Under the mine expansion plan, the production of radioactive tailings, stored above ground, will increase from the current 10 million tonnes per year, to 68 million tonnes per year. The tailings contain a toxic acidic soup of radionuclides and heavy metals. It is estimated that by the mines closure, these tailings will total nearly nine billion tonnes, equivalent to nine times the volume of Sydney Harbour, which BHP intends to leave on the surface of the land, forever. Once all tailings dams are commissioned they will cover 4400 hectares.