Memorandum The Power of Commitment 12552081 1 16 June 2021 To Mark Burroughs, Oceana Gold NZ Ltd. Copy to Thomas Gardner, Oceana Gold NZ Ltd.; Ian Jenkins, AECOM NZ Ltd. From Carlos Hillman, Tim Mulliner Tel +64 3 378 0900 Subject WKP Waste Rock Field Column Testing Set-up Project no. 12552081 Introduction and Background GHD Limited (GHD) has been engaged by Oceana Gold New Zealand Ltd (Oceana Gold) to undertake Geochemical characterisation of the WKP tunnel and mine spoil. This memorandum outlines specifications, set up and operational procedures for the field column tests to aid the geochemical characterisation and assessment. The purpose of the column tests is to investigate the onset of acid producing leachate and leachate water quality from the waste rock material associated with the WKP Ore Body. Data gathered will enable geochemical characterisation of waste material and its similarity or dissimilarity to waste material currently handled at the existing and proposed Waihi operations. This will then aid methodology for the development of backfill placement and estimating WKP tunnel inflow water quality. The methodology outlined here is an adaptation of the methodology as outlined in AECOM, 20171 Column Setup and Specification The existing columns on site (dimensions approximately 800 mm high, 300 mm diameter equalling a total volume of approximately 0.057 m3 each) will be utilised. The existing columns should be prepared for use by emptying and cleaning, replacing all tubing and buckets (with sealed lids) with food grade plastic and setting up the columns as outlined in Figure 1. Any new or pre-existing equipment should be thoroughly flushed with an acid wash to remove any existing contaminants. It is recommended that if possible, the column cylinders be replaced. K1 gravel material is recommended at the base of the columns and placed at a thickness that will allow free drainage of leachate to occur (approximately 100 mm). Tubing should be sealed to the base of the columns to collect drainage and avoid any leakage. The length of the tubing should be sufficient so that it can be connected to the collection buckets beneath the columns and long enough so the outlet of the piping can be attached to the side of the column at a height above the maximum level of the waste rock within the column (introducing a head pressure gradient to enable the column to become fully saturated). Tubing should be secured in place (at side of column and top of bucket) in a way that it can easily be released (when sampling) and repositioned when required. Where the tubing connects at the top of the leachate buckets it should be ‘sealed’ in a manner that avoids water other than leachate entering the buckets and enables the removal of the tubing for sampling during the column operation. An approximate tubing length of 1000 – 2000 mm is therefore recommended. 1 Standard Operating Procedure for PYE Field Columns, Waihi – Set up and sample collection. AECOM, (2017).
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