Electrical Resistance Heating: a Hot New Approach to Soil and Groundwater Remediation

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Courtesy of TRS Group, Inc.

Electrical Resistance Heating (ERH) is an aggressive remediation technology that can quickly reduce the mass of volatile organic compounds (VOCs) in soil and groundwater by over 99%. The process is often used to clean sites where other technologies have had limited success. Larger ERH sites are cleaned within 6 to 12 months and smaller sites can be cleaned in half that time or less.

The technology is not affected by soil type and can be applied almost anywhere, even under operating facilities and public areas. Currently, no other technology can offer equal levels of chlorinated non-aqueous phase liquids (NAPLs) cleanup in the same time frame and for the same price as ERH. Because ERH is so robust, it is possible for site owners to obtain price and performance guarantees for most site cleanups.ERH quickly and evenly heats the subsurface to the boiling point of water by passing electrical current through contaminated soil and groundwater. This gentle heating evaporates volatile contaminants in situ and steam strips them from the subsurface.

Vapors and steam are then extracted, cooled, and treated using standard methods. The technology has been demonstrated as an effective method for the removal of volatile and semivolatile chlorinated and petroleum hydrocarbons from both vadose and saturated zones regardless of soil permeability or heterogeneity2. Developed for the US Department of Energy in the early 1990s by Battelle NW Laboratories, ERH can be applied using three or six phases of electricity. Three-phase heating is generally more applicable for full-scale treatments and the general term “electrical resistance heating” is now used to describe the remediation technique regardless of the electrical phases used. About 50 ERH remediations have now been completed.

ERH can be used to steam strip volatile organic compounds (VOCs) from the subsurface, enhance vapor and multi-phase extraction systems, and increase biological degradation and chemical dechlorination reaction rates. During a typical ERH site remediation, all of these processes are utilized to ensure an effective and lasting remediation is achieved.

Deploying ERH requires a power control unit (PCU) to condition and control the application of power, electrodes to deliver power to the subsurface, recovery wells to collect steam and contaminant vapors, a steam condenser, a vapor treatment system, and control and data acquisition systems. The training and experience of the personnel applying the technology is critical to a successful deployment.

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