Arizona approves higher arsenic limits at uranium mine nine miles from Grand Canyon

Three of the four wells across the Grand Canyon region with average arsenic levels exceeding the EPA's drinking water standard are located at a single uranium mine nine miles from the canyon's South Rim, according to a new analysis of federal and state groundwater data.

The Pinyon Plain Mine sits within a national monument on land the Havasupai Tribe considers sacred. The tribe's only water source, Havasu Creek, is fed directly by the deeper aquifer the mine drills into, and tribal leaders say they were never adequately consulted before Arizona regulators raised the mine's allowable arsenic levels earlier this year.

What the 32-year groundwater record shows

The Grand Canyon Trust, a nonprofit advocating for protection of the canyon and the Colorado Plateau, compiled the analysis from 32 years of sampling across 40 sites by the U.S. Geological Survey and the Arizona Department of Environmental Quality. The data shows the mine's monitoring wells contain water at nearly two, three, and six times the EPA's safe drinking water limit for arsenic. Groundwater in the mine's sump is over 3,000 times that limit.

One monitoring well at the site exceeded permitted alert levels for arsenic four times since 2025, according to Inside Climate News. Rather than investigate the cause, Energy Fuels Resources Inc. applied to amend its permit to allow higher arsenic concentrations, and ADEQ approved the request.

A dispute over what is causing the rise

The company and ADEQ attribute the elevated arsenic to natural conditions. They claim the mine's groundwater pumping creates a "cone of depression" that draws in water with naturally occurring arsenic from farther reaches of the aquifer.

Independent researchers reject that explanation. "If arsenic concentrations in groundwater outside the mine are lower than inside, how can drawing low concentration outside increase the already high and increasing arsenic concentrations inside the property," asked Dave Kreamer, emeritus professor of hydrology at the University of Nevada, Las Vegas. "You would think that adding cleaner water, groundwater from outside, shouldn't it dilute the high concentrations inside? I've been asking this question of ADEQ monthly since June 1, and have not got an answer yet."

Laura Crossey, an emeritus professor of earth science at the University of New Mexico who has studied the region's hydrogeology for decades, offered her own analogy. Dismissing data showing the aquifers are connected and that contamination can spread is "like studying the traffic pattern of Phoenix by only looking at the side streets and ignoring the interstates that move through, that are carrying much higher volumes, much higher speeds."

Why the Havasupai Tribe is fighting the decision

The Havasupai Tribe's reservation lies within the Grand Canyon, and Havasu Creek, famed for its blue-green waters, is its only water source. The creek is fed directly by the Redwall-Mauv aquifer, the same deep regional groundwater the mine's shallow aquifer connects to, according to reviews by the U.S. Geological Survey and the Environmental Protection Agency that found more research is needed to understand if the mine poses a threat to the region's water quality.

"Our people drink this water," said Havasupai Tribal Chairwoman Melinda Yaiva at a press conference announcing the findings. "We cook with it. We grow food with it. We care for our animals with it, and depend on it every day. It is also part of our ceremonies, our traditions, and our culture, and our identity as Havasupai people."

The tribe appealed ADEQ's decision to raise allowable arsenic levels at the mine. The agency's appeals board dismissed the case, ruling the tribe lacked standing. Yaiva said the tribe is considering other options, including legal action.

The gap in the monitoring program

Brad Esser, a retired environmental radiochemistry researcher at Lawrence Livermore National Laboratory, said the core problem is uncertainty. "This is a kind of a failure in the monitoring program and the regulatory process, because at the present time, we don't really know why the arsenic is rising, because it hasn't been thoroughly investigated."

If the mine's evaporation pond is leaking, it can be patched. If groundwater pumping is altering flow patterns, limits can be placed on pumping. But without a definitive study, no mitigation plan can be put in place.

Misael Cabrera, senior vice president of environment, safety and sustainability for Energy Fuels, defended the company's position. "Despite all of the evidence that we have on record, despite all of the regulatory approvals, despite the multiple court cases, we are still being assumed to be guilty before proven innocent," he said. Cabrera was director of ADEQ when the mine was being permitted.

What removes arsenic from drinking water

Arsenic is odorless and tasteless. Standard carbon filters do not remove it. Effective treatment requires either reverse osmosis, distillation, or specialized adsorptive media designed for arsenic removal. For point-of-use systems, the certification to look for is NSF/ANSI 53 or 58 with a specific arsenic reduction claim.

Reverse osmosis systems certified to NSF/ANSI 58 reduce arsenic at the membrane stage. Our reverse osmosis guide covers under-sink and countertop systems that meet this standard. For whole-house treatment on well water, specialized arsenic removal media can be added to a whole-house filtration system. If you are unsure what your well contains, start with a comprehensive water test before choosing a treatment approach.