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In April 2024, CL:AIRE published Guidance on the Assessment and Monitoring of Natural Attenuation of Contaminants in Groundwater.

Monitored natural attenuation (MNA) can be a sustainable risk management strategy for a wide range of groundwater contaminants, where environmental data are collected and assessed that demonstrate natural attenuation will protect receptors from pollution or harm. Natural attenuation refers to the combination of physical, chemical and biological processes that act, without human intervention, to reduce contaminant concentrations, flux or toxicity.

The Environment Agency originally published technical guidance for MNA in 2000 in its R&D Publication 95. Since then, significant scientific advances have been made in understanding contaminant behaviour and reactive transport in the subsurface, alongside ongoing developments in site characterisation, monitoring and predictive modelling approaches and technologies, that are captured in this updated guidance.

CL:AIRE would like to gratefully acknowledge the Environment Agency for its seed funding for this project and the individuals of the working group for their time in authoring sections along with their technical discussions and review of the guidance. The final document has kindly been reviewed and supported by the Environment Agency, Natural Resources Wales, Scottish Environment Protection Agency and the Northern Ireland Environment Agency (NIEA), an agency within the Department of Agriculture, Environment and Rural Affairs (DAERA). CL:AIRE would also like to thank its Technology and Research Group for their peer review of the document prior to publication.


Working Group
George Flower – Arcadis
Thomas Grosjean – BP
Nicola Harries – CL:AIRE
Kirsten Johnstone – Environment Agency
Ian Jones – Natural Resources Wales
Matt Llewhellin – Natural Resources Wales
Brian McVeigh – formerly Northern Ireland Environment Agency
James Rayner – Geosyntec
Matt Riding – WSP
Isla Smail – Scottish Environment Protection Agency
Jonathan Smith – Shell
Rob Sweeney – CL:AIRE
Alan Thomas – ERM
Russell Thomas – WSP
Gary Wealthall – Geosyntec (retired)

The MNA guidance document can be downloaded for free at (PDF 9MB).

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