Characterization of an onshore–offshore aquifer system in the Venetian Friulian Plain and north Adriatic Basin: a 3D modeling approach

Abstract Continental coastal aquifer systems are well-studied worldwide and are often characterized on the basis of extensive and diverse borehole datasets. However, while it is postulated that in some cases, these aquifers may extend offshore, their seaward reach remains widely unknown due to the frequently limited availability of data, particularly for subsurface sediments and their pore water salinity. This paper presents a valuable characterization of the onshore aquifers in the Venetian-Friulian Plain (northeastern Italy) and their offshore extension in the Northern Adriatic Shelf, within ~20 km from the coastline. Three-dimensional digital geological and stratigraphic modeling was used to investigate geometries of the layered artesian aquifer system hosted in the Middle to Late Pleistocene sedimentary succession. Near-coastal and offshore aquifers are found to have mainly formed during coastline migration driven by sea level changes and low-permeability layers, sealing these aquifers, result from fine alluvial sediments during sea level lowstands or fine marine sediments during highstands. This study suggests that Quaternary glacio-eustatic fluctuations are mainly responsible for the genesis of the layered aquifer system in the study area. Given the consistency of depositional processes active in the Northern Adriatic Basin since Middle-Pleistocene, and that coastal fresh groundwater extends hundreds of meters below the topographic surface, this study confirms that the Northern Adriatic Basin has significant potential to host widespread offshore freshened groundwater aquifers. This resource might represent an additional freshwater supply in the future.