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BILANS ET IMPACTS DE LA MISE EN DEPOT DE SEDIMENTS FLUVIAUX URBAINS DANS LE BASSIN DE LA SEINE

Abstract : In the river Seine basin, dredging removes, on average, 150 000 m3 each year. Sediments frequently accumulate pollutants, consequently, the management of dredged materials (DM) is of great environmental concern. The aim of this work was to improve our knowledge on this particular field. We first established a summary of international regulations concerning DM management. We noticed that the situation in Europe and especially in France is far from being clear. Besides, we described the different steps of the sediments management from the dredging operation to the final destination of the DM. In order to determine the quality of sediments before dredging, sediments were sampled in the Seine river before dredging, and analysed. Geographic distribution showed that the peaks of micropollutant concentrations were mostly found at the direct vicinity of the pollution source. We describe the different sampling sites and analytical methods used to follow the evolution of the Rouillard underwater disposal site (Verneuil-sur-Seine, 78, France). From June 1999 to September 2001, this site received 200 000 m3 of the DM from the river Seine basin. The DM was dumped hydraulically into the disposal site, i.e. the DM was re-suspended with Seine water to enable pumping. This dumping technique modifies the physico-chemical properties of the DM which can lead to the mobilisation of pollutants initially present in the sediment. Therefore, we monitored the quality (in situ parameters, organic matter, micropollutants) of superficial water and sediment in the disposal site, as well as the quality of the underground water situated below the studied pond. The monitoring of superficial waters reveals that the major impact of the specific dumping technique used in the river Seine basin is the nutrient release, and more specifically ammonium and to a lesser extent organic carbon release. This nutrient input leads to eutrophication that was confirmed by Chlorophyll 'a' monitoring. In addition, we did not observe any organic or metallic micropollutant release in the superficial water during this 3 years study. Nevertheless, long term studies and monitoring still need to be carried out. Sediments settled in the pond played an important role in the mobilisation of pollutants. In fact, diagenesis processes take place within the sediment and we clearly noticed the occurrence of ammonification and denitrification processes. We also observed organic matter decay leading to the release of organic carbon and phosphorus. The pond sediment also played the role of a micropollutant well since we observed the accumulation of these pollutants at the surface of the dumped sediment. The monitoring of underground waters did not reveal any modification of their quality. We assessed pollutant fluxes passing through the pond: the water balance confirms our hypothesis about major water movements, i.e water seeped from the outside of the pond (underground water or Seine water) into the pond. In addition, flux calculations confirmed the trends we already deduced from the pollutant concentrations. Taking into account sustainable management of DM, this work leads to proposals regarding DM treatment before disposal in the river Seine basin. We also propose further studies in order to improve our knowledge on processes already observed during the field studies, by performing batch and pilot scale experiments.
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  • HAL Id : tel-00861382, version 1

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Sonia Carpentier. BILANS ET IMPACTS DE LA MISE EN DEPOT DE SEDIMENTS FLUVIAUX URBAINS DANS LE BASSIN DE LA SEINE. Environnement et Société. Université Paris XII Val de Marne, 2002. Français. ⟨tel-00861382⟩

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