To counteract the ongoing salinization of coastal aquifers, which poses a significant environmental and socioeconomic challenge to local communities, it is necessary to first understand the origin and mechanisms of this phenomenon. This study investigates the origins of salinity in the Volturno River lowland in Southern Italy and reveals that the primary source in the area is paleo-seawater entrapped within sediments that were subject to evapoconcentration processes. By systematically collecting sediment samples at variable depths and locations and extracting porewaters, a comprehensive understanding of the interplay between freshwater and saline water was gained, including complex patterns of vertical stratification of groundwater salinity. The study highlights the limitations of traditional methods that rely on salinity monitoring via integral depth sampling, particularly in capturing the vertical redox and salinity gradients characteristics of layered aquifer/aquitard systems. On the contrary, environmental tracers, like chloride and bromide, provide valuable insights into the sources of groundwater salinity, distinguishing between current seawater intrusion and other causes, such as paleo-seawater and return flow from drained agricultural land. Results suggest that the majority of salinity does not originate from modern seawater intrusion or recent evaporation. Instead, it can be attributed to paleo-seawater affected by evapoconcentration processes. This study has broader implications for the sustainable management of coastal aquifers and the safeguarding of freshwater resources. While our findings are specific to the Volturno River coastal area, the methodologies and insights here presented can be reproduced in every coastal region facing similar salinity challenges.

Groundwater budgets and fluxes are affected by human activities and climate change. Numerical models are cost-effective tools to investigate the different components of the hydrologic cycle. In this study, a groundwater flow model of the unconfined aquifers of the Campania region (Italy) has been developed and calibrated in Processing Modflow 11, resulting in an accurate assessment of groundwater fluxes and their trends over fifteen years (2000–2015). The model was implemented using a high-resolution grid to capture small hydrogeological features such as wells and rivers and informed by time variable datasets used as boundary conditions (i.e., river and sea levels, aquifer recharge, evapotranspiration, and discharge from adjacent systems). Good calibration and validation performances were achieved for piezometric heads (R² = 0.958). A set of scenarios was developed using constant boundary conditions (i.e., constant sea-level BC, uniform extinction depth BC), and the outputs were compared, quantitively assessing differences in groundwater fluxes. Simulations pointed out that using time series to inform boundary conditions in the model does not always result in a significant change in the computed fluxes. Overall, non-uniform extinction depth was the most influential condition, while both rivers and sea level conditions barely affected groundwater budgets. In addition, results highlighted the need for an accurate estimation of spatiotemporal variations of both recharge and evapotranspiration, due to their strong seasonal variability and their massive contribution to the hydrogeological cycle. Finally, a marked increase of evapotranspiration fluxes controlled by interannual variability of precipitation and atmospheric temperatures has been quantified over the modelled period.

In shallow alluvial aquifers characterized by coarse sediments, the evapotranspiration rates from groundwater are often not accounted for due to their low capillarity. Nevertheless, this assumption can lead to errors in the hydrogeological balance estimation. To quantify such impacts, a numerical flow model using MODFLOW was set up for the Tronto river alluvial aquifer (Italy). Different estimates of evapotranspiration rates were retrieved from the online Moderate Resolution Imaging Spectroradiometer (MODIS) database and used as input values. The numerical model was calibrated against piezometric heads collected in two snapshots (mid-January 2007 and mid-June 2007) in monitoring wells distributed along the whole alluvial aquifer. The model performance was excellent, with all the statistical parameters indicating very good agreement between calculated and observed heads. The model validation was performed using baseflow data of the Tronto river compared with the calculated aquifer–river exchanges in both of the simulated periods. Then, a series of numerical scenarios indicated that, although the model performance did not vary appreciably regardless of whether it included evapotranspiration from groundwater, the aquifer–river exchanges were influenced significantly. This study showed that evapotranspiration from shallow groundwater accounts for up to 21% of the hydrogeological balance at the aquifer scale and that baseflow observations are pivotal in quantifying the evapotranspiration impact.

Low-permeability fractured rocks, which are the bedrock of many regions worldwide, show highly complex and varied drawdown-time trends when pumped due to their extreme heterogeneity and anisotropy. Understanding their behavior is essential for operational choices, such as using of wells for water supply. This study examines Miocene dacitic-andesitic rocks, comparing rock mass characteristics with pumping test results to provide useful insights for the sustainable management of wells and the long-term preservation of groundwater resources. To achieve this, comprehensive investigations, including analysis of rock mass fracturing, core main technical properties, groundwater level monitoring and nine single-well pumping tests, were conducted on a test site. Results show that the dacitic-andesitic aquifer is extremely heterogeneous at the scale relevant for well design and pumping assessment. The heterogeneous pumping responses observed are due to the continuity and spatial distribution of discontinuities, their dispersed orientation, the presence of discontinuous volcanic breccia and the intercalations of quartz veins, dikes or filled fractures within the rock mass. In this complex environment, the temporal evolution of drawdown and recovery is a more crucial indicator for sustainable planning pumping, than the hydrogeological parameters values derived from conventional pumping test interpretation. Consequently, the duration of pumping tests becomes a critical factor, as it allows the identification of successive flow regimes and provides insight into the scale-dependent transmissivity of the aquifer. This finding has direct implications for the management of highly heterogeneous volcanic and low-permeability fractured aquifer, allowing to accurately assess the sustainable yield and appropriate usage timing of wells.