A half-mile underground beneath a windswept field in the southeast corner of New Mexico, hundreds of workers haul drums of radioactive waste into a salt mine that will entomb them for at least 10,000 years.

Up on the surface, federal officials overseeing the Energy Department's Waste Isolation Pilot Plant (WIPP) are working harder than ever to smooth over tensions with state officials and skeptics in the state capital so the facility can meet its mission: cleaning up the country's nuclear weapons production sites.

WIPP is the only geologic repository for nuclear waste in the country. Since 1999, the Energy Department has used it for one of the world's largest environmental cleanup missions.

The mine employs about 1,500 people and now holds drums full of roughly 2.6 million cubic feet of tools, clothing, soil, and other objects contaminated by research and development of the atomic bomb and the nuclear arms race.

People in Carlsbad, N.M., near WIPP, have always liked it for the jobs. That kind of community support for storing nuclear waste will need to be replicated if the U.S. is to meet President Joe Biden's goal of decarbonizing its power sector, relying partly on nuclear power plants.

But New Mexico regulators - under pressure from nuclear opponents, who worry the state has become a nuclear waste dumping ground - want the authority under a 10-year hazardous waste permit to halt shipments if they see an environmental or health threat or if new legislation from Washington increases its disposal limit. New Mexico also wants the Energy Department to begin looking for repositories in other states.

"We need to reclaim our authority in many ways that the permit is going to do," said James Kenney, the state's environment secretary, who says the Energy Department has treated New Mexico as an afterthought. "We need authority to stop shipments, to stop waste streams, to require investigations if there are problems."

The state's stance infuriates community leaders in Carlsbad, a town of 32,000. Local officials, hoping to wean off boom-and-bust industries like oil, see WIPP as a stable economic driver and good neighbor. They want more nuclear facilities, including on a nearby private site where a developer plans to store spent fuel from civilian reactors. They, and others in the nuclear industry, have touted that project as a model for the department's efforts to garner community consent for nuclear waste.

WIPP is a "marvelous project and a national treasure," said John Heaton, a former Democratic state representative from Carlsbad, who has an honorary room in the mine complete with an autographed bolt hammered in the ceiling.

Nuclear industry opponents who influenced the state's draft permit have little understanding, Heaton said, of the facility's safeguards. "The way that is written is absolutely absurd and makes no sense," he said. The permit "becomes a way to stop WIPP, and it would be a tragedy to stop WIPP."

The Energy Department declined to comment on how the proposed permit conditions would affect operations. But officials have acknowledged they need to do better in New Mexico as nuclear waste piles up nationwide.

When state officials complained about the department's shortcomings, "I took that to heart," said Ike White, who leads the department's Office of Environmental Management, which has a $8.3 billion annual budget and more than 30,000 employees and contractors working on waste cleanup at 15 sites in 11 states.

New Mexico's draft permit contains "areas of fairly significant agreement," White said. On the contentious points, he pledged constructive negotiations.

In the 1980s, Congress established a national nuclear waste disposal program that sought to set up repositories for different categories of waste from weapons sites and civilian power plants.

Lawmakers designated Yucca Mountain, about 90 miles northwest of Las Vegas, as the country's sole burial site for spent nuclear fuel and the most highly radioactive waste. The plan eventually foundered due to strong public and political opposition in Nevada, and as a result, U.S. nuclear waste remains stored across the country at 75 nuclear power plant sites in 33 states.

Things went differently in New Mexico. The Carlsbad area was confronting a downturn in industries that had sustained it. Potash mining struggled to compete with cheaper imports. An oil and gas drilling boom hadn't yet arrived, and unpredictable commodity price swings challenged local budgets.

When Congress passed the Waste Isolation Pilot Plant Land Withdrawal Act in 1992, the facility moved forward. WIPP would store up to 6.2 million cubic feet of transuranic waste, a designation that includes contaminated clothing, rags, soils, tools and other elements. It was expected to fill up by 2024, but the law didn't stipulate a closure date.

As the first trucks with waste passed through Santa Fe, dozens of protesters jeered them, horrified that their communities were subjected to the threat of an accident that would sicken hundreds of people.

But when the shipments arrived in Carlsbad, hundreds of people cheered along the highway. Scientists, miners and construction workers flooded the area to build and operate the site.

"It really changed the whole DNA of our town," said Jack Volpato, chairman of the Carlsbad mayor's nuclear task force.

WIPP appears unremarkable at first. Beige buildings, a hoist and a mound of mined salt emerge from the grassland about a 40-minute drive from Carlsbad.

Inside the heavily guarded security gate, the site is busier than at any time since the 2014 incident.

Crews work on a new ventilation system. Workers check waste that arrives in double-lined steel shipping casks on semitrailers to ensure they meet WIPP's criteria, and then take them 2,150 feet underground - a five-minute elevator ride into the pearly white walls of the Delaware Basin.

Workers haul the drums through the vast underground network, geothermally heated to about 82 degrees Fahrenheit at all times. Salt crunching under their boots, they navigate with handheld maps, posted coordinates and color-coded emergency escape routes. The drums are stacked in rooms nearly as long as a football field. Workers often end their shift with a salty aftertaste.

The salt seam is naturally elastic, WIPP officials say, so when one panel closes, the salt gradually collapses and molds tightly around the drums. Elsewhere, mammoth mining machines chew new passages through the seam, installing bolts to keep the migrating salt at bay.

WIPP today is 42% full, and shipments could run another 60 years before hitting the legal limit, according to department estimates. Delays stem from slower-than-expected waste cleanup and a 2014 radioactive release at WIPP that halted shipments for more than three years.

This year's permit comes at a "particularly critical time," said Don Hancock, who has been advocating against the facility since 1975. His office in Albuquerque is filled with newspaper clippings and with binders of WIPP permit documents. A sign hangs in his window: "Another Business Against Forever WIPP."

"What we need the state to do, in our view, is send some clear messages in the permit," Hancock said, "that they're serious about limiting WIPP, including its lifetime."

The 2014 incident fueled concerns. Investigators determined Los Alamos workers mistakenly used the wrong type of kitty litter - a common absorbent of liquid nuclear waste - which caused one drum to burst. Tests showed 35 employees absorbed elevated levels of radioactivity, though most showed a dose akin to a chest X-ray, the department found.

When the facility reopened in 2017, it installed filters underground for radioactive particles. Those filters required a new $486 million ventilation system, which is years behind schedule and nearly 70% over budget, government auditors discovered last year.

WIPP "was never designed to deal with radioactive releases in the underground because it wasn't going to happen," Hancock said. "It happened in the first 15 years."

The facility could soon receive another waste stream: plutonium from weapons production that would be diluted to meet WIPP acceptance criteria.

The state and some local officials have derided the "dilute and dispose" plan as an illegal expansion that will cause more traffic on the roads around the state. New Mexico Governor Michelle Lujan Grisham protested to Energy Secretary Jennifer Granholm. The department insists the plan fits within WIPP's original mission.

In March, the tension escalated beyond WIPP when Lujan Grisham signed a law banning permits for the $3 billion spent fuel storage facility in southeast New Mexico proposed by Holtec International to hold fuel from civilian reactors.

Future negotiations about where to put nuclear waste in the U.S. will likely involve players like Anna Hansen, chair of the Santa Fe Board of County Commissioners, who has advocated against WIPP and called the plutonium disposal plan "insanity" and "an endangerment to my constituents."

Recently, however, she has been a diplomat of sorts between the governor and Energy Department officials. She described the meetings in Washington as a positive sign of thawing relations.

The department offered an olive branch to Kenney, the state environmental director: a new engagement and messaging strategy formalizing its plans to work better with New Mexico. So far, the department has organized public forums in Santa Fe - and Hansen moderated the third one in April.

"The lines of communication are open," she said.

Volpato, the Carlsbad nuclear task force chair, said greater outreach could help his neighbors up north see WIPP's value. As a high-schooler, he was against the project - until the Energy Department and local supporters held meetings to explain the science and quell fears.

"As time went on, and I got educated on exactly what they were doing, you know, you get the big picture of something," Volpato said. He ended up joining a construction crew that built the roads leading to WIPP today.

"I came around to be a believer and supporter of WIPP," he said. "And I think that was a lot of people in the area."