How are lakes made

Neutralization of the post-mining lakes Hainer See, Störmthaler See and Zwenkauer See: questions and answers

The three post-mining lakes have been Hainer See, Störmthaler See and Zwenkau lake treated to counteract the existing acidification of the lakes. The most important questions about the current measure are answered here.

Why do the lakes acidify?

After the end of mining and the subsequent rise in groundwater, the substances created by the aeration of the subsoil and pyrite weathering, such as iron, sulfate and acid, enter the groundwater. The groundwater flowing into the post-mining lakes leads to the acidification of the lakes, i. H. Too low pH values ​​in the sea water. Long-term follow-up of the water quality is therefore necessary.

How does the neutralization work?

A water treatment ship is used, in which a mixture of seawater with a maximum of 3% lime content is produced on the ship and then brought under the surface of the lake. To do this, the ship sails across the entire lake area except for the designated prohibited areas. The limestone powder is stored on the ship. The ship is loaded at a loading point on the lake, which is in the non-public area.

The post-mining lakes are treated one after the other. The time and duration of ship operations depend on the respective pH value situation in the lakes. An assignment lasts 4 to 6 weeks. Depending on the development of the pH value, several missions per year per lake may be possible. The lanes, the amount of lime and their effects on the sea water quality are monitored and documented in parallel.

How much lime is brought into the lakes?

The annual entry of up to 6,650 tons of limestone powder is approved by water law. According to the current status, up to 2,250 tons of limestone powder are planned for the Störmthaler See, a further 3,000 tons for the Zwenkauer See and 1,400 tons for the Hainer See.

Does it harm the environment or humans?

The limestone powder used is harmless to both humans and the environment. It is non-irritating to the skin, non-irritating to the eyes and non-toxic. In a dissolved state, it is a natural and indispensable part of natural waters.

Can I swim and go boating in the lake while the calcification is taking place?

Yes, the lakes can still be used without restrictions. However, you should not swim through the limestone plume to avoid deposits on your skin and swimwear. Boat owners and swimmers should keep an appropriate distance from the water treatment vessel in order to avoid any danger to one another.

Are other lakes also affected?

Most of the Central German post-mining lakes already have good water quality and pH values ​​in the neutral range. In addition to the above-mentioned post-mining lakes, the Kahnsdorfer See and Bockwitzer See also tend to re-acidify due to their geological boundary conditions. According to the current status, no deployment is planned there.

What pH value do you want to achieve?

The target value for the post-mining lakes is a pH value of 6 - 8.