A tailings dam at Los Frailes mine, 45km west of Seville in Spain, was breached on 25 April 1998. The dam failure resulted in 5M m3 of acidic water and solids being discharged from the tailings pond across 21,000ha of surrounding farm land, and into the nearby Rio Agrio — unconfirmed reports suggest that 6350kg of dead fish have been collected from lagoons in the area. The dam was ruptured along a 50m section, with initial inspections suggesting that the earth below the dam foundations had slipped, causing the instability.
Canadian-Swedish mining company Boliden, owners of the mine, reported that two days after the incident the ruptured dam had been sealed and the discharge stopped. Jim Borland, vice president of Boliden, said that a working group has been set up to co-ordinate cleaning up the spill, while independent Spanish and foreign consultants are trying to determine the cause of the incident. ‘The situation is currently under assessment,’ Borland explained, ‘and we do not know yet what caused it. Our primary concern is to clean up the spillage.’ Criticism has been directed at the company, claiming that it has taken too long to carry out remedial action at the dam — the clean-up operation began on 3 May. In reply, Anders Bülow, president of Boliden, said that while it was important to remove debris as soon as possible to prevent further damage to the surrounding environment, it was also necessary to determine the extent of the spill and the best response.
Bülow added that until now the company had been ‘a model with respect to environmental matters’ and as a consequence it was ‘very concerned’ about what had happened. Boliden is reported to be co-operating with government authorities, who are supervising the clean-up operations, and is also advancing an estimated US$6.5M to farmers whose harvests have been ruined by the discharge from the dam.
Spanish government ministers have expressed their support for rebuilding the tailings dam, or building a new dam as soon as possible. The government would like to see the mine re-opened promptly as the facility is reported to be important to the economic prosperity of the area. However, Borland commented that although the company is currently investigating alternatives to tailings dams, such as the new tailings paste technology (see IWP&DC, November 1997, pp30&31), he could not say at the present time whether the current dam would be rebuilt or replaced.
Asked if the incident had dented the company’s confidence in the integrity of tailings dams, Borland would not commit himself. ‘My confidence is not an issue,’ he said. ‘We are just working to clean up the spill and minimise the negative impacts of the incident.’ The ruptured dam has attracted a wide spectrum of media coverage, along with speculation that Boliden might have been in doubt about the stability of the structure. Borland admitted that studies had been carried out during the winter of 1995/6 to assess the stability of the dam and the extent of its seepage, but stated that these were carried out following heavy rainfall in the area.
‘The seepage study recommended that certain action should be taken and this was implemented,’ he said. ‘The stability report gave the dam a clean bill of health. The two studies also coincided with regular checks which are required to ensure that standards are maintained, as is necessitated by the permit for the mine,’ Borland added. He also reiterated the fact that no signs of instability were detected prior to the dam failure.