SECTION 3 Groundwater Effects Assessment – WUG Access Tunnel 10 Figure 7 Andesite Piezometric Surface Map Groundwater Levels The water table surface shown generally reflects the topography, except to the east of Martha Pit where the water table has been affected by drainage due to the exposure of younger volcanic rocks in the pit. At the location of the WUG access tunnel, the inferred water table is relatively flat and lies between approximately 1110 m RL near Union Hill rising to 1120 m RL at Wharry Road. At the decline section of the tunnel, in the vicinity of the WTP, groundwater monitoring (P60, P61, P64, P75) indicates a lowered or absent water table in the near surface and depressurised conditions in the andesite due to existing mine dewatering. Hydraulic Gradients The groundwater flow direction in the area of the southern half of the WUG access tunnel is to the west and the tunnel will be perpendicular to the groundwater flow direction. In this area the hydraulic gradient is relatively flat being around 0.001. As the WUG access tunnel passes beneath the hill approaching Willows Farm, the hydraulic gradient steepens to around 0.04. A downward vertical gradient is expected throughout much of the tunnel alignment, with an upward gradient and discharge zone likely near the Ohinemuri River.
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