This ESTCP project monitored and evaluated an in situ electrokinetic process in which an electrical field is created in a soil matrix by applying a low-voltage direct current (DC) to an array of electrodes placed in the soil. The intent of this process is to develop the formation of a pH front between the electrodes resulting in solubilization of metal contaminants from the soil particles. Once contaminants are present in ionic form in the soil pore fluid, they migrate to the electrode well opposite in polarity under the applied electric field. Extraction and removal of the contaminants may be accomplished by electrodeposition, precipitation or co-precipitation at the electrode, or removal and treatment of water containing the mobile contaminant species from the electrode wells. The demonstration was conducted at a metals contaminated site at the Naval Air Weapons Station Point Mugu, California.
Control of the electrokinetically mobilized contaminants within the confined and unconfined treatment areas could not be assessed due to poor performance of the technology during the demonstration. The process control zone monitoring indicated that metal contaminants were mobilized during the later stages of the system's operation. Piezometer well monitoring did not detect any pH effect or mobilized metal contaminants from the artificially confined treatment area during this period. Although mobilized metals were not detected, an accurate assessment of contaminant mobility control could not be made until significant treatment occurred. No data was collected to assess the technology's ability to control contaminant movement in the uncontrolled treatment area because this test cell was never activated. Gas emissions produced at the anode and cathode wells were chlorine, oxygen, hydrogen, and hydrogen sulfide.
This demonstration indicated the importance of conducting bench tests that accurately reflect the effects that site conditions would have on the technology. Many vendors have marketed the potential of electrokinetic remediation for metals contaminated soils; however, no large scale field demonstrations had previously been conducted. Issues such as control of contaminant movement, ability to achieve cleanup goals, byproduct formation, and treatment effects on the soil matrix had not been addressed by the bench tests conducted as part of this demonstration. Interest in electrokinetic remediation has been driven by demand for cost effective technologies that will eliminate long-term liability incurred by landfilling of contaminants.
The technology had an impact toward increasing organic contaminant levels at the site. This was primarily a result of the trihalomethane production resulting from the chlorine buildup in the anode wells. To note, the site characteristic that most affected the treatment performance was the high chloride concentration in groundwater. The volatile organic compound data also indicated an increase in the vinyl chloride concentrations in some of the wells, attributed to acceleration of the naturally occurring dehalogenation of perchloroethylene and trichloroethylene as a result of the electrokinetic process. (Project Completed - 2000)