This week's PISA episode dives into the Moselle river, exploring the treasures that were discovered by previous generations, explaining the river's importance to the shipping industry, as well as going underground inside the hidden Dolomite mines of Grevenmacher and Wasserbillig.

RTL Today has teamed up with PISA, the Luxembourgish science magazine, to reproduce their original videos in English for our site. Presenter Olivier Catani this week aims to find the gold coins that were once found in these waters, and speaks to a miner that worked in the Dolomite mines for seven years.

This video is part of the PISA series for RTL Today. Watch all English videos on RTL Play, or discover the wide range of subjects previously covered in Luxembourgish here (there are 13 seasons, mind you! We'll try and catch up...). Our previous episodes covered the history of the tramLuxembourg airport, explained how the coronavirus vaccine works, asked why traffic lights always seem to be red, investigated where our tap water comes from and looked at Luxembourg's railways since 1859.

Excavating resources from the Moselle...and finding gold

Over millions of years, the Moselle has built up large sand and gravel deposits. These different types of stone are essential materials in the construction sector, and thus excavations have led to the creation of several borrow pits in the last decades.

Jean-Pierre Hein has been involved in the sand business for half a century. He is the head of the last company in Luxembourg which is excavating sand and gravel from the ground. This material is deposited in large pits and separated, filtering out larger materials. This process uses about 288 m3 of water per hour - that is 120 times the amount used in the Coque swimming pool.

At the end, you are left with six different materials - from pure sand to round gravel and broken stones. All of them are used in the construction of cement floors, drainage, and concrete.

There were also times when workers stumbled upon hidden treasures. There was an occasional gold coin shining in the sand. How they ended up in the Moselle is not known, but they are thought to have belonged to a Roman centurion, minted in Trier. Some are now on display at the capital's Art & History Museum.

Usually, the Environment Agency asks companies to fill up the holes again after the resources have been extracted. Either with stones or soil, that is to say untreated material, so that the location may be repurposed as a field, vineyard, or meadow… There are thus no plans to add any new excavation lakes in the future. At least not at the current excavation sites.

Important shipping route

For about 36 kilometres, the Moselle acts as a natural border between Luxembourg and Germany.

However, the border does not run straight across the middle of the river. The border is the entire river. More of a border stripe, so to speak. This is called a "condominium", meaning the Moselle belongs to both countries. And both countries work together to determine who is allowed to do what on the river.

A ship is deployed whenever mud and stone deposits start to accumulate at the bottom of the Moselle. The water must be at least three meters deep at all times, otherwise fully loaded cargo ships might get stuck. This is why authorities from Germany and Luxembourg keep an eye on water levels, dig up residues and remove items that may block the riverbed.

On average, they pull out between five and ten objects per year from the water. The person who dumped them has to bear the costs of the operation, so process-tracing takes place.

Construction work for the route started in 1958. 53 years ago, the new transport route was formally inaugurated. At the beginning, it grants the French steel industry in particular a better connection to the international markets. The Moselle connects France through Luxembourg with the Rhine.

Unfortunately, the Moselle does not always flow this peacefully through the valley. The worst floods since the canalisation occurred in April 1983. In Remich, the Moselle's water levels rose over eight metres high. This meant that the water was four metres higher than the quays… In the decades that followed, the river's water levels regularly rose to six metres and above.

Read also: Archive footage shows Remich floods of 1957

The Dolomite Mines of Grevenmacher and Wasserbillig

The Moselle is also famous for its dry masonry. Much of it comes from the galleries that were operational between 1937 and 1985.

Dolomite is a calcium magnesium carbonate, an essential mineral, in particular for Luxembourg's steel industry. But the steel crisis was one of several reasons that led to a decrease in demand for raw dolomite. The work inside the mountain became increasingly less profitable.

They are almost eight metres high and penetrate hundreds of metres into the mountain. Grevenmacher's galleries spread over a surface area of almost nine football pitches. In Wasserbillig, meanwhile, there are two levels. Here, the surface area adds up to over eleven football pitches.

The Dolomite layer runs slightly skewed down into the mountain. Today, about a third of the mine is flooded. In the past, this water had to be pumped out on a regular basis. After all, people wanted to blow their way deeper into the mountain. Explosions would take place every evening towards the end of the shift, so that the dust could settle overnight.