Therefore, for all scenarios, the severity of damage and loss for the impacts on the owner’s business is classified as ’ Major ’.
6.2.3.3 Health and social impacts
Flooding from a dam break would reach the township of Mt Morgan. People whose properties are damaged or destroyed will need to be compensated, as well as compensation for loss of life. Furthermore, employment within the mine may be affected under all failure scenarios. It is estimated that due to the dam break, restrictions in mine operations may result in the loss of between 50 and 100 jobs. Additionally, 100 to 1000 people could be displaced as a consequence of the event. Although some staff could potentially be re-deployed in remediation roles. Therefore, the health and social impacts in all scenarios have been considered to be ‘ Medium ’. 6.2.3.4 Environmental impacts The degree of damage to the environment was assessed considering the impacts to the local MSES [30], as presented in Section 1.4. The failure discharge for all scenarios is attenuated in the OCP, leading to a dilution of the 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 Dee River, the tailings concentration is low, minimizing the impact. The extents of impact through the areas of concerned varied from between 2 and 5 km 2 for Scenario 1 and 2 (Stage 1 and Stage 3 Sunny Day) to greater than 5 km 2 in Scenario 3 (Stage 5 Sunny Day). Therefore, for both Stage 1 and 3 scenarios, the severity of damage and loss for the environmental impacts has been classified as ‘Medium , and ‘Major for the Stage 5 scenario .
6.2.4 Consequence Classification assessment
The dam break Consequence Classification assessment (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 OCP, consideration of the PLL is considered suitable for this assessment.
Table 6.8
Consequence Category Assessment for Sandstone Gully TSF
Structure
Scenario PLL Overall
Consequence category
Overall Consequence category
severity of damage and loss
Sandstone Gully TSF
1 (Stage 1)
33.9 Major
High A
High A
2 (Stage 3)
59.1 Major
Extreme
Extreme
3 (Stage 5)
102.5 Major
Extreme
Extreme
6.2.4.2 DESI Table 6.9 presents the dam break CCA results as per the DESI guidelines, considering the PAR, PLL and environmental significance for all assessed scenarios.
Project No PS213278 Sandstone Gully TSF Dam Break and Consequence Category Assessments Mount Morgan Gold Mine Heritage Minerals
WSP January 2025 Page 30
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