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DETSI Comment
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erosion to confirm stability. Although the area appears inactive with no disturbance, the risk of reactivation under intense rainfall or vegetation clearing must be considered. Any activation of gully and sediment ingress into pond, even after all tailings are placed, is a risk to TSF dam hydraulic performance and must be considered
failure events (e.g., Vajont Dam in Italy) but it’s typically not assessed for a TSF. An options assessment in Section 2.3 determined that the Upper Mundic Gully area is the preferred location for construction and operation of the TSF primarily due to the favourable topography that allows a valley TSF geometry. Valley TSFs reduce stability risks as they leverage existing landforms as buttresses. 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 being less than 5m. Creating diversions across the slope would require significant cutting and disturb far more material than what is required to construct the TSF. Any potential activation of sediment during construction activities will be controlled by standard erosion and sedimental controls. A completed water balance report is provided in its entirety in Appendix H. A summary of key information relevant to the application is presented in Section 4.3.4. The water balance model calculates the min (1%) and max (99%) events as seen in Figures 24 and 25
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A completed water balance modelling report, including assumptions and limitations, must be provided to support water quality risk assessments and the management of tailings and water during all phases of the TSF. This must also include worst-case scenario assumptions (i.e., full tailings storage and full water ponding).
Section 4.3.4 and Appendix H. Figures 24 and 25
In terms of surface water management
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Is clean water diverted? Management of upstream catchment must be detailed. 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.
Section 4.3.9
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