SECTION 4 Assessment of Effects 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 38 information available at this time, the western Rhyolite flow is of low permeability and the structure is compartmentalised with respect to groundwater flow, with the spring water sourced from up hydraulic gradient. On that basis a reduction in spring flow at the Teawaotemutu Stream headwater springs is not expected. The Edmonds Stream headwater springs are along the strike of the EG vein system and are potentially more hydraulically connected than elsewhere. We note, however, that the flow at these headwater springs from deep groundwater contributions is small (1.5 L/s) compared to the Teawaotemutu Stream headwater spring flows. A reduction in such a small spring flow is considered to be immeasurable at a catchment scale. The headwater springs at the Thomson Stream are not expected to be affected by dewatering of the Rhyolite rockmass as these springs emanate from post mineralisation Andesite in which the stream is bedded. In summary, this assessment indicates that there is some limited potential for mine dewatering to affect headwater spring discharges locally. Whether a reduction in spring flow is observed is a function of the assumed rockmass permeability with the overall catchment drainage pattern will also playing a part in whether deep, down gradient depressurisation effect propagate more widely. This is presently the subject of ongoing 3D numerical modelling work being undertaken by Flosolutions. Cessation of Warm Spring It is expected that the warm spring discharging from the EG vein on the southern side of the Wharekirauponga Stream bank will cease for the duration of mining, resulting in an estimated loss of surface water flow of at least 3 L/s. Based on the May 2020 low flow gauging event at WKP1 of 68 L/s this loss would represent <5% of the catchment baseflow. We note, however, gauging site WKP1 does not include flows from the sub-catchment to the north of Wharekirauponga, so the effect on the total catchment water balance would be less than that and likely within the accuracy of the gaugings. Given the higher mineral load of the spring discharge compared to surface waters, the quality of the stream water may improve modestly as a result of the spring discharge ceasing. Regolith Soil Water Aside from deep groundwater inputs to surface waters, interflow from Regolith soils is the other input to surface waters and is by far the most dominant input. Based on the gaugings undertaken, interflow could contribute 90% of the surface water flows. This water will continue to discharge into the catchment and will be unaffected by mining as it is a function of climatic conditions and sits in the unsaturated zone above the permanent water table as shown in Figure 33. Regolith water and interflow are not expected to change as a consequence of dewatering the Rhyolite rockmass.
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