3 Seepage management approach The seepage management approach for the proposed UMG TSF is structured as a staged and iterative process. The approach is designed to progressively improve the level of understanding of site hydrogeological conditions, seepage pathways, and system response through successive numerical assessments and targeted data collection. Each stage builds on the outcomes of the previous stage, increasing confidence in seepage prediction and supporting informed decision-making regarding TSF design, monitoring requirements, and, where required, the evaluation and incorporation of mitigation measures. This adaptive staged approach provides a framework to reduced uncertainties and evaluate seepage risk over time, ultimately supporting appropriate design and management responses consistently with the evolving level of site knowledge. An overview of the proposed staged approach is in presented in Figure 3.1, below:
Figure 3.1
Proposed seepage management approach
The SMP identifies the following key stages of Project development as:
Stage 1 – Initial Conceptualisation, Data Gap Identification and Field Investigation Scoping
Establish a preliminary understanding of the hydrogeological and geological setting, including groundwater flow, stratigraphy, and potential seepage pathways, and identify key data gaps, uncertainties, and limitations that influence confidence in this understanding, and scoping field investigation requirements to address these gaps and improve the reliability of the conceptual model.
Stage 2 – Field Campaigns, Numerical Seepage Modelling and Risk Characterisation
Address data gaps undertaking those field investigations identified in stage 1, develop and apply numerical assessments to evaluate potential seepage behaviour, including groundwater responses and migration pathways, and to define the level of seepage risk under the updated conceptual understanding.
Stage 3 – Impact Assessment, Consequence Evaluation and Mitigation Assessment
Assess the potential impacts of identified seepage pathways in stage 2 on groundwater receptors, evaluate implications for consequence categorisation, and determine whether mitigation or management measures may be required.
Stage 4 – TSF Design Refinement and Monitoring Framework Definition
Refine the TSF design and define monitoring and management requirements in response to the assessed seepage behaviour and level of risk identified in stage 3, with the aim of improving control and verification of seepage processes.
Project No PS213278 Mount Morgan Mine - Upper Mundic Gully TSF Seepage Management Plan Heritage Minerals
WSP May 2026 Page 6
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