redeposition of treated tailings into the Sandstone Gully TSF, OCP and the Upper Mundic Gully TSF (if approved). This will result in the removal of the source of ARD generating material from across the site reducing recharge of and seepage from mine waste structures. This will reduce impacts from the Mount Morgan Mine to the receiving environment including the Dee River in accordance with the State’s Rehabilitation Plan (Unger et al, 2003) and Phase 3 Agreement. Contaminated water seepage and runoff from the Mount Morgan Mine is currently managed by the State via the seepage interception system. While this has reduced contamination loads, the system cannot collect all contaminated water and water quality values in the Dee River remain adversely affected. Mine affected water created from seepage or surface runoff is currently accumulated in numerous facilities i.e. Shepherds Holding, No 2 Mill, Frog Hollow and Mundic West structures. Once collected, the seepage and/or surface runoff is either left to evaporate or pumped back into the OCP, with this location being the primary storage location for contaminated water. The potential for the Upper Mundic Gully TSF to impact on groundwater values is considered unlikely due to limited hydraulic conductivity and recharge of the underlying bedrock, referenced in Section 6.6, and implementation of engineering controls. The TSF design has considered potential direct or indirect releases to groundwater and mitigated through design undertaken by a RPEQ, installation of liners, regular TSF inspections to be undertaken by the engineer of record and proposed groundwater monitoring. The proposed installation of a liner on the upstream batter of the embankment to mitigate potential seepage through the embankment. A geomembrane liner will be required as no suitable low permeability clay material is found at the site. The liner bedding will be selectively borrowed from finer mine waste, however as it is difficult to remove coarse particles, a more robust bituminous geomembrane liner is proposed. 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, the tailings materials are generally considered benign to ecological receptors. This proposed amendment provides commitments for the installation of a groundwater monitoring array around the Upper Mundic Gully TSF to assess potential groundwater impacts. Removal of contaminant sources from the environment is likely to reduce inflows into existing sumps from groundwater and sub-surface flows in comparison to those under existing conditions. This is expected to result in improved performance of the existing seepage interception system and reduction in poor quality seepage expressing to the receiving environment i.e. Dee River. Disposal of tailings generated through reprocessing is unavailable however the proposed Upper Mundic Gully location and design reduces the likelihood of groundwater impact from occurring. Based on the above, these proposed amendments are unlikely to result in further impacts to groundwater values and Dee River downstream riverine systems. Overall, the recommencement of operations 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 existing volume of mine affected seepage. As a result, it is anticipated that groundwater quality will improve during and post mining and that there will be no actual or potential adverse effect on groundwater from the operation of the activity. 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. 7.4.3
Project number: 25B061
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