Contribution of isotopic indicators to the assessment of groundwater mixture between Continental Intercalaire and Djeffara Aquifers (South-Eastern Tunisia)

The Continental Intercalate and the Djeffara aquifers are the most important groundwater resources in Southern Tunisia. Previous hydrogeologic and isotopic studies (180, 2H, 3H, 14C) allow to define the main hydrodynamic and hydrochemical characteristics for each aquifer. The Continental Intercalaire aquifer, which has important water reserves contains very old groundwater with low 14C activities and very depleted values of stable isotopes (18O, 2H). This is why this aquifer is considered as fossil and contains non renewable resources. Compared to the Continental Intercalate aquifer, Djeffara aquifer has more scattered stable isotopes values which confirms that there are different, water origins. Near to the El Hamma faults, isotopic contents of Djeffara aquifer are very similar to the isotopic signature of the Continental Intercalate, indicating mixing flows between the two systems and showing that the recharge of Djeffara of Gabes is partially ensured by the discharge of the old water of the Continental Intercalate through faults. (author)