5.3.2.5 Consequence Classification DETSI Table 27 presents the dam break CCA results as per the DETSI guidelines, considering the PAR, PLL and environmental significance for all assessed scenarios. Table 27. Consequence Category Assessment - DETSI (Dam Break scenario)
PAR
Stage 1
Stage 2
Low People are not routinely present in the failure path and no loss of life is expected. Contamination of waters used for human consumption is not expected to affect human health. Low It is expected that the outflow will reach areas of MSES, which may cause some impact to the existing ecosystem, but the area of damage is expected to be less than 1 km 2 . Low Harm to third-party assets in the failure path is expected to require less than $1 million or in rehabilitation, compensation, repair or rectification costs.
Low A PAR of 4 with a PLL of less than 1 was estimated along the failure path. Contamination of waters used for human consumption is also not expected to affect human health. Low It is expected that the outflow will reach areas of MSES, which may cause some impact to the existing ecosystem, but the area of damage is expected to be less than 1 km 2 . Significant Harm to third-party assets in the failure path is expected to require $1 million or greater (but less than $10 million) in rehabilitation, compensation, repair or rectification costs.
Harm to humans (1)
General environmental harm
General economic loss or property damage (2)
Low
Significant
Overall consequence classification
(1) The PLL was calculated without the mining personnel (2) General economic loss or proper damage does not include the holder’s own mine production, on-site industrial or commercial assets or infrastructure solely for servicing the dam owner Environmental Spill/Failure to contain (Overtopping Consequence) An embankment overtopping was deemed as non-credible for the proposed Upper Mundic Gully TSF, given the storage design that allows containment of a 120-hr PMP storm volume. After such an extreme storm, a subsequent storm of a sufficient magnitude to cause catastrophic damage or failure of the dam is unlikely to occur prior to the water level being drawn down. 5.3.2.6 Therefore, the environmental spill/overtopping consequence has been based on a more frequent event following a PMP storm, which is considered to be a credible failure scenario. Note, this scenario is not expected to sufficiently erode the embankment to induce a breach. It is expected that any spills would be largely attenuated by the OCP and contained in the downstream drainage infrastructure and Dee River. Environmental Spill/Failure to contain (Overtopping Consequence) – ANCOLD Table 28 presents the consequence category assessment for Upper Mundic Gully TSF according 5.3.2.7
to ANCOLD for the “Environmental spill” scenario of both embankment stages. Table 28. Consequence Category Assessment – ANCOLD (Environmental Spill)
Item
Stage 1
Stage 2
Minor Minimal repairs are expected since there is no risk of a dam break. The repairs are more related to correcting erosion and addressing minor issues in the embankment.
Same as Stage 1
Total infrastructure costs
Project number: 25B061
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