GHD | Oceana Gold (New Zealand) Ltd | 12552081 | Waihi North 9 A.1 Introduction Site investigations have been carried out to support the assessment of proposed activities for the Waihi North Project (WNP). These investigations were undertaken to: – Refine the conceptual understanding of each area, where changes to the site have occurred since previous studies were completed (particularly in response to changes in site operations, such as dewatering). – Provide sufficient information to assess effects on groundwater and surface water that may be associated with the proposed activities. – The site investigations focused on assessing the geology to up to 80 m depth in the areas of new mine components. Nested monitoring wells were installed to assess groundwater levels, hydraulic gradients, hydraulic conductivities, as well as identify groundwater recharge/discharge areas and surface water/groundwater interactions. Details of the site investigation are provided in the following appendices: – Appendix A: Site investigation methodology. – Appendix B: Borehole data, concluding maps of well locations, noting: Bore series “DH” refers to EGL bores drilling in 1995-1996 across NRS and TSF3 sites. Bore series “P” refers to OGNZL bores drilled for site monitoring at Waihi East (Favona and TSF2). Bore series “GLD” refers to GHD drilled bores at Gladstone. Bore series “AP” refers to GHD and EGL bores drilled at TSF3 for the current assessment. Bore series “WRS” refers to the previous naming convection for NRS. – Appendix C: Groundwater level data (monitoring data, contour maps). – Appendix D: Permeability testing results. – Appendix E: Water quality results – Appendix F: Surface water flow data. TSF3: Additional investigations that have informed the geological understanding include sterilisation drilling undertaken between TSF3 and TSF1A by OGNZL in 2017 and drilling of two new bores (AP21 and AP22) in October 2020. The EGL GFR provides a detailed description of the local geology and origins; Figure 12 of the 2018 EGL report provides the geology for the proposed TSF3 area. The wellhead elevations of the installed groundwater monitoring wells were surveyed by OGNZL and are presented in mRL to the mine datum, which is 1,000 m above sea level (asl). A.2 Review of existing data Groundwater monitoring wells OGNZL have an extensive network of existing groundwater monitoring wells and drill hole data. Existing data was reviewed from the following locations: – DH-series wells, which are detailed in an older report prepared by Engineering Geology Limited (EGL; Volume 2 of EGL,1996); – P-series wells, which are regularly monitored for groundwater levels by OGNZL; and – Other wells (MW, FAV series wells), regularly monitored for groundwater level and water quality. This information was used to inform the 2017 drilling programme described below. Surface water flow and quality OGNZL undertake daily monitoring of flow rates at the Ohinemuri River and the Ruahorehore Stream (a tributary of the Ohinemuri), and regular monitoring at various surface water locations across the wider site. Data is provided in Appendix F.
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