1 Tonkin & Taylor Ltd Hazardous Substances Technical Assessment – Waihi North Project - Waihi Processing Plant, Water Treatment Plant and Development Site Oceana Gold (New Zealand) Limited June 2022 Job No: 1015212.1000 vRev0 1 Introduction 1.1 Overview Oceana Gold (New Zealand) Ltd (OGNZL) operates various mines and mining infrastructure at Waihi, Waikato. OGNZL is seeking to extend the life of mining activities at Waihi with the Waihi North Project (WNP) and continued activities at the Martha Mine. As such, OGNZL is seeking resource consent from the Hauraki District Council (HDC) for proposed upgrades to the existing Ore Processing Plant and expansion of the Water Treatment Plant in Waihi as part of the WNP, as well as to establish a new Class 1 explosives storage facility to service the ongoing mining operations. The current operation and maintenance of the existing Processing Plant (and associated Water Treatment Plant) and two existing explosives magazines are authorised as a permitted activity, subject to conditions or performance standards, by Rule 5.17.4.1 P1 of the Hauraki District Plan. Hazardous substances associated with the proposed upgrades to the Processing Plant include caustic soda, hydrochloric acid, cyanide (liquid and solid), liquified petroleum gas (LPG), diesel, liquified oxygen gas and lime. The Water Treatment Plant which is located to the north of the Processing Plant proposes to expand storage of ferric chloride, hydrated lime and hydrogen peroxide to treat runoff, mine water and leachate from OGNZL’s tailings storage facilities. The proposed new explosives storage facility will comprise of up to seven individual magazine units to the east of the existing facilities. The proposed storage and use of hazardous substances at these locations within the Martha Mineral Zone is a non-complying activity under Rule 7.7.10 of the Hauraki District Plan (HDP). OGNZL’s existing hazardous facilities in this area that are not subject to change as part of the WNP have not been assessed, except where there is potential for cumulative impacts with the upgraded or new facilities. Tonkin & Taylor Ltd (T+T) has been engaged by OGNZL to prepare this hazardous substances assessment to support its resource consent application for the Waihi North Project. This report has been prepared in accordance with our engagement and variation letter dated 27 August 2021 (reference: OG-3219). 1.2 Waihi North Project The WNP includes the following activities and infrastructure changes to extend the mining activities within the Waihi area: A new underground mine at the Wharekirauponga resource (referred to as the “WUG” mine), located approximately 11 km north-west of the existing processing facilities in Waihi. The upgraded Processing Plant and associated facilities will be accessed via a new underground portal (WUG Portal), to be located north-west of the current Processing Plant location. Associated site infrastructure is proposed to support mining operations on OGNZL owned farmland located at the end of Willows Road which is the subject of a separate hazardous substances assessment1. A new open mine pit, Gladstone Open Pit (GOP), centred over Gladstone Hill, location shown inFigure 1.1. This is located west of the existing Processing Plant. Once mining is complete, the GOP will be converted into a tailings storage area. 1 Tonkin & Taylor Ltd. Hazardous substances technical assessment, Waihi North Project - Storage and use of hazardous substances at Willows Road site, December 2021
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