The International Information Center for Geotechnical Engineers

Thermal Desorption - Regulatory Considerations

The regulations applicable to thermal desorption are somewhat fluid because no one definition of thermal desorption is widely accepted. The EPA defines thermal desorption as:


“…an ex-situ remedial technology that uses heat to physically separate petroleum hydrocarbons from excavated soils. Thermal desorbers are designed to heat soils to temperatures sufficient to cause constituents to volatilize and desorb (physically separate) from the soil. Although they are not designed to decompose organic constituents, thermal desorbers can, depending upon the specific organics present and the temperature of the desorber system, cause some of the constituents to completely or partially decompose” (USEPA, 1994).


This definition does not define thermal desorption as an incineration process, but leaves that option open by saying that “although they are not designed to decompose organic constituents, thermal desorbers can… cause some of the constituents to completely or partially decompose,” (EPA, 1994) meaning that they are incinerated. Because of this definition, thermal desorption may have differing regulations depending on operating conditions.


According to the NFESC there are two main regulatory considerations for thermal desorption that have to be taken into consideration, siting regulations and operational regulations (NFESC, 1998a).


Siting Regulations

Siting regulations deal with what must be done before a thermal desorption unit is placed. These siting regulations are similar to regulations that involve siting for a building. For example, a thermal desorption unit may not be placed in a regulated wetland, or transition zone without proper permitting. These regulations are generally easier to meet than operational regulations.


Operational Regulations

Operational regulations deal with the daily operation of the thermal desorption system and involve regulation of the influent and effluent material. Applicable regulations include the Clean Air Act, the National Pollutant Discharge Elimination System (NPDES), the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) Regulations, and may include the Resource Conservation and Recovery Act (RCRA) regulations.


Clean Air Act and NPDES

Both of these regulations relate to the effluent stream of the thermal desorption unit. The Clean Air Act relates primarily to the effluent gas stream generated by volatilization of the contaminants, but could also relate to the effluent soil if particles are small enough to be suspended in the air. The NPDES relates to wastewater point sources that will reach natural waters. The NPDES is of concern for thermal desorption systems because condensation of the gas stream may be discharged onsite and would require permitting or treatment.



CERCLA regulations typically involve the selection of the remedial technology being used. Several factors need to be considered before a given remedial technology can be implemented. These factors include long-term effectiveness, reduction of toxicity, implementability, cost, and state acceptance among others. Generally these CERCLA regulations must be considered before selection of thermal desorption as the remedial technology of choice.



The RCRA specifically applies to treatment of hazardous waste, i.e. how it is generated, treated, stored, and disposed. The RCRA must be considered when the soil being treated is classified as hazardous, meaning that it exhibits a hazardous characteristic, or contains a hazardous waste. Many times, thermal desorption is used to remediate hazardous material, therefore requiring RCRA permitting.


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