Marine Sediments from a Contaminated Site: Geotechnical Properties and Chemo-Mechanical Coupling Processes

Abstract

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...

A geo-chemo-mechanical study of a highly polluted marine system (Taranto, Italy) for the enhancement of the conceptual site model

“…2 and 5 ), in front of the Military Shipyard. As reported by 35 , 57 , 58 , the geotechnical properties of the sediments occurring down to about 4–6 m depth were found to differ from those expected according to the soil skeleton composition. Such observation has suggested that the significant presence of organic matter and of either organic or inorganic contaminants in the sediments may be prompting coupled chemo-mechanical phenomena in the sediments, which modify their hydro-mechanical properties.…”

“…The pore water salinity has been found to range between 30 g/L and 36 g/L within the 1 st LTU , and to be about 32 g/L within the deep sediments of the 3rd LTU 58 . Therefore, the salinity of the pore water in th Holocene sediments remains high with increasing depth.…”

“…2 ). All the tests were carried out according to the standard procedures set by American Standards Test Methods (ASTM) and British Standards (BS), adapted to take account of the presence of brackish fluid and contaminants in the soil, as well as of fragments of shells and fossils 58 , 68 , 69 . An integrated system (hardware and software), named GeoLab, for the geotechnical measurements was also developed 70 in order to increase speed, accuracy, and productivity during testing.…”

Evaluation of Zeolite as a Potential Reactive Medium in a Permeable Reactive Barrier (PRB): Batch and Column Studies

“…Industrial and human activities have generated wastes composed of different chemical compounds that can contaminate environmental compartments, such as groundwater. Such contamination can affect the availability of water for human use and for environmental functions [1][2][3]. The focus on this type of contamination is constantly increasing because groundwater is the main water source in several parts of the world [4].…”

“…Several types of reactive materials (natural and industrial) with different sorption characteristics have proven to be efficient in PRBs in terms of the removal of different groups of contaminants present in groundwater. Such materials include (1) modified natural materials, such as brown coal [23], modified montmorillonite [24], modified and treated zeolites [12,25] and zero-valent iron [26]; (2) natural materials, such as zeolites [27][28][29], limestones [30], laterites [13] and sericite [31]; and (3) combined materials, such as sand and zeolite [32,33] and zero-valent iron and zeolite [14,20].…”