The feasibility was evaluated of using electrokinetic injection of benzoic acid cometabolite to enhance the biodegradation of a representative recalcitrant contaminant, trichloroethene (TCE). Whereas in flask studies, sulfate ion alone enhanced TCE (at 6 ppm) degradation rates over those found in the absence of suitable additives, benzoic acid showed enhanced degradation rates for TCE at 6-50 ppm levels. Following injection of benzoic acid cometabolite into a 1 m column of TCE contaminated Loess clay, the TCE first order degradation rate at the periphery was determined to be (0.039±0.007) day-1, a value in good agreement with an anaerobic slurry flask tests at 30°C, (0.047±0.009) day-1. However, unless the rate of injection of an additive is made compatible with its rate of consumption, these column results and a theoretical model reveal that homogeneous penetration of additive is not achieved. It is cautioned that knowledge of the rate of degradation of a carbon source enhancer (or additive) is critical for engineering its homogeneous injection, whether by hydraulic or electrokinetic methods. These results demonstrate that electrokinetic degradation of recalcitrant wastes may be practical, in particular for those sites whose soil media have low coefficients of hydraulic permeability (clay deposits, silty clays, etc.) where traditional pump and treat technology is ineffective. (C) 2000 Elsevier Science Ltd.