Site Investigation


Environmental Risk Assessment

For an environmental risk assessment of contaminated land to be successful, the site investigation and sampling should be under the full time direction of either a Chartered Engineer, Chartered Geologist or equivalent.  All the recovered soil samples should be screened on site for any visual or olfactory evidence of contamination including the presence of VOCs.  Samples should be selected from trial pits and boreholes on the basis of those which are most likely to be contaminated and those which will give the most appropriate indication of the spread of any contaminants.  The samples should be stored in either glass or plastic containers and where necessary kept in cooled conditions.  Testing should be carried to UKAS accredited procedures in accordance with MCERTS performance standards.


The initial aim of this is to make a preliminarily assessment of the level of any contamination on the site in order to determine if there are any significant risk associated with contaminants in respect of both human health and the environment, including controlled waters.


The Contaminated Land Report (CLR) series of documents have been produced by the Department for Environment, Food and Rural Affairs (DEFRA) and the Environment Agency, to provide regulators with "relevant, appropriate, authoritative and scientifically based information and advice on the assessment of risk from contamination in soils".


The Environment Agency has issued a number of Soil Guideline Values (SGVs) which, whilst non-binding, may be used as guidance in the assessment of land and in setting remediation targets.  They should only be applied to human health assessments.


The SGVs have been derived using the Contaminated Land Exposure Assessment Model (CLEA) and are based on assumptions relating to soil conditions, pollutant type and behaviour, land use patterns and the availability of receptors.  SGVs are also subject to statistical assessment.  The CLR documentation requires that the results of laboratory testing are subject to statistical analysis to remove uncertainty over a so-called 'averaging area'.


To date selective SGVs have been issued for the following land-uses as follows;


  • Residential with and without plant uptake (SGVres)
  • Allotments
  • Commercial/Industrial  (SGVcomm)


DEFRA have issued the “Outcome of the Way Forward Exercise on Soil Guideline Values”.  This document is intended to provide guidance to determine if there is a Significant Possibility of Significant Harm (SPOSH) i.e. whether land meets the legal trigger of being contaminated land.


The CLEA model has been revised.  SGV values are also currently being revised and some further SGVs are to be issued shortly.  The older SGVs have been withdrawn in the light of this.  The latest guidance on CLEA modelling states:


In the context of Part 2A, a risk assessor using an SGV can conclude the following (DEFRA, 2008).


  • At a representative average soil concentration at or below an SGV, it is very unlikely that there will be a significant possibility of significant harm (SPOSH).


  • At a representative average soil concentration above an SGV, there might be a significant possibility of significant harm with the significance linked to the margin of exceedance, the duration and frequency of exposure, and other site-specific factors that the enforcing authority may wish to take into account.  Further site investigation and/or detailed evaluation will usually be required.


Results can be compared to limits set for drinking water in the Water Supply Regulations 2010 and the Environmental Quality Standards (EQS) set out in “Technical advice to third parties on pollution of controlled waters for Part IIA of the Environment Agency Act 1990”. 


In order to determine the mobility of any chemicals, leachability testing can also be carried out on samples.  The results can again be compared to the limits set for drinking water as prescribed by the Water Supply Regulations 2010 and the Environmental Quality Standards (EQS) set out in “Technical advice to third parties on pollution of controlled waters for Part 11A of the Environment Agency Act 1990”. 


Waste Acceptance Criteria


The Landfill Directive sets out procedures for waste acceptance at landfills and the types of waste for each class of landfill as specified by Waste Acceptance Criteria (WAC).  The WAC are predominantly lists of “limit values” for certain parameters obtained from standard leaching tests of wastes going to landfills.  WAC are set out in the Landfill Directive itself.  Full details can be found in the Environment Agency document “Guidance for waste destined for disposal in landfills” Version 2, June 2006.