Table 6.9
Consequence Category assessment for STSF – DESI (Dam Break scenario)
Item
Response
Scenario
1
2
3
Significant The PAR is estimated to be 8.0, and the PLL in this case was assessed to be less than 0.1.
High the incremental PAR is estimated to be 125.7, and the PLL in this case was assessed to be 13.8.
High The PAR is estimated to be 330.3, and the PLL in this case was assessed to be 57.5.
Harm to humans (1)
Significant It is expected that the
Significant It is expected that the
High It is expected that the
outflow will reach areas of MSES, which will cause an alteration of the existing ecosystem. The area of impact is expected to be larger than 2 km 2 , but less than 5 km 2 High It is expected to require $10 million or greater in rehabilitation, compensation, repair or rectification costs.
outflow will reach areas of MSES, which will cause an alteration of the existing ecosystem. The area of impact is expected to be larger than 2 km 2 , but less than 5 km 2 High It is expected to require $10 million or greater in rehabilitation, compensation, repair or rectification costs.
outflow will reach areas of MSES, which will cause an alteration of the existing ecosystem. The area of impact is expected to be larger than 5 km 2 .
General environmental harm
High It is expected to require $10 million or greater in rehabilitation, compensation, repair or rectification costs.
General economic loss or property damage
Overall Consequence Classification and description
High
High
High
(1) The PLL was calculated without the mining personnel.
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 Sandstone Gully TSF, given the storage design that allows containment of a 120-hr PMP storm volume for Stages 1 and 3, spillway capacity of Stage 5 to convey the PMP event, as detailed in the DFS report [5]. 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 event, 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.
Project No PS213278 Sandstone Gully TSF Dam Break and Consequence Category Assessments Mount Morgan Gold Mine Heritage Minerals
WSP January 2025 Page 31
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