Team Delta- Soil Vapor Extraction by Andrew Watson

Soil Vapor Extraction
Andrew Watson
Soil vapor extraction (SVE) is an in situ (in place) process which removes volatile organic compounds (VOCs) primarily from the vadose zone of the ground. VOCs such as, gasoline, jet fuel, and solvents are removed by inducing air flow through the soil and up to the surface with the use of blowers or vacuum pumps. The contaminated air flow is channeled through piping and exhausted to the open air or through air treatment systems such as an air stripper, carbon beds, or a combustion unit. If the contamination has reached the saturated zone, other methods may be used, in conjunction with SVE, to extract contaminates from the ground.
There are advantages and disadvantages to soil vapor extraction and both need to be evaluated to determine if SVE will be a suitable choice. A SVE system is simple to install and has minimal disturbance of the contaminated site. A SVE system can reach areas of contamination such as under buildings, parking lots, or other occupied places that would typically be disturbed for the ground to be remediated. Treatment times are typically between 6-24 months and average between $ 20-50 per ton of contaminated soil. Also, other technologies can be used in conjunction with SVE such as, air sparging, steam injection, hot air injection, pneumatic fracturing, electrical resistance heating, and radio frequency heating to assist or expedite the remediation process. Although the advantages may be appealing, there are disadvantages to consider. A SVE system can only attain ~90% contamination reduction which means another method may have to be used to treat the remaining 10%. SVE systems are not very effective in low permeability or stratified soils and will need the use of other technologies to remove contamination from those areas such as air sparging to promote mobility. Depending on concentration levels and local regulations, the extracted vapors may need to be treated before being released to the environment. This can greatly increase costs and require permitting from local, state, or federal authorities.
At first, SVE may look like a silver bullet solution to remediate all VOC contamination at a site. However, important studies need to be performed to determine soil characteristics, vapor concentrations, the location and depth of contamination, and if the SVE equipment is suitable for the remediation or will other technologies need to be used. All these need to be considered to ensure the contamination will be remediated correctly and completely.
References:
http://chemelab.ucsd.edu/sve/ProjSum.htm
http://sve.ucdavis.edu/AlternativesDesc.htm
http://www.epa.gov/swertio1/download/remed/sveresgd.pdf
http://www.epa.gov/oust/cat/SVE1.HTM
http://www.cpeo.org/techtree/ttdescript/soilve.htm
http://www.cee.vt.edu/ewr/environmental/teach/gwprimer/svent/svent.html
Pichtel, John (2007). Fundamentals of Site Remediation. Lanham, Maryland: Scarecrow press, Inc.