B-2 – Area 2 - Assessment of Environmental Effects 16 in the Waihi Ecological District. Boffa Miskell (2022b) consider the discrete Mataura wetland to have ‘Moderate’ ecological value. 2.11 GEOLOGY The geology of the site is described in WSP (2022a) a copy of which is provided in Part H of these application documents. Investigative drilling along the alignment of the decline to the Dual Tunnel, as well as various other test pits and boreholes encountered weak, highly weathered andesite or tuff and strong to very strong andesite. This rock is overlaid by fine grained soils comprising weathered volcanic ash, residual weathered volcanic rock and colluvium. At the proposed site of the Willows Portal, the ground conditions encountered through test pits boreholes and outcrops were fine grained soils to 1.0 m below ground level (‘BGL’), then highly weathered andesite to 5.0 m BGL, with moderately weathered, moderately strong andesite, lapilli tuff and tuff breccia at more than 5.0 m BGL. At the proposed ventilation raise site within the Willows Road Farm, a borehole drilled to 231 m BGL initially encountered weak to moderately strong volcanic rock, then strong rock from approximately 130 m BGL to the end of the hole. At the terraces onsite nearer the Mataura Stream, WSP (2022a) report alluvial soils including gravels, sands and silts, often containing boulders of volcanic rock. 2.12 HYDROGEOLOGY The sites hydrogeology is described in GWS (2022), WSP (2022a) and GHD (2022b), copies of which are provided in Part H of these application documents. The site’s hydrogeology has been investigated by way of test pits and some 20 machine drilled bores at the likely locations of site infrastructure, shown below. The conceptual hydrogeologic model for the site shows that interflow makes the largest contribution to surface waters, with some baseflow sourced from the rockmass. The drillhole to 231 m BGL that was developed at the site of the proposed ventilation raise recorded groundwater at around 10 m depth. WSP (2022a) estimate that this groundwater level is generally consistent across the site. The estimated assumed average rock mass hydraulic conductivity is approximately 2.5 x 10-8 m/s and fault zones were indicated to have hydraulic conductivity of 1.0 x 10-5 m/s.
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