The Use of Multiple Environmental Tracers in Age Interpretation of the Mount Amba Aquifer, Kinshasa, Democratic Republic of Congo

The apparent tracer ages and mean residences time of recently recharged groundwater from the Mount Amba aquifer (Kinshasa, DR Congo) were evaluated using measurements of radiocarbon (14C), tritium (3H), sulphur hexafluoride (SF6), chlorofluorocarbons (CFCs: CFC-11, CFC-12, CFC-113), using tracer input functions suitable for the Southern Hemisphere. The apparent tracer age (assuming unmixed groundwater samples) is discussed and compared with different mixing models in age interpretation. Using a binary mixing model, a wide range of mixtures with young fraction ages of 0-30 years was found. Exponential mixing models indicated mean residence times from 12-42 years. In age interpretation, radiocarbon was used as a stable isotope tracer on the anthropogenic timescale (past 50 years) in this carbonate free aquifer. (author)