Application of environmental isotope to assess the renewability of groundwater of continental intercalaire aquifer of Sokoto Basin in Northwestern Nigeria

The southeast sector of Iullemmeden Basin is located in Nigeria and referred to as the Sokoto Basin. The aquifer system of Sokoto Basin is multilayered with Continental Intercalaire (CI) aquifer also known as Gundumi-Illo Formation at the bottom, overlain by the Rima Group, Sokoto Group and Continental Terminal (Gwandu Formation). This study is aimed at determining the validity of the statement that the Continental Intercalaire of the basin receives no recharge, through application of environmental isotopes of water molecules (3H, 2H, and 18O) and characteristics deuterium excess (d-excess). The isotope result of oxygen-18 (δ18O) content ranges between −7.72‰ and 3.69‰, and deuterium (δ2H) content from −51‰ to 9.42‰. These results indicates presence of three categories of water, the waters depleted slightly in isotope signature, the moderately depleted waters and waters highly depleted in δ18O and δ2H. These results suggests that the waters depleted slightly in isotope signature may be evaporated waters, while moderately depleted values of 18O and 2H of water content from the Continental Intercalaire designates the modern waters and waters highly depleted in isotope signature may be regarded as paleowaters. The tritium (3H) value recorded falls within the range of 0.5-4 TU represents a mixture of pre-1952 and post-1952 water origin. It is thus concluded from the results that Continental Intercalaire aquifer of Sokoto Basin receives modern water as recharge.