REDBANK Tunnel will be filled with rock, sealed and revegetated in the coming months as Xstrata Coal completes its multimillion-dollar project to divert the railway line in north Tahmoor.
Xstrata began diverting the main southern line around Redbank Hill in June last year in the "interests of safety".
Tahmoor Colliery expects to start mining under the tunnel next year.
An Xstrata Coal spokesman said there was a chance the tunnel could have subsided when longwall mining had reached the area.
"Subsidence was predicted to be more substantial while mining took place directly underneath it [Redbank Tunnel]," he said.
The first train travelled across the new track in December after more than 1.5 kilometres of track was moved around Redbank Hill.
Xstrata expects to finish the project in June, which includes re-vegetating the area.
Noise levels will be measured in the coming months to ensure the projections made before the line was moved are accurate.
"Some residents have advised that they can still hear trains passing," the Xstrata spokesman said.
"Development of a large noise control barrier meant noise levels were well below the maximum noise limits required by the NSW Department of Planning's noise guidelines for rail infrastructure projects."
Tahmoor resident Gloria Tommy said a small part of the community had paid a price for the diversion.
"We [a group of residents who back onto the railway] have all suffered some loss of amenity.
"I would like an independent [noise] assessment, so that [noise] predictions from the development application can be compared with actual readings," she said.
"It's not what was expected from where we live."
Xstrata offered short-term relocation to people living close to the construction in December when the tracks were commissioned and the work was around the clock.
Railway historian James Whitfield of Tahmoor said that the safety of passengers and railway crews was paramount.
"The Redbank Tunnel at Tahmoor really has little historic significance unlike the original single line tunnel at Picton," he said.
"The company has done a wonderful job with the deviation in such a short time, and when all the earthworks are completed around it, except for the cattle crossing bridge, it will look like it has always been there."