From the "preliminary study for a risk analysis of potential contaminated sites from mining and war" the following emerges about this location:
The lowest entrance to the Mehlbach tunnel system has been buried since April 30, 2016 at the latest. The burial was systematically created and the permanent watercourse emerging from the tunnel was temporarily channeled through a drain pipe inserted into the burial.
This may cause the water level inside the cave to rise.
The permanent air flow inside the tunnel is interrupted by the burial.
Reducing ventilation can lead to an increase in humidity inside the tunnel system, which could theoretically promote oxidation processes. Oxide formation in lead-containing rocks can lead, among other things, to the formation of lead (II,IV) oxide, commonly known as "lead menninge". A simultaneous increase in the water level inside the tunnels can lead to increased leaching of toxic substances and contamination of the downstream waters (Mehlbach, Bleidenbach).