Effective and Efficient Soil and Groundwater Remediation
The Power of Soil Vapor Extraction and Air Sparging
When it comes to soil and groundwater remediation, a few techniques stand out from the others. Categorized as “Above-Ground Treatment Technologies,” these time-tested, cost-effective, and reliable remediation techniques remain the go-to solutions for most remedial alternative evaluations, implementing the principle of physically extracting matter to facilitate the transfer of contaminants from the subsurface ahead of above-ground treatment. In fact, soil vapor extraction (SVE) and air sparging technologies can remediate significant dissolved, sorbed, and even some free-phase concentrations of volatile chlorinated and petroleum compounds.
Soil Vapor Extraction
SVE systems are implemented to target contaminants in the section between the ground surface and water table, known as the vadose zone. Certain volatile organic compounds (VOCs) can be easily transferred to the vapor phase and treated at the surface before being discharged into the atmosphere. The equipment required for effective treatment depends on specific characteristics of the project site, including soil type, porosity, organic content, moisture, groundwater elevation, and treatment volume.
Groundwater impacts can also be addressed using the principle of forcing a phase change by injecting air into the ground, a process known as air sparging. Air sparge systems involve a network of air injection wells screened below the contaminant mass. As the air bubbles navigate through the saturated soil, VOCs are stripped from the sorbed and dissolved phases and transferred to the unsaturated zone in the vapor phase. These vapors typically require collection and treatment, creating the need to operate an SVE system in conjunction with an air sparge system.
Aligning these two systems—SVE and air sparging—can trigger another beneficial phenomenon that occurs harmoniously during the phase transfer. Introducing artificially high oxygen levels stimulates aerobic activity, which creates oxidizing conditions that potentially reach areas where physical influence alone cannot be relied on. However, the combination of SVE and air sparge systems can penetrate those areas and successfully remove mass, VOCs, and some low-volatility organic compounds. Stimulation of aerobic conditions can be used alone at sites where vapor transfer is not expected to occur. Known as biosparging, this method does not require an SVE system and the air sparge system can be downgraded to maintain a saturated dissolved oxygen concentration only.
Designing and implementing successful SVE, air sparge, and bio-sparging systems can be labor and power-intensive, and they often dominate the treatment surface area during the construction and remediation phases. While these systems tend to fall on the more expensive side of remedial alternatives in terms of capital and operational costs, they can significantly reduce contaminant mass quickly.
By combining experience, proper planning, and good site characterization with pilot testing, pneumatic modeling, an effective Operation, Maintenance, and Monitoring Plan, and periodic performance optimization, Langan provides these remedial options as cost-effective solutions at sites across the country.
Matthew Wenrick, PE has over 10 years of environmental engineering experience. His remediation expertise includes in-situ chemical oxidation, bio and air sparging, soil-vapor extraction. He also specializes in field and construction oversight of remediation activities including the installation, start-up, and operation of complex pump and treat systems.