By the occurrence of mountain water in the tunnel area, the water pressure to is reduced (especially at high rock overburden). During the construction of the Lötschberg Base tunnel measurements showed that already 1 meter behind the outbreak edge, the water pressure increase by 50 bar. This pressure difference, combined with the high content of CO2 in underground water, means that the dissolved carbon dioxide in the mountain water escapes. Due to the reduction of the dissolved CO2 the calcium deposits are formed.

This gas exchange depends on the difference between the CO2-content / pressure in the mountain water and the CO2-content/pressure in the surrounding air and not from the absolute pressure of the surrounding atmosphere.

It makes sense to keep the CO2-content/ pressure in the surrounding atmosphere as high as possible. It makes no sense to create a surrounding atmosphere at high air pressure, which contains no CO2 because the gas exchange depends only on the same gas units (in our case by CO2 molecules). So it makes sense, but it is not easy, to enrich the drainage system with CO2 gas. The easiest way to accomplish this, can be made with air-tight manhole covers, which ensure that over the time the CO2 content in the drainage system increases. But this system will only work optimally in tunnels with little overlap (up to a water pressure of 3 bar). Using a conventional siphon system the possibilities for building up gas pressure in a drainage system are limited.
Higher CO2 partial pressures can not be influenced – because the gas surplus of CO2 will escape anyway (despite and over the siphon in the drainage system).