Origin of the shallow groundwater system in the southern Voltaian Sedimentary Basin of Ghana: an isotopic approach

Abstract

The development and management of groundwater resources require an ability to understand and identify the recharge source to the groundwater system. Stable and radioactive isotope data have been used to investigate the source of recharge and the age of the shallow groundwater system within the southern Voltaian Sedimentary Basin (SVSB) of Ghana as part of an on going groundwater development project. The tritium concentrations in the groundwater samples are very low and range from less than 1–7.2T.U., while measured 14C content ranges from 43 to 108% modern carbon. The tritium concentration of rainfall ranges from less than 1–4T.U. The δ18O values of groundwater samples range from −4.2 to −2.6‰ while the δD values range from −21 to −10‰. Stable isotopic data of the groundwater samples lie either on or close to the global meteoric water line (GMWL) on the δD–δ18O plot and indicate that the shallow groundwater in the area is derived from meteoric water that has undergone no significant degree of kinetic evaporation during recharge. No indication of paleo recharge can be inferred from the 18O and 2H composition of the groundwater. Current tritium concentration in the groundwater is generally low, however, it proved useful in the qualitative identification of modern recharge. Radiocarbon-deduced ages range from about 3200±350years B.P. to modern and indicate young recharge to the shallow groundwater system.