GHD | Oceana Gold (New Zealand) Ltd | 12552081 | Waihi North 38 . Deep groundwater levels Water levels in the deep groundwater system have been recorded as below and are summarised in Table 3.3. Well locations are presented in Figure 3.8. – A groundwater level range of 1,064 – 1,089 mRL was recorded in the monitoring wells in Table 3.3 prior to dewatering of the Favona system, with downward vertical hydraulic gradients recorded in areas of elevated topography as the shallow groundwater provides recharge to the deep groundwater system (Figure 3.9). – Upward vertical hydraulic gradients between the shallow and deep system have been recorded at lower topographic elevations adjacent to the Ohinemuri River (GLD04 well series). This well series was installed to replace the P68 well series due to damage and concerns regarding well integrity. Previous groundwater levels recorded at P68, prior to dewatering of the Favona vein system, recorded a downwards vertical hydraulic gradient between the shallow and deep system. – Deep groundwater piezometers within and/or immediately adjacent to mineralised vein zones north and northeast of the proposed Gladstone Pit (P64D, P64A, P60) are dry, reflecting the influence of local mine dewatering. – Immediately west of the proposed Gladstone Pit, and slightly offset from the Gladstone vein system (P79 series), the deep groundwater shows gradual, long-term reductions in levels, reflective of a minor influence of dewatering. Figure 3.9 provides the long-term water level record for the P79 well series illustrating this response. – Deep groundwater levels and flow directions from 1983 are presented in Figure 3.8, indicating that deep groundwater levels in the vicinity of Gladstone were approximately 1,100 mRL with a flow direction towards the west. Groundwater level data and vertical hydraulic gradients are presented in Appendix C. Table 3.3 Deep groundwater system well properties Piezometer Screen (mRL) Hydraulic conductivity (m/s) Approximate water level (mRL) Comments P60 1,043 – 1,029(1) 5x10-7 (1) 1,065 prior to Favona dewatering.(1) Recorded as dry from 2005. Installed in altered andesite west of Favona vein system to monitor for dewatering effects. Collapsed 2011. P61 1,089 – 1,076.5(1) 7x10-9 (1) 1,084 Installed in altered andesite west of Favona vein system to monitor for dewatering effects. No impacts have been observed from dewatering. Obstructed 2019. P64I(2) 1,086 – 1,085.5(1) - 1,098.5 Installed in shallow groundwater system above Favona vein system. P64D 1,069 – 1,063(1) 6x10-9 (1) 1,078 prior to Favona dewatering.(1) Dry from 2006. Installed in altered andesite to monitor Favona vein system. P64A 960 – 930 (open hole) 5x10-4 (1) 1,064 prior to Favona dewatering.(1) Dry from 2006. Installed within Favona vein structure. No significant water loss occurred during drilling of this well until deep into the vein system. P79d 1,050 – 1,047 4x10-7 1,078 – 1,094. Declining average conditions. Installed in altered andesite to monitor effects from Moonlight vein system. GLD04d 1,027 – 1,021 - 1,085 Installed in andesite along Gladstone vein strike adjacent to Ohinemuri river. Andesite highly fractured. 1. URS, 2003. 2. This bore is not installed in the deep groundwater system but has been included to assist with CGM discussion.
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