Soil Guideline Values (SGVs) are figures which are used in non-statutory technical guidance for assessors carrying out risk assessments to determine whether land is considered "contaminated" under United Kingdom law, that is "land which appears to... be in such a condition, by reason of substances in, on or under the land, that (a) significant harm is being caused or there is a significant possibility of such harm being caused..."[1]
This guidance stipulates three stages in such risk assessments:
Soil Guideline Values are used in the second stage, GQRA, to determine whether harm caused by long-term exposure to a given soil concentrationofchemicals may present an unacceptable risk to human health in some generic land-use scenario. The SGVs are therefore conservative estimates for a given scenario. Exceedance of a SGV does not confirm that there is a "significant possibility of significant harm", merely that the possibility exists and therefore more detailed, site-specific investigation of contaminants present, pathways and receptors is required.[2]
SGVs are derived by the Environment Agency using the CLEA model (which can also be customised or used for DQRA[3]). However, there are no currently valid SGVs for many important and common elements, such as copper, zinc, leadorchromium. The only body mandated to produce these values is the Environment Agency, following extensive consultation with other government departments.
In lieu of such figures, equivalent values known as "Generic Assessment Criteria" (GAC) may be calculated by any individual or organisation, starting from toxicity and relevant data and using the CLEA model, just as the Environment Agency calculates SGVs. SGVs are in fact GAC derived and published by the environment agency. For example, a range of GACs for more complex chemicals has been calculated and been made publicly available by charity CL:AIRE,[4] with input from a range of authoritative sources including the Environment Agency. That said, GACs are not always openly published, as deriving them is a complex matter and thus these values do hold commercial value for consultancies who have undertaken such calculations.
There are three generic land-use scenarios for which SGVs are published, and most derivations of GACs also follow these scenarios:[5]
SGVs and GACs derived from these scenarios may only be used if the scenarios apply exactly or otherwise it is clearly demonstrated that the scenarios are more conservative than the real-world situation. For example, in the case of a playing field, it could be argued that the residential scenario is suitably conservative: