This article describes the design and implementation of the permanent closure for the Water Mill Mine (Mina Engenho d'Água), a former gold mining operation in Minas Gerais (MG), Brazil. The government of MG urgently commissioned the project following the catastrophic failures of the Fundão and Brumadinho dams. It was critically driven by the mine's proximity – only 2 km downstream – to the primary water intake for the city of Belo Horizonte. A core element of the geotechnical investigation was piezocone testing (cone penetration test with pore water pressure measurement (CPTU)) for a rigorous liquefaction assessment. The CPTU analysis confirmed that the tailings exhibited dilative/non-liquefiable behaviour, ensuring stability against static flow failure. The final closure solution was a multi-barrier design focused on long-term physical stability and environmental protection. Key measures included water mitigation (the installation and operation of a temporary water treatment plant to safely process and discharge contaminated water from the lower reservoir), encapsulation (geomembrane encapsulation of the tailings within the reservoirs to prevent rainwater infiltration and leaching and stability (the implementation of a comprehensive surface drainage system and geotechnical stability analyses, confirming proper safety factors against failure). The implementation of these measures successfully ensured the safety and sustainability of the site.
Ortigao et al. (Fri,) studied this question.