Hydrogeological characterization of the complex hydrogeological system of the Brescia metropolitan area (N Italy) in the framework of Water Safety Plan

The Water Safety Plan (WSP) is an integrated approach to ensuring drinking water quality, based on detailed risk assessment and management throughout the water supply chain. Mandated in Italy by Legislative Decree 18/2023, the WSP requires the identification of all processes affecting water quality, which for groundwater can be achieved by integrating hydrogeological, hydrodynamic, and hydrochemical data of the tapped aquifers. This study presents the hydrogeological characterization of the Brescia metropolitan area (N Italy) based on geological information, high-frequency water level measurements, and routine chemical monitoring data of 72 wells and 14 springs, provided by the water supplier A2A Ciclo Idrico SpA. By combining the results of a cluster analysis on major ions with the time series analysis of groundwater levels and the available hydrogeological cross-sections, 8 zones with different features were identified: 1) Central Val Trompia and 2) Nave valley, where recharge inputs mainly come from fractured bedrock and run-off; 3) Southern Val Trompia, with the same recharge processes as zones 1 and 2 but less vulnerable to anthropogenic impacts due to the local geology; 4) Northern Brescia, where the recharge comes mainly from the mountain karst system, the upgradient zones 2 and 3, and local infiltration, which determine a higher anthropic impact than northern areas; 5) Piedmont Area, showing intermediate conditions between mountain springs and plain area groundwater; 6) Western Plain Area, with different conditions from the rest of the plain due to differences in land use, recharge sources, and groundwater flow direction; 7) Central Plain Area, where the reduced water table depth and the recharge from upstream zones and local infiltrations determine the highest anthropic impact, and 8) Eastern Plain Area, where recharge is mainly due to excess irrigation water sourced from the Chiese River, with chemistry similar to zones at the mountain-plain interface.