Electrical signatures of ethanol–liquid mixtures: Implications for monitoring biofuels migration in the subsurface Yves Robert Personna a, ⁎, Lee Slater a , Dimitrios Ntarlagiannis a , Dale Werkema b , Zoltan Szabo c a Department of Earth and Environmental Sciences, Rutgers University, 101 Warren Street, Newark, New Jersey, 07102 USA b U.S. EPA, NERL, ESD-LV, CMB, 944 E. Harmon Ave. Las Vegas, NV. 89119, USA c U.S. Geological Survey, New Jersey Water Science Center, 810 Bear Tavern Rd., Room 206, W. Trenton, New Jersey, 08628, USA article info abstract Article history: Received 20 February 2012 Received in revised form 4 October 2012 Accepted 8 October 2012 Available online 1 November 2012 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 ≤0.4 v/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. © 2012 Elsevier B.V. All rights reserved. Keywords: Geophysical methods Ethanol Biofuels Subsurface 1. Introduction In the last two decades, the production of EtOH, one of the most common biofuels in the USA, has substantially increased due to regulations aimed at reducing air pollution and providing a supplement to petroleum. Accidental releases of large volumes of EtOH, particularly during transportation (Spalding et al., 2011) and at storage facilities (McDowell et al., 2003), have raised concerns about its environmental fate and potential risks to groundwater (Powers et al., 2001a). Ethanol is currently treated as an emerging contaminant (Gomez and Alvarez, 2010) that may induce substantial adverse effects in the subsurface environment (EPA, 2011). As a powerful disinfectant that has been long used as an antiseptic, EtOH at concentrations as low as 6% v/v is toxic to soil and aquifer microorganisms (Nelson et al., 2010). Ethanol toxicity can lead to major alterations in microbial growth, metabolism, viability (Ingram, 1990; Nelson et al., 2010) and community structure (Cápiro et al., 2008; Ma et al., 2011). The persistence of EtOH toxicity in the subsurface may ultimately lead to a substantial decrease in microbial population and activity, thus affecting the overall subsurface microbial pro- cesses including biodegradation of contaminants. Journal of Contaminant Hydrology 144 (2013) 99–107 ⁎ Corresponding author. Tel.: +1 973 353 5100; fax: +1 973 353 1965. E-mail addresses: personna@pegasus.rutgers.edu (Y.R. Personna), LSlater@andromeda.rutgers.edu (L. Slater), dimntar@andromeda.rutgers.edu (D. Ntarlagiannis), Werkema.D@epamail.epa.gov (D. Werkema), zszabo@usgs.gov (Z. Szabo). 0169-7722/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jconhyd.2012.10.011 Contents lists available at SciVerse ScienceDirect Journal of Contaminant Hydrology journal homepage: www.elsevier.com/locate/jconhyd