Lessons Learned Through the Implementation of Electrical Resistive Heating Technology at Various Sites

·         Contaminants must be amenable to mobilization, volatilization, or degradation by heat.

·         Resistive heating can heat sandy, silty, or clay soils and low and high permeability soils.  However, aquifer heterogeneities and preferential flow paths can make capturing contaminants in the extraction system more difficult.

·         If overheated, aquifers with slow recharge can completely dry out causing the technology application to fail. This happens because the electricity passage depends on the groundwater for conduction. This problem can be alleviated by reinjecting treated groundwater to rewet soil around the electrodes to increase electrical conductivity.

·         Because of high voltages involved, safety controls must be in place in the treatment area.

·         Regulatory acceptance is important for this application. Improvements in vapor recovery and hydraulic control are necessary to increase acceptance.

·         Adding remote monitoring instrumentation enhances the ability to troubleshoot in case of a shutdown of the system.

·         Establishing a hot floor in the deepest portion of the target treatment region may help mitigate the potential for downward DNAPL migration.

·         While the site may heat up quickly (after a few weeks to a month or so), it may take more than a year to cool down to ambient temperatures. This can be an issue if the Record of Decision or property transfer is contingent upon successful documentation based on sampling when conditions are at ambient temperatures.

·         There is increasing evidence that microbial activity is enhanced at elevated temperatures, thus adding to the treatment efficiency of the process. Additional research may be required in this area.

·         Typical ERH costs range from $55 to $400 per cubic yard with a median cost of $120 per cubic yard. Due to the high capital costs involved, performance based contracting may be appropriate for this technology where a vendor submits a cost to achieve a given performance standard. Details of the performance standard must be carefully considered upfront and agreed upon by all parties prior to awarding a contract.  These performance standards may specify average ground water concentrations, average soil concentrations, or not to exceed concentrations.  The contract may also specify the number and location of monitoring points and other project specific details.

·         ERH is a source zone treatment technology. When developing performance objectives for the ERH application, it is not always necessary to reach the final cleanup standards (e.g. drinking water standards) immediately after ERH is completed.  Instead, remediation may be completed via natural attenuation over an extended time period (e.g. 30 years).

·         This treatment train approach of ERH followed by natural attenuation can help to optimize expenditures and be used to determine the extent of ERH treatment required to cost effectively reach cleanup goals over time.