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 31 4. Assessment of Effects 4.1 Groundwater Inflows In order to provide an understanding of the likely volume of inflows encountered during mining, numerical groundwater modelling has been undertaken using SEEP/W. The modelling assumes the EG vein is mined to an elevation of -300 m RL and the T-Stream Vein mined to an elevation of -300 m RL. Based on the veins’ lengths being 1,000 m, the groundwater modelling indicates short term inflows of up to approximately 5,200 m3/d reducing to approximately 2,400 m3/d. These values are generally consistent with the volumes of groundwater encountered during mining of the Favona deposit (4,500 m3/d reducing to 1,500 m3/d) in Waihi, which has similar dimensions. The Golden cross mine, the closest analogous deposit to Wharekirauponga, is understood to have been dewatered at similar rates to this. We note that these inflow volumes have been calculated adopting a rockmass permeability of 8x10-8 m/s, essentially representing an unfractured rockmass. The modelling has shown, however, that the problem is sensitive to the adopted rockmass permeability. These inflow volumes should be taken as preliminary and verified following the development of the 3D groundwater- surface water model by Flosolutions. 4.2 Effects on the Groundwater Resource The Wharekirauponga vein system is not within any specific aquifer management area identified by the Waikato Regional Council. For the purpose of this assessment, we have assumed the take to be from the Otahu catchment and an assessment of groundwater availability has been determined as shown in Table 8. Table 8 Otahu Catchment Groundwater Availability Deep Aquifer Recharge (10% Rainfall) 15,407,000 m3/year a Availability (35% Recharge) 5,392,450 m3/year Existing Allocated 0 m3/year S14 Takes (10%) 539,245 m3/year Dual Tunnel Section (9,200 m3/d x 365 days) 3,358,000 m3/year Mine Dewatering (2,500 m3/d x 365 days) 1,277,500 m3/year Allocation Remaining 217,705 m3/year a - Deep non-coastal aquifer Based on this assessment, there is sufficient groundwater available for the proposed takes to be granted. This assessment of groundwater availability should be taken as an interim assessment pending the results of 3D modelling by Flosolutions. 4.3 Drawdown Effects The 2D numerical modelling undertaken enables initial predictions of how the rockmass might depressurize as a result of dewatering the veins and whether groundwater levels will change in different geologic units. As can be seen from Figure 28, the model predicts that when the EG
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