Poor construction and management of dams can cause devastating toxic spills from mining waste

During the last six years there has been an average of two major tailing dam accidents every year, according to Tailings Dams: Risk of Dangerous Occurrences – Lessons Learned from Practical Experiences by the United Nation’s Environment Programme (UNEP) and the International Commission on Large Dams (ICOLD). The study of 221 case studies of incidents, has revealed that the main causes were a general lack of understanding of safety controls, a lack of power over the water balance, and a lack of control over construction. There were also a few accidents caused by unpredictable events or by unexpected climatic conditions including earthquakes.

Whereas traditional embankment dams for profitably storing water for drinking or hydroelectricity are prestigious structures, tailings dams are often designed for minimum cost – due to the reduction in the market values of minerals, often built to one height originally, but then raised further on subsequent occasions to suit circumstances. Problems include trouble with foundations – with insufficient investigations, slope instability and lack of erosion control.

Most of the responsibility for the safety of tailings dams lies with the owners and operators, says the report. In order to reduce risks, the design, construction and operation of dams should include:

• detailed site investigations by experienced geologists and geotechnical engineers, including in situ and laboratory testing of foundation materials to determine their properties;
• the use of state of the art design procedures;
• expert construction supervision and inspection;
• laboratory testing;
• routine monitoring;
• safety evaluation;
• dam break studies;
• contingency plans; and
• periodic safety audits.

Regulatory authorities should also be more concerned about the safety of tailings dams, says the report. However, the UNEP and ICOLD are not simply calling for tougher regulation, but a review of the structure of regulation in order to assess its effectiveness. In some cases this may mean more effective implementation of exiting regulation, or further training of regulators.

The issue of regulation will not be pushed by legislation alone, says the UNEP. Financiers and insurers are also now becoming increasingly concerned with the risks and financial consequences of tailings accidents. Recently some companies have gone into receivership as a direct result of the costs of an accident, including interrupted production, clean-up costs, re-engineering and reconstruction costs and legal proceedings. Shareholder and employee concern over the image of companies is also driving better practices.