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Fossil Groundwater, a Source of Drinking Water for Billions of People, Contaminated with Nuclear Radiation

Some of the world's deepest wells tap into underground aquifers that store water believed to be over 12,000 years old. Yet, while that fossil groundwater is stored deep below the Earth's surface, it is not immune to contamination by modern day practices, as previously assumed.

Groundwater is the term given to all forms of water that are stored below the surface of the Earth in spaces between soil particles and within fractures in underground rock formations. Groundwater provides an important source of water used for irrigation purposes, as well as drinking water serving billions of people globally.

A recent study conducted by Scott Jasechko, a hydro-geologist at the University of Calgary, together with a team of international researchers, which was recently published in the scientific journal Nature Geoscience, has revealed the presence of radioactive nuclear material in fossil water stored in deep wells.


For their study, the scientists dated groundwater samples collected from over 6,000 wells around the world. The researchers were able to determine how old the water was by measuring the radioactive carbon content in the samples. They learned that most of the groundwater stored below the Earth's surface (42-85% of all the freshwater held in soil and rock within a kilometer below the Earth's surface) consists of fossil groundwater resulting from precipitation that fell to Earth over 12,000 years ago.

Prior to this study, scientists believed that fossil groundwater was immune from modern contaminants. However, this study has shown that this is not the case.

"The unfortunate finding is that even though deep wells pump mostly fossil groundwater, many still contain some recent rain and snow melt, which is vulnerable to modern contamination," explains Jasechko. "Our results imply that water quality in deep wells can be impacted by the land management decisions we make today."

Jasechko explains that precipitation that fell to Earth since the 1950s contains traces of tritium — a radioactive material that is found around the globe due to testing of nuclear weapons. Shockingly, traces of radioactive tritium were found in waters within deep wells, indicating that recent rainwater and snow melt can potentially mix with the ancient groundwater stored deep underground, and in so doing has the potential to contaminate fossil water believed to be untainted and pure.

"Roughly half of the wells contained some fraction of recent groundwater less than 50 or 60 years old," Co-author James Kirchner, a Professor at of the Swiss Federal Institute of Technology in Zurich, who uses the analogy of grandkids visiting their grandparents to explain the consequences: "It is a bit like going to a giant old people's home and suddenly realizing there are lots of kids running around. That is great, except if the little kids have the flu!"

According to Jasechko, the results of this study have important ramifications on how humans should use groundwater stored deep below the Earth in future.

"The upshot is that when we use fossil groundwater we should consider water quality risk in addition to sustainable use," says Jasechko. "We may do well to develop land management plans that protect fossil groundwaters from pollutants so that these resources are available for future generations."

Journal Reference

Scott Jasechko, et al. Global aquifers dominated by fossil groundwaters but wells vulnerable to modern contamination. Nature Geoscience (25 April, 2017). DOI:10.1038/ngeo2943

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