Carbon-14 dating of groundwater

The expected age distribution in different types of aquifers is discussed and examples given. In 'secondary' aquifers remarkably uniform flow is observed over distances of several kilometres and average flow rates can be deduced, even where the strata are too heterogeneous to apply pumping tests. It is further shown that the apparent age of spring water emerging from an unconfined aquifer, as calculated from the 14C or tritium contents, can be used to calculate the average age of the water in the aquifer and thence the rate of recharge and storage capacity. Such apparent ages provide a means of directly comparing tritium and 14C data. The initial 14C content of groundwater is found to be (85 ± 5)% in both humid and arid climatic regions. The magnitude of a possible loss of 14C from the groundwater by isotope exchange with solid carbonate appears to be relatively small in practice and 14C ages are probably no more than 20 to 30% too high, even under unfavourable conditions. (author)