Pit water management

Active mining has ended, but the pit water must still be pumped away. “Pit” is the miners’ traditional term for an underground mine. It originated during the era when the top layers of hard coal could be extracted from open-air pits. Pit water is rainwater that has seeped into the low-lying parts of a mine through cracks and crevices. 

In modern mines, some of which have been excavated to depths of 1,400 meters and more, rainwater naturally requires some time to reach the lowest levels. But it nonetheless seeps downward, slowly but surely, along rock strata and through fissures into the mine workings. These are the vertical shafts and horizontal galleries—that is, the roadways leading to the working faces—and all the other cavities that have been created underground by human beings.

When the pit water started to accumulate in these cavities during active mining operations, it posed certain risks—for example, it could have disabled sensitive electrical systems—and it threatened the miners’ safety. If no preventive measures had been taken, the pit water would have risen until coal extraction was no longer possible. That’s why during the era of active mining operations the pit water was already being constantly pumped out of the mine workings and up to the surface, then channelled into streams and rivers.

Of course the pit water is not drying up today simply because mining activities have been discontinued. If it were left alone, its level would slowly rise. As the underground water flows and its level rises, it dissolves sediments and minerals such as salts in the layers of rock. That’s why it must be prevented from connecting with the higher layers of rock that hold potable water. As a result, pumping off and regulating pit water at the former mining sites in the Ruhr region is a never-ending task—a perpetual obligation.

The level of engineering that is being marshalled in the Ruhr region to pump pit water to the surface and then channel it into nearby watercourses will probably not be necessary in the former hard coal mining locations in the Saarland and at Ibbenbüren. In these regions there is a possibility that one day the pit water will naturally flow directly into the Saar River or, in Ibbenbüren, into the Aa River—without any need for pumping. This solution, which would require no technical assistance, will probably be possible in both regions because of the characteristics of the local terrain and the location of the potable water reserves. However, before this natural outflow can be realized, the planners need to conduct extensive studies and comply with the relevant authorization processes in order to exclude all the conceivable risks.

Polder measures

Ground water purification