Figure 33. Stage 2 Sunny Day Failure Maximum Depth (m)
5.12 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 22, 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. Potential impacts of future deposition expansion Heritage Minerals has authorisation through the EA to increase tailings storage capacity by constructing the Sandstone Gully TSF. 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. 5.13
Project number: 25B061
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