Hydrochemical characteristics and flow of the Nubian Aquifer System in Tazerbo Wellfield, SE Libya

The desert of eastern Libya forms one of the most arid regions of the Sahara. Libya suffers from a shortage in water resources due to its arid climate. On the other hand, Libya has large resources of good-quality groundwater distributed in six basin systems beneath the Sahara. In order to deal with the shortage of water in most coastal cities, the Libyan government established the Great Man-Made River Project to transport millions of cubic meters of water a day from desert wellfields to the coastal cities, where over 80% of the population lives. In this paper, a hydrogeochemical study is presented for the Nubian Sandstone Aquifer in Tazerbo Wellfield, SE Libya, based on chemical analyses and physical parameters for 108 wells. Samples were collected from 108 borewells of the Nubian Aquifer (Akakus Formation) from depth range between 280 m in the north and 500 m in the south. This study is the first hydrochemical investigation in Tazerbo and also in the whole Sahara, which introduces the importance of considering the end members and the synsedimentary influence for the interpretation of the groundwater hydrochemistry. The results of the analyses indicate soft to moderately hard, lowly mineralized, slightly alkaline groundwater, with Mg²⁺ as the main cation and HCO₃ ⁻ as the main anion. The major hydrogeochemical processes that affect the quality of water in sediments of the Nubian system at Tazerbo have been identified; the water type is mostly fresh MgHCO_3, while NaHCO₃ and KHCO₃ are also found for some wells. These water types indicate that groundwater chemistry is changed by cation exchange reactions during flushing of the aquifer by freshwater from the south.