From: Public Services and Procurement Canada
Hot water injection is an in situ remediation technology that was developed to facilitate the movement of free phase products or the desorption of adsorbed phases to an extraction system or an in situ treatment zone. This technology is a variation of the most general soil heating technology.
The injection of hot water into the aquifer increases the ambient temperature, which consequently reduces the viscosity of the free-phase products, decreases their adsorption onto soil particles or organic matter and increases the dissolution of contaminants.
A hot water injection system includes the installation of a network of wells or other structures that are used to inject water into the treatment area.
A vapour containment and recovery system above the hot water treatment area are recommended to prevent volatilization of contaminants and emission of gas to the soil surface. The hot water injection technique must be combined with a system for extracting products in dissolved and/or free phases, such as a pumping system or an in situ system for the treatment of contaminants.
The implementation of this technology may include:
The development of wells or trenches generally requires drilling or excavation activities in contaminated areas. This results in the handling of contaminated soils that will have to be removed off-site.
Recovered free-phase products will be accumulated inside a tank. These products will then have to be managed off-site.
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 recommended to determine the effect of increased temperatures on the free-phase products. These trials will also provide important information for the design of the hot water injection system (injection pressure, water temperature, time of injection, type of injection wells, zone of influence, etc.) and the design of the extraction system.
Hot water injection is not always appropriate in remote areas that do not have easy access to utilities or local labour to operate and maintain the system. The development of this type of system in a northern environment may require climate-adapted techniques that consider, deep freezing of the soil, seasonal changes in soil conditions and long periods without intervention by the system operator. The operating costs of this type of system, in northern environments, could be high, because of the energy required for heating water.
Free-phase product levels and thicknesses should be monitored when the recovery work is stopped and recovery devices may be required again if free-phase product is newly measured.
In highly contaminated sites where the goal is to reach specific residual levels, this technology may not be able to achieve low concentrations. Potential polishing techniques are soil washing by adding solvents or surfactants, bioremediation or chemical oxidation.
A vapour extraction and treatment system may also be required.
The following site provides in application example:
Hot water injection is rarely effective because it is affected by soil permeability, solubility of the contaminant, and it is very energy intensive and requires a lot of control methods. Its use is limited to very specific conditions.
Main exposure mechanisms
Applies or does not apply
Monitoring and mitigation
Dust
Does not apply
N/A
Atmospheric/Steam Emissions—Point Sources or Chimneys
Applies
Emissions monitoring (choice of parameters and levels of intervention depending on source, risk and local requirements).
Atmospheric/Steam Emissions—Non-point Sources
Modelling the effects of water injection, model validation and soil vapour migration monitoring.
Air/steam—by-products
Emissions monitoring (choice of parameters, types of samples and type of intervention [source, risk or local requirements]).
Runoff
Groundwater—displacement
Modelling of the water injection network and mobilization of the free phase and monitoring of the groundwater level using pressure sensors
Groundwater—chemical/ geochemical mobilization
Groundwater—by-product
Accident/Failure—damage to public services
File verification and licensing of pre-drilling or excavation work, development of special excavation or 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 or explosion (inflammable vapour)
Other—Handling contaminated soils or other Solids
Composed by : Josée Thibodeau, M.Sc, National Research Council
Updated by : Martin Désilets, B.Sc., National Research Council
Updated Date : April 17, 2013
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
