The raw salt that is extracted from underground saline deposits and processed into chemical fertilizer contains varying concentrations of a number of minerals. The Hattorf and Wintershall potash plants in the regional state of Hesse alone produce approximately 10 million tons of waste material and 11 million cubic meters of process water annually that must be disposed of. The potash plants on the Werra river in Hesse and Thuringia, as well as the monitoring stations used for the Werra/Ulster measuring program, are shown on the map.
The Dorndorf and Merkers potash plants were closed in 1991 and 1993 respectively owing to financial difficulties.
In 1992 an administrative agreement was concluded between the federal government and regional-state governments regarding the funding of a desalination program for the potash plants on the Werra in Thuringia, where ultimately only the Unterbreizbach facility remained in operation. The agreement called for the following measures to be taken:

Weekly homogenization of the salt effluent in stacked basins

Annual homogenization of the effluent by injecting and channeling salt effluent into porous underground rock

Depositing solid residues (for the most part sodium chloride) underground

The reduction of salt input was additionally monitored by a programme to preserve evidence.

By the end of 1998, the new system had brought about a substantial reduction and homogenization of salt concentrations at the Gerstungen monitoring station.

Stacked basins at Merkers

Hattorf potash plant in Hesse