Groundwater age dating

These tests which were mainly performed in the early s, led to an increase of tritium in precipitation over the continents of the northern hemisphere from roughly 5 TU to levels of the order of TU. One TU Tritium Unit means a tritium to hydrogen ratio of 10 Whereas the addition of bomb tritium to the environment practically eliminated the use of natural tritium as a tracer, it offered a new tool, i. If the tritium delivery as a function of time can be reconstructed, this penetration process can be used for quantitative studies of water movement through identification of the bomb peak in certain ground water bodies.

Basics of 3H/3He dating

However, there are natural limits to this method because tritium decay and dispersion make it increasingly difficult to identify the bomb peak in groundwater. These problems can be overcome by using tritium in combination with its decay product 3 He 3 He trit as first suggested by Tolstykhin and Kamensky and experimentally confirmed by Torgersen et al. If both the tritium and 3 He trit concentrations are measured in TU, it can be calculated as. Uranium Disequilibrium Nickname: Confusing, Game Player Half-life: A little about me: U-disequilibrium is a bit mind-bending and requires a very thorough understanding the of the nuclear and geochemical processes at work in your sample location.

These bullets of helium break the crystal lattice of the minerals around the U atom allowing groundwater the get in. The groundwater then preferentially dissolves some of the U grand-daughter, U.

GROUNDWATER DATING

This means there is more U than U dissolved in the water by activity. This means you can correlate the ratio you measure to an age.

Will you put in the hard work? It is similar to 36Cl in that it requires an AMS to measure, and they are both halogens. This makes it a tracer of modern groundwater and allows it to constrain the age of water that is less than 80 million years old as well!

Estimates of Groundwater Age from Till and Carbonate Bedrock Hydrogeologic Units at Jefferson Provin

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You may use these HTML tags and attributes: Leave this field empty. Can you find a match? Matt Herod is a Ph. His research focuses on the geochemistry of iodine and the radioactive isotope iodine For example, some of the rain that falls on an area percolates trickles down through soil and rock until it reaches the water table.

Groundwater Speed Dating! Can you find a match?

Once this water reaches the water table, it moves though the aquifer. The time it takes to travel to a given location, known as the groundwater age, can vary from days to thousands of years. Hydrologists employ a variety of techniques to measure groundwater age. For relatively young groundwater, chlorofluorocarbons CFCs often are used.

CFCs are human-made compounds that are stable in the environment.


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Atmospheric CFC concentrations increased from the time of their development in the s until the s, and hydrologists now know how atmospheric CFC concentrations have changed over time. CFCs can be used to determine groundwater age because water that is in contact with the atmosphere picks up CFCs from the atmosphere. Thus, CFCs are incorporated in the water before it enters an aquifer.

Measuring Groundwater Ages in Years

Once water enters an aquifer, it becomes isolated from the atmosphere, and it carries a CFC signature a distinctive chemical composition as it travels through the aquifer. This signature reflects the atmospheric concentration when the water was at the surface.


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  7. By measuring the CFC concentration in groundwater, hydrologists know how long ago the water entered the aquifer. In the United States and other developed countries, CFCs are being phased out of use because they contribute to atmospheric ozone depletion.

    As a consequence, atmospheric CFC concentrations have begun to decrease.