U.S. Geological Survey Develops Approach to Assess Baseline Chemical and Radiological Conditions Prior to Uranium Mining near Grand Canyon National Park

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U.S. Geological Survey (USGS) scientists developed an approach and collected baseline data to quantitatively assess offsite migration of mine-related contaminants and to identify critical contaminant exposure pathways that could result from uranium mining activities in the Grand Canyon region.

Canyon Mine Sampling

USGS scientists collecting soil samples at Canyon Mine.

(Credit: Katie Walton-Day, US Geological Survey. Public domain.)

This study established chemical and radiological baselines in the environment within and surrounding the Canyon Uranium Mine (located approximately 12 miles south of Grand Canyon National Park) in northern Arizona prior to ore extraction. This study is part of a larger, 15-year study whose goals are to reduce uncertainties related to the effects of mining on water quality and quantity, understand the potential toxicological and radiological effects of mining on wildlife, and to evaluate potential effects on cultural and tribal resources.

A map showing the locations of decision units surrounding the Canyon Mine, Arizona

A map showing the locations of decision units surrounding the Canyon Mine, Arizona. The scientists used a incremental sampling methodology to collect samples from the predefined decision units. The points (squares and circles) indicate locations where surface soil subsamples were collected during June 2013. Modified from figure 2 from Naftz and Walton-Day, 2016.

(Public domain.)

The approach used in the study included newly developed incremental sampling methodologies combined with multivariate statistical methods to produce repeatable and scientifically defensible datasets that will be compared to similar datasets during and after ore extraction.

Soil and streambed sediment samples were collected in June 2013 and analyzed for uranium and 41 other elements including arsenic, cobalt, copper, chromium, molybdenum, nickel, lead, antimony, selenium, vanadium, and zinc. Surface radiation was measured at selected sampling sites. Preliminary results from the baseline data collection indicate some naturally occurring contaminants (uranium, arsenic, molybdenum, and vanadium) in the environment are elevated within the mine perimeter as compared to soils outside the mine perimeter.

Companion baseline and comparative studies are also being conducted on water (where available), dust, plants, and animals at the same sites as part of a comprehensive USGS study in this region. Together these studies will provide foundational environmental datasets on occurrence, distribution, and exposures to contaminants associated with uranium mining activities.

Environmental Health Considerations

Citing the need for more scientific information to assess the effects of uranium mining, previous Secretary of Interior Ken Salazar withdrew just more than 1 million acres of Federal land near Grand Canyon National Park in 2012 for 20 years. USGS scientists with different areas of expertise are working together to conduct studies that are helping address information gaps related to the effects of uranium exploration and mining activities on people and environmental resources. Results will help inform the Secretary's decision to continue, modify, or end the mining withdrawal in 2032. The USGS is the lead Department of the Interior bureau tasked with developing the science to address these critical data gaps.

This study was funded by the USGS Toxic Substances Hydrology Program.

Frequently Asked Questions

USGS Scientists Collecting Soil Samples on the Canyon Mine Property

U.S. Geological Survey (USGS) scientists collecting soil samples on the Canyon Mine property, Arizona. The mine's headframe and mine workshop are visible in the background. Photo Credit: Katie Walton-Day, USGS.


1. What is the most important thing people should know about this study?

This study provides robust data describing baseline geochemical and radiological conditions around and within the Canyon Mine.

2. Why is this important? How will your findings be used?

These data provide a benchmark against which to measure changes that might occur during future mining activity. We demonstrate application of sampling and statistical techniques that can be repeated in the future to help assess these changes in a defensible manner.

3. Do your findings indicate there is any threat to human health?

While resource extraction has not begun at this mine there has been premining construction activity to prepare the site. Preliminary results indicate there has not been mobilization of any contaminants from the ore body to the surface environment, nor from the mine site to the surrounding environment.

4. What kind of samples did you take?

We collected soil samples and stream sediment samples (in dry streams) for laboratory analysis of chemical and radiological contaminants. We also collected field measurements of gamma radiation at the ground surface.

5. What contaminants did you look for?

The report discusses results primarily for geogenic contaminants that could be associated with the geological formations present and underlying uranium ore including arsenic, cobalt, chromium, copper, molybdenum, nickel, lead, antimony, selenium, uranium, vanadium, and zinc.

6. Is the mine operational?

In preparation for resource extraction the mine is deepening the main shaft down to the depth of ore. But, ore is not yet being mined and brought to the surface.

7. If this area is within the 2012 withdrawal, why is the mine still there?

The 2012 withdrawal exempted mines with valid and existing rights. This mine was permitted for operations before the 2012 withdrawal and is therefore allowed to continue to operate.

8. Was there anything surprising about your findings?

Not really. A few geogenic contaminants such as arsenic, molybdenum, uranium, and vanadium were present within the mine-property perimeter in concentrations that were higher than we expected based on general soil chemistry of the area but at this time we are not alarmed. Our subsequent research will follow this result closely and determine the sources of the contaminants, their environmental exposure pathways to humans and biota that might be associated with resource extraction as the mine becomes fully operational.

9. Why are you studying this area?

The Canyon Mine is being studied by the USGS as part of our 15-year science plan to better understand the potential human and ecological exposures to contaminants associated with uranium mining throughout the Grand Canyon Region. This plan, which supports the science needed to inform decisions related to the withdrawal, includes studying soils, biota, and dust at mine sites before, during, and after mining to help understand how mining may introduce elements associated with the uranium ore into the surface ecosystem. See Department of Interior Press Release: Secretary Salazar Announces Decision to Withdraw Public Lands near Grand Canyon from New Mining Claims.

10. What's next?

We are working to evaluate other data that were collected at the Canyon Mine to form a complete picture of pre-mining conditions at the mine in soils, dust, water, and biota. If the Canyon Mine goes into production during the time we are conducting the rest of the 15-year Science plan, we will re-sample to learn how mining and reclamation at the site might affect environmental pathways of exposure to uranium and associated elements in soils, dust, and biota in the area. In addition, we are evaluating data collected at nearby active mines to compare with data collected at the Canyon Mine. All of this work is being conducted in collaboration with biologists who are assessing exposures, uptake, and effects of contaminants in biota.


This article was featured in the USGS GeoHealth Newsletter, Vol. 13, No. 1, 2016

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