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

USGS scientists collecting soil samples at a mine
USGS scientists collecting soil samples inside the perimeter fence at the Canyon Mine, Arizona. The mine's headframe and mine workshop are visible in the background. Photo Credit: Kit MacDonald, U.S. Forest Service.

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.

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.

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.

Map showing decision units and sampling locations around Canyon Mine
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. 2015 base map data from Google Earth©.

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.

References

Naftz, D., and Walton-Day, K., 2016, Establishing a pre-mining geochemical baseline at a uranium mine near Grand Canyon National Park, USA: Geoderma Regional, v. 7, no. 1, p. 76-92, doi:10.1016/j.geodrs.2016.01.004.

Hinck, J.E., Linder, G., Darrah, A.J., Drost, C.A., Duniway, M.C., Johnson, M.J., Mendez-Harclerode, F.M., Nowak, E.M., Valdez, E.W., Wolff, S., and van Riper Iii, C., 2014, Exposure pathways and biological receptors--Baseline data for the Canyon Uranium Mine, Coconino County, Arizona: Journal of Fish and Wildlife Management, v. 5, no. 2, p. 422-440, doi:10.3996/052014-JFWM-039.

More Information

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

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Campbell, K.M., Gallegos, T.J., and Landa, E.R., 2014, Biogeochemical aspects of uranium mineralization, mining, milling, and remediation: Applied Geochemistry, v. 57, p. 206-235, doi:10.1016/j.apgeochem.2014.07.022.

Gallegos, T.J., Campbell, K.M., Zielinski, R.A., Reimus, P.W., Clay, J.T., Janot, N., J. R. Bargar, and Benzel, W.M., 2015, Persistent U(IV) and U(VI) following in-situ recovery (ISR) mining of a sandstone uranium deposit, Wyoming, USA: Applied Geochemistry, v. 63, p. 222-234, doi:10.1016/j.apgeochem.2015.08.017.

Gallegos, T.J., Fuller, C.C., Webb, S.M., and Betterton, W., 2013, Uranium(VI) interactions with mackinawite in the presence and absence of bicarbonate and oxygen: Environmental Science and Technology, v. 47, no. 13, p. 7357-7364, doi:10.1021/es400450z.

 

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