SECTION 7 Northern Rock Stack C:\D Data\GWS C Drive\GWS\Client Files\1344 OGL - WKP\4 Deliverables\WUG Effects Summary\June 2022\WNP Groundwater Effects Summary_Final_Rev_0.docx 28 7.4 Summary of Effects Groundwater Diversion During construction, groundwater is expected to be intercepted during construction of the uphill diversion drain (240 m) at the south-eastern boundary of the NRS of up to 70 m3/d. This water would otherwise report to the Ohinemuri River. The effects associated with this diversion are considered to be immeasurable. Land Discharge Effects Once constructed the NRS drainage system will collect most of the leachate as shown in Figure 31. The assessment undertaken indicates the proportion of leachate not captured by the containment system that will discharge to land is between 70 – 100 m3/day during the operational scenario reducing to 50 m3/d post closure. This will impact groundwater quality and is predicted to migrate to the Ohinemuri River. Figure 31 NRS Section Following Closure (From GHD 2022) The land discharges have been assessed by GHD with respect to their effects on groundwater and surface water quality and are stated to be within the RWQC at the compliance point in the Ohinemuri River. This is principally due the the high flows in the River having significant dilution potential. Monitoring Monitoring of groundwater levels and quality is proposed as well as surface water flow gaugings and water quality. Specific requirements will be detailed in an overarching Water Monitoring and Contingency Plan. The plan will include requirements for baseline monitoring (for comparative analysis to provide a degree of confidence in the assessment), trigger levels, and contingency measures to manage any potential exceedances.
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