The paper presents the results of the analysis of the geo-chemo-mechanical data gathered through an innovative multidisciplinary investigation campaign in the Mar Piccolo basin, a heavily polluted marine bay aside the town of Taranto (Southern Italy). The basin is part of an area declared at high environmental risk by the Italian government. The cutting-edge approach to the environmental characterization of the site was promoted by the Special Commissioner for urgent measures of reclamation, environmental improvements and redevelopment of Taranto and involved experts from several research fields, who cooperated to gather a new insight into the origin, distribution, mobility and fate of the contaminants within the basin. The investigation campaign was designed to implement advanced research methodologies and testing strategies. Differently from traditional investigation campaigns, aimed solely at the assessment of the contamination state within sediments lying in the top layers, the new campaign provided an interpretation of the geo-chemo-mechanical properties and state of the sediments forming the deposit at the seafloor. The integrated, multidisciplinary and holistic approach, that considered geotechnical engineering, electrical and electronical engineering, geological, sedimentological, mineralogical, hydraulic engineering, hydrological, chemical, geochemical, biological fields, supported a comprehensive understanding of the influence of the contamination on the hydro-mechanical properties of the sediments, which need to be accounted for in the selection and design of the risk mitigation measures. The findings of the research represent the input ingredients of the conceptual model of the site, premise to model the evolutionary contamination scenarios within the basin, of guidance for the environmental risk management. The study testifies the importance of the cooperative approach among researchers of different fields to fulfil the interpretation of complex polluted eco-systems.

The city of Taranto in the south of Italy is one of the areas declared as "at high risk of environmental crisis" by the Italian government because it represents one of the most complex industrial sites in Europe, located near urban areas of high population density. The rich ecosystem of the Mar Piccolo basin, located at north of Taranto, started exhibiting unconfutable signs of environmental pollution, confirmed by the high concentrations of organic and inorganic contaminants. Among the different aspects involved in the environmental studies aiming at the basin remediation, this paper focuses on submarine sediments and reports some results of the geotechnical laboratory investigations which made also use of non-standard equipment and revised procedures for data interpretation in order to take account of the sediments' contamination and heterogeneities. The geotechnical laboratory tests show that, despite the Mar Piccolo recent Holocene sediments having similar origin and composition to those of the Sub-Apennine clay basic formation, their behavioral facets appear to be altered by the presence of contaminants of both natural and anthropogenic origin. Results of washing tests are also presented as a first attempt to quantify the effects of chemo-mechanical coupling processes on the plasticity properties of the shallow sediments.Geosciences 2019, 9, 333 2 of 20 of chemo-mechanical coupling processes on the index properties of kaolinite, smectite, and mixed clay samples, observed after mixing the clay with solutions of different chemical compositions were discussed by several authors [3][4][5][6][7][8]. The potential of chemical-mechanical coupling is greatest in fine-grained soils at low confinement and such coupling may prompt highly variable effects for different clay fabric conditions [9]. In this context, the research on Mar Piccolo (MP) sediments aims to add an original contribution on the behavior of fine-grained sediments affected by a real pattern of contamination.The MP basin in the South of Italy represents a natural site characterized by the presence of contaminants of different sources and composition. The basin is located just behind the coast of the city of Taranto (Figure 1a), one of the most important industrial sites in Europe and represents, at the same time, an unusual ecosystem from a naturalistic point of view, with several animal and plant protected species and wide areas for mussel cultivation and fishing activity. Due to these peculiar conditions, the MP basin has been declared 'at high risk of environmental crisis' [10] and included in the list of the Sites of National Interest (SIN; [11]), to be subjected to comprehensive investigation for a preliminary selection of sustainable strategies for both its remediation and management. The paper shows the environmental boundary conditions of the MP and focuses on the results of geotechnical characterisation of marine sediments, that has been carried out to derive a geotechnical model of the area up to depths of engineering interest. The data of so...

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