From: Public Services and Procurement Canada
The principle of the frozen barrier is to artificially freeze the water contained in the pores of the soil. Its freeze causes a decrease in permeability and can form an impermeable barrier. This barrier prevents the migration of contaminants.
To do this, a piping system consisting of refrigerating tubes which circulates a refrigerant, such as liquid carbon dioxide, is installed in the area where the migration of contaminants must be limited. The tubes are installed in boreholes, downstream from the contaminated area and perpendicular to the direction of groundwater flow, to prevent the migration of contaminants. These freezing boreholes are called thermoprobes, freezing probes or freezing wells.
This system permits chilling of the soil matrix to temperatures ranging from -20 °C to -40 °C. By thermal conduction, the groundwater in soil pores surrounding the refrigerant tubes freezes to a thickness of up to 20 m. The aquifer is thereby frozen, and acts as an impermeable wall containing the dissolved contamination. This type of wall can be installed without excavation and down to depths of 300 m. Soil freezing can also be achieved by using a thermosiphon (a passive heat transfer device used for permafrost stabilization) if the ambient temperatures are sufficiently cold.
Sources:
A frozen barrier involves the installation of wells and piping that allow refrigerant circulation within freezing probes installed through the soil, in order to freeze the water in the soil and produce a barrier.
The implementation of such a system may include:
Materials and Storage
Residues and Discharges
The installation and the operation of a frozen barrier generate few residues and discharges with the exception of drill cuttings resulting from the development of probes or wells for the implementation of piping.
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.
The establishment of a frozen barrier is possible in northern regions but requires a good power supply and constant monitoring of the ground temperatures to validate the integrity of the barrier. This type of environment favours the use of thermosiphon passively because of the cold temperatures of the ambient air. These devices do not require power supply.
Allows control of the dissolved contamination only.
During barrier operation, monitoring of ground temperatures and groundwater levels are required upstream and in barrier position. In addition, monitoring the quality of groundwater downstream of the barrier must also be done.
System maintenance and the presence of a back-up power source in case of power failure are also recommended especially if the contamination is very mobile.
The frozen barrier does not produce any by-products since this technology only allows the control of contaminant migration rather than the treatment of the contamination.
A frozen barrier does not treat groundwater, but only limit its migration. Thus, the dissolved contamination upstream of the barrier must be pumped and treated by a groundwater abstraction and treatment system.
Required Secondary Treatments
Does not apply.
There is currently no information regarding required secondary treatment.
Frozen barrier technology has been field-tested, certified and documented by US DOE Innovative Technology (DOE/EM-0273).
The following sites provide application examples:
The frozen wall technology was efficient in the containment of contaminated groundwater at the Oak Ridge site, Tennessee (U.S. EPA, 1997). To maintain the frozen wall, the system required 288 kilowatts of electricity per hour.
Main Exposure Mechanisms
Applies or Does Not Apply
Monitoring and Mitigation
Dust
Does not apply
N/A
Atmospheric / Steam Emissions—Point Sources or Chimneys
Don't apply
Atmospheric / Steam Emissions—Non-point Sources
Air / steam—by-products
Runoff
Groundwater—displacement
Applies
Modelling the effects of the required barrier and monitoring using pressure sensors.
Groundwater—chemical/ geochemical mobilization
Groundwater—by-product
Accident/Failure—damage to public services
File checks and obtaining pre-drilling licences, development of 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 drill cuttings
Applies for the management of drill cuttings resulting from the realization of wells for the installation of piping.
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
