From: Public Services and Procurement Canada
Air sparging is an in situ technology that involves injecting air into the saturated zone and below the upper groundwater table to oxygenate groundwater and promote the volatilization of contaminants from the water or soils. This technology generally applies to volatile organic compounds.
During this treatment, pressurized air is injected into the contaminated saturated zone. Once in contact with air, the organic compounds are volatilized and migrate to the vadose zone to be recovered. The gas injection can be performed using vertical or horizontal wells, and from trenches or reactive barriers.
Contaminants are not destroyed by this technology but are physically transferred from the liquid phase or adsorbed into the gas phase to facilitate their recovery. Air sparging is often done in conjunction with a vapour extraction system in the soil, so that gaseous contaminants can be captured and treated.
Air sparging also stimulates the biodegradation of organic compounds in the vadose zone and in the saturated zone as a result of the oxygen supply (see the fact sheet: Biosparging).
Sources:
An air sparging treatment system includes the installation of a network of air injection wells developed in the saturated zone. The injection wells network is designed so that the entire area to be treated is aerated. The zone of influence of each must overlap wells. Air suppressors are used to convey air under pressure.
The flow rates and pressure of the injected air are based on the site conditions, defined during the investigation phase and refined during pilot tests. These values can be adjusted during the rehabilitation phase, to consider the observed results and to increase the effectiveness of the treatment.
When a vapour extraction system is used simultaneously, a network of vapour extraction wells is also provided in the vadose zone and vacuum pumps (including a piping system) are used to create a negative pressure to extract the vapours from the soil.
Aboveground equipment may include a gas-liquid separator connected to the vapour extraction and treatment systems. For more information, the fact sheet: Soil vapour extraction can be consulted.
The implementation of an air sparging system may include:
If the technology is combined with a vapour extraction system, then the stages of implementation of this technology should also be considered.
The majority of air sparging systems use air as the active gas. However, the remediation of chlorinated solvents can be achieved using a cometabolic process of methane or injected propane. The efficiency of this technology can also be increased by adding heat, fracturing the soil to increase airflow (hydraulic or pneumatic fracturing), or by sealing the soil surface to avoid “short-circuiting.”
The implementation of the system could lead to the management of contaminated soils resulting from drilling or excavation activities. In this case, these soils must be removed off-site.
The waste generated is minimal and depends on the types of atmospheric emissions controls used. Used adsorbent materials (activated carbon) or other products used in the treatment must be recovered and disposed offsite in an authorized centre.
Notes:
Tests examining the effect of temperature change on hydraulic conductivity and establishing the zone of freezing with a pilot scale tubing system are recommended to properly design the full-scale containment system.
Air sparging is used to treat dissolved contamination and is efficient for the treatment of semi-volatile and volatile organic compounds, and halogenated and non-halogenated organic compounds such as trichlorethylene and benzene, toluene, ethylbenzene and xylenes.
This technology is efficient in homogeneous soil with high permeability.
Air sparging is not always appropriate in remote areas that do not have easy access to utilities or local labour to operate and maintain the system. Cold temperatures can affect the biodegradation and volatilization of shallow materials, but the temperature of deeper soils is relatively constant throughout the year. Nordic systems generally require climate-adapted techniques, taking into consideration deep ground freezing, seasonal changes in soil conditions and long periods without system operator intervention, refuelling and removal of sorbents. The recovery of the vapours generated by the air sparging can become complex and/or more limited in the permafrost zones. In areas of low population density, risk analysis may require less intensive monitoring and mitigation measures than those typically used in more developed areas.
After removal of the treatment system, monitoring of groundwater quality may be required.
Air sparging is not a destructive technology and does not generate any by-products because the contaminants are transferred from the aqueous phase to the gas phase. However, the biodegradation of some contaminants caused by the injection of oxygen-containing air into the saturated zone can produce toxic metabolites.
Air sparging technology is often combined with vapour extraction and treatment systems.
The following website provides an application example:
This technology generally achieves the remediation plan objectives within a 6-month to 3-year period (Miller 1996).
Main Exposure Mechanisms
Applies or Does Not Apply
Monitoring and Mitigation
Dust
Applies
Emissions monitoring at the source (choice of parameters, types of samples and type of intervention [source, risk or local requirements]).
Atmospheric / Steam Emissions—Point Sources or Chimneys
Emissions monitoring [choice of parameters, types of samples and intervention levels depending on source, risk and local requirements].
Atmospheric / Steam Emissions—Non-point Sources
Modelling the effects of air injection, validation of the model and monitoring the migration of soil vapours.
Air / steam—byproducts
Runoff
Does not apply
N/A
Groundwater—displacement
Modelling and monitoring using pressure sensors.
Groundwater—chemical/ geochemical mobilization
Groundwater—by-product
Accident/Failure—damage to public services
Records checks and pre-excavation permits, development of excavation or drilling procedures and emergency response.
Accident/Failure—leak or spill
Risk review, development of accident and emergency response plans, monitoring and inspection of unsafe conditions.
Accident/Failure—fire/explosion
Other—management of contaminated soils
Applies for soil management resulting from drilling and excavation activities
Composed by : Mahaut Ricciardi-Rigault, M.Sc., MCEBR
Updated by : Karine Drouin, M.Sc., National Research Council
Updated Date : July 20, 2018
Latest update provided by : Nathalie Arel, P.Eng., M.Sc., Christian Gosselin, P.Eng., M.Eng. and Sylvain Hains, P.Eng., M.Sc., Golder Associés Ltée
Updated Date : March 22, 2019
