GHD | Oceana Gold (New Zealand) Ltd | 12552081 | Waihi North 103 Table I.23 Water quality assessment scenarios and input sources Scenario Concentrations Volume 1. The influence of all TSF3 discharges on local groundwater: a. Operational to closure b. Long-term C1 = Groundwater well AP01a median water quality values V1 = Groundwater flow for both local and full aquifer mixing (Section I.3.3). C2 = Mean tailings pore water quality and median embankment leachate median water quality (AECOM, 2021a) V2 =TSF3 discharges (Table I.18) 2. The influence of all TSF3 discharges on the Ohinemuri River: a. Operational to closure b. Long-term C1 = Ohinemuri River OH1 median water quality values V1 = Median flow data from the OGNZL FRENDRUPS gauge on the Ohinemuri River (Section 2.2.1 of the main report). C2 = Mean tailings pore water quality and median embankment leachate median water quality (AECOM, 2021a) V2 =TSF3 discharges (Table I.18) 3. The influence of collection pond leakage on the Ruahorehore Stream: a. Operational to closure b. Long-term C1 = Ruahorehore Stream RU03 and RU10 median water quality values V1 = Measured stream baseflow (Section 5.3.5 of the main report). C2 = Median embankment leachate median water quality (AECOM, 2021a) V2 =Collection pond discharge (Section I.3.3) I.4.2 Results The predicted water quality outputs from the mixing analysis are presented in full in Section 5.6.2 of the main report. The ranges provided in the groundwater results table (Table 5.13 of the report) reflect the results for local/direct mixing to groundwater versus full mixing within the aquifer (refer to Table I.22). The mass flux of parameters entering the Ohinemuri River catchment via groundwater discharge were calculated by multiplying the predicted leachate concentrations in Table 5.14 of the main report with the volume of leachate discharged to the receiving environment (Table I.18). The results are provided in Table 5.15 of the main report. I.5 Sensitivity testing This sensitivity testing focuses on the primary analysis, Cross-section 1, which has informed the key assessment of tailings discharge to the receiving environment. The key aspects considered are (Table I.23): – Leakage through the HDPE liner. – Tailings permeability, which provides one of the key controls on the volume of tailings seepage leaving the facility. – Hydraulic conductivity of the geology underlying the tailings (rhyolite tuff), which is interpreted to provide TSF3 discharge from directly entering the Ruahorehore Stream at the embankment toe. Due to the complexity of the model, it was not recalibrated for the K change. Table I.23 TSF3 sensitivity testing scenarios Model aspect: Boundary condition - water flux (m/d) Tailings K (m/s) Rhyolite tuff K (m/s) Scenario 3 Scenario 5 Base model values: 1.7 x 10-5 1 x 10-5 1 x 10-8 1 x 10-7 Sensitivity test no. Change to model Sens.1 Liner leakage 4.3 x 10-6 Sens.2 Tailings 1 x 10-6 1 x 10-7 Sens.3 Tailings 1 x 10-8 1 x 10-9 Sens.4 Geology K 1 x 10-6 Sens.5 Geology K 1 x 10-8
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