A Dam Break, Not Again!

[Walter L. Pohl]

Shaming all mining professions, last week a mud flow broke from a slimes dam near Ajka in western Hungary. The heavy liquid flooded the 1.5 km distant village Kolontár and two others downstream. Eight persons were killed and many suffered injury.

The dam received so-called red mud from an alumina factory at Ajka township. Red mud is the residue of bauxite processing. Run-of-mine bauxite is leached with NaOH. From the aluminate solution alumina Al2O3.xH2O is precipitated. After drying, the precipitate is mixed with natural or synthetic cryolite Na3AlF6, fluorite, LiCO3 and NaCl, and is reduced by electrolysis to metallic aluminium in an electric arc furnace.

Insoluble residue of leaching is alkaline (pH 8-13.5) “red mud” which contains mainly quartz, calcite, hematite and goethite. Often, the trace elements Sc, Ga, V, U, Th, REE, P and Ti are enriched. In some cases, Sc, V and Ga are extracted from red mud. Commonly, red mud is disposed in settling ponds but increasingly, the material is used in environmental technology (e.g. to combat acidity).

Numerous karst-type deposits in the Lake Balaton-Bakony area source the bauxite. This district is part of the large Alpidic (Meso- to Cenozoic) metallogenetic bauxite province which extends from the Provence (France) to Greece.

Dam breaks, landslides and mud flows are in most cases induced by exceptionally heavy rains. Dam failure by overflow or by piping is the most frequent cause for these accidents.

Hydrologic studies for licensing and environmental impact statements are often based on only one annual cycle. It is impossible, however, to predict extreme precipitation and flooding from one year’s data. Yet, extreme events are the common cause of dam breaks, landslides and mud flows. Clearly, error analysis of data is required and upper and lower bounds of all possible hydrologic conditions affecting a facility must be determined.

All this is well known, dam stability and flow nets can be sketched on the back of a used letter envelope. Observation may provide timely warning of incipient piping or overflow. SP geophysical surveys locate hidden flow in a leaky tailings dam by an effect that is termed “streaming potential”. Urgency measures how to help endangered people must be planned ahead. And so on, and so on.

Let us raise a call throughout the industry to comply with the minimum standards of dam safety – or else our social license to operate is ever more reduced.

Walter L. Pohl

[Andy Barnes]

I agree that dam failure is one of the most visual and devestating environmental impacts that can occur from a mining operation. However, industry best practice does ensure that suitable factors of safety are engineered to ensure dam safety.

I have done a simple web search that has pulled up several occurances of dam failures and I didnt realise there is an online tailings database:


I think the main problem is with older tailings dams that were constructed prior to modern safety practicies were introduced and also modern dams that are produced by companies who do not adhear to international best practice. Unfortunatly there is not a lot that can be done to change the latter.

I do agree that undertaking geophysical and geotechnical investigations on older dams would be extreamly beneficial.

Does anyone know if any governments have implemented such a regiem?

[magdageo]

There is one tailing dam in Poland, which is monitored, I think, in every possible way (geotechnical, geophysical, hydrogeological, hydrological). There's no governmental regulations for tailings dams monitoring yet, but they are on way.
This tailings website is very interesting - I didn't realise that there were so many tailings related accidents in last century ...

[Andy Barnes]

It suprised me too. I think the term 'Dam' is used very generously where tailings are concererned; until recently anyway.

What we need is a tailings engineer to give us the a summary of modern safety practices.

What I do nottice in designs I have seen recently is that spill ways and seepage collection systems are commonly employed to prevent overtopping and piping. But still most tailings dams are made from compacted earth. I think the costs would be far to prohibitory if different materials were to be used (such as concrete cores).

There seem to be limited tailings failures in the UK especially from metal mines. I assume that the reason for this is most mines didnt even have tailings dams? Discharge directly to water courses prior to any regulation.

[kzamzow]

Dave Chambers, a professional geophysicist with CSP2, co-authored a review of tailings dam failures:
http://www.csp2.org/reports/Long%20Term ... 0Oct11.pdf

Here in Alaska, we just had 2 recent dam failures (Nixon Fork, Rock Creek). They didn't collapse, but they did overtop and the Rock Creek mine is now going through closure.