Tritium age dating groundwater
Tritium is produced naturally in the upper atmosphere by interaction of nitrogen, and, to a lesser extent, oxygen with cosmic rays.
After oxidation to HTO, it takes part in the natural water cycle.
This increased reliance on the groundwater in concert with the strict regulation on water quality has led to a need by water managers and regulators to understand: Characterization of mean groundwater age and recharge temperature through the use of noble gas techniques provides information that is relevant to answering these questions and that is not accessible through traditional hydrogeologic approaches.
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.
CFCs have been increasingly used in oceanic studies since the late 1970s as tracers of oceanic circulation, ventilation, and mixing processes.
CFCs also can be used to trace seepage from rivers into ground-water systems, provide diagnostic tools for detection and early warning of leakage from landfills and septic tanks, and to assess susceptibility of water-supply wells to contamination from near-surface sources.
During the past 50 years, human activities have released an array of chemical and isotopic substances to the atmosphere.
Prior to the late 1980s, however, there were no reliable means of dating ground water recharged during this time scale and, until recently, none of those methods were considered practical for use in establishing regional patterns.
In the early 1990s, USGS scientists (Busenberg and Plummer, 1992) developed a method to date ground water on the basis of chlorofluorocarbon (CFC) content of the water that is practical, cost-effective, and applicable to most shallow ground-water systems.
It is independent of the initial tritium concentration of the water sample which is one of the advantages of the method because it eliminates the necessity to establish the exact time- dependent tritium delivery to the aquifer.