Deep wells around the world that contain fossil groundwater that is thought to be over 12,000 years old have been found to contain signs of rainwater from present day – even at depths of over 250m.

This is according to new research from the University of Calgary, which has found that human activity is putting this pristine water at risk. Groundwater – either melted ice or rain – filters down through the layers of the earth to build up in subterranean aquifers, a process that can take millions of years, AFP reports.

This is then pumped to the surface for irrigation and drinking by deep wells, supplying approximately one-third of all water needs for people, including safe drinking water.

The researchers used the carbon signature of fossil H2O to differentiate it from younger groundwater, which has more radioactive carbon in it because of being more recently exposed to the atmosphere and shallow soil. The comparison revealed that a big share of fresh waters around the world are of fossil age but only a small share of global groundwater has been replenished over years or decades.

An assessment of the potential for contamination found that snowmelt and rain often mixed with reservoirs of fossil groundwater.

The conclusion was that “this observation questions the common perception that fossil groundwaters are largely immune to modern contamination”.

Co-author of the study Scott Jasechko went on to tell the news source: “Securing safe drinking water remains a key challenge for hundreds of millions of individuals around the globe.”

So how exactly does fossil groundwater become contaminated in the first place? Mining is one of the main ways this can happen, in spite of the safeguards that those engaging in such activities put in place. It’s also important to bear in mind that groundwater pollution and contamination takes place on a very different timescale to surface water because flow rates are variable and pollution can take years to appear in wells.

Sources of groundwater pollution include surface contamination when this water migrates by infiltration through the soil. Pollutants like oils, salts, fertilisers and more can find their way into the groundwater. Another source includes landfill and waste disposal – modern sites are typically designed to prevent runoff from filtering down into the groundwater but occasionally protective measures can fail and older sites do not have such protections in place.

Atmospheric contamination is also a concern in this regard, with pollutants that are released into the atmosphere eventually combing back to the earth thanks to precipitation. For example, sulphates and nitrates from power plants and factories can result in acid rain, which will then filter through the soil and acidify groundwater.

To help reduce groundwater contamination, make sure all waste is properly disposed of, minimise the use of chemicals where possible, store all fuels and chemicals properly, pump and inspect onsite septic systems every five years and ensure that land use regulations protect well fields and water supply aquifers, among other steps.

Do you need help with water purity testing? Get in touch with us at TESS today.