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

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 1-7.2 T.U., while measured C-14 content ranges from 43 to 108% modern carbon. The tritium concentration of rainfall ranges from less than 1-4 T.U, The delta(18)O values of groundwater samples range from -4.2 to -2.6 parts per thousand while the delta D values range from -21 to - 10 parts per thousand. Stable isotopic data of the groundwater samples lie either on or close to the global meteoric water line (GMWL) on the delta D-delta(18)O 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 O-18 and H-2 composition of the groundwater. Current tritium concentration in the groundwater is generally low, however, it proved useful in the qualitative identification of modem recharge. Radiocarbon-deduced ages range from about 3200 +/- 350 years B.P. to modern and indicate young recharge to the shallow groundwater system. (C) 2000 Elsevier Science B.V. All rights reserved.