Tritium 3 H, half-life of Tritium input to ground water has occurred in a series of spikes following periods of atmospheric testing of nuclear devices that began in and reached a maximum in Concentrations of 3 H in precipitation have decreased since the mids bomb peak, except for some small increases from French and Chinese tests in the late s. Radioactive decay of 3 H produces the noble gas helium-3 3 He.
Radiocarbon dating of groundwater is used in combination with the primary measurements of classical hydrological and chemical analyses. Radiocarbon dating will produce the best results when it involves multiple measurements or sequential sampling. The most useful data come from these comparisons and not from absolute ages. In the case of multiple measurements, the apparent ages of the groundwater taken from pumps that are at varying distances from the aquifer outcrop could be a means of verifying flow rate and also indicate situations of over-pumping.
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The age of groundwater is defined as the time that has elapsed since the water first entered the aquifer. For example, some of the rain that falls on an area percolates trickles down through soil and rock until it reaches the water table. Once this water reaches the water table, it moves though the aquifer.