www.valenza-engineering.com 381_R_04_Rev 0 OGNZL_WUG_Phase1_Conceptual_Mitigation 48 9. CONCLUSIONS & RECOMMENDATIONS This preliminary, Phase 1, concept report covers the definition of the conceptual methods to be applied to avoid mine dewatering impacting surrounding shallow groundwaters and surface waters. It is based on the analysis of the current conceptual hydrogeological and geological models and simple analytical models. This phase of work will be followed by the review of the numerical model and the confirmation of the implementation strategy in the Phase 2 work program. The avoidance of 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 and modified adaptive management approaches to be developed (Phase 2). This method will be combined with the conceptual and numerical modelling approach developed in the Australian groundwater modelling guidelines. The application of the proposed method is summarised as follows: 1. Initial preliminary data acquisition (monitoring and testing). 2. Conceptualisation, and assessment of inflows and drawdown using Analytical and Numerical Modelling (NM) methods. Define initial mitigation concepts (Phase 1 and Phase 2). 3. Install monitoring instruments in zones of potential impacts determined by NM and build a robust and defensible baseline. 4. Refine the conceptualisation and confirm the connectivity of aquifers and pathways. Define a detailed mining and water management approach aligned with mine planning. 5. Conduct probing and hydraulic testing before and during construction of the tunnel to confirm the zone and sequence of water management measures. Install instrumentation. 6. Conduct progress grouting and drainage within tunnels and drive. If confirmed by modelling, complete localised depressurisation and grouting of the upper horizons of the mine before mining. Analyse monitoring data and adapt measures progressively. 7. Once pathways are sealed at a sufficient level, implement dewatering measures (deep hole dewatering, sump pumping), drainage and depressurisation. 8. Apply a progressive (P) modelling (M) and mitigation measures design (D) and implementation (I) strategy consistent with the OM. Monitor impact and conduct secondary and tertiary grouting from UG infrastructure as required. The preliminary groundwater control and mitigation measures applicable to the WUG project are as follows: • Monitoring and Instrumentation (from the surface (if available) and underground locations, using qualitative and quantitative methods, including water sampling, pore pressure and mine inflows monitoring). • Probing (pilot hole before development using diamond drilling methods, without recourse to directional drilling, and advanced probing with development jumbo during mine development). • Pre-development grouting from surface pads, underground chambers, declines and drives. • Secondary grouting during development, associated with depressurisation (drain holes) and dewatering (sump pumping, dewatering wells equipped with submersible pumps).
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