MINING in the Hunter Valley could leave a legacy of more than 10,000 hectares of land consumed as ‘‘final voids’’, or giant holes left by mines, prompting a push for the state government to investigate their cumulative impacts on the region’s water table and agriculture.
The independent Planning Assessment Commission has urged the government to undertake the study, and branded as ‘‘unacceptable’’ mining giant Rio Tinto’s proposal for a 950-hectare final void at its Mount Thorley mine site – an area it notes is four times the size of Sydney’s Centennial Park or about a sixth of Sydney Harbour.
In advice issued to the commission, the Department of Planning has revealed it is ‘‘not aware of the total size’’ of existing and approved voids in the Hunter.
But approval had been given for about 30 to be developed that on a ‘‘conservative estimate’’ would cover 7500 to 10,000 hectares, it said.
The commission rebuked the department’s assurance this would amount to only a small area of the region’s total land, saying instead that ‘‘the commission does not accept that a mining legacy of large voids across the Hunter Valley is acceptable’’.
The issue was raised as part of the commission’s report on an expansion of Mount Thorley-Warkworth, which concluded last week that the project could be approved but recommended the company be forced to reduce the size of the mine’s proposed final void.
Rio Tinto said the proposed combined void for the expansion would actually be smaller than the total of two separate voids that it already has approval for at its existing operations.
‘‘The final void will be largely hidden from view due to the surrounding landscape and extensive rehabilitation works planned after mining,’’ a company spokesman said.
The department estimated it would cost at least $2billion over the life of the mine to completely fill the void, and it would ‘‘not be reasonable to impose a condition that requires Rio Tinto to completely or even partially backfill the final void’’.
It also told the commission there would be risks to water resources from filling the void as it ‘‘may not act as a groundwater sink and therefore saline water may migrate off the site’’.
Despite its huge size, the void would not be the largest left in the Hunter, the department said. BHP’s Mount Arthur mine would leave one of about 1500hectares.
The commission said the government should look at the voids’ cumulative impacts on the water table and future of agriculture.
A spokesman for Resources Minister Anthony Roberts said the government was considering the commission’s report.