v adjacent to the tunnel is proposed near existing groundwater users to ensure their supply remains unaffected. The WUG access transport tunnel will connect to the Willows Farm site at some 300 m depth below ground level at the location of the first vent shaft and commencement of the dual decline. The Willow access tunnel commences from a portal at the surface of the property at an elevation above the groundwater level. The drive then declines and connects with the WUG access tunnel and dual tunnels. The initial part of the access portal and tunnel will be within the shallow groundwater system hosted by the andesite rocks. The andesite rockmass at Willows Farm has been demonstrated to be of low permeability and, therefore, is not expected to drain readily. In the worst case, our assessment indicates that up to 15 m3/d could potentially be lost due to flow paths being diverted from the Mataura Stream while the access tunnel remains dewatered. There are, however, two locations where the Willows access tunnel drives through inferred fault or fracture zones beneath the Mataura Stream. Given there is a potential short term hydraulic connection between the tunnel and stream bed, an assessment of potential surface water losses was undertaken. This assessment has indicated that the short-term losses from a potential fracture zone would be in the order of 35 m3/d and any surface water losses are considered to be small relative to stream flow and would be indiscernible. The vent shaft at Willows Farm is assumed to be sealed off from groundwater as it is advanced. Some groundwater inflow is expected during construction and these volumes have been incorporated into the predicted dewatering volumes needed for the project. No significant drawdown effects are likely to develop from construction of the vent shaft. Monitoring of shallow groundwater is recommended using the existing network of wells to ensure sustained lowering of groundwater levels does not occur and that there is no potential for long term stream loss. The dual tunnels will be driven from the connection at Willows Farm to WUG at depths ranging from 150 m to 480 m below ground level within andesite. The andesite is the same rockmass present elsewhere in Waihi and will have a similar response to dewatering in that it will be limited to areas immediately adjacent to the tunnels. No effects are expected in the near surface groundwater or on surface waters. There are some locations where inferred structural features will be driven through and these may need to be sealed to prevent groundwater ingress as per the same methodology already stated. There are a further four vent shafts at the end of the dual tunnels and the bottom-up construction methodology will limit groundwater inflows. No significant drawdown effects are likely to develop as a consequence of the vent shaft construction. Given the depth of the dual tunnels and mitigating construction methodology, no groundwater monitoring is deemed necessary, nor is proposed over the alignment.
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