From: Public Services and Procurement Canada
Hydraulic containment is used to control the migration of dissolved contaminants. There are two approaches commonly used to perform hydraulic containment: the use of pumping wells to change the hydraulic gradient and the excavation of trenches or installation of drains to intercept the contaminant plume. This technology requires a simple operation system. Targeted contaminants include non-aqueous phase liquid (NAPL), light and dense, and a wide range of dissolved contaminants.
When using pumping wells, the goal is to modify the groundwater gradient to slow down or stop the migration of the contaminated plume. The pumped groundwater is either treated or disposed-of in an appropriate manner.
Trenches and drains are used for shallow groundwater contamination or in an emergency where the contamination migrating towards a sensitive environmental receptor. Trenches and drains may be installed upstream of the contamination to prevent the non-contaminated groundwater from entering a contaminated plume, or downstream to prevent the contaminated water from migrating towards an environmental receptor. The contaminated water is pumped from trenches or drainage systems, and is directed into an on-site treatment system or sent to an authorized disposal facility.
The process may include:
This method relies on traditional/commonly available water well, drainage, water works and utility construction equipment and methods. Conveyance is typically by pressurized, full-pipe flow. Gravity drainage has been employed at a small number of hydraulically suitable sites. Extraction and conveyance usually require energy and maintenance chemicals to periodically clean out scaling or fouling.
Hydraulic containment requires in depth hydrogeological knowledge of the site (including modelling) and is often implemented initially on a “pilot” scale. Once the system is online, pumping data may allow for more detailed analysis of the capture zone, which in turn may lead to modifications to the pumping system in order to improve its effectiveness in capturing or containing groundwater contamination.
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.
Remote and northern sites are prone to high mobilization and installation costs and limited equipment availability. Active groundwater extraction and treatment systems may not be appropriate for remote northern sites without access to utilities or local operations and maintenance labour. Conveyance piping installation in permafrost may present challenges and be cost prohibitive for such sites. Passive technologies such as “Permeable/Passive Reactive Barriers” maybe considered as an alternative. Northern systems typically require climate-appropriate design, including consideration of deep frost, seasonal changes in ground conditions and long periods without operator intervention.
Hydraulic containment may be in operation for varying time frames, from a few years to decades, depending on the objective of the installation. As this is not a source remediation approach, the operation time frame can be infinite.
When a system is initially taken off-line, “rebound” is often observed. In “rebound,” contaminant concentrations in groundwater increase after groundwater level returns to its normal level due to potential residual contaminants sorbed to the soil while operating the containment system. Long-term monitoring is required to ensure that post-shutdown groundwater concentration stay below levels of concern.
Hydraulic containment techniques prevent the migration of dissolved contaminant plumes, and do not transform nor destroy contaminants. There is no by-product production during the application of these techniques.
However, within a given treatment system, incomplete reaction may result in hazardous degradation products.
Treatment of the contaminated water is required and can be performed using several ex situ technologies.
Pump and treat are mainly a recovery technique that applies to a wide range of contaminants. There are a variety of above ground (ex situ) treatment systems that can remove or destroy the contaminants within the groundwater.
Examples of techniques to treat pumped groundwater is presented below but this list is not exhaustive:
Application examples are available at these addresses:
Performance of hydraulic containment techniques is influenced by the hydrogeological conditions of the contaminated site. A well-adapted system of hydraulic containment is efficient over short to long periods of time.
Unavailable for this fact sheet
Composed by : Josée Thibodeau, M.Sc, National Research Council
Updated by : Jennifer Holdner, M.Sc., Public Works Government Services Canada
Updated Date : April 30, 2014
Latest update provided by : Marianne Brien, P.Eng., Christian Gosselin, P.Eng., M.Eng., Golder Associés Ltée
Updated Date : March 31, 2018
