GHD | Oceana Gold New Zealand Ltd. | 12552081 | Waihi North Project 6 2 BACKGROUND INFORMATION 2.1 Water Management Approach OGNZL’s water treatment plant (WTP) is consented to treat water from mining activities in any part of the Waihi Epithermal District. Areas that currently generate water requiring treatment associated with OGNZL’s Waihi operations are: Martha Open Pit – stormwater runoff and groundwater Martha Underground (and previous underground mines) – groundwater dewatering Processing plant and WTP area runoff Decant pond water – currently from TSF1A Collection pond water – stormwater runoff from rock storage areas Seepage – from TSF1A and TSF2 including embankment structures Cyanide is used in the gold recovery process and is present in the tailings that are pumped to the active TSF. TSF decant water thus contains cyanide as does seepage from the TSFs; there is also potential for cyanide content in the ponds that collect stormwater runoff from the process area. Water sources containing cyanide are referred to as “cyanide water”. Water sources that do not have any contact with cyanide can require treatment due to contact with potentially acid forming (PAF) rock. Rock is extracted to gain access to the mineralized ore containing the gold and silver and is comprised of non-acid forming (NAF) and PAF rock types. When PAF rocks are exposed to oxygen, low pH conditions can develop and water contacting the material can give rise to elevated sulphate and trace elements (soluble metals). Water pumped from the underground workings, and water captured in the collection ponds can contain runoff water and contact water from PAF rock (but no cyanide) and is referred to collectively as “minewater”. Decant water from TSF2 has not been treated since October 2007 when testing showed that the pond water quality was suitable for direct discharge to the Ohinemuri River. Tailings deposition to TSF2 ceased in July 2005 and the TSF2 decant pond currently discharges to the river through an unnamed tributary to the north of the Waste Disposal Area under RC 971323. Figure 4 provides a schematic representation of the current water management system, its sources, pathways and discharges and Figure 5 provides an aerial image of OGNZL’s Waihi operations with TSF2 and TSF1A visible to the right, Martha Open Pit to the left and the processing plant area (including the WTP) located in the centre of the image. The Ohinemuri River runs immediately to the right of the processing plant area. Minewater, cyanide water and potentially impacted runoff water are treated at the WTP on site before discharge to the Ohinemuri River at two locations (E1 and E2) via multi-port diffusers (refer Figure 6). Treated water is stored in Polishing Ponds prior to discharge where it is tested for compliance with the relevant discharge criteria. The volumes and water quality of the various minewater and cyanide water sources are heavily dependent on a number of environmental and operational variables. The primary controlling variables are rainfall, ore and rock geochemistry, processing rate and type, dewatering rate, river flow rate, and tailings facility rehabilitation.
RkJQdWJsaXNoZXIy MjE2NDg3