Processes Involved in Field Applications

Electrokinetics involves the application of low-level direct current (DC) between electrodes placed in a contaminated area. Different variations of this process were developed to suit the needs of each case. The processes adopted at each site differ with each other in one or many aspects. Basically, two approaches are defined depending on the type of contaminant. The first approach is the enhanced removal in which the contaminants are transported by electromigration and/or by electro-osmosis toward the electrodes for subsequent removal, and the second approach is the treatment without removal, which involves the electroosmotic transport of contaminants through the treatment zones and may also include the frequent reversal of polarity of electrodes to control the direction of contaminant movement (USEPA, 1997). The first approach is applicable for the removal of heavy metals, whereas the second approach was developed for the removal of organic species from contami- 

2 In Situ Electrokinetic Extraction (ISEE) System, Sandia National Laboratories (SNL) 

In 1996, as part of the Superfund Innovative Technology Evaluation (SITE) Program, the United States Environmental Protection Agency (USEPA) demonstrated the ISEE system at the SNL chemical waste landfill site in Albuquerque, New Mexico (USEPA, 1998). The ISEE system was developed by SNL for removing hexavalent chromium from unsaturated soil. This was a cutting edge, since most of the laboratory-scale studies were carried out in saturated soil samples. In a saturated sample, the contact of the interstitial fluid with the solid particles is more effective and aids in the extraction and transportation of pollutants. The two primary transport mechanisms in electrokinetics (electromigration and electroosmosis) require a liquid medium (water), but in the unsaturated soil zone, the lack of water in the interstices makes the solubilization and transportation of the heavy metals precipitated or adsorbed on the solid particles surface more difficult. 

The ISEE technology is applicable for treating unsaturated soil contaminated with hexavalent chromium. According to SNL, this technology can be modified to 

TABLE 29.1. Reported Field Application of Electrokinetic Remediation of Heavy Metal Contaminated Soils 

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