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Contaminated Land Exposure Assessment
Kevin Eaton discusses the new Contaminated Land Exposure Assessment model and its ability to derive site-specific assessment criteria

The Contaminated Land Exposure Assessment (CLEA) model was first published in 2002, and its application as part of the contaminated land assessment process has become widely accepted.

However, the initial model was restricted to only a number of generic scenarios, and it was therefore recognised by the Environment Agency (EA) that there was a need to provide practitioners with a model able to derive site-specific assessment criteria (SSAC).

In response to these needs, CLEA UK has been developed and was made available to the public in November last year.

Within the UK contaminated-land regime, there is a clear framework in which
to apply risk assessment - source-pathway-target - in order to evaluate the site-specific impact of identified contamination. The CLEA model was developed by Defra and the EA to provide a consistent and scientific framework for assessing health risks from land contamination in accordance with UK guidance.

The Soil Guideline Values (SGVs) are a subset of generic assessment criteria derived by Defra and the EA using the CLEA model. These have been determined using a set of standard assumptions relat-ing to land use, receptor behaviour, site, building and soil characteristics.

Initially, SGVs were published for eight metals, with subsequent additions, including ethylbenzene and toluene. There is an ongoing programme by the EA to publish toxicological (TOX) and SGV reports for a wide range of contaminants and eventually it is expected that this guidance will cover over 50 key contaminants. Importantly, it will include a range of chemicals which had not been addressed in the past UK published criteria.

However, SGVs are not statutory standards. Where chemical data exceeds the SGV, a more informed judgement should consider further assessment and not necessarily remedial action. There have already been concerns about the legality of applying SGVs as the only basis for determining sites as contaminated land, particularly as the published SGVs are based on a conservative assessment of risk. Defra recently released further guidance to local authorities on this.

CLEA UK is a software tool that estimates intake by humans of contaminants from soil from various exposure pathways. It does this by combining information about contaminant properties, soil, site and building characteristics and modelling approaches for predicting the fate and transport of the contaminants.

The new CLEA UK software can be used to:
  • Derive generic assessment criteria (GAC)
  • Derive site-specific assessment criteria (SSAC)
  • Calculate average daily exposure/health-criteria ratios
The new model allows SSAC to be derived for contaminants for which no TOX or SGV report has been published by the EA as well as allowing a range of land-use type, receptor type, start and end age class, exposure pathways, building type and soil type (from the selections available) to be applied.

Given the ability of CLEA UK to generate SSAC for a wide range of scenarios, it
is likely the regulatory authorities will request it more often in support of the evaluation of contaminated land assessment, particularly prior to site development and to justify remedial action.

Also, with greater reliance placed on the results of risk assessment, it should be authorised by suitably qualified practitioners.
· Kevin Eaton is a principal in Environ's Leeds office. Email keaton@uk.environcorp.com

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