title: Electrical signatures of ethanol-liquid mixtures: implications for monitoring biofuels migration in the subsurface.
abstract: Ethanol (EtOH), an emerging contaminant with potential direct and indirect environmental effects, poses threats to water supplies when spilled in large volumes. A series of experiments was directed at understanding the electrical geophysical signatures arising from groundwater contamination by ethanol. Conductivity measurements were performed at the laboratory scale on EtOH-water mixtures (0 to 0.97 v/v EtOH) and EtOH-salt solution mixtures (0 to 0.99 v/v EtOH) with and without a sand matrix using a conductivity probe and a four-electrode electrical measurement over the low frequency range (1-1000 Hz). A Lichtenecker-Rother (L-R) type mixing model was used to simulate electrical conductivity as a function of EtOH concentration in the mixture. For all three experimental treatments increasing EtOH concentration resulted in a decrease in measured conductivity magnitude (|σ|). The applied L-R model fitted the experimental data at concentration ≤0.4v/v EtOH, presumably due to predominant and symmetric intermolecular (EtOH-water) interaction in the mixture. The deviation of the experimental |σ| data from the model prediction at higher EtOH concentrations may be associated with hydrophobic effects of EtOH-EtOH interactions in the mixture. The |σ| data presumably reflected changes in relative strength of the three types of interactions (water-water, EtOH-water, and EtOH-EtOH) occurring simultaneously in EtOH-water mixtures as the ratio of EtOH to water changed. No evidence of measurable polarization effects at the EtOH-water and EtOH-water-mineral interfaces over the investigated frequency range was found. Our results indicate the potential for using electrical measurements to characterize and monitor EtOH spills in the subsurface.
authors.affiliation: Department of Earth and Environmental Sciences, Rutgers University, Newark, New Jersey 07102, USA. personna@pegasus.rutgers.edu
authors.forename: Yves Robert
authors.initials: YR
authors.lastname: Personna
authors.forename: Lee
authors.initials: L
authors.lastname: Slater
authors.forename: Dimitrios
authors.initials: D
authors.lastname: Ntarlagiannis
authors.forename: Dale
authors.initials: D
authors.lastname: Werkema
authors.forename: Zoltan
authors.initials: Z
authors.lastname: Szabo
mesh_terms: D056804:Biofuels; D004553:Electric Conductivity; D004784:Environmental Monitoring / Q000379:methods*; D000431:Ethanol / Q000737:chemistry*; D055593:Geological Phenomena; D060587:Groundwater; D008962:Models, Theoretical; D012996:Solutions; D014867:Water / Q000737:chemistry*; D014874:Water Pollutants, Chemical / Q000032:analysis*; D014876:Water Pollution / Q000032:analysis
chemical_list: D056804:Biofuels; D012996:Solutions; D014874:Water Pollutants, Chemical; D014867:Water; D000431:Ethanol