Waste sealed in underground mines

France has officially approved the permanent sealing of 42,000 tons of industrial waste buried 500 meters underground in Wittelsheim, Haut-Rhin, near an aquifer supplying drinking water to about two million people. The Administrative Court of Strasbourg validated the decision, which concludes a legal process spanning over thirty years.

Toxic substances stored for decades

The waste, consisting of substances such as arsenic, mercury, asbestos, chromium, and incineration residues, was stored in former potash mines since 1990. A fire in 2002 halted operations and exposed vulnerabilities in the containment system.

Concrete barriers chosen for containment

Authorities opted for confinement using concrete barriers and the backfilling of access shafts, citing the technical impossibility of safely removing all the waste. The court deemed this the only viable solution for long-term watertightness, although experts note that concrete is not an eternal material.

Degradation risks over time

A 2023 report warned of progressive degradation of gallery linings and highlighted that beyond 100 meters of depth, it becomes mathematically impossible to guarantee the durability of these structures. The decision to abandon further removal of waste in favor of burial was announced in January 2021, following a partial removal between 2015 and 2017.

Opposition to the final decision

This choice faced opposition from the European Collectivity of Alsace, Alsace Nature, and local residents, who argued that a safer solution could have been found with more time and resources. The process involved judicial challenges and work suspensions before the final court approval.

Long-term risks to water supply

Experts warn that the Rhine aquifer, which supplies drinking water to over seven million people across France, Germany, and Switzerland, may eventually be contaminated due to the lack of absolute watertightness guarantees. The long-term risk of pollutants migrating into the aquifer is considered inevitable by many technical experts, despite the sealing measures. This case highlights the limitations of current approaches to managing hazardous waste and the uncertainties of relying on artificial barriers to contain toxic materials indefinitely.