56 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 disposal to an authorised facility. Environmental monitoring will be undertaken to monitor emissions to below occupational exposure limits. A key risk that has been identified which could result in an off-site human effect is a spill of the cyanide due to its high degree of hazard to human health, especially if the cyanide enters waterbodies. OGNZL provides secondary containment facilities as described in Section 4.10 to capture and retain liquid hazardous substances. In the unlikely event of a spill escaping these containment controls, tertiary containment is also available the form of engineered ponds as described in Section 4.10. The ponds are located on the eastern side of the plant, between the reagent store and the Ohinemuri River, and can be pumped back to the WTP in the event of a spill. Taking into account the controls in place, secondary containment, the large separation distances from storage areas to the OGNZL landholding boundary and the ponds to contain site runoff and spills, the effects on people from a spill of hazardous liquid associated with the activities has been assessed as less than minor. 8.2.2 Effects on ecosystems The Ohinemuri River is located along the eastern boundary of the Processing Plant and WTP areas and is approximately 70 m away at the closest point to any hazardous substance storage. Black Hill located to the south is a reserve and significant natural area. The adjacent OGNZL owned land to the southwest of the Processing Plant is proposed to be mined by OGNZL as part of the WNP. The hazard to the environment is through spills of ecotoxic substances being released to the environment. As outlined when considering the spill risk to people, the liquid hazardous substances are stored with secondary containment. Lime and solid cyanide are stored in a solid state and do not require secondary containment, though the solid cyanide is stored within a designated secure shed. Management and controls of substances are in place through the WEMP and the HSMP which set out the standards and procedures for hazardous substances. The management and controls include provision of secondary containment, integrity of systems particularly for those in contact with corrosive substances, automation of processes to avoid operator error, overfilling and potential spills, staff training to ensure competency when working with substances, safe transport procedures, separation of mixing and distribution systems, emergency response plans and dedicated response teams in the event of accidental release. Mercury will be a by-product of the ore processing that can have adverse effects on the environment. This substance will be securely contained within the electrowinning building on a concrete floor and removed under the supervision of a certified handler to an authorised disposal facility, the anticipated effect of the environment is less than minor. Some of the maintenance oils and greases stored and used in the workshops at the Processing Plant and Development Site have ecotoxicity hazards. The risk of a spill of these oils is managed through provision of enclosed bunded workshops, dedicated bunded storage locations to contain the substances in the event of a leak, and unloading of substances in dedicated sealed areas by staff trained in spill response procedures should damage to a container occur. Of the substances stored on-site, a spill of highly environmentally hazard substances cyanide or diesel could have adverse effects on the environment. As stated above, OGNZL has provided structural controls for this higher risk through provision of secondary containment and engineered tertiary containment ponds on the eastern boundary of the Processing Plant and WTP area to retain the cyanide or any other product in the event of a spill and failure of secondary containment. The diesel containers also are provided with structural controls including double skinned containment, bunded pumping equipment and all refuelling bays drain to oil-water separator devices to treat any residual contamination from the refuelling activities.
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