From: Public Services and Procurement Canada
Soil Vapor Extraction (SVE) is an in situ technology that removes residual or free phase contaminant(s) from the vadose zone. SVE applies to volatile and semi-volatile organic compounds (VOCs and SVOCs, respectively), and light to medium petroleum hydrocarbons such as gasoline, diesel, heating oil, and kerosene.
The treatment principle consists of applying a vacuum within the soil vadose zone to create a movement of air through the soil pores and induce a transfer of the contaminant, by advection and diffusion, to the airstream. Contaminated vapours are extracted from the soil through horizontal or vertical extraction wells and are treated prior to release into the atmosphere. A geomembrane, asphalt or bentonite can be used to cover the soil surface to prevent vapour migration into the atmosphere and to increase the radius of influence of the extraction wells.
SVE systems are usually combined with other in situ technologies targeting volatile and semi-volatile contaminants, such as air sparging, thermal desorption and chemical oxidation. The circulation of air within the soil vadose zone when applying vacuum increases the oxygen concentration and stimulates biodegradation.
4.8 Soil Vapor Extraction—FRTR Remediation Technologies Screening Matrix and Reference Guide, Version 4.0
Soil vapour extraction systems use relatively large amounts of energy to create relatively high subsurface vacuums and gas flow rates, stripping volatile contaminants out of the soil. Wells, trenches, permeable drains or other structures are used to extract air. Extracted air is treated prior to being released into the environment.
On-site pilot tests are necessary to determine the type of wells, the radius of influence and spacing of the extraction wells and the system operation settings (flow, pressure, intermittent extraction cycle, etc.).
SVE systems may include:
Mobilization, site access and temporary facilities
Installation of extraction wells;
Installation of an air extraction system consisting of a pipe network and an extraction and treatment unit. The unit normally includes a vacuum pump (or blower), an air-water separator (“knockout drums”) and a treatment system, such as activated carbon filters, biofilters or a thermal oxidizer Monitoring of air emissions
Decommissioning of extraction wells and system is also required
Air extraction and treatment units must be stored on site. Otherwise, SVE typically require very little on-site storage. Storage could include auxiliary fuel for thermal oxidizers and new and contaminated air treatment media such as granular activated carbon.
There are few to no residual generated, depending, on the air emissions controls used.
Spent air treatment sorbent (for example, activated carbon) could require periodic off-site transport and regeneration or disposal.
Extraction systems may require periodic draining and off-site disposal of contaminated water from the air/water separator.
Catalytic oxidation of chlorinated organics produces acid gasses. These are typically managed with a caustic scrubber. In such a case, scrubber water would then require periodic neutralization and disposal.
Targeted contaminant groups for SVE are primarily VOCs but SVOCs could also be targeted, and certain residual or free phase petroleum hydrocarbons within the vadose zone
Generally applies to contaminants with a vapour pressure above 0.5 mm Hg and to soils with a minimal air permeability.
Certain complementary technologies increase the efficiency of total contaminant removal.
Vapour emission migration is controlled by the SVE system, which reduces the risk of inhalation and explosion.
Low installation costs.
This technology is well accepted by regulators and the public in general when combined with an air treatment system.
Intensive soil vapour extraction may not be appropriate for remote northern sites without access to utilities or local operations & maintenance labour. Extreme cold can hamper volatilization in shallow material, but deep soil temperatures are relatively constant over the course of the year. Northern systems require climate-appropriate design, including consideration of deep frost, permafrost, seasonal changes in saturation and air permeability and long periods without operator intervention, fuel supply or sorbent removal.
Notes:
Treatment time may take months to years. SVE is prone to “tailing” behaviour (where extracted vapour concentrations fall over time but still remain above desired levels) very similar to that observed with groundwater pumps and treat systems.
None. SVE does not affect soil properties and structure.
The application of the SVE system enhances the volatilization of the contaminant(s) and the vapours produced during treatment must be collected and treated. Management of treatment system by-products is a part of normal treatment system operation.
SVE treatment can stimulate biodegradation of certain contaminants within the vadose zone through enhanced air circulation and aeration. The biodegradation of monocyclic and polycyclic aromatic hydrocarbons (MAHs and PAHs, respectively) and petroleum hydrocarbons does not produce toxic by-products. The biodegradation of certain aliphatic chlorinated hydrocarbons can generate toxic metabolites (e.g. the biological transformation of dichloroethene produces vinyl chloride).
In situ biological treatment (bioventilation, biosparging,...)
Thermal treatments (electromagnetic, electrical resistance, hot air injection or vapour injection) enhance the volatilization of less volatile contaminant(s) and accelerate the biodegradation process when the temperature is kept below 40oC. It allows the less volatile compounds to be volatilized.
Decreasing the water table level can increase the depth of application of the SVE technology, and improve the treatment of the soil capillary fringe. It is not a recommended technology when light NAPL is present.
Geomembranes or bentonite covering the soil surface prevents short circuiting and increase the radius of influence of the extraction wells.
Air injection technologies facilitate the volatilization and extraction of deep contamination, contamination in low permeability soils and contamination in the saturated zone (air sparging).
Increasing soil fractures with a mechanic or pneumatic system improves soil permeability.
Extraction systems typically require treatment of extracted vapours before discharge to air. Extracted soil vapour is first directed through “knockout drums” (air/water separators) before treatment in an air emissions control systems using either adsorption (granular activated carbon), biofiltation or thermal oxidation (with or without a catalyst). Those thermal oxidation systems, if improperly configured, can discharge products of incomplete combustion in the atmosphere.
Several pilot studies and full-scale application examples of the SVE technology are available on the US EPA website. There are also several private companies that offer the SVE technology as a remediation solution.
Some application examples are available at these addresses:
Soil Vapor Extraction and In Situ Chemical Oxidation at Swift Cleaners, Jacksonville, Florida (case 404)—Costperformance.org—FRTR
Air Sparging and Soil Vapor Extraction at Landfill 4, Fort Lewis, Washington (case 84)—Costperformance.org—FRTR
Abstracts of Remediation Case Studies Volume 4—FRTR—US EPA pdf
In Situ Bioremediation and Soil Vapor Extraction at the Former Beaches Laundry & Cleaners—FRTR
The SVE technology is a low cost, well tested and known technology.
SVE is effective only where gas flow in soil can be induced. To extend its effectiveness below the water table, it may be enhanced by dewatering or by air sparging (the injection of air below the water table, which oxygenates the groundwater and/or strip contaminants out of the saturated zone and transports them to the unsaturated zone with a stream of bubbles).
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Composed by : Josée Thibodeau, M.Sc, National Research Council
Updated by : Martin Désilets, B.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 22, 2019
