Air Sparge System Description
Air sparge is an in-situ groundwater remediation technology which uses vertical or horizontal wells to transfer a continuous or pulsed flow air into the groundwater. The purpose of air sparge is to reduce the concentrations of volatile organic compounds (VOCs) in groundwater through one or several of the following mass transfer mechanisms: (1) enhanced mass transfer of VOCs to the soil vapor; (2) formation of barriers to reduce dispersion VOCs; (3) enhanced oxidation of VOCs by transferring oxygen to the subsurface; and (4) enhanced biodegradation.
The mass transfer mechanisms are further described below:
- Enhanced Mass Transfer – The air sparge system injects clean air below the groundwater capillary fringe. The VOC mass transfer is enhanced through mechanical agitation of groundwater and transfer of VOC mass to the vadose zone, and enhanced VOC mass transfer from the groundwater into air bubbles.
- Dispersion Barriers – Air sparge wells can be arranged to create oxidation barriers or limit hydraulic dispersion, and limit groundwater flow.
- Enhanced Oxidation – Air sparge with oxygen increases dissolved oxygen concentrations in groundwater which in turn enhances oxidation of VOCs such as gasoline range organics.
- Enhanced Biodegradation – Aerobic remediation at the Site is further accelerated by biological treatment. Air sparge provides additional oxygen which may be the limiting factor.
Air sparge will increase dissolved oxygen concentrations in groundwater and may stimulate biodegradation in of chemicals in groundwater including hydrocarbon-impacted groundwater. Air sparge is generally used in combination with SVE to capture off-gases which if left unmanaged may increase the risk of vapor intrusion pathways. Biodegradation of VOCs in groundwater is a function of several uncontrolled factors including nutrient availability, dissolved oxygen distribution, and lithology. Generally speaking, air sparge systems are designed considering that primary remediation mechanism is air stripping. Evidence of biological biodegradation in groundwater can be obtained during groundwater monitoring activities.
Air sparge systems offer key advantages which include: lower ongoing maintenance costs; higher uptimes associated with simpler design; fewer regulatory and discharge monitoring requirements beyond site monitoring activities. An air sparge system is not an effective technology at sites impacted with non-VOCs, or at locations where hydraulic containment is required.
Air Sparge systems are generally used in combination with and Soil Vapor Extraction Systems (SVE systems) to capture the VOC emissions.
Air sparge system implementation requires the following:
- Feasibility Studies
- Remedial Action Plan
- Pilot Testing
- Remediation System Design
- Operation and Maintenance Manuals
- Operation and Maintenance
- Remediation System Optimization
- Estimation of Mass Removal Rates
- Biodegradation and Microbiological Tests
- Reporting to Clients and Regulatory Agencies
- Annual Performance Assessment Reports