Ramsey County now wants to build as many as 2,500 new houses and apartments on the massive Twin Cities Army Ammunition Plant (TCAAP) site, to the surprise of Arden Hills officials.

That’s significantly more than the 1,460 homes and apartments laid out in a 2016 preliminary master plan approved by both the county and the city of Arden Hills.

County staff revealed the higher housing target for the 427-acre site in a report released this week. They say more homes and apartments should be built to make the project financially viable and in response to the region’s mounting affordable housing crisis.

At least 20 percent of sites on what is now called Rice Creek Commons should be affordable, the report states.

“In simple terms, the closer the density moves toward a maximum development scenario of 2,500 total housing units, the easier the project will be to finance and successfully deliver,” according to the report.

Arden Hills leaders said Friday they’re stunned.

The county has “never given us that number,” said Arden Hills Mayor David Grant. “I am shocked. They are backing out on their deal.”

“Those numbers would put the city of Arden Hills at financial risk,” said City Council Member Brenda Holden.

Sara Thatcher, Ramsey County’s spokesperson for the Rice Creek Commons, said the 2,500 number is the ceiling — and it isn’t new. It had been contemplated as the maximum number of homes that could be built on the site as early as 2014.

The county’s report, which was prepared for Tuesday’s County Board meeting, is the latest salvo as the partnership between Ramsey County and Arden Hills has soured in recent months.

The County Board will vote Tuesday on whether to explore legal options to end its formal power-sharing agreement with the city, which has guided development of the project for the past seven years.

Arden Hills and Ramsey County entered into a joint powers agreement in 2012 to guide redevelopment of the shuttered ammunition site. Ramsey County purchased the land from the federal government in 2013, and the two entities have worked together to develop it.

City leaders envisioned a spacious suburban community that mirrored the surrounding area, while county leaders pushed for a higher-density design with more affordable options.

The preliminary plan approved by both city and county in 2016 called for a mix of offices, businesses and 1,460 housing units with 10 percent of them affordable.

But county officials, confronted with a ballooning regional housing shortage, now want to build more homes.

Arden Hills leaders, fearful that the project could swamp the city financially, want to stick with the 2016 plan.

Rice Creek Commons, which covers about the same area as downtown St. Paul, is considered the largest shovel-ready tract of land in Ramsey County.

The county has already spent more than $40 million on the project.

Some Arden Hills residents say they back their city leaders’ efforts to rein in the project.

“It just seems like quite a rash decision to change what’s been worked on for several years,” said resident Kelly Balthazor. “It will have a huge impact on our community. It’s the largest development project in our lifetime.”