EGL Ref: 9018 22 June 2022 Page 11 WAI-985-000-REP-LC-0006_Rev0.docx This report shall only be read in its entirety. rhyolite). The deep andesite, which outcrops to the west of the Ohinemuri River, is present below 200 m depth at the NRS due to the dip of the unit and faulting (Golden Valley Fault). All wells at NRS are installed in the shallow system, with some paired between the water table and deeper within the shallow system (up to 25 m bgl; referred to as “deeper” wells or groundwater in this section), to provide an understanding of vertical hydraulic gradients beneath the site. Overall, whilst slight differences in groundwater are apparent between the shallow and deeper groundwater, it is interpreted that this groundwater collectively discharges to the Ohinemuri River west of the NRS. The conceptual groundwater model developed by GHD is focused on the shallow system to 25 m depth. 5.2. Groundwater system Monitoring wells installed at the proposed NRS site are located between 100 m to 770 m east of the Ohinemuri River. The majority of monitoring wells at NRS have recorded groundwater levels at less than 5 m below ground level (bgl), with some locations within 10 m bgl (1,095 – 1,106 m RL). The groundwater levels in the well pair located at the foot of the rhyolite dome (WRS03 and WRS03a) 770 m east of the river, record groundwater levels much higher than the rest of the NRS wells (approximately 1,130 m RL) due to their elevated location. Groundwater recharge is expected to occur from rainfall infiltration over the elevated rhyolite dome, as well as across the alluvial river plain. Recharge to the elevated rhyolite drives the upward vertical groundwater gradients at the base of the hill, east of the proposed NRS footprint. Groundwater and surface water levels recorded in a number of locations across the site are summarised below: • The water table nearest to the Ohinemuri River and tributary show the greatest response to rainfall. The rapid response of groundwater is likely to be due to the higher permeability of the shallow geological units (completely weathered to residual volcanics in wells WRS04, WRS05, WRS08). • Conversely, near tributary location TB1a the deeper groundwater levels demonstrate the greatest response to rainfall when compared to the water table (DH05/DH05a/WRS06). This is considered to be a function of the higher transmissivity of the ignimbrite paleochannel and underlying boulder and cobble alluvium at depth, providing a preferential groundwater flow pathway at depth (WRS06 and DH05a) and allowing transmission of recharge from higher in the catchment. The water table and deeper groundwater contours demonstrate the influence that this preferential pathway has on groundwater flow directions. • Downward vertical gradients are observed near the Ohinemuri River and along the tributary, with deeper groundwater inferred to be recharged in these areas. The strongest downward vertical gradients during summer baseflow conditions are observed south of the site near the existing northern stockpile. Milder downward gradients are observed closer towards the Ohinemuri River, where groundwater levels and vertical gradients suggests that both shallow and deeper groundwater is expected to be discharging to the river (WRS04 and WRS05).
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