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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.
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.
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.
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.
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.
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).
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.
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)
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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