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'hot spots' of large concentrations coexist with
a background of data below the detection limit
(censored observations) (Goovaerts, 1999). An
alternative approach to the probabilistic analysis
based on the methods of the classical statistics
can be that of analyzing and quantifying the spa-
tial uncertainty using geostatistical techniques.
Geostatistics offers a series of extremely useful
instruments to operate any decisional processes
in that it allows to recognize the structures that
normally characterize the spatial distributions of
the studied properties.
This paper is aimed at providing a geostatistical
method for modeling the uncertainty connected to
the input parameters in a probabilistic procedure of
risk assessment. It is structured in such a way: the
first section will provide some legislative notions
on risk assessment's role within the remediation
procedure of a contaminated area, the intermediate
sections will deal with how to treat uncertainties
in risk assessment, whether with classical (sto-
chastic), or geostatistical approaches. In this part
the application of geostatistics is described for the
delimitation of the potentially contaminated area,
the determination of the Source Representative
Concentration, and also of the optimal sampling
designs for site characterization, an important
phase of the remediation procedure. In the final
part three case studies are proposed, in which the
concepts explained in the theory are applied to
contaminated areas.
step concerns the delimitation of the potentially
contaminated area, to be submitted to risk assess-
ment and subsequently to eventual remediation
treatments.
The current Italian legislation makes reference
to two thresholds criteria of interventions: the
former is the Threshold Concentration of Con-
tamination (CSC) that is considered as an alert
limit, that, once exceeded, makes it necessary to
carry out a risk assessment; the latter is the Risk
Threshold Concentration (CSR), that identifies
the acceptable levels of residual contamination,
on which to plan remediation interventions. An
area is potentially contaminated if the pollutant
concentrations exceed the CSC values (tabulated);
it is declared contaminated if the pollutant con-
centrations exceed the CSR values, obtained by
means of a risk assessment, to be carried out on
the basis of the results of the investigations.
Uncertainty and Variability in
Risk Assessment Data
The legislative decree n. 152/06 attributes a
great importance to risk assessment and defines
the general criteria for its elaboration; the risk is
estimated in unquestionably deterministic terms
and is expressed by a single numerical value. The
principle at the basis of the procedure is that of
considering always the “Worst Case” that assures
conservative estimation values, in that it provides
higher values than the average estimated ones,
in favour of the environment and human health.
Nevertheless, in the execution of a risk assessment
the most conservative result is not always guaran-
teed as the data on which the analysis is based are
characterized for the most part by a high degree
of variability and often also by uncertainty. The
character of uncertainty and variability of the risk
assessment, an intrinsic property of this procedure,
is explicitly recognized by the D.lgs 152/06 that
reports: “the elaboration of the analytic results
has to express the uncertainty in the concentration
value determined for each sample..”.
the risk Assessment in the
current Italian legislation
The risk assessment procedure is considered by
the current Italian legislation (D.lgs 152/06) as a
support tool to establish first of all if it is necessary
to remediate an area or not and, if so, the reme-
diation targets to reach in order to annul eventual
harmful effects for human health according to the
predefined acceptability criteria. When an area is
subjected to investigations in order to ascertain
the eventual state of contamination, one decisive
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