Repairing the landscape after millions of tonnes of topsoil have been shifted and even larger amounts of coal have been extracted requires continuous monitoring, as revealed in the Idemitsu mine report.

That analysis, compiled by Eco Logical Australia last October, found problems with the amount of topsoil retained and the fate of vegetation restored to the mine site.

Idemitsu failed to meet its required targets for pasture rehabilitation on all five areas examined. Most woodland rehabilitation sites also did not meet requirements, with areas of the non-endemic wattle species, Acacia saligna, found to be dying.

However, the company said its Muswellbrook operation undertakes an annual review of its rehabilitation plan to ensure environmental consent obligations can be met.

“The company is fully committed to achieving its approved rehabilitation plan and confirms the Muswellbrook operation is currently in compliance with its regulatory obligations,” a company spokesperson said.

A spokesperson for the Department of Regional NSW confirmed that at the start of this year, the government held $3.3 billion in security bonds for rehabilitation. The sum had risen $1.1 billion over the past five years.

“All titleholders must provide a rehabilitation security deposit that covers the full cost of rehabilitation,” the spokesperson said, adding the bond is not returned until the land is returned to the final approved landform.

“Rehabilitation obligations are legally enforceable and mining companies are responsible for all rehabilitation, even after the mine’s closure,” the spokesperson said.

The future of coal has been a central issue in the Upper Hunter byelection set for May 22 that was triggered by the sudden resignation of Nationals MP Michael Johnsen.

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The Herald sought comments on the rehabilitation issue from several candidates, including from the major parties.

“Mining companies should no longer be given free kicks by the coalition in terms of rehabilitation,” Sue Abbott, the Greens candidate said. “The mining companies should be starting proper ‘true-cost’ rehabilitation now and right the way through to the end of their mine’s production life and after.”

Ravi Naidu, head of the Cooperative Research Centre for Contamination Assessment and Remediation of the Environment, said he largely agreed with the Australia Institute’s findings.

“While environmental sustainability must be a focus for coal-mining operations, it won’t stop overnight, regardless of the shift to renewables,” Professor Naidu said. “Therefore, we need significant investment for research and development of strategies to protect and repair environmental damage from mining.”

The Australia Institute report also found Hunter coal mines in 2020 were operating at less than two-thirds of their approved 241 million tonnes of output a year. Production was about 150 million tonnes, implying “there is absolutely no need for any new coal mines”, Mr Campbell said.

“This research undermines the case for new coal projects as existing approvals can easily meet existing and likely future demand,” he said. “The key reason for this gap is that the world is not demanding all this coal.”

The Herald also approached the Minerals Council for comment.