Fact sheet: Pump and Treat

From: Public Services and Procurement Canada

On this page

Description

Pump and treat technologies are probably the most commonly used systems for the remediation of contaminated groundwater. These techniques are convenient for treating a wide range of contaminants, as long as the contaminants are to some degree soluble. These technologies involve increasing the hydraulic gradient in the saturated zone with a pumping system(s) to enhance the migration of contaminants and contaminated groundwater toward the pumping well(s). The contaminated groundwater is pumped and treated above ground before being disposed of or returned to the aquifer. The use of pump and treat technologies can help control the migration and spread of the contaminant plume.

The decontamination of a site can be a difficult and lengthy process, taking from years to decades to accomplish. In some cases, pump and treat techniques are used when non-aqueous phase liquids (NAPLs) are present on site, particularly when the NAPL is associated with dissolved contamination. More information regarding the use of the pump and treat techniques for NAPL decontamination is available in the technical sheets “Drawdown pumping system for NAPL” and “Pump and Treat for Dense Non-Aqueous Phase Liquids (DNAPL)”.

Effective use of pump and treat technologies requires a thorough knowledge of the physical properties of the contaminant(s) and of the geological and hydrogeological conditions of the contaminated site in order to allow the installation of the most efficient pumping system.

Internet links:

Implementation of the technology

  • The system may include:
  • Detailed environmental, hydrological and geological site characterization
  • Mobilization, preparation of the site and site access and set-up of temporary facilities
  • Installation of groundwater pumping wells and observation wells
  • Groundwater pumping and controls, typically using electric or pneumatic pumps
  • Installation of pumps conveyance pipe (often underground in trenches engineered for frost and traffic protection)
  • Accumulation in tanks of separated NAPL, if present, for off-site disposal
  • Groundwater treatment system installation; this may require a small building or container; treatment varies depending on the contaminant but may include filtration or coagulation/precipitation, activated carbon sorption, air stripping, chemical and/or UV oxidation, biological treatment, ion exchange or reverse osmosis, evaporation, dissolved air floatation, skimming/oil-water separation, electro coagulation, phytoremediation (treatment wetlands), steam stripping, and liquid/liquid extraction
  • If vapours are generated (e.g. by air stripping), vapour/off-gas treatment which may include thermal oxidation, catalytic oxidation, biofiltration or granular activated carbon sorption
  • Discharge system installation, such as discharge to existing pipelines, new surface water outfall, re-injection into the ground, to injection wells, infiltration field or infiltration pond, to local stormwater or sanitary sewer systems or to surface water
  • Pumping well and treatment plant decommissioning
  • Long-term monitoring is required to ensure that groundwater concentrations are below regulatory levels after the shutdown

Pump and treat require in-depth hydrogeological knowledge of the site and is often implemented based on a number of field tests such as slug tests and pumping tests, followed by a groundwater modelling study.  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 aimed at improving its effectiveness in capturing or containing groundwater contamination.

Materials and storage

  • Pump and treat systems rely on traditional water well, drainage, water works and utility methods and commonly available construction equipment. Conveyance is typically achieved by pressurized, full-pipe flow. Gravity drainage has been employed at a small number of hydraulically suitable sites. Extraction and conveyance usually require energy input
  • Maintenance chemicals are required to periodically clean out scaling or fouling.
  • Construction activities are typically low-impact, with minimal on-site stores
  • Treatment systems typically stock fresh reactants and process chemicals as well as collected residuals, such as concentrated brines, spent sorption media or collected sludge. These may include a range of oxidants (such as hydrogen peroxide or chlorine), reductants (such as polysulphides), biological substrates, sorbents, regenerant brines, anti-foulants, anti-scaling compounds (including phosphonates, polyphosphates, sulphamic acid), emulsion breakers (solvents, non-ionic surfactants, various amines, specialty polymers), antifoaming agents, etc.

Waste and Discharges

  • System installation typically requires drilling or excavating in contaminated areas, resulting in the handling and disposal of contaminated soils, which are typically containerized and disposed of 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, such as 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, or ozonation treatments systems are used. In rare cases, the groundwater itself off-gasses to a significant degree (for example, effervescent mineral waters)
    • Free product (NAPL) is typically batched in drums or tanks for eventual shipping off-site. On-site use or destruction (typically by incineration or co-firing with other fuels) may be applied. Note that waste fuel, dirty fuel and/or waste oil combustion in unspecialized equipment may cause deleterious emissions to air
  • In theory, treated groundwater should meet applicable criteria for release and doesn’t constitute a high-risk discharge. Inadequately treated discharge containing by-products, excess reactants or at unacceptable pH levels may constitute a hazard to downstream receptors

Recommended analyses for detailed characterization

Physical analysis

  • Soil granulometry
  • Type and concentration of mineral salts in contaminated matrix

Recommended trials for detailed characterization

Hydrogeological trials

  • Permeability test
  • Pumping trials

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
  • Characterization of the hydrogeological system including:
    • the direction and speed of the groundwater flow
    • the hydraulic conductivity
    • the seasonal fluctuations
    • the hydraulic gradient

Applications

  • 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
  • Operation and maintenance of the system are simple
  • Soils must be sufficiently permeable to allow the movement of the contaminant(s) toward the pumping wells. Soils with permeability greater than 10-4 cm/s allow for sufficient contaminant circulation
  • Pumping may increase aeration of the vadose zone, which enhances biological activity.  This secondary effect is particularly pronounced within the cone of aquifer depression where residual contaminants tend to accumulate

Applications to sites in northern regions

Remote and northern sites typically entail high mobilization and installation costs and may suffer from limited equipment availability.  Active groundwater extraction and treatment systems may not be appropriate for remote northern sites without access to utilities or local operations & maintenance labour.  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
Applies
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
With restrictions
Metals
With restrictions
Monocyclic aromatic hydrocarbons
Applies
Non metalic inorganic compounds
Applies
Pesticides
With restrictions
Petroleum hydrocarbons
Applies
Phenolic compounds
With restrictions
Policyclic aromatic hydrocarbons
With restrictions
Polychlorinated biphenyls
With restrictions

Treatment time

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

Notes:

Pump and treat systems maybe in operation for a period of years to decades. These systems are prone to “tailing,” in which contaminant concentrations in groundwater asymptotically approach a steady state value above the remediation criteria, necessitating the indefinite operation of the collection and treatment system.

Long-term considerations (following remediation work)

When a system is initially taken off-line, “rebound” is often observed. “Rebound” refers to the increase in contaminant concentrations in groundwater which is sometimes observed after flushing/dilution by the pump-and-treat system ends. Long-term monitoring is required to ensure that post-shutdown groundwater concentrations stay below levels of concern. When further contaminant recovery becomes uneconomic, the system is often replaced with an alternative residual impact management strategy, such as bioremediation or monitored natural attenuation.

Secondary by-products and/or metabolites

Generally, there are no in-situ by-products from pump and treat operations. However, within a given treatment system, incomplete reaction may result in hazardous degradation products. In rare cases where chlorination is employed, disinfection by-products such as trichloromethane may be formed.

To limit the potential for adding deleterious substances to water during treatment, some practitioners specify that reagents certified for drinking water treatment is used (for example, NSF/ANSI Standard 60, WQA Gold Seal).

Limitations and Undesirable Effects of the Technology

  • Treatment time can be long and indefinite
  • The treatment cost may be significant considering the duration of treatment
  • Residual contamination is difficult to treat
  • Soil permeability must be greater than 10-4 cm/s
  • A large quantity of water must be treated and managed
  • Presence of impermeable sub-layers or preferential pathways can reduce the efficiency of contaminant recovery
  • Clogging or biofouling (excessive growth of microorganisms) of the extraction wells and associated treatment equipment may occur and will require additional maintenance requirements
  • Major changes to groundwater flow have the potential to alter infiltration, transport and discharge, which in turn may alter qualities such as pH and oxidation-reduction potential
  • Pumping (with or without re-injection) substantially changes groundwater hydraulics. Re-injection and infiltration also change flow paths, creating groundwater “mounds” that may drive flow in new directions
  • Collection/conveyance accidents are unlikely to affect off-site receptors with the exception of scenarios in which leaks of contaminated water to uncontaminated areas occur
  • Inadequate or inappropriate treatment may expose receptors downstream to contaminants or by-products
  • Treatment chemicals may include strong acids, bases, oxidants or reductants, improper handling and storage of which can result in spill or explosion

Complementary technologies that improve treatment effectiveness

  • Thermal treatment may increase the movement of the residual contaminant(s) toward the pumping wells
  • Thermal treatment combined with a vapour extraction system may increase the movement of the residual contaminant(s) toward the pumping wells when treating NAPL contamination
  • The injection of surfactant or solvent solutions may increase recovery of the contamination by the pumping system
  • Soil fracturing maybe used to create new transport pathways and increase groundwater yields
  • Applying a vacuum at the well head may increase the movement of water and contaminants. This technique is known as Vacuum-enhanced recovery (VER)

Required secondary treatments

Pump and treat is primarily a recovery technique and can be applied to a wide range of soluble contaminants. The choice of an appropriate above ground treatment system depends on the nature of contaminants identified and the properties of the groundwater.  Treatment options can be considered in two categories, those used for organic dissolved contamination and those appropriate for inorganic dissolved contamination. The list below present examples of treatment methods.

  • Chemical oxidation to treat volatile and semi-volatile organic compounds (VOCs and SVOCs, respectively) and pesticides
  • Air or vapour stripping to treat VOCs
  • Adsorption onto matrices, such as activated carbon, to treat SVOCs and heavy metal contamination
  • 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
  • Adsorption on a matrix such as activated carbon to treat heavy metal contamination
  • Membrane separation
  • Ion exchange
  • Heavy metal precipitation
  • Coagulation and flocculation;
  • Filtration

Application examples

The following web link provides three application examples:

U.S. EPA. Hydraulic Optimization Demonstration for Groundwater Pump-and— Treat Systems, Volume I—Pre-Optimization Screening (Method and Demonstration)

Performance

  • Pump and treat is a proven method of controlling the migration of contaminants in groundwater
  • Pump and treat is a long-term treatment and is often not efficient and costly
  • Complete remediation of a site is often not possible with pump and treat systems

Measures to improve sustainability or promote ecological remediation

  • Ensure pump size is appropriate and pump is energy efficient
  • Optimize scheduling to reduce resources and minimize mobilization days
  • Use of renewable energy and energy-efficient machinery (such as solar energy for pumps, geothermal or solar energy for treatment plant)
  • Optimize pumping flow rates in both the pumping system and the water treatment unit to reduce energy
  • Ensure water treatment process is efficient and reduce wastes and consumables such as activated carbon

Potential impacts of the application of the technology on human health

Unavailable for this fact sheet

References

Author and update

Composed by : Martin Désilets, B.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:
1.2.1