What is air sparging?
Air sparging is an in situ remedial technology that removes volatile organic compounds, for example petroleum products and chlorinated solvents, that are adsorbed to soils and dissolved in groundwater. This involves the injection of air into the saturated zone causing a phase transfer of hydrocarbons from a dissolved state to a vapour phase. Compressed air is injected into the ground generally using a regular grid of injection boreholes. The air is then vented through the unsaturated zone. The injected air has several functions:
- Volatilises dissolved organic compounds (VOCs) in the groundwater.
- Supplies oxygen to the aquifer which stimulates bioremediation.
- As the air moves upward it volatilises VOCs in the capillary zone and the unsaturated (vadose) zone.
Advantages and limitations of air sparging
Air sparging is an effective method of remediating sites contaminated with petroleum hydrocarbons and causes minimum disturbance to site activities. This method of remediation results in the physical removal of volatile organic compounds, for example components of petrol, benzene and toluene from below the water table.
Air sparging systems are usually used in combination with soil vapour extraction (SVE) to capture any vapours that may be produced. When air sparging is combined with SVE, the SVE system creates a negative pressure in the unsaturated zone through a series of extraction wells to control the vapour plume migration. The main components of typical air sparging system are:
- Air sparging boreholes.
- Compressor or blower to supply contaminant-free air.
- Interconnecting pipework with valves and controls for adjusting pressure and flow rates.
- A soil vapour extraction system to control and collect released vapours.
- Control system to allow automatic operation of the combined air sparging / soil vapour extraction system.
Although air sparging is a useful technology for treating soil and groundwater contaminated with volatile organic compounds, there are certain circumstances when it should not be used, for example:
- If significant free product is present. Air sparging can create groundwater mounding which could potentially cause free product to migrate and contamination to spread.
- Where there are nearby basements, sewers, or other subsurface confined spaces are present at the site. Potentially dangerous vapour concentrations could accumulate in confined spaces unless a vapour extraction system is used to control vapour migration.
- Where contaminated groundwater is in a confined aquifer system. Air sparging cannot be used to treat groundwater in a confined aquifer because the injected air would be trapped by the saturated confining layer and not able escape to the unsaturated zone.
Contaminants treated by air sparging
Typical volatile contaminants that can be removed from the ground using air sparging include:
- Other volatile solvents
Air sparging case studies
- Contaminated Land Remediation on a Housing Development
- Contaminated Land Remediation by Dual Phase Extraction
- Remediation of a Large Development Site
- Remediation of a Former Petrol Station