www.valenza-engineering.com 381_R_04_Rev 0 OGNZL_WUG_Phase1_Conceptual_Mitigation 29 6. GROUNDWATER MITIGATION MANAGEMENT 6.1. GROUNDWATER CONTROL STRATEGY The mitigation 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 (OM) developed in soil mechanics and geotechnics by Terzaghi (1943), Rankine and Peck (1969). The observational method is a framework “wherein construction and design procedures and details of a geotechnical engineering project are adjusted based upon observations and measurements made as construction proceeds” (Eurocode 7, 2012). This method has been successfully and widely applied in the civil engineering and mining industries since its development. Applications to dewatering, drainage and grouting in complex ground conditions such as exist at WUG are not uncommon and are described in CIRIA 185: “The Observational Method in ground engineering is a continuous, managed, integrated, the process of design, construction control, monitoring and review that enables previously defined modifications to be incorporated during or after construction as appropriate. All these aspects have to be demonstrably robust. The objective is to achieve greater overall economy without compromising safety.” (ref 18). This method will be combined with the conceptual and numerical modelling approach developed in the Australian groundwater modelling guidelines, AGMG (ref 19). The AGMG describes the modelling process as “one of continual iteration and rereviews rough a series of stages. For example, there is often a need to revisit the conceptual model during the subsequent stages in the process. There might also be a need to revisit the modelling objectives and more particularly reconsider the type of model that is desired once calibration has been completed.” The feedback loop process described in the AGMG and applied to the WUG project is presented in Figure 6-1. The application of the combined OM described in the Eurocode and the AGMG to the WUG project can be summarised as follows: Phase 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 and Numerical Modelling (NM) methods. Define initial mitigation concepts (Phase 1) and report on overall strategy. Phase 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 NM and build a robust and defensible baseline. 5. Refine the conceptualisation and confirm the connectivity of aquifers and pathways. Define detailed mining and mitigation approach aligned with mine planning. Report on detailed methods and develop TARPs and OM trigger plans. Phase 3: Installation of operational monitoring and implementation of pre-development mitigation measures.
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