The results of the geochemical modelling provided in Table 33 indicate that the final tailings solution analytes do not exceed any of the HILs and it is concluded that leaching from the tailings material is benign to human health. When tailings are appropriately stored in a well maintained TSF subject to regular inspections and monitoring, tailings materials are generally considered benign ecological receptors. Additional groundwater monitoring bores are proposed to be installed to monitoring for any potential COCs. Heritage Minerals Project accountabilities do not extent to the treatment and discharge of mine affected water to the Dee River. The State (via DNRMMRRD) maintains responsibility for water management, treatment and discharge from the OCP in accordance with the Phase 3 Agreement. Based on the above, the proposed amendments are unlikely to result in further impacts to surface water values in the Dee River and downstream riverine systems. Heritage Minerals will not be discharging water into the Dee River as part of mining operations. Overall, the latent tailings and waste rock recovery and reprocessing at Mount Morgan is expected to result in the reduction of contaminant sources via the reprocessing of mineralised tailings dams and remediation of operational areas, which will reduce the volume of mine affected surface water runoff. As a result, it is anticipated that surface water quality will improve during and post mining. Acid Sulfate Soils Acid Sulfate Soils (ASS) form in coastal areas lower than 5 mAHD. The Project is located above 5 mAHD and the risk of encountering ASS is considered negligible, therefore no impacts relating to ASS are expected. 7.3.2.2 7.3.2.3 Acid Producing Rock As noted in other parts of this document, the presence of heavy metals and sulphur bearing compounds (iron, pyrite, zinc, molybdenum and others) within latent tailings and waste material have caused a number of legacy issues on the site, predominantly concerned with the issue of acid rock drainage and water quality impacts on the environment. Heritage Minerals proposed operations intent to remove sources of AMD contamination through processing of latent tailings with subsequent processed tailings to be permanently disposed in engineering TSFs. As the Heritage Minerals project will remove latent tailings without the need to remove overburden, there will be no additional acid producing rock generated as part of the overall project and the Upper Mundic Gully TSF construction and operation. The Upper Mundic Gully TSF is designed to tie into the Western Dump which evidently shows exposed batters that could be contributing to further ARD seepage into the environment. Sealing the exposed batters will assist with reducing potential leaching of contaminants from the Western Dump. 7.3.3 Management Practices The primary objective for groundwater management will be to minimise the release of mine affected seepage from Project operational areas while progressive tailing reprocessing and Mount Morgan Mine remediation occurs in accordance with the State’s Rehabilitation Plan (Unger et al, 2003) and Phase 3 Agreement. This will protect EVs and WQOs of receiving groundwaters from further degradation. As with the existing Regulated Structures contained in the EA, the Upper Mundic Gully TSF will be subjected to annual regular maintenance inspections in accordance with EA conditions in Schedule H and the Manual for Assessing Consequence Categories and Hydraulic Performance of Structures (ESR/2016/1933) . These inspections must be undertaken by a suitably qualified and experienced person. In addition to these inspections, the Heritage Minerals Water Management Procedure provides standard controls for various Project activities including tailings and water management, chemical
Project number: 25B061
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