17 Apr 2015
April 17, 2015


No, we haven’t discovered the name of a new droid in the forthcoming Star Wars Episode VII. C4SLs are Category 4 Screening Levels and they arose out of the Department for Environment, Farms and Rural Affairs (Defra) revision of the Statutory Guidance for Part IIA of the Environmental Protection Act (1990).  The revision identified a new four category approach for classifying land affected by contamination.  Category 4 represents land that would not meet the requirements for classification as contaminated under Part IIA of the Environmental Protection Act.

Defra funded a research project to identify a methodology for determining C4SLs with respect to human health and trialed the methodology on a selected number of common contaminants (arsenic, cadmium, chromium (VI), lead, benzo(a)pyrene and benzene).  The methodology that was implemented is deemed, by Defra, to be strongly precautionary but pragmatic for contaminated land assessment purposes as it identifies an “acceptably low” risk to human health. The previous approach, adopted by the Environment Agency, was that risks to human health should be “minimal”. It has been considered that the previous “minimal” risk methodology is too precautionary to be useful as a screening tool to identify land as “contaminated”. The C4SLs, therefore, provide a more realistic test for deciding when land is suitable for use and definitely not “contaminated”.

The National Planning Policy Framework requires that sites for development be assessed using the same criteria for determining land as “contaminated” under Part IIA. Defra, in its documentation of the C4SL research state that it is envisaged that C4SLs can be used as a screening tool under planning. The Department for Communities and Local Government (DCLG), the government department responsible for planning policy, has issued a statement to confirm that C4SLs are appropriate for use under planning.

At Crossfield Consulting we are implementing the six Defra C4SLs and other “Suitable for Use” criteria using the Defra methodology to provide a more pragmatic generic quantitative risk assessment for development sites. As we have always done, where feasible, we will also undertake site-specific risk assessments so that realistic assessments of risks to human health (and also other receptors such as controlled waters) are provided. This approach can eliminate remediation works that might otherwise be necessary if only a generic quantitative risk assessment is undertaken.

It should be noted that the Defra review applies only to contaminated land and the planning regime in England and Wales. Our assessments of potentially contaminated land in Scotland will continue to use the “minimal” risk methodology, in line with Scottish planning policy.