Predicting groundwater salinity changes in the coastal aquifer of Arborea (Central Western Sardinia)

Abstract

The area of Arborea, extending over roughly 70 km2, is located in the Northern Campidano plain (central-western Sardinia - Italy). The plain, that was formed in a tectonic trough of the Tertiary, is characterised by Quaternary deposits of fluvial, lacustrine, marine and eolian facies. The Quaternary formation is several hundred meters thick. The stratigraphic sequence, whose characteristics vary from one place to another, is generally represented by gravelly, sandy, silty and clayey deposits. The aquifer basin consists of two main units, a shallow phreatic aquifer (around ten meters thick) and a deeper semiconfined - confined unit, separated by a variable thickness aquitard. The system is recharged by rainfall, irrigation and by lateral inflow from the volcanic rock aquifers bordering the plain. Owing to inadequate water management policies, the Arborea coastal aquifer system has been contaminated by seawater intrusion as a result of overexploitation during the frequent droughts that affect Sardinia. Groundwater withdrawals have caused saltwater to encroach landward and upward toward the withdrawal points. Periodic monitoring, carried out for several years by the Department of Land Engineering at the University of Cagliari showed a varying degree of salt water intrusion along the coast. High electrical conductivity values were found mostly in the deeper aquifer, as it is locally overexploited, whereas lower values were recorded in the shallow phreatic aquifer. Nevertheless, in the shallow aquifer the extension of contaminated areas is larger than in the deep aquifer. In this work an extensive quality assessment of the data was performed to characterise the area overlying the Arborea aquifer system. In this context we set up a geographical information system and applied an environmental model to study the migration of the contaminants. A preliminary model, elaborated with the CODESA 3D code, was implemented to simulate the impact of land management (different groundwater abstraction schemes, artificial recharge etc.) on the salt dispersion process.