6.2.3.4
Environmental impacts
The degree of damage to the environment was assessed considering the impacts to the local MSES [27], as presented in Section 1.4. The failure discharge for all scenarios is attenuated in the OCP, leading to retention and dilution of the discharged tailings. As a result, the flows downstream of the OCP have a low tailings concentration. When water reaches Dee River, although the impacted water may be carried towards the protected areas around this water course, the tailings concentration is low, minimising the impact. The extents of impact through the areas of concerned are expected to be less than 1 km 2 for both scenarios. Therefore, the severity of damage and loss for the environmental impacts has been classified as ‘Minor’ for both scenarios
6.2.4
Consequence Classification
The dam break CCA results for each of the guidelines considered are presented in the following sections.
6.2.4.1
ANCOLD
Table 6.8 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 [2] 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.
Consequence Category Assessment for Upper Mundic Gully TSF
Table 6.8
Overall severity of damage and loss
Consequence category
Embankment
PAR
PLL
Stage 1
<1
<0.1
Major
Significant
Stage 2
53
0.6
Major
High B
6.2.4.2
DETSI
Table 6.9 presents the dam break CCA results as per the DETSI guidelines, considering the PAR, PLL and environmental significance for all assessed scenarios.
Consequence Category assessment for Upper Mundic Gully TSF – DETSI (Dam Break scenario)
Table 6.9
Item
Stage 1
Stage 2
Low
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.
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.
Harm to humans (1)
Project No PS213278 Upper Mundic Gully TSF Stage 1 and 2 DBA and CCA Mount Morgan Gold Mine Heritage Minerals
WSP JUly 2025 Page 30
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