Item
Description
Information Requested
Response
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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ISO 9001 • ISO 14001 • ISO 45001
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