Assessment of the suitability of the CDF option for the management of harbour sediment: an Italian case study
Type:
Presented during:
WODCON XVII: "Dredging in a Sensitive Environment" - 2004, Hamburg, Germany
Authors:
C. Mugnai, S. Macchia, F. Mela, S. Ferrari, F. Pilato, D. Pellegrini
Abstract: The first Italian Confined Disposal Facility (CDF) has been built next to Livorno harbour to be filled up with dredged material. It consists of a basin closed by a continuous enclosure dyke, with a storage capacity of approximately 1.600.000 m3. Following indications from the Italian Ministry of Environment, the initial CDF design was changed splitting it into secondary internal basins for materials coming from different harbour areas.
An experimental study was carried out using the first filled basin (100.000 m3 of dredged materials) as a precautionary model to study the impact of the disposal inside a CDF monitoring the main basin, without affecting the sea directly. Out-flowing waters from that compartment, deriving from hydraulic dredging, were sampled almost weekly during the discharge (June-September 2002) and on these samples physical-chemical and ecotoxicological analyses were performed. Moreover, 5 sampling stations were placed along a seaward transect in the main basin, starting from the outflow of the compartment. On these, surficial sediment samples were collected and analyzed for grain size, content of metals and organic compound, and some bioassays were carried out. The results demonstrate the existence of a transport of fine material in the main basin, that determines some alteration of the environmental quality. This is particularly evident for heavy metal (Cd, Hg, Pb, Zn and Cu) and organic compounds (PAHs and PCBs), that decrease moving seaward along the transect.
Significant difference in terms of toxicity cannot be found between the situation before and after the disposal of materials in the compartment.
Keywords: confined disposal facility, sediment management, monitoring, chemical analyses, suspended solid, bioassays.