EGL Ref: 8983 23 June 2022 Page 17 WAI-985-000-REP-LC-0004_Rev0.docx This report shall only be read in its entirety. 10.4. Embankment permanent surface water collection systems Surface water drainage systems on the embankments are to be sized for a 100 year ARI flow. 10.5. Collection pond design The collection ponds will be sized to manage runoff from a 10 year ARI (24 hour storm). 10.6. NAF Stockpile The NAF stockpile shown in Figures 16-20 will reach its maximum size during operation and will be partially depleted before closure. In closure it will be rehabilitated to an engineered landform and pasture or vegetation will be established. It will likely be suitable for farming as the remaining stockpile material will be over consolidated. The proposed design criteria are detailed in Table 2. Table 2: STORAGE 3 STOCKPILE DESIGN CRITERIA Design Parameter Design Criteria Earthquake loading • OBE Probabilistic 150 year return period • SEE Probabilistic 500 year return period Geotechnical stability • Static • Seismic - Temporary benches in stockpile Factor of Safety (FOS)≥1.2 - Rehabilitated benches in stockpile Factor of Safety (FOS)≥1.5 - Stockpile global stability FOS≥1.5 - Post-earthquake conditions FOS 1.2 OBE: The performance requirement for the OBE is that the stockpile remain functional and that the resulting damage is minor and easily repairable. SEE: The performance requirement for the SEE is that there is no major instability when the stockpile is subjected to the seismic load imposed by the SEE. Damage to the rehabilitated surface and surface drains may have occurred, however, it is readily recoverable.
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