in the Manual for Assessing Consequence Categories and Hydraulic Performance of Structures (ESR/2016/1933), the DSA, ESS and mandatory reporting levels (MRL) requirements must be addressed for those dams assessed as having a “significant’ or ‘high’ consequence for the “failure to contain – overtopping’ scenario. If a dam was assessed in the low consequence category for the ‘failure to contain – overtopping’ scenario, the determinations for a DSA, ESS and MRL are not required even if the dam is otherwise a regulated structure. Based on results provided in Section 5.2, the Upper Mundic Gully TSF does not require an operational spillway, DSA or ESS requirements in Table H3 of the EA. A closure spillway will be designed following cessation of tailings deposition, once final tailings surface levels, settlement, and surrounding infrastructure are known. Updated DBA/CCA and PMF modelling incorporating the closure spillway will be undertaken at that time. The closure spillway will be designed to avoid connecting the Upper Mundic Gully TSF and Dam 8. No spillway will be constructed between the Upper Mundic Gully TSF and Dam 8. 5.5 Deposition Volumes Tailings deposition into the Upper Mundic Gully TSF was modelled using Muck3D to estimate the maximum available tailings storage and to develop the construction staging of the embankment. The estimated volumes for the two embankment stages are presented in Table 31 including sufficient storage to contain the PMP runoff. Table 31. Estimated Tailings Storage
Stage
Elevation (m RL)
Tailings beach (m RL)
Tailings Storage (Mm 3 )
Tailings Storage (Mt)
Water Storage (Mm 3 )1
1
360
350.3
1.15
1.26
1.32
2
390
386.8
8.09
8.9
1.32
Total
NA
NA
9.24
10.16
1.32
(1) Required PMP storage does not include operational pond volumes
Resultant tailings beach surface stage-storage curves are presented in Figure 24 to Figure 27.
Project number: 25B061
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