EGL Ref: 9215 23 June 2022 Page 15 This report shall only be read in its entirety. File: WAI-985-000-REP-LC-0002_Rev0.docx. TABLE 2: HIRDS (V4) RAINFALL INTENSITY FOR ANNUAL RECURRENCE INTERVAL *PMP stands for Probable Maximum Precipitation 3.5. Hydrogeology The hydrogeology of the Waihi Mine area is currently controlled by the Ohinemuri River and dewatering of the current underground and open pit mines. Around the Mine Site to the west of the Ohinemuri River the current underground and open pit mines draw down the natural ground water table. Groundwater is drawn down to the west of the Ohinemuri River at the Development Site because the underground mines and pits are below the riverbed level. Once mining stops, water levels will return close to the surface and groundwater will flow back to the Ohinemuri River. To the east of the Ohinemuri River at the Development Site the ground water flows to the Ruahorehore Stream and the Ohinemuri River as there are no open pits or underground mines to draw the groundwater down and the surrounding ground and TSFs are higher. Subsoil drains beneath the TSFs intercept groundwater, which is flowing beneath the TSFs, driven by the head or water in the surrounding hills. 4.0 WAIHI OPERATION – EXISTING TAILINGS STORAGE AND ROCK DISPOSAL 4.1. Nature of the ore and overburden at Waihi Typically, mining operations remove both ore-bearing rock and non-ore-bearing rock. At Waihi ore bearing rock is crushed, ground and processed to extract the gold and silver and forms the by-product known as tailings (See Section 4.2). The non-ore bearing rock and overlying soils at Waihi associated with Martha Open Pit and the underground mines requires transfer and placement for long term storage. This material is currently placed in the TSF embankments and associated stockpiles. ARI (yrs) AEP Duration 10min 20min 30min 1hr 2hr 6hr 12hr 24hr 48hr 72hr 1.58 0.633 56.3mm/hr 44.2 38.1 29 21.5 12.5 8.46 5.46 3.35 2.45 2 0.5 62.3 48.9 42.2 32.1 23.8 13.8 9.31 6.01 3.68 2.7 5 0.2 83.7 65.6 56.4 42.8 31.6 18.3 12.3 7.91 4.84 3.54 10 0.1 100 78.4 67.3 51 37.6 21.7 14.6 9.35 5.71 4.17 20 0.05 118 91.9 78.9 59.6 43.9 25.2 16.9 10.8 6.61 4.82 30 0.033 129 100 86 64.9 47.7 27.4 18.4 11.8 7.16 5.22 40 0.025 136 106 91.1 68.8 50.5 29 19.4 12.4 7.55 5.5 50 0.02 143 111 95.2 71.8 52.8 30.2 20.2 12.9 7.86 5.73 60 0.017 148 115 98.6 74.4 54.6 31.3 20.9 13.4 8.12 5.91 80 0.012 156 122 104 78.4 57.5 32.9 22 14 8.53 6.21 100 0.01 163 127 108 81.6 59.8 34.2 22.8 14.6 8.84 6.44 250 0.004 190 148 126 94.9 69.4 39.5 26.4 16.8 10.2 7.39 1000 0.001 223.5 173.7 148.3 111.3 81.5 46.2 30.8 19.6 11.9 8.6 10000 0.0001 278.6 216.4 184.7 138.5 101.3 57.4 38.2 24.3 14.7 10.7 PMP* 16.7
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