• Phase 1 (Month 0-11): Modelling of the construction phase including dewatering of Sandstone
Gully to OCP;
• Phase 2 (Month 12-51): Modelling of the period where the OCP functions as the TSF;
• Phase 3 (Month 52-73): Modelling of the period where the Upper Mundic Gully TSF functions
as the TSF; and
• Phase 4 (Month 74-94): Modelling of remaining five years where the Upper Mundic Gully TSF
functions as the TSF.
Results of the water balance modelling indicate that the newly proposed Upper Mundic Gully TSF shows
general seasonal increases through the wet season in Phases 1 and 2 (see Figure 24), assuming that
the tunnel to the Dam 8 is sealed. Once Upper Mundic Gully becomes the receiving TSF (from Phase
3 onwards), the base levels begin to rise with the tailings deposited, with only minor fluctuations in water
levels due to the reuse of the water being released form the deposited tailings. The results presented
in this figure also confirm that the TSF was not simulated to spill based on the maximum level as
simulated in this study, using the historical climatic data. The results presented for OCP water levels
(Figure 25) were assessed for the following key levels in OCP as specified by Heritage Minerals:
267.3 m AHD;
•
263.0 m AHD; and
•
• 259.3 m AHD to sustain a 1% AEP buffer volume.
Table 27 presents the simulated key water levels along with corresponding dates. All simulated dates
fall within Phase 2 except for the date associated with a relative level of 259.3m AHD in OCP, which
occurred during Phase 3. During Phase 3, late 2029 (UMG as TSF), OCP water levels were simulated
to continue dropping further at an increased rate. The spill level of the OCP is at 273.52 m AHD and
the simulations show that there is negligible spill risk as shown in Figure 25, due to the declining water
level.
Table 27. Simulated dates for OCP levels at various RLs
Relative Level (mAHD)
July Simulations
50 th
75 th
267.3
21/06/2026
05/10/2026
263
25/01/2028
16/10/2028
18/08/2029 1
18/11/2029 1
259.3
1 Phase 3
90
Wulguru Technical Services Pty Ltd – Supporting Information to Amend an Environmental Authority
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