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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., (Copyright © 2012 Elsevier B.V. All rights reserved.)

The characterization of pore‐space connectivity in porous media at the sediment/water interface is critical in understanding contaminant transport and reactive biogeochemical processes in zones of groundwater and surface‐water exchange. Previous in situ studies of dual‐domain (i.e., mobile/less‐mobile porosity) systems have been limited to solute tracer injections at scales of meters to hundreds of meters and subsequent numerical model parameterization using fluid concentration histories. Pairing fine‐scale (e.g., sub‐meter) geoelectrical measurements with fluid tracer data over time alleviates dependence on flowpath‐scale experiments, enabling spatially targeted characterization of shallow sediment/water interface media where biogeochemical reactivity is often high. The Dual‐Domain Porosity Apparatus is a field‐tested device capable of variable rate‐controlled downward flow experiments. The Dual‐Domain Porosity Apparatus facilitates inference of dual‐domain parameters, i.e., mobile/less‐mobile exchange rate coefficient and the ratio of less mobile to mobile porosity. The Dual‐Domain Porosity Apparatus experimental procedure uses water electrical conductivity as a conservative tracer of differential loading and flushing of pore spaces within the region of measurement. Variable injection rates permit the direct quantification of the flow‐dependence of dual‐domain parameters, which has been theorized for decades but remains challenging to assess using existing experimental methodologies. Article impact statement: Introducing a novel instrument designed to study the exchange of solute between mobile and less‐mobile porosity (i.e., dual‐domain behavior) near the sediment/water interface. [ABSTRACT FROM AUTHOR]