GHD | Oceana Gold (New Zealand) Ltd | 12552081 | Waihi North 49 G.1.1.4 Groundwater model calibration The two SEEP/W model cross sections that represent the current conditions scenario were calibrated to measured groundwater levels and vertical hydraulic gradients. To achieve model calibration, and in line with the conceptual site understanding, hydraulic conductivity and anisotropy of geological units were iteratively adjusted within reasonable ranges based on field investigation data, as well as recharge rates across the ground surface. Additionally, observed groundwater discharge locations and flow gauging results were taken into consideration. The calibrated anisotropy and hydraulic conductivity values for each geological unit are presented in Table G.6. The measured and modelled groundwater levels after calibration are presented in Table G.7. Table G.6 Gladstone Pit calibrated hydrogeological parameters Unit Adopted volumetric water content function(1) Calibrated anisotropy (Ky/Kx) Calibrated hydraulic conductivity (m/s)(2) Justification Ash/Regolith Clayey silt 0.5 (N, E, W) 6.0 x 10-6 (N, E, W) P68s and P61s hydraulic tests(3). P68s water level(3) 1.0 (S) 1.5 x 10-8 (S) GLD01 hydraulic test and water level Rhyolitic Tuff (RT) Clayey silt 0.5 (N, E, W) 2.7 x 10-7 (N, E, W) P79i hydraulic test. P79s and P68s(3) water levels 0.1 (S) 5.5 x 10-9 (S) GLD01a hydraulic test and water level Sandy Ignimbrite Silty sand 0.5 1.0 x 10-5 P79s and P68d(3) hydraulic tests and water levels Volcaniclastic Silty sand 0.3 1.0 x 10-6 Shallow groundwater system water levels. Similar properties to dacite. Hydrothermal Breccia Clayey silt 0.1 5.0 x 10-10 Shallow groundwater system water levels Dacite Sandy clayey silt 0.1 (S) 5.0 x 10-8 (S) GLD03 and GLD03a hydraulic tests and water levels 0.1 (E) 3 x 10-6 (E) Favona wells hydraulic testing(4) Weathered Andesite Silty sand 0.1 5 x 10-9 Shallow groundwater system water levels. P61 hydraulic test(3) Andesite Silty sand 1.0 (E, W) 4.2 x 10-7 Upper end of recorded range away from faults/crush zones (1 x 10-8 – 1 x 10-5 m/s)(3) 2.0 (N, S) Anisotropy reflects expected fracture alignment associated with Gladstone vein. 1. SEEP 2012 materials database 2. N, E, S, W refer to geology on different sides of the pit where material properties differ. 3. URS, 2003. Favona Underground Mine. Assessment of Groundwater Issues. 4. Geomean shallow dacite hydraulic conductivity from hydraulic testing by GHD in 2017 in OGNZL bores P87 & P89 and GLD bores FVN01 and FVN02 (installed by GHD in 2017).
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