LARGE-SCALE PILOT FOR TREATMENT AND USE OF CONTAMINATED DREDGED MATERIAL IN THE NETHERLANDS; PRELIMINARY RESULTS AND POLICY

摘要

A yearly quantity of about 30 million cubic meters of dredged material has to be dredged in the Netherlands. Most of these sediments are clean or slightly contaminated and are relocated at sea, placed at riverbanks and, to a smaller extent, used beneficially. A minor part of the dredged material is too contaminated for relocation or reuse and has to be disposed. A number of large-scale sub-aquatic confined disposal facilities (CDF) have been constructed for this purpose. Because of the limited storage capacity of these CDF's and signals from the private sector that treatment of dredged material can be a feasible alternative, the Dutch government started a large-scale pilot in 2003 for the treatment and use of contaminated dredged material. The aim of this pilot is to investigate the financial and technical possibilities for the treatment and use of contaminated dredged material compared to disposal in CDF's. The outcome of the pilot will be input for the future policy on treatment and use of dredged material. Starting point of the pilot is to encourage the industry to treat as much as possible contaminated sediments. The Directorate-General for Public Works and Water Management (in Dutch 'Rijkswaterstaat') assigned various dredging projects from which the contractors can choose contaminated dredged material for treatment. In May 2004, two contracts were awarded to the companies BAG/Van Oord Dredging and Marine Contractors (the Netherlands) and Jan de Nul/ENVISAN (Belgium). In November 2004, BAG/Van Oord Dredging and Marine Contractors started treatment of contaminated dredged material from maintenance of the river Maas near locks between the cities of Roermond and Den Bosch. The dredged material is mainly treated by natural dewatering (ripening) in lagoons and by sand separation. A smaller part of the dredged material, dredged from the floodplains of the river Maas, was treated by chemical immobilization and reused as a capping layer on a disposal site. In 2007, Jan de Nul/Envisan will start treatment (natural dewatering/landfarming, sand separation and mechanical dewatering) on its treatment plant in Gent. This concerns dredged material from maintenance of the Canal Gent-Terneuzen. Based on the preliminary results of the pilot it can already be concluded that treatment and use is not the general solution for the problem of contaminated dredged material in the Netherlands. Only in certain circumstances, treatment and reuse of contaminated dredged material can be an economic viable alternative to disposal in CDF's. These circumstances vary for each dredging project, so in each case the consideration has to be made to determine if treatment is a feasible alternative for disposal in a CDF. The present policy states that treatment is no longer considered as a policy objective, but as a means to arrive at beneficial use. Cost-effectiveness is the most important criterion for decisions on treatment of dredged material, which are taken on a case-by-case basis.