Hello everyone!
In my last post, we explored the Pump-and-Treat method for groundwater remediation. In this post, we will be talking about another method called Air Sparging and Soil Vapor Extraction (SVE).
This method is used for the treatment of groundwater that is contaminated by volatile organic compounds (VOCs) (Speight, 2020). VOCs are compounds that have a high vapor pressure, meaning they are usually found in a gaseous state. Many VOCs are synthesized and are widely used in a lot of products and as industrial solvents (EPA, 2019).
Air sparging involves the drilling of one or more injection wells into the target contaminated zone. Air is pumped underground through the wells by air compressors at the surface. As air bubbles through the groundwater, VOCs and semi-VOCs will undergo mass transfer to the air bubbles and move upwards towards the vadose zone, the unsaturated zone (Environmental Protection Agency, 2012). As the contaminants move into the soil, the mixture of air and vapors is then extracted by the SVE system for treatment. Similarly, SVE involves the drilling of one or more extraction wells into the contaminated soil, however, unlike the air sparging, it is above the groundwater table. A blower or vacuum pump is attached to the wells to create a vacuum to pull the air and vapors through the soil and up to the surface for treatment. This is better illustrated below (Environmental Protection Agency, 2012). 
The extracted air is then treated usually using activated carbon filter before being released back to the atmosphere once it reaches a certain standard. For a better illustration of how SVE works do watch this video by EcologiaEnvironment.
When properly designed and operated, air sparging and SVE pose little risk to on-site workers and the community. No harmful chemicals are required and chemical vapors are contained from extraction to treatment.
However, one disadvantage is that SVE is applicable only for unsaturated soil and soils with high permeability. Saturated soils can prevent vapor extraction because of the amount of water that may get into the wells and low permeability soils do not allow for sufficient airflow. Secondly, during excavation, there is a possibility that contaminated air may escape into the atmosphere. The treatment system may require permits and a large amount of land for adequate facilities which may increase the cost (Sharma & Reddy, 2004). The duration and costs of the systems vary widely from site to site based on the different site conditions, the nature and amount of contamination, and the hydrogeological setting. Based on 12 remediation cases by the Federal Technologies Roundtable, project durations ranged from 8 months to 8 years and total cost from $76,000 to $43 million (USEPA, 1998). There is no one design that can fit all locations making this challenging in terms of design perspective and not feasible at some sites.
Although in theory, this method seems to be very effective and full-proof, in reality, however, there are various challenges that can hamper its effectiveness.
That brings me to the end of this post
See you guys soon!
Reference
Environmental Protection Agency. (2012). A Citizen’s Guide to Soil Vapor Extraction and Air Sparging [Brochure]. United States: Author. Retrieved September 11, 2020, from https://clu-in.org/download/Citizens/a_citizens_guide_to_soil_vapor_extraction_and_air_sparging.pdf
EPA. (2019, August 01). What are volatile organic compounds (VOCs)? Retrieved September 11, 2020, from https://www.epa.gov/indoor-air-quality-iaq/what-are-volatile-organic-compounds-vocs
Sharma, H. D., & Reddy, K. R. (2004). Geoenvironmental engineering: Site remediation and in-situ containment. Hoboken, NJ: Wiley.
Speight, J. G. (2020). Remediation technologies. Natural Water Remediation, 263-303. doi:10.1016/b978-0-12-803810-9.00008-5
USEPA (1998). “Remediation Case Studies: In Situ Soil Treatment Technologies (Soil Vapor Extraction, Thermal Processes).” Volume 8, EPA/542/R-98/012, United States Environmental Protection Agency, Washington, DC
