Investigation of groundwater flow with radiocarbon

An interesting potentiality of the radiocarbon dating of groundwater is the deduction of recharge rates of aquifers. The relationships between the age at a point in the water-body and the recharge depends on whether the aquifer is confined or unconfined. For an unconfined aquifer receiving recharge over the whole surface area a simple relationship is deduced. Such an aquifer can be characterized by its age at half-depth. Natural radiocarbon has been used to study flow patterns and flow-rates of subterranean water bodies in different regions in the Netherlands. The deep groundwater in the south-east region of the IJsselmeer presents a complicated situation caused by the inhomogeneity of the strata. Flow-rates are therefore not so readily deduced, but the different aquifers can be distinguished by using the isotopes 14C, 13C and 18O as natural tracers. In the province of Friesland the deep groundwater shows a more consistent picture with flow times of several thousand years corresponding to a quite acceptable flow-rate of around 10 m/yr. A much faster turnover time is observed in the unconfined fresh-water aquifer on the island of Schiermonnikoog. The hydrological parameters as deduced from 14C and tritium measurements compare reasonably well with expectation. (author)