General queries


Select the FAQ you wish to read below.


Why do we need SSVs or WSVs?


ATRISKsoil is an online database providing Soil Screening Values (SSVs) and Water Screening Values (WSVs) applicable to the UK for use in assessing chronic human health exposure to commonly occurring contaminants.


In 2002 the Department for Environment, Food and Rural Affairs (Defra) and the Environment Agency (EA) launched the CLEA (Contaminated Land Exposure Assessment) framework together with associated documentation and software (Contaminated Land Report (CLR) 9, CLR10, CLEA 2002 software) and a limited suite of Soil Guideline Values (SGVs) and associated toxicology reports. The framework was updated in 2002-2005 with the publication of CLEA Briefing Notes 1-4, additional SGV and toxicology reports, the CLEA handbook and CLEA UK software. The CLEA 2002 software was withdrawn.


In 2008, the CLEA framework was revised and CLR9, CLR10, the SGVs and CLEA UK were withdrawn. They were replaced with draft versions of Science Report (SR) 2, SR3, SR4, SR7 and the CLEA v1.03 software. These documents were finalised in 2009 and a suite of SGVs and revised toxicology reports were released along with the CLEA v1.04 software.  The CLEA v1.05 software was released later in 2009 to correct for lifetime exposure and was replaced shortly afterwards with v1.06 to correct for a password protection issue.


The SGVs are applicable to long-term human exposure to soil contaminants and were derived according to three land uses:

  • Residential with the consumption of homegrown produce;
  • Allotments; and
  • Commercial.


SGVs were released for arsenic, cadmium, mercury (inorganic, elemental, methyl-), nickel, selenium, benzene, toluene, ethylbenzene, xylenes, phenol and dioxins, furans and dioxin-like PCBs for a sandy loam soil with a 6% soil organic matter (SOM).


Further to these, there is a requirement for additional screening values so that a wider array of commonly encountered contaminants, both organic and inorganic, can be effectively assessed at a generic level for a wider range of land uses.


In 2014 DEFRA published Category 4 Screening Levels (C4SLs), which were derived on the basis of a ‘Low Level of Toxicological Concern’ (LLTC) following a toxicology review. The project derived C4SLs for six substances (arsenic, benzene, benzo(a)pyrene, cadmium, hexavalent chromium and lead) for a number of standard land uses as well as two new land uses (Public Open Space Residential and Public Open Space Parks).


This project was intended by DEFRA, as detailed in a letter from Lord de Mauley to English Local Authorities (September 2014), to provide a “simple test for deciding when land is suitable for use and definitely not contaminated (i.e. it is in category 4)”. However, since their publication, some of our subscribers (including Contaminated Land Officers) have informed us that values based on toxicological assessment of minimal risk remain of use. Therefore the ATRISKsoil SSVs have been updated based on minimal risk toxicology.


In December 2014, it was announced that an industry led initiative would be formed to derive Category 4 Screening Levels (C4SLs) for up to 50 substances. It is understood by Atkins that support would be sought from the wider Contaminated Land industry to help undertake the toxicological reviews and exposure assessment modelling, as was the case for the Soil Generic Assessment Criteria for Human Health Risk Assessment report, jointly published by the AGS, EIC and CL:AIRE in January 2010.


In Autumn 2015, the latest version of CLEA (v1.071) was released by the Environment Agency. This version of CLEA enables the derivation of assessment criteria using the original CLEA or new C4SL methodology.


Soil Screening Values

Where SGVs are not available or have been withdrawn, Atkins has calculated SSVs. The SSVs have been derived using the CLEA software v1.071 utilising the updated exposure parameters detailed in the C4SL Project Methodology documentation and relevant toxicological data based on minimal risk (as per Environment Agency guidance (SR2).

Atkins have derived SSVs for a sand soil type at 1% SOM and for a sandy loam soil type at 6% SOM for the following land uses:


  • Residential with the consumption of home grown produce;
  • Residential without the consumption of home grown produce;
  • Commercial;
  • Allotments (sandy loam and 6% SOM only);
  • Public Open Space (Residential); and
  • Public Open Space (Parks).


The SSVs can be applied to concentrations of contaminants identified in unsaturated soil. The SSVs are based on the CLEA framework and are, in general, considered to be based on Minimal Risk Levels. They may not, however, meet the tests for unacceptable intake laid out within the Part 2A Contaminated Land Statutory Guidance (April 2012).


Water Screening Values

Since the inception of the ATRISKsoil SSVs, Atkins has identified a requirement for human health WSVs for assessing the inhalation of vapours from shallow groundwater or perched water. WSVs have not been published by the Environment Agency to date. In the absence of such values, many use Drinking Water Standards which are based on oral toxicity data, taste, colouration or smell rather than inhalation toxicity data, or simply don’t assess groundwater or perched water. Atkins has therefore derived WSVs using the RBCA v2.5 software for the following land uses:


  • Residential
  • Commercial


The WSVs can be applied to concentrations of contaminants identified in a shallow groundwater or perched water source and can provide a preliminary indication as to whether further assessment would be required.



Why and how have the SSVs changed in the Summer 2017 update?

The C4SL project methodology released by DEFRA in December 2014 was a step-change in the approach to the assessment of land contamination in the UK. The C4SLs introduced a change to toxicological appraisal that defined 'low risk', updated exposure parameters for the standard SR3 land uses and, following a review of relevant literature and Atkins own SSV approach, introduced the Public Open Space (Residential) and Public Open Space (Parks) land uses. These changes in exposure and land use were formalised in an update to the CLEA software with the release of CLEA v1.071 in September 2015.


Atkins recognises that our subscribers and clients have been asking for updated values that take into account the new C4SL exposure assumptions and land uses, but many Local Authorities are still wary of widespread adoption of generic assessment criteria based on low rather than minimal risks.


Therefore, Atkins have updated the SSVs using CLEA v1.071 to incorporate the following changes:


  • Updated exposure assumptions for the standard residential, commercial land uses as set out in the C4SL project methodology for 1% SOM sand and 6% SOM sandy loam soil types;
  • Updated exposure assumptions for the standard allotments land use as set out in the C4SL project methodology for the 6% SOM sandy loam soil type;
  • Derivation of the ‘top two’ produce for all contaminants for the residential and allotments land uses and inclusion of this method in the consumption of home grown produce pathway; and
  • Inclusion of SSVs derived for the Public Open Space (residential) and Public Open Space (parks) land uses as set out in the C4SL project methodology at 1% SOM sand and 6% SOM sandy loam soil types.


Furthermore, as part of our routine updates we have updated the toxicological assessment of ten contaminants (based on minimal risks as set out in Environment Agency SR2 Guidance).


We understand that further C4SLs based on ‘Low Levels of Toxicological Concern’ are to be derived by an industry led initiative in the future and Atkins is fully supportive of this effort.


Do the confidentiality clauses in the Terms and Conditions for the use of ATRISKsoil prohibit practical use of the SSVs?


No, not at all. The confidentiality clauses are designed to prevent wholesale copying and distribution of the SSVs and WSVs and supporting data to non-subscribers. It is felt that this could result in misapplication, and in due course the use of out of date values, as well as compromising Atkins intellectual property rights.

However, it is understood that to use these values in the manner intended (e.g. to appraise screening values quoted in reports, to appraise the need for site-specific detailed quantitative risk assessment, or to identify potential mistakes in approaches taken to risk assessment) there may be a need for a subscriber occasionally to present both specific SSVs and selected background information to a third party. This is why toxicological information which supports the use of the SSVs is available to subscribers and our SSVs are modelled in accordance with existing and widely available UK guidance published by DEFRA, the Environment Agency, and CL:AIRE. Such use of the information contained on the website would not be considered by Atkins to be a breach of the subscription agreement.


Who do I contact if I have a question about the website?


Please fill in the Contact form which can be found in the 'Contact' link at the top of this page with any questions you might have.