DOI: http://dx.doi.org/10.1065/jss2001.09.027 --- While remediation and storage of contaminated dredged
materials is a key issue at harbour sites, there is another type of
sediment pollution problem, which mainly originates from large-scale
dispersion of contaminants in flood-plains, dike foreshores
and polder areas. In recent years, catastrophic cases of sediment
contaminations have occurred in connection with the failure of
tailing dams from mines. Unlike problems related to conventional
polluted sites, the risks here are primarily connected with the transporting
and depositing of contaminated solids in a catchment area,
especially in downstream regions.
A special example demonstrating the dispersion of highly contaminated
sediments in a large catchment area will be shown from the
so-called Chemistry Triangle of the upper Elbe River system, Germany.
The Spittelwasser area, situated there, was chosen by the
organisers of the international conference ConSoil 2000 for a case
comparison and four expert teams from Denmark, Germany, the
Netherlands and the UK were invited to participate in this Case
Study. Evaluation of the plan was done by members of the networks
of NICOLE (Network for Industrially Contaminated Land)
and CLARINET (Contaminated Land Rehabilition Network).
In the study of the German team, five major groups of technical
measures have been identified by the environmental authorities
to be discussed in relation to the Spittelwasser case or for similar
problem solutions in contaminated flood-plain areas. The team came to the conclusion that none of these techniques would
be applicable as an individual measure. Instead, a stepwise approach
combining different monitoring techniques and remediation measures was proposed. These would include point
excavations of critical material, promotion of plant growth as
an element for stabilising the soil and flood sediments, as well
as the installation of sediment traps.
At the Spittelwasser site, investigations are planned on the effects
of natural attenuation processes of organic and inorganic contaminants
in flood-plain sediments and soils. In the practice of this concept, non-destructive, ntrinsic bonding mechanisms and
their temporal development have thus far found much less recognition
compared to destructive processes such as biological degradation.
Yet these so-called diagenetic effects, which apart from chemical processes involve an enhanced mechanical consolidation
of soil and sediment components by compaction, loss of water, and mineral precipitations in the pore space, may induce a quite
essential reduction of the reactivity of solid matrices [see Part I Improving Chemical and Biological Criteria (JSS - Journal of
Soils and Sediments, Vol 1, No 1, pp 30-36)]. |
