GHD | Oceana Gold New Zealand Ltd. | 12552081 | Waihi North Project E-5 WTP 1.79 0.8 Cyanide Notes: Martha pit is accounted for in the dewatering calculations, silt ponds are not included in this summary Runoff from the TSF1A, TSF2 and TSF3 embankments is captured within the collection ponds as defined in Table 1 and is treated as minewater in the WTP. Where the river flow is above the 80th percentile or when the ponds are re-designated as silt ponds via consent they can overflow to the river if full. The process area ponds collect runoff from the catchments around the WTP and processing plant area and are treated as cyanide water in the model (note this is a conservative assumption since in actuality treatment through the minewater stream generally applies). Overflow of these ponds is not permitted before the date specified in the model. There is provision on site for water to be pumped between these ponds and with consideration to this the process area ponds’ volume and catchment areas are amalgamated in the model. During high rainfall events water from the process area ponds can also be pumped into the active TSF as an emergency storage facility, then later treated as decant water. River Flow River flow data is derived using the Australian Water Balance Model (AWBM) (Boughton 20044) based on the measured daily rainfall data. The model is calibrated to Ohinemuri River and Ruahorehore Stream flow data measured at the Frendrups and Ruddock gauges between 28/3/1985 and 19/4/2017. Calibration of the model places emphasis on periods where flow rates affect the consented discharge regimes. In addition, river flow data is also derived for the Mataura Stream using the AWBM. The calibration of the Mataura Stream with the GoldSim generated flow is based on the monitoring data during 2020 and 2021 (refer Section 3.2.1). Four separate discharge locations (O1 to O4 in Figure 2) are modelled to maintain clarity of the discharge from each source, though these are not necessarily representative of site layout. The WTP discharges into O1. Overflow from the TSF’s, collection ponds and process area ponds discharges into O2, O3 and O4 respectively and the resultant river flow is defined at O5. WUG Groundwater Inflow volumes of groundwater into the WUG Access Tunnel, WUG tunnel to the processing plant area and WUG Mine are detailed in GWS, 2022. The WBM assumes this water is directed directly to the WTP where it is treated as Priority One water. MUG Dewatering and Dust Suppression The WBM allows dewatering to be represented by two methods. The first method specifies a mean annual dewatering rate and the WTP aims to treat the flow where capacity allows. Where the WTP does not have the required capacity the excess is identified as a deficit on the extraction target. A cumulative deficit is indicative that the chosen pump rate is too low to meet dewatering targets. The second method calculates dewatering based on a model of the Martha underground water system and a target dewatering level. A maximum dewatering pump capacity is specified and the model aims to meet the dewatering targets within the constraints of the dewatering pump capacity and the WTP discharge capacity. Drawdown of the water table is determined by the actual volume of water extracted, such that the pumps and WTP will work at full capacity until the target level is reached. 4 Boughton, W. 2004. The Australian water balance model, Environmental Modelling & Software. 19(10), 943-956.
RkJQdWJsaXNoZXIy MjE2NDg3