28 agosto 2018
In Western Australia, the closure and rehabilitation of the former Beenup Titanium Minerals Project has focused on protecting the water quality of downstream river systems.
In April 1999, mining at Beenup ceased due to technical issues related to insufficient consolidation of the clay tailings, which impacted production. Deposits of sub-aqueous tailings were necessary because the site is underlain by zones of pyritic soils. Pyrite is a naturally occurring sulphide mineral that has the potential to oxidise and form acid when exposed to air. Pyrite stockpiled during trial mining excavations at Beenup had oxidised, generating a pocket of acid soils.
At the time of closure, 335 hectares of land had been disturbed, including a 2.1 kilometre dredge pond and a 40 hectare dam containing the initial volume of sand and clay excavated from the dredge pond. Two temporary dams were also constructed to contain clay fines while technical studies were carried out. The total amount of water in the pond and storage dams at closure was estimated to be 5.5 million cubic metres.
We undertook extensive community consultation with the Beenup Consultative group, which had been involved in the Beenup project since 1989. The group helped develop a rehabilitation program to establish permanent wetlands surrounded by native vegetation that link with the Scott National Park. When fully established, these wetlands will receive water from and discharge to the surrounding creeks and rivers.
Rehabilitation of the site was largely completed in FY2018, although monitoring and inspection of spillways and other engineered structures continues. Dredge pond water has been treated and disposed of, with treated water used for irrigation. Pyrite material has been managed through acid neutralisation and permanent saturation. Surface water drainage has been reinstated to reflect the baseline qualities of nearby water systems. The resulting wetlands, established in collaboration with the Western Australian Botanic Gardens and Parks Authority, are now host to four declared rare flora species. Independent assessment concluded that the wetlands support substantial ecological values, both aquatic and terrestrial, demonstrating the effectiveness of the rehabilitation efforts. These wetlands also have the potential to provide opportunities for environmental education, research and eco-tourism.