4.3.9. Clean Water Diversion
Design drawings show the potential for migration of sediment into the TSF is minimal as a vast majority
of the catchment will be occupied with the TSF. The embankment longitudinal section for Stage 2,
shown in Figure 23, indicate an inferred vertical topographical distance between the top of the
catchment and the crest of the TSF less than 5m. Potential activation of sediment during construction
activities will be managed by standard erosion and sedimental controls.
As such clean water diversion drains have not been designed for or simulated in the water balance. For
the Upper Mundic Gully TSF, the contributing catchment is very steep and small relative to the size of
the TSF. Further, this system would function as a sink, requiring a sump and pump system to remove
the clean water. As such, there is no significant benefit in including clean water diversions upstream of
the TSF, especially given the complexities that constructing on steep slopes would add.
However, for the OCP, a coffer dam wall has been constructed between Sandstone Gully and the OCP.
As such, this will effectively keep the mine impacted stormwater runoff generated upstream of this coffer
dam out of the OCP, acting as a form of catchment segregation and aiding in water management. The
Sandstone Gully has no outlet from the mine site, other than through evaporative losses.
4.3.10. Potential impacts of future deposition expansion
Heritage Minerals has authorisation through the EA to increase tailings storage capacity by constructing
an adjacent TSF in Sandstone Gully. A DBA and CCA for the Sandstone Gully TSF have already been
undertaken by WSP assigning an overall Consequence Category of Extreme for the final embankment
stage.
In an expansion scenario, where both TSFs are constructed and used, the results of the DBA and CCA
of Upper Mundic Gully TSF may be impacted because of the Sandstone Gully TSF.
The current failure extents for both stages of the Upper Mundic Gully TSF indicate a potential for a
portion the discharged outflow to interact with the location where the proposed Sandstone Gully TSF is
to be constructed, as indicated in Figure 35. Flood severity (based on the depth/velocity product) at that
intersection was rated at the H6 category, which indicate the potential for embankment erosion. In the
worst-case scenario, where erosion progresses into a breach initiation, cascade failure of Sandstone
Gully TSF would become a credible failure mode, and the overall Consequence Category of Upper
Mundic Gully TSF could be elevated to “Extreme” (matching Sandstone Gully TSF).
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Wulguru Technical Services Pty Ltd – Supporting Information to Amend an Environmental Authority
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