Water Management

OZ Minerals operates in different climatic regimes and within varying social environments where water has different inherent value. Our extraction of water in areas of other beneficial use, the efficiency with which we use water and the quality of our wastewater discharge are key aspects of our operational performance. Furthermore, these aspects are of significant importance to our regulators, local communities and the protection of ecosystems in the catchments where we operate.

Water is used in all aspects of our activities and operations including exploration, mining and processing. Where we operate in arid areas where supply may be limited we aim to use water efficiently by reducing our extraction of water from the environment and recycling. In areas of excess water, we have to manage discharges to minimise impacts on the environment and communities. Where water is discharged from our sites, this occurs according to water quality discharge limits. Water treatment is commonly undertaken to enable us to comply with our limits.

Details of water management in OZ Minerals over the reporting period are listed by operation in the table below in terms of:

  • Water input – water that is taken from the environment or otherwise enters the site where it is either used or directly discharged without use
  • Recycling - the recovery and treatment of water for use more than once at the site before it is returned to the environment, and
  • Water discharge – Water that leaves the site following use or as a result of direct discharge without use

The total water input to our operations during the reporting period was 31,122 megalitres. Twenty-seven per cent of water input was from the removal of groundwater to enable safe access to mineral resources, 40 per cent was sourced from groundwater bores, and a further 16 per cent is estimated to have entered our sites as direct rainfall (Figure 1). Century mine had the greatest input of water and accounted for 15,201 megalitres (49 per cent) of the group total input. In addition to this inventory for our operating sites, an estimated 1,166 megalitres of water was input to our exploration and key project activities in Australia, Canada and Asia.

Fresh water accounted for 26,422 megalitres (85 per cent) of the total water input across the group. At our Prominent Hill and Golden Grove operations, both of which are located in arid to semi arid parts of Australia, total water input was 3,436 megalitres (11 per cent) of the group total. Fresh water input at Prominent Hill and Golden Grove was 177 megalitres (5 per cent) of the total water input at those sites.

Situated in a location with low average annual rainfall of approximately 160 millimetres, the Prominent Hill site is dependent on the supply of groundwater to allow its development and ultimately sustain its operation. Various water supply options were evaluated as part of the project assessment, with a groundwater resource in the Arkaringa Basin selected as the preferred option. Importantly, it was recognised that the use of this groundwater resource was not expected to impact upon the springs within the Great Artesian Basin that support local oases of endangered animals and plants in an otherwise dry and barren environment. Monitoring of water levels will remain an ongoing part of operations so that any changes to environmental conditions can be identified and addressed.

Recycling of water at our operations is achieved principally by the recirculation of water that is captured in water control dams and removed from tailings storage facilities. Recycling is an effective way of improving water use efficiency and reducing our dependence on fresh water supply. During the reporting period 9,624 megalitres of water was recycled for further use within our operations. All of this water was of poor quality and required treatment before it could be reused. The volume of recycled water use represented thirty-one per cent of our total water input, and thirty-six per cent of fresh water input. At Golden Grove, the volume of recycled water used was 133 per cent of total water input, indicating a very significant rate of water recycling for a site located in a water deficient environment.

Over the reporting period we returned 28,700 megalitres of water to the environment. Of that discharge, 17,053 megalitres (59 per cent) was water discharged directly without use and 6,139 megalitres (21 per cent) was water discharged after use and treatment (Figure 2). Other water was lost mainly through seepage and evaporation. Of the total volume of water returned to the environment by the group, 24,613 megalitres (86 per cent) was from the Century, Rosebery and Sepon operations. These operations are all located in environments where rainfall significantly exceeds evaporation. In addition to this inventory for our operating sites, an estimated 1,166 megalitres of water was discharged by our exploration and key project activities in Australia, Canada and Asia.

While each operation measures and reports on discharge water quality, these data cannot be aggregated across the group with any real meaning since discharge effects are localised. However, an indication of the types of aspects being managed for the more important discharge parameters is shown below:

  • Century and Sepon were the only operations that reported cyanide loadings. Total loading amounted to 26 tonnes. Cyanide does not persist in water or soil and chronic environmental effects are therefore rare. However in certain chemical forms, cyanide can be acutely toxic. Discharge limits are set to manage that risk. At Sepon, residual cyanide is removed using hydrogen peroxide and other chemical agents that are used to precipitate residual metals. The treated water is analysed prior to discharge to ensure compliance with World Bank guidelines.
  • Sepon, Rosebery and Golden Grove accounted for an estimated 373 tonnes of suspended solids discharge. High levels of suspended solids in water create an aesthetic issue and can impact upon the people that depend upon affected water bodies for their livelihoods. Moreover, they can reduce the ability of a water body to support aquatic life. The operations control these issues by minimising erosion and through the installation of drainage and sediment control structures designed to reduce the sediment load in discharge water.
  • Over the reporting period 321 tonnes of biological oxygen demand (BOD) was discharged by Sepon and Century’s Karumba port facility. BOD is used as a measure for the pollution of water bodies since it reflects the amount of organic compounds in water. At Karumba, an activated sludge treatment process is used to reduce BOD levels in water discharge entering the Norman River. Although four exceedances of the licence limit occurred over the reporting period, BOD levels at Karumba have reduced significantly since 2005 when treatment commenced.
  • The majority of operations contributed to the discharge of soluble metal loading over the reporting period. This is aggregated across the group to an estimated 0.58 tonnes of arsenic, 2.13 tonnes of copper, 1.24 tonnes of lead, 0.36 tonnes of cadmium, 5.3 tonnes of zinc and 26.8 tonnes of manganese. All operations that discharge water after use treat the water, commonly through the addition of lime, to achieve pH adjustment and reduce metal loadings in order to meet operation discharge criteria.

In relation to water discharge, the quantities of water quality parameters discharged from our operations includes a proportion that was based on estimation or irregular frequency of sample collection. This reflects that this is the first period for which we collected this data as OZ Minerals and that further work will be undertaken to standardise and align environmental data collection and reporting across the operations.