Groundwater-Related Risk Assessment - Dealing with Contaminated Sites: From Theory Towards Practical Application - page 781

A site-specific Risk Assessment is needed to evaluate the risk posed by a cer-
tain activity and to ensure that inputs into groundwater do not cause deterioration.
An additional trend assessment is also required to verify that an existing plume of
contamination does not present a risk to human health or the environment.
17.8 Site-Specific Assessment of Exposure Through
Contaminant Transport
In many countries, a tiered approach is used to be able to assess the site-specific
human health risks due to contaminant transport in a scientifically based and effi-
cient way. An example of this is given in Otte et al. ( 2007 ), who described the
tiered approach used in the Netherlands within the framework of the determination
of the urgency of remediation. In each tier successively the degree of conservatism
decreases, while the site-specificity increases. As a consequence, the complexity,
and hence the effort and finances needed, also increase in each tier. When in a
specific tier unacceptable groundwater-related risks cannot be excluded, an assess-
ment in the following tier then has to be performed. The underlying principle is:
simple when possible and complex when necessary. The Dutch tiered approach is
laid out as follows: Tier 0 relates to the 'Initial Characterization' which is based
on three criteria: the presence of Non Aqueous Phase Liquids (NAPLs), vulner-
able objects and/or a contaminated groundwater body in which the Intervention
Value (the Dutch quality criterion for serious soil contamination) is exceeded in
a groundwater volume of at least 6000 m 3 . In Tier 1 a simple generic contami-
nant transport calculation is performed based on a conservative scenario. In Tier 2,
a more complex site-specific calculation is performed based on the same concepts
as in Tier 1, but instead of generic data, site-specific (i.e., measured) data needs to
be used. Alternative options are also offered in Tier 2 to assess contaminant trans-
port, for example, by extrapolating contaminant transport historical data to future
transport estimates and including the possibility of degradation. Finally, in Tier 3,
monitoring activities can be performed and complex numerical models can be used.
Furthermore, leaching is taken into account in this tier, and special attention is given
to Total Petroleum Hydrocarbons (TPH), a frequently occurring contaminant in
groundwater.
References
Anderson J (2003) The environmental benefits of water recycling and reuse. Water Sci Technol:
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Baynes S (2004) Water efficient toilets: a canadian perspective. Canada Mortgage and Housing
Corporation (electronic version). Retrieved 16 Oct 2009
Bruell CJ, Inyang HI (2000) The fundamentals of remediation in rock masses, chapter 1. In: Inyang
HI, Bruell CJ (eds) Remediation in rock masses. ASCE, pp 1-11
Burke JJ, Moench MH (2000) Groundwater and society: resources, tensions and opportunities.
United Nations Publication ST/ESA/205, New York