Fact sheet: Hydraulic containment

From: Public Services and Procurement Canada

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Description

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.

Pumping Wells

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

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.

Internet links:

Implementation of the technology

The process may include:

  • Detailed hydrological and geological site investigation;
  • Mobilization, site access and set-up of temporary facilities;
  • Installation of groundwater interception system using either trenches, drains or pumping wells;
  • Pumps (typically electric or pneumatic pumps) and conveyance pipe (often underground in trenches engineered for frost and traffic protection) installation;
  • Treatment system installation. This may require a small building or container. Groundwater treatment components depends on the contaminant. For petroleum hydrocarbons, systems usually can include oil/water separation, air stripping, activated carbon adsorption, while metal removal could include filtration, coagulation/precipitation, ion exchange or reverse osmosis. A more comprehensive list is presented in a section below;
  • Discharge system installation, such as discharge to existing pipelines (local stormwater or sanitary sewer system), new surface water outfall, re-injection into the ground or into injection wells, infiltration field, or infiltration pond;
  • Long-term monitoring is required to ensure that groundwater concentrations are below regulatory levels after the shutdown.

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.

Materials and storage

  • Construction activities related to hydraulic containment are typically low-impact, with minimal on-site stores;
  • The groundwater treatment systems typically stock fresh reactants, process chemicals and treatment residuals. Depending on the type of treatment used, it may include oxidants (such as hydrogen peroxide or chlorine), reductants (such as polysulphides), biological substrates, spent sorption media, collected sludge, sorbents and antifoaming agents.

Waste and Discharges

  • System installation typically requires drilling or excavating in contaminated areas, resulting in the handling and disposal of contaminated soils, typically containerized and disposed off-site. Drill cuttings and downhole equipment may be highly contaminated; 
  • The groundwater treatment systems may generate extensive solid, liquid and gaseous residuals. For example:
    • Spent sorbent (for example, activated carbon) and collected solids (sludge) require collection and off-site transport;
    • Waste brine from reverse osmosis reject flow or ion exchange regeneration solutions may contain concentrated contaminants;
    • Biological systems may off-gas compounds such as carbon dioxide, methane and hydrogen sulphide; skimming tanks may off-gas volatile contaminants that have accumulated; 
    • Vapour emissions may be of concern if, for example, air stripping, aeration, ozonation, treatment systems are used. In rare cases, groundwater off-gasses to a significant degree (for example, effervescent mineral waters);
  • In theory, treated groundwater should meet applicable criteria for release and doesn’t constitute a high-risk discharge. Inadequately treated streams containing by-products, excess reactants or at unacceptable pH levels may constitute a hazard to downstream receptors.

Recommended analyses for detailed characterization

Chemical analysis

  • pH
  • Contaminant concentrations present in the following phases:
    • adsorbed
    • dissolved
    • free

Physical analysis

  • Soil granulometry
  • Presence of non-aqueous phase liquids (NAPLs)

Recommended trials for detailed characterization

Hydrogeological trials

  • Permeability test
  • Pumping trials
  • Tracer tests

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.

Other information recommended for detailed characterization

Phase II

  • Contaminant delineation (area and depth)
  • Presence of receptors:
    • presence of potential environmental receptors
    • presence of above and below ground infrastructure
    • the risk of off-site migration

Phase III

  • Soil stratigraphy
  • Identification of preferential pathways for contaminant migration
  • Verify whether a confined aquifer is present
  • Conceptual site model with hydrogeological and geochemical inputs
  • Characterization of the hydrogeological system including:
    • the direction and speed of the groundwater flow
    • the hydraulic conductivity
    • the seasonal fluctuations
    • the hydraulic gradient

Applications

  • Hydraulic containment is used to prevent and/or reduce the migration of dissolved contamination;
  • Containment techniques can offer a short-term solution before or during the rehabilitation of a site;
  • Allows for the recovery of a wide range of dissolved contaminants;
  • Allows for the recovery of NAPL (light or dense);
  • Must be combined with an above ground treatment system to treat the contaminated groundwater.

Applications to sites in northern regions

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.  

Treatment type

Treatment type
Treatment typeApplies or Does not apply
In situ
Applies
Ex situ
Does not apply
Biological
Does not exist
Chemical
Does not exist
Control
Applies
Dissolved contamination
Applies
Free Phase
Does not exist
Physical
Applies
Residual contamination
Does not exist
Resorption
Does not exist
Thermal
Does not exist

State of technology

State of technology
State of technologyExist or Does not exist
Testing
Does not exist
Commercialization
Exist

Target contaminants

Target contaminantsApplies, Does not apply or With restrictions
Aliphatic chlorinated hydrocarbons
Applies
Chlorobenzenes
Applies
Explosives
Applies
Metals
Applies
Monocyclic aromatic hydrocarbons
Applies
Non metalic inorganic compounds
Applies
Pesticides
Applies
Petroleum hydrocarbons
Applies
Phenolic compounds
Applies
Policyclic aromatic hydrocarbons
Applies
Polychlorinated biphenyls
Applies

Notes:

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.

Treatment time

Treatment time
Treatment timeApplies or Does not apply
Less than 1 year
Applies
1 to 3 years
Applies
3 to 5 years
Applies
More than 5 years
Applies

Notes:

Hydraulic containment techniques are non-specific technologies that prevent the spread of a contaminant plume and are applicable to all kinds of dissolved contaminants.

Long-term considerations (following remediation work)

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.

Secondary by-products and/or metabolites

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.

Limitations and Undesirable Effects of the Technology

  • Hydraulic containment techniques are not suitable for all aquifers;
  • Hydrogeological conditions of the contaminated site may change during the pumping (such as seasonable variations), in which case, the containment system may need to be adjusted, modified or replaced;
  • Trenches or drainage systems are difficult to implement when the contamination is located more than 10 m below the soil surface;
  • For hydraulic containment using open-air trenches, the limitations to soil excavation in general apply (slope stability considerations and protection, groundwater dewatering, protection of infrastructure, safety measures, etc.);
  • Major changes to groundwater flow have the potential to alter infiltration, transport and discharge, which has the potential to change geochemical properties of groundwater such as pH and oxidation-reduction potential and fate of metals;
  • Pumping with or without re-injection can affect groundwater flow outside of the treatment area;
  • Spills of conveyance piping with contaminated water could affect uncontaminated areas;
  • Inadequate or inappropriate treatment may expose receptors downstream to contaminants or by-products.

Complementary technologies that improve treatment effectiveness

  • Soil fracturing maybe used to create new transport pathways and increase the groundwater yields;
  • The use of underground structures to contain and divert flow towards the hydraulic containment system such as sheet piles and cement/bentonite walls is possible;
  • Funnel and gate systems where the hydraulic system is installed in the gate can be used.  

Required secondary treatments

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:

  • Skimming/oil-water separation;
  • Chemical and/or UV oxidation to treat volatile and semi-volatile organic compounds (VOCs and SVOCs, respectively), some hydrocarbons and pesticides;
  • Air or vapour stripping to treat VOCs;
  • Adsorption onto matrices, such as activated carbon, to treat SVOCs and some metals;
  • Bioreactor treatment to treat non-halogenated VOCs, SVOCs, and petroleum hydrocarbons;
  • Membrane separation to treat VOC and SVOC hydrocarbons;
  • Redox reactors to treat ferrous iron, hexavalent chromium, lead, and mercury;
  • Reverse osmosis;
  • Ion exchange;
  • Heavy metal precipitation;
  • Coagulation and flocculation;
  • Filtration;
  • Electro coagulation;
  • Phytoremediation (in the form of treatment wetlands);
  • Liquid/liquid extraction.

Application examples

Application examples are available at these addresses:

Performance

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.

Measures to improve sustainability or promote ecological remediation

  • Ensure pump size is appropriate and pump is energy efficient;
  • Optimize scheduling to reduce resources and the days of mobilization;
  • Use of renewable energy and energy-efficient equipment (such as solar energy for pumps, geothermal or solar energy for treatment systems);
  • Optimize pumping flow rates to reduce energy (pumping system and water treatment);
  • Ensure water treatment process is efficient and reduce wastes and consumables such as replacing activated carbon with biofilters.                        

Potential impacts of the application of the technology on human health

Unavailable for this fact sheet

References

Author and update

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

Version:
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