Environmental tracers age dating young groundwater
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.H), and other chemical and isotopic substances in ground water, can be used to trace the flow of young water (water recharged within the past 50 years) and to determine the time elapsed since recharge.
The sampling and analytical methods for the four techniques used to determine the age of ground water are briefly described below in table 1.
Hydrofluorocarbons and hydrochlorofluorocarbons (HFCs and HCFCs) are among them.
USGS scientists have recently developed a high-sensitivity technique to measure two of these compounds (HCFC-22 and HFC-134a) in groundwater and the unsaturated zone.
Shallow ground-water systems are commonly used for drinking water sources and they make up a large part of the baseflow in rivers and lakes.
However, shallow ground-water supplies are generally young (recently recharged) and, because there has been a wide variety of man-made pollutants produced in the 20th century, are more susceptible to contamination than deeper ground water.