EGL Ref: 9018 22 June 2022 Page iii CONTENTS Page No. 1.0 INTRODUCTION 1 2.0 BACKGROUND AND CURRENT SITE FACILITIES 2 2.1. Location and existing stockpiles 2 2.2. Construction and operation 2 2.3. Current stockpiles 3 2.4. Management of current stockpiles with zonation, liming and drainage 4 2.5. Annual monitoring and surveillance 4 2.6. Performance to date 5 3.0 DESCRIPTION OF WAIHI NORTH PROJECT AND NORTHERN ROCK STACK 5 3.1. Waihi North Project 5 Material characteristics 6 Stockpiling requirements 6 3.2. Proposed Northern Rock Stack 7 4.0 GEOTECHNICAL INVESTIGATIONS AND SITE GEOLOGY 7 4.1. Overview 7 4.2. Topsoil 8 4.3. Volcanic ash 8 4.4. Colluvium 8 4.5. Surficial alluvium 8 4.6. Ignimbrite 9 4.7. Boulder & cobble alluvium 9 4.8. Rhyolite tuff (Homunga Rhyolite) 9 4.9. Rhyolite flow (Homunga Rhyolite) 9 4.10. Dacite flow (Uretata Formation) 10 5.0 HYDROGEOLOGY 10 5.1. Overview 10 5.2. Groundwater system 11 6.0 SEISMIC HAZARD 12 7.0 FLOOD HAZARD 12 8.0 DESIGN BASIS 13 8.1. Geotechnical stability 13 8.2. Uphill diversion drain sizing 13
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