Tuesday, January 29, 2019

Damn these Dams

As rescuers in Brazil search for survivors of a dam collapse, questions abound about the health and safety and the environmental risks of the thick, metal-laden mine waste.  The United Nations and others have warned that dam failures in the mining industry are becoming increasingly catastrophic because the structures are growing larger and more numerous around the globe. There are an estimated 18,000 tailings dams worldwide. A 2017 U.N report identified 40 significant dam failures over the prior decade — including in Canada, China, Brazil and Chile.
Mine tailings are large volumes of waste rock and other material left behind after companies dig up mineral-bearing ore and run it through mechanical and chemical processes to remove the most valuable components. The tailings are disposed of in ponds or other “impoundments,” often in a mud-like mixture of water and rock known as slurry. A single large mine can produce hundreds of thousands of tons of tailings each day that are typically pumped into a massive holding area behind a dam, where the waste can remain for decades. Tailings piles can be dry enough on the surface to allow people to walk on them, but the inside is often wet, with a jelly-like consistency. A breach can release a runny, muddy material.

The  disaster in Brumadinho dam that failed was 282 feet (86 meters) high and held more than 15 million cubic yards (11.7 million cubic meters) of waste material, according to its owner, Brazilian-mining company Vale.
A similar disaster in 2015 at a Vale-operated mine in the same region of Brazil killed 19 people and released 78 million cubic yards (60 million cubic meters) of mud that polluted hundreds of miles of rivers and streams. In that case, a U.N. report found that the waste “contained high levels of toxic heavy metals.” The 2015 accident, in the city of Mariana in Minas Gerais state, left 250,000 people without drinking water after downstream supply systems were tainted or otherwise disrupted by mud.
David Chambers with the Center for Science in Public Participation, which consults with government agencies and private groups on mining pollution issues.
“We can’t tell you where a failure is going to occur, but statistically we can tell you they are going to happen.” 

Critics say reforms have yielded few changes and more dam failures are inevitable without stepped-up construction practices and inspection regimes.

“We have the technology and we have the expertise, and the mining industry frankly has fought making those changes,” said Payal Sampat with the U.S.-based environmental group Earthworks.


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