A report published recently in Nature Geoscience revealed that pristine groundwater is vulnerable to modern-day pollution, and once contaminated, it could stay like that for as long as thousands of years.

Groundwater is usually found 820 feet under the Earth's surface. It is also called "fossil water" because it's believed to be 12,000 years old. Given that they are found in the deepest parts of the Earth, they are also believed to be pure. As such, it provides drinking and irrigation water for billions of people around the world today.

For the study, the researchers collected samples of groundwater. Results showed that traces of rain and snow mixed with tritium are present, indicating the presence of younger water. Tritium is a radioactive element found as a result of thermonuclear bomb testing during the 1950s.

As noted by Tech Times, the tritium contamination, although not at an alarming level, was seen at roughly 50 percent of the groundwater. The result has perplexed the researchers, citing that it is almost implausible to think that groundwater as old as 12,000 years could be polluted by modern-day contaminants.

The researchers write that although the mechanism is not clear, the study revealed that young groundwater may introduce other contaminants (i.e., fertilizers, pesticides, and industrial runoff from the Earth's surface) to ancient water through leaks and holes in wells, which people use to draw groundwater.

"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," University of Calgary hydro-geologist Scott Jasechko, lead author of the paper, in a statement"Our results imply that water quality in deep wells can be impacted by the land management decisions we make today."

The findings were presented at a European Geosciences Union meeting in Vienna, Austria.