SECTION 4 Willows Farm Infrastructure C:\D Data\GWS C Drive\GWS\Client Files\1344 OGL - WKP\4 Deliverables\WUG Effects Summary\June 2022\WNP Groundwater Effects Summary_Final_Rev_0.docx 15 Figure 17 Willows Farm Conceptual Hydrogeologic Model 4.4 Summary of Effects Groundwater Inflows This assessment indicates that the decline would generate in the order of 500 m3/d groundwater from the rockmass during construction. Drawdown Extent With respect to the portal and tunnel decline, no associated drawdown effects are expected to manifest based on the mitigating construction methodology where major inflows will be sealed off. Where the geologic model indicates potential structural features (faults or fracture zones) short term drawdown effects may develop however assessment has indicated no discernable effects on surface water flows. The vent shaft is positioned within low permeability rock and due to this and the construction method, inflows are limited as are the associated drawdown effects. No effects on surface water are expected as a results of the vent shaft construction. Other Effects Related to the Take Given the absence of drawdown effects associated with development of the tunnels, no effects are expected on surface waters, other groundwater users, plant growth, other aquifer or water quality. Effect on Water Quality Once the tunnels are 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 rock, 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 and therefore surface water quality are expected from the tunnels while dewatered or following closure.
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