Fact Sheet on Soil Vapor Extraction

What is soil vapor extraction (SVE)?

Soil vapor extraction, also known as soil venting or vacuum extraction, is a cleanup technology commonly used to remove volatile and certain semi-volatile organic compounds (VOCs) in vapor from contaminated property. A typical SVE system consists of vapor extraction wells, a vacuum blower or a pump, air/water separator, and a vapor treatment system. Removal of volatile compounds by SVE involves creating a vacuum at the extraction wells. Air in the surrounding soil containing the contaminated vapors then rushes to fill the vacuum, which is then extracted and treated before being released to the atmosphere.

Granulated activated carbon (GAC) and thermal or catalytic oxidation are the most commonly used vapor treatment technologies for VOCs. Selecting the appropriate vapor treatment system depends on the type of contaminants and their concentrations. GAC does not directly treat the vapors but removes contaminants from the vapor by adsorption of the organic contaminants onto the carbon surface. When the carbon becomes saturated with contaminants, it no longer performs and must be regenerated or disposed of as hazardous waste.

Thermal and catalytic oxidation are technologies which destroy contaminants in the soil vapor by heat or chemical reaction. Even though the destruction of contaminants could be as high as 99.99%, there are usually low levels of residual contaminants and combustion by-products emitted from such treatment units. Since dioxins can be formed at low levels as a by-product when chlorinated VOCs are treated, concerns have been raised over the use of thermal and catalytic oxidation as a remedial technology. Some community members argue that since background dioxin in the environment already presents a health concern, treatment technologies generating dioxin emissions as a by-product should be avoided.

What are dioxins?

"Dioxins" are chemical compounds consisting of 75 variations of chlorinated dibenzo-p-dioxins and 135 variations of chlorinated dibenzofurans. Furans which are formed concurrently with dioxins in combustion processes, have similar structures and cause similar toxic effects as dioxin. Therefore, they are included in this group as well. Dioxins are not produced intentionally or used commercially in the U.S. They are formed as unwanted by-products in some industrial processes (such as in paper production and the combustion of chlorinated compounds), as well as through natural occurences (such as forest and brush fires).

Exposure to dioxin can cause health problems. Dioxin is recognized as a carcinogen and included on California's Proposition 65 list of chemicals that are known to cause cancer. The most noted health effect in people exposed to large amounts of 2,3,7,8-TCDD is chloracne. Chloracne is a severe skin disease with acne-like lesions that occur mainly on the face and upper body.

Most of the population has a low level of exposure to dioxins through their diet. Meat, dairy products, and fish make up more than 90% of the intake of dioxins for the general population. Smaller amounts of exposure occur from breathing air containing trace amounts of dioxins, drinking low levels in water, skin contact with certain pesticides and herbicides, inadvertent ingestion of soil containing dioxins, and skin contact with air, soil or water containing dioxins.

Because the various dioxin compounds are not equally toxic or equally potent as carcinogens, a toxic equivalent (TEQ) scale is used for the purpose of assessing the risks associated with dioxins. 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8 TCDD) is the most toxic form and is assigned a Toxicity Equivalent Factor (TEF) of 1.0, while all other dioxin-like compounds have TEF values of less than one. The risks from all other dioxin and furan compounds are compared to the most toxic form and summed up to give a TEQ or concentration comparable to 2,3,7,8 TCDD.

Limited field data from catalytic oxidizers at cleanup sites show dioxin and furan emissions ranging from 0.001 nanograms TEQ per cubic meter (ng TEQ/m³⁾ to 1.07 ng TEQ/m³ with the average emissions of 0.108 ng TEQ/m³. The average emissions of 0.108 ng TEQ/m³ from oxidizers is equivalent to dioxin emissions from 126 cars, or to 1 fireplace or wood stove burning clean wood, or from 1/4 of a typical landfill gas flare. Data for the comparisons were taken from the EPA dioxin re-assessment.

The risk from dioxin emissions from thermal and/or catalytic oxidation is weighed against the risk of taking alternative actions or no action at a contaminated site.

Actions Taken by DTSC:

In response to community concern and in an effort to address potential dioxin emissions from thermal and/or catalytic oxidation units, the Department of Toxic Substances Control (DTSC) has taken the following actions.

1. A workgroup consisting of federal and state agencies, environmental organizations and the public has been established. The focus of the workgroup is to research alternatives to thermal and catalytic oxidation as well as making information on these technologies easily available for the public.

2. A database for thermal and/or catalytic oxidation units has been developed for sites where DTSC is involved in the oversight of the site cleanup.

3. Dioxin testing efforts are underway at several sites to assess the presence and levels of dioxin emissions from thermal and/or catalytic oxidation units.

4. Technologies are being evaluated to identify viable alternatives to thermal and catalytic oxidations.

5. A web site is being created to provide the public with information on chlorinated vapor treatment technologies.

Community Notification/Information:

Several federal and state environmental regulations require public participation during the site cleanup process. The Department of Toxic Substances Control (DTSC) complies with the public participation requirements of the Comprehensive Environmental Responsibility, Compensation and Liabillity Act of 1980, Superfund Amendments and Reauthorization Act, National Contingency Plan, Health and Safety Code, and the California Environmental Quality Act. Different levels of public participation are required at different stages of the cleanup process.

Establishing a local information repository near the site is one of the requirements before remedial investigation begins or initiating any remedial action at a site in the site mitigation program. Usually, information repositories are established at local libraries near the site. Project files that contain key documents on site related remedial activities are placed in the information repositories. These key documents include the preliminary endangerment assessment, site investigation, remedial investigation/feasibility study, removal and remedial action documents, public participation plan, administrative record and any relevant information. In addition to the local information repositories, the project file is available for public review at DTSC and RWQCB offices (if the RWQCB is involved in oversight). Air permit information may also be available from the local air pollution control or air quality management district for the vapor treatment units.

Furthermore, in compliance with SB 47 (Chapter 23, Stats. 1999 or Health & Safety Code Chapter 6.8), based upon community survey, DTSC provides opportunity for public involvement (public meeting/public comments) at key stages of the response action process. Key stages include the health risk assessment, preliminary assessment, site inspection, remedial investigation and feasibility study. If DTSC determines that public meetings or comment is not appropriate at these stages, then DTSC sends notice of the decision to the affected community.

DTSC provides this generic fact sheet to inform the general public about SVE and issues associated with its use at hazardous waste sites. DTSC encourages the public to use this information in conjunction with the site specific fact sheet and related documents when participating in the decision making process.

Press Here to Return to Homepage or Press Back Button to Return to Previous Page