From: Public Services and Procurement Canada
A permeable reactive/passive barrier consists of reactive materials placed in the ground, downgradient of the dissolved contamination enclave and generally perpendicular to the direction of groundwater flow, with the intent that contaminated groundwater will pass through the reactive materials for treatment. Contaminants that pass through the permeable reactive/passive barrier will be adsorbed, degraded, or converted to non-toxic or reduced toxicity compounds.
The reactive/passive barrier can be installed permanently or temporarily. Barrier materials can be adsorbents such as peat and granular activated carbon, biodegradation enhancers such as oxygen release compounds, or chelating agents or zero-valent iron that cause the transformation of contaminants into non-toxic or immobile species.
Many installation techniques are possible to create a permeable reactive/passive barrier. The two main ones are the excavation of a trench and the installation of reactive materials and their injection through injection wells or other injection techniques used in drilling.
Reactive/passive permeable barriers are often proposed as an alternative to pump and treat groundwater remediation technology. Ideally, the systems are passive and require very little regular maintenance following installation.
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Reactive/passive barrier technology can include:
Note:
In some cases, barriers will need to be excavated at the end of their useful life. This may be necessary, for example, for the replacement of reactive materials.
On-site storage may include reactive materials and injection system, if applicable, fuels, lubricants, and other site materials required for the operation of machinery or equipment to implement the process. Other materials required for the development of the process area may be stored on site during construction. Once the systems are installed, little or no material is kept on site unless the system requires an active component, such as an oxygen diffuser or an amendment injection system (hydrogen peroxide, nutrients).
Potentially contaminated soils will need to be disposed of properly when excavation is required and soils are replaced with reactive barrier materials or when injection wells are installed. Treated groundwater flows out of the treatment area hydraulically downstream and may contain residual contaminants.
Some processes within the barriers may generate releases. For example, some biological processes may release methane or hydrogen sulphide; systems with active air diffusers may cause some degree of in situ volatilization of volatile contaminants, which are then released to the atmosphere.
None.
Notes:
Preliminary tests, treatability tests and a pilot test may be required to evaluate:
Reactive/passive barrier technology is applicable in both low and high permeability aquifers and preferably in relatively homogeneous environments. However, the installation of the barrier by excavation may be limited by depth and rock. Under these conditions, a reactive zone can be established by injecting the reactive materials via injection wells.
The treatment time can be very long and even indefinite. As long as the source of contamination is present and active, the barrier may be required.
Since the barrier may be required for a long period of time or indefinitely, regular groundwater quality monitoring activities upstream and hydraulically downstream of the barrier should be maintained to verify barrier performance.
The consumption of reactive materials can lead to a decrease in efficiency over time. Also, a reduction in the permeability of the barrier may occur over time (fouling, precipitation, clogging). These phenomena will reduce its performance. A replacement or a cleaning may then be required.
Generally, this technology does not generate secondary products. Nevertheless, it can modify the conditions encountered in soils where certain compounds can be transformed into toxic substances, for example. The by-products depend on the contaminants, the reactive materials and the characteristics of the groundwater. For example, the processing of chlorinated solvents can result in the creation of dichloroethylene and/or vinyl chloride
Impermeable barriers can be used to direct groundwater to a reactive/passive barrier of limited size for treatment. In addition, reactive barriers can be used in conjunction with other in situ treatment technologies, such as non-aqueous phase immiscible liquid recovery, a groundwater recirculation system to increase the residence time of contaminants in the barrier.
A system for the recovery and treatment of vapour emissions may be required.
The following links provide application examples:
Several studies and demonstrations have proven the effectiveness of permeable reactive/passive barriers in reducing contamination to remediation goals with efficiency greater than 95%.
Unavailable for this fact sheet
Composed by : Mélanie Bathalon, B.Sc, MCEBR
Updated by : Jennifer Holdner, M.Sc., Public Works Government Services Canada
Updated Date : April 29, 2014
Latest update provided by : Nathalie Arel ing., M.Sc., Frédéric Gagnon CPI., Sylvain Hains ing., M.Sc., Golder Associates Ltd.
Updated Date : March 21, 2022
