Heritage Minerals has a unique approach to solving the economic barriers to treating low-grade tailings. A combination of the worlds best technology and many years of operational experience can turn around projects that are otherwise not feasible. Heritage Minerals designs and implements innovative solutions for technically tricky projects. They are also a environmentally and socially responsible problem solver.
SGME T-02 Memorandum
29 May 2026
Date
Mikaela Dry, Sarah De Vries
To
Peter Mellor, John Frankish, Sam Pegg, Craig Wilson, Tim Hanmore
CC
Lachlan McQuire
From
Application to amend environmental authority EPML00433013 – Information Request response
Subject
Dear Mikaela and Sarah, The Mount Morgan Mine site is one of Queensland's most historically significant former mining operations and carries a substantial legacy of environmental harm accumulated over more than a century of prior activity. This environmental harm extends beyond the areas currently authorised for disturbance in the Environmental Authority (EA). The broad mine site and the surrounding receptors have been heavily impacted by the historical mining operations and resultant spread of contaminants from the abandoned mine. Heritage Minerals' rehabilitation project is informed by the Phase 3 Agreement between the State of Queensland and Heritage Minerals (the applicant). The Phase 3 Agreement reflects a deliberate policy decision by the Queensland Government to leverage private commercial investment to address legacy mine rehabilitation liabilities at Mount Morgan, with a view that commercial reprocessing of the tailings for gold would help to support site remediation. The Agreement allocates responsibility for activities on site between Heritage Minerals and the State of Queensland and is intended to drive Heritage Minerals to make environmentally focussed investments in carrying commercially-driven environmental rehabilitation of the site, while limiting the liability of Heritage Minerals for the legacy mining disturbance. Heritage Minerals is seeking authorisation for the location of the Upper Mundic Gully TSF by including it as a mine feature in the EA. To obtain authorisation for these activities, an amendment to EA EPML00433013 is required. An EA Amendment Application Supporting Document for the proposed activities was submitted to the Queensland Department of Environment, Tourism, Science and Innovation (DETSI) on 29 October 2025. Since then, the following activities have occurred: ∕ An Assessment Level Decision (ALD) was received from DETSI on 26 November 2025 stating that the proposed amendment to the EA is a major amendment; ∕ An Information Request (IR) was received from DETSI on 23 January 2026; ∕ Meetings were held between DETSI and the applicant to discuss the IR on 18 February and 20 March 2026; ∕ A site inspection was held on 14 May 2026 attended by representatives from DETSI, representatives from the Department of Natural Resources and Mines, Manufacturing and Regional and Rural Development and the applicant; ∕ A post site inspection meeting between DETSI and the applicant was held on 22 May 2026; and ∕ Public notification for the major amendment is scheduled to commence on 29 May 2026. To address the IR and guide DETSI’s review, the table below has been prepared which provides a response to each IR item raised and where responses can be found in the application material. The EA Amendment Application Supporting Document, including relevant appendices, has been revised and updated accordingly. If you require any further clarifications, please do not hesitate to contact us. Yours sincerely,
Lachlan McQuire Principal Environmental Advisor lmcquire@sgme.au
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Corresponding Sections
Off lease dist.
Provide advice on this off-lease discrepancy identified and detail how this will be rectified via this amendment.
The application, including figures and associated spatial files, has been updated to ensure that the Red Ox and Q Dump areas/polygons are contained within ML boundaries. This change to disturbance areas has resulted in a reduction of the approved areas for mining in the revised Table A1. Additionally, the portion of the haul road that exists off tenure has been removed from this application.
Section 2.3.2
The proposed revision of figure 1 (Mine Area Location) of environmental authority (EA) EPML00433013 is depicted in figure 9 of the application material (Wulguru, 2025)[1]. It appears disturbance footprints extend outside of tenure boundaries. Specifically, the Red Oxide Tails, Q Dump and a section of haul road northeast of the mining/contractor yard. Mining related disturbance subject of the EA is not authorised outside of tenure boundaries.
1
Regional interest development approval
Clarify if there is an intention to include a mine equipment park up and workshop area to the EA. If so, provide all necessary information for its inclusion. For example, description of the infrastructure, location, footprint size, identification of environmental values and the associated risks, impacts and management measures, and rehabilitation information for this feature.
The equipment park up and workshop from the approved RIDA is no longer going ahead as would impact on the amenity of the lookout. A new laydown area inclusive of the heavy vehicle maintenance area has been identified and included in the application, as stated in response to Item #3. An application to amend the current RIDA will be conducted following EA amendment approval but before proposed EA activities are undertaken
Not applicable (NA)
It is identified that regional interest development approval RPI17/001 is approved for the project. Upon review of the documents publicly available related to RPI17/001, it is acknowledged that a ‘mine equipment park up and workshop’ is proposed downstream of the proposed Upper Mundic Gully Tailings Storage Facility (UGM TSF), however, this is not reflected in this application.
2
Ancillary infrastructure
Provide revised application material which describes all ancillary infrastructure required for the construction and operation of the UGM TSF. If ancillary infrastructure is proposed provide: a) A description of each feature proposed including an assessment against the environmental values, impacts and risks to environmental values and the management and monitoring measures, and rehabilitation information. b) A description of the location, including maps, GPS co-ordinates and total disturbance area in hectares (ha) for each feature. Information should be provided in the same format as Schedule A1 (Authorised mining activities and locations) of the EA.
a) The Application has been updated to describe each new proposed feature, assessment of EVs, impacts and the rehabilitation strategy for the following new features: - New topsoil stockpile - New pipe corridor from process plant to UMG - New nursery - Haul road extension into UMG TSF footprint - New laydown area inclusive of heavy vehicle maintenance b) The description of location, maps, coordinates, total disturbance area for each feature identified above has been included in the proposed replacement Table A1 of the revised application a) The design basis for the UMG TSF embankment is intended to match that of Sandstone Gully TSF whereby the use of selected rock fill, borrowed from the western dump, will be used as zone 3A material used in embankment construction. This design basis is pending further detailed design works and RPEQ confirmation. Placing selected rock from western dump into the UMG is a similar concept to placing PAF material within NAF material to reduce potential for contaminant migration. The use of selected rock from Western Dump within the embankment, where it will be enclosed by verified clean material, is a better environmental outcome than the status quo whereby uncontrolled discharge of ARD into surface water features is occurring as evidenced by the surface water results described in Section Error! Reference source not found. . The application has been updated to include management measures to be implemented to prevent ARD mobilisation from the TSF to any receiving environment during operation and construction b) The Western Dump, which is not a feature authorised for disturbance in the EA, is seeping contaminants into the adjacent ephemeral dam as demonstrated through surface water quality sampling results. The reshaping of the western dump and selective placement of some material into the UMG TSF embankment is expected to improve the environmental outcome of the site by containing some of the acid generating material. The operation of the UMG TSF is not expected to exacerbate ongoing ARD leaching from the Western Dump. The UMG TSF embankment will reduce ARD generation and some waste rock material will be encapsulated in the development of the embankment. The UMG TSF design basis includes the installation of a liner on the upstream batter of the embankment to mitigate potential seepage through the embankment. As described in section 5.15.1 of the supporting information report, the tailings to be discharged into UMG TSF will not be acidic. The pH of the tailings material is moderately alkaline, whilst the
a) Section 5.2 describes the ancillary infrastructure features and environmental values, whilst the rehabilitation strategy is provided in Section 7.5.3 b) Section 2.3.2
Limited information is presented regarding if ancillary infrastructure is required to support the construction and operation of the UGM TSF. For example, this may include laydown areas potentially for pump systems, haul roads, access tracks, tailings pipeline and topsoil stockpiles. Further, as indicated in information request item 2, this may also involve a mine equipment park up and workshop area.
3
Western dump
Provide revised application material which:
a) Embankment design basis and management measures to avoid environmental harm are described in Section 5.9. b) Section 5.15.1. Water quality of the ephemeral dam is provided in Section 4.3. Seepage management plan is provided in Appendix H c) Proposed conditioning related to conducting geotechnical investigations is provided in Section 2.3. A forward works plan is provided in Section 9.
The UGM TSF is proposed to be built over a portion of the existing western dump. It is acknowledged in the application that the western dump is likely contributing to acid rock drainage (ARD), however, this has not been confirmed via submission of site data or investigations. It is stated the exposed face of the western dump will be sealed, further reducing potential ARD seepage. However, no information is presented regarding the material or methods to be utilised to support the assertion this will reduce potential ARD. there is no understanding regarding the extent of the proposed reshaping or its implications for areas of the dump that fall outside of the proposed UGM TSF. No information is presented confirming the suitability of constructing the foundation and embankment over the existing dump and the potential risks of exacerbation of the suggested ARD. The application material suggests construction of the UGM TSF will involve reshaping of the western dump, however,
a) Details the proposed reshaping requirements necessary for the western dump, the potential implications for the entire western dump and the proposed management measures to avoid environmental harm caused by this action, where necessary. b) Details the risks and management measures required to ensure ARD isn’t exacerbated via the construction of the UGM TSF embankment over the existing western dump. Detail how it will be demonstrated that ARD isn’t exacerbated and how it will be determined and demonstrated potential impacts from the UGM TSF will be differentiated from the western dump. c) Confirms the suitability of the building the foundation and embankment of the UGM TSF over the existing western dump. This should involve a discussion of the findings of the relevant geotechnical investigations as recommended in the UGM TSF Design Report (WSP, 2025)[2].
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Corresponding Sections
pH of the waste rock material will be acidic, as observed through site wide impacts and the sampling activities that have occurred in the ephemeral dam adjacent to the western dump. An assessment of the hydraulic conductivity of the western dump has been undertaken based on the original groundwater model established for the site, which suggests a highly variable, moderate to high permeability that promotes rapid infiltration and seepage. A seepage management plan has been developed and included in the updated application. The Seepage management plan incorporates available data into a structured management framework to guide seepage monitoring, ongoing risk management and future works. (c) The UMG TSF design is at concept stage and has not advanced to detailed design stage where geotechnical investigations are undertaken. If the EA amendment is approved, Heritage will be unable to construct the UMG TSF until the RPEQ certifies the issued for construction (IFC) design drawings. Undertaking the detailed design requires completion of the future works identified in Section 9 of this application, which will require geotechnical investigations. Under these conditions, and in accordance with the Manual for assessing consequence categories and hydraulic performance of structures, the RPEQ tasked with the detailed design of the UMG TSF must at that stage: - confirm that the TSF is designed to prevent seepage risk and is structurally stable (including aspects of the TSF involving reshaping the Western Dump); and - confirm that appropriate geotechnical investigations have been undertaken to support the design plan 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 compared to conventional turkey’s nest TSFs as they leverage existing landforms as buttresses. A forward works plan that includes the completion of geotechnical studies to support the detailed design phase has been included in the application. Proposed conditioning has been included in the revised application that require the completion of geotechnical investigations to support complying with existing condition H4 of the EA “All regulated structures must be designed by, and constructed under the supervision of, a suitably qualified and experienced person in accordance with the requirements of the Manual for Assessing Consequence Categories and Hydraulic Performance of Structures (EM635) . “ a) Under current conditions, impacted water from the ephemeral dam has the potential to migrate through the tunnel and daylight into Dam 8, which is located off the mining tenure, and is not a mine feature included in the EA. It is acknowledged that a moderate rainfall event must occur to facilitate the flow event between the two areas. Water quality sampling results obtained from a sampling event undertaken during February 2026, using pH as the primary contaminants of concern, did not indicate that Dam 8 is impacted. As described in the application, the tunnel will be plugged prior to TSF construction to mitigate potential deformation or collapse of the tunnel void beneath the embankment fill and seal the pathway between the two features. An assessment of the hydraulic conductivity of the western dump has been undertaken based on the original groundwater model established for the site, which suggests a highly variable, moderate to high permeability that promotes rapid infiltration and seepage. The application has been updated to include management measures to be implemented to prevent ARD mobilisation from the TSF to any receiving environment during operation and construction b) Water quality sampling of Dam 8, which is a feature located off the mining lease, has been undertaken and results provided in the application. The environmental values of Dam 8 have been assessed and included. A seepage management plan has been developed and included in the updated application. The seepage management plan incorporates available data into a structured management framework to guide seepage monitoring, ongoing risk management and future works. The critical controls to limit the potential seepage from UMG TSF to Dam 8 include the installation of a liner on the inner embankment wall. The seepage management plan commits to further intrusive investigations, ongoing sampling and updating conceptual site models. Implementation of the monitoring and investigation measures outlined in this SMP will support progressive improvement in confidence regarding seepage pathways, groundwater responses,
Dam 8 Dam 8 is not authorised under the EA however it is stated Heritage Minerals Pty Ltd use water from Dam 8 for construction and processing activities. This is further supported by the water balance technical memorandum (WBM Memo) (GHD, 2025)[3] which includes provisions for Dam 8 water transfers to the plant at 0.4 megalitres per day (ML/d) in Stages 2 and 4 of the project’s operation. By way of sealing the tunnel to Dam 8 via the construction of the UGM TSF it cannot be determined if this impacts the State acting through Department of Natural Resources and Mines, Manufacturing and Regional and Rural Development (DNRMMRRD) or Heritage Minerals Pty Ltd activities. An understanding on the environmental values of Dam 8 and the potential implications the proposed activity has on any sensitive values is not described. This may include reduction in water contributions and potential flow pathways impacting the water quality of Dam 8. The application material states a concrete plug, and mine spoil will be utilised to seal the tunnel. The mine spoil and its characteristics have not been described to confirm if this is suitable or has the potential to leach through to Dam 8 in the event the concrete plug has not sealed the entrance.
a) Section 5.10 and Section 6.6.2 b) Section 4.4 and Appendix H. c) Section 4.4.7
Provide revised application material which: a) Detail how water contributions to Dam 8 may be impacted via the construction of the UGM TSF and how this will be managed in order to ensure activities undertaken by Heritage Minerals Pty Ltd and the DNRMMRRD are not affected. b) Describe the environmental values of Dam 8 and the potential implications in the event seepage flow pathways from the UGM TSF are identified towards Dam 8. Describe the mitigation and management measures proposed to avoid impacts to Dam 8. c) Detail the properties and characteristics of the mine spoil proposed to fill the tunnel and confirm its suitability to ensure potential leachate from tailings material will be avoided.
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Corresponding Sections
and interactions with nearby surface water receptors. As additional geological, hydrogeological, and monitoring data become available, the SMP will be reviewed and updated to reflect improved site knowledge and evolving project conditions. This iterative approach ensures seepage management remains evidence ‑ based, proportionate to risk, and aligned with regulatory expectations throughout the life of the Project. c) The design has been updated and no longer refers to mine spoil. The plug will be constructed of concrete A revised CCA for the SSG TSF has been completed and provided in the updated application. The UMG TSF will be the primary TSF and upon cessation of deposition into UMG TSF, tailings will then discharge into SSG TSF. The two TSFs will never be operating at the same time. The draft DBA and CCA prepared for UMG TSF results in a “High B” and “Significant” classification for the Stage 2 configuration, based on ANCOLD and DETSI respectively. The hydraulic design criteria for these consequence category classifications are provided in the application documentation. The design basis adopted for the UMG TSF aligns with the hydraulic design criteria for an ANCOLD “High B” classification, is consistent with industry practices and exceeds all DETSI requirements. The proposed construction of SSG TSF downstream of UMG TSF is identified in the draft CCA as a potential change. WSP is satisfied that the CCA reflects the current site configuration and any changes will trigger a review of the CCA at that time. As the concept design provides storage allowance to contain the PMF design flood, increasing the DETSI consequence classification would not result in any change to the adopted design criteria, while increasing the ANCOLD classification to Extreme would only impact the wet season and storm event storage which can be contained within current allowances. The concept design for UMG TSF currently includes allowances to store the design flood (PMF) however the closure spillway for the UMG TSF will discharge to the west to Turner Creek after placement of a suitable cover system. The UMG TSF draft CCA has been updated to reflect the above understanding of spillway configuration and potential direction of any overtopping events. a) The application has been updated to reflect that the SSG TSF will not be operational at the same time as the UMG TSF. Once the UMG TSF is approved, the SSG TSF will be reserved for Stage 2 of mine plan development, which is not yet authorised or planned. It would be misleading to include the SSG TSF in any WBM, because it will not exist during the life of the UMG TSF. b) The application material has been updated to reflect that there is no proposal to construct the SSG TSF during the life of the UMG TSF or during the life of mining activities that are currently approved under the EA. The presence of latent conditions in the Sandstone Gully TSF, whereby there is more latent tailings present than originally estimated, will result in a much slower excavation process. As such the timeframes to construct the Sandstone Gully TSF can not be surmised at this stage as dewatering and excavation timeframes can not be established until remining commences. c) The GHD report (2025) correctly identifies the "SSG area" as "an additional area within the mine site" (as opposed to an "additional mine area" as noted in the IR), rather than a TSF for the purposes of the WBM. There is no change to the classification of the SSG TSF under the EA. The EA amendment application to request new mine features does not relate to the SSG TSF. d) Nothing in the GHD report (2025) nor the EA amendment application should be taken as an application to amend the EA in a way that relates to the SSG TSF. The SSG TSF will continue to be approved in the EA. The applicant has confirmed that it does not propose to construct SSG TSF during stage 1 of their mine plan e) The area designated for the SSG TSF is intentionally not modelled as a TSF in the water balance model, so there would be no potential interactions or implications of 'removing' it from the model. f) and g) The application material has been updated to reiterate that the SSG TSF will remain as an approved structure, and will not be built during stage 1 of operations. To include a non- existent structure in a WBM would over-state the water storage potential of the site, thereby under-stating the over-topping risk of the OCP, and would be counter-productive and misleading.
Sandstone Gully Tailings Storage Facility (SSG TSF)
Provide a suitable CCA for the SSG TSF demonstrating the hydraulic performance criteria as proposed. Alternatively, revise and submit a CCA for the approved SSG TSF confirming the appropriate hydraulic performance criteria for the structure.
Section 2.3.2 and Appendix N
The hydraulic performance criteria for the SSG TSF is proposed to be amended. The application material, which includes the SSG TSF Report (Golder, 2020)[4], does not include information supporting the assertion that the consequence category assessment (CCA) for SSG TSF determined the consequence category as ‘high’ for dam break and ‘low’ for overtopping and seepage. As such, it cannot be determined if the proposed amendments are appropriate.
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Water balance model (SSG TSF) The water balance technical memorandum confirms that SSG TSF is not considered a TSF in the assessment and instead ‘an additional area within the mine site’ (GHD, 2025). This change necessitates urgent clarification regarding the structures purpose, alignment with the sites approved activities and proposed water management strategies. Without incorporating the SSG TSF as a tailing’s dams into the water balance model or formally excluding it from the approved activities, the representation of water inputs, outputs, and storage cannot be considered accurate or reflective of the site's authorised operations. Consequently, the risks and findings presented in the report cannot be reliably validated.
Provide revised application material which: a) Provide a detailed explanation and clarify what is ‘an additional mine area’ and what its intended purpose is as it relates to the SSG TSF footprint. b) Confirm whether there is an intention to construct the SSG TSF. If so, provide a timeframe for the proposed construction which must consider the extreme failure events identified and the required revision of the dam break and consequence category assessments if both facilities are built (WSP, 2025a)[5]. c) Confirm and provide detail whether the reclassification of the SSG TSF as ‘an additional mine area’ aligns with the authorisation currently stated in the EA. d) If the SSG TSF is no longer intended to function as a tailing’s storage facility, confirm whether it will be decommissioned or repurposed. Provide an assessment against the environmental values, impacts and risks to environmental values and the management and monitoring measures, and rehabilitation information as a result of this change. If Heritage Minerals Pty Ltd plans to maintain the SSG TSF as ‘an additional mine area’, the SSG TSF should be removed as an authorised tailings storage facility from the EA as its purpose will no longer align with the current approved activities. e) If SSG TSF remains classified as ‘an additional mine area” in the model, provide an assessment that includes a risk evaluation of the potential interactions and implications of removing the SSG TSF as a tailing’s storage facility from the water balance model. Provide an evaluation of how this change impacts the water management risks associated with the site's approved activities. f) If SSG TSF is intended to be maintained as a tailing’s storage facility, update and include this approved activity into the water balance model and present the findings. g) Demonstrate how the updated water balance model accounts for water inputs, outputs and storages across the site, and detail how this aligns with the approved and proposed activities.
a) Section 5.3 b) Section 5.3 c) NA d) NA e) NA f) and g) 5.14
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Corresponding Sections
Water balance model report The WBM Memo is a technical memorandum and not a comprehensive water balance model report. The referenced report Water Balance Modelling Report – Heritage Minerals EA Amendment Application, Revision 3 (GHD, 2022) was not provided in support of this application. It is understood the UGM TSF is intended to provide a more resilient tailings and water management strategy which can better accommodate more extreme climatic conditions and further reduce water balance risks (Wulguru, 2025). Despite this, the transfer of water under extreme climatic conditions nor climate change impacts have been modelled. It is assumed based on the WBM Memo, the UGM TSF construction and status prior to it receiving reprocessed tailings will potentially be fifty-two (52) months. During that time, it is acknowledged the UGM TSF area will naturally retain water from the contributing catchment runoff, however, this has not been simulated in the model. An understanding of why this was not included in the model, and the destination of this water is required. Consideration must also be applied detailing if this water is likely to be contaminated given the western dump surface area. Further, it is acknowledged a sump and pump system will be required for the UGM TSF, however, no further information is provided. Notwithstanding information request item 7, the following assumptions within the WBM Memo require clarification: a) The DNRMMRRD water treatment plant is assumed to be actively pumping throughout the entire simulation period (4.8 ML/d). It is unclear who operates and maintains the DNRMMRRD water treatment plant, with the value applied requiring confirmation. b) The evaporators nominate a throughput capacity of 3.35 ML/d. No data is presented supporting this assumption. c) Table 3.1 of the WBM Memo suggests the UGM TSF return water to plant is 7.8 ML/d in Stages 3 and 4. However, clarity is required regarding the purpose of this water transfer and its source (i.e., decant water and/or runoff). d) Table 3.1 also suggests in Stages 3 and 4, the Open Cut Pit (OCP) to UGM TSF transfers is 0.5 ML/d. However, clarity is required regarding the purpose of this water transfer and the simulated rate. Further, this does not appear to align with the operational design aspects of the UGM TSF which states ‘no operational pond level’.
Provide revised application material which:
a) The application has been modified to reflect that water transfer between the OCP and UMG TSF will not occur. Reference to the GHD report (2022) has been removed from this application b) The application has been updated to remove references to the transfer of water to the UMG TSF c) As discussed throughout this application, the TSF design is at concept stage and the design of pumping infrastructure has not been undertaken. A forward works plan in Section 9 commits to undertaking the design of infrastructure during detailed design d) Heritage Minerals operate the water treatment plant on behalf of the DNRMMRRD e) DNRMMRRD operate and maintain the evaporators. Therefore the applicant does not maintain performance datasets. Assumptions that underpin the water model were based on previous reporting (Engeny, 2018). f) The Upper Mundic Gully TSF has been designed on the basis of no operational pond volume. Tailings deposition will be managed to minimise ponding, with systems to be installed to return any operational water to the process plant. The design includes sufficient freeboard to accommodate the PMP event without requiring any operational spillway. The estimated return volumes is calculated by considering the beach surface and tailings density. g) The application has been updated to remove references to the transfer of water to the UMG TSF
a) NA b) NA c) Section 9
a) Provide the comprehensive water balance model report prepared by GHD (2022) referenced in the adjacent column. b) Update the water balance model report to incorporate scenarios of the extreme climatic conditions which control the transfer of water to the UGM TSF, and climate change impacts. Present the findings clearly and ensure the updated comprehensive water balance model report is provided. c) Clarify why the clean water entering the system from the contributing catchment was not simulated and demonstrate this is suitable to not include in the model. Provide further information on the proposed sump and pump system, including the expected quantity and quality, the destination of the water pumped through this infrastructure and if this is suitable and aligns with the sites approved activities. d) Clarify who operates the DNRMMRRD water treatment plant and confirm the assumption applied is appropriate. e) Clarify who operates and maintains the evaporators and detail the reliability and efficiency of the evaporators. Provide the site data which supports the evaporators throughput capacity applied in the model. Apply a sensitivity scenario which removes the evaporators from the model and present the findings. f) Clarify the transfer of water from UGM TSF to plant (7.8 ML/d), what this is attributed to how this has been calculated. g) Clarify the transfer of water from OCP to UGM TSF (0.5 ML/d), why this is required and how this has been calculated. Confirm this aligns with the proposed operational design aspects of the UGM TSF and the overall best practice management of tailings dams.
d) NA e) NA f) NA g) NA
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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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Item
Description
Information Requested
Response
Corresponding Sections
Groundwater It is stated the UGM TSF is determined to be of negligible risk to all environmental values (WTS, 2025). There is no understanding of groundwater environmental values within the UGM TSF footprint or close proximity. To support the assertion made, groundwater environmental values must be investigated. This information cannot be delayed via proposed conditioning and must be provided to support the application to understand the baseline conditions, the predicted and potential impacts and risks to groundwater to appropriately inform the mitigation and management measures. The application material, although related to the Mundic Creek Catchment and not the UGM TSF, identifies seepage may occur through the shallow bedrock. It is also stated groundwater flow and influence is not understood and the influence of the OCP and western dump on the UGM TSF is unknown. A comprehensive understanding on all seepage flows and pathways from the UGM TSF must be provided. Further, the high liquid content of the tailing’s slurry, coupled with the intention to store water on the facility under extreme climatic events increases the potential for seepage and groundwater contamination, necessitating a comprehensive groundwater assessment.
Provide all relevant information in accordance with the Guideline Application requirements for activities with impacts to water (DETSI, 2026)[6]. The revised application must also include: a) Investigate, nominate and implement groundwater monitoring bores within and surrounding the proposed UGM TSF at appropriate and representative locations. The bores must be located in areas to effectively capture baseline conditions and detect potential impacts from the proposed activity. b) Undertake and submit detailed groundwater monitoring information including:i. Background quality and characteristics. ii. Groundwater level and depth. iii. Hydraulically conductivity, transmissivity and flow rate. iv. Seasonal variations and influences.As per DES (2021) , a minimum of 18 samples over at least 12 and preferably 24 months is required to calculate limits. Alternatively, if there is urgency in the application, the department may consider a minimum of 8 monthly datapoints, if the concentrations are relatively stable and consistent. c) Provide further detail on the composition of tailings material including:i. Identification of potential contaminants of concerns.ii. Describe the results of leachate testing to determine the potential for contaminants to leach into groundwater.iii. Potential impacts on ecological systems and groundwater environmental values. d) Identify and describe all seepage pathways and flows from the UGM TSF including the receiving receptors. e) Provide a seepage management plan which includes: i. Design specifications to mitigate or manage potential flows through the facility, including evidence of the liner's ability to withstand the hydraulic pressure from the high liquid content and storage of water under extreme climatic events, and prevent seepage.ii. Proposed measures to minimise seepage, including monitoring and maintenance strategies.iii. Contingency measures in the event of seepage detection. f) Describe in detail the potential impacts due to the proposed activity and all associated risks to the groundwater environmental values in consideration of the above requested information. Consideration must be given on whether the identified impact on receiving waters supports the management intent for those waters, to the extent practicable. g) Describe in detail the strategies to mitigate and manage the identified risks to groundwater environmental values. For example: i. The locations, depths and purpose of the monitoring bores. ii. Frequency and parameters for groundwater quality and level monitoring. h) Submit a long-term groundwater monitoring plan for the UGM TSF, including post- closure monitoring requirements and measures to ensure the long-term stability of the facility and the prevention of groundwater contamination after closure from the facility. The information requested above must demonstrate the UGM TSF will not further impact waters environmental values of the receiving environment of the Mount Morgan Mine. Consideration can be given to the approved activities as a whole, however, reduction of the contaminant load to the receiving environment as a result of the approved activities must be demonstrated via modelling or other supporting evidence.
Since lodgement of the initial EA amendment application, three groundwater monitoring bores have been installed within the Upper Mundic Gully catchment. The application has been updated to include the information obtained from the drilling and subsequent groundwater sampling to inform potential risks to environmental values a) Three groundwater bores were installed within the UMG TSF footprint and surrounds during December 2025 and the application has been updated to include this information. The forward works plan commits to the installation of further groundwater monitoring bores to address data gaps. b) Whilst there are long term existing groundwater records from across the mining lease, there is only a limited dataset of groundwater information from UMG TSF. The Forward works plan commits to the installation of additional groundwater monitoring bores to be sampled at a monthly frequency. Updates to existing table W1 in the EA are proposed whereby the locations of the monitoring bores to be installed are conditioned. c) i. A tailings geochemical characterisation assessment was undertaken with information summarised in Section 5.14.1 of the supporting information report and the complete report provided in Appendix G. Bench testing indicates that Heritage Minerals processing activities will reduce metals in solids as they become leached by the cyanide. Although these metals were leached from the solids, they were absorbed onto the resin to be subsequently recovered, resulting in a lower final solution of metals. The potential residual contaminants of concern in the tailings include residual salts expressed as electrical conductivity. ii. Geochemical characterisation of the processed tailings to be discharged has been extensively studied by Hydrobiology in the report titled “Mt Morgan Open Cut Pit Water Quality Modelling Stage 2 (March 2025)”, provided in Appendix G. The Hydrobiology report provides a predicted water quality of the new tailings assuming a range of OCP water qualities based on extensive leach testing iii. The results of the geochemical modelling indicate that the final tailings solution analytes do no exceed any of the HILs and it is concluded that any leaching from the tailings material is benign to human health. Potential impacts on ecological systems and groundwater environmental values are proposed to be further understood through completion of additional groundwater installation programs and updates to the site wide groundwater model. d) Identification of potential seepage pathways has been provided in the seepage management plan. The seepage management plan has been developed based on the current conceptual understanding of the hydrogeologic and geological conditions at the site including the interpreted groundwater flow regime, stratigraphic framework and potential seepage pathways associated with the proposed UMG TSF. This SMP presents an initial characterisation of potential seepage behaviour during operations and in the period following completion, recognising the current level of site understanding. e) A seepage management plan has been provided in the updated application. f) The existing risk assessment provided in Section 7 of the supporting information report has been updated (g) The existing risk assessment provided in Section 7 of the supporting information report has been updated. h) development of a long term groundwater plan has been included in the forward works plan As stated in Section 6.6.7 of the current supporting information report, a groundwater model exists for the site. This is a validated and calibrated groundwater model developed in FEFLOW that provides explanation on mechanisms by which contaminants can migrate through groundwater and impact receptors. The groundwater model mesh grid covers an area of 7.7km 2 . The model calculates contaminant load from each catchment and was relied upon by the State to inform rehabilitation strategies. This model provides a characterisation of all catchments that occur within the mine lease boundaries. The application has been updated to commit to further updates to the groundwater model to incorporate site specific data obtained from the UMG TSF footprint and surrounds.
a) Section 6.6.1 and Section 9 b) Section 6.6.8 and Section 9, c) Section 5.15.1 and Appendix G d) Section 5.10 and Appendix H e) Section 5.10 and Appendix H
f) Section 7 g) Section 7 h) Section 9
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Groundwater modelling In the absence of a groundwater model, it is significantly challenging to assess impacts to groundwater from the proposed UGM TSF. A numerical groundwater model must be developed to assess the risks and potential impacts with the resulting report to be provided.
Complete numerical groundwater modelling for the UGM TSF. The groundwater model report to be submitted must include: a) A hydrogeological model of the UGM TSF and its receptors, including: i. Geological cross sections. ii. Aquifer connectivity and flow dynamics. iii. Recharge and discharge zones. iv. The potential interactions between surface water groundwater. This model must be based on field verified data and information within the UGM TSF area and proximity. b) The basis for the numerical groundwater model parameters, assumptions and model design. It must be demonstrated the model domain extent is sufficient to the extent necessary to understand potential impacts from the UGM TSF.
a) – i) Section 6.6.9 and Section 9
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Item
Description
Information Requested
Response
Corresponding Sections
c) Steady-state and transient calibration results (with sufficient monitoring points surrounding the proposed UGM TSF) d) An operational scenario which reflects the proposed design of the UGM TSF (including expected foundation conditions and any other design elements that could influence the impact to groundwater) e) Particle tracking around the perimeter for the proposed UGM TSF to assess potential pathways. f) An assessment of risk to groundwater from the UGM TSF. g) Conduct and submit contaminant transport modelling to predict the movement of potential contaminants from the UGM TSF through the groundwater system. The report to be provided must include : i. Predictions of contaminant concentrations at potential receptors over time and at closure. ii. Details of the modelling approach, assumptions, and parameters used, such as hydraulic conductivity, porosity, and seepage rates. iii. Estimated seepage rates considering the high liquid content of the tailings slurry, the permeability of the tailings material and the underlying geology. iv. Sensitivity analyses to evaluate how changes in liquid content (i.e., due to rainfall or evaporation, and the intention to store water on the facility under extreme climatic events) could affect contaminant transport) h) Sensitivity and uncertainty modelling to provide an indication of the potential risk to groundwater receptors. i) Closure modelling.
a) – i) SLR proposes a phased approach to update the groundwater model to support the EA amendment to include the Upper Mundic TSF. The first phase involves updating the site- wide groundwater flow model developed by RGC (2011) and supporting conceptual model to better understand local groundwater conditions in the Upper Mundic valley and the adjacent catchments that could be affected by the construction of the Upper Mundic TSF (e.g. Spring Creek and Patty Creek). The second phase of modelling would involve the development of a solute transport model to simulate the transport of selected constituents in groundwater within the Mount Morgan Mine Site and provide simulated contaminant loads to the Dee River during the process of reprocessing tailings and post- rehabilitation. Further details are provided in the supporting information request .
Groundwater dependent ecosystems (GDEs)
Provide revised application material which:
A GDE impact assessment was undertaken in accordance with the EIS information Guideline and the supporting information has been updated that describes this assessment in more detail. a) The application has been updated to provide information relating to the spatial extent of impact from the proposed activity on mapped GDEs b) A ground truthing field assessment undertaken in accordance with the guidelines. The results of the survey have been included in the updated information. Considering the conceptual site model where groundwater was encountered at 110m below ground within UMG TSF footprint, the outcome of the assessments was that there are no GDE receptors that could be potentially impacted by TSF construction or operation. c) As the ground truthing did not indicate potential impacts to GDEs, the formulation of additional avoidance and mitigation measures above what is already proposed was not warranted d) A revised CCA has been included in the application
a) Section 6.7.5 b) Section 6.7.5 c) NA d) Appendix C
There is moderate potential terrestrial GDEs and potential GDE aquifers mapped within and around the proposed UGM TSF. Field surveys have not been undertaken to verify the mapped information and the potential risks and impacts via changes in groundwater levels and quality has not been detailed. It is stated, the affected terrestrial GDEs are upslope of the seepage flow direction, however, seepage pathways from the facility have not been field verified or demonstrated.
a) Determines the spatial extent of impact from the proposed activity on mapped GDEs. b) Confirms that mapped GDEs within and surrounding the proposed activity (extent of impact zone), have been ground truthed. In the absence of ground truthed information, the application assessment in relation to consideration of the significance of impacts to the receiving environment will assume that mapped GDEs are present (based on the current mapping available). c) Based on the information developed in relation to item (b), provide: i. The baseline conditions of all GDEs that have the potential to be impacted by the proposed amendment, or otherwise indirectly impacted. ii. A description of any potential risks and impacts to all GDEs to be impacted or likely to be impacted by the proposed activity. This must include potential changes to groundwater level and quality, including the expected locality and extent of the groundwater level and quality changes. iii. Proposed management and monitoring strategies and/or program to detect potential impact on GDEs and any corrective action(s) if impacts are detected. iv. Incorporate this information into the groundwater model accordingly. d) Revise the consequence category assessment with consideration of the information requested above. Please consider relevant guidance material to determine and assess impacts to GDEs, including the EIS Information Guideline (2024)
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