EGL Ref: 9018 22 June 2022 Page 16 WAI-985-000-REP-LC-0006_Rev0.docx This report shall only be read in its entirety. • Compaction and lining of PAF material with short lag times from GOP. • Outer capping layer consisting of topsoil, 0.5 m thick Zone H NAF vegetation growth layer, 1.5 m thick Zone G NAF/low mercury low permeability liner layer, 1.5m thick Zone F PAF drainage layer against the stockpile bulk fill zone (refer s9.2). 9.2. Northern Rock Stack zonation To achieve the design objectives, the NRS is designed as a zoned embankment structure. The primary functions of the different zones are summarized below: Zone A Zone B - - Low permeability zone that restricts seepage from waste rock into underlying ground. Low permeability zone that restricts seepage from waste rock into underlying ground. Used above Zone A to provide additional protection against seepage in locations where settlement causing strain on the liner may be possible. Stockpile bulk fill zone - Bulk fill zone for general fill. Material placement will depend on strength and zones will be defined during operation (conceptual Zones D2, D3 and E shown on drawings and stability analyses). Zone F - Structural fill zone on outside shoulder that also provides a transition between the coarser material in bulk fill zone and finer material in Zone G. Also provides a drainage path for leachate. Zone G - Outer sealing layer of the embankment that restricts entry of oxygen and water Zone H - Plant growth layer Zone I - Structural fill forming downstream section of the perimeter road where it is in fill. PAF waste rock and rock with high mercury contents is not permitted for use in Zones A, G, H and I. PAF rock is not permitted for use in Zones A, G, and H. It is only permitted in the stockpile bulk fill zone and Zone F. Design of the NRS is undertaken with the purpose of providing a long term geotechnically and geochemically stable landform of earth and rock. Geotechnically, the stability is assessed against industry standard geotechnical Factors of Safety (FOS) for static stability and post-earthquake stability, and performance criteria for earthquake induced deformation. Geochemically, the design follows the wellestablished and effective practices at Waihi for the disposal of PAF rock within the TSF embankments which is described in this report. In operation, weaker material may need to be confined to particular areas or toe bunds may need to be constructed to ensure geotechnical stability. The weakest overburden material can flow when tipped in wet conditions, but it eventually consolidates and can become useable. This practice has been effective in the Northern and East Stockpiles in the past.
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