U.S. EPA Contaminated Site Cleanup Information (CLU-IN)

U.S. Environmental Protection Agency
U.S. EPA Technology Innovation and Field Services Division

Dense Nonaqueous Phase Liquids (DNAPLs)

Treatment Technologies

Thermal Processes: In Situ

Electrical Resistance Heating

Electrical resistance heating (ERH) involves passing electrical current through moisture in the soil between an array of electrodes. As the current flows through the moisture in soil pores, the resistance of the soil produces heat. Originally, ERH for remediation purposes was developed by DOE and Battelle using six-phase electricity and hexagonal electrode arrays; however, expansion of a six-phase hexagonal array may result in the creation of cold and hot spots within the target subsurface area. Three-phase power and triangular electrode arrays generally are more applicable to irregularly shaped cleanup areas for full-scale treatment and are commonly used today (Beyke and Fleming 2005).

Electrodes can be thought of as wells that are equipped to deliver electric power at selected depths and also act as vapor recovery wells. When groundwater flow rates are high and/or a semivolatile NAPL is to be recovered, liquids can also be extracted (Beyke and Fleming 2002). Electrodes may be installed using conventional drilling rigs. Installation can also be done using horizontal or angular drilling techniques. Care should be taken to ensure that the potential for stray currents is accounted for in the design. ERH systems can be deployed to any depth and used in both the vadose and saturated zone. If the system is deployed only in the vadose zone, water should be added at the electrodes to maintain the moisture content and thus the flow of electricity (U.S. EPA 2004).

The horizontal spacing between electrodes is usually between 14 and 24 feet (Beyke and Fleming 2005). The trade-off in distance is between the cost of installing more electrodes and heating the soil more quickly or installing fewer electrodes and heating the soil over a longer time.

While heating all soil, ERH preferentially heats the more conductive silt and clay first. Temperatures over 100°C can be generated in the saturated zone, and these temperatures produce steam and steam stripping, which is especially beneficial for the silts and clays as contaminant movement in them is usually diffusion limited.

Volatilization and steam stripping with SVE-capture are the predominant removal mechanisms for most contaminants using this technology. (Beyke and Fleming 2005). Soil with a high natural organic carbon content will slow or prevent the recovery of some organic contaminants.

U.S. EPA (2004) provides remediation cost estimates of $32 and $73 per cubic yard at two full-scale ERH sites. Beyke and Fleming (2005) estimate that ERH costs $200,000, plus $40 to $70 per cubic yard. The technology is proven and has been used at a number of sites. The number of vendors offering the technology is limited.

Information on applications of electrical resistance heating technology specific to a chemical class can be found in the class subsections listed to the right.

This discussion is taken from Adobe PDF LogoEngineering Forum Issue Paper: In Situ Treatment Technologies for Contaminated Soil, EPA 542-F-06-013, 2006.

General Resources

Adobe PDF LogoElectrical Resistance Heating (ERH): Design and Performance Criteria
Battelle, presentation from Remediation Innovative Technology Seminar (RITS), 68 pp, 2007.

Adobe PDF LogoFull-Scale Removal of DNAPL Constituents Using Steam-Enhanced Extraction and Electrical Resistance Heating
G. Heron, S. Carroll, and S. Nielsen.
Ground Water Monitoring & Remediation, Vol 25 No 4, p 97-107, 2005

Discusses the full scale remediation of Area A of the Northeast Site at the Young-Rainey STAR Center, Largo, FL. The site was contaminated with NAPL constituents such as TCE, cis-1,2-DCE, methylene chloride, toluene, and petroleum hydrocarbons. The hydrogeology consists of a fine-grained sand aquifer underlain by Hawthorne clay at 30 feet depth. The upper 5 feet of this clay formed part of the remediation volume, as DNAPL was present in this layer. Steam enhanced extraction and electrical resistance heating were used to remediate the site.

Adobe PDF LogoIn Situ Thermal Remediation of DNAPL and LNAPL Using Electrical Resistance Heating
G. Beyke and D. Fleming.
Remediation, Vol 15 No 3, p 5-22, 2005

Provides a history of ERH, how it works, and two TCE case studies.

Adobe PDF LogoProject Overview: Successful Field-Scale In Situ Thermal NAPL Remediation
M. Butherus, D.S. Ingle, R. Juhlin, and J. Daniel.
Third International Conference on Oxidation and Reduction Technologies for Soil and Groundwater San Diego, CA, October 24-28, 2004

Provides a case study of the application of steam heating and ERH to a mixture of DNAPL chemicals and LNAPL oils at the Young-Rainey Science, Technology, and Research (STAR) Center, Largo, FL.

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