Southeast Rockford

Low Temperature Thermal Desorption

Southeast Rockford Groundwater Contamination Superfund Project

February 2001

Background. The contaminants in the Southeast Rockford Groundwater Contamination Superfund Project are mainly industrial solvents in a class of chemicals called volatile organic compounds (VOCs). "Volatile" means they are converted to gas (vapor) readily, especially in the presence of heat. "Organic" means they contain carbon. The Illinois Environmental Protection Agency (Illinois EPA) and the U.S. Environmental Protection Agency (U.S.EPA) are proposing low temperature thermal desorption (LTTD) as the method to remove and destroy VOCs in the soil of Source Area 4.

How does LTTD remove and destroy contaminants? The VOC contaminated soil would be placed into the LTTD primary chamber (first box in below diagram), and the soil would be heated to about 900°F. This temperature causes the VOCs to change into gas (vapor) and evaporate out of the soil. The soil would be therefore cleaned. This process is call desorption.

The VOC vapors from the soil would be directed to the baghouse where dust would be removed. The dust-free vapors would then be directed to the afterburner where they would be heated to 1400ºF - 1800ºF. The high temperature causes oxygen to react with the hydrogen and carbon in the VOC vapors, forming water and carbon dioxide. Carbon dioxide is the same compound people exhale and is non-toxic. Hydrochloric acid would also be formed from the chlorine in the VOCs. The carbon dioxide, water and hydrochloric acid would be directed to the scrubber where the acid would be neutralized, forming water and salt. Carbon dioxide and water would be released into the air. Water, meeting state and federal water quality standards, would be discharged from the scrubber into a nearby drainage ditch.

How would the hydrochloric acid be neutralized? The hydrochloric acid would be treated in the scrubber with a substance such as calcium carbonate, forming water and salt. Neutralized scrubber water would be discharged into a nearby drainage ditch. The discharged water must meet all state and federal water quality requirements.

What air emissions come out of a LTTD treatment system? Carbon dioxide and water would be the primary compounds released to the air from the system.

Can other compounds be created when the vapors are heated in the afterburner? Sometimes when temperatures are not high enough or vapors are not held in the afterburner for a sufficient length of time, other compounds can be created. Those of the most concern are a group of compounds called dioxins. The Illinois EPA would carefully regulate and closely monitor the unit to ensure that it meets all state and federal requirements for environmental protection. The agency also would take other precautionary measures, described below, to ensure that the unit would be operated safely.

What laws and regulations would the unit be required to meet? The LTTD unit would be required to meet the substantive requirements of all state and federal laws and regulations for such a unit, but no actual permit would be issued since the unit would be operated on a federal Superfund site. These requirements include those of:

  • The Clean Air Act, which regulates emissions into the air.
  • The National Pollutant Discharge Elimination System (NPDES), which regulates discharges into the waters of the state.

How would the Illinois EPA ensure that these and other safety requirements are met?

  • Proof of performance test before regular operations. Before regular operations begin, the unit would be required to pass a proof of performance test. Tests conducted during the proof of performance would include tests of:
    • Air emissions for site-related hazardous air pollutants, total volatile organic compounds, carbon monoxide, dioxins and hydrochloric acid. For some of these parameters, such as dioxins and hazardous air pollutants, samples of air emissions from the stack would be collected and sent to a laboratory for analysis. The unit would be shut down until laboratory results are available showing that emission standards were met.

      There are no federal or Illinois standards regulating the release of dioxins from LTTD units. However, U. S EPA has established a dioxin standard for incinerators that burn hazardous waste commercially. If LTTD were chosen for Area 4, the Illinois EPA and U.S.EPA would require the LTTD unit meet this stringent standard. This standard is 0.20 nanograms per dry standard cubic meter of air (air with moisture removed). A nanogram is 1 billionth (0.000000001) of a gram and a gram is approximately 4 hundredths (0.04) of an ounce.1
    • Operating conditions such as temperature, residence time (the length of time the vapors are in the afterburner), rate that soil would be fed into the unit, oxygen, carbon monoxide and other parameters that can be monitored in real time. Real time monitoring means the monitoring results are available immediately.

1The air and soil in Rockford may already contain small amounts of dioxins. Industrial and residential activities (such as burning plastic) provide conditions suitable for the creation of dioxins. If dioxins are detected in the air emissions from the LTTD, it would be difficult to tell whether the unit created the dioxins or if the dioxins were already present in the air or soil before the LTTD unit began operation. In any event, the Illinois EPA and U.S.EPA would require that the unit meet the strict air emission requirements discussed above.


  • Continuous monitoring during regular operations. During regular operations, real time monitoring for parameters such as temperature, oxygen, carbon monoxide and flow rate would be conducted to make sure that the unit would be meeting the same conditions as it did during a successful proof of performance test.
  • Automatic shut down of the feed. The system will be equipped with a mechanism that will shut down the unit if it fails to meet requirements. For example, if the control panel loses electrical power, if there is loss of proper airflow or loss of flame, or if temperatures or fuel pressure are not in the required ranges, the system will automatically shut down.
  • Monitoring of water discharged to the drainage ditch. The water from the scrubber would be tested to make sure it is neutral before it is discharged into the nearby drainage ditch.

What happens to the treated soil? The treated soil would be tested. Soil that meets the cleanup objectives for the site would be placed back in the excavation hole. After excavation and treatment are complete, the area would be restored to its pre-excavation condition, which is primarily a parking lot. Since some of the contaminated soil appears to be under the building, the building may have to be demolished. In such an event, the building would not be restored.

Why are the Illinois EPA and U.S. EPA proposing low temperature thermal desorption? Unlike the other three source areas, the subsurface contamination in Area 4 is fairly well defined. It is also of a size and location suitable for excavation of the soils. LTTD is a well-known technology for treatment of soils contaminated with VOCs. When a LTTD is accompanied by an afterburner and a scrubber it is a safe and effective method of destroying the contaminants present in Area 4. In addition, excavation and LTTD take a much shorter time than other treatment technologies, and the method is cost effective when compared to other options.

What would the treatment unit look like and where would it be located? Most LTTD units like the one proposed for Area 4 are mounted on two trailers of a tractor-trailer truck. The system would have a stack approximately 24 feet tall. The system would be located in the Area 4 parking lot. The Area 4 fact sheet for the feasibility study and proposed plan contains a figure that shows the temporary location of the treatment system.

How long would the treatment unit operate? The thermal treatment unit at Area 4 would be expected to operate for approximately one month. It would then be moved off site. Treatment of the leachate by soil vapor extraction, the method being proposed by the Illinois EPA and the U.S. EPA, could take an additional 25 to 35 years.

Would operations create dust, odors or noise? Problems with dust are not expected and can be controlled easily by adding water to the soil. If odors or airborne contaminants are problematic during soil excavation, a temporary enclosure would be installed over the excavation. Some noise may be created during daylight hours by excavation equipment (i.e. backhoe) and the LTTD unit, but Illinois EPA would take steps to reduce this noise as much as possible. The LTTD unit would not operate at night, and excavation would not occur at night.

Who would operate the treatment system? The Illinois EPA would contract with a firm that specializes in LTTD treatment. A thorough review process would be conducted to ensure the selected firm has the proper equipment and that the personnel have the proper training to operate the system. The Illinois EPA would oversee operation of the system.

For Additional Information:

Contacts: For more information about the project including fact sheets on the remedial investigation results, feasibility studies and proposed plans for each of the four major source areas, you may contact the Illinois EPA staff listed below:

Tammy Mitchell
Community Relations Coord.
Illinois EPA
1021 N. Grand Ave. E.
Box 19276
Springfield, Illinois 62794-9276
Phone: (217) 524-2292
Thomas Williams
Project Manager
Illinois EPA
1021 N. Grand Ave. E.
Box 19276
Springfield, Illinois 62794-9276
Phone: (815) 223-1714

Repositories: Full reports for the project may be reviewed at the following locations.

Rock River Branch
Rockford Public Library
3128 S. 11th Street
Rockford, IL 61109
815-398-7514
(Call for hours)
Ken-Rock Community Center
3218 S. 11th Street
Rockford, IL 61109
815-398-8864
(Call for hours)

Administrative record file: The administrative record file is located at the Illinois EPA headquarters in Springfield, Illinois. Call 217/782-9878 for an appointment. The administrative record file will also be located on microfiche at the Main Branch of the Rockford Public Library at 215 N. Wyman in Rockford.