EHS Support conducted a comprehensive technical assessment of Consolidated Leached Ash (CLA) to provide technical insights supporting a proposal to submerge the CLA material beneath at least 1 meter of low-permeability clay-rich fill material, aligning with the clients Geotechnical Engineering Design (GED). EHS Support’s work involved:
- Conducting field investigations within the CLA area to collect multiple samples for the measurement of permeability and chemical characterisation of materials encountered within and surrounding the consolidated leached ash
- Developing a numerical model using GeoStudio SEEP/W software simulating the hydraulic behaviour of rising water body and groundwater levels and potential groundwater seepage into the fill material under steady-state and transient conditions; this included particle tracking to observe movement of particles representative of a conservative (not subject to attenuation or retardation) constituent within the model domain. The model was run under various scenarios including natural water body filling (46 years), fast filling (10 years), and under a rapid fill typeevent (less than 1 year)
- Completing a detailed risk assessment in accordance with Part 3 Division 6 Section 44 of the Mineral Resources Sustainable Development (Mineral Industries) Regulations 2019 assessing risks associated with submerging the CLA material located in the south-east corner of the mine
- Identifying appropriate performance criteria, counter measures, and monitoring criteria for ongoing monitoring and management of the risks into the future
- Engaging BlueSphere Environmental Pty Ltd to conduct an independent peer review of the entire technical assessment and all of its key elements. The independent peer review identified a number of improvement opportunities during the process which have been actioned and included as part of this final technical assessment, significantly improving the level of confidence in the conclusions reached
This assessment confirmed that environmental risks, including those to surface water and groundwater, remain minimal to the greatest extent feasible in both the short and long term, irrespective of the water body fill strategy.