Desalinization of Field Soil Using Radial Electromigration and Electroosmosis

Road salt storage piles, improperly managed, can cause contamination of drinking water aquifers due to precipitation runoff that ultimately contaminates the groundwater. The contamination at such sites can be remediated using DC electric fields in conjunction with relatively inexpensive direct-push wells. When soil and groundwater are subjected to DC electric fields, the pore water moves toward the cathode via electroosmosis while cations also migrate to the cathode and anions migrate toward the anode by electromigration. A series of anode and cathode wells placed in the soil can be used to separate and remove chloride (${\mathrm{Cl}}^{-}$) and sodium (${\mathrm{Na}}^{+}$), respectively. To accommodate the use of well-based electrodes on a large-scale basis, a two-dimensional model, approximating a cylinder, was developed to simulate the electromigration and electroosmosis aspects of sodium and chloride transport in soil with a center cathode surrounded by anodes. To validate the model with a field soil, a small pilot-sized experiment was conducted and sodium was used as the primary monitored ion due to its conservativeness and stability at the cathode. The model predicted a sodium transport time of 4 days for sodium ions to travel the 8-in. distance and reach the cathode. The actual sodium flow into the cathodes peaked after the first day and then steadily declined, almost linearly, for the next 21 days. Based on whole hexagon and background soil samples, 85% of the sodium was removed. The removal rate, however, was only one-third that predicted by the model. Therefore, with a retardation factor of three, the model can be used to predict and optimize removal rate and cost for a full-scale implementation.