On the trail of salt water

An internal milestone has been reached, but the containment of the salt water flowing into the Asse II mine remains an unstable system. “Since the main collection point for inflowing salt water in the Asse mine became increasingly dry in 2024 and finally dried up completely, the search for water has been like a game of cat and mouse,” says Iris Graffunder, Chair of the Management Board of the Bundesgesellschaft für Endlagerung (BGE). Since then, experts from the BGE and miners have been searching for the salt water at various locations in the mine. Their aim is to collect the solution again before it penetrates deeper into the mine. Until now, it has been possible to intercept the solution above the main emplacement level containing the radioactive waste, but this does not provide a stable basis for retrieval.

A few days ago, the miners at Asse reached the southern end of excavation 3, above the old liner of the former main collection point at a depth of 658 metres. At that location, they came across a fissure and could hear a rushing sound. A few days later, during a camera inspection of the fissure in question, they saw water running down the wall. According to the chemical composition analyses carried out to date, this is the salt water that was collected at the main collection point for many years. The BGE now wants to get even closer to the fissure and aims to stabilise the collection of the solution again. Ideally, it would resume collection of the water at the main collection point via a new route.

Since 1988, salt water from the overburden has been entering the Asse II salt mine, which is now over 100 years old, via the southern flank. From 1996 to 2024, most of the solution was collected at the main collection point at a depth of 658 metres and then pumped above ground. Most recently, the volumes of influent solution there were around 12 cubic metres per day. At the beginning of 2024, salt water ceased to arrive on the liner at the main collection point. As a result, a few weeks later, the quantities collected at a depth of 725 metres increased. Since then, BGE experts have been able to pump out large quantities of salt water several times at Asse through boreholes above the 725-metre level. Whenever this was successful, smaller volumes of salt water arrived at a depth of 725 metres accordingly.

However, the salt water inflow has changed course several times. For example, miners have drilled several exploratory boreholes beneath the liner of the main collection point at a depth of 658 metres. In one of these boreholes, designated 9.19, they were able to pump out large quantities of salt water over several weeks in autumn 2025. Meanwhile, the influx has shifted to a borehole further east that is designated 9.25. There, too, the miners have observed that the influx is moving further eastwards. The two boreholes are now to be widened so that the water can be collected more stably.

At the same time, the miners have been carefully working their way upwards above the containment liner of excavation 3 over a period of several months. They have carefully removed the gravel that stabilises the chamber, steadily putting new support pillars in place to secure the ceiling. In recent days, the miners have reached the southern end of this excavation. Pumping the solution out of the fissure at the edge of the excavation has not been very successful due to the limited scope for movement. The BGE experts are currently examining several options so that the solution can be collected more stably again.