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In April 2024, CL:AIRE published Guidance on Natural Source Zone Depletion.

Natural source zone depletion (NSZD) can be a sustainable risk-management strategy for petroleum hydrocarbon light non-aqueous phase liquids (LNAPLs) impacting the subsurface. NSZD refers to the combination of naturally occurring processes – biodegradation, vaporisation, volatilisation and dissolution – that act to reduce LNAPL mass, saturation and mobility in the subsurface.

Recent advances in NSZD are captured in this document, alongside a decision-making framework, to provide technical guidance for practitioners, regulators and liability owners on the science and practical considerations for the application of NSZD-based risk management strategies in the UK.

This guidance has been written by James Rayner of Geosyntec and steered by a collaborative technical review group incorporating representatives from industry, consultancy, and regulators across the devolved administrations.

CL:AIRE would like to gratefully acknowledge the Environment Agency for their seed funding for this project. 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.

Technical Review Group
Sarah Budworth – Environment Agency
Stuart Cory – WSP
George Flower – Arcadis
Richard-Thomas Gill – Shell
Thomas Grosjean – BP
Nicola Harries – CL:AIRE
Kirsten Johnstone – Environment Agency
Ian Jones – Natural Resources Wales
Matt Llewhellin – Natural Resources Wales
David Pearks – Scottish Environment Protection Agency
Sarah Poulton – Natural Resources Wales
Isla Smail – Scottish Environment Protection Agency
Rob Sweeney – CL:AIRE
Alan Thomas – ERM
Steve Wilson – EPG Ltd
Gary Wealthall – Geosyntec (retired)

The NSZD guidance document can be downloaded for free at (PDF 14MB).

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