The Arizona Department of Environmental Quality has agreed to revise groundwater arsenic limits for a monitoring well at the Pinyon Plain uranium mine south of the Grand Canyon, concluding that higher arsenic levels in the well were naturally occurring.
The Havasupai Tribe raised concerns about the proposal, sought by mine operator Energy Fuels Inc., to allow higher levels of arsenic in a groundwater monitoring well near the mine, warning that the changes threaten Havasu Creek, the tribe's sole water source.
Chairwoman Melinda Yaiva said ADEQ "could have stood with the Havasu ‘Baaja and the people of Arizona and honored its obligation to protect our most precious resource. Instead, it chose to lower the bar for pollution and weaken environmental protections."
"That decision does not simply affect the Havasu ‘Baaja — it affects every Arizonan who depends on clean groundwater today and every child who will depend on it in the future. We cannot replace a contaminated aquifer. We cannot recreate a sacred spring," said Yaiva.
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The Arizona Department of Environmental Quality has agreed to revise groundwater arsenic limits for a monitoring well at the Pinyon Plain uranium mine south of the Grand Canyon.
"We can only protect them before they are lost," Yaiva said. "The Havasu ‘Baaja will never stop defending the waters that have sustained us since our beginning, because protecting water is protecting life itself."
Energy Fuels sought the permit amendment after collecting about 4½ years of groundwater data, including enhanced monthly monitoring that began in January 2025.
Tribe: Decisions should reflect 'highest standard of care'
The proposed changes would increase the aquifer quality limit for arsenic at one monitoring well (the North Well, or MW-02) from 0.050 to 0.055 milligrams per liter. The amendment to the permit would also raise the associated alert level, an early warning threshold, from 0.040 to 0.050 milligrams per liter, according to ADEQ.
The Havasupai Tribe strongly condemned the state agency's approval of Energy Fuels' request, saying ADEQ ignored the concerns of the tribe, other tribal nations, elected officials, scientists, conservation groups and members of the public who urged officials to prioritize Arizona's groundwater over the interests of a foreign-owned mining company.
"For the Havasupai Tribe, Havasu Creek is our only permanent source of water and the heart of our culture, homeland, economy, and identity," Yaiva said. "Arizona is an arid state where clean water is increasingly precious, every decision affecting groundwater should reflect the highest standard of care. Once an aquifer is contaminated, the consequences may endure for generations."
Before ADEQ made its decision, U.S. Rep. Adelita Grijalva wrote a letter to Wendy Eikenberry, manager of groundwater mining and industrial permits at the agency, expressing concern about the request to increase aquifer alert levels and water quality limits for arsenic. Because of what it could mean for public health and environmental oversight, she urged the department to deny the request.
"As I understand it, additional studies and analyses help determine whether the elevated arsenic levels are naturally occurring or the result of mining activity has not yet been completed," she said. "Therefore, the company’s claim that these increases are naturally occurring remains unverified."
State officials say arsenic is naturally occurring
ADEQ had noted earlier that the changes were not the result of pollutants discharged from the mine into the aquifer, but of naturally occurring arsenic, which is why the agency decided to support Energy Fuels' request.
ADEQ said its decision followed a comprehensive review of data collected by Energy Fuels. The agency concluded the data show that naturally occurring arsenic from surrounding geology is moving toward the mine's perimeter wells because of a hydraulic sink created by the mineshaft, that the company is not adding arsenic to the groundwater, and that ongoing mining operations, including dewatering, will maintain the hydraulic sink throughout the life of the mine.
The Center for Biological Diversity and scientists specializing in hydrology and geology submitted comments before ADEQ made its decision, questioning the adequacy of the investigation and the technical basis for Energy Fuels' claim that naturally occurring conditions justify raising the arsenic limit.
"Whether pollutants are linked to facility discharge isn’t the right question. The question is whether the pollution is the result of mining operations, and they haven’t shown that it’s not," said Taylor McKinnon, Southwest director of the Center for Biological Diversity.
Bradley K. Esser, a retired scientist, group leader and project leader from Lawrence Livermore National Laboratory, who holds a PhD in geology and geophysics from Yale University, submitted technical comments to ADEQ identifying what he said were serious deficiencies in the investigation and technical demonstration submitted by Energy Fuels Inc.
He wrote about Energy Fuels' claim that water seeping into the mine shaft has created a draw that pulls groundwater toward the mine. The company argues that, as a result, monitoring well MW-02 is collecting groundwater from farther away that naturally contains higher arsenic levels, rather than water affected by mining.
Esser noted that this explanation is possible, but he argued it has not been backed by enough evidence. He said Energy Fuels Inc. has not shown that groundwater outside the mine contains arsenic levels similar to those found at MW-02 or ruled out the possibility that mining operations are causing the higher arsenic levels.
