A decline in the watertable due to a long period of low rainfall, and the disturbance of sulfidic peat soils by dewatering and excavation in the Perth suburb of Stirling, has led to widespread acidification of groundwater at the watertable in a residential area and contamination of groundwater by arsenic and metals. The acidification has been caused by the oxidation of sulfide minerals within the peat, which contains up to 15% by weight of oxidiseable sulfur. Groundwater of pH 1.9 has been measured in shallow monitoring bores in the area, as well as high arsenic (up to 7 mg/L), aluminium (up to 290 mg/L), and iron (up to 1300 mg/L) concentrations. Contaminated groundwater pumped from affected domestic garden bores caused plant deaths in gardens and has given rise to health concerns because of high arsenic and metal concentrations. Drilling has indicated that acidic groundwater generally extends 5-10 m below the watertable, and that deeper groundwater is currently unaffected by contamination. As groundwater forms 70% of Perth's total water usage and sulfide-rich peat soils are common in the region, acid sulfate soil risk maps and management policies need to be developed and implemented as a matter of urgency to prevent similar acidity problems occurring elsewhere in Perth.

Cloudbreak is an iron ore mine located in the Pilbara region of Western Australia. The mine extends 40 km east-west, 5 km north-south and has excavations up to 70 m depth. It is home to one of Australia's largest and most complex Managed Aquifer Recharge (MAR) operations. It also adjoins the new Christmas Creek mine, currently under development to the east, of similar scale and characteristics. The two mines form a single water managed entity. Ninety percent of the ore body is below the water table, the ore body itself containing the main aquifer of brackish water. The mine is bounded to the south by the Fortescue Marsh – an internally draining, periodically flooded wetland of national significance. The marsh and the ore body are underlain by hyper saline conditions in an irregular pattern trending more saline towards the marsh and with depth. MAR is the chosen method of dewatering operation to preserve the fresh and brackish water source, manage the quality of the remaining unexcavated ore body, safeguard groundwater levels at the marsh, and maintain balance to local ecology by zero surface discharge. Through an evolution of review and optimisation, a mix of infrastructure components have been installed and commissioned alongside ongoing mine expansion, within a very dynamic operational environment. The scheme currently includes 200 abstraction bores (60 operational at any time), ten in-pit sumps, 200 km of pipeline, six major transfer or settlement ponds, 100 brackish injection bores (50 operational, others for standby or future use) and 20 saline injection bores (currently operating five at a time on a trial basis). These numbers are due to be significantly augmented as dewatering license limits increase and the mine progressively develops. Hydraulic network modelling software is applied for system design and optimisation. The system is operated using a mix of manual and automatic controls, with regular monitoring for compliance and optimising system performance. This paper focuses on how the self contained MAR system has been designed, developed and operated successfully, though many challenges remain.