Tritium-hydrologic research: Some results of the U.S. Geological Survey Research Program

In general tritium is of limited usefulness as a tool in hydrologic studies because the tritium content of ground water, as a result of radioactive decay, becomes too low to be detectable after about 50 years. Nevertheless, a unique study was made of the hydrologic cycle of small stream basins in Wisconsin and New Jersey on the basis of measurements relative to the peak of tritium fallout in the spring of 1958. The continental and the coastal basins received approximately the same tritium fallout. Approximately 30 percent went into ground-water storage, the remainder being exported as runoff and evapotranspiration. The mean residence time for ground-water recharge for the two basins was 45 and 30 days, respectively.