Fact sheet: Solidification/Stabilization—in situ

From: Public Services and Procurement Canada

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In situ solidification/stabilization is used to trap and limit the migration of contaminants in soils. This technology does not treat or eliminate contaminated materials, but it does reduce their potential impact on the environment.

The solidification/stabilization process consists of mixing contaminated soils, present at shallow or deep depths, with stabilizers and/or binding agents such as gypsum, lime, bentonite clay, Portland cement and various additives such as pozzolans, fly ash, sulfur and blast furnace slag. Polymers, organic materials (biosolids, manure and compost) and various minerals can also be used as admixtures.    

Stabilization involves a transformation of the chemical properties of the contaminants present in the soil matrix by decreasing their solubility in water, their mobility and, therefore, their toxicity.

In addition, solidification involves a transformation of the physical properties of the treated matrix through the addition of binding agents that compact it, modify its pore size and reduce its hydraulic conductivity. The addition of binding agents can maximize the stabilization process.

There are two in situ solidification/stabilization technologies:

  • the first technique involves mixing a binder/stabilizer with the contaminated matrix using an auger driven under pressure and rotation.
  • the second method uses a high-pressure injection system to force a binder/stabilizer in solution into the pores of the contaminated matrix. 

Internet links:

Implementation of the technology

In situ solidification/stabilization technology can include:

  • mobilization, site access and preparation, and the establishment of temporary facilities;
  • the implementation of equipment for the preparation of stabilizers and/or binding agents;
  • the installation of mixing and/or injection equipment;
  • demobilization at the end of the works.

In addition, if volatile components are present or if there is a potential for vapour emissions during stabilization/solidification operations, then a system for collecting and treating these emissions may be required.

Materials and Storage

In-situ soil stabilization/solidification may involve the use of specialized machinery or equipment that may require special installation conditions. On-site storage may include binding agents, admixtures and water required for the process, as well as fuels, lubricants and other site materials required for the operation of machinery or equipment for the process.

Residues and Discharges

Stabilized contaminated soils are not usually considered waste, although they remain in place. However, there is a risk that liquid and vapour residues may be emitted from the system or during the solidification/stabilization process. Similarly, dust may be emitted during mixing operations. Water with added additives could also run off during the work.

Recommended analyses for detailed characterization

Chemical analysis

  • pH
  • Alkalinity
  • Organic matter content
  • Contaminant concentrations present in the following phases:
    • absorbed
  • Groundwater quality upstream, downstream and in the vicinity of the pollution source if stabilized soils are put back in place:
    • Nature and concentrations of contaminants
    • pH
    • Dissolved oxygen
    • Temperature
    • Electrical conductivity
    • Total organic carbon content
    • Concentration of metals

Physical analysis

  • Soil water content
  • Soil granulometry
  • Presence of light or dense immiscible liquids
  • Porosity

Recommended trials for detailed characterization


Other information recommended for detailed characterization

Phase II

  • Presence of potential environmental receptors
  • Presence of above and below ground infrastructure
  • Characterization and delimitation of the extent of the contamination
  • Hydrogeological characterization
  • Determination of the risk and monitoring of the migration of contamination from solidification/stabilization systems

Phase III

  • Volume of contaminated material to treat
  • Characterization of the hydrogeological system including:
    • the direction and speed of the groundwater flow
    • the hydraulic conductivity
    • the seasonal fluctuations
    • the hydraulic gradient
  • Geochemical and/or hydrogeological modeling
  • Determination of preferential pathways for contaminant migration if soils are reused on site


A treatability test is recommended to determine the type and optimal amount of binder/stabilizer to add and to validate the stability of the products for several chemical and physical parameters. These tests also establish the geotechnical properties of the stabilized materials.


Solidification/stabilization technology is only applicable to solid contaminated matrices such as soils, sludges and sediments. Solidification/stabilization technology is used in the unsaturated zone to a depth of approximately 30 m. In addition, it is usually easier to implement in silty, sandy or gravelly soils, as opposed to soils with high clay content, since a uniform mixture is easier to achieve in this case. Soils containing clay tend to leave unmixed and destabilized residual clay lenses.

Applications to sites in northern regions

  • The technology is applicable in northern environments; however, remote sites require more mobilization, resulting in higher on-site supervision costs. In addition, equipment availability is limited and work season is relatively short.
  • Deep freezing, permafrost, and freeze/thaw cycles can limit the depth to which the technology can be effectively installed. Freeze/thaw cycles can also affect the long-term integrity of stabilized media.

Treatment type

Treatment type
Treatment typeApplies or Does not apply
In situ
Ex situ
Does not apply
Does not exist
Dissolved contamination
Does not exist
Free Phase
Residual contamination
Does not exist

State of technology

State of technology
State of technologyExist or Does not exist

Target contaminants

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


For Phenolic compounds, applies to pentachlorophenol (PCP) only.

Treatment time

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

Long-term considerations (following remediation work)

Long-term monitoring of in situ solidification/stabilization performance is generally required to validate its continued effectiveness. Long-term performance monitoring may include groundwater quality monitoring to ensure that contaminants are not leaching from the stabilized soil areas. Long-term monitoring may also include an evaluation of the physical integrity of the stabilized zone and the maintenance of its geotechnical properties over time; the integrity of the stabilized soil zone may also be validated by long-term monitoring of vapour emissions.

Secondary by-products and/or metabolites

There are no by-products generated during the implementation of the in situ solidification/stabilization technology. However, this technology does not treat the contaminants and they are still present on site following stabilization. They are retained within the matrix as long as the integrity of the matrix is maintained. 

Limitations and Undesirable Effects of the Technology

  • Solidification/stabilization technology is a remediation technique that controls only the migration of contaminants in soils
  • The performance of solidification/stabilization technologies depends on site characteristics and thus cannot be estimated.
  • The depth of contamination may limit certain types of application processes, introduction of binding or stabilizing agents, and sampling campaigns.
  • Solidified/stabilized material may be susceptible to leaching after some time, depending on factors such as climate.
  • Mineral salts, strong acids or bases present in the contaminated matrix may interfere with the solidification/stabilization process.
  • The presence of large debris or blocks can interfere with the solidification/stabilization process.
  • It can be difficult to formulate an effective binding agent for heterogeneous mixtures of waste materials.
  • Soil heterogeneity can limit the depth and efficiency of the solidification/stabilization process
  • Soil amendments used for in situ stabilization can impact the pH and organic content of the soil.
  • Injection and mixing of binders should be controlled to minimize the spread of contaminants into uncontaminated areas.
  • The use of the site may be changed or restrictions may be imposed as a result of the implementation of the technology (e.g., planting of deep-rooted trees or other subsurface activities that would require approval).
  • The solidification/stabilization in situ reduce water infiltration into soil. 
  • Some stabilization/solidification processes increase the volume of the treated matrix.
  • Frequent rain and freeze/thaw cycles can reduce the life expectancy of solidified/stabilized material and thus increase the mobility of contaminants.
  • The use of certain binding agents can cause an exothermic reaction (temperature increase) in the presence of certain contaminants such as waste oil or tar. There will then be a potential for increased volatilization of certain contaminants (vapour emissions).

Complementary technologies that improve treatment effectiveness

Soil screening may be required to separate the uncontaminated soil particle fractions and reduce the amount of material to be processed. 

Required secondary treatments

  • Collected vapour emissions (if applicable) may have to be treated with a recovery system before being released to the atmosphere.

Application examples

The following links provide application examples: 


  • This technique can treat up to 100 m3/d depending on the environmental conditions of the treatment site. 
  • Contaminant concentrations in leachate can be reduced by 95% or more after soil stabilization. 

Measures to improve sustainability or promote ecological remediation

  • Carrying out treatability tests to optimize the mixture and reduce the need for chemical amendments.
  • Use of renewable energy and energy-efficient equipment for technology implementation.
  • Optimization of the planning schedule to promote resource sharing and reduce the number of mobilization days.
  • Consideration for locally available and/or recycled materials in system design;
  • Use of residual materials or by-products from industrial processes, if appropriate, as additives or amendments (such as cement kiln dust from cement manufacturing);
  • Optimization of the process to reduce waste and consumables.
  • Consideration of climate change is required at the design stage and for the development of the long-term performance monitoring program.
  • Use of the TRIAD approach for the planning and execution of site characterization steps in order to optimize characterization efforts and reduce the ecological footprint of this work.
  • Technology implementation and site remediation that optimizes the protection of ecological habitats and/or improves the quality of these habitats.

Potential impacts of the application of the technology on human health

Unavailable for this fact sheet


Author and update

Composed by : Martin Désilets, B.Sc., National Research Council

Updated by : Martin Désilets, B.Sc., National Research Council

Updated Date : April 1, 2008

Latest update provided by : Nathalie Arel ing., M.Sc., Frédéric Gagnon CPI., Sylvain Hains ing., M.Sc., Golder Associates Ltd.

Updated Date : March 2, 2022