Groundwater recharge areas of the Continental Intercalaire aquifer-hydrogeochemical and environmental isotopes: Southern Tunisia and Algeria

Abstract

The Continental Intercalaire (C.I.) aquifer is one of the two aquifer members that constitutes the North-Western Sahara Aquifer System (NWSAS) shared by Algeria, Tunisia and Libya extending over an area of more than one million km2. The Continental Intercalaire (C.I.) aquifer is one of the largest confined-to semi confined aquifers in the world, comparable in scale to the Nubian Sandstone Aquifer System (NSAS) shared by Egypt, Sudan, Libya, and Chad, as well as the Great Artesian Basin of Australia, and covers some 600,000 km2 with a potential reservoir thickness of between 120 and 1000 m. The aquifer is mostly unconfined, unlike the eastern part. Its depth increases from north to south and from west to east. It has a shape of a depression that disappears further south where it becomes confined. TDS increases southward along the recognized flow path (0.7 ≤ TDS ≤ 8.7 g/l). Major elements increase with the increase of TDS. The radiocarbon activities of the groundwater are very low, varying between 0.27 and 70.3% modern carbon. The confined part of the reservoir shows depleted stable isotopes data and low 14C content, reflecting the absence of modern water at the discharge zone. The combined evidence shows that the recharge coincides with cooler, humid periods during the Late Pleistocene, which existed across the whole of Saharan Africa.