Wisconsin Resources Protection Council

by Al Gedicks
Wisconsin Resources Protection Council
agedicks@eagle.uwlax.edu

Aquila’s “Upstream” dam construction method poses unacceptable risks to downstream communities and the Menominee River

The proposed Back Forty tailings waste storage uses the upstream dam construction method. A 2017 Columbia University study on tailings dam failures found miners typically choose the upstream design because it is the lowest-cost option when constructing dams (see http://water.colombia.edu/files/2019/01/TSF-paper-CWCrev2.pdf) The only reason it is considered the lowest-cost option is because mining companies fail to assess the cost of a collapsed dam. According to the database World Mine Tailings Failures, there were 46 “serious” or “very serious” collapses – such as the recent Brumadinho, Brazilian dam disaster – between 1998 and 2017.

A tailings dam can be constructed by piling up rock and earth to produce an impermeable barrier. But most tailings dams, such as the one that collapsed at Brumadinho and the one proposed for the Back Forty project, are built using the far cheaper upstream method. This involves banking up the tailings themselves, and then increasing the height of the dam as mining progresses, by adding more material as the tailings dry out. Dams made with the upstream method are more likely to fail because the tailings are more sand-like and less dense than rocks and soil brought in from elsewhere.
It means regular inspections and maintenance are required to ensure that the tailings in the dam do not become unstable or get eroded by water.

Who in the DEQ will be responsible for inspecting the dam to insure that excess water does not cause a breach in the dike wall? Aquila cannot be relied upon to hire inspectors to report on the safety of the dam. This is precisely the problem that contributed to the Brazilian tailings dam disaster. Vale, the owner of the Brumadinho tailings dam, was able to hire the auditors and provide all the documentation that they analyze. The Brumadinho dam was certified as “stable” just before the dam failed.

The literature on tailings dam failures says the majority of failures can be attributed to the lack of management continuity and inadequate financing for the facility. Bowker and Chambers (2015) found a significant correlation between an increase in the severity of tailings dam failures and economic conditions that squeeze cash flow for miners, such as a decrease in metal prices and an increase in production costs (due to lower grades of ore). Aquila has not demonstrated that it has the financial resources to invest in monitoring and maintenance of a tailings dam for the many years until it reaches final design height, let alone for the perpetual maintenance after mine closure (see https://files.dnr.state.mn.us/input/environmentalreview/polymet/requet/exhibit3.pdf)
Why were other, safer, dam construction methods not considered by Aquila?

Dr. Chambers technical review of the Back Forty Mine Permit Amendment Application (February 11, 2019), notes that using the downstream or centerline construction design was not considered in the Dam Safety Permit Application, MPAA, or the EIAA. According to Dr. Chambers, “It is not clear…why the cost savings gained with upstream impoundment construction is more important than the increased long-term risk to the public of impoundment failure. It is significant that use of the downstream or centerline construction for the impoundment was never raised.”

Mining industry engineers condemn the upstream design as “inherently dangerous structures”

Because these types of tailings dams are waterlogged, they are easily susceptible to cracks and other damage that can cause bursts like the one that occurred at the Brumadinho, Brazil tailings dam. “A tailings dam may look safe, but it’s still retaining a lot of moisture behind it,” according to Dermot Ross-Brown, a mining industry engineer who teaches at the Colorado School of Mines. “They’re inherently dangerous structures.”

According to William F. Marcuson III, a former president of the American Society of Civil Engineers, “I wouldn’t buy a home downstream of a tailings dam built in an upstream fashion. And I wouldn’t allow my mother to rent or live in a home downstream of a tailings dam built in an upstream fashion.” (see Matthew Bloch et al, “Where Brazilians Live in High-Risk Areas Downhill from Mining Dams,” New York Times, February 14, 2019).

Dr. A. Mac G Robertson gave the keynote address at a 2011 tailings dam conference. He said that “many of the same features of modern mining that create economic feasibility in lower grades of ore also pose greater challenges for the management of mine waste and waste water. One of the manifestations of these challenges is a greater frequency of Very Serious tailings dam failures with significant levels of social and economic consequence, sometimes non remediable.” (see Bowker and Chambers, 2015).

Eduardo Leao, a director at the National Mining Agency of Brazil, issued an ordinance that all upstream tailings dams be taken down or converted into other types of dams. Brazil has 88 upstream tailings dams, according to Leao. (see Jake Spring, “Brazil set to ban upstream tailings dams after collapse kills hundreds,” Reuters, February 7, 2019.

Who pays the costs of tailings dam disasters?

There is no provision to insure taxpayer protection from the costs of environmental disasters like that of Mount Polley in British Columbia in 2014 or the January 25, 2019 tailings dam disaster in Brumadinho in southeastern Brazil. While mining companies have to bond the cleanup of their mines, those IOUs don’t cover dam failures because federal and state agencies don’t consider them to be reasonably foreseeable events. According to Dr. Chambers, mining companies should be required to post surety bonds to cover the costs of a dam failure. A mandatory bond would give mining companies a financial incentive to make sure their dams are safe. Tailings dams become permanent features of the landscape once the valuable mineral ores have been extracted and the mining companies leave the mess to taxpayers.

The Brazilian Institute for the Environment and Renewable Natural Resources (IBAMA) fined Vale, the owner of the Brumadinho failed dam, $250 million for the social and environmental catastrophe. Brazilian courts have ordered Vale to set aside $2.9 billion to pay for damages caused by the dam collapse. At least 150 people were killed and 182 are missing and presumed dead after the disaster in the town of Brumadinho. (see https://www.nytimes.com/2019/01/27/world/americas/brazil-dam-brumadinho.html).

A recent report by Earthworks documented tailings spills at nine US mine operations, and a partial failure of the tailings impoundment at four of fourteen mines (28%). The total cost for just 7 of these 16 large failures was $3.8 billion, at an average cost of $543 million per failure (see https://www.earthworksaction.org/files/publications/Porphry_Copper_Mines_Track-Record -8-2012.pdf)

The Earthworks study projects 11 very serious failures between 2010-2020 at a total unfundable public cost of $6 billion. “There is no organized industry attempt to cover these losses in a risk management loss prevention program, and no political jurisdiction issuing permits is large enough to prefund a low frequency high consequence loss of this scale. The inevitable result is either government pays or the damages go uncompensated.”

Upstream dam construction increases the risk of liquefaction

Upstream tailings dams are, in essence, lakes of thick, semi-hardened mud, consisting of water and the solid byproducts of ore mining, known as tailings. Their unique construction makes them vulnerable to a potentially devastating process called liquefaction, when seemingly solid material can abruptly become a murky liquid, flowing downhill. Even a subtle change like an increase in water content – because of especially heavy rains or poor management – can create enough internal pressure to push apart the solid tailings and liquefy the mud. (see “A Tidal Wave of Toxic Mud,” New York Times, February 10, 2019).

Based upon the record of historical failures, two distinct failure mechanisms seem to be dominant. “The first mechanism is related to the development of progressive failure in a weak soil layer in the dam foundation (“Tailings Dam Stability, 4th World Landslide Forum, Slovenia, 2017).” Appendix A of the Golder Report states that the project site is typically covered with topsoil underlain by a variable thickness of silty sand overburden soil of very loose to loose relative density. “The second dominant failure mechanism is related to static or dynamic liquefaction of loose tailings material at a critical state (WLF, 2017).” “Static liquefaction is the sudden loss of strength when loose soil, typically granular material such as tailings sands, are loaded and cannot drain (Klohn Crippen Berger, 2018).” Loading and deformation produce a tendency for the materials to contract and develop excessive pore pressure faster than drainage systems can relieve the pressure. Static or dynamic liquefaction of loose tailings may occur at a critical condition, where a rapid (undrained) small increase in the shear strain results in a large increase in pore pressure, reduced effective stresses and a dramatic reduction of shear strength. Typical for these types of failures is that they occur rapidly with no warning, so it is an extremely dangerous phenomenon.

Although it is called static liquefaction, a triggering event usually causes the rapid strength loss.

There are many potential triggers, including:

vibrations from construction equipment
rise in water pressure in a slope
stress increase due to a dam raise
stress concentrations due to a higher dam
loss of horizontal confining stress due to lateral strains in the foundation or dam

Source: Klohn Crippen Berger, “Static Liquefaction and Strength Loss in Tailings Dams,” posted on April 11, 2018. Available at https://www.klohn.com/blog/static-liquefaction-strength-loss-tailings-dams/

Static liquefaction and strength loss of tailings dams due to undrained failure has become a major concern in tailings management following the Mariana, Brazil and Mount Polley tailings dam failures. At both Mount Polley, British Columbia and the Samarco mine in Brazil, the companies failure to act on warnings and prepare for possible disasters, points to an alarming corporate practice of putting production and profit ahead of safety concerns.
Source: Judith Marshall, “Tailings dam spills at Mount Polley and Mariana: Chronicles of Disasters Foretold,” Canadian Centre for Policy Alternatives, August 2018. Available at https://www.policyalternatives.ca/tailings-disasters

Aquila has underestimated the risks of geological foundation failure

The October 30, 2018 Golder report on the tailings dam permit support design (Report No. 1899291 [8000]-Doc 03C) describes the subsurface conditions at the project site as “underlain by a variable thickness of silty sand overburden soil” and “very loose to loose relative density” (p. 2). This layer of weak glacial deposits, consisting of silty sand and overburden soil may make the tailings storage facility design inappropriate for the site. The government of British Columbia’s expert commission on the 2014 Mount Polley tailings dam disaster found that a breach occurred suddenly in the Perimeter Embankment of the tailings dam as a result of foundation failure. They concluded that the tailings dam was not appropriate for the site because it did not take into account the underlying geology.

Aquila omits any risk assessment of a tailings dam failure on the social fabric of communities or the environment

Between 2008 and 2017, there were 27 serious or very serious failures of tailings dams – up from 19 failures during the period between 1998 and 2007, according to a database managed by Dr. David Chambers of the Center for Science in Public Participation. Despite this track record, the Golder report on Aquila’s tailings dam omits any risk assessment of a tailings dam disaster on the social fabric of communities or the environment. Communities can suffer death and destruction of homes, income and the environment. Some of these community impacts may be long-lasting if drinking water is polluted, fish and wildlife habitat destroyed and tourism and recreational opportunities around the Menominee River are lost.

Mental health impacts from tailings dam failures also need to be recognized. People feel grief, loss and anger when destruction affects their environment and their sense of place. When the Brazilian dam broke in Brumadinho, Guy (Anahkwet) Reiter, a Menominee tribal member said: “It hurts my heart to think that this could possibly happen to the Menominee River and the people depending on it to survive. Even more so that we as Menominee people who come from that river and have a connection that leads back for thousands of years. The river holds memory, it knows our deep connection. The river is the center of our universe. We look to it to be reminded that we must always keep moving.”

Sociologists have documented that “one can speak of traumatized communities as something distinct from assemblies of traumatized persons. Sometimes the tissues of community can be damaged in much the same way as the tissues of mind and body…traumatic wounds inflicted on individuals can combine to create a mood, an ethos—a group culture, almost,– that is different from (and more than) the sum of the private wounds that make it up. Trauma, that is, has a social dimension.”
(see Kai Erikson, A New Species of Trouble: The Human Experience of Modern Disasters (New York: W.W. Norton, 1994, pp. 230-231).