22 August 2023
Western Australia Iron Ore (WAIO) will become increasingly reliant on mining below water table (BWT) tonnes, with approximately 40 per cent of our ore planned to be accessed from below the water table by FY2040. This translates to approximately a four-fold increase in dewatering volumes to those in FY2022 and an increase in surplus water. Our intent is to utilise our surplus water for beneficial use as much as practical and manage via sustainable water management practices.
We have reviewed WAIO’s water management practices and are installing additional surplus water management schemes to align with WAIO’s context-based water target and BHP’s 2030 Healthy environment goal. This also aligns with BHP’s vision for a ‘water secure’ world by 2030 and is consistent with the United Nations Sustainable Development Goals.
WAIO recently developed a context-based water target that by FY2030 at least 50 per cent of surplus water (dewatering volumes that are excess to operational requirements) will be prioritised for beneficial use (e.g. measures that contribute to environmental resilience, such as returning surplus water back into aquifers to reduce impacts on regional groundwater resources) to improve the sustainability of regional groundwater resources or generate social value.
Figure 1 Location Plan – Mining Area C
WAIO’s Mining Area C (MAC), located approximately 350 kilometres south of Port Hedland (Figure 1), has a complex mine dewatering and surplus water network which includes 34 operational dewatering bores, 16 operational reinjection bores and a large number of associated monitoring bores. Dewatering volumes at MAC are significantly larger than site water demand and so a large surplus volume is generated. In FY2023, collective abstraction was 45 megalitres per day (ML/day) (>500 litres per second (L/s)) with 21 ML/day (~240 L/s) of this being surplus to site requirements (Figure 2). Return to nearby groundwater aquifers benefits the environment by mitigating drawdown from nearby mines and storing water so that it is preserved for environmental or human benefit. Increasing the return to ground capacity has allowed our reliance on creek discharge to be progressively reduced.
Figure 2 MAC Surplus Water Beneficial Use (2020 to 2023)
At MAC, the surplus schemes were approved (subject to conditions) by the Western Australian Minister for Environment under Part IV of the Environmental Protection Act 1986 (WA) (Ministerial Statement 1072). The surplus schemes consist of the Juna Downs managed aquifer recharge (MAR), South Flank MAR, Runaway Valley infiltration ponds, as well as Western and Central sediment basins (Figure 3). Ministerial Statement 1072 contains conditions for these surplus schemes, including those relating to Juna Downs MAR, which requires management and protection of nearby environmental receptors (Figure 4 shows the closest environmental receptor to this surplus scheme - Coondewanna Flats). These schemes use surplus water for beneficial use where water is returned to the environment to improve the sustainability of the regional groundwater resource.
Fig 3 Existing Surplus Water Network – Mining Area C
Based on the design and capacity of these surplus schemes, MAC was able to return 79 per cent (16.5 ML/d or 188 L/s) of the FY2023 surplus water to regional aquifers to offset potential drawdown and preserve water for future beneficial use (for example Juna Downs MAR, which contributes to groundwater recovery offsetting drawdown in the Coondewanna Flats region).
Beyond FY2023, we are seeking to expand the use of water management schemes, including additional aquifer reinjections, bores and infiltration ponds as the surplus volumes increase, so that the majority of surplus water is returned to ground for beneficial use. Our current forecasts estimate that by FY2030, MAC has the potential for up to 75 per cent of surplus water to be return to ground.
Figure 4 Coondewanna Flats – nearby environmental receptor