On April 25, 1998 the dam of the mining residual tank of a pyrite mine in Aznalcollar, Spain suffered a rupture, releasing sludge and contaminated wastewater. The wastewater entered the Guadiamar River, polluting the river with heavy metals such as cadmium, lead, zinc and copper. It affected an area of 4.634 hectares, contaminating 2.703 hectares with sludge and 1.931 with acidic water.
The river pollution caused cultivation lands and forests to be affected. Harvests were no longer fit for consumption, causing financial problems for farmers in the area. Major fish mortality occurred and birds died as a result of consumption of polluted fish. It took one whole month for the river water to recover to its original state.
After the wastewater flow had entered the river a major cleanup operation started, including the installation of walls to prevent further spreading of contaminants and the removal of contaminated sludge. The pH values of the soil were restored by liming and arsenic was removed by adding iron oxyhydroxides, causing a precipitation reaction.
Company technicians stated that the rupture of the residual tank was caused by a deep landslide, which provoked the movement of a certain section of the wall. Authorities also researched the cause of the disaster. Apparently the dam was a weak construction and warnings of possible breakthrough were neglected. The Canadian/ Swedish corporation Boliden was held responsible for the wastewater spill. The company was sentenced to financing the cleanup operation and paying compensation to victims.
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