Zuffianò, L. E.

Carbonate aquifers, located in foreland tectonic settings, could represent important thermal water resources outside the volcanic areas, supplying spas or geothermal installations. Thermal springs constitute the discharge areas of deep marine and continental groundwaters flowing within these carbonate aquifers whose hydraulic conductivity and the relevant geothermal fluid migration are strictly controlled by both the discontinuity network and the karst processes involving the foreland environment. An example of these springs occurs along the south-easternmost portion of the Apulia region (Southern Italy) where some sulphurous and warm waters (22-33 °C) flow out in partially submerged caves located along the coast, thus supplying the spas of Santa Cesarea Terme. These springs are known from ancient times (Aristotele in III century BC) and the physical-chemical features of their thermal waters resulted to be partly influenced by the sea level variations. Some hypotheses about the origin of these warm waters were proposed up to now by previous researches but some uncertainties still exist. For this reason, the area has been selected in order to define the conceptual model of the geothermal resources related to the thermal springs and, as a consequence, the origin of the thermal springs. It is one of the pilot site of the Vigor Project (Evaluation of the geothermal potential of Regions of Convergence), promoted by the Italian Ministry of Economic Development and National Research Council. Santa Cesarea Terme zone is located within the Apulia carbonate platform, the foreland of the southern Apennines, which consists of Jurassic-Cretaceous limestones, thick more than 5 km in the study area and affected by intense karst processes, resting above the Late Triassic evaporite (Burano Fm) and, unconformably, overlaid by Cenozoic calcareous successions. Belonging to a coastal area, the studied groundwater, whose top is located almost to the sea level, is involved in saltwater intrusion and therefore the salt-fresh water interface occurs at some meters below the sea level moving inland. Geological and hydrogeological surveys, including geo-electrical prospecting, and chemical and isotopic analyses of both groundwater and seawater have been carried out. Stable isotopes (δ18O, δD) were used to define the origin of the thermal waters and the recharge mechanism of the geothermal systems while the unstable isotope (3H) was determined for estimating the age of the thermal waters and to define the conceptual model of this low temperature geothermal resource. All the data have been analysed to improve the knowledge of the groundwater flow system, thus assessing the possibility of using low-temperature geothermal fluids to fulfil the thermal needs of the town of Santa Cesarea Terme. In this narrow area, the source of geogenic salinization of spring groundwater was referred to ascending very deep groundwater, more saline than current sea water.The geochemical composition and the physical features of the sampled waters suggest that thermal waters should be moving from ancient seawaters subjected to intense evaporation processes, infiltrated at great depth within the seabed substratum. Afterwards, these thermal fluids should flow up through the almost vertical structures, related to the transtensional structures, identified within a narrow sector of the studied territory.

The coastal carbonate Apulian aquifers, located in southern Italy, feed numerous coastal cold springs and constitute the main local source of high quality water. The group of Santa Cesarea springs constitutes the unique occurrence of thermal groundwater outflow, observed in partially submerged coastal caves. The spring water is rich of hydrogen sulfide; temperature ranges from 25 to 33 C°. For their properties, spring waters are used for spa activities from several decades. Hydrogeological spring conceptualisations proposed up now were not able to justify water geochemical peculiarities or were not completely confirmed up now. To reduce these uncertainties, a complex hydrogeological survey has been defined. Geological and structural surveys, chemical and isotopic groundwater analyses, spring and well discharge measurements, well loggings, multi-parameters spring automatized measurements, and cave explorations are ongoing. All available data have been used to improve the knowledge of groundwater flow system, including the valuable deep aquifer, the origin of the thermal waters, and to investigate the possibility of using low-enthalpy geothermal fluids to fulfil the thermal needs of the town of Santa Cesarea Terme.

The Mar Piccolo (literally “narrow sea”), a sea internal basin which is part of the Taranto Gulf, located along the Ionian coast in southern Italy (Apulia region), represents both a peculiar and sensitive environmental area and a national environmental and social emergency due to the level of sea water pollution due to the pollutants coming from the close industrial area of Taranto. The area, located between the southern part of the Murgia plateau and the Ionian sea, is geologically characterized by a sequence of Mesozoic limestone (the Apulian carbonate platform) constituting the foreland of the southern Apennines chain. The Mesozoic sequence is intensely fissured and karstified, and forms an important groundwater reservoir. The aquifer occurring in the carbonate sequence of the Murgia plateau feeds numerous coastal springs and constitute the main local source of pure fresh groundwater. Galeso, Battentieri and Riso are the main subaerial springs located along the coast of Mar Piccolo, not far from the town of Taranto. This area is also characterized by several submarine springs, locally called “Citri”. Submarine freshwater discharge plays an important, though not well quantified, role in the hydrogeological equilibrium of the system, but also the source of the spreading of many pollutants in the Mar Piccolo area due to the close presence of one of the largest European steel mill together a number of hazardous industrial activities of other types. The paper describes the efforts and the preliminary results to define a detailed conceptualisation of the aquifer as main support to characterise the hydrological balance of the internal sea and the quality of sea water and the effect on of the ecological equilibrium of the coastal environment.

The Mar Piccolo basin is an internal sea basin located along the Ionian coast (Southern Italy), and it is surrounded primarily by fractured carbonate karstic environment. Because of the karstic features, the main continental water inflow is from groundwater discharge. The Mar Piccolo basin represents a peculiar and sensitive environment and a social emergency because of sea water and sediments pollution. This pollution appears to be caused by the overlapping effects of dangerous anthropogenic activities, including heavy industries and commercial and navy dockyards. The paper aims to define the contribution of subaerial and submarine coastal springs to the hydrological dynamic equilibrium of this internal sea basin. A general approach was defined, including a hydrogeological basin border assessment to detect inflowing springs, detailed geological and hydrogeological conceptualisation, in situ submarine and subaerial spring measurements, and flow numerical modelling. Multiple sources of data were obtained to define a relevant geodatabase, and it contained information on approximately 2,000 wells, located in the study area (1,600 km2). The conceptualisation of the hydrogeological basin, which is 978 km2 wide, was supported by a 3D geological model that interpolated 716 stratigraphic logs. The variability in hydraulic conductivity was determined using hundreds of pumping tests. Five surveys were performed to acquire hydro-geochemical data and spring flow-yield measurements; the isotope groundwater age was assessed and used for model validation. The mean annual volume exchanged by the hydrogeological basin was assessed equal to 106.93 106 m3. The numerical modelling permitted an assessment of the mean monthly yield of each spring outflow (surveyed or not), travel time, and main path flow.