How to protect deep groundwaters

New method allows forecast of quality development

Drilling rig with hardware of the new multi-level measuring point. © Ruhr-University Bochum
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Deep groundwaters that dangle up to thousands of feet below the surface are considered the largest and cleanest freshwater reserves in the world. That is why they are very popular, for example with beverage manufacturers. What it means for a deep groundwater reservoir to be tapped, is a question in which research has so far "fished in the mud". New facilities developed by geologists of the Ruhr-Universität Bochum (RUB) now finally allow quality measurements at different depths. This will not only allow scientists to draw conclusions about the future development of deep groundwaters, but also to specifically protect them.

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Groundwater near the surface is often polluted by human influence. Especially nitrate from the fertilizers of agriculture affects its quality. In addition, the reserves are often limited, so you dodge to deeper groundwater. They are usually in great depth for a very long time and are therefore very clean.

"By withdrawing water, however, the hydraulic flow regime can change, so that contaminated near-surface groundwater can penetrate more rapidly to these greater depths, " explains Wolfgang Leuchs of the State Office for Nature, Environment and Consumer Protection NRW. In addition, the entry of oxygen or nitrate can dissolve the mineral phases which are stable under the conditions at great depth and contribute to a further deterioration of the quality.

New methods bring insights into deep waters

Apart from the fact that, according to experts, deep groundwater should be used only in exceptional cases, it is therefore important to closely observe the effects of exploitation and to calculate the future quality of groundwater. For this purpose, hydro geologists of the RUB have developed a so-called multi-level technique, which determines different measurements at different depths and thus allows conclusions about the status of deep groundwaters. display

"So far, the sophisticated technology has been used in waterworks and mining operations to depths of about 70 meters. However, a project with Stadtwerke Willich made it necessary to build a multi-level measuring point down to a depth of approximately 170 meters, "says Professor Frank Wisotzky from the Department of Hydrogeology. Lignite mining also revealed findings on deep groundwater. Since the mining areas have to be dehydrated to the deepest soles, one inevitably comes in contact with deep groundwaters.

"With the extraction of groundwater from great depth, the exploration and observation program was extended at the same time, which has contributed to the compression of hydrogeological knowledge, " said Thomas Oswald of RWE-Power. Thus one gained knowledge about the independent hydraulics in great depth and the water temperatures. In the deep, they usually rise. Irregularities may indicate, for example, vertical movements of the water.

Targeted protection where necessary

With the new findings on the behavior of deep and near-surface groundwaters, the scientists can also develop targeted protective measures. In the Raesfeld area in NRW, for example, the deep water is mixed with young, near-surface water, which has increased nitrate contents as a result of agricultural inputs.

Three-part display length of the multi-level expansion before installation in the bore. Ruhr-University Bochum

"Since 1993, great efforts have been made in cooperation with local agriculture to reduce nitrate inputs, " explains geologist Angela Herzberg from the Rheinisch-Westf lische Wasserwerksgesellschaft (RWW ). In the Dorsten area, however, measurements have shown that such measures are not necessary. There, the water is due to special geological boundary conditions so long in the deep reservoirs on the way that no such contamination takes place.

(idw - Ruhr-University Bochum, 18.09.2007 - DLO)