Electrokinetically enhanced in-situ flushing for HOC-contaminated soils

Hydrophobic organic compound (HOC) contamination affects the soils and groundwater at numerous sites throughout the United States, posing a serious risk to human health and the environment. Electrokinetically enhanced in-situ flushing offers great potential for HOC remediation, especially when the contaminants are located in difficult subsurface conditions where moist, low permeability, argillaceous and/or organic soils exist. A comprehensive laboratory research program was conducted to evaluate and optimize this technique, and this program involved batch testing and 1-D and 2-D bench-scale electrokinetic experiments. The batch tests provided valuable information concerning the remedial efficiency of different flushing solutions, but the results from the 1-D experiments revealed that the mass transport and contaminant removal mechanisms that function during electrokinetics are quite different from those that function during batch tests. A systematic analysis of electrokinetic variables, such as surfactant or buffering concentration, soil type, voltage gradient, or mode of voltage application, revealed that the critical factors responsible for a large (91%) amount of contaminant removal were the use of a high, 2.0 VDC/cm, voltage gradient and a periodic mode of voltage application. The results suggest that the pulsing or kinetic mass transfer mechanisms that occur as a result of the periodic voltage application are essential to the remedial process. The optimized electrokinetic variables were then applied to larger-scale 2-D experiments that employed heterogeneous (lens, layer, and mixture) soil profiles containing two soils, sand and clay, of extremely different hydraulic conductivity, and the results from these experiments indicated that electrokinetically enhancing the in-situ flushing process can significantly increase HOC removal from heterogeneous soil conditions.