From: Public Services and Procurement Canada
Steam injection is a variation of the more general in situ soil heating technology. Steam injection involves increasing the temperature of the contaminated medium to promote the volatilization and desorption of volatile and semi-volatile organic compounds, as well as petroleum hydrocarbons. The injection of steam into soils with free-phase contaminants allows the contaminants to be moved to extraction systems. Steam injection is usually done in the unsaturated zone but can also be applied below the groundwater level by steam stripping. The same principles of extraction as stripping apply in this case, namely the transfer of contaminants in the vapour phase by volatilization.
The gaseous emissions that are released into the vadose zone by the process are recovered via a vapour extraction system, followed by a treatment.
Steam injection therefore applies to free-phase contaminants, dissolved contamination or residual contamination present in both the vadose zone and in the saturated zone.
A steam injection system includes the installation of wells, supply lines, trenches, permeable drains or other structures for injecting steam. When steam is injected, monitoring points are installed to track steam migration and temperature changes.
Contaminated gaseous emissions are recovered by a vapour extraction system, also composed of wells, trenches or other, installed around the steam injection wells. The vapours extracted from the soil are usually moist. They are often directed to a gas-liquid separator connected to the extraction system before being treated. Treatment systems are generally composed of combustion units (thermal oxidation, catalytic oxidation) or filtration/adsorption units (activated carbon, biofiltration).
The implementation of this technology may include:
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.
Small-scale studies are required to establish the effect of steam injection on treatment efficiency using variables such as the steam injection pressure, the temperature of the steam, the quality of the steam, the time of injection of the steam, etc. Trials are required to determine the optimal design and type of injection and extraction system to be installed (well location, number, type, etc.).
In situ treatment of soils in the vadose zone.
Applicable for VOCs (chlorinated solvents and fuel) and SVOCs (certain pesticides and diesel) present in the free, dissolved or residual phase.
Efficient in sandy and homogeneous soils.
For the mobilization of the free phase, the level and thickness must be monitored at the end of the recovery work, and the installation of recovery devices may be required again if the free-phase product is once more measured in the wells.
Steam injection enhances the volatilization and desorption of volatile and semi-volatile organic compounds. This technology does not produce by-products or metabolites because the contaminants are transferred to the aqueous or gaseous phase. The free, aqueous or gaseous phases must be collected and treated.
Treatment efficiency can be increased by adding soil fracturing to increase airflow (hydraulic or pneumatic fracturing), or by sealing the soil surface to avoid "short-circuiting".
The steam injection must be combined with a system for extracting and treating the extracted vapours.
The following site provides an application example:
The first field trials of steam injection for groundwater treatment occurred in 1983 (Davis 1998). Since then, numerous studies have examined various aspects of the steam injection system. Today, many private companies offer steam injection as a remediation technique.
Composed by : Josée Thibodeau, M.Sc, National Research Council
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
