The process of Monitored Natural Attenuation


Groundwater contamination through anthropogenic activities is a widespread problem in the brownfield urban environment with mobile groundwater pollution often resulting in the migration of contaminants. Natural Attenuation (NA) is the successful demonstration that naturally occurring processes are sufficient to mitigate against the risk of exposure to dissolved contaminants. Monitored Natural Attenuation comprises the monitoring of these process.




The Environment Agency (EA) Defines NA in Groundwater as: “The effect of naturally occurring physical, chemical and biological processes, or any combination of those processes to reduce the load, concentration, flux or toxicity of polluting substances in groundwater. For natural attenuation to be effective as a remedial action, the rate at which those processes occur must be sufficient to prevent polluting substances entering identified receptors and to minimise expansion of pollutant plumes into currently unpolluted groundwater. Dilution within a receptor, such as in a river or borehole, is not natural attenuation.”

With Monitored Natural Attenuation (MNA) defined as: “Monitoring of groundwater to confirm whether NA processes are acting at a sufficient rate to ensure that the wider environment is unaffected and that remedial objectives will be achieved within a reasonable timescale; this will typically be less than one generation or 30 years.”

NA relates mainly to organic environmental contaminants that can be biodegradable under aerobic and/or anaerobic conditions and it is this principle that NA utilises as a remediation method for groundwater contamination in place of less sustainable and more costly techniques such as “pump, treat and inject” or air sparging.

Use the link below to download an in-depth introduction to Monitored Natural Attenuation.

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