Oskar Rischewski

The Grands sentiers led by Anne Bossé, invites you to explore the area on foot, by walking. This action is as much a manifesto as it is a tool for apprehending spaces, enabling us to adopt a posture at the scale of the body in movement. With a strong focus on architectural research on Nantes, the project aims to create a major metropolitan trail by the end of its fourth and final edition in 2024. More information is available in the dedicated Hypothèse booklet https://gdsentiers.hypotheses.org/which compiles the genesis and approach of each project developed, including the Parlement de Tougas but also Reconnecter le Boire de la Coudrouse, my final year project completed in this same studio.

What should be done with the 5 million tonnes of decomposing waste under the Tougas plateau, located west of the city of Nantes? The former landfill site, which opened in 1960 and closed in 1992, is about to make headlines again. After 30 years of post-operational monitoring, it has become clear that within five years, large quantities of leachate, highly polluted percolation water, are likely to spill into the Loire River. However, solutions already exist. These include decontaminating the site by treating the decomposing waste, which has already been done in the oldest part of the landfill. Another solution is to develop the wet meadows left fallow to collect runoff water, clean it up and allow it to infiltrate the soil. All of this is possible today, but it is not being done due to a lack of political will and public mobilisation. We need to push this debate into the public arena so that the implementation of solutions can be discussed.

Here are the issues behind the project to Parlement de Tougas, which then becomes a manifesto architecture intended not to be realised as it stands one day, but to fuel political debate and highlight this collective issue in space.

Located at the very heart of the Loire estuary's floodplain, the Tougas plain is part of the Loire meadows, a brackish tidal area grazed communally by local farmers. This alternation in water salinity and the maintenance of low vegetation allows for a profusion of habitats along the estuary. A large number of native species can be found here. These wetlands, rich in biodiversity, were gradually drained by humans at the turn of the 20th century to provide more dry land areas for the estuary and its commercial outlets.

Gradually, an illegal landfill site developed and was made official after the land was purchased by the municipality of Indre in 1960. Waste storage continued until the landfill site ceased operations in 1992, at which point it contained more than 5 million tonnes of waste. The easternmost part of the site was cleaned up and rehabilitated as a motocross track, and the plateau became the collection area for one of the metropolitan area's 11 waste collection centres.

These 700,000 m² of grassland now enclose the equivalent of around eight Bretagne towers within a floodplain criss-crossed by infrastructure that cuts through the continuity of the environment. This fragmentation is all the more advanced given that the Tougas plateau, an anthropogenic barrier par excellence, is nevertheless integrated into the ‘Coulée verte herblinoise’, a collection of grasslands, parks and wetlands brought together in the municipality of St-Herblain.

But the Tougas plateau is far from returning to its former state as grassland. Hidden beneath the ground are some 78 gas collection wells and 86 water pumps used to manage the putrefaction and decomposition of waste that is still present. These organic and artificial elements, which will remain present for several thousand years, continue to pollute in the form of landfill gas, a mixture of methane and carbon dioxide that is very prevalent at the beginning of decomposition, but above all in the form of leachate, water that becomes laden with solvents, pesticides, heavy metals, medicines and other soluble elements through percolation. If this water is not pumped out and treated quickly, it will seep through the soil and contaminate the water table, in this case the Loire aquifer. Leaks already exist and have been identified, but it is estimated that they will gradually increase as the geotextile tears.

The project of Parlement de Tougas proposes to raise the question of the future of the Tougas plateau by highlighting the chemical and political processes at work on the site. The architecture accompanies the runoff of leachate pumped up by the pumps, which is gradually phyto-purified before being released back into the environment. This gravity-fed runoff is complemented by a space for collective discussion of the future of Tougas in the form of an amphitheatre in the heart of the waste.

Designed as a cross-section of the plateau, the layout reveals successive layers of waste that bear witness to different eras, consumption patterns and methods of managing unwanted materials. The soil is held in place by a system of concrete posts that structure the space, embedded deep into the ground like the Berlin Wall. The whole structure is stabilised by tie rods anchored directly into the waste soil.

The Parlement de Tougas leads to a body of water created in the channel. This stagnant water allows oxygen-dependent bacteria to proliferate and complete the water treatment process. Finally, at the tip of the device, the water is discharged into the surface water network, joining the nearby water table or estuary.