The Danish EPA is re-evaluating their strategy for handling of polluted sediments and sludge from harbors. As part of this strategy evaluation, DHI has performed a study of the exposure pertaining to disposal under varying physical and chemical conditions. Two scenarios for dumping sediments at sea were evaluated; in one scenario, sediments were dumped at relatively unprotected places where bottom-currents could induce re-suspension of polluted sediments leading to spreading of pollution. Re-suspension events were analyzed using the MIKE 21 MT model. In another scenario sediments were dumped at relatively well-protected depressions at the sea bottom, where the only means of pollution was diffusion.
For in-land deposition two scenarios were evaluated; a near coastal deposition, e.g. for expansion of harbors, where the deposited material was kept under water at reduced conditions, and deposition in traditional land-fills where the leachate was collected. An interesting aspect of the project was the study of leaching of metals and organic pollutants (PAH and TBT) under different redox conditions, which was evaluated by use of the geochemical code PHREEQC. To improve the data material for evaluation of the pollution levels in different harbor types and for the leaching behavior under different conditions, the EPA has now launched an additional project with DHI, in which samples of sediments will be gathered from three differently sized harbors and subjected to conditions similar to those encountered for various deposition strategies.
For further information please contact Jesper Holm