Background Numerical groundwater modelling has been undertaken to assess a number of the project components to assess groundwater inflows and extent of drawdown associated with dewatering. This included the vent shafts for the WUG project, defects at a shallow elevation that could create a connection to the Mataura Stream and the dual tunnels. The following provides a high level overview of the SEEP/W numerical modelling undertaken. Vent Shaft Models Model Setup The vent shaft models were set up as being a large diameter well using an axis-symmetric solution. Each model replicates a shaft of differing elevation and depth as specified in Table D1. Table D1 Ventilation Shaft Metrics The model domain is 600 m wide and has a grid spacing of 20 m x 20 m. A typical model section is shown in Figure D1. Figure D1 Typical SEEP/W Shaft Model Setup Material Properties The shafts were all simulated to have a hydraulic conductivity of 2.5 x10-8 m/s, this being the geometric mean of the packer test results undertaken at Shaft 1 location characterised by WNDD007. Shaft Location Chainage Depth Diameter Ground m m m m RL Shaft 1 Willow Farm 1400 250 3 1225 Shaft 2 DoC Land 4000 400 3 1340 Shaft 3 WKP (Egress) 6400 110 3 1275 Shaft 4 WKP (RAR) 6900 200 5 1210 Shaft 5 WKP (FAR) 7000 300 3 1215
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