143 5 The Northern Rock Stack stockpile crest shall not exceed a height of 173 m RL (Mine Datum less 1000 m). 6 The Northern Rock Stack shall be constructed in general accordance with the design outlined in the document titled “OceanaGold (New Zealand) Limited –Waihi North Project -Tailings Storage and Rock Disposal Volume 4 –Northern Rock StackRL173-Proposed Rock Disposal Facility –Technical Report’ included in Part H of the application documents. 7 The Consent Holder shall ensure the entire footprint of the Northern Rock Stack is underlain by a low permeability liner which provides for secure long-term containment and which: a. Has no acid forming potential; b. Has a permeability of not greater than 1x10-8 m/s; and c. If constructed of natural materials has a minimum thickness of 750 mm, or, if constructed wholly or partly from synthetic materials the design shall provide for protection against damage or penetration of the liner during construction and operation. In addition, the Consent Holder shall line all leachate drains with a 3 m wide 1.5 mm HDPE (or other similar synthetic liner approved by the Waikato Regional Council). 8 The Consent Holder shall ensure all perimeter drains are constructed from or lined with materials which provide for secure long-term containment and which: a. Have no acid forming potential; and b. Are lined with 1.5 mm HDPE (or other similar synthetic liner approved by the Waikato Regional Council) to a height of 0.3 m from the base, and with a 0.5 m protective cover layer 9 The Consent Holder shall ensure that all PAF material stored outside the footprint of the Northern Rock Stack , and which is intended for disposal into the Northern Rock Stack, shall only be stored on a pad constructed in accordance with the requirements set out below. Any such pad shall be constructed from or lined with at least 600 mm of natural, non-acid forming materials with a permeability of less than or equal to 1x10-8 m/s. The pads shall be constructed to direct any seepage so that it reports to a point from where it can be monitored, and if necessary, directed to the Water Treatment Plant for treatment prior to discharge. Monitoring of the groundwater down-gradient of any such storage pad shall be undertaken. That monitoring may form part of any monitoring programme already undertaken at the Site.
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