VICTORIA - The home of a family staunchly opposed to the Site C dam will be seized under British Columbia's Expropriation Act to make way for the controversial hydroelectric project, says BC Hydro's president and chief executive officer.

Jessica McDonald said Monday the terms of the expropriation mean Ken and Arlene Boon must be out of their home by May 31 to allow highway realignment work linked to the $8.8-billion megaproject to start early next year.

But McDonald said the agreement allows the family to continuing farming their land for two more years before they must leave the property. The agreement was not reached by consent but was signed last week by the Boons and the B.C. government.

"We were not able to come to a consensual agreement with the Boons and so we have acquired their property through expropriation," said McDonald at a Site C project briefing with reporters. "We have agreed with the Boons that they will remain in their home until the end of May and that they will have the rights and ability to continue farming the land for an additional two year period of time."

Site C will flood more than 5,500 hectares of land along the Peace River, creating an 83-kilometre-long reservoir and provide enough power to light up 400,000 homes. Project construction started in the summer of 2015 and is scheduled for completion in 2024.

The Boons are long-time farmers in northeastern B.C. and have fought the project in court. They could not be reached for comment.

An online petition to stop the dam includes photos of the Boons on their property.

Arlene Boon states in the petition that their farmhouse was built by her grandfather and "Hydro's plan is to flood our property and destroy it."

McDonald said the value of the Boon expropriation agreement will be subject to negotiations over the next year.

"It sets out that they have committed they won't physically interfere with the project in any way, not just on their lands," said McDonald.

Hydro recently reached consensual property agreements with six other landowners in the area to make room for the highway project. McDonald said Hydro also expropriated the home of another landowner, who had a rental property on his land.

Hydro officials also said about 30 homes in the Peace River Valley area near Fort St. John will be affected by the dam over the course of construction, but 20 of those can be moved to other locations within their property boundaries.