GHD | Oceana Gold (New Zealand) Ltd | 12552081 | Waihi North iv from the WRS and collection drains will be installed within the WRS gully to collect seepage from the rock stack. The WRS is intended to be a short-term facility, expected to be operated and decommissioned within eight years, with all of the rock to be returned to WUG as backfill. Following use, the site will be rehabilitated and largely returned to its natural configuration. Effects associated with development of WRS have been assessed as follows: – Groundwater: The majority of water infiltrating into the WRS will be captured by the seepage drain system positioned at the base of the WRS gully. Localised increase in groundwater levels beneath the WRS is predicted to occur as a result of a small increase in local seepage to the underlying andesite. Localised influence on groundwater quality is expected, however, given the temporary nature of the facility, the effects to groundwater quality are likewise considered to be temporary. – Surface water: The flow from the WRS gully tributary will be captured as part of the WRS drainage system, which is temporarily expected to reduce the flow of the Mataura Stream a small amount. The amount is expected to be unmeasurable within the context of flow gauging error. Seepage from the WRS will flow with groundwater to the Mataura Stream. Small but measurable increases in major ion concentrations, such as sulphate, are conservatively predicted within the stream, with predicted trace elements increases not expected to be measurable. No parameter concentrations are expected to exceed the RWQC. – Water users: No water users are expected to be measurably affected by the WRS seepage, owing to the minor discharge volume and significant dilution within surface water. – Monitoring and management: As with other rock storage facilities, monitoring of groundwater, surface water and drainage water quality is recommended to validate the assessment findings and identify potential issues associated with water quality. Cumulative effects to surface water The findings of this assessment of WNP mine components contributes to the assessment of cumulative effects of WNP discharges to the Ohinemuri River, which is provided in the GHD (2021a) Water Management Report.
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