Uranium Mining and Groundwater in the Grand Canyon Region

In the arid Grand Canyon region of northwestern Arizona, water comes mainly from the Colorado River and its tributaries, and from groundwater that surfaces as seeps and springs. That groundwater supplies people and sustains rich ecosystems around each spring. The region is also full of uranium — in deposits both mined and unmined — that can interact with the water. This summarizes what U.S. Geological Survey (USGS) studies from 2012 to 2023 learned.

Where the water is

Rain and snowmelt soak into the ground on high country such as the Kaibab Plateau and San Francisco Mountain (the "San Francisco Peaks") and collect in two main aquifers — layers of rock whose cracks and pores are full of water:

The Havasupai Tribe has relied on R-aquifer groundwater as the main water source for Supai for its entire existence.

Havasu Falls, fed by R-aquifer groundwater from Havasu Springs, one of the region's largest springs. Credit: U.S. Geological Survey.

How fast it moves

Groundwater here takes both fast and slow routes. Fractures, joints and faults can carry water quickly; tight mineral bonds and fault damage slow or block it; and those pathways change as rocks shift and openings widen or fill.

• Slow: water can take several hundred to tens of thousands of years to travel from rain and snowmelt on San Francisco Mountain to springs along the South Rim.
• Fast: in a few places with open pathways, water can move from the C-aquifer down to the R-aquifer in years to decades.

A telling example: on the South Rim, treated wastewater from Grand Canyon National Park is released into the usually dry Bright Angel Wash along the Bright Angel Fault. Compounds from it — pharmaceuticals, nutrients, artificial sweeteners and PFAS — have turned up at a spring known locally as "Monument spring," meaning surface water got down through several thousand feet of rock in a matter of years. Nearby springs don't show that mix; their chemistry points to older water that entered the ground before the 1950s.

Breccia pipes and uranium

Breccia pipes are underground, chimney-like structures that can hold high concentrations of uranium, copper, arsenic, lead and zinc. They were once pathways for fluids, but mostly sealed over time as uranium and other minerals were deposited. Rooted in the Redwall Limestone, they can rise several thousand feet through the C-aquifer and the Kaibab and Toroweap Formations. Several have been mined.

Schematic, not to scale: an unmined breccia pipe (left) and the Orphan Mine and its breccia pipe (right). Dashed blue lines show how water may interact with the mine workings. Credit: U.S. Geological Survey.

The metals occur naturally, but mining can open new routes for water to travel deeper, and how water behaves in those routes over a mine's life — and along fast pathways near mines — isn't well understood. That's why USGS focused studies on water chemistry near mines.

What the measurements show

• Mostly below the standard. Uranium in the region's waters is generally lower than the Environmental Protection Agency's drinking water standard of 30 micrograms per liter (µg/L); only a few sites are higher.
• Horn Creek. The highest uranium USGS has measured in the region — 293 µg/L — was at a spring in Horn Creek on the South Rim, near the Orphan Mine, a former breccia pipe copper and uranium mine that may have pathways for water through its workings.
• Pigeon Spring. Uranium measured 50–92 µg/L at Pigeon Spring, near the Pigeon Mine north of the canyon — but a focused investigation suggested it comes from elsewhere, not from the mine.

The warning sign at Horn Creek. Credit: U.S. Geological Survey.

These studies have added to what is known about the region's scarce water — how long it spends underground and where its elements come from — and USGS research continues on groundwater movement and the sources of uranium and other trace elements.

Sources

Based on "Water Resources Related to Breccia Pipe Uranium Mining in the Grand Canyon Region," USGS Fact Sheet 2024–3055, U.S. Geological Survey; a work of the United States government in the public domain. Full text.