Over intense opposition from the Havasupai Tribal Council, state officials quietly reclassified a request from the Pinyon Plain uranium mine to adjust acceptable levels of toxic chemicals in a critical shared aquifer.
The aquifer supports Havasu Falls, a tributary of the Grand Canyon that sees 40,000 visitors every year (Photo: Putt Sakdhnagool/Getty Images)
Published July 8, 2026 03:36PM
Arizona officials just voted to allow a uranium mine near Grand Canyon National Park to raise the allowable levels of the highly toxic heavy metal arsenic level in a monitoring well located near the Grand Canyon.
The mine, called the Pinyon Plain Mine, also sits atop an aquifer that provides the sole water source for a local tribe, and the source of Havasu Creek, a tributary of the Grand Canyon.
On July 6, the Arizona Department of Environmental Quality (ADEQ) raised the allowable levels of arsenic in Pinyon Plain Mine’s monitoring well from 50 to 55 micrograms per liter. Environmental groups and the Havasupai Tribe say the decision could have large ramifications for the Grand Canyon National Park and beyond.
“These monitoring wells are the canaries in the coal mine. They tell you something’s off here,” Amber Reimondo, energy director for the nonprofit Grand Canyon Trust, told Outside. “The original maximum allowed level was already five times the drinking water standard.”
The Environmental Protection Agency (EPA), by comparison, sets the arsenic standard for drinking water at ten micrograms per liter due to its potential to cause several types of cancer, including bladder, lung, skin, kidney, liver, and prostate.
In an email to Outside, ADEQ spokesperson Caroline Oppleman said that the decision does not allow the “introduction of pollution or a weakening of safeguards.”
“Over four-and-a-half years of rigorous, site-specific data confirm that the mine is not adding arsenic to the groundwater,” she said. “Rather, the physical structure of the mineshaft has created a hydraulic sink that draws existing, naturally-occurring geological arsenic from the surrounding area toward the perimeter wells. Adjusting these limits simply reflects this natural geological reality.”
Located seven miles south of Grand Canyon National Park, the Pinyon Plain Mine was built in the eighties, spans 17 acres, and runs nearly 1,500 feet deep. The mine also sits atop the Redwall-Muav aquifer, which is both the sole water source for the local Havasupai people and the source of Havasu Creek, a tributary of the Grand Canyon famous for its iconic turquoise waterfalls. As many as 40,000 tourists visit these falls each year.
Nonprofits like the Grand Canyon Trust say that shifting the arsenic limits in the mine’s monitoring well introduces a dangerous variable into a fragile ecosystem. If arsenic seeps into the deep groundwater pathways, it could reach the aquifer and permanently pollute the canyon’s natural springs, the group said.
“These arsenic increases were detected back in January 2025, but we only happened to find out about it this January, when I noticed that there was a permit in progress at Pinyon Plain Mine,” Reimondo said. “If arsenic increases are detected, that should trigger an intensive investigation to understand the cause, not just changing the level at which alarm bells go off.”
Hydrology in the Grand Canyon is complex, Reimondo said, making it difficult to determine where water runs and the extent of potential contamination.
“It’s difficult to know, if water is contaminated at a given point, where it can go. It can travel vast distances horizontally and vertically. Mining in the region has the potential to cause contamination to the springs both inside the Grand Canyon and the groundwater,” she said.
Havasupai Tribal Council chairwoman Melinda Yaiva opposed the decision, said in a Facebook post the decision is “a profound attack on the Tribe’s inherent responsibility to guard and protect the waters of the Grand Canyon.”
Environmental groups like the Sierra Club say the decision could put the aquifer and the waters of the Grand Canyon at risk and, as a result, public health. Arsenic could also pose a major risk to backcountry hikers—standard backpacking filters catch bacteria, but not dissolved heavy metals like arsenic.
“ADEQ ignored the voices of the Havasupai Tribe, other Tribal Nations, elected officials, scientists, conservation organizations, and countless members of the public who urged ADEQ to place the protection of Arizona’s groundwater above the interests of a foreign mining company,” Yaiva said.
