Item
Stage 1
Stage 2
General economic loss or property damage (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.
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.
Overall consequence classification
Low
Significant
(1) The PLL was calculated without the mining personnel. (2) General economic loss or property damage
production, on-site industrial or commercial
assets or infrastructure solely for servicing the dam owner.
6.3 Environmental spill/failure to contain (overtopping) consequence As discussed in Section 3.1, 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. 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. 6.3.1 Population at risk No PAR is expected for both embankment stages, as overtopping is anticipated to be heavily attenuated. It is expected that overtopped flows would be conveyed southeast and mainly contained within the banks of the Dee River further downstream.
6.3.2 Potential loss of life
Similarly to PAR, no PLL is expected for both embankment stages.
6.3.3 Environmental considerations Environmental spills from the Upper Mundic Gully TSF are expected to be heavily attenuated, with excess discharge expected to be contained within the Dee River banks and the environmental impacts are expected to be low for both embankment stages. Note that the concurrent rainfall event causing the spill is expected to dilute the TSF decant discharge, with further dilution anticipated within Dee River from local catchment stormwater runoff.
Project No PS213278 Upper Mundic Gully TSF Stage 1 and 2 DBA and CCA Mount Morgan Gold Mine Heritage Minerals
WSP May 2026 Page 31
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