Polsum I

Polsum I is a disused mining site near Marl. It covers about 10 hectares that I bought from RAG.


Project profile

The most important information at a glance.


Polsum near Marl


approx. 10.5 ha


former mine

Depth of the shaft






Acquisition year


About the project

The site is ecologically interesting for two main reasons, among others:


1. The diversity of species and the variety of biotopes is decidedly limited, since nature is only slowly “reclaiming” the areas and the previous construction and sealing naturally precluded or hindered biotope developments. Targeted ecological enhancement is therefore quite possible, and, thanks to the unusual site conditions, the forest areas show some special features that the biologists are excited about. A new, post-fossil biotope type is emerging here, which gives us a picture of how areas develop after industrial use.


2. The material excavated from the sinking of the mineshaft was crushed and distributed across the site, which was raised several meters as a result. This upper soil layer consists of nutrient-poor rock (without humus) and can provide a home for such plants and animals as no longer find a habitat in the otherwise mostly over-fertilized open spaces of Germany.


Polsum I is thus well suited for the development of a nutrient-poor open landscape and the establishment of those species at home on rare barren soils. The forest edges and transitions should be able to support a diversity of life forms.

Project planning

Buildings and sealed areas such as the parking lot in the west have been demolished by RAG and excavated to a depth of 0.5 m below ground level.


Even this deconstruction is not done according to the classical methods, but is done as ecologically soundly as possible and with close consultation between RAG and me. The idea is to leave parts of the basement and foundations in place in order to reduce the amount of excavation work (which also consumes resources) and to slow down the process of topsoiling with nutrient-rich substrates. If possible, we do not want to completely backfill building foundations that are already full of rainwater, but only partially demolish them and develop them into wetland biotopes. Observations in two former transformer houses show that this can be promising: Water has collected here, and several amphibian species have actually settled between building remains and trash.


However, the exact seepage characteristics and potential of partial areas can only be accurately assessed during demolition. Therefore, biotope planning is also still in full swing.

Long-term approach

Since this project is long-term and there is hardly any specific experience available for such idiosyncratic brownfields, I am planning “organically” with my team of biologists. That means we will observe how nature reacts to measures and how it unfolds. In this way, we make nature the decisive architect. Only along natural development trends can we proceed ecologically and sustainably—especially in times of climate change, which brings with it unpredictability.


For the same reason, we are initially leaving the forested areas as untouched as possible. Depending on how these very distinctive early forest formations, shaped by industrial use, develop over the years, we will implement suitable enhancement measures if necessary.

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The ventilation systems of the former mine.

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Dirk Gratzel’s path to green zero.

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