Remediation Technologies / Permeable Reactive Barriers

A Permeable Reactive Barrier (PRB) is a treatment zone of reactive material that is built below ground to clean up polluted groundwater. The reactive zone may be installed as a wall to intercept a migrating plume of contaminated groundwater. Alternatively, the contamination can be funnelled by low permeability barriers (e.g. slurry walls) to a gate or vessel containing the reactive media – funnel and gate method.

The reactive media is selected to absorb or adsorb the pollutants from the groundwater or to convert harmful chemicals to harmless by-products. Typical examples of reactive media are:

• Activated carbon for absorption of organics
• Ion exchange resins for adsorption of metals and radionuclides
• Zero valent iron for dechlorination of halogenated solvents, absorption of carbon disulphide or reduction of oxymetal ions (e.g chromate)
• Limestone for precipitation of metals
• Sand / gravel beds with the addition of nutrients and oxygen to promote microbial degradation of organic contaminants

Cleaning groundwater with a PRB may take many years. The time taken depends on the amount of pollution present in the groundwater and how fast the groundwater moves through the PRB.

There are several advantages of using a PRB to remediate contaminated groundwater:

• The installation is beneath ground preventing human contact with the contamination
• Low operating and maintenance costs
• No energy requirement as the system relies on natural groundwater flows
• No pumps, moving parts or associated noise
• Invisible after installation
• Allows continued use of the site after installation

PRBs have been installed at more than 80 sites i