UNECE WORSHOP ON TDS, YEREVAN, November 2007 LOS FRAILES April 25, 1998 tailings dam failure of the Los Frailes lead-zinc mine at Aznalcóllar near Seville, Spain, released 4-5 million cubic meters of toxic tailings slurries and liquid into nearby Río Agrio, a tributary to Río Guadiamar.