7.5.2.2 Rehabilitation Methodology The performance outcomes for Land provides for an obligation to achieve a safe, stable and non- polluting landform able to sustain an appropriate land use after rehabilitation or restoration. The proposed rehabilitation commitments are as follows: ∕ Completely backfilled with tailings. PAF waste rock exposed during construction transferred to void; ∕ Water removed from surface; ∕ Dry cover – store and release installed; and ∕ Drainage system constructed. Based on these proposed EA conditions, the rehabilitation methodology for the Upper Mundic Gully TSF will involves the following aspects: ∕ Fill the TSF to the maximum permissible RL to achieve the final landform; ∕ Shaping of the tailings surface to provide a direct flow path to the spillway and minimise or prevent ponding of water; ∕ Runoff management systems installed on the embankment; ∕ Conduct a soil investigation to determine if the tailings material presents any hazards to human health or ecological receptors and inform the cover design; ∕ Conduct seepage and groundwater assessments to determine if the structure is potentially polluting to the receiving environment; ∕ Installation of a cover over the tailings to prevent tailings erosion and to reduce potential for capillary rise; ∕ Installation of a closure spillway capable of conveying runoff generated by the PMF; and ∕ Verifying that the nominal factor of safety for long-term drained (steady state seepage at normal operating level) from ANCOLD has been achieved. Cover Systems Application of a cover system at the Mount Morgan Mine is severely limited by the lack of suitable sources of material that have not been impacted from previous mining activities. Best practice as informed from the PRCP Guideline identifies that an EA holder, over the course of operations, should plan for the conservation of soil material to facilitate rehabilitation planning. As the Mount Morgan mine is situated on a former highly disturbed mine site there has been limited opportunities for the State and previous operators to stockpile topsoil and other capping material required for both their own and third parties’ (Heritage Minerals) rehabilitation activities. Given the uniqueness of this area whereby the site has been maintained by the state since mining operations ceased in 1990, Heritage Minerals have not been accountable for stockpiling material to support rehabilitation. 7.5.2.3 As stated in Section 5.12, 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 the environment inclusive of ecological receptors. As the project progresses and deposition into the relevant TSFs occur, ongoing monitoring of the tailings quality will be undertaken to better inform rehabilitation and closure strategies. It is only following cessation of tailings deposition that more detailed soil studies can be conducted to obtain both physical and chemical soil parameters to confirm the rehabilitation and closure strategies. Based on the lack of available cover material and considering that only at cessation of deposition can soil investigations be undertaken to determine the chemical and physical properties of the
Project number: 25B061
Page 157
Powered by FlippingBook