∕ 1) Failure to contain – Overtopping, spills or releases from the structure that result from loss of containment due to overtopping of the structure. ∕ 2) Dam break, collapse of the structure due to any possible cause. ∕ 3) Failure to contain – Seepage, spills, or releases to ground and/or groundwater via seepage from the floor and/or sides of the structure. Dam Break Consequence Results For Scenario 1 (Stage 1), no mine personnel or Mt Morgan dwellings are expected to be impacted by the floodwaters, and the PAR was considered zero for both DETSI and ANCOLD methodologies. For Scenario 2 (Stage 2), mine personnel would be impacted at the process plant and the No. 2 Mill Tailings areas, yielding a total PAR of 45 for those locations, accounted for using the ANCOLD methodology. Additionally, four dwellings within the urban area of Mt Morgan were impacted for Stage 2 using the ANCOLD methodology, which yielded a PAR of 8. This number reduced to two dwellings for the DETSI methodology, where flood depths are required to be greater than 300 mm for there to be persons at risk. 5.3.2.3 Table 24 presents the total PAR for each scenario, according to ANCOLD and Table 25 presents the permanent and itinerant PAR for each scenario, according to DETSI. As noted in the CCA report, the latter discounts mine personnel or persons located in an area with inundation depths lower
than 0.3 m from the estimates. Table 24. PAR estimates (ANCOLD)
Stage 1
Stage 2
PAR
0
45
Mining operations
0
8 (1)
Township of Mt Morgan
<1 53 (1) PAR corresponds to four properties identified within flood extents
Total
Table 25. PAR Estimates (DETSI)
Stage 1
Stage 2
PAR
0
0
Mining operations
0
4 (1)
Township of Mt Morgan
<1 4 (1) PAR corresponds to four properties identified within flood extents
Total
5.3.2.4 Consequence Classification ANCOLD Table 26 presents the dam break CCA results as per the ANCOLD guidelines, considering the PAR and overall severity of damage and loss. It is noted that ANCOLD specifically recommends that consequence category for tailings dams is to be evaluated against the PAR rather than PLL due to the nature of the released material and uncertainty in estimating fatality estimates for tailings outflow. However, due to the expected displacement of water in the Open Pit, consideration of the PLL was also deemed suitable for this assessment. Table 26. Consequence Category Assessment for Upper Mundic Gully TSF
Embankment
PAR
PLL
Overall severity of damage and loss
Consequence category
<1
<0.1
Major
Significant
Stage 1
53
0.6
Major
High B
Stage 2
Project number: 25B061
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