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BOC Immingham Dissolved Acetylene Project Environmental Statement: Vol. 2 Main Text
Land Contamination Risk Assessment
Conceptual Site Model
7.30 Land contamination can present an unacceptable risk to a proposed development, or the
proposed development itself may increase a risk that existing land contamination already poses.
Therefore, a preliminary conceptual site model (CSM) has been prepared to aid in the
identification and assessment of potential impacts and associated effects of the proposed
development and any land contamination that may be present. A CSM describes the relationship
between potential sources of contamination (resulting from both on site and offsite historical and
recent activities) and receptors to the potential contamination. As part of the CSM development,
three elements, the source of contamination and associated contaminants, receptors to that
contamination and the pathways between the two are identified and assessed. Where all three
elements are present or are likely to be present, they are described as potential pollutant linkages
(PPLs). Identification of PPLs, also called source-pathway-receptor linkages, underpins the CSM
and enables the potential risk posed by any contamination to be assessed and thus, potential
impacts and effects to be identified.
UK Guidance and Approach to Land Contamination
7.31 Primary guidance for assessing and managing land contamination is presented in CLR 11 35 . The
process of contamination risk assessment as defined in CLR 11 35 includes:
� developing a preliminary CSM by a desk study review of available documentary information
and identifying the potential hazards sources, pathways and receptors relevant to the site
and the PPLs which may be present;
� gathering site-specific information on the CSM through site investigation to identify the
presence, nature, potential concentrations and spatial distribution of contamination, details of
pathways for migration of contamination and specific information on the receptors to update
the CSM; and
� risk assessment by applying criteria that will enable a judgement as to whether the
concentrations of contaminants represent an unacceptable risk. These criteria must be
relevant to each PPL and can be generic or site-specific. Generic assessment criteria are
concentrations of a contaminant below which the risk is acceptable. Site-specific assessment
criteria are concentrations of a contaminant above which there is likely to be an unacceptable
risk. If a site fails on the site-specific assessment criteria, remediation may be required.
7.32 The process of contamination risk assessment as defined in CLR 11 35 has been adopted as
follows:
� hazard identification (establishing contaminant sources) and hazard assessment
(establishing pathways and receptors and identifying PPLs). Both the hazard identification
and assessment stages conclude in development of the CSM;
� risk estimation which predicts the likelihood (probability assessment) and degree
(consequence assessment) of harm pollution occurring. Risk estimation has two
components: firstly probability assessment which relates to whether pollution harm will occur
in the short and or long term (risk estimation is only undertaken when a PPL exists); and
secondly consequence assessment which is the magnitude of harm that would occur
because of the PPL, that is, the degree of harm pollution considering the sensitivity of the
receptor. Therefore, the consequence is whether the PPL would be a significant pollutant
linkage; and
� risk evaluation which is the process of deciding whether a risk is acceptable or not and
entails the application of evaluation criteria. These evaluation criteria are set in relation to a
level of harm or pollution to the specific receptor. They may be absolute standards or
recommended limit values, for example, a health criterion value for the intake of a substance.
5100935.404 Environmental Statement August 2011 95