Michael Dodson¹

(1) Thermal Remediation Systems, Longview, WA

ABSTRACT: In Situ DNAPL Remediation using Resistive Electrical Heating

The in situ cleanup of dense nonaqueous phase liquids (DNAPL) remains one of the remediation industry's toughest challenges. Traditional remediation technologies often require years of continued application to produce even marginal results at DNAPL sites. In the last three years, Six-Phase Heating (SPH) has been successful in remediating DNAPLs in demonstration and full-scale remediation applications.

SPH is a polyphase electrical technology that uses in situ electrical resistive heating and steam stripping to achieve subsurface remediation. Developed to enhance the removal of volatile contaminants from low-permeability soils, SPH has subsequently proven capable of remediating DNAPLs from saturated zones.

SPH power control units convert regular three-phase electricity into six separate phases. These electrical phases are then delivered throughout the treatment volume by electrodes that are inserted using standard drilling techniques. Resistance by the subsurface environment to this flow of electrical current uniformly heats the soil and groundwater between the electrodes. Because electrically conductive intervals can be installed at various depth intervals, and the application of energy to the various parts of the electrode field can be controlled, it is possible to heat separate subsurface zones either independently or in unison.

SPH can quickly increase subsurface temperatures to the boiling point of water and is equally effective in all soil types, including clay and fractured rock, under both vadose and saturated conditions. As the subsurface is resistively heated, contaminants are volatilized and soil moisture and groundwater are converted to steam. The production of steam during SPH operations effectively provides in situ steam stripping of VOC contaminants from the soil matrix. By raising subsurface temperatures above the boiling point of the mixture of targeted contaminants and groundwater, SPH significantly enhances the speed and effectiveness of physical contaminant removal.

SPH accelerates VOC remediation by the following principle mechanisms:

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado