Understanding Soil Vapor Extraction
Remediation by means of Soil Vapor Extraction (SVE) is a process that occurs in its natural occurring place and
the soil contamination is removed by either steam or air. The extracted earth vapors may then be separated into
vapors and liquids, or treated entirely as waste-gas and treated directly. Soil vapor extraction is suitable for
removing a variety of soil contaminants that have an elevated vapor pressure and/or lower boiling points when
compared to H2O, an example would be chlorinated hydrocarbons. Soil vapor extraction can cope with higher
concentrations of contaminant, which include contaminants in the form of a non-aqueous phase liquid. The
methods in which contaminants located in the soil are typically removed are either by air or steam. Air or steam
may be directly injected into the ground. When the process uses injecting air into the ground by a means of high
pressure blowers and injection wells it is called air sparging.
Another method to treat soil contaminates is to increase the soil temperature high enough to change the liquid
into a vapor, when this occurs there is an increase in soil pressure. Increasing the soil temperature can
appreciably minimize the time needed to achieve objective levels of remediation. Modest soil heating can be
achieved using an underground heat exchange system. Heating to higher temperatures can be achieved with
electrical resistance heating. The process includes installing electrodes in the earth area of treatment and
applying higher phase electricity to the electrodes.
Electrical current flowing through the soil will generate heat through resistant heating; this causes the soil
contaminants to turn into a vapor. The vaporized soil contaminants will then be transported through the soil
vapor extraction collection system to the surface, where the containments may be collected.
Extracted soil vapor can then be cooled if necessary to convert some of the vapor into a liquid. The liquid
material; then separated can be treated by alternate means, while treating the vapor by thermal oxidation. When
designing the treatment system one should take into account the expected concentration of contaminants in both
the liquid and vapor phases.
For the liquid phase, a more common treatment is to run the contaminants through a granulated activated
carbon system, and then to send the cleaned H2O to the sewer or discharge it to a local body of water. For the
vapor contaminant phase, the following methods may be used:
(A) Granulated Activated Carbon Bio-Filtration (GACBF) System, using the carbon bed to contain the
contaminate or trap the emissions and secondary microbes as the biological method to destroy the volatile
organic compounds (VOCs). Destruction rate 99%+.
(B) Treatment by oxidation using a thermal oxidizer (without use of a heat recovery bed), after oxidation of the
highly concentrated vapors a ceramic media heat recovery bed may be inserted into the regenerative thermal
oxidizer to capture the still high but lower volatile energy, as treatment continues one may convert the
regenerative thermal oxidizer to a regenerative catalytic oxidizer by means of placing a 3" layer of catalyst on top
of the current ceramic media for final disposition or oxidation during the lowest level vapor destruction phase.
Make sure you purchase technology capable of conversion during the various phases.
Various thermal oxidation equipment, carbon adsorption and bio-filtration systems are the three most common
technologies used for Soil Vapor Extraction off-gas treatment. These technologies are robust and are mature
vapor treatment methods that address a wide variety of contaminants and concentrations. The selection of
off-gas treatment technologies for Soil Vapor Extraction is based on cost and operational considerations that
differentiate thermal oxidation, carbon adsorption and bio-filtration systems.
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