Despite the aquifers in the Milan metropolitan area are a valuable groundwater resource for a large population (1,336,364 inhabitants in the Milan Municipality; 3,195,629 in the metropolitan area, data at November 2014) and a highly industrialized area, a hydro-geochemical characterization is still missing. In this study, we perform a hydrochemical analysis of the groundwater in the Milan metropolitan area through concentration maps, probability plots and concentration versus depth plots for some major ions (Ca2+, Na+, Cl-, SiO2), trace elements (As, Fe, Mn) and for two common contaminants (NO3- and SO42-) usually deriving from a mixture of point, multipoint and diffuse sources such as leaky sewers, coal gasification work, landfill leachate, septic effluent, house building and recreational areas. In order to attain this characterization, we built a complete and reliable geodatabase concerning the physical and chemical characteristics of the groundwater, starting from multiple different datasets. This database (covering the period 1983-2014) has been explored by classical and multivariate statistical analyses to provide relationships among the more influential lithological, hydrogeological and hydrochemical variables associated to the presence of specific elements and contaminants. The interaction between the phreatic aquifer and the semi-confined/confined aquifer has been also analysed.
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