GHD | Oceana Gold (New Zealand) Ltd | 12552081 | Waihi North 23 . 2.5 Water resource users Registered bores, consented groundwater and surface water takes and any other identified water resource users have been considered within the individual assessments for GOP (Section 3; Figure 3.11), NRS (Section 4; Figure 3.11), TSF3 (Section 5; Figure 5.11) and WRS (Section 6; Figure 6.7). It is noted that an assessment against the national environmental standards for sources of human drinking water (NES-DW, 2021) has not been included as there are no registered drinking water supplies (that provide for more than 501 people) located within the assessed envelope of effects for the proposed activities of the WNP. 2.6 Performance of existing TSFs Seepage from the existing TSFs is authorised as part of the mining consents, subject to conditions. OGNZL undertakes extensive quality monitoring across the site, and the results are reviewed and interpreted by GWS (e.g. GWS, 2019 and 2020; OGNZL, 2020). Overall, the existing TSFs are reported by GWS to have generally demonstrated compliance with consent conditions: – TSF2 operated between 1989 and 1999. Groundwater discharges from this facility are interpreted by to go to the Ohinemuri River. – TSF1A was initiated in 2000 and is still in use. Groundwater discharges from this facility are inferred to go to the Ruahorehore Stream. – Monitoring includes continuous or routine sampling of groundwater monitoring wells, TSF2 pond discharge, underdrain collection systems (including leachate) for the existing TSFs and surface water for each component of the mine site. The results are compared against trigger levels specific to each sampling location. – Surface water monitoring locations are shown in Figure 2.6. The consent conditions for any watercourse (river, springs, wetlands) require that the water quality within the Ohinemuri River meets the receiving water quality criteria (RWQC) as set out in Table 2.3 and defined in the existing site discharge consent (WRC, 1999). A review of the data presented within the GWS (2019 and 2020) and OGNZL (2020) reports by GHD indicates the following: – Some toe drain and monitoring well sample results periodically exceed trigger levels for some parameters, indicating a change from historical conditions. Periodic increases in parameters are not unexpected given the significant changes (i.e. mining activities) in the surrounding environment. These trends are expected to stabilise and water quality improve once active disturbance lessens. Ultimately, no trends are considered to indicate failure of containment of the tailings or rock facilities. – Concentrations of trace elements in groundwater tend to decrease with increasing distance from the TSFs, which suggests that in-ground conditions promote attenuation such as the precipitation of iron hydroxide minerals and adsorption reactions. Such processes are key to limiting the extent to which contaminants released from mine tailings and mineralised rock may be seen in groundwater. As such, the area of impacted groundwater is limited to within OGNZL land. – Long-term monitoring of the Ohinemuri River indicates that changes in the river water quality have occurred as result of the WTP discharge, primarily as changes in the major anions and cations (e.g. sulphate, bicarbonate, chloride) rather than trace element contaminants. It has been interpreted that river water quality remains unaffected by discharges to groundwater from the existing storage facilities. – Periodic exceedances of the receiving water quality criteria (RWQC) (Table 2.3) have occurred along the Ohinemuri River (including upstream of the treated water discharge). However, these are infrequent events that do not indicate long-term exceedances as a result of mine related discharges.
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