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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.

Phase 1 Project

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 Assessment (SOBRA) The project officially started in 2018. Phase 2 will develop 19 C4SLs for a range of contaminants which have been selected following a consultative process choosing the contaminants which would be most useful to industry. Subsequent funding has been received from Environment Agency in 2023 to develop the 20th substance for PFAS. 

The full list of contaminants that C4SLs are being derived are as follows and those in green are now available to download (as pdf):

Vinyl Chloride

Cis-1,2-Dichloroethene   Free Cyanide Toluene Vanadium


Trans-1,2-Dichloroethene Complex Cyanide Ethylbenzene Nickel
(Ethylene Dichloride)
Inorganic Mercury

(o-xylene, m-xylene, p-xylene)

Methyl tertiary butyl ether
Naphthalene 1,1,1-Trichloroethane Beryllium 1,2,3-Trimethylbenzene,
1,2,4- Trimethylbenzene &1,3,5-Trimethylbenzene

The project is being 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 (TARA Consulting); Camilla Alexander-White (MK Tox & Co Ltd) and George Kowalczyk (GK Toxicology Consulting).

Tier 2 Toxicologists: Natasha Glynn (Atkins)Gareth Wills (WSP); Jo Wilding (Independent); Laura Aspinall and Andrew Fellows (RSK); Melinda Evans (Soilfix); Adam Symonds, Duncan Grew & Peter Sheppard (Worley) and Kate Baker (Antea Group UK).

Exposure Modellers: Dave Brooks (Sirius); Gareth Barns (Geosyntec); Robert Reuter (Wardell Armstrong LLP); 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, UKHSA, 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.  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 National Brownfield Forum minutes ( and CL:AIRE News (

Soil Guideline Values (SGV) and supporting technical guidance are intended to assist professionals in the assessment of long-term risk to health from human exposure to chemical contamination in soil.

There are different SGVs according to land-use (residential, allotments, commercial) because people use land differently and this effects who and how people may be exposed to soil contamination.

SGV are 'trigger values' for screening-out low risk areas of land contamination. They give an indication of representative average levels of chemicals in soil below which the long-term health risks are likely to be minimal. Exceeding an SGV does not mean that remediation is always necessary, although in many cases some further investigation and evaluation of the risk will be carried out.

SGV should not be used where they are not representative of the site under investigation. They do not assess other types of risk to human health such as fire, suffocation, explosion, or short-term and acute exposures. They also cannot be used to assess risks to controlled waters, property, pets and livestock, or ecological receptors.

SGV are available only for a limited number of chemical substances. However, the framework reports and software provide a starting point for the assessment of a much wider range of chemicals.

Professionals and regulators assessing risks to health from land contamination are not required to use SGV and the supporting technical guidance. Alternative approaches can be used provided that they satisfy the legislative requirements.

Framework Reports

The principles and method used to derive SGV is described in two main framework reports:

Professionals should be familiar with the information in these reports before using SGV in site assessments.

SGV and TOX Reports

The EA published SGV Reports and TOX Reports for a small number of soil contaminants. TOX Reports describe the toxicology of specific chemicals or groups of related chemicals including a summary of expert group evaluations. They also set out the recommended health criteria values (HCV) used in SGV derivation.

SGV Reports discuss the available evidence for the presence of specific chemicals in soil and their fate and transport in soil systems. In addition to the SGV themselves, the SGV Reports contain other useful information to assist risk assessors.

CLEA Software

The EA published the calculations for deriving SGV as described in the framework reports as a spreadsheet for use by professionals in conjunction with the wider guidance. The CLEA software is written using Microsoft Excel and uses VBA macros to support functionality. In addition, a specific spreadsheet has been published to support the assessment of dioxins in soil.


The Environment Agency compiled a list of the most frequently asked questions (PDF, 121KB).

SGV Reports and supplementary information for specific chemicals and groups of chemicals are available for download below.

It is recommended that professionals using SGV Reports are familiar with the information in the framework reports (see below). SGV Reports published before 2009 have been withdrawn. They were prepared using previous framework guidance (R&D Publications CLR7 – 10) published in 2002, which have been superseded.

Introduction to Soil Guideline Values

Heavy metals and other inorganic compounds



Other organic compounds

Supplementary information for the derivation of SGVs

Heavy metals and other inorganic compounds



Other organic compounds