Petrol spill linked to Aargau drinking-water contamination

A petrol spill at a motorway service station in Würenlos, Aargau, is likely responsible for petrol odours and taste in drinking water in the Limmat Valley, Swiss public broadcaster SRF reported. The incident occurred on September 3, 2025, but the petrol additive ETBE reached the groundwater only months later.

An investigation by Aargau’s Department of the Environment found that a pipe connected to an underground tank at the Shell station was not properly tightened. Petrol filled the shaft around the tank and then overflowed above ground through the shaft cover.

Emergency crews contained the spill in a collection basin and pumped it out. At the time, officials did not expect the petrol to seep into the ground, said Jürg Kürsteiner, head of the department’s emergency response service. When residents later reported that their drinking water smelled and tasted of petrol, the connection to the Würenlos incident was immediately suspected.

The groundwater level beneath the service station lies about 30 metres below ground. Rain gradually carried the petrol through the gravelly soil towards the groundwater. The unusually long delay may have been linked to the dry summer, which lowered the groundwater level and slowed the process.

The affected substance is ETBE, an anti-knock additive mixed into petrol. It can be detected by smell or taste in drinking water even at low concentrations. The municipality of Würenlos and the canton of Aargau said the water remained safe, suitable for consumption and fully usable, including for food production.

ETBE stands for ethyl tert-butyl ether. It is an organic chemical compound with an ether-like smell and taste. The additive replaced toxic lead in petrol and prevents the fuel mixture from igniting too early or uncontrollably in an engine. Switzerland’s limit for ETBE in drinking water is 5 micrograms per litre, according to the federal government’s website.

The contamination affects the groundwater flow in the Aargau Limmat Valley between Würenlos and Baden, although not all municipalities in the valley are affected. Officials described the spread across several municipalities and the presence of ETBE in drinking water as unusual.

Boiling the water removes the taste, but not the ETBE itself. The canton said removing the additive from groundwater would require extensive technical measures and could not be done quickly.

Cantonal experts and a geological laboratory do not expect the contamination to increase further. Because its full extent has not yet been established, the affected municipalities are taking frequent drinking-water samples under a monitoring plan.

It also remains unclear whether the incident will have criminal-law consequences. Investigations will determine whether misconduct led to the petrol spill.