PCB Treatment Options for Soil

An Overview

There are numerous treatment technologies available for soil contaminated with PCBs. These treatments fall into three categories:

Destruction (when the PCB molecule is destroyed)
Separation (when the PCBs are separated from the soil)
Immobilization (when the PCB-bearing soil is prevented from moving)

Destruction Technologies for PCBs in Soil

• Incineration
• Chemical Dechlorination
• Biodegradation
• Vitrification

Incineration: PCBs are destroyed at high temperatures. Incineration is the remedy required by the Consent Decree for the Bloomington PCB sites, but it is no longer being pursued and alternatives to incineration are under consideration. The general description of incineration provided on this BBS currently does NOT describe the experimental municipal-waste fueled incinerator originally proposed for Bloomington, because no information describing this application was found.

Chemical Dechlorination: The chemical composition of the PCB molecule is changed by adding dechlorinating chemicals to the PCB-bearing soil. This technology is commercially available from a number of vendors and enjoys regulatory and community acceptability. For large volumes of waste, it is cost competitive with landfilling.

Biodegradation: Naturally occurring microorganisms that consume all or part of the PCB molecule are used to clean up contaminated soil. Biodegradation is an attractive treatment option and has been demonstrated to successfully remediate many organic chemicals, but biodegradation of PCBs in soil is not yet a commercially viable treatment alternative.

Vitrification: PCBs and soil are exposed to extremely high temperatures that destroy the organics and melt the soil. When the molten material cools, it forms a chemically resistant and structurally durable glass-like material. This technology is commercially available, and one vendor has been awarded a National TSCA treatment permit.

Separation Technologies for PCBs in Soil

• Thermal Desorption
• Solvent Extraction
• Soil Washing

Thermal Desorption: PCBs are separated from soil by exposing them to moderately elevated temperatures (much lower temperature than is used in incinerators), causing them to volatilize. The PCBs are carried off in the gas stream, then condensed into a small volume of oily liquid that requires further treatment or disposal. Thermal desorption is commercially available and has been demonstrated to be effective for PCB remediation.

Solvent Extraction: PCBs are separated from soil by dissolving them in a solvent, which is then recovered. The small volume of concentrated liquid containing PCBs requires further treatment or disposal. Solvent extraction is commercially available and has been demonstrated to be effective for PCB remediation, and at least one vendor has been awarded a National TSCA treatment permit.

Soil Washing: Soil washing uses mechanical or chemical methods of separating fine PCB-bearing soil particles from generally clean coarse grained soil particles. The wash water and fine/organic particles would require further treatment or disposal. This technology is commercially available and has been demonstrated to be effective for PCB remediation.

Immobilization Technologies for PCBs in Soil

• Solidification
• Landfilling
• Capping
• Groundwater Barriers
• Vaulting

Solidification: PCB-bearing soil is immobilized in a structurally sound cement-like mass. This process uses common construction equipment and has been used successfully for many years for inorganic contaminants (metals), and it appears to be effective for PCBs as well.

Landfilling: Modern hazardous waste landfills have several layers of bottom liners and leachate collection systems. They are located in areas that minimize the potential for ground water or surface water contamination. When full, the landfills are capped to prevent erosion and rain infiltration, and monitoring continues indefinitely.

Capping: Capping involves placement of an impermeable cover over soil that remains in place. This is used when the soil cannot be excavated, when groundwater cannot reach the contaminated soil, and when surface runoff is prevented from saturating the soil. Capping is often combined with groundwater barriers, described below.

Groundwater Barriers: Ground water barriers are walls constructed in the ground to prevent groundwater flowing laterally from encountering contaminated soil, or to contain contaminated groundwater within its boundary. The barriers can be constructed of a variety of materials (e.g., grout, metal), a perimeter of groundwater extraction or injection wells can control flow, or a below ground barrier of frozen soil and water can be maintained by electrodes in boreholes encircling the site. These technologies are commercially available and have been used in the construction and environmental remediation fields for years. Their effectiveness in karst terrane, however, can be severely limited.

Vaulting: Vaulting is equivalent to an above-ground landfill. A structure is built to contain the waste, equipped with controls to prevent leachate and gas migration from the site.

Continue for more information on remediating PCBs in soil.