Major construction work is nearing completion, eleven years after one of Europe’s largest man-made landslides destroyed infrastructure at the Mondercange landfill site.
Around one million cubic metres of soil slid down from the slag heap in Mondercange after an exceptionally wet winter had weakened the foundations of the landfill. While most of the visible damage has since been repaired, the legacy of industrial and domestic waste buried at the site is expected to continue posing challenges for generations.
Four hectares of land had collapsed, burying the road between Esch-sur-Alzette and Mondercange. Today, the western section of the landfill is nearly complete, and efforts are now focused on controlling water infiltration.
Mondercange mayor Jeannot Fürpass explained that significant progress has been made in recent years, adding that they can finally see light at the end of the tunnel. He said that the municipality, the State, ArcelorMittal, and the site operator Cloos have worked closely together to understand the causes of the collapse and to develop a long-term remediation plan. According to Fürpass, the investigations have confirmed that water played a decisive role in the disaster.
As Fürpass explained, groundwater and drainage systems are now at the heart of the reconstruction. He described how, during the extremely wet winter of 2014, the groundwater table rose sharply, infiltrating geological layers beneath the landfill and causing the slope to give way under pressure. To stabilise the site, engineers installed a 1.4-kilometre deep drainage network, buried two to four metres underground, to redirect groundwater in two directions, he said. Fürpass noted that an additional clay layer is being applied over the surface to form a mineral seal that prevents further infiltration and keeps the soil as dry as possible.
The eastern side of the site, however, remains more problematic because it partly contains toxic industrial waste. A project engineer explained that the landfill was originally used by the steel industry, which dumped various slags and metal residues, some of which are particularly hazardous. Work is now starting to seal this section, he said.
Another engineer outlined that this will involve a mineral barrier reinforced with a synthetic liner and an artificial waterproof cover to limit the environmental impact and control runoff water. The upper layers will then be covered with a drainage system designed to handle rainwater infiltration, she said.
At the foot of the hill, contaminated water from the landfill is treated through a lagoon filtration system, one of the engineers explained. He said that as the water passes through the lagoons, it is neutralised and its nitrogen content reduced through bacterial activity, resulting in much cleaner water being released into the nearby stream.
In the long term, the landfill will be fully stabilised through these sealing measures. Rainwater running off the slopes will be collected in a retention basin to prevent it from reaching the stream all at once. By 2028, the plateau is set to host a solar park capable of producing enough electricity for around 1,250 households.
The total cost of the remediation and redevelopment project amounts to €16.3 million. Despite these significant efforts, Mondercange cannot yet fully turn the page on its heavy industrial legacy. The site will continue to be closely monitored for decades to come, though current measures are expected to ensure stability for at least a hundred years.
