6
Consequence Category assessment
6.1
Method Overview
A Consequence Category assessment (CCA) was prepared for Upper Mundic Gully TSF in accordance with the criteria outlined in ANCOLD [1] [2] and DETSI [3]. An overview of the methods is provided in the following sections.
6.1.1
ANCOLD guidelines
According to the ANCOLD [1] [2] guidelines, the following two consequence categories need to be assessed as part of a TSF design, considering the risk to human life and severity of damage and loss estimates: 1 Dam Failure Consequence Category: consequence assessed against the impacts of a catastrophic release of water and tailings following an embankment breach. 2 Environmental Spill Consequence Category: assessment considering the effects of spilling of water from the dam during a flood or extreme wet period.
Risk to human life is expressed either as Population at Risk (PAR) or Potential Loss of Life (PLL):
— PAR: Number of buildings or other places of occupation within the failure impact zone, or people working or travelling through a potential impacted zone. Occupancy rate of the impacted areas, duration, and frequency, considering itinerant and non-itinerant populations are used to calculate the PAR.
— PLL: Based on PAR and expected fatality rates, which are based on a combination of flow depth and flow velocity.
The severity of loss and damage has been estimated using the maximum flood inundation and severity. The overall severity is determined based on four categories:
— Total infrastructure cost.
— Impact on owner’s business.
— Health and social impacts.
— Environmental impacts.
The assessment table for both approaches are presented in Table 6.1 and Table 6.2.
Table 6.1
Consequence Category criteria based on PAR [2]
Severity of damage and loss
Population at risk
Minor
Medium
Major
Catastrophic
<1
Very Low
Low
Significant
High C
Significant (1)
Significant (1)
≥1 to <10
High C
High B
≥10 to <100
High C
High C
High B
High A
≥100 to <1000
High B
High A
Extreme
(2)
(2)
≥1000
Extreme
Extreme
(1) Change to “High C” where there is potential of one of more lives being lost.
(2) With a PAR in excess of 100, it is unlikely damage will be minor. Similarly with a PAR in excess of 1,000 it is unlikely damage will be classified as medium.
Project No PS213278 Upper Mundic Gully TSF Stage 1 and 2 DBA and CCA Mount Morgan Gold Mine Heritage Minerals
WSP JUly 2025 Page 22
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