Item
Description
Information Requested
Response
Corresponding Sections
Water management (UGM TSF) It is stated the UGM TSF will provide additional capacity in a potential worst-case scenario should the OCP be at risk of overtopping (GHD, 2025). There is no understanding on the trigger for water transfers to the UGM TSF should the OCP be at risk, nor the potential implications and risks, and the management proposed under the worst-case scenario. The storage of water on tailings dams is not considered best practice and presents a considerable risk, coupled with the reprocessed tailings material containing a 60% liquid content. The UGM TSF Design Report (WSP, 2025) requires clarification as it is stated the water storage requirements assumes ‘no operational pond level’. Given the intentions outlined above, clarification is required regarding this operational objective. Further, there is no discussion on potential drainage requirements with advice stating an operational decant pond will be incorporated in the next stage of the design (WSP, 2025). It is acknowledged that a spillway with the capacity to pass the Probable Maximum Flood (PMF) event will be required for Stage 2 and closure of the UGM TSF (WSP, 2025). Despite this, a spillway for Stage 2 has not been nominated nor detailed, with advice suggesting further studies are required to assess suitable locations to discharge outflows. TSF) Assumptions applied in the UGM TSF CCA Report (WSP, 2025a) for seepage suggest seepage is determined to be of ‘low’ consequence category rating with flows from UGM TSF directed towards the OCP with the preferential direction of groundwater flow from the OCP east towards Mundic Creek. This has not been demonstrated via field verified data or modelling. Consequence category assessment (UGM Geotechnical investigations It is stated that geotechnical investigations are needed to assess potential seepage impacts (WSP, 2025). Sections 7.8 and 8 of the UGM TSF Design Report include several recommendations required, however, there is no forwards works plan provided to address the information gaps. In the absence of necessary geotechnical information to support the application, it is significantly challenging to assess the stability, safety, and suitability of the proposed tailings dam design, as well as its potential environmental, operational and closure risks.
Provide revised application material which a) Detail the trigger to transfer water from the OCP to the UGM TSF and demonstrate all risks to environmental values via a risk assessment can be managed. This must include a description of the water quality from the OCP, the anticipated water volume to be stored on the UGM TSF, the timeframe for its storage and the water content of the reprocessed tailings within the UGM TSF. Provide a robust water management strategy and plan under such event which must demonstrate potential environmental impacts are avoided, mitigated or managed. b) Provide clarification on the ‘no operational pond level’ proposed for the UGM TSF with consideration to the intention to store water on the facility under specific circumstances, the water content of the tailings and the transfer of water from the OCP at 0.5 ML/d. This must include a robust water management strategy including the operational practices required to maintain no operational pond level to ensure this operational objective can be met. c) Provide the designs, configuration and discharge outflows of the Stage 2 spillway for the UGM TSF and revise all necessary reports to include the spillway and present the findings.
a) The application has been updated to remove references to the transfer of water to the UMG TSF b) No transfer of water from the OCP to the Upper Mundic Gully TSF is proposed as part of this amendment. All references to an OCP-to-Upper Mundic Gully water transfer in the water balance report reflect a contingency scenario that was assessed for completeness of the risk assessment only and does not form part of the design or operational basis of the Upper Mundic Gully TSF c) The CCA has been updated to state that the closure spillway for UMG TSF is proposed to discharge west to Turner Creek after placement of a suitable cover system on the tailings beach
a) Section 2.1.1 b) Section 2.1.1 c) Appendix C
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Demonstrate via field verified data and modelling the assumptions utilised for seepage and groundwater flows from the UGM TSF are appropriate. If required, revise the CCA with verified information regarding seepage and groundwater flow pathways.
The CCA has been updated and the failure to contain (seepage) consequence category has been determined as significant. Following the completion of site investigations committed to in the forward works plan, the consequence categories will be reassessed and the CCA will be updated WSP have developed a seepage management plan that serves as a guiding framework to inform targeted investigations and assessments required to address current knowledge gaps and to test and refine the current understanding of seepage processes. The SMP defines the information requirements, monitoring activities and further studies necessary to improve confidence in seepage risk characterisation and to support the progressive refinement of seepage assessments as additional data is collated and the project advances. The application represents concept engineering and describes the location and storage capacity of the water infrastructure on the site The UMG TSF design is at concept stage and has not advanced to detailed design stage where geotechnical investigations are typically undertaken. This application has adhered to the intent of the Manual for assessing consequence categories and hydraulic performance of structures (ESR/2016/1993) (the Manual) and Guideline: Structures which are dams or levees constructed as part of environmentally relevant activities (ESR/2016/1934 (the Guideline), specifically regarding performing the initial consequence assessment In accordance with the manual and Guideline, the RPEQ tasked with the detailed design of the UMG TSF will ensure that appropriate geotechnical investigations have been undertaken to inform the design. Heritage Minerals will continue to be subject to the model conditions contained in the EA relating to design, construction and operation of regulated structures. The geotechnical risk for the UMG TSF will be addressed during the detailed design stage in accordance with the model conditions in the EA, during which the AQP and RPEQ will assess the stability, safety, and suitability of the proposed tailings dam design, as well as its potential environmental, operational and closure risks. In addition to the model conditions in the EA, a condition committing the EA holder to completing geotechnical investigations is proposed for inclusion in the EA:
Appendix C
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As outlined in the UGM TSF Design Report, provide revised application material that demonstrates the implementation and finalisation of the identified recommendations, along with the associated findings. This must include an assessment on the geotechnical stability of the UGM TSF, considering the increased hydraulic pressure from the proposed storage of water under extreme climatic events and the liquid content of the tailings.
Section 5.8 and Section 9
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ISO 9001 • ISO 14001 • ISO 45001
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