What USGS Has Learned About Uranium Mining Around the Grand Canyon

The Colorado Plateau, including the Grand Canyon, holds natural deposits of uranium and other elements that have been mined for decades, and mining changes the landscape and the environment. The Grand Canyon is of immeasurable importance to Indigenous peoples who have lived in the region for thousands of years; it is a World Heritage Site that drew almost 5 million visitors in 2023; and the area includes Baaj Nwaavjo I'tah Kukveni–Ancestral Footprints National Monument, established in 2023.

The Grand Canyon region of northwestern Arizona, with major landholders and some of its uranium mines (status and Tribal land names as of January 2024). USGS.

Breccia pipes

The region has hundreds of distinctive geologic features called breccia pipes. A few contain uranium and other elements about 1,000 feet underground — some of the highest-grade uranium ore in the nation — and some have been mined; uranium is used to generate electricity. Since August 2023 new mining has been barred inside the new national monument, though a small number of existing mines there may continue, and pipes outside it could be mined in the future.

A breccia pipe uranium deposit: ore at depth, mainly in the Coconino Sandstone, reached by underground workings, with perched aquifers feeding local springs and the regional aquifer below. USGS, modified from Alpine (2010).

The studies

In 2012 the Department of the Interior directed the U.S. Geological Survey to study the effects of uranium mining in the region. Studies designed with resource managers are finished or under way, and their results are public.

What mining does to what people use

• It's not only uranium. The ore is rich in many elements — arsenic, cadmium, cobalt, copper, lead, molybdenum, nickel, selenium, silver, sulfur, uranium and zinc.
• Soil. Mining raises levels of uranium and some of these elements in the soil around mine sites.
• Dust. Wind carries dust containing these elements into surrounding areas.
• Radon. During active mining, ore piles give off more radon gas than the mine vent does, though wind and rain keep it from building up. Radon is known to be hazardous to people, but there are no outdoor risk thresholds for it.

Effects on plants and animals

• Uranium is not always the biggest worry; other ore-related elements matter too. Traditional and new tools were used to trace how elements move through local food webs — by eating, breathing, absorption and diet.
• Health risks from these elements were low for the land animals studied. Arsenic, cadmium, copper and zinc posed the greatest risk, to animals that eat ants and other invertebrates at mine sites. Risks to aquatic animals are unknown.
• Harm to plants and land animals is unlikely even after long-term (30-year) exposure.
• Radiation levels in plants and animals were low. Rodents take in radiation through soil — burrowing, incidental swallowing, dust bathing — and food, but radium-226, the radionuclide of most concern for them, stayed below harmful levels.
• Plants and animals do absorb mining-related radionuclides, uranium and other elements, but direct effects such as death or stunted growth were not found. Arsenic and selenium in water at mine sites, though, may harm aquatic animals such as tadpoles.

USGS research at breccia pipe mines: a pipe in cross section, soil sampling at a mine, the plants and animals studied, water-quality work and aquatic invertebrate sampling at a spring, and the Colorado River. The rock pinnacles at upper right are what the Havasupai Tribe calls Wi'i Gileeva. USGS.

Water

• Mines aren't the only source. Uranium occurs naturally in groundwater and the springs it feeds. In some Grand Canyon springs it is bound up with bicarbonate, a form water-dwelling invertebrates generally don't absorb.
• The Colorado River carries low levels of uranium and related elements. Tributaries where mining has occurred or could occur sometimes have more, but usually add very little to the river.
• Groundwater age matters: old water is mostly cut off from surface contamination. The deep groundwater feeding most South Rim springs is mostly old, though some springs include younger water, which is easier to contaminate.
• Aquatic insects such as mayfly larvae take up little uranium, partly because they don't absorb the forms in their water; most uranium in their food passes through, and what reaches mayfly tissue is quickly removed. So they are unlikely to carry uranium onto land.

Open questions

Many questions remain: how dust carries uranium and other elements off mine sites over a mine's whole life cycle, from natural state to reclamation; how these elements affect animals not yet studied, such as elk, which local Tribes traditionally hunt; where the uranium in springs and groundwater comes from — a sign in Grand Canyon National Park warns hikers not to drink uranium-contaminated water in Horn Creek, and Havasu Falls is fed by groundwater springs; and what exposures occur during cultural uses of resources. USGS continues this work with partners, and resource managers can use the results in decisions about mining on federal lands.

Aspects of uranium mining that are still poorly understood: dust from ore trucks, the mine life cycle, effects on elk, uranium in springs such as Horn Creek, and the groundwater behind Havasu Falls. USGS.

Sources

Rewritten from the U.S. Geological Survey Fact Sheet 2024–3003, "Balancing natural resource use and extraction of uranium and other elements in the Grand Canyon region" (public domain), in hubnx's own words.