In the atmosphere, these substances have mixed and spread worldwide.These atmospheric substances, such as tritium (H) in water vapor from detonation of nuclear bombs in the 1950s and early 1960s,and chlorofluorocarbons (CFCs) from refrigeration and other uses from the 1950s through the 1980s, dissolve in precipitation, become incorporated in the Earths hydrologic cycle, and can be found in ground water that has been recharged within the past 50 years.This system represents a capability for characterizing groundwater recharge conditions by dissolved gas analysis that is unmatched by any other laboratory. GNS provides a number of complementary age tracer methods to date water samples.Sampling for tracers The feasibility of using CFCs as tracers of recent recharge and indicators of ground-water age was first recognized in the 1970s (see Plummer and Busenberg, 1997 and references therein).CFCs have been increasingly used in oceanic studies since the late 1970s as tracers of oceanic circulation, ventilation, and mixing processes. Tritium is produced naturally in the upper atmosphere by interaction of nitrogen, and, to a lesser extent, oxygen with cosmic rays.
Water in rain, oceans, lakes, streams and glacial ice pick up these tracers through contact with the atmosphere.However, there are natural limits to this method because tritium decay and dispersion make it increasingly difficult to identify the bomb peak in groundwater.These problems can be overcome by using tritium in combination with its decay product He age formally calculated from equation (1) is an apparent age.LLNL has developed a noble gas mass spectrometry facility that houses a state-of-the-art water-gas separation manifold and mass spectrometry system designed specifically for high throughput of groundwater samples. scientists with cutting-edge expertise in the measurement and interpretation of noble gases and tritium in groundwater.The fully automated, computer-controlled manifold system allows analysis of the full suite of noble gases (3He/4He, He, Ne, Ar, Kr, and Xe concentrations), along with low level tritium for reporting of derived quantities that include tritium/helium-3 groundwater age, noble gas recharge temperature, and dissolved excess air concentration.