The Corkhill Brothers group stands to make at least $139 million on its crossborder land venture with the ACT government, after the government paid $4.5m two years ago for the land the family owned on the ACT side of the border.
The housing estate in West Belconnen, Ginninderry, is being developed by the landscaping company's subsidiary property development group, Riverview, and the territory government.
Construction on the first of about 30 stages of the residential development began in April, with 11,500 new homes expected over the next three decades.
Documents released under freedom of information laws show the joint venture is valued at about $1.6 billion, with the ACT government to make about $208 million in profit. Given the profits are to be shared 60:40, Riverview stands to make $139 million.
Riverview Development's managing director, David Maxwell, said financial information related to the joint venture was commercial in confidence.
But the government's decision to develop the land with Corkhill and split the costs and profits stands in stark contrast to the swathe of other properties it has bought in the Murrumbidgee corridor.
In other cases, the subject of a recent audit report, the government has bought land off farmers to develop itself in the future.
The government justifies its decision to share profits with the Corkhill family by saying the Corkhills also bring their own land to the deal over the NSW border.
As part of the joint venture, Corkhill surrenders its NSW land holdings to the territory government.
However, the ACT government bought the Corkhills' land on the ACT side of the border for $4.5 million in 2016.
Corkhill bought the 1000-hectare block from the Shepherd family in 2004 for $800,000. It has owned most of the land on the NSW side of the border since 1984.
The ACT and NSW land will be combined for the new Ginninderry estate, although the NSW land will only be developed if NSW agrees to rezone it.
Riverview has 15 years to get the zone change through, with development on the NSW side of the estate expected to begin in 2033. If NSW doesn't agree to rezone by then, the Corkhills hand their NSW land to the ACT government for $1.
Asked whether the share of the profits was fair, given the ACT government had paid for the ACT land already, Mr Maxwell said, "It is important to note that it was considered by the ACT Government between 2006 and 2015, and was approved to proceed".
"Riverview Developments is proud to be working with the ACT government to create a world-class, sustainable community for the people of Canberra and our region," Mr Maxwell said.
Mr Maxwell said a revised NSW rezoning gateway determination was issued by the NSW Department of Planning and Environment last Wednesday.
"Community consultation on the NSW rezoning at this stage is anticipated to occur in early 2019 with a decision from the NSW Government likely in late 2019," Mr Maxwell said.
"Subject to rezoning, no development will occur in NSW until at least 2033."
If the land is rezoned, the entire Ginninderry estate is expected to supply greenfield blocks for the next 40 years.
About 6500 homes will be built on the ACT side of the border, while about 5000 will be built in the NSW.
Construction on the first stage of the project, the new suburb of Straithnairn, began in April after the Ginninderra Falls Association withdrew its appeal against ACT planning officials' approval of the development in February.
About 350 homes will be built as part of stage one, and the suburb will be the first in Canberra to be built without any gas infrastructure.
Mr Maxwell said 204 blocks had already been sold in Strathnairn.
The next hurdle will be gaining approval for stage two of the development, which involves the construction of 809 homes.
Mr Maxwell said pending the planning minister's decision on whether the development was exempt from requiring an environmental impact statement, a DA would be lodged by the end of this year.
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