Site Specific Risk Assessment
A risk assessment represents the structured gathering of
information in order to form a judgement about the risks associated
with contaminants at a site, given its environmental setting.
Further information on the Environment Agency Model Procedures
for the Management of Land Contamination, CLR 11, can be
found here 
.
The process of risk assessment is built around an iterative
approach whereby initial information enables a picture of the site
to be formulated. This picture, or conceptual site model, is
refined as further information is obtained, for example, through
desk studies, walkover surveys and intrusive investigations.
It is important that the actual problem is defined before the
risks are considered in detail, to ensure that all sources,
pathways and receptors, and potential linkages between them, are
considered.
The first stage of any risk assessment is to identify and assess
the hazards present, that is to say the substances with the
potential to cause harm to the receptors. It is usual in a
quantitative assessment to consider a threshold above which harm
may be caused. However, in some circumstances it may be possible to
form a judgement based on a qualitative assessment.
The second stage in a risk assessment is to consider how much,
how often and for how long the receptor is exposed to the hazard
(exposure assessment), as well as the effect on the receptor of the
exposure (consequence assessment). This will enable a concentration
to be estimated which can then be related back to the hazard
assessment.
The final stage in a risk assessment is to integrate the
outcomes of the above stages with risk estimation, in which the
consequences and probability of the risk is considered, with risk
evaluation in which the significance or seriousness of the risk is
considered. A risk assessment culminates in considering whether the
risks are tolerable and the assessment may be reiterated using
additional information to obtain a more informed view about the
tolerability of the risk.