Présentations Colloques

Session 8.08: Mineral and Thermal water: an indicator of deep processes and source of economically valuable minerals
Parrone (orateur)
Linking geochemistry and aquifer mineralogy in a groundwater body in Central Italy
Several processes can affect the concentration of dissolved substances in groundwater- water-rock interaction, geothermal upwelling fluids, biological activity, residence time, human activities, etc. As long been recognized, the first two processes are often considered the main cause of the arsenic presence in volcanic or volcanic-sedimentary aquifers in Central Italy. **The study area is located North of Rome. During three campaigns (from 2012 to 2015) we collected groundwater samples from several private wells. The periodical monitoring of groundwater allowed us to investigate the annual water quality variation. The investigated aquifers are mainly bicarbonate-alkaline-earth type and show variable levels of potentially toxic elements such as As, F, V and U. Some parameters (PO43-, V and Al) show a decreasing trend from North to South, while others (As and F) showed an uneven distribution with no trend and localized peaks. In addition, 20 rock samples have been collected from outcrops, to identify the possible mineralogical source of As released in the studied aquifers. Solid and aqueous matrices have been studied, in order to evaluate any significant connections between chemical and mineralogical patterns. **The area is characterized by the presence of Pleistocene volcanites (mainly tuffs) which have been sampled and analyzed, so as to determine the total content of As and other metals. Results show As rock content in the range of 10.6 - 28.5 mg kg, with a mean value of 18.4 mg kg. Selective Sequential Extraction allowed us to discriminate the different solid fractions containing As and to better understand processes governing As mobility. Leaching tests provide an estimate of the release rates of arsenic and other elements under simulated real conditions. The study of the distribution of some elements in different geochemical spheres and the analysis of water-rock interaction processes, provided a comprehensive framework on the origin and evolution of geogenic contaminants in groundwater.