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Groundwater

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is

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always

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on

...

the

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move

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and

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interacts

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with

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soil,

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surface

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waters

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and

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sediments

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Basically,
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soil,
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groundwater,
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surface
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water
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and
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sediments
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cannot
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be
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separated
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and
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should
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be
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dealt
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with
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as
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parts
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of
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one
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system.
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In
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risk
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based
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management
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the
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interaction
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pathways
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(determining
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the
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emission
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pathways
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between
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contaminant
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sources
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and
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water
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systems
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to
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be
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protected)
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need
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to
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be
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taken
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into
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account.
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Two
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major
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pathways
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can
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be
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considered:
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Subsurface
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interactions
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(Soil
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-
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groundwater
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– surface
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water
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interactions):
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This
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concerns
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groundwater
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quality/quantity
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and
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the
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functioning
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of
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the
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soil
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as
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filter/buffer/transform/storage
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medium.
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In
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megasite
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management,
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the
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understanding
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and
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the
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use
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of
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soil
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and
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acquifers
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and
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their
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natural
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filter
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and
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clean-up
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processes
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is
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very
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important.
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Technologies
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as
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enhanced
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and
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natural
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attenuation
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and
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heavy
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metal
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immobilisation
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are
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based
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on
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these
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processes.
...
These
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technologies
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are
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crucial
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parts
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of
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management
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scenarios
...
for
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practical
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any
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megasite.
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In
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the
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risk
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based
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approach,
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groundwater
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systems
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can
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be
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sources,
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pathways
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or
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receptors.
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Groundwater
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pressure
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areas
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(receptors)
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need
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to
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be
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dealt
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with
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in
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relation
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to
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the
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Groundwater
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Daughter
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Directive.
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Surface
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interactions
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(Soil/floodplains
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– sediments – surface water interactions):
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Surface
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water
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system
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affect
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soil
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(for
...
instance
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river
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systems
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affect
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floodplain
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soils
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through
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inundation)
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and
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vice
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versa.
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Suspended
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solids
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are
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the
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main
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quality
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determining
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medium
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for
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surface
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water,
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sediments,
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and
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floodplain
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soils.
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Particulate
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matter
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transport
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from
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land
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towards
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surface
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waters
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by
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precipitation,
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surface
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run-off
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or
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wind
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erosion,
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and
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deposition
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of
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vaporised
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contaminants
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into
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water
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systems
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can
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affect
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surface
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water
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and
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sediment
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quality.
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Sediments
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and
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flood-plain
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soils
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mirror
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long
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term
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trends
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in
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lake
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and
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river
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basin
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water
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quality.
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Land-use,
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large
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scale
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historical
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contamination
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(i.e.
...
megasites),
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diffuse
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pollution,
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surface
...
run-off
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and
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wind
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erosion,
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are
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key
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factors
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in
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surface
...
water
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quality
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at
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the
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scale
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of
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catchments
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as
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well
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as
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river
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basins.
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These
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processes,
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and
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possible
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intervention
...
measures
...
are
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taken
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into
...
account
...
in
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the
...
risk
...
based
...
management
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approach
...
for
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megasitesas
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developed
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in
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the
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IMS.
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The
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Water
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Framework
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Directive
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requires
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the
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set
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up
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of
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River
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Basin
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Management
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plans
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to
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tackle
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these
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types
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of
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problems.
...
The
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welcome
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IMS
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helps
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to
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establish
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megasite
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management
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plans
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as
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part
...
of
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River
...
Basin
...
Management
...
Plans.
...

Both
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subsurface
...
and
...
surface
...
interactions
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are
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taken
...
into
...
account
...
in
...
the
...
risk
...
based
...
approach
...
developed
...
in
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the
...
IMS.
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This
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starts
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with
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the
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conceptual
...
model
...
building
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and
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is
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subsequently
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further
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developed
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in
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the
...
risk
...
assessment
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and
...
building/evaluation
...
of
...
scenarios.
...
In
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the
...
IMS
...
approach,
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most
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attention
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is
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given
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to
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subsurface
...
interactions
...
and
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emission
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pathways
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through
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groundwater
...
water
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systems.
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Therefore
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some
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additional
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background
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information
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is
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given
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on
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this
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subject
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below.
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Basic

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description

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of

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a

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groundwater

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system

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Groundwater
...
systems
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are
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characterized
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by
...
the
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flow
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of
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the
...
water.
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The
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flow
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of
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the
...
water
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can
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be
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characterized
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by
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its
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physical
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dimensions
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like
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position
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of
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infiltration,
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length
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of
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the
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pathway,
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groundwater
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velocity,
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position
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of
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seepage,
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etc.
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These
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dimensions
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are
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dependent
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on
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the
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soil
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characteristic
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(e.g.
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porosity).
...
Traditionally
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geohydrologists
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have
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focussed
...
on
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groundwater
...
quantity,
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because
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groundwater
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basically
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was
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free
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of
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pathogens
...
and
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contaminants,
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due
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to
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the
...
filtering
...
capacity
...
of
...
the
...
soil.
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When
...
groundwater
...
quality
...
became
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an
...
issue,
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knowledge
...
about
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the
...
fate
...
and
...
transport
...
of
...
micro-contaminants
...
was
...
added
...
to
...
the
...
quantitative
...
knowledge
...
of
...
the
...
water
...
system.

Image Added

Classification of groundwater systems

Though the basic model is very simple, natural diversity of soils make the systems very complex. With a closer look one could discern several ‘systems’ on different scales, overlapping, interdependent and changing in time and space. This complexity makes it impossible to understand most groundwater systems, without quantitative computer models. The models are validated by geohydrological data, like water pressures, flows, etc.
Because there is a lot of experience in modelling groundwater systems, it is possible to recognize patterns in the groundwater systems and to classify them. Groundwater systems could be classified based on:

Geological scale (local systems, subregional systems, regional systems)
Human interference (natural systems, manmade systems)
Dominant surface water (Rhine system, Ruhr-system, etc.)
Functionality (drinking water area, salty systems, contaminated systems)
Territorial dimensions (city systems, nature reserve systems, industrial area systems)

Groundwater systems in the IMS

Knowledge of the groundwater system of a megasite, and its interaction with surrounding groundwater and surface water systems, is the core of the IMS. Due to the characteristics of a megasite (many sources of contamination, polluted groundwater, effects over a long time-scale and over a large geographical scale) it is not possible to assess risks and to define remedial actions without detailed knowledge of the groundwater system.

Knowledge of the groundwater system is built up in tiers:

The first tier is to collect perceptual knowledge of the surface aspects of the system (geography, soil type, surface water, groundwater extractions, etc) and to get a rough idea of the system. This kind of knowledge is needed to feed the story that starts the IMS.
The second tier is to collect existing data and use it to make a conceptual model of the groundwater system and its functioning.
The third step is to go into detail, collect specific additional data and make a computer model of the system and its behaviour over time.
The fourth step is to translate the specialist model information into management information that could be used in the IMS.

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