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The Aurul S.A. tailings dam failure (Baia Mare, Romania)

(last updated 8 Jan 2001)

The dam failure and its impacts

On January 30, 2000, a tailings dam failure at the Aurul S.A. plant in Baia Mare, Romania, resulted in the release of 100,000 m³ of cyanide-contaminated liquid into the Lapus stream, tributary of the Somes/Szamos, Tisza/Theiss, and Danube Rivers, killing tonnes of fish in these rivers and poisoning the drinking water of more than 2 million people in Hungary.

The failed Aurul tailings dam is part of an operation of retreatment of gold tailings from the old unlined Meda tailings pond, originally containing 4.43 million tonnes of solids, with a recoverable gold grade of 0.60 grams per tonne. Starting in May 1999, the tailings were pumped from the Meda pond to the Aurul S.A. processing plant, where sodium cyanide was added for recovery of residual gold. After gold and silver extraction, the remaining tailings contained total cyanide concentrations of 400 mg/Litre, with free cyanide concentrations of 120 mg/Litre. These tailings were pumped over a distance of 6.5 km to the new Aurul tailings pond, which is lined with a plastic membrane and covers some 93 hectares.

Aurul SA recommenced operation on June 13, 2000, upon obtaining government approval.

On July 11, 2000, the Hungarian Government lodged a $179 million compensation claim against Esmeralda Exploration.

The causes of the dam failure

The tailings dam failure resulted from an overflow of the ponding liquid, caused from heavy rain and melting snow. The dam crest was washed away over a length of 25 meters. (see also: Dam Failure from excessive water level rise)

The Aurul tailings dam was designed by Knight-Piésold . The embankments of this pond consist of small starter dams which, during the filling process, were sequentially raised from the coarse fraction of the tailings. The slimes fraction was deposited in the impoundment. At the time of the failure, there obviously was insufficient storage capacity in the impoundment for the precipitation occuring at that time. (for details, see p.10-15 of the UNEP/OCHA Assessment Mission Report and the annex with the Report of the Dam Team)

On Dec. 16, 2000, Tom Garvey, the head of an European Union task force investigating the spill said there is no doubt the mine was at fault and is responsible for the environmental disaster. "No doubt what ever it was a direct result of a hundred tonnes plus of cyanide going into the Pau, the Somas and the Tisza River and killing everything in its wake," he said.
The investigation concluded that the accident was caused by the inappropriately designed tailings dams, the inadequate monitoring of the construction and operation of those dams and by severe - though not exceptional - weather conditions. (Australian Broadcasting Corporation Dec. 16, 2000)

> download Report of the International Task Force for Assessing the Baia Mare Accident, Dec. 2000 (530k PDF)