7 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 3 Description of proposed activities and substances 3.1 Introduction OGNZL currently operates a Processing Plant in Waihi, which refines ore from a variety of sources in the region. OGNZL proposes to upgrade the plant, including upgrade of existing equipment and acquiring additional equipment to increase throughput. Minor upgrades to the associated Water Treatment Plant are also proposed to accommodate the increased water inflows. To further support mining activities in the region, a new Class 1 explosives storage site is also proposed to be established in a segregated area referred to as the Development Site. 3.2 Processing Plant The ore refining process at the Waihi site principally involves crushing and grinding the mined ore into a slurry, adding reagents such as cyanide to aid gold separation, and finally extraction of gold from the slurry using the ‘carbon in pulp’ process. In addition to gold and silver, some other metals and metalloids are found at elevated concentrations in the geology in and around Waihi. OGNZL anticipate elevated levels of mercury in the ore sourced from the proposed mining of Gladstone Open Pit. Without effective management, mercury within the ore would be released to the environment through stack discharges at the Processing Plant2. As part of the WNP, OGNZL propose to install a mercury retort oven in the gold room of the electrowinning building to condense mercury vapour from the waste gas stream and retain it as a liquid for safe disposal, minimising the discharges to air. As part of the upgrade to the Processing Plant equipment, a new substation is proposed to be constructed at the site of the existing LPG tanks. The substation will consist of two 33kV/11kV transformers and one smaller Station Services Transformer. The existing LPG tanks will be relocated approximately 270 m east across the Ohinemuri River to a central area of the Development Site. No new hazardous substances will be used in the proposed upgrades to the Processing Plant, however, the quantities of some of the substances stored will increase to achieve the increased throughput capacity. In total, the proposed hazardous substances associated with the Processing Plant will include the following: Up to 200,000 L diesel in eight portable tanks located around the surface facilities and within the underground mines. Two tank types are proposed: 40,000 L self-bunded isotainers and 6,000 L self-bunded relocatable stationary tanks in a refuelling unit; A 70 tonne quicklime silo located west of the Processing Plant; Cryogenic oxygen in a 30,000 L tank adjacent to the electrowinning process where it is used in the ore recovery process; Hydrochloric acid in a 24,000 L tank west of the electrowinning building; Sodium hydroxide (caustic soda) in a 24,000 L tank also west of the electrowinning building; Solid sodium cyanide 77,000 kg in a dedicated storage shed and a 112,000 L liquid cyanide solution tank on the eastern side of the Processing Plant in the reagents storage area; Up to 10 kg of recovered mercury metal from the mercury retort oven in the gold room; Up to 8,000 L of maintenance oils and greases in intermediate bulk container or drum units; and Up to 8,740 L of mineral oil in the transformers at the new substation. 2 Discharges to air from this activity are the subject of a separate assessment prepared by BECA Ltd, Waihi North Project – Air Discharge Assessment – Waihi Facilities, dated May 2022
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