Mount Morgan Mine Upper Mundic Gully TSF EA Amendment

6.3.4 Consequence classification

6.3.4.1 ANCOLD

Table 6.10 presents the consequence category assessment for Upper Mundic Gully according to ANCOLD for the Environmental spill scenario of both embankment stages.

Table6.10

Consequence Category Assessment for Upper Mundic Gully TSF ANCOLD (environmental spill)

Item

Stage 1

Stage 2

Total infrastructure costs

Minor Minimal repairs are expected since there is no risk of a dam break. The repairs are more related to correcting erosion and addressing minor issues in the embankment.

Same as Stage 1

Minor Some restrictions.

Same as Stage 1

business

Health and social impacts

Minor No dwellings, roads or any other third-party assets are expected to be harmed. However, it is expected that the discharged outflows cause minor impacts (less than $1 million in rehabilitation/compensation) to farm supply/use downstream. Minor It is expected that the spills from TSF will be contained in Dee River banks.

Same as Stage 1

Environmental impacts

Same as Stage 1

Overall consequence classification

Low

Low

6.3.4.2 DETSI

Table 6.11 presents the consequence category assessment for Upper Mundic Gully according to DETSI to Contain of both embankment stages.

Table6.11

Consequence Category Assessment for Upper Mundic Gully TSF DETSI (failure to contain overtopping)

Item

Stage 1

Stage 2

Harm to humans

Low No loss of life is expected. No contamination of water used for human consumption.

Same as Stage 1.

General environmental harm Low

Same as Stage 1.

It is expected that the spills from TSF will be contained in the banks of the Dee River.

Project No PS213278 Upper Mundic Gully TSF Stage 1 and 2 DBA and CCA Mount Morgan Gold Mine Heritage Minerals

WSP May 2026 Page 32

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