An environmental group’s long-running lawsuit against southeast Utah’s White Mesa uranium mill has been dismissed in federal court, after state regulators testified on the company’s behalf and convinced the judge that their own actions on the mill’s radioactive emissions were invalid.

The Grand Canyon Trust, an Arizona-based advocacy group, sued the mill in 2014 after discovering its owner, Energy Fuels, had self-reported violations of radon emissions standards from one of the site’s tailings cells.

The group’s lawsuit, filed in U.S. District Court in Salt Lake City, sought to speed up the cell’s closure and reclamation in order to limit the impact on the nearby communities of Bluff and White Mesa from the radon, a harmful gas associated with radioactive decay and linked to lung cancer.

Residents of White Mesa, a Ute Mountain Ute reservation town about five miles from the mill, and Bluff, about 15 miles farther south, testified that they no longer used areas near the mill for recreation or cultural purposes, fearing exposure to radon gas.

But after a series of court filings by state officials, U.S. District Judge Clark Waddoups last month dismissed the case, ruling that regulatory standards the mill had violated did not actually apply to the waste storage cell in question, known as Tailings Cell 2.

Waddoups also turned aside other claims raised by the Grand Canyon Trust — including that the mill was operating more tailings cells that federal rules allow — on the basis that the state had not found any violations.

In a statement, officials with Colorado-based Energy Fuels said they were “obviously pleased that the District Court, after careful consideration, found in our favor.”

“It has been our position from the very beginning that the White Mesa Mill operates in compliance with the law, and the court confirmed our position in their decision,” they said in an email statement. “We also believe that this was a victory for the State of Utah, and their ability to regulate the mill in an effective manner that is protective of public health and the environment.”

But Aaron Paul, a staff attorney for the Grand Canyon Trust, said Waddoups’ ruling took the group by surprise.

“Frankly, it’s heartbreaking,” Paul said. “We put a lot of time and effort into that case, and we believed in it.”

Energy Fuels had not disputed the basic facts of the case — including that the company indeed detected levels of radon in excess of federal standards at Tailings Cell 2 in 2012 and 2013. Energy Fuels reported those violations, which the Utah Department of Environmental Quality acknowledged.

State regulators did not issue a formal notice of violation but instead required the mill to increase the depth of the cover on top of the tailings cell to stop the radon emissions and ordered increased monitoring of the cell to ensure the remedy had worked.

In his ruling, however, Waddoups found the state’s actions “directly contradicted the plain language of the regulation.” The radon rule that both Energy Fuels and state officials believed the mill had violated did not apply to Tailings Cell 2, Waddoups wrote, because it applies only to tailings cells that actively receive waste from a uranium mill.

This particular storage area, he noted, had not received new materials since 2008.

A top Utah regulator explained that the state took its initial action against Energy Fuels because mill managers had never told them the cell was no longer in operation.

“Typically when a source is no longer subject to a regulation, it’s in their interest to track that, and that pathway wasn’t triggered,” said Bryce Bird, director of the Utah Division of Air Quality.

In hindsight, Bird said he agreed with the court’s findings that the rule that sparked the state’s initial action against Energy Fuels did not apply.

Records suggested regulators then stopped enforcing the radon rule at the mill altogether in summer 2014.

The state Division of Radiation Control sent Energy Fuels a letter on July 23, 2014, “to clarify the regulatory status of Tailings Cell 2” and to formerly end monthly monitoring at the cell — on the condition that no additional waste materials be added to it.

According to the state’s letter, that clarification was actually requested by Energy Fuels in a letter dated May 30, 2014 — one month after the Grand Canyon Trust filed its lawsuit against the uranium mill. That request, according to Energy Fuels spokesman Curtis Moore, was made not long after the company acquired the mill in 2012.

At Energy Fuels’ behest, Bird and Phil Goble, a radioactive-materials manager with the state’s Division of Waste Management and Radiation Control, filed affidavits in the Grand Canyon Trust lawsuit on cell’s history from regulators’ perspective. Bird said he did not consider the move unusual.

But Paul, Grand Canyon Trust’s lawyer, said the regulators’ testimony effectively sank the case against the mill. He called the move “a bit unusual.”

“The state said in its own reports that Energy Fuels was in violation of the law,” Paul said. “When we sued, the story changed, and both the company and the state said, ‘In hindsight, we think that at least one of these waste pits was closed and had been closed for six years, even though everyone acted as thought it was open and needed to be monitored for radon.’ ”

Nonetheless, Grand Canyon Trust has decided against appealing Waddoups’ ruling, Paul said — in light of recent changes to federal regulations that would make the case even harder to win. Instead, he said, the group plans to push state regulators to include strict deadlines for the cell’s closure as part of the company’s operating permit.