Roşia Montană and Baia Mare: should they be compared?
Dr. Suzanne Lacasse and Kaare Höeg are technical experts at the Norwegian Geotechnical Institute (NGI).
The media, when discussing the Roşia Montană project, always mention the 2000 Baia Mare disaster in Romania. At times, the 1971 Certej disaster, also in Romania, is also mentioned.
While it is certainly relevant to recall these accidents, the media omit to mention the major differences in the design of the tailings dams that failed and the design of the Roşia Montană Tailings Management Facility (TMF). The earlier failures are extremely important and relevant for the planning at Roşia Montană, but mainly as lessons to learn to prevent such disasters occurring again.
In all aspects, the Roşia Montană project has learned lessons from the Baia Mare and Certej disasters and provided improved design. With respect to safety, the design of the Roşia Montană Tailings Management Facility belongs to an entirely different class of dams than the Baia Mare facility.
In terms of design, Roşia Montană follows the good practice for hydropower dams and compares well with the best large dams designed today. Reliability analyses performed by NGI show that the Roşia Montană TMF is less likely to breach than other tailings dams by a factor of 1,000, and that the possibility of a breach is much lower than that considered acceptable for large dams. Actually, the safety margin calculated for the Roşia Montană dam is much higher than that used today for the design of most engineered structures.
Compared to other hydropower dams and dams for containing mine tailings, and especially when comparing with the Baia Mare and the Certej tailings dams, the Roşia Montană dam has at least six (6) significant improvements:
- The 90-m high Starter dam is a very high-quality earth core rockfill dam with rockfill shoulders, both on the upstream and downstream sides of the core. The quality of the dam is planned to be as high as the highest quality hydropower dams in the world. The additional 90-m dam built above the Starter dam also uses a good quality rockfill for the downstream shoulder of the dam (not usually done for tailings dams).
- Among different types of embankment dams, a rockfill dam is the safest.
- The dam has gentle downstream slopes of 1:3 (gentler than normally used).
- The dam has the capacity (freeboard) to store at all times twice the volume of extremely severe precipitation and its associated flood waters (this is twice the allowance generally made in dam design).
- The spillway is designed to release excess water in a controlled manner, and there is a secondary dam to catch any additional release (added safety compared to other large dams).
- RMGC has designed a safety monitoring system to warn of any early signs of unexpected performance, and a preparedness program to remediate the effects of any indication of unexpected behaviour (not done for earlier dams).
In comparison, the Starter dam and the embankment of the Baia Mare tailings facility were built from the coarse portion of the tailings pumped to the site (but the hydrocyclones to do the separation did not work well). There was no emergency discharge of the waters. There was insufficient storage capacity and the balance between dam height and pond water level was not maintained. The design and the monitoring of the dam were “inappropriate”. There was no emergency preparedness plan. One of the contributors to the failure was severe, but not exceptional, weather (precipitation) conditions.
Again in comparison, the Starter dam of the Certej tailings dam was built out of manually compacted red clay coming from borrow pits from the vicinity. The main embankment dam was built from the coarse portions of the tailings. The embankment had a steeper slope than the Roşia Montană embankment. Lessons from the Certej failure include the importance of the geomorphologic conditions, the need for geotechnical studies at the site, the necessity for a stable dam with high freeboard and embankment with gentle slopes, and the necessity for supervision and visual inspection, instrumentation, and monitoring of the tailings facility. All of these “lessons learned” are implemented in the design of Roşia Montană Tailings Management Facility.
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