Australian dams at extreme risk
REVIEWS of the risks associated with tailings dams around the world have revealed that some structures built in Australia to store mining waste carry the highest possible risk classification under global standards, with catastrophic results expected if any of them collapsed.
A BHP Dam Risk Review showed that Mt Whaleback iron ore mine in WA, and two at the Olympic Dam mine in South Australia, were at extreme risk.
Meanwhile, in a Rio Tinto audit of its global facilities, the miner assessed more than 20 Rio Tinto Australian sites as being at high risk.
The BHP review had been carried out to assess the management of its tailings facilities following the failure of the Fundão dam at Samarco, Brazil, in 2015.
BHP was a joint venture partner with Vale at the Samarco mine when the dam collapsed, killing 19 people and devastating the environment.
BHP primarily ranks dams according to both the classification system of the Canadian Dam Association (CDA) and the Australian National Committee on Large Dams (ANCOLD).
The categories do not measure the stability of the dams or likelihood of them breaking, but rather estimate the hypothetical loss of life and damage to surrounding areas if a worst case scenario failure occurred without controls in place.
The Extreme category covers dams for which a major loss of more than 100 lives is anticipated in the case of failure, with major environmental losses and restoration deemed impossible.
Dams classed in the Very High consequence category are those which are tipped to lead to less than 100 lives in case of failure while causing significant environmental damage, and with a highly impractical likelihood of restoration.
BHP’s three Extreme risk sites in Australia are among five in the world with such ratings, the other two being in Peru and the USA.
There are also two Very High risk Australian dams: the Goonyella Riverside coal operation in Queensland, and Nickel West nickel operation in Leinster, WA.
The Rio Tinto audit assigned the highest risk levels to two dams at the Weipa bauxite operations in Queensland, listed as its Andoom tailings storage facility (TSF) and Torro TSF.
The “high A” classification, based on the ANCOLD scale, indicates catastrophic environmental damage and a significant population at risk in the event of a dam breakdown.
A “high B” rating was given to two tailings dams at the Ranger uranium mine at Kakadu National Park, indicating highly hazardous status.
The rating is expected to put pressure on how Ranger will be rehabilitated when it closes in 2021. Tailings from one of the dams are slated to be removed in 2020, with deconstruction to follow.
A Rio statement said it employed an integrated approach to managing the potential risks posed by its tailings facilities, which are based on three levels of governance and assurance that are applied to all facilities.
A BHP dam taskforce, established in April, has been charged with enhancing the company’s focus on tailings, including the continued improvement and assurance for BHP’s global tailings storage facilities, progressing its technology efforts and leading ongoing participation in the setting of new international tailings management standards.
The International Council on Mining and Metals (ICMM) launched an expert panel in February to develop an international standard for tailings facilities for its member companies.
The ICMM made clear its desire for the mining sector to move away from wet tailings towards dry tailings storage, which is considered safer.