SECTION 6 Gladstone Open Pit and TSF C:\D Data\GWS C Drive\GWS\Client Files\1344 OGL - WKP\4 Deliverables\WUG Effects Summary\June 2022\WNP Groundwater Effects Summary_Final_Rev_0.docx 20 6. Gladstone Open Pit and TSF 6.1 Description The proposed Gladstone Open Pit (GOP) will be situated predominantly over Gladstone Hill and part of Winner Hill. The pit will disturb an area of approximately 18.7ha and will be about 95 m deep (1005mRL), 375m wide and 625m long. The pit outline is shown in Figure 19. The pit will be mined over a period of approximately six years and then converted to a Tailing Storage Facility (TSF). No tailings will be discharged in GOP until the production from the Martha Underground (MUG) operation has ceased. After closure of the open pit, a drainage system will be constructed to capture tailings seepage and reduce pore water pressure on the liner. The pit will be backfilled with rock (PAF and NAF) to a minimum elevation of 1,060 mRL to form a base upon which a liner subgrade and geosynthetic liner will be placed. All PAF will be lime treated to reduce Acid Rock Drainage (ARD). Tailings will be placed to a maximum elevation of 1,103 mRL. The drainage water will be collected and taken back to the WTP. Following settlement of the tailings, a cap with a minimum thickness of 1 m NAF backfill and a low permeability layer will be constructed. Figure 21 Proposed Gladstone Open Pit
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