Multitracing and multisampling in hydrological studies

A fair number of natural tracers may now be applied to complement hydrological observations in groundwater studies. These include the various dissolved ions, the stable hydrogen and oxygen isotopes, natural and man-made tritium and carbon-14, radiogenic radium, helium and argon, and the dissolved atmospheric noble gases. Each tracer provides specific information and all of them together answer questions such as the number of water components that mix in a water system, quality of water, location of recharge intake, age of water, source of dissolved salts, thermal history, extent of aquifers, and vertical successions of phreatic and confined waters. Groundwater systems are complicated in the three space dimensions and vary in time. Hence, sampling of many water sources in a studied area is highly informative and so are repeated seasonal samplings in single water sources, sampling during pumping tests and sampling at different depths in a drill. The various tracers provide complementary information and models based on one tracer may be checked by the others. The application of the various tracers serves to check hydrological models and to modify them. (author)