BHP has committed to a long-term goal of becoming a global leader in water stewardship. Western Australia Iron Ore (WAIO) has five mining operations in the Pilbara region of Western Australia. The volume of below water table ore mined by WAIO has increased and will continue to do so over the next 5 years. The volume of water required to dewater the below water table pits exceeds the local mine site demands for water, producing a surplus. The water is a precious resource and BHP’s WAIO operations have a goal to “preserve surplus water for beneficial use, to the extent practicable”. These ‘beneficial uses” may include preserving social and cultural values, retaining environmental function, or future use of the water resource by BHP or other parties. BHP’s primary way of achieving this goal is through Managed Aquifer Recharge (MAR) of surplus water.
WAIO has a number of MAR schemes at various stages of development. Juna Downs MAR scheme is a 20 ML/d system with injection into a shallow karstic dolomite aquifer up gradient from the Coondwanna Flats region (an area of ecological and cultural significance). Ninga MAR scheme is a 8 ML/d reinjection system with water directed into a fractured rock aquifer consisting of mineralised Marra Mamba Iron Formation and karstic Dolomite of the Paraburdoo Member of the Wittenoom Formation. The Ninga MAR scheme provides a storage of surplus water for future beneficial use. The Ophthalmia Dam MAR scheme is the first MAR scheme built in the Pilbara, and one of the earliest major MAR systems in Australia. It consists of a detention basin (the Dam) and recharge basins constructed in the shallow calcrete of the Fortescue River. The operation of the recharge basins returns water to the sensitive Ethel Gorge area, mitigating impact from dewatering from neighbouring operations and accelerating groundwater recovery in adjacent backfilled mine voids.