Active underground hazardous-waste repository at Heringen (Werra), operating since 1972 in the disused workings of a former potash mine, functioning as the world's largest and oldest underground facility of its kind.
The Schacht Herfa (Neurode), located in the Herfa-Grund valley near Heringen (Werra) in the Landkreis Hersfeld-Rotenburg in Hessen, forms part of the Werra-Fulda potash mining region. The Doppelschachtanlage Herfa-Neurode was developed from 1910, with both shafts sunk between 1911 and 1913 in the Herfa valley by the Gewerkschaft Hattorf. Schacht Herfa reached 767 metres and Schacht Neurode 731 metres.
Production of potash salts from the Werra-Formation began in 1913 and was transported by works railway to the Wintershall processing plant. The loss of Germany's potash export monopoly after the First World War caused production to cease in 1920. Following the National Socialist seizure of power, the Reichswehr commandeered the installation in 1936 and converted the underground workings into a Munitionsanstalt (MUNA), a concealed munitions storage and production facility.
In 1943 the Bibliothek des Reichspatentamtes was also stored underground. After the United States Army liberated the camp at Hera in April 1945, the winding cages were dropped into the shafts and the headframes blown up. Following munitions clearance, completed by the end of 1948, the mine was consolidated into the enlarged Kaligrube Wintershall from 1967.
The hoisting shafts Herfa and Neurode were formally decommissioned in 1970. In 1972 the world's first and largest underground hazardous-waste repository was established in the disused workings. The Untertagedeponie Herfa-Neurode (UTD), operated by the K+S group, receives more than 20 categories of non-radioactive hazardous waste at depths of 700–800 metres and holds more than 3.5 million tonnes of material as of 2025.
The potash deposits beneath the Herfa-Grund valley were identified by systematic drilling from 1910. The Gewerkschaft Hattorf was awarded the extraction licences for the field and sank two shafts in the narrow valley of the Herfa stream between 1911 and 1913. Schacht Herfa reached a depth of 767 metres; Schacht Neurode reached 731 metres. After completion in 1913, potash salts extracted from the Werra-Formation — Zechstein evaporites deposited more than 250 million years ago — were hoisted to the surface and transported by a dedicated works railway to the Wintershall processing plant at Heringen for refining. The Kali-Syndikat quota arrangements were complex and financially precarious; after only seven years of production the loss of Germany's potash export monopoly following the First World War caused the installation to be shut down in 1920 under the Stillegungsverordnung (closure ordinance).
By the mid-1930s, the two shafts, their surface buildings, and the extensive dry underground voids represented a significant unused asset in an otherwise difficult political economy. The NS regime's need for concealed munitions storage — difficult to verify under the terms of the Versailles Treaty — made abandoned mine workings attractive. The Reichswehr took over the Herfa-Neurode installation in summer 1936 and converted it into a Munitionsanstalt (MUNA), a munitions depot and production facility. A forced-labour camp (Lager Hera) was established at the surface site to supply the workforce; witnesses describe strict supervision, long working hours, and poor conditions. A railway branch with connections to the Muna complex, the Leichtmetallfabrik at Heringen, and the Kaliwerk Wintershall served the installation. In 1943, the collection of the Bibliothek des Reichspatentamtes was stored in the underground galleries; the Wehrgeologenstellen library was also sheltered there. In April 1945 the United States Army advanced into the Werra valley, liberated the Lager Hera detainees, and immediately rendered the surface infrastructure inoperable: the winding cages were dropped to the shaft bottoms and the headframes were demolished by explosive charge. A train of munitions at Heringen station was also destroyed. The question of how to deal with the underground munitions stock occupied the occupying forces for a year; options including flooding and full demolition of the mine were considered. The decision was finally taken to restore the hoisting infrastructure and clear the stockpile; this work was completed by the end of 1948. The barracks of the former Lager Hera were not demolished at this point and served until the mid-1950s as a reception camp for Heimatvertriebene (displaced persons).
In 1967 the Schachtanlage Herfa-Neurode was formally integrated into the expanded Kaligrube Wintershall, which now technically and organisationally united the four shafts in the Herfa-Heringen area: alongside the 767-metre Herfa and 731-metre Neurode, the Grimberg (531 metres, sunk 1900–1902 at Heringen station) and the Heringen shaft (472 metres, sunk 1907–1911) formed the ensemble. By 1971, a new Zentralförderschacht at the Grimberg shaft made the Herfa shaft the sole remaining means of personnel transport. Both the Herfa and Neurode shafts ceased all production hoisting in 1970 when the enlarged Schacht Grimberg rendered them redundant.
The decommissioning of the Herfa-Neurode workings coincided with growing pressure in West Germany to find permanent disposal solutions for non-radioactive hazardous industrial waste. The geology of the disused Werra-Formation salt workings — seated at 700–800 metres depth, overlain by approximately 100 metres of impermeable clay and a further 400 metres of Buntsandstein, and isolated from the biosphere — was evaluated as an ideal multi-barrier containment system. The first operating licence for a Untertage-Deponie (UTD) was granted by the Hessian state government and the world's first underground hazardous-waste repository was officially opened on 21 June 1972. Initial authorisation was granted for a restricted range of chemical-toxin waste from BASF at Ludwigshafen as the exclusive customer; these restrictions were progressively relaxed as demand from other industrial generators grew rapidly. The usable area of the UTD extends over twelve square kilometres, with deposition rooms ranging from 700 to 800 metres depth. Accepted material falls into 20 defined hazard categories including dioxin- and furan-bearing wastes, mercury-containing waste, cyanides, and arsenic; radioactive, explosive, self-igniting, and liquid materials are excluded. By 2025 more than 3.5 million tonnes of hazardous materials have been deposited. The Untertagedeponie Herfa-Neurode is operated by K+S Entsorgung GmbH, part of the K+S group, and employs approximately 70 staff.