Electrokinetic barriers to contaminant transport, numerical modelling and laboratory-scale experimentation

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Narasimhan, Balaji
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Vertical barriers such as cutoff walls, grout curtains or sheet piles are frequently used for containing the contaminants in place during remediation of contaminated soil and groundwater. The electrokinetic barrier is an emerging technique which can be used as a low-cost alternative for containing the spread of contaminants. An electrical potential gradient applied across the electrodes inserted in the subsurface could create an electro-osmotic counter gradient high enough to stop the flow of water due to the hydraulic gradient. A laboratory scale experiment was conducted to study the effectiveness of electrokinetic barriers in containing the spread of contaminants. Potassium chloride was used as a tracer to find the effectiveness of electrokinetic barriers. Laboratory-experiments in sandy clay soils showed that without electrokinetic barriers the K+ ions migrated at a rate of 2 mm.d -1 whereas, with the electrokinetic barriers the K+ ions migrated at a rate of 0.1 mm.d-1. Hence, electrokinetic barriers could be used as an effective system for preventing the spread of the contaminants in the subsurface. A two-dimensional finite element model was developed to investigate the contaminant migration under hydraulic, electrical, and chemical gradients. Migration of a pH front due to the electrolysis reactions at the anode and the cathode and development of non-linear hydraulic and electrical potential gradients brought about by the changes in the electrical properties of the soil could be simulated by the model developed in this thesis. The model results compared well with the experimental results. The numerical model developed in this thesis was also used to evaluate the effectiveness of different electrode configurations for possible field applications.