Combining piezometry, isotopes, and emerging contaminants to assess aquifer recharge operations: case studies of Korba and Kairouan sites (Northeast and Central Tunisia)

In many semi-arid and Mediterranean regions, scarce water resources face an ever-increasing demand for water. A possible response is to complement the natural groundwater recharge by infiltrating treated wastewater, but this addresses the question of the future of this water, in quantitative and qualitative terms. Two contrasting artificial recharge sites with treated wastewater were chosen at the centre and northeast of Tunisia. The study was focused on field measurements (water table level, total mineralisation) and groundwater sampling (stable isotopes of the water molecule, emerging contaminants). Data from 2020 were compared with historical records. A suspect-screening analysis of 137 organic compounds was also performed at the first site. The hydrodynamic survey and the total mineralisation of groundwater underline a common feature of the two sites: the strong heterogeneity of the hydrogeological information, especially disturbed by agricultural pumping. The positive piezometric effect of groundwater artificial recharge is not clearly, observed due to the combined effects of intense pumping and the relatively small recharge volume. A slight increase in groundwater salinity is observed at both sites. In the coastal area of Korba, the isotopic data show that the recharged area is less vulnerable to seawater intrusion compared to other parts of the coastal aquifer. Stable isotope analysis showed an evaporative water only at the site where the water is transferred over a long distance and spread over the ground surface. Emerging compounds, especially carbamazepine, provided a much finer definition of the recharge plumes. The results of the suspect screening and non-target analysis were consistent with the historical location of the sites and the relocation of the discharge point for the first site. Together, the results underlined the limitation of the classical tools of hydrogeology (hydrodynamics, major ions, stable isotopes) and the significant added value of integrating emerging compounds in the analysis.