The owner of a uranium mine near the Grand Canyon wants state regulators to allow a higher level of arsenic in groundwater under the facility.
Two scientists, however, object to the proposal, arguing regulators shouldn’t approve it until a more robust investigation into the elevated arsenic levels takes place. Energy Fuels Resources, the owner of the Pinyon Plain Mine, says its investigation was thorough and that operators aren’t at fault.
The mine sits near the South Rim of the Grand Canyon and Red Butte, a geographical feature the Havasupai Tribe considers their place of emergence.
An aquifer thousands of feet underground serves as the sole source of drinking water for the tribe, which opposes the mine.
How we got here
In January 2026, Energy Fuels asked the state Department of Environmental Quality (ADEQ) to sign off on amending a water quality permit for one of the mine’s monitoring wells after the company noticed elevated arsenic levels.
If approved, the amendment would allow a higher arsenic level by raising it from 0.05 mg/L to 0.055 mg/L.
In its application, Energy Fuels wrote that there’s a higher arsenic level because of natural phenomena, not because of discharge from the mine or its activities.
According to the application, that phenomenon is a widening cone of depression in the perched Coconino aquifer that draws groundwater with naturally higher arsenic concentrations to the monitoring well.
Curtis Moore, Energy Fuels’ senior vice president of marketing and corporate development, tells KNAU that the presence of arsenic in groundwater is a byproduct of the mine’s proximity to minerals like uranium, arsenic and copper.
“It's not surprising that there are elevated levels of arsenic next to this ore body,” says Moore. “That's why we put a mine there, because there's an ore body there. But, you know, there's really no evidence that demonstrates that arsenic is leaving the site. In fact, it's coming into the mine.”
Some scientists disagree
But Brad Esser, a retired scientist who worked at Lawrence Livermore National Laboratory, calls Energy Fuels’ explanation for the higher arsenic levels a hypothesis, not a proven fact. Esser specializes in groundwater science and environmental geochemistry.
In a technical comment sent to ADEQ, Esser wrote that the agency shouldn’t approve the minor permit amendment without first requiring more analysis from Energy Fuels. Another comment submitted to ADEQ by David Kreamer, a professor emeritus at the University of Nevada, Las Vegas, makes similar points to Esser’s.
“It sets the wrong incentive,” Esser says. “The response to high levels that get close to or exceed your permit levels is to try to understand what's going on, not just simply raise the permit levels.”
The conservation nonprofit Grand Canyon Trust, which opposes the Pinyon Plain Mine, asked Esser to review Energy Fuels’ permit application. In the past, Esser says he volunteered for the nonprofit by helping with pollinator gardens and building small dams.
He says he received no payment from Grand Canyon Trust for writing his technical comment. An employee with the trust told KNAU in a text message the nonprofit did not ask Kreamer to submit a comment or reach out to him.
While Esser and Kreamer say it’s certainly possible Energy Fuels’ explanation for higher arsenic levels is accurate and that the mine is not the cause, they argue it’s more likely the operations of the Pinyon Plain Mine are directly related to the increase.
They say the mine’s ventilation shafts and exploratory bore holes could be creating oxygen-rich groundwater, causing arsenic minerals to dissolve and thereby raising the levels in the monitoring well.
Above all, Esser says Energy Fuels didn’t provide enough evidence to support its explanation for why the company should get a revised permit from ADEQ, and that it should have explored alternative explanations, like the impact of oxygen-rich groundwater.
But Moore says that’s not true. He called the theories in Esser’s technical comment “unlikely assumption[s]” which the available data refutes.
“They are really just far more plausible scientific explanations for why arsenic is rising in that single monitoring well,” he says, pointing to the proximity of the mine to the ore body.
In an emailed statement about Esser’s comment, ADEQ wrote, “While the agency appreciates the technical perspective provided, our internal scientific evaluation—based on site-specific hydrogeological data—supports a different conclusion.”
Their conclusion appears to align with Energy Fuels: That nearby high-arsenic groundwater is flowing toward the mine and causing the increase.
“ADEQ confirms this phenomenon by monitoring water withdrawal rates and groundwater levels at perimeter wells,” the agency wrote.
At the end of the day, Esser says if ADEQ approves Energy Fuels’ permit amendment, it would be “setting a precedent whereby rising contamination levels lead to rising permit levels, [and] that defeats the purpose of monitoring.”
He worries arsenic could one day reach the Havasupai people’s drinking water.
“Groundwater systems can operate very slowly, so it could be decades before we see the impact of these high arsenic ground waters at the mine site in, for instance, … [a] spring that the Havasupai are using,” Esser says.
Moore says that’s not going to happen.
“Those are perched, isolated aquifers not connected to any regional groundwater systems,” he says.
ADEQ is in the final stages of evaluating Energy Fuels’ request. It expects to announce its permitting decision in June.
