SECTION 2 Existing Environment 5 dacite intrusives, lava flows and domes, tuff and tuff breccias with intercalated volcaniclastic sediments and local welded dacitic ignimbrite. Older rocks of the Coromandel Group have been emplaced by faulting. These rocks comprise lithic and pumice-rich ignimbrites and local rhyolite and obsidian-rich pumice breccia deposits and tuff. Extensive hydrothermal alteration occurs locally. The rocks will be intercepted at the termination of the tunnel. Tauranga Group sediments infill faulted and erosional depressions. These materials comprise pumiceous alluvial gravelly sand, silty clay and peat; estuarine silt and mud interbedded with ignimbrite; and tephra from the Taupo Volcanic zone and are the host rocks of the Wharekirauponga deposit. A northeast trending fault is inferred in the Waiharakeke valley with a strong north to northeast trending fault block at the tunnel termination. Less prominent faulting may occur along the other valleys and, if present, may be penetrated by the proposed tunnel. 2.2 Regional Hydrogeology Groundwater distribution and movement in the area will be controlled by the topography, together with the stratigraphy and structural trends. Recharge would be expected to occur in the elevated areas with downward moving groundwater. In the deeply incised valleys, upward moving groundwater (discharge) would be expected. The quantum of groundwater movement would depend on the particular type of deposit present, modified by postdepositional structures and alteration and weathering. Where fracturing has developed, such as typically in lavas, groundwater movement may be greater. Fine grained tuffs would have lesser groundwater movement. Fault zones, along which valley systems have eroded lengthwise and downwards, are linear features and are expected to concentrate groundwater and can act as both conduits and/or perpendicular impediments to groundwater movement depending on whether faulting was extensional or compressional. Hydrothermal alteration can result in clay-rich fault zones which can impede groundwater flow. Underground mine development at Waihi and the Waitekauri Valley Golden Cross mine have encountered low groundwater inflows outside the vein systems in hydrothermally altered rocks. Such rocks are expected to be encountered towards the completion of the exploration drive and while zones of altered rock may be encountered along the exploration drive alignment, the majority of the rock units encountered are likely to be unaltered. Faults are expected as the alignment passes beneath valleys and possibly beneath defined stream locations. 2.3 Regional Hydrology The tunnels elements traverse two surface water catchments. The Willows Farm access tunnel and the WUG access tunnel fall within the Waihou surface water catchment area. The Waihou catchment is a large catchment (circa 1,990 km2) extending from Rotorua to the Firth
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