SECTION 5 Conclusions & Recommendations C:\D Data\GWS C Drive\GWS\Client Files\1344 OGL - WKP\4 Deliverables\WKP Final Draft Report\June Report\WAI-985-000-REP-LC-0030. Final_Rev_0.docx 41 5. Conclusions and Recommendations 5.1 Conclusions Exploration drilling and mapping of the Wharekirauponga deposit has provided a significant database of geological and geotechnical information that provides a detailed characterisation of the mineralised structures and host rocks. Extrapolation of hydrologic and hydrogeologic testing data collected has enabled a preliminary Conceptual Groundwater Model to be developed that provides the basis for understanding what effects, if any, might occur from the proposed dewatering of the vein system. At a catchment scale, the CGM concludes that where post mineralisation Andesite is present, a shallow groundwater system is present and dewatering effects from the underlying rockmass do not propagate to the surface. That is because the Andesite has a naturally low permeability that retains infiltrating water. There is also a weathering profile on the surface of the underlying Rhyolite rocks that acts as an aquitard at the base of the Andesite, limiting the ability for shallow groundwater to move downward. Where Andesite is present at the surface, streams are perched on these units and are not in contact with the deeper groundwater system, meaning no effects on surface water can take place from deep dewatering. It is only where Rhyolite rocks are present in the near-surface that dewatering effects have the potential to develop where the shallow and deeper groundwater systems are connected. If deep dewatering affects affect the shallow groundwater system, the potential to affect surface water flows exists. At a catchment scale, the area of Rhyolite rocks exposed at the surface is limited (circa 1.5 km2) and, therefore, so too is the spatial extent to which any potential effects might develop. The CGM emphasises that it is the shallow groundwater connections to surface waters that are the key mechanism for effects that require further consideration for the project. In that regard, the following effects are seen as important to further understand: - The significance of losing the warm spring discharge into the Wharkirauponga Stream for the duration of mining and what this means to catchment hydrology, surface water chemistry and the ecology. - Stream bed losses and losses to surface water from permeable structures are mechanisms that could result in depletion of stream flows. This assessment has indicated that these mechanisms are unlikely to result in any discernible reduction in stream flows and that options to avoid or mitigate such effects exist. Further quantification of this potential effect is being undertaken by Flosolutions and mitigation is being designed by Valenza Engineering. - Loss of headwater spring flows due to deep rockmass depressurisation has been identified as a potential risk to surface water flows. This initial assessment has indicated that the Teawaotemutu Stream and Thompson Stream headwater springs are unlikely to be affected by deep dewatering due to being hydraulically separated by low permeability rocks. The Edmonds Stream headwater springs, being along strike of the
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