Public Services and Procurement Canada
In situ electromagnetic heating of soils, also called radio-frequency heating, consists of the emission of electromagnetic waves at different frequencies in order to accelerate molecular movement and to increase the temperature within a soil matrix. Electromagnetic technologies add sufficient heat to the subsurface to exceed the boiling point of groundwater, a temperature which is typically sufficient to volatilize the target contaminants. The resultant vapour (water and volatile contaminants) is extracted through collection wells using a multiphase extraction system or soil vapour extraction system and treated at the ground surface. Electromagnetic heating of soils may be performed using radio frequencies or microwaves. The heat generated increases volatilization of volatile and semi-volatile organic compounds (VOCs and SVOCs, respectively) in the soil.
This technique also applies to pure products such as light non-aqueous phase liquid (LNAPL). The electromagnetic heating technique can increase the soil temperature up to 300 °C and is effective in low-permeability soils and bedrock.
Electromagnetic heating has been known for decades to be an effective technique for heating large volumes of subsurface soils. Applications to oil extraction and soil remediation are well studied; however, commercial development of this technique remains incomplete.
Electromagnetic heating systems may include:
Extraction wells (MPE or SVE) contain significant water. The above-ground treatment system must include provisions for air-liquid separation, vapour condensation, vapour, condensate and liquid cooling, non-aqueous liquid phase separation, water treatment and vapour treatment. The water treatment system can consist of cooling towers and carbon adsorption units. Vapour treatment systems are commonly comprised of combustion (thermal oxidation, catalytic oxidation) or filtration/sorption (activated carbon, biofiltration) units.
Process equipment is generally provided by one of a limited number of specialized remediation subcontractors.
Sufficient storage space is required to house the electromagnetic heating unit as well as the water and vapour treatment units.
Electromagnetic heating is a short-term technology. Treatment time frames should vary between 6 and 18 months but the number of application examples is limited.
ERH has not been observed to adversely affect geotechnical properties. However, care should be taken when treating soils around or under buildings or infrastructure.
In situ biological technologies (biostimulation, bioaugmentation, and bioventilation) can be used when temperatures are less than 40 °C of after thermal treatment application. Elevated temperatures result in more rapid biodegradation; there is some evidence that microbial recolonization of aquifers occurs rapidly following thermal treatment.
Application examples are available at these addresses:
The performance of a combined vapour extraction and electromagnetic treatment system varies according to the nature of the soil matrix and the chemical properties of the contaminant(s).
During a pilot study at Savannah River, U.S.A., electromagnetic heating was responsible for the extraction of over 170 kilograms of chlorinated solvents from contaminated sediments. The system destroyed the contaminants with an efficiency ranging from 80 to 95%. This result is an example of the performance of the electromagnetic heating technology for TCE and PCE contamination.
Composed by : Mahaut Ricciardi-Rigault, M.Sc., MCEBR
Updated by : Josée Thibodeau, M.Sc, National Research Council
Updated Date : March 1, 2008
Latest update provided by : Marianne Brien, P.Eng., Christian Gosselin, P.Eng., M.Eng., Golder Associés Ltée
Updated Date : March 31, 2018