Introduction to Contaminated Site Management - Dealing with Contaminated Sites: From Theory Towards Practical Application - page 66

1.8.4 A More Pragmatic Approach
1.8.4.1 Mentality Change
Since the mid 1990s a significant change in mentality in terms of contaminated site
management has taken place in most developed countries. Gradually, the general
idea has settled in that the present philosophy on contaminated site management was
solid, but too rigid and not efficient enough to make the desired progress. Desired
progress, in this perspective, is mainly expressed in terms such as percentage of
the total contaminated site load that has been restored. Mainly within the larger
municipalities, contaminated sites had resulted in stagnation in building activity.
As a response, the basic concept of management of contaminated sites has
evolved into the adage 'environmentally acceptable and financially feasible'.
Fitness-for-Use and cost-efficiency have become important boundary conditions
in contaminated site management. It has become widely accepted that not every
risk means an unacceptable risk. Therefore, the remediation objectives, at least for
immobile contaminants in the upper soil layer, need not relate to 'no risk', but
to 'an acceptable risk' for the specific land use (land use-specific remediation).
Moreover, it was widely accepted that more cost-efficient methodologies should
become available.
At the same time, many governments have developed procedures for financial
support, such as sharing financial risks, the provision of subsidy grants, co-financing
structures, tax benefits and 'green' investments.
1.8.4.2 Natural Attenuation
The concept of using biodegradation as a Risk Management solution, which gen-
erated enormous interest in the 1990s and could count on broad support from
decision-makers, initiated a very important innovation, that is, extensive in situ
remediation technologies (bio-restoration). Although this is the oldest remediation
technology, since organisms have been breaking down organic contaminants ever
since contaminants were present in the soil, it was not greatly accepted in the early
days of contaminated site management. The reason for this was the relatively long
time span that was needed for complete restoration of the site. Moreover, it was
difficult to predict the progress of this kind of remediation. However, this change
in mentality has come up with the general idea that 'contaminants that have been
in soil for many decades need not necessarily be removed within a time-span of
months on up to a few years'.
This insight led to numerous investigations, mainly in the second half of the
1990s, for the purpose of understanding the processes better along with improving
efficiency and predicting the time span needed. The process is now called Natural
Attenuation (aka: intrinsic remediation), which often also includes dilution by trans-
port processes such as molecular diffusion and hydrodynamic dispersion. Natural
Attenuation is often considered as a Risk Management solution rather than as a
remediation technology. Despite sometimes high starting costs, the overall budget
for this Risk Management procedure is relatively low. Besides this, it results in a