The Bickham proposal, south of Murrurundi, has divided public opinion since it came to attention in 2002.

Bickham director John Richards said yesterday the comprehensive water study on display through the NSW Department of Planning showed conclusively that the mine would not adversely affect the river.

He said the mine's owners, the Cant family behind Bloomfield colliery and the Foster family behind Maitland Diesel, had spent more than $10 million in developing the project.

The water study has done little if anything to soften the opposition of residents including downstream property owner Patrice Newell.

Ms Newell said she was yet to read the full report but the Government should never have allowed even exploratory mining in such an ecologically important area.

"For nearly 10 years the coal company has said it will be able to mine this coal without damaging the river, but our view has always been that to create a huge void at the head of the catchment is very risky," Ms Newell said.

She was referring to a 70-hectare hole that Mr Richards said would be left after Bickham finished mining its 216-hectare footprint.

The mine would be about 900 metres wide and 3.9 kilometres long with a break across the centre because of a geological fault in the coal.

Hydrologist Peter Dundon said the mine impact had been modelled under all possible conditions.

"I believe it can be strongly demonstrated that no existing groundwater or surface water supplies will be adversely affected," Mr Dundon said.