It was meant to be a remediation program to repair extensive mine subsidence damage to Sugarloaf State Conservation Area in the Lower Hunter.
Instead it turned one environmental disaster into another.
Contractors working for coal giant Glencore Xstrata pumped more than 180 tonnes of concrete into a tributary of Cockle Creek at Lake Macquarie.
The concrete creek, uncovered as part of Fairfax Media's investigation into mine subsidence at the state conservation area, stretches more than 400 metres down a hillside and dries up less than a kilometre from Cockle Creek that leads to Lake Macquarie.
In some places it is more than one metre deep and five metres wide.
A worker who had been involved in the remediation project described the creek grouting as an "absolute catastrophe".
He said Orica Mining Services employees, contracted by Glencore Xstrata, were attempting to grout a large subsidence crack at the top of a ridge in the reserve in June.
They were unaware that more than 12 concrete trucks worth of grout was spewing out another crack at the bottom and running straight into the creek.
"There was an unsupported ridge above the grouting area, so there was no one monitoring the end of the pipe," he said.
"It was running for a very long time before anyone realised. I have no idea how it can be cleaned up, the problem is just too massive."
Discovery of the creek comes just a day after Glencore Xstrata's spokesman assured Hunter residents that the mine was working to "provide appropriate remediation of mining impacts and operate in a responsible manner".
On Wednesday night he said the mine was "extremely disappointed" by the subsidence damage at the reserve and admitted it was "greater than predicted".
He said West Wallsend Colliery was fully committed to "working with all parties" to remediate the creek.
Almost three months after the creek was grouted and on the day Fairfax Media revealed the mine subsidence damage in the reserve, the Office of Environment and Heritage moved on Wednesday night to force the company to clean up the mess.
Chief executive Sally Barnes, who described the area's conservation value as "very great", said an agreement was made to cease the mine's remediation project after the creek was grouted in June.
"We have given them a direction today to remove the grout ... it's a legal direction and they have until September to come up with a plan," she said.
"We have had specialist investigators up there and we are looking at regulatory action that might be appropriate, including possible prosecution."
The Environment Minister, Robyn Parker, said on Wednesday she was "concerned" about the "two reported incidents in relation to mining activity below Sugarloaf State Conservation Area".
"I'm advised that the National Parks and Wildlife Service has requested a review of the current subsidence plan, including advice of potential future impacts from the Department of Planning and Infrastructure," she said.
The story Mining company's failed environmental repair job creates concrete creek first appeared on The Sydney Morning Herald.