Predictive and diagnostic simulation of in situ electrical heating in contaminated, low-permeability soils

By in situ heating, contaminants can be mobilized by vaporization, modified into a harmless chemical state, or entrapped by soil vitrification. However, effective heating may be difficult or impossible by depending solely upon conduction of heat externally applied to a contaminated target layer. Heating a layer internally by passing an electric current through it has been employed in several different in-situ remediation field experiments. The authors present a three-dimensional computer model of groundwater flow and transport in an electrically heated, partially saturated, porous regime. Simulations are used to show that the uniformity of heating can be enhanced by increasing the number of electrical phases employed in supplying current to the electrodes. However, a more serious concern for the field-scale application of this internal heating method is the nonuniform heating of the target layer because of large heating-rate differences between the near-electrode region and the center of the array. Finally, for a dissolved solvent like TCE, the authors show that ohmic heating is exceptionally effective at clearing the layer by vapor-phase partitioning. Once expelled from the low-permeability layer, the solvent that is not already thermally destroyed by a pyrolytic reaction is available for extraction. (A)