This document provides advice on the use of statistical techniques in the assessment of soil contamination data. It forms one part of the package of improved UK guidance highlighted iin Defra’s discussion paper Assessing risks from land contamination – a proportionate approach. Soil guideline values: the Way Forward (CLAN 06/2006) on the role and use of Soil Guideline Values (SGV) for managing the risks associated with soil contamination.

It up-dates and supersedes the advice on the statistical testing of soil contamination data contained in CLR7, 2002. Its overall aim is to increase understanding amongst stakeholders of the role that statistics can play in quantifying the uncertainty attached to estimates of the mean concentration of contaminants in soil thereby creating a more informed basis for regulatory decision-making.

The guidance presents a structured process that users can follow when employing statistical techniques for data assessment purposes. The process directs users to (and reinforces the importance of) other relevant guidance on sampling and data  assessment and encourages practitioners to undertake appropriate scrutiny and organisation of data in preparation for statistical testing.

It is expected that the guidance will be useful to all those with an interest in or responsibility for land contamination. Note, however, that the statistical procedures set out in the document are drafted from the perspective of a regulator operating under either the planning system or Part 2A of the Environmental Protection Act 1990.

CL:AIRE is pleased to announce that "Professional Guidance: Comparing Soil Contamination Data with a Critical Concentration" has been published and is now available to download for free.

The new guidance was written by statistician Nigel Marriott, supported by a steering group comprising representatives from Environment Agency, Nuclear Decommissioning Authority (NDA), RSK, Soil and Groundwater Technology Association (SAGTA), Society of Brownfield Risk Assessment (SoBRA), and Yorkshire and Lincolnshire Pollution Advisory Group (YALPAG).

The guidance updates a 2008 document of a similar name that was published by CL:AIRE and the Chartered Institute of Environmental Health, supported by SAGTA. As the guidance adopts an entirely different approach to the previous guidance, it completely supersedes it and the 2008 document has now been withdrawn.

The 2020 revision addresses the problem of potentially erroneous conclusions by dropping the reliance on a single scientific test and emphasises the importance of a comprehensive understanding of the datasets in the context of the conceptual site model.

SAGTA, NDA, Environment Agency and RSK are gratefully acknowledged for their funding of this project.

Version 1.1 of Professional Guidance: Comparing Soil Contamination Data with a Critical Concentration, released in February 2021, includes several minor amendments to the original version (September 2020) and these are described in the Version Control Sheet in this pdf.