WAI-985-000-REP-LC-0056 Revision 0 Page 15 of 21 Waihi North Project – Tailings and Rock Storage – Functional Need Assessment • Problematic implementation / integration with operations, especially in early years. The costs of dewatering and practicality of operating a dry stack in wet climates rendered this approach uneconomic for the WNP. TSF North of TSF2 and GOP TSF The option of constructing a TSF north of TSF2 was considered. This option provides sufficient tailings storage for the WNP. This would extend further than the NRS footprint and like TSF3 it impacts vegetation within a designated Significant Natural Area and streams. The East Stockpile would need to be extended to provide sufficient stockpiling area to manage the construction material for the development of the TSF embankment. Development of this site has limited potential for adding additional tailings storage beyond the Waihi North Project and a new site would then be required for an additional resource at WUG. A new site would likely be TSF3. Whereas TSF3 can provide storage for additional resource, provided it can be paired with a material source for embankment construction. The longer-term viability of TSF3 makes it a more feasible and practical site over a TSF North of TSF2. OGNZL also does not own all the land required for this facility. Purchase of the land would require Overseas Investment Office approval. Alternative technologies OGNZL has been considering a range of alternative technologies primarily to produce material for the construction sector which include the use of parts of the tailings stream for: • Brick production • Concrete production • Cementitious fill While these alternatives may be able to divert a small portion of the tailing stream to other uses, they are unlikely to represent an alternative which would notably change the storage decisions for the Waihi North Project. These are not viable options to avoid the need for TSF3. 3.1 Summary: Raising the existing TSF’s using upstream construction has been ruled out. OGC Company policy restricts construction of new tailings facilities to either centreline or downstream construction which avoids the potential complexities and greater risks that can be associated with the design and construction of upstream TSFs if not properly managed. For TSF1A, TSF2 and TSF3 a downstream embankment design constructed of earth and rockfill with relatively modest slope angles has been used or is proposed. A downstream earth and rockfill embankment with appropriate slopes are inherently more robust than an upstream TSF. Upstream TSFs rely on the strength of the tailings and effective drainage to keep the tailings profile unsaturated to avoid the phenomenon of liquefaction which is the cause of many of the failures in upstream facilities. The capacity offered by additional lifts using upstream construction on existing facilities TSF1A and TSF2 was removed from consideration for this reason. OGNZL also considered if there were options to avoid the tributary of the Ruahorehore Stream on the TSF3 site. This is not possible as the tributary run right in the centre of the main storage capacity and there is a geotechnical constraint (weaker ground) beyond the toe of the proposed TSF3 perimeter embankment. For the Waihi North Project OGNZL could reduce the footprint of TSF3 and lower the uphill clean water diversion drain, however, the position of the downstream toe is positioned prudently for potential future raising of TSF3 using a downstream embankment profile for the Martha Open Pit Project.
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