www.valenza-engineering.com 381_R_04_Rev 0 OGNZL_WUG_Phase1_Conceptual_Mitigation 36 6.3.1.1. WUG ACCESS TUNNEL Groundwater control within the access tunnel will adopt the standard instrumentation, probing and grouting sequence presented in Figure 6-4. A series of detailed patterns and methodology will be provided once the inflow assessment from the Phase 2 modelling is complete and predicted pre- and postmitigation flows are better understood. These strategies have been implemented successfully on numerous occasions as illustrated in section 6.6. 6.3.1.2. WUG PRE-DEVELOPMENT Predevelopment instrumentation, including any works that can be completed from surface positions, probing, grouting and dewatering, will be mainly completed from these locations and will follow the sequence below. • Place shallow instruments between the receptors (surface water features) and the proposed development zones from existing drill pads. • Use shafts and inclines to grout in high-K zones, concentrating on the EGV area above the upper mine stope extent. Complete fan grouting pattern (variable dip and azimuth drillholes) to cover vein intersections. Adopt multiple intersections and grouting lengths within each drillhole to cover EGV stringers. T-Stream vein system is not targeted at this stage, but this may change depending on further assessment and needs to be considered for internal reporting within the future mining schedule. Directional drilling is unlikely to provide any benefit but may be considered dependent on drilling contractor capabilities (i.e., to allow better targeting of grout placement). • Depressurisation will be completed using drain holes as required. This measure is expected to be limited in time and location during the pre-development phase. Detailed monitoring and mitigation measure implementation programs will be defined as part of the Phase 2 works, combining the analysis of additional monitoring and testing data with the findings of the numerical modelling to be produced by Flo Solutions. 6.3.1.3. WUG OPERATIONAL CONTROL Operational controls will follow the program developed as part of the OM and will meet the following requirements: • Monitoring of pore pressure, inflows and sampling at a frequency adapted to the rate of progression of the mine development. Installation of new instruments ahead of the development within probe holes (instruments will be installed from dedicated instrumentation cuddies). • Completion of dewatering and management of seepage as required (using a combination of deep dewatering wells and sump pumping. • Implementation of secondary and tertiary grouting based on alert levels defined as part of the trigger plan developed in the TARPs. Pre-development grouting is not expected to require substantial depressurisation as static conditions are likely to be encountered, except at the face or within chambers which will have been grouted before.
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