\\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 4 of 6 During this period the leachate should be monitored weekly. During monitoring, it is recommended that the leachate tubing is removed carefully from the bucket and leachate within the tubing and at the base of the column is collected directly from the tubing into laboratory supplied containers suitable for the analysis of the parameters detailed in Table 2 in week 2, 4 and 6 of operation. Once all containers are full or during weeks 1, 3 and 5 of operation when samples are not required, leachate should be collected directly into a clean beaker.in a clean beaker. Field parameters should be collected utilising a calibrated multi-parameter (or similar individual meters) and the following field parameters recorded: • pH • Conductivity • Temperature The remaining leachate should be left to drain into the bucket until the tubing runs dry. The volume of leachate within the bucket should be recorded and sampled before reconnecting the tubing to the empty bucket. In the event that insufficient leachate drains from the tubing and base of column to enable the collection of water samples and/or accurate measurement of field parameters, static water within the bucket should be utilised. If no leachate water (or insufficient leachate water) is available, a measured volume of 500 mL of deionised water should be poured into the column at the top, and the leachate should be collected as described above. Where this is required it should be recorded on the sampling sheet. The water level of the columns and buckets should be monitoring during and after heavy rainfall events in order to prevent overflow. If leachate buckets need emptying in between the weekly sample cycle, it is recommend that field parameters (as above) be recorded prior to the disposal of the leachate water. 5.0 Ongoing Column Operation Results should be forwarded to AECOM upon receipt and will be reviewed in terms of the acid generating status. Once the columns are verified as being acid producing (generally based on a measured pH <3 and elevated sulphate) one column comprising material collected adjacent to the Gladstone pit and one column comprising material collected from within the Gladstone pit should be operated as follows: Column A (Fully Saturated) These columns should remain fully saturated. The tubing should be attached to a point in the column that is above the placement of the waste rock to ensure that the columns remain saturated. The tubing should then be attached to the leachate collection buckets. The column should then be filled with rainwater so that all of the waste rock within the column is beneath the static water column. The column should then be left exposed to atmospheric conditions to enable a variable unsaturated / saturated cyclic state. Column B (Limestone Treated) A layer of limestone should be placed on top of the waste rock. The quantity of limestone introduced will depend on the initial monitoring data and will be calculated by AECOM once the initial operation and sampling has been completed. The tubing from the column should drain to the collection buckets as per the initial setup and the column should remain exposed at the top to enable a variable unsaturated / saturated cyclic state. Column C (No Treatment) The column should remain as per the initial set up with tubing from the column draining to the collection buckets. The column should remain exposed at the top to enable a variable unsaturated / saturated cyclic state.
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