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The C4SL research project (Phase 1) provided technical guidance to support Defra's revised Statutory Guidance (SG) for Part 2A of the Environmental Protection Act 1990 (Part 2A). Part 2A was originally introduced to ensure that the risks from land contamination to human health, property and the environment are managed appropriately, with the revised SG being designed to address concerns regarding its real-world application. The revised SG presents a new four category system for classifying land under Part 2A, ranging from Category 4, where the level of risk posed is acceptably low, to Category 1, where the level of risk is clearly unacceptable.

The Phase 1 project produced, demonstrated and communicated a methodology for developing C4SLs which represents as wide a consensus as possible in the field of land contamination risk assessment. The C4SLs represent a new set of generic screening levels for 6 contaminants which are more pragmatic (but still strongly precautionary) compared to the existing soil guideline values (SGVs) and other similarly derived numbers. The C4SLs consist of cautious estimates of contaminant concentrations in soil that are still considered to present an acceptable level of risk, within the context of Part 2A, by combining information on human health toxicology, exposure assessment and normal ambient levels of contaminants in the environment. Within the Phase 1 Defra publication, it was emphasised that further work to expand C4SLs for other contaminants would need to be led by industry.

Phase 2 Project

The Soil and Groundwater Technology Association (SAGTA) is leading a collaborative industry initiative which started formulating and developing a project framework in 2015.  Funding for this phase has been secured from SAGTA members, with in kind contribution from a number of consultants and a financial grant from the Society of Brownfield Risk Asssessment (SOBRA)  Phase 2 will develop 20 C4SLs for a range of contaminants which have been selected following a consultative process choosing the contaminants which would be most useful to industry.

The full list of contaminants that C4SLs are being derived are as follows:

Naphthalene Cis-1,2-Dichloroethene   Free Cyanide Toluene Vanadium
Chloroethene (Vinyl Chloride) Trans-1,2-Dichloroethene Complex Cyanide Ethylbenzene Nickel
Trichloroethene 1,2-Dichloroethane Inorganic Mercury Xylenes (o-xylene, m-xylene, p-xylene) Methyl tertiary butyl ether (MTBE)
Tetrachloroethene 1,1,1-Trichloroethane Beryllium 1,2,3-Trimethylbenzene, 1,2,4- Trimethylbenzene &1,3,5-Trimethylbenzene  

The project will be delivered by a consortium of partners which include the following:

Project Manager: CL:AIRE supported by Simon Firth (Firth Consultants Ltd) and Naomi Earl (Freelance Consultant)

Tier 1 Toxicologists: Sarah Bull; Camilla Alexander-White (MK Tox); George Kowalczyk (GK Toxicology Consulting) and Steve Ruckman (RSK ADAS).

Tier 2 Toxicologists: Simon Cole (AECOM); Sonja Trewavas, Natasha Glynn & Andrew Fellows (Atkins); Barry Mitcheson (Wood); Gareth Wills (WSP); Jo Wilding & Laura Aspinall (RSK); Meera Cush (Ramboll); Melinda Evans (Soilfix); Adam Symonds, Duncan Grew & Peter Sheppard (Advisian) and Kate Baker (LEAP Environmental).

Exposure Modellers: Dave Brooks (Sirius); Gareth Barns (WYG); Robert Reuter (Wardell Armstrong); Catherine Cussell (RSK); Lucy Burn (Advisian) and James Lymer

Steering Group

The project is being overseen by a Project Steering Group, led by Hannah White on behalf of SAGTA and consists of representatives from the following organisations:

SAGTA, Defra, Welsh Government, Public Health England, Public Health Wales, Foods Standards Agency, Environment Agency, Natural Resources Wales, Homes England, Lancaster City Council, YALPAG, Wiltshire Council, Welsh Contaminated Land group, Mole Valley District Council, SoBRA, NHBC, AGS, EPUK, EIC and HBF.


The project will endeavour to deliver the C4SLs in a timely manner and is aiming for completion in two years.  However as this project is relying on a lot of industry goodwill and until we know the exact hurdles that we may face we will provide updates to industry as to how the project is progressing through the Land Forum minutes ( and CL:AIRE News (