B-7 – Area 7 - Assessment of Environmental Effects 34 Compliance with the New Zealand Society on Large Dams (“NZSOLD”) Dam Safety Guidelines; Geotechnical conditions, including weak gully infill materials and volcanic ash soils of varying strength and permeability overlying rhyolitic rock at varying depths; The need to restrict seepage from the tailings, including the use of a low permeability geomembrane liner across the base of the impoundment, and to collect any seepage that does form for pumping to treatment; The scheduling and delivery of rock and the availability of different rock types to meet the low permeability fill zones, non-acid forming sealing layers and long-term stability and closure requirements; The need to encapsulate potentially acid-forming rock with low permeability non-acid forming (“NAF”) rock to minimise the potential for sulphide oxidation and the generation of acid leachate, and to collect and contain any leachate that does form for pumping to treatment; The need to add crushed limestone to any potentially acid forming material within the TSF3 embankment to delay acid generation during construction until the capping layers are in place;2 The diversion of clean runoff from the hills above TSF3, around the facility, directly to Ruahorehore Stream; and The diversion of run off from within work areas and directing it to the collection ponds, before being treated at the WTP. It is noted that the upstream toe position of the 155 m RL embankment is set to allow sufficient space downstream to raise the facility in the future using a downstream embankment profile to 177 m RL should it be required for future mining activities. Any increase in height from 155 m RL will be subject to a separate resource consent application. 2 As has occurred previously, this will be added via an existing silo on the conveyor which transports this material to TSF3 and, as required, will be spread by tractor.
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