\\na.aecomnet.com\lfs\apac\christchurch-nzchc1\legacy\projects\605x\60544823\6. draft docs\6.1 reports\waihi north\app d - kinetic and column testing\appendix d - attachment a.docx 2 of 6 Figure 1. Column Set up (Current / Conceptual). The base of the columns should be free draining and therefore it is recommended K1 gravel material is placed at a thickness that will allow free drainage of leachate to occur (approximately 100 mm) from the base of the columns. 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). An approximate tubing length of 1-2 metres is therefore recommended, however, this may need to be longer depending on the flexibility of the tubing material. During initial operation, tubing should circulate around the wooden structure holding the columns, above the lowest point of the column (discharge point) to approximately 10 cm above this location, before attaching the draining end to the top of the buckets underneath. This will prevent rapid free drainage of leachate from the columns and introduce a pressure head gradient within the water column. 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 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. 3.0 Waste Rock Selection. Three columns of materials each consisting of approximately 60 kg of waste rock representative of the breccia and andesite waste rock within and adjacent to the Gladstone pit are required. Waste rock should be sourced from core material as identified by AECOM in the provided spreadsheet (to be provided separately) which has been selected based on core logs, assay data and photos previously provided to AECOM from Oceana Gold.
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