...
Defining
...
Risk
...
Clusters
...
The
...
scale
...
and
...
complexity
...
related
...
to
...
soil
...
and
...
groundwater
...
contamination
...
at
...
the
...
megasite
...
require
...
a
...
systematic
...
approach
...
for
...
an
...
appropriate
...
assessment
...
and
...
management
...
of
...
the
...
risks.
...
For
...
this
...
purpose
...
the
...
risk
...
management
...
zone
...
(RMZ)
...
is
...
subdivided
...
into
...
the
...
so-called
...
risk
...
clusters
...
(see
...
figure
...
below).
...
A
...
risk-cluster
...
is
...
a
...
geographical
...
subdivision
...
of
...
the
...
risk
...
management
...
zone
...
(RMZ)
...
with
...
source-pathway-receptor
...
sequences
...
that
...
can
...
be
...
grouped
...
together
...
into
...
one
...
unit
...
for
...
which
...
jointly:
...
1)
...
risks
...
can
...
be
...
quantified
...
and,
...
2)
...
risk
...
management
...
scenarios
...
can
...
be
...
developed.
...
Risk
...
clusters
...
form
...
the
...
units
...
on
...
which
...
the
...
megasite
...
risk
...
management
...
plan
...
will
...
be
...
based.
...
The
...
risk
...
clusters
...
are
...
used
...
in
...
further
...
development
...
and
...
evaluation
...
of
...
risk
...
management
...
scenarios,
...
and
...
the
...
selection
...
of
...
the
...
final
...
risk
...
management
...
scenario
...
for
...
the
...
megasite
...
of
...
concern.
...
The risks clusters are related to a source-pathway-receptor
...
sequence.
...
The
...
conceptual
...
model
...
and
...
the
...
RMZ
...
are
...
therefore
...
the
...
initial
...
basis
...
for
...
defining
...
risk
...
clusters.
...
The
...
second
...
information
...
source
...
used
...
is
...
the
...
set
...
of
...
megasite
...
characterization
...
data
...
organized
...
in
...
a
...
database
...
related
...
to
...
the
...
GIS,
...
which
...
holds
...
information
...
on:
...
- the
...
- contamination
...
- situation
...
- of
...
- soil
...
- and
...
- groundwater
...
- (sources);
...
- the
...
- geological
...
- and
...
- hydro-geological
...
- characteristics
...
- of
...
- the
...
- site
...
- (pathways);
...
- the
...
- receptors.
...
Clustering
...
is
...
an
...
iterative,
...
cyclical
...
process,
...
depending
...
on
...
the
...
information
...
available
...
at
...
different
...
stages
...
of
...
the
...
management
...
process.
...
The
...
formation
...
of
...
preliminary
...
risk
...
clusters
...
done
...
by
...
technical
...
experts
...
requires
...
an
...
analysis
...
of
...
the
...
single
...
elements
...
of
...
the
...
source-pathway-receptor
...
sequences
...
and
...
makes
...
use
...
of
...
the
...
GIS
...
to
...
create
...
maps
...
of
...
the
...
risk
...
clusters.
...
The
...
preliminary
...
risk
...
clusters
...
are
...
subsequently
...
presented
...
to
...
the
...
group
...
of
...
stakeholders
...
(GOS),
...
who
...
have
...
to
...
agree
...
(and
...
possibly
...
suggest
...
adjustments)
...
on
...
the
...
subdivision
...
of
...
the
...
megasite
...
into
...
these
...
clusters.
...
Also
...
a
...
prioritization
...
of
...
the
...
different
...
risk
...
clusters
...
can
...
be
...
carried
...
out
...
in
...
interaction
...
with
...
the
...
GOS.
...
In
...
the
...
following
...
two
...
steps
...
(see:
...
Risk
...
Assessment
...
->
...
Modelling)
...
and
...
(see:
...
Risk
...
Assessment
...
->
...
Determining
...
risks)
...
the
...
risks
...
are
...
further
...
quantified.
...
The
...
results
...
of
...
these
...
steps
...
are
...
again
...
presented
...
to
...
the
...
GOS
...
and
...
the
...
final
...
risk
...
clusters
...
are
...
established
...
in
...
the
...
final
...
step
...
of
...
this
...
IMS
...
risk
...
assessment
...
phase
...
(see:
...
Risk
...
Assessment
...
->
...
Finalize
...
clustering).
...
During or after defining the preliminary risk clusters, additional site characterization may be needed for sources, pathways and receptors, to gather sufficient data for the fate and transport modelling and the quantification of risks. For data gathering and evaluation the same tools should be used as before (See: Risk assessment -> Megasite characterization).
Output
The subdivision of the RMZ into risk clusters is done. They are used in identification, overview maps, and prioritization of risks in terms of manageable units, and form the basis for the megasite management plan to be further developed. The preliminary risk clusters defined at this stage need to be fine-tuned and adjusted in the next steps of the IMS.