Supporting Technical Assessments

EGL Ref: 8983 23 June 2022 Page iii WAI-985-000-REP-LC-0004_Rev0.docx This report shall only be read in its entirety. 11.1. Design Concepts 18 11.2. Collection Ponds 18 11.3. Initial Embankment and Impoundment 20 11.4. Main Embankment West Abutment with Storage 1A 20 11.5. Main Embankment across lower valley floor 21 11.6. Main Embankment over the toe of east rhyolite ridge 21 11.7. Main Embankment against east rhyolite ridge 21 11.8. Impoundment against the Northern Slopes 22 11.9. Impoundment over East Stockpile 22 11.10. Subsurface Drainage 22 11.11. Impoundment Liner System 22 11.12. Embankment Liner System 23 11.13. Leachate Collector Drains 23 11.14. Uphill Diversion Drain 23 11.15. Haul Route B Behind Storage 1A 23 11.16. Storage 3 Stockpiles 23 11.17. Tailings Storage Capacity and Surface Profile 24 11.18. Construction Aspects 24 11.19. Closure Plan 28 11.20. Surface Water 28 12.0 POTENTIAL FAILURE MODES 28 13.0 DESIGN ASSESSMENT 31 13.1. Embankment geotechnical stability 31 13.2. Embankment seismic shakedown settlements 32 13.3. Embankment consolidation settlement 32 13.4. Freeboard scenarios 32 13.5. Geomembrane liner performance 35 13.6. Groundwater and leachate seepage estimation 35 13.7. Uphill diversion drain sizing 35 13.8. Perimeter drain sizing 35 13.9. Collection pond sizing 35 13.10. Embankment surface water drainage sizing 36 13.11. Paleo Gully Undercut Settlement Effects on Storage 1A 36 14.0 DRAWINGS 36 15.0 CONSTRUCTION 37 16.0 DAM SAFETY MANAGEMENT 39

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