381_M_05_Rev0 - WUG Monitoring and Testing Program 2 The approach proposed addresses the immediate and long-term gap, with the acquisition of additional baseline information, the definition of key parameters such as streambed conductance and vertical gradients and the introduction of induced/natural stress tests furthering the current understanding on aquifer connectivity and parameters. This memorandum summarises the key elements of the proposed mitigation strategy and the approach suggested by the group of groundwater experts assisting OGNZL for further data acquisition and ultimately understanding of inter-connectivity of the system and therefore potential impact of the mining operation. 2. GROUNDWATER MITIGATION MANAGEMENT 2.1. GROUNDWATER CONTROL STRATEGY The analysis of mitigation factors of potential surface water and groundwater impacts for the WUG project will be completed using industry best practice frameworks and will adopt principles described in the Observational Method (OM) and Australian groundwater modelling guidelines (AGMG) referred to in the Phase 1 report (381_R_04, May 2022). The application of the combined OM described in the Eurocode and the AGMG to the WUG project can be summarised as follows: Stage 1: Preliminary data acquisition and overall mine concept development 1. Initial preliminary data acquisition (monitoring and testing). 2. Conceptualisation, and assessment of inflows and drawdown using Analytical modelling methods. Define initial mitigation concepts (Phase 1) and report on overall strategy. Stage 2: Data refinement, numerical modelling and mitigation measures refinement 3. Conduct preliminary numerical modelling, and assess main inflow zones, expected drawdown impact and water budget within hydrogeological units and at model boundaries. 4. Install monitoring instruments in zones of potential impacts determined by Numerical Modelling (NM) methods and build a representative baseline. 5. Refine the conceptualisation and confirm the connectivity of aquifers and pathways that connect to the surface water system. Define detailed mining and mitigation approach aligned with mine planning. Report on detailed methods and develop Trigger Action Response Plans (TARPs) and OM trigger plans. Stage 3: Installation of operational monitoring and implementation of pre-development mitigation measures. 6. Conduct probing and hydraulic testing before and during the development of the tunnel and mined area infrastructure to confirm zones, approaches and sequences for water management measures. Install operational instrumentation. 7. Conduct pre-development grouting and depressurisation and activate TARPs and OM framework developed in Phase 2. This phase of work corresponds to the implementation of TARPs during the exploratory and decline construction phase, where the grouting is implemented when trigger levels in the periphery of the infrastructure voids are exceeded until measurements stabilise.
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