The NSW Environment Protection Authority is investigating the collapse of a second open-cut mine dam wall in the Hunter Valley.
Millions of litres of sediment-laden water escaped when a bund wall partially collapsed at Rio Tinto’s Mount Thorley Warkworth mine on January 6.
It follows a similar incident Peabody’s Wambo mine last week, which allowed an estimated 3 million litres of water to spill into the environment.
The company blamed several days of continuous rain for softening the dam wall.
A Rio Tinto spokesman said the collapse had been voluntarily reported to the Environment Protection Authority and Singleton Council on the day of the incident.
“An engineer was sent to inspect the site and confirm there was no risk to motorists,” he said.
“The dam contained runoff water from pre-mining activities and flowed through culverts under Wallaby Scrub Road on to Coal & Allied owned land.”
An EPA spokeswoman said on Friday that the company advised that it had undertaken work to contain the sediment laden water.
“The EPA has requested additional information from Warkworth and will be conducting a site inspection to assess the impact. Depending on the outcome of the investigation, the EPA will consider further regulatory action,” she said.
“The EPA has also directed the company to clean-up the site to prevent further mobilisation of sediment, both on and off the site, and clean up the accumulated sediment that has already left the site.”
Lock The Gate's Hunter coordinator Steve Phillips said Hunter coal mines were failing the region’s environment and communities.
“On top of air pollution, loss of biodiversity and agricultural land, and the atrophy of local communities, we can now add major water pollution events,” he said.
“Considering that the coal industry's economic viability into the future is increasingly being called into doubt, the question has to be asked – is it worth it? How does our region benefit from the reign of King Coal?”
He said the state government needed to improve the environmental management.
“What are they doing to ensure we don't see more pollution events?,” he said.