Residents of the village of Mitholz in the Bernese Alps may have to leave their homes for ten years due to a large-scale operation to clean up and secure an old ammunition depot containing 3,500 tonnes of ammunition and explosives, authorities have said.

Preparations for the operation will also last a decade, with costs expected to run to over a billion francs, Defence Minister Viola Amherd said on Tuesday in Mitholz.

The plans for clearance come after a report by the Federal Office for the Environmentexternal link concluded last year that the 3,500 tonnes of ammunition and explosives stored in the underground site posed a bigger danger than previously assumed.

The defence ministry says that never before has a former weapons stockpile been cleared under such difficult conditions.

For example, the ‘Dreispitz’ rock formation which covers the stockpile is unstable and can only be removed in layers; while a new road may also need to be built to ensure that the towns of Kandersteg and the municipality of Kandergrund remain connected.

Meanwhile, some 170 residents of the village may have to leave their homes to facilitate the clearance, but not until 2031 at the earliest, when the preparation work is completed.

A contingency plan of covering the whole area with rock and burying the ammunition remains an option, but is neither the preferred choice of authorities nor of residents, who do not wish to leave “a toxic gift for descendants”, as project manager Hanspeter Aellig said at a media conference on Tuesday.

The Mitholz site was the scene of a tragedy in 1947, when 7,000 tonnes of explosives in the underground depot, which consisted of six rooms under a mountain connected by a trans-alpine railway tunnel, exploded and killed nine people. 

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