Hydrogeological backgrounds: Speaking to a senior geologist

To gain more insight into the subsurface situation in the Buna area, we spoke to a geologist working and teaching at Martin-Luther-University Halle-Wittenberg. Specialized in hydrogeology and groundwater modeling, he has worked on the environmental remediation of sites contaminated by the chemical industry, namely the former industrial sites of Bitterfeld-Wolfen, which are also part of the German Chemical Triangle. Asked about Buna, he led us to the Beesen waterworks in the first place.

First of all, however, we spoke with him about the geological situation in the Buna area. In the fluvial structures predominating the area, groundwater flows within a layer of gravel (see green areas in Figure 20). This gravel layer has a thickness of 3-5 m and is a very good waterconductor. It is covered by alluvial clay representing the surface layer of 1-5 m thickness, which is typical for floodplains. Underneath the gravel lies the lower-Triassic mottled sandstone (also referred to as bunter) that has a fissured structure. In an area between the Saale River and the Laucha creek, right where the Buna Werke are situated (see light green area in Figure 20), the fluvial bedrock recedes, and the sandstone reaches to the surface (usually still covered by a layer of soil).

This sandstone is crucial to the hydrogeology of the area in multiple ways. On one hand, it represents the confining bed of the aquifer, being less permeable than the gravel on top and channeling groundwater flow through its fissures with relatively high flow rates. On the other hand, it is not completely impermeable and tends to absorb substances carried in the groundwater. The geologist pointed out that different chemical substances have different pathways within soil and groundwater: While organic compounds (e.g. halogenated hydrocarbons) float in water and are usually deposited in the alluvial clay surface, other substances, as chlorinated hydrocarbons (CHC), are heavier than water and accumulate in the sandstone layer, where they can hardly be removed.

After the conversation we understood more clearly how groundwater flows from the Buna plot to the surrounding rivers and lakes (see also Stop 3 & 4) and how it carries the substances gathered underneath the chemical plant to different layers of the soil and into the alluvial plains. Our interlocutor also called our attention to the waterworks, with their long and eventful history, right across the Saale River. Accordingly, it was only a logical consequence of the ongoing pollution in the groundwater that the Beesen waterworks were eventually shut down.

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