Environmental Engineering Reference
In-Depth Information
Oak Ridge National Laboratory Screening Benchmarks; or
Serious Risk Concentrations (SRCs) derived by the National Institute for Public
Health and the Environment (RIVM) in the Netherlands.
If supplementary SSVs are required for a Tier 1 assessment, their source and
concentration must be agreed with the relevant stakeholders, including the
nature conservation agency; ideally this should be done when performing the
desk study/CSM so that the ERA can be planned appropriately. In truth, it is
unlikely that SSVs from other sources will be acceptable because they will
already have been assessed in the derivation of the UK SSVs and deemed
unsuitable (Environment Agency
2008c
). If a suitable value cannot be found
from any of the recommended sources, the site must automatically proceed to
Tier 2 of the ERA framework.
Although SSVs are essentially used as comparison thresholds, there may
be circumstances where simply comparing the concentration of a contam-
inant in the soil with its corresponding SSV is not sufficient. For example,
the contaminant in question might occur naturally at the site, and the back-
ground concentration in soil is greater than the SSV, or where physico-
chemical properties of the soil modify the contaminant to such an extent
that comparison with total soil concentration is meaningless (Environment
Agency
2008c
).
Where background levels of a contaminant exist, the recommended
approach is to consider the total concentration (both background and anthro-
pogenic) to pose a risk (Total Risk Approach, TRA) because the ecosystem is
unable to differentiate between background and anthropogenic and the con-
taminant exists as a combined concentration.
Where physio-chemical modification of the contaminant is likely, this can
usually be corrected using chemical kinetic equations, and expressed as the
concentration that is biologically available (i.e., can actually be taken up by the
organism) (Environment Agency
2008c
). The Environment Agency is also
developing a decision tool (using Microsoft Excel) to facilitate in this process,
although it is not yet available.
If concentrations of all contaminants on a site are below their respective
SSVs, the risk assessor can document the results and exit the ERA. If the
concentration of a contaminant is greater than the SSV, or if no suitable
SSV can be found for the contaminant in question, the ERA must progress to
Tier 2.
Tier 2
By the time a site has progressed to Tier 2, it has been established that the Part 2A
regime applies to the site, that there is a contaminant present, a receptor
present and a plausible, potential exposure linkage from the contaminant to
