INSIDE GeoLaB - Everything flows!

Christoph Schüth is a professor of hydrogeology at the Institute of Applied Geosciences at TU Darmstadt. One of his areas of expertise is groundwater protection. Since November 2025, he has been investigating the water resources of the Tromm for GeoLaB as part of a large-scale hydrogeological monitoring programme. 

How should one picture the investigation of the water bodies around the Tromm?

Groundwater protection is a key priority for me as a hydrogeologist, and also for GeoLaB. Furthermore, the water authorities have strict requirements, which we will, of course, adhere to rigorously. To this end, we are documenting the current status of both the quantity and quality of water in the Tromm area. We call this hydrogeological monitoring, and it includes, amongst other things, water balances in the most important catchment areas. We have currently set up a weather station, four rain gauges, six soil moisture monitoring stations and four discharge monitoring stations. In addition, water samples are taken monthly from wells, springs and surface waters at a total of 35 points and analysed in detail. This wealth of data is needed to document the current situation as accurately as possible. This enables any changes to be identified during the GeoLaB construction and operational phases, and measures to be taken. This is a crucial aspect of risk management.

What happens to the data?

Data is automatically collected from the various measuring devices on site, such as water levels and the electrical conductivity of the water. This also includes soil moisture and weather data such as air temperatures and rainfall levels. This data is stored by the probes and sensors – depending on the programming, this can be at intervals of seconds, minutes or hours. We then regularly retrieve it on site. There is also a second method, whereby the data is transmitted directly to our computers via the mobile phone network. Added to this are the results of the water sample analyses carried out at TU Darmstadt and in external laboratories. All the data serves to provide as accurate a picture as possible of the water resources on the Tromm.
 

What’s the situation on the Tromm – is everything flowing?

The volume of water crucial to the water supply flows from the slopes down into the valleys close to the surface. This occurs mainly in the upper, weathered areas of the granite. ‘Vergrust’ means that the granite weathers in a ‘wool sack’ pattern, that is, into irregularly shaped pieces. You can see what this looks like, for example, in the nearby Lautertal ‘Felsenmeer’. On the Tromm, we observe how this near-surface area reacts following rainfall. There are many springs on the slopes there, which fill up very quickly when it has rained. However, most of them dry up again quickly because the water drains away near the surface. This means that we probably do not find any significant circulation of rainwater there. From this, we conclude that the water does not flow down into the unweathered, deeper parts of the granite, or only to a minimal extent.

Which substances do you analyse in the water?

As part of our monitoring programme, we analyse the chemical composition of the groundwater. We measure the pH value, dissolved salts and minerals, which provide information about water quality and natural processes in the subsurface. Trace organic substances such as pesticides, pharmaceuticals or fuel components provide information about the extent of human influence. We also analyse trace elements, the organic carbon content and stable water isotopes (natural variants of water molecules with slightly different masses). These provide clues as to the water’s origin and flow paths. All the measurements help us to detect changes in the groundwater at an early stage and to monitor its development. 

How long will the monitoring programme run in total?

We began analysing existing data in autumn 2024 and started setting up the monitoring network and carrying out monitoring last year, in November 2025. We will continue this until at least October 2027. As soon as the location for the GeoLaB tunnel entrance has been finalised, monitoring in this area will be significantly expanded to ensure the best possible surveillance. This will, of course, also continue during the construction phase and whilst the underground laboratory is in operation. This is absolutely crucial, as we compare the data obtained with the measurements taken before construction began. This enables us to determine whether there have been any changes or whether everything remains as it was at the start of the monitoring programme. 

How does the Tromm region benefit from the monitoring?

We work closely with the local water suppliers and have agreed in writing in advance that we will share data with one another. The data we collect is made available to the water suppliers. We use the data provided by the water suppliers to gain a better overall picture. So both sides benefit from this. Even when new groundwater monitoring points are installed as part of the construction work, this is, of course, always carried out in collaboration with the local water suppliers. Our investigations provide them with an overview of the water balances in the individual catchment areas. How much water is actually available – and what is its quality? These are crucial factors for the future planning of water management in the region. 

What role does the ‘digital twin’ play? 

Understanding the system and future scenarios are important – both in the GeoLaB project and for water suppliers’ planning. It is essential to be able to estimate how much water will be available in the future. This is one of the most important aspects for local water suppliers. To do this, we need as accurate an overview as possible of the current conditions. The so-called digital twin – a virtual representation of the Tromm region – can help with this.  And that is what we are working on in the GeoDT project: the digital twin visualises the research results in digital form and in a virtual environment. Data from our hydrogeological monitoring is also incorporated here. This enables computer simulations to be created to forecast the impacts of construction works carried out as part of the GeoLaB project. The models could also serve as a basis for other calculations, such as predictions of water availability under changing climatic conditions – a virtual glimpse into the future.