Geochemical Markers as a Tool for the Characterization of a Multi-Layer Urban Aquifer: The Case Study of Como (Northern Italy)

The analysis of geochemical markers is a known valid tool to explore the water sources and
understand the main factors affecting natural water quality, which are known issues of interest in
environmental science. This study reports the application of geochemical markers to characterize
and understand the recharge areas of the multi-layer urban aquifer of Como city (northern Italy).
This area presents a perfect case study to test geochemical markers: The hydrogeological setting is
affected by a layered karst and fractured aquifer in bedrock, a phreatic aquifer hosted in Holocene
sediments and connected with a large freshwater body (Lake Como); the aquifers recharge areas and
the water geochemistry are unknown; the possible effect of the tectonic setting on water flow was
overlooked. In total, 37 water samples were collected including water from two stacked aquifers and
surface water to characterize hydrochemical features. Moreover, six sediment samples in the recent
palustrine deposits of the Como subsurface were collected from cores and analyzed to understand
the main geochemistry and mineralogy of the hosting material. The chemical analyses of water
allow to observe a remarkable difference between the shallow and deep aquifers of the study area,
highlighting different recharge areas, as well as a different permanence time in the aquifers. The

sediment geochemistry, moreover, confirms the differences in trace elements derived from sediment-
water interaction in the aquifers. Finally, an anomalous concentration of As in the Como deep aquifer

was observed, suggesting the need of more detailed analyses to understand the origin of this element
in water. This study confirms the potentials of geochemical markers to characterize main factors
affecting natural water quality, as well as a tool for the reconstruction of recharge areas.