Numerous expert reports, discussions and public debates were held following this fire to decide on the future of the site. In particular, due to the presence of the Alsace water table located 500 m above the repository, these expertises studied the impact of the waste currently stored in the event of a possible rise by the “syringe effect” of brine. which would have been polluted in contact with them.
Following this public consultation, the prefectural decree of March 23, 2017 authorized the unlimited containment of waste and imposed measures to guarantee a high level of protection of the water table in Alsace:
- more than 95% of mercury waste, which is the most polluting for groundwater, was removed from storage between 2015 and 2017;
- the decree imposes containment of the waste remaining at the bottom, according to the best international techniques;
- in addition to confinement, the decree imposes the implementation of additional measures (tunnel bypassing infiltration water, decompression sounding, etc.) to prevent any rise in polluted brine;
- Finally, the decree imposes monitoring of the water table and the upwelling of water.
A parliamentary mission on StocaMine, carried out in 2018, nonetheless underlined the potential interest of continuing to remove waste subject to two conditions:
- assess, with an additional study, the overall risk of additional waste destocking (excluding the burned block) in the light of the experience drawn from the partial destocking carried out between 2015 and 2017;
- ensure the existence of a waste restocking solution offering better guarantees than the StocaMine site in terms of environmental protection.
International and independent expertise has been coordinated by BRGM at the request of the State. She concluded that:
- the removal of waste, excluding the burned block, was still technically possible, although with increasing technical difficulties from 2025 given the convergence of the underground galleries;
- this additional destocking would nevertheless involve risks for operators and the environment;
- the impact of soluble waste, in the event of failure of the protective measures detailed above, would be very limited given the volume of contaminated brine likely to rise (less than 1m3 per year) compared to the total volume of the water table (35 billion m3). In addition, such a rise in brine, if it were to take place, would have no impact on the potability of the water table.
In order for all the scenarios to be assessed, a technical and economic feasibility study on the pursuit of additional destocking was carried out by the group of private consultants Antéa Group - Tractebel, independent of the State and of the MDPA company, which operates the site. This study concludes that:
- all the destocking scenarios studied expose workers to high occupational risks;
- the environmental benefit for the Alsace aquifer of additional destocking has not been demonstrated;
- the waste removed from storage cannot be recovered and must therefore be re-stored in other underground installations or surface storage facilities;
- the completion, as soon as possible, of the containment and ancillary work provided for by the prefectural decree remains essential to protect the Alsace water table in the long term.
However, to be carried out under optimal conditions guaranteeing their effectiveness, these containment operations and ancillary work must be undertaken as soon as possible given the convergence of the underground galleries which makes them increasingly difficult to access.
Anxious to learn about the situation on the ground, Barbara Pompili, Minister of Ecological Transition, went down into the mine on January 5, 2021 and was able to discuss with elected officials, associations and citizens during a public meeting to discuss the best solution to protect the Alsace water table and operators.
The Minister heard and shared the legitimate questions about the reversibility commitments made before the fire and the importance unanimously given to the protection of the Alsace water table.
The minister came to the conclusion that the conditions for additional destocking, set by the 2018 parliamentary mission, are not met. The potential advantages of additional waste removal have not been demonstrated and this would present significant risks for workers, while the achievement of containment in optimal conditions is essential to ensure the protection of the Alsace water table.
Under these conditions, the Minister of Ecological Transition decides to launch the realization of the containment of the site without additional destocking. In parallel with this decision, it decided to dedicate a financial envelope of 50 million euros under the leadership of ADEME to allow a protection plan for the Alsace aquifer over the next 5 years. Several former industrial sites located above the Alsace water table will thus be cleaned up (in particular the PCUK site in Wintzenheim where 750 tonnes of lindane are buried) in order to avoid its contamination by infiltration from the surface, which is the main source of groundwater pollution.