Mitigating groundwater storage depletion and seawater intrusion through treated wastewater reuse and aquifer recharge in a Mediterranean coastal aquifer

Prolonged droughts combined with intensive groundwater abstraction can lead to severe aquifer depletion and degradation of water quality, especially in coastal settings prone to seawater intrusion. We investigated groundwater storage depletion and salinization in the Marsala–Mazara del Vallo coastal aquifer, southwestern Sicily (Italy), during the recent drought period from January 2024 to May 2025, with a cumulate precipitation of approximately 600 mm, well below long-term average. Furthermore, we evaluated the impact of having in place two managed aquifer recharge schemes infiltrating tertiary treated wastewater during the winter time along with that of using the reclaimed water in the irrigation season.

A density-dependent groundwater flow and solute transport model was developed using the SEAWAT code, integrated within the FREEWAT-Q3 platform. The model couples groundwater flow with chloride transport to simulate seawater intrusion under transient pumping conditions. We calibrated the model using observed groundwater heads and electrical conductivity data (transformed in chloride concentrations). The implemented model includes meteoric recharge, river–aquifer interactions, coastal wetlands, and extensive groundwater abstractions for drinking water and irrigation purposes.

Results show reduced recharge and sustained pumping during drought significantly depleted groundwater storage, reverse hydraulic gradients, and enhance inland migration of saline water, particularly in low-lying sectors of the coastal aquifer. Measured electrical conductivity trends and simulated chloride distributions confirm progressive seawater encroachment, particularly along the coastline and in heavily pumped areas. Conjunctive simulation of tertiary  treated wastewater reuse for irrigation, substituting groundwater, and recharging the aquifer using such reclaimed water, when not used for irrigation, demonstrates non-conventional water resources may alleviate the impact of drought periods.

Overall, our simulation results underline the need for drought-adapted groundwater management strategies, including seasonal pumping regulation, use of non conventional waters, and continuous monitoring of groundwater levels and salinity.