Electrokinetic barrier to prevent subsurface contaminant migration: theoretical model development and validation

The application of a DC electric field down gradient to the contaminated zo ne in the subsurface can create an electrokinetic barrier. The electrical p otential gradient causes the movement of ions which in turn imposes a visco us drag on the pore water. In clayey soils, this viscous drag can generate a high enough pore water pressure capable of counteracting the ground water gradient. This phenomenon can be used effectively as a barrier to prevent contaminant migration. A finite element model was developed to simulate the contaminant migration in soil under coupled hydraulic, electrical and chem ical gradients. The model is also capable of predicting the associated chan ges in the soil like the pore water pressure, pH and voltage gradient as a function of time and distance from the electrode. This model was validated using the experimental data presented by Yeung [Yeung, A.T., 1990. Electro- kinetic barrier to contaminant transport through compacted clay. PhD Thesis , University of California, Berkeley, 260 pp.]. The results indicate Very g ood agreement between the experimental and simulated results. The model pre dications show that when the anode is placed down gradient of the cathode, the cation migration could be completely arrested. However, the anions were found to move faster in the direction of the ground water flow and reduce the effectiveness of the barrier. This could be avoided by carefully design ing the placement of the electrodes. If the contaminant of interest is eith er a cation or an anion, a simple double row of anode and cathode electrode arrangement could serve as an effective barrier. On the other hand, if the contaminant includes both anions and cations, then a triple-row configurat ion of electrodes need to be implemented. The model simulations could be us ed to assess different electrode configurations and current application str ategies. (C) 2000 Elsevier Science B.V. All rights reserved.