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 36 the amount of loss to ground and this will be influenced by fracture filling etc. Further work to understand the significance of stream bed conductance to mine water losses is presently being undertaken by Flosolutions. In reality, surface water losses through stream beds can be largely avoided by maintaining separation of the deep and shallow groundwater systems flow paths i.e. proximity of mining advance to the surface. Assessing the potential for such an effect to occur would be done through shallow groundwater level and surface water flow monitoring and, should it be deemed necessary, mitigated using various grouting techniques to reduce mine inflows. A mitigating grouting strategy is presently being designed by Valenza Engineering and the effectiveness of this strategy will be evaluated by Flosolutions in their 3D numerical modelling to confirm the conclusions made in this assessment. Spring Flow Reduction from Permeable Structures Discharges from springs could be affected by dewatering where the streams cross highly fractured rockmass or veins that are presently contributing to stream flow. Again, the extent to which this can happen is limited spatially being the areas where Rhyolite flow is exposed at the surface. Based on the present level of knowledge, the T-Stream vein is already dewatered to stream level and may contribute to stream flows. The hanging wall rockmass does not appear to result in notable losses or gains based on gaugings and the groundwater level is near stream level based on piezometer data. The EG vein structure is contributing to surface water flows at least from the Warm Spring, but may also have contributions down stream of this location (yet to be confirmed from gaugings). The head driving discharges through these structures is from infiltrating rainfall on the hill slopes adjacent to the streams. One potential option is, therefore, to ensure the shallow flow paths reporting to the steams are maintained and not lost to the mine. In reality, surface water losses from permeable structures can be largely avoided by maintaining separation of the deep and shallow groundwater systems flow paths i.e. how close to the surface mining advances. Assessing the potential for such an effect to occur would be done through shallow groundwater level and surface water flow monitoring and, should it be deemed necessary, mitigated using the typical grouting techniques used to manage mine inflows. A mitigating grouting strategy is presently being designed by Valenza Engineering and the effectiveness of this strategy will be evaluated by Flosolutions in their 3D numerical modelling to confirm the conclusions made in this assessment. Spring Flow Reduction at Headwater Springs Stream gaugings and radon sampling have indicted groundwater is discharging into the streams from locations near the headwaters of the Teawaotemutu Stream and Edmonds Streams as shown in Figure 31. Reviewing the geological model of the area suggests the headwater discharges are springs associated with Rhyolite flow exposures below the contact of the western Rhyolite dome and the overlying post mineralisation Andesite. These localised area of Rhyolite flows are assumed to have a high permeability due to silicification and fracturing, providing the conduits for water to discharge. Groundwater pressures are provided by throughflow from recharge higher up in the catchment as illustrated in Figure 32. There is,
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