EGL Ref: 9018 22 June 2022 Page 28 WAI-985-000-REP-LC-0006_Rev0.docx This report shall only be read in its entirety. construction to confirm design assumptions, advise on any design amendments, inspect critical details to ensure they are in accordance with the design, and confirm that construction standards meet specified requirements. 4. The risks associated with poor construction will be mitigated by using a Contractor with experience in the construction and operation of similar facilities. 5. The main design risks are the stability of the stockpile and the management of PAF materials in the stockpile. These risks can be mitigated by design, construction, and operation in accordance with high standards. Specific design, construction and monitoring features include removal of weak foundation soils, the adoption of appropriate geometry and zoning, placement and compaction of fill in structural zones to specified standards, controls on layer thickness and locations of bulk fill, subsurface drains to intercept seepage beneath and within the NRS to control the level of saturation, appropriate detailing of liners and drains and monitoring of groundwater levels within, beneath and downstream of the NRS. 6. Potential geotechnical risks have been investigated by comprehensive geotechnical investigations. Extensive investigations have been undertaken and are documented in the NRS site GFR. 7. A cut to rock to form a shear key at the downstream toe will minimise risks associated with instability in the foundations. 8. The outer surface of the NRS has slopes of 3h to 1v slopes with capping and internal drainage within the stockpile. These features will ensure good performance of the stockpile when subject to earthquake ground motions. 9. Erosion and sediment control plans will be prepared for the works. The layout of the site allows for effective erosion and sediment control measures to be prepared. Specific plans depend on the staging of the works. 10. Water for construction is available at the existing operation. 11. Dust will be controlled by spraying dry surfaces with water. Water will also be required to condition the earthfill in the liners and this will assist in reducing the potential for dust. 12. Potential environmental risks will be controlled and managed during operation by appropriate operation, maintenance, and surveillance. This is to ensure the NRS is maintained in a geotechnically and geochemically stable condition to protect the environment downstream. The requirements will be incorporated in an Operation, Maintenance and Surveillance Manual. 17.0 CONCLUSIONS The proposed NRS rock storage facility as part of WNP has a maximum working crest level of RL173 (76m high) and will be an operational stockpile, located north of Storage 2 at the Waihi Development Site. It will be closed as an engineered landform with a maximum crest of RL148 (51m high).
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