Settlement talks collapsed weeks ago between the Department of Energy and environmental groups who sued the agency over its plan to produce nuclear-weapons cores in South Carolina, a Tuesday court filing shows.

“Both parties were hopeful that the nearly two-month mediation process would bear fruit and focused their attention on those settlement efforts,” Todd Kim, assistant attorney general for the environment and natural resources division at the Department of Justice, wrote in Tuesday’s filing. But “it became clear several weeks ago that an amicable resolution of this dispute is unlikely.”

With a settlement out of the question, the parties have asked the U.S. District Court for South Carolina for two more weeks to complete briefings in the long-running lawsuit from June 2021, which has now dragged on for more than two years and eight months.

If the judge grants the request for an extension, the government and the environmentalists would finish briefing their cases by June 28. The next filing in the case, a joint stipulation of facts that catalogs things the parties agree about, was supposed to be due April 5th, according to Tuesday’s filing.

Plaintiffs in the suit are Savannah River Site Watch of South Carolina; Tom Clements, director of Savannah River Site Watch; The Gullah Geechee Sea Island Coalition, a group representing the interests of some descendants of enslaved Africans dwelling on the lower Atlantic coast; Nuclear Watch New Mexico of Santa Fe, N.M.; and the Tri-Valley Communities Against a Radioactive Environment, of Livermore, Calif.

The environmentalists say that the Department of Energy’s National Nuclear Security Administration (NNSA) cannot build the Savannah River Plutonium Production Facility before completing a programmatic environmental impact statement about the agency’s plan to produce plutonium pits, nuclear-weapon first-stage cores, at the Savannah River Site and the Los Alamos National Lab in New Mexico.

The NNSA said it satisfied its environmental obligations for the Savannah River Plutonium Production Facility by completing a site-specific review of the planned facility, which will be constructed from the partially completed Mixed Oxide Fuel Fabrication Facility.

The estimated cost of the Savannah River pit plant has soared in recent years. In its 2025 budget request, the NNSA estimated the final construction bill could be between $18 billion and $25 billion, or up to double the estimate provided last year in the agency’s 2024 budget request.

Los Alamos will be the first of the two sites to start casting pits for the planned W87-1 land-based, intercontinental ballistic missile warhead. Lab officials estimate they will begin producing pits for the stockpile by December and be making 30 pits per year in 2028.

The agency has a legally binding deadline to make at least 30 pits a year by 2026 and at least 80 a year by 2030, when the Savannah River facility was supposed to open. The South Carolina plant now may not begin making pits until sometime next decade, the NNSA has said.