EGL Ref: 8983 23 June 2022 Page 6 WAI-985-000-REP-LC-0004_Rev0.docx This report shall only be read in its entirety. Matuschka of EGL has been the Project Engineer for the Storage 2 since 1987 and EGL is the Design Engineer of Storage 1A TSF and subsequent modifications. 2.2. Construction and operation Previously the mine was operated by the Waihi Gold Company Limited, which was owned by Newmont before OGNZL purchased the mine operation. McMahon Contractors Ltd was contracted to undertake construction of Storage 1A from 1 July 1998 to 28 May 2015 when surface mining was halted due to a slip in the Martha Open pit. Since then, construction of the Storage 1A embankment and associated facilities has been undertaken by C&R Developments Limited under the supervision of OGNZL. Since May 2001 virtually all tailings have been disposed of into Storage 1A and no tailings have been deposited within Storage 2 since July 2005. 2.3. Monitoring and Surveillance A comprehensive monitoring and surveillance program is in place to enable the performance and condition of Storage 1A and 2 to be assessed. This is documented in the Operations, Maintenance and Surveillance Manual (Ref. 6). The manual was originally developed in accordance with the 2000 version of the New Zealand Dam Safety Guidelines (Ref. 7) and was updated and re-issued in September 2019 to comply with updates in the 2015 New Zealand Dam Safety Guidelines (NZDSG - Ref. 4). Monitoring and surveillance associated with the tailings embankment includes: • visual inspection on a regular basis; • measurements of supernatant decant pond water volumes and levels; • measurements of freeboard; • measurement of pore pressures within the embankment fill; • tailings and foundations by pneumatic, standpipe and vibrating wire piezometers; • measurement of underdrain and toe drain flows; • deformation monitoring; and • monitoring of materials and construction standards to ensure that the Contract Specification is adhered to. The data from the monitoring and surveillance programme are provided to the Designer at regular intervals for review. The data is provided annually to Waikato Regional Council and Hauraki District Council in annual reports and are independently peer reviewed by the Peer Review Panel (PRP) which is engaged by OGNZL as required by the existing resource consent conditions. The annual reports cover structural integrity, geochemistry, groundwater,underdrainage and rehabilitation related to the TSFs. The latest Annual Structural Integrity Reports for Storage 2 and 1A were prepared by EGL in June 2021 (Ref. 8 and Ref. 9). OGNZL monitoring and surveillance is documented in the Tailings Storage Facility Monitoring Plan (TSFMP) (Ref. 10).
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