New research suggests ancient underground water sources long believed to be shielded from modern-day contaminants may not be as safe as previously thought.
The study, led by University of Calgary hydrogeologist Scott Jasechko, involved delving into data collected from 6,000 groundwater wells around the world.
The paper was published Monday in the journal Nature Geoscience.
The research yielded two interesting findings – up to 85 per cent of the fresh, unfrozen water in the upper kilometre of the earth's crust is more than 12,000 years old and it's possible for ancient and recent water sources to mingle deep underground.
"The implication of that finding is that, unfortunately, even deep wells are vulnerable to modern land uses," said Jasechko.
The scientists got clues from what might seem an unlikely source – hydrogen bomb tests from the 1950s and 1960s.
The tests released a specific radioactive hydrogen isotope into the environment called tritium, which has been useful in dating water samples. Trace levels of tritium – too low to pose any danger – were found in deep groundwater wells, demonstrating there is a way for old and new water to mix.
"Its presence alone indicates that some of the water in the well is recent rain and snow," said Jasechko. "And the fact that we find that at deep depths implies that even deep wells are vulnerable to modern-era contaminants."
Grant Ferguson, an associate professor in geological engineering at the University of Saskatchewan, said he was taken aback by how widespread the potential for contamination was.
"We know that there's a mechanism for water to get from the surface to these deep water supplies. They're not as protected. The barrier's not there like we thought it was," said Ferguson, who contributed to the research.
"It makes us question some of the working assumptions we've had for groundwater protection."
Billions of people around the world rely on groundwater stored beneath the earth's surface in pockets within soil and rock.
"Groundwater is a precious resource and it already supplies about one-third of the water we use as humans on this planet for growing food, for drinking, for industry," said Jasechko.
"We should consider, not only the amount of water we have on the planet, but also its quality and susceptibility to contamination.
"We need to protect it and conserve it for future generations."