Clubbing together to assess the risk

Remediation experts have collaborated to produce a detailed set of generic assessment criteria for 35 contaminants sometimes encountered on contaminated land. Simon Firth explains the process behind the initiative.

The appropriate assessment and management of risks from contamination – both anthropogenic and naturally occurring – is a key requirement for new developments, especially those built on brownfield sites. CLR11 guidance from Defra and Environment Agency recommends a tiered approach to the assessment of these risks to help ensure they are assessed in a systematic and transparent manner, and avoid the need for further investigation or more complex risk assessment where not necessary.

Generic assessment criteria (GAC) form an important part of the tiered assessment process. GAC can vastly simplify the assessment of risks by screening out individual contaminants or even entire sites from more complex detailed quantitative risk assessment. The CLEA methodology was first published by the Environment Agency in 2002 and was intended as a basis for deriving soil guideline values (SGV).

However, SGV were only published for a handful of contaminants, so many practitioners were forced to independently derive GAC for the remaining key contaminants to enable them to use the recommended tiered assessment approach on the sites they were assessing. This resulted in a plethora of different GAC being used, which created difficulties for environmental health officers and others reviewing consultant reports.

To overcome this problem, the Environmental Industries Commission (EIC), with the support of the Association of Geotechnical & Geoenvironmental Specialists (AGS) and CL:AIRE initiated a collaborative work programme to develop an industry agreed set of GAC for 35 contaminants.

These complement the SGV and LQM/CIEH second edition GAC, and together provide practitioners with screening criteria for human health risk assessment for more than 120 of the most commonly encountered contaminants in UK soils.

Pulling together with people power

The EIC/AGS/CL:AIRE initiative was conducted on a voluntary basis and involved 47 experienced human health risk assessors from 26 member companies of EIC’s contaminated land working group working together. An initial workshop was held to identify the contaminants for consideration and to agree a framework for deriving the GAC. It was agreed that the GAC should be derived, as far as possible, in accordance with the CLEA SR2, SR3 and SR7 guidance documents, and that their derivation should be fully transparent.

The volunteers then reviewed the physico-chemico and toxicological data for 44 contaminants. This data was captured in a series of Excel-based proformas along with justification for the parameter inputs to CLEA. Each contaminant was worked on independently by two consultants who then reviewed each other’s proformas to check for discrepancies. A second workshop was held to discuss any unresolved discrepancies and to finalise the rules for parameter value selection.

Two review panels – one for the physico-chemico data and one for the toxicological and background exposure data – were then held to review the proformas and check consistency in approach and of the professional judgements made. A final technical review was conducted to check overall consistency and accuracy. The resulting agreed set of parameter values were used in the CLEA model to produce sets of GAC for four generic land-uses – residential with and without consumption of homegrown produce, allotments and commercial.

A report with was then prepared to present the GAC and describe how they were derived and how they should be used. A pre-publication version of this report was issued to various external organisations for their comment, including the Environment Agency, HPA, Royal Environmental Health Institute of Scotland, Environmental Protection UK, Chartered Institute of Environmental Health, Northern Ireland Environment Agency and Scottish Environment Protection Agency.

Their comments were addressed in the final version of the report published by CL:AIRE. This report includes the proformas for all 44 contaminants and makes the derivation and assumptions used for deriving the GAC transparent. The report is accompanied by an excel spreadsheet of the CLEA contaminant database with the relevant parameter values for all 44 contaminants, which practitioners can upload to their own CLEA model to perform site-specific assessments.

Unique in its remit

This project has been unique in various ways. Firstly, it involved the collaborative effort of 47 experienced risk assessors who were all involved in the parameter review and selection process. Thus the derived GAC are based on the agreed opinions of a large group of assessors from industry. Secondly, the work was conducted on an entirely voluntary basis, and we are grateful to the volunteering organisations and the individuals involved for their effort and to CL:AIRE who published the report.

The combined efforts of the volunteering organisations has produced a robust set of GAC for 35 contaminants and parameter values for 44 contaminants that are available to all to facilitate the assessment of risks from soil contamination. The report and excel spreadsheet can be downloaded free of charge at

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