SECTION 4 Groundwater Effects Assessment – Willows Farm Access Tunnel 25 4.3.6 Potential for Effects on Groundwater or Surface Water Quality During tunnel dewatering there will be no consequential change in groundwater quality due to the water take. Groundwater will seep into the tunnel at a low rate, with cement grouting reducing localised inflows. The groundwater that flows into the tunnel will be pumped back to the treatment plant in Waihi and discharge to surface waters at a permissible standard. Once the tunnel is no longer required rewatering will occur and the groundwater system will return to its previous state. Some groundwater will come into contact with the cement grout and backfilled wasterock, however this is not expected to change the overall quality in the aquifer due to the limited contact area relative to the system throughflow. This statement is similarly applicable to the vent shaft following construction. In summary, no adverse effects on groundwater quality are expected from the tunnel. Given the limited connections between groundwater and surface waters, and the lack of expected effects on groundwater, the effects on surface water quality is similarly expected also to be negligible. 4.3.7 Potential for Saline Intrusion The access tunnel is 7 km from the ocean, which is too far for any effect to develop and the elevation is above sea level within Willows Farm. For these reasons we consider the potential for saline intrusion to occur to be less than minor. 4.3.8 Potential for Ground Settlement Effects The groundwater drawdown relationship to distance is shown for the Weathered Tuff is shown in Figure 20. The weathered tuff is considered relevant to assess given the andesite rock is a largely incompressible media. Figure 20 Distance Drawdown for Weathered Tuff
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