Fact sheet: Air sparging

From: Public Services and Procurement Canada

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Description

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:

Implementation of the technology

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:

  • Mobilization, access to the site and setting up temporary facilities.
  • The development of air injection points (wells, trenches or reactive barriers).
  • The installation of an air injection system consisting of individual blowers or a central blower and a set of distribution lines.
  • Dismantling of equipment and removal of injection and extraction points if applicable.

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.”

Materials and Storage

  • This technology is implemented using traditional methods and equipment that are commonly available for wells development and installation.
  • Treatment units can be built on-site or pre-assembled and transported in shipping containers, trailers or pallets.
  • Certain equipment requires the installation of a power source and may require the use of maintenance products.
  • Construction and landscaping generally have a minimal impact and require few on-site storage.

Residues and Rejects

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.

Recommended analyses for detailed characterization

Chemical analysis

  • Contaminant concentrations present in the following phases:
    • adsorbed
    • dissolved
  • iron
  • manganese

Physical analysis

  • Soil granulometry
  • Contaminant physical characteristics including:
    • viscosity
    • density
    • solubility
    • vapour pressure
    • etc.
  • Presence of non-aqueous phase liquids (NAPLs)

Recommended trials for detailed characterization

Physical trials

  • Gas permeability trials
  • Vapour survey
  • Evaluation of the radius of influence
  • Airflow rate
  • Evaluation of operating pressure/vacuum

Hydrogeological trials

  • Tracer tests

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.

  • Hydraulic conductivity testing
  • Other information recommended for detailed characterization

    Phase II

    • Contaminant delineation (area and depth)
    • Presence of receptors:
      • presence of potential environmental receptors
      • presence of above and below ground infrastructure
      • the risk of off-site migration

    Phase III

    • Identification of preferential pathways for contaminant migration
    • Characterization of the hydrogeological system including:
      • the direction and speed of the groundwater flow
      • the hydraulic conductivity
      • the seasonal fluctuations
      • the hydraulic gradient

    Notes:

    Field tests are recommended to evaluate the effectiveness of this technology and to determine the injection wells installation scheme, injection wells radius, air injection rate, and design of a vapour extraction system, if required, adapted to the specific conditions of the site.

    Applications

    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.

    Applications to sites in northern regions

    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.

    Treatment type

    Treatment typeApplies or Does not apply
    In situ
    Applies
    Ex situ
    Does not apply
    Biological
    Applies
    Chemical
    Does not exist
    Control
    Does not exist
    Dissolved contamination
    Applies
    Free Phase
    Applies
    Physical
    Applies
    Residual contamination
    Applies
    Resorption
    Applies
    Thermal
    Does not exist

    State of technology

    State of technologyExist or Does not exist
    Testing
    Does not exist
    Commercialization
    Exist

    Target contaminants

    Target contaminantsApplies, Does not apply or With restrictions
    Aliphatic chlorinated hydrocarbons
    Applies
    Chlorobenzenes
    Applies
    Explosives
    Does not apply
    Metals
    Does not apply
    Monocyclic aromatic hydrocarbons
    Applies
    Non metalic inorganic compounds
    Does not apply
    Pesticides
    Does not apply
    Petroleum hydrocarbons
    With restrictions
    Phenolic compounds
    Applies
    Policyclic aromatic hydrocarbons
    With restrictions
    Polychlorinated biphenyls
    Does not apply

    Treatment time

    Treatment timeApplies or Does not apply
    Less than 1 year
    Does not apply
    1 to 3 years
    Applies
    3 to 5 years
    Applies
    More than 5 years
    Applies

    Long-term considerations (following remediation work)

    After removal of the treatment system, monitoring of groundwater quality may be required.

    Secondary by-products and/or metabolites

    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.

    Limitations and Undesirable Effects of the Technology

    • Airflow through the saturated zone may not be uniform due to factors such as the heterogeneity of the hydrogeological system.
    • A vapour extraction system and gas intrusion monitoring are required when there are buildings and/or below-grade infrastructure on or near the contaminated site.
    • Injected air can seep into foundation drains, utility trenches, or other preferred pathways on the site being treated.
    • Presence of free phase can create groundwater mounding which could potentially cause free product migration and spreading of the contamination.
    • Biosparging cannot be applied in a confined aquifer.
    • Intrinsic soil permeability (k) should be higher than 10-5 cm/s.
    • Air or gas injection enhances clogging of injection wells and soil pores when high ferrous iron and/or dissolved manganese concentrations are present.
    • The uncontrolled migration of vapours can affect off-site receivers.

    Complementary technologies that improve treatment effectiveness

    • Hot air injection increases the performance of the air sparging technique and allows for treatment of certain semi-volatile organic compounds such as ketones.
    • Biosparging can be used for the bioremediation of non-volatile and semi-volatile organic compounds.
    • Methane can be used as additives to injected air to improve the co-metabolism of chlorinated organic products.
    • Some hydraulic containment techniques help to stabilize the contamination plume and facilitate the application of an air sparging treatment.

    Required secondary treatments

    Air sparging technology is often combined with vapour extraction and treatment systems.

    Application examples

    The following website provides an application example:

    Performance

    This technology generally achieves the remediation plan objectives within a 6-month to 3-year period (Miller 1996).

    Measures to improve sustainability or promote ecological remediation

    • Optimization of the calendar to promote the sharing of resources and reduce the number of days of mobilization.
    • Use of renewable energy and low-energy equipment (geothermal or solar).
    • Optimization of equipment size.
    • Use of biofilters for air treatment reduces energy demand and waste generation.
    • Allow a longer treatment time to avoid winter operation, eliminating the need to winterize the system while reducing the amount of energy required.
    • Evaluate the benefits of a pulsed oxygen injection system over a continuous injection system.
    • Limit the number of field visits using telemetry for remote monitoring of system conditions (e.g. pressure and injected airflow).

    Potential impacts of the application of the technology on human health

    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

    Applies

    Emissions monitoring [choice of parameters, types of samples and intervention levels depending on source, risk and local requirements].

    Atmospheric / Steam Emissions—Non-point Sources

    Applies

    Modelling the effects of air injection, validation of the model and monitoring the migration of soil vapours.

    Air / steam—byproducts

    Applies

    Emissions monitoring [choice of parameters, types of samples and intervention levels depending on source, risk and local requirements].

    Runoff

    Does not apply

    N/A

    Groundwater—displacement

    Applies

    Modelling and monitoring using pressure sensors.

    Groundwater—chemical/ geochemical mobilization

    Does not apply

    N/A

    Groundwater—by-product

    Does not apply

    N/A

    Accident/Failure—damage to public services

    Applies

    Records checks and pre-excavation permits, development of excavation or drilling procedures and emergency response.

    Accident/Failure—leak or spill

    Applies

    Risk review, development of accident and emergency response plans, monitoring and inspection of unsafe conditions.

    Accident/Failure—fire/explosion

    Applies

    Risk review, development of accident and emergency response plans, monitoring and inspection of unsafe conditions.

    Other—management of contaminated soils

    Applies for soil management resulting from drilling and excavation activities

    Risk review, development of accident and emergency response plans, monitoring and inspection of unsafe conditions.

    References

    Author and update

    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

    Date Modified: