Hoyerswerda Ground Water Lowering System:

Before closing the open lignite mining pits in the Lausitz area at the beginning of the 90th the ground water was held down over decades. Now the ground water level is rising again. Due to the rise of ground water the infrastructure of the city of Hoyerswerda is endangered to be damaged.

Three collector wells are the basic installation of a system to stabilize and control the ground water at a relevant level.

The Lowering system was constructed in three lots. In general the system consists of the following components:
- three collector wells (RCW) which are necessary for collecting and pumping the ground water
- a subterrestrial pipeline through the city of Hoyerswerda from the collector wells into a discharge trench ("Westrandgraben").
- and a number of monitoring wells which are used for controlling and operating the system automatically.

BHG Brechtel GmbH (former: PST Spezialtiefbau GmbH, comp. History of BHG) was responsible for the construction of the collector wells, with its entire installations (rising pipes, fittings, measurement facilities and eletrical installations) and the construction of the monitoring wells.

The caissons were sunk to a depth of approx. 25 m (ca. 82 ft) and have an inner diameter of 2,80 m each. They were constructed as "dry caissons". Each of the laterals is connected to the installed piping system. Therefore the ground water is pumped without any contact to the air through the piping system and pipelines from the collector wells to the "Westrandgraben", the artificially built discharge trench.

Due to the high content of iron in the ground water it is neccesary to avoid the precipitation of iron hydroxide in the piping system before discharge into the "Westrandgraben". Imediatelly after air contact, the iron in the ground water will precipitate. The sedimentation of iron whould be a risk to the efficient fuction of the ground water lowering system.

In each shaft a ring pipe is installed and connects all laterals with the pumps. The pumps are integrated in special pump chambers. Gate valves can seperate sections of the ring pipes. This way service works can be done during the normal operation of the other part of the ring pipe.

In each of the underground well operating rooms a switchgear is managing and operating the entire collector well equipment. In regular operation all three collector wells, all installations of the pipeline system and all monitoring wells are connected with a main computer system. This computer system manages the ground water lowering system depending on hydrological conditions. There is also the possibility to operate and manage a single collector well by its own switchgear.

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