Hydrogeological and structural controls on radon concentration in aquifers from alluvial areas: A case study of the Pordenonese plain (NE Italy)

This study aims to investigate the complex relationship between hydrogeological processes and tectonic structures which influence the spatial distribution of radon within alluvial aquifers in the Pordenonese Plain (PP). The results suggest that the source of dissolved 222Rn is primarily linked to the intrinsic radioactivity of plain's sediments. Seasonal fluctuations in radon concentrations, which are closely related to recharge inputs into aquifers, have been observed for shallower unconfined and semi-confined aquifers, (i.e., those responding rapidly to meteoric inputs), while no significant variations have been observed in the deeper confined aquifers. Meteoric recharge leads to a dilution effect, thereby reducing radon concentrations during periods of increased precipitation. The spatial distribution of dissolved 222Rn shows a correlation between anomalous concentrations and the seismogenic structures crossing the study area, i.e. the Polcenigo-Maniago Thrust Fault (PMTF), the Cansiglio Thrust Fault (CTF), and the Vigonovo Thrust Fault (VTF), suggesting that the fracture network likely plays an important role in favouring its migration. This work establishes the baseline for 222Rn concentrations in the sedimentary aquifers of the PP, while also illustrating the role of climatic factors in their variability. The findings provide valuable insights for future multidisciplinary monitoring efforts, enhancing the understanding of tectonic processes in the PP and contributing to the development of more effective seismic risk management strategies.