Environmental Health - Toxic Substances Hydrology Program
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.
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.
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.
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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.