EGL Ref: 8983 23 June 2022 Page 13 WAI-985-000-REP-LC-0004_Rev0.docx This report shall only be read in its entirety. 5.7. Dacite – Tuff Breccia Dacite tuff breccia is observed from 156 m to 191 m vertical depth in the GT020 drillhole below Storage 3. There are no dacite outcrops on the Storage 3 site. Dacite outcrops to the west of Storage 2 along the Ohinemuri River, and east of Storage 3 in cuttings on Trig Road North. Dacite is also present at 16.5 m depth in one localised borehole (WG4) at the southwest extent of Storage 1A on the east side of Collection Pond S3. 5.8. Andesite – Tuff and Lava Flow Below the dacite, andesite tuff is observed from 191 m to 206 m vertical depth in the GT020 drillhole. From 206 m to the base of the drillhole at 350 m is andesite lava flow. 6.0 SEISMIC HAZARD Estimates of seismic hazard for the site have been provided by GNS Science in 2007 and 2017 (Ref. 17). The 2017 update incorporated the latest knowledge of the Kerepehi Fault System (Ref. 18) and the Hikurangi Subduction Zone and updated estimates of background seismicity. The tectonic environment and seismic hazard estimates are discussed in more detail in Volume 1 (Ref. 1). In summary there are no active faults on the Storage 3 site and the nearest known active fault expressed at the surface is the Kerepehi Fault System at 23 km distance. Peak Ground Acceleration (PGA) values and corresponding average magnitudes at the Storage 3 site (on rock) are as follows: 150-year return period PGA = 0.10g, Mw = 6.3 84th percentile level for maximum controlling earthquake: PGA = 0.23g Mw =7.3 2,500-year return period PGA = 0.27g Mw =6.6 10,000-year return period: PGA = 0.39g, Mw = 6.9 Uniform hazard spectra (spectral acceleration) for the probabilistic and deterministic estimates of seismic hazard are shown in Figure 14. The spectra are 5% damped larger horizontal component acceleration spectra for Site Class B rock conditions. 7.0 FLOOD HAZARD Waihi is subject to regular heavy rainfall events with an annual average rainfall of between 1500 mm to 3100 mm (Ref. 1). The proposed Storage 3 site is away from the main flood hazard area associated with the Ohinemuri River. Flooding from the Ruahorehore Stream is relatively minor and does not pose a notable threat to the proposed TSF site. The catchment above Storage 3 is approximately 50 ha, which is greater than the catchments above Storage 1A and 2. However, runoff can be diverted away with a diversion drain as is done for the existing TSFs. Refer to Section 10 for the design basis for water management.
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