Los Frailes mining disaster
Coordinates: 37 ° 31 ′ 0 ″ N , 6 ° 15 ′ 0 ″ W.
The dam of the sedimentation basin of the Los Frailes zinc and lead mine in Aznalcóllar near Seville in Andalusia ( Spain ) broke on April 25, 1998 .
When the 25 m high dam broke, 4 to 5, perhaps 7 million m³ of toxic spoil sludge from the Aznalcóllar mine ended up in the nearby Río Agrio, a tributary of the Río Guadiamar . The mud covered 4,000 hectares of arable land and threatened the Coto de Doñana National Park, a UNESCO World Heritage site . It was a great ecological disaster; There were no fatalities. For years, conservationists had pointed out the lack of safety in the facility.
The mine is owned by Boliden Ltd., a Swedish-Canadian company.
The time of the break could later be reconstructed as 1:00 a.m., because a power line failed at that time. At around 3:00 a.m., an electrician inspected the pipeline route and noticed cracks in the dam crest and little water in the basin, which meant that most of it had leaked before 3:00 a.m. A gauge at Sanlúcar la Mayor determined the maximum discharge at 3:30 a.m. The basin drain ceased at 8:00 a.m. The water level fell to normal by 6:00 p.m. The breach in the dam was finally 20 m wide. The dam had been moved up to 60 m.
The cause is a shear failure of a separating dam between two individual basins suspected, which then caused the break of the main dam. Weak points are said to have been discovered two years earlier in a geotechnical report.