Toxic waste in French mine threatens EU water supply

Millions of Europeans could face drinking water contamination due to toxic waste stored in an old mine in Alsace, France. Scientists fear that thousands of tonnes of hazardous substances, currently sealed in mining tunnels near Wittelsheim, could eventually leach into a vital aquifer. The facility, known as Stocamine, was once a potash mine serves as a storage site for chemical waste. According to a recent court ruling, the waste is allowed to stay there, causing a possible threat to the Upper Rhine aquifer.

Concerns about the safety of the storage site were highlighted in an extensive article in The Guardian, published in June. Scientists warn that the mine’s seals could eventually fail, allowing toxic materials, including mercury, arsenic, and cyanide, to leak into the groundwater. Environmental organisation Alsace Nature brought the issue before the European Court of Human Rights, arguing that the site posed a serious threat to public health. In June the court ruled, that the waste could remain underground, citing that deteriorated tunnel conditions made removal too dangerous.

Aquifer under threat

The aquifer lies just five metres below the surface, while the mine shafts extend 500 metres underground through layers of pink and white rock. Within the vast network of 125 kilometres of tunnels, an area roughly equivalent to seven football fields now holds the toxic waste. Some reports also suggest illegal waste may have been deposited. But geological movement in the area is causing the rock to shift. Temperatures of 30°C, combined with pressure from nearby mining operations, are leading to subsidence. The mine’s ceilings are sagging, and the walls are collapsing at a rate of two centimetres per year. Experts fear that some containers may already be unreachable.

The mine will be flooded eventually

Scientific models suggest that over the next three centuries, groundwater will slowly infiltrate the mine. While some researchers believe that sealing the tunnels with concrete can contain the threat or delay contamination, others argue that the only reliable solution is to remove the waste entirely. The French government has opted to fill the galleries with concrete and seal the shafts to make the facility watertight. These measures are intended to keep the waste underground permanently. Environmental groups, however, say this approach is reckless, especially given the unpredictable nature of the geology. Water quality in the Rhine is already under pressure, even without this new threat. In 2022 industrial pollution of the Rhine again to a new high following a trend of poor results for the 1,230-kilometre long waterway.

Remove the waste immediately

Subterranean environments are inherently unstable, and buried materials can resurface in unforeseen ways. While Stocamine is expected to flood gradually, the consequences of water interacting with waste remain uncertain. The Stocamine case has drawn the attention of hydrologists, geochemists, and geologists, who are trying to assess the long-term risks. Among them is Swiss geologist Marcos Buser, who began studying the site in 2010 as part of a government-appointed steering committee. His view remains unchanged: “The waste can and must be removed. It’s best to do it now and not leave these risks to future generations,” he said.

A moral issue

Buser argues that the practice of burying hazardous waste and assuming it will remain contained is fundamentally flawed. “The history of landfill disposal of toxic waste is a history of failures,” he says. Containment measures typically degrade within a few decades, after which clean-up becomes costly and complex. Stocamine, Buser stresses, is not just a technical challenge — it’s also a moral one. “We must change how we manage waste. Disposing of dangerous materials in the environment is short-sighted — it always comes back,” he warns. Instead, he advocates for a circular economy, where hazardous waste is avoided or neutralised rather than entombed. “We are simply passing this burden on to our children and grandchildren,” he concludes.