Environmental Engineering Reference
In-Depth Information
Natural Attenuation (MNA), is nowadays widely advocated as a low cost solution
for soil remediation (see Chapter 22 by Peter et al., this topic). It involves degrada-
tion of contamination by natural processes. These methods are less costly. But they
require more time, have less predictable results and may require long time moni-
toring and aftercare. This is a drawback if land can only be reused after a lengthy
remediation.
A possibility to combine fast-acting measures with a longer term extensive treat-
ments becomes interesting in these situations, since it may provide an optimal
balance of Risk Management, maximising wider environmental merit and limiting
costs. Moreover, the soil itself has some interesting characteristics, which may help
in reducing the risk. Soil has a natural capacity to act as a barrier, which can be used
in containment approaches and it has a natural capacity to biodegrade contaminants.
If these natural capacities can be used, the costs of solutions as well as unwanted
side effects like CO 2 -emissions through energy consumption will decrease. The use
of the natural capacities of soils in contaminated site management solutions need to
be further explored both from a scientific and a regulatory point of view, in order to
meet the general sustainability requirements of soil protection.
Whether natural attenuation is actually successful will depend on site-specific
conditions. These are never completely known, and processes like biodegradation
and chemical and physical behaviour of contaminants may be difficult to predict.
Natural attenuation may better be considered as an experiment under controlled
conditions. The authorities will have to provide some room for these experiments in
terms of time and space. The control of these experiments will require monitoring
of the process. At certain points in time one must be able to decide whether natural
attenuation is performing as expected or whether one has to resort to more intensive
Risk Management options.
Natural attenuation may also be enhanced by addition of contaminants to soil
and groundwater in order to stimulate microbial activity. If the presence of these
contaminants and residual contamination is temporal or has negligible effects on
the quality of the groundwater, this may be considered acceptable from a soil and
groundwater protection point of view. It is up to the policymakers to find the right
balance between soil remediation and soil protection in these cases, but it is clear
that MNA solutions require longer-term management by the competent authorities.
The network discussions provided valuable ideas how this management approach
should be developed.
23.5 A Policy Maker's View on Risk Assessment
for Contaminated Sites
Although “Risk” is becoming a central concept in environmental policies, this
does not mean that risk is an easy and well-defined concept. Definitions do
abound, at least 20 definitions ranging from informal to very formal (mathematical)
were mentioned by Vlek ( 1990 ). Risk Assessment, risk analysis, risk perception,
policy-making and decision-making are being quite extensively studied in the
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