the presence of ethanol. Inclusion of iron reduction with negligible growth of iron-reducers was required to reproduce the observed constant degradation rate of benzene. Modeling suggested that vertical dispersion and diffusion of sulfate from an adjacent aquitard were important sources of sulfate in the aquifer. Matching of methane data required incorporating initial fermentation of ethanol to acetate, methane loss by outgassing, and methane oxidation coupled to sulfate and iron reduction. Simulation of microbial growth using dual Monod kinetics, and including inhibition by more favorable electron acceptors, generally resulted in reasonable yields for microbial growth of 0.01-0.05.

Effect of different transport observations on inverse modeling results: case study of a long-term groundwater tracer test monitored at high resolution

“…The transverse horizontal dispersivity value estimated by the second approach was 0.02 times the corresponding longitudinal dispersivity value, which is within the expected range of this parameter based on the available knowledge from this site (e.g., Rasa et al 2013). …”

An Empirical Evaluation of the Influence of Ethanol on Natural Attenuation of Gasoline Constituents

“…; Rasa et al. ). While such assumptions may be appropriate when identifying potential worst‐case scenarios, the complexity of microbial interactions and subsurface heterogeneity may limit the influence of ethanol releases.…”

Increased fermentation activity and persistent methanogenesis in a model aquifer system following source removal of an ethanol blend release

“…A primary concern associated with ethanol-blend releases has been that the presence of ethanol may increase the persistence and region of influence (and thus the exposure risk) of co-occurring or pre-existing toxic aromatic hydrocarbons such as benzene, toluene, ethylbenzene and xylenes (BTEX) (Corseuil et al, 1998;Gomez et al, 2008;Mackay et al, 2006;Rasa et al, 2013;Zhang et al, 2006). However, as higher ethanol blends (e.g.…”