On Monday, 14 September 2026, an incident occurred involving a heat pump at the heating plant of Wärmeverbund Leimental AG (operated by Primeo Energie), located near the Birsig wastewater treatment plant in Therwil. Ammonia was released.

Emergency services attended the site with a large response and brought the situation under control. There was no danger to the public. The heat supply remains secured. The affected heat pump will remain out of operation for the time being. The cause of the incident is being investigated.