Multi-isotopic regional-scale screening on drinking groundwater in Lombardy Region (Italy)

Groundwater is the main and safest source of water used for drinking purposes in many urban and rural communities worldwide. A deep knowledge of aquifer systems in terms of quality, vulnerability and renewability is fundamental to preserving groundwater resources. Thanks to contributions by different members of Water Alliance in synergy with Sapienza University, during November 2019 a multiisotopic regional scale analysis was carried out on groundwater tapped for drinking purposes in a wide area of the Lombardy Region. The study aimed to improve knowledge of recharge mechanisms, the groundwater's relative age, and the impact of human activities on groundwater quality. Each Water Alliance supplier selected some wells and springs drawing water from different aquifer groups and distributed from north to south, for a total of 121 samples. Groundwater stable isotope analyses were performed on all the monitoring points, while tritium, nitrogen isotopes (15N and 18O in nitrates), sulphate isotopes (34S and 18O) and 13C isotope in Dissolved Inorganic Carbon (DIC) were analysed in selected monitoring wells based on previous data and major ion concentration results. The results confirm the key role of a multi-isotopic approach in defining aquifer recharge processes, relative groundwater age and the origin of pollutants, offering a useful tool to highlight local issues which could be investigated in depth by each water supplier.