Confronted with an affordable housing crisis, Ramsey County commissioners say they can’t in good conscience build a new neighborhood in the well-heeled north suburbs that isn’t at least 20 percent affordable.

That’s why Ramsey County officials moved Wednesday to terminate their collaborative agreement with Arden Hills to redevelop the 427-acre Rice Creek Commons, the largest shovel-ready tract of land in the county.

Ramsey County, which owns the land that once was the site of the Twin Cities Army Ammunition Plant, known as TCAAP, still plans to build out the property with a mix of businesses and homes. But officials said it will do so through a more conventional development process, with the county and developer on one side of the table and city officials on the other.

“We will move forward in the traditional path as a landowner — Ramsey County working with its developer in the city of Arden Hills,” said Ramsey County Board Chairman Jim McDonough.

Arden Hills city leaders, noting that the Rice Creek Commons project will double the size of their city, have said they want to ensure that the huge project doesn’t jeopardize city finances or the quality of life for existing residents. They have accused the county of backing out of a 2016 preliminary master plan that called for businesses, shops and 1,460 housing units, with 10 percent of the housing considered affordable.

Ramsey County officials sent a letter Friday to Arden Hills officials, seeking termination of their joint powers agreement (JPA).

“If the city is not willing to terminate the JPA and dissolve the JPA, the county will pursue legal options to do so,” wrote Assistant Ramsey County Attorney Amy Schmidt.

Arden Hills City Administrator Dave Perrault said Wednesday that the city had just received the county’s letter. “The council will need to discuss and give directions as a future meeting,” he said.

The developer, Minneapolis-based Alatus, said it supports dissolving the joint powers agreement so it can move forward on the project, including purchasing land from the county, completing engineering and starting construction either late this year or early in 2020.

It’s expected to take 15 years or longer to build out the site.

Alatus President Bob Lux said he believes that over time his company’s quality work will build the community’s trust and that Alatus will be able to achieve the county’s affordability goals.

“It’s an aspirational and exciting project,” Lux said. “The best communities are those that have diverse offerings including a variety of housing types. That is what makes a great community. It just takes time.”

County leaders, who have already invested more than $40 million in the project, say that the need for affordable housing means that they must push for more of it. Increasing the density of the project will allow for more such housing, they say.

“Hardly a day goes by without someone talking about the affordability crisis in this community and the impacts,” said McDonough, who worked in construction before joining the County Board. “There are just not enough affordable housing options in our region to address those needs.”

Wednesday’s letter is the latest in a series of terse correspondence and exchanges between the county and the city that go back years.

After they entered into the joint powers agreement in 2012, the county bought the polluted land from the federal government and cleaned it up. But anything built there needs city approval.

In 2016, the city and county seemed to reach an agreement for a mixed-use development. But in November, County Administrator Ryan O’Connor sent a letter to Arden Hills officials saying the project needed more affordable housing and more housing in general.

Ramsey County last month asked for mediation, but the city rejected that move and said the county was being vague about its wants.

“It is impossible for the city or the public to evaluate the traffic, environmental and service delivery impacts of ‘more,’ ” according to a letter sent by Arden Hills city officials to the County Board.