The $650 million gas-fired power station would be twice as big as the original one proposed for Tuggeranong.

ActewAGL is in negotiations to buy a privately owned, 210ha grazing property at Williamsdale, south of Canberra, for the project.

The property is owned by Queanbeyan resident Winston Nash. Mr Nash did not want to comment about the project but confirmed he had been approached by the ActewAGL consortium and that contracts were being drawn up.

Bob Moore's 500ha property is 200m from the proposed development boundary. His home is less than 700m from the property.

Three generations of Mr Moore's family have run sheep on the property.

Mr Moore said he would have to be compensated if the proposal went ahead.

''Unless they build a completely clean power plant,'' he said.

Mr Nash's property is in NSW and the ACT. The plant would be on the territory's side of the border.

A business case should be completed by the end of this year for the 500MW gas-fired peaking plant, which would generate electricity at times of peak demand.

This is more than double the size of the 210MW plant proposed for Tuggeranong, which was reduced to 28MW after an outcry from residents.

The site would be 8km from Tharwa and away from large populations, but Williamsdale resident Val Johanson said that was not good enough,

''It seems every time they have to move something from populated areas they choose Williamsdale,'' Mrs Johanson said.

''I'm sure they have better options.''

Mrs Johanson and her husband live about 3km from the proposed development.

A gas pipeline would run along the Monaro Highway to the site near a substation connected to the Canberra power supply and the national grid.

The consultation period for the $1 billion data centre and power plant at Tuggeranong ends tomorrow.

ActewAGL and the consortium behind the Canberra Technology City are confident the scaled-down proposal meets environmental and health guidelines.

Canberrans for Power Station Relocation spokesman Dugald Holmes said the group was not against the proposal but said it should be far from housing.

''We request that an environmental impact statement be undertaken,'' Mr Holmes said.

''We believe this is a legal requirement as well as a social responsibility.''