German criminal investigators have searched offices and production facilities of potash and salt producer K+S as well as the homes of senior managers, searching for clues to confirm suspicions of illegal waste dumping – in particular of salt residues –  between 1999 and 2007.

The Kassel, Germany-based company, which is currently fighting a hostile takeover from Canadian rival Potash Corp, has declined comment on the investigation.

Altogether, authorities in the two German states where the company is active are investigating 15 K+S managers, along with two employees of the state waste disposal agency in Thuringia, who they suspect helped the company obtain disposal permits.

In one case under investigation, K+S is suspected of illegally storing 9.5 million cbm of salt wastes in underground caverns near the town of Gerstungen. While the company can produce a permit for the storage, state authorities said the geological formations were not suitable and the disposal should never have been issued.

To relieve the burden on the Werra River, which for years has been burdened by salt mining in the former separate East and West German states – the mines straddle the former border – the company is in the process of building a 140-km salt disposal pipeline to pump waste into a bigger river. The pipeline is scheduled to be completed in 2021.

Since 1972, K+S has operated for the government of the state of Hesse near the town of Herfa-Neurode one of the world’s largest waste storage facilities for wastes more toxic than salt. The repository is thought so impermeable against groundwater contamination that it once was under consideration as a repository for Germany’s nuclear waste.