USE OF TRITIUM IN HYDROLOGIC RESEARCH-PROBLEMS AND LIMITATIONS

Abstract

Abstract The use of tritium content to determine the age of ground water is commonly an uncertain undertaking because most ground water pumped from water-table wells, particularly uncased wells, is a mixture of water of different ages and differing tritium content. Age designation of such mixed waters is meaningless. A recent publication of the International Atomic Energy Agency states that the absence of tritium in ground water indicates an age greater than 50 years, which therefore excludes the possibility of full-scale utilization of the water. Presumably the authors deduce that no recharge is occurring in such an area. The publication further states that the presence of bomb-produced tritium in a ground-water body indicates recent recharge and the consequent feasibility of utilization. These misleading statements fail to take into account that all aquifers in humid to semi-arid environments contain post-bomb recharge just below the water table and that movement of water even in highly permeable aquifers is so slow that generally ground water that occurs more than about 30 meters below the water table and down gradient from the intake area is older than 50 years. Even in arid regions where present-day recharge and tritium content of ground water are negligible, large quantities of ground water are frequently available from storage. The use of the tritium content of water is not now, nor will it ever be, a substitute for detailed geologic and hydrologic investigations of aquifers by adequately trained hydrologists. At most it can be only a supplementary tool, useful principally to veritfy, quantify, or supplement conclusions reached by less spectacular but more meaningful geohydrologic studies.