Public Services and Procurement Canada
The ex-situ solidification/stabilization process is used to trap and limit the migration of contaminants in soils. This technology does not include treatment or disposal of 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 within 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 matrix to be treated by 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.
The method for performing ex-situ solidification/stabilization is to excavate the contaminated matrix, add an agent/stabilizer, mix and then allow it to settle (for setting, curing and hardening) prior to transporting it off-site and disposing of it or reusing it on site as backfill or construction material. The ex situ solidification/stabilization process can be carried out in a processing plant/centre or in a unit (mobile or fixed) set up on site.
Ex situ solidification/stabilization technology can include:
Ex-situ soil stabilization/solidification requires the use of machinery for excavation as well as specialized fixed or mobile equipment for soil treatment. 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 implementation of the process. Temporary piles of contaminated materials may also be located on the site pending treatment.
Treated soils would not be considered waste if they are reused as backfill on the site. Dust may be emitted during excavation, processing, and temporary stockpiling. Water with additives may also be released during the operations. There is a risk of air emissions from equipment exhaust or volatilization of contaminants from fresh excavation walls or temporary piles. If dewatering of the excavation is required, dewatering water may have to be monitored and treated.
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 usually easier to implement in silty, sandy or gravelly soils, as opposed to soils with a high clay content, since it is easier to achieve a uniform mixture. Soils containing clay tend to leave residual clay lenses unmixed and untreated.
Phenolic compounds refer to pentachlorophenol (PCP) only.
If the treated materials are reused on site, long-term monitoring of the ex 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 assessment of the physical integrity of the stabilized area and the maintenance of its geotechnical properties over time, and the integrity of the stabilized soil area may also be validated by long-term monitoring of the vapour emission.
There are no by-products generated during the implementation of the ex situ solidification/stabilization technology. However, this technology does not destroy the contaminants and they are still present following their stabilization. They are retained within the matrix as long as the integrity of the matrix is maintained.
Soil screening may be required to separate the uncontaminated soil particle fractions and reduce the amount of material to be processed.
The following links provide application examples:
Unavailable for this fact sheet
Composed by : Mahaut Ricciardi-Rigault, M.Sc., MCEBR
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