Study warns of oil and pollutants beneath Blatten debris

An environmental study obtained by SRF estimates that about 150,000 litres of heating oil and fuel were located in the area of Blatten, the village buried by a mountain and glacier collapse in May 2025.

Cars, heating-oil tanks, machinery, batteries and cooling equipment were also buried beneath the debris. Oil stains soon appeared on the lake that formed behind the debris cone.

The study, commissioned by the canton of Valais, identifies mineral oil hydrocarbons as by far the greatest environmental risk. It remains unclear how much oil and fuel leaked during the collapse and how much is still contained in tanks or buried in the debris. The authors say that recovering all the pollutants would be disproportionate because their locations are not known precisely.

The oil stains show that some of the buried heating oil and fuel has already escaped. The authors warn that pollutants could enter the groundwater, although measurements taken so far have shown no abnormalities.

Because water can penetrate the debris relatively easily, monitoring of surface water and groundwater should continue and be expanded over the long term, the study says. The canton plans to carry out this monitoring throughout the Lötschental.

The study was based on questionnaires sent to Blatten residents, who were asked whether they had an oil tank and which other substances were stored in their buildings when the collapse occurred. A total of 220 questionnaires were completed, covering about 80 percent of the buried households and buildings. The survey also recorded engine and transmission oils, batteries, cooling equipment, paints, solvents, gas cylinders and ammunition.

The canton considers reconstruction feasible. “It would be disproportionate to say that it is not possible to build here again,” said Christine Genolet-Leubin, head of the Valais environmental office.

Updated hazard maps show where construction could generally resume, including parts of the debris covering the former village. How construction is carried out will be crucial, Genolet-Leubin said, including how deeply workers dig and how high they build up the ground. Authorities are also considering whether drainage systems will be needed because some substances could potentially be released into the air.

Geologist and contaminated-sites expert Walter Wildi, who analysed the study for SRF, said some oil tanks were damaged and leaking, while others could rust through over time. “Sooner or later, the oil will then enter surface water or possibly groundwater,” he said.

Environmental measures are already being incorporated into the reconstruction work. The first residents are expected to return to the new Blatten from 2029. Blatten Mayor Matthias Bellwald said the timetable could be met if the environmental work proceeded in parallel.