Science for Decision Making on Uranium Mining in Arizona

Characterize Surface Radiation and Soil and Dust Chemistry through the Mine Life Cycle

At Little Robinson Tank

Little Robinson Tank Life Cycle

Little Robinson Tank is an unmineralized reference and background site.

Breccia-pipe uranium mineral deposits contain radioactive material and radiation may be detected at the surface, even before mining activity commences. Measurements and maps of surface radiation before, during, and after mining, and after reclamation help determine if mining affects the amount of surface radiation. High levels of radiation can affect the health of the surficial ecosystem, and biota (including humans) that interact with that ecosystem.

Breccia-pipe uranium mineral deposits contain elevated concentrations of uranium and related trace elements, some of which are toxic to biota. Activities during mining including ore extraction, surface storage, and transport to the milling location in Blanding, Utah, have the potential to redistribute uranium and associated trace elements to the surrounding surface environment and ecosystems. Soil is one possible receptacle for these trace elements and represents a pathway where these potentially toxic trace elements may be introduced into surrounding ecosystems, surface drainage systems, and biota.

Questions this study could help answer

  • Does surface radiation increase during mining activity?
  • If so, by how much, in what areas, and what processes (mining and natural) are responsible for increased surface radiation?
  • What is the range and geographic distribution of element concentrations in soils before, during, and after mining, and after reclamation?
  • Where in the very shallow subsurface (up to about 50 centimeters depth) are trace elements concentrated, and what does that tell us about their origin?
  • Is dust transport an important exposure pathway?
  • How do trace element concentrations in soils at these sites relate to benchmark concentrations?


Compare gamma radiation and soil trace-element concentrations maps to similar maps constructed at other sites before and during mining, and during and after reclamation to understand how mining and reclamation change surficial radiation and trace-element distributions in soil above and around breccia-pipe uranium deposits.

Little Robinson Tank Activities

Little Robinson Tank is a stock tank surrounded by natural soil having no known underlying uranium breccia-pipe deposit. It represents background conditions. In November 2016, collection of surficial soil samples1, 2, shallow soil cores, and measurement of surface gamma radiation was completed directly around the tank in a configuration and areal extent similar to that used on the breccia-pipe mine sites.



Specific Tasks

Task 5a: Compile/evaluate existing and newly collected monitoring data from various agencies/sources
Task 5c: Collect/analyze samples from biota with focus on trust resources
Task 7a: Conduct species surveys
Task 7b: Collect/analyze water and sediment samples
Task 7d: Collect/analyze soils including deeper horizons to characterize vertical distributions
Task 11: Characterize the wind dispersion characteristics of uranium and trace elements associated with uranium mining and the subsequent risk to biota.


Little Robinson Tank Sources:

1 Walton-Day, K., Bern, C.R., Naftz, D.L., Gross, T.A., and O'Shea, P.M., 2019, Surface Materials Data from Breccia-Pipe Uranium Mine and Reference Sites, Arizona, USA: U.S. Geological Survey data release

2 Bern, C.R., Walton-Day, K., and Naftz, D.L., 2019, Improved enrichment factor calculations through principal component analysis: examples from soils near breccia pipe uranium mines, Arizona, USA: Environmental Pollution, 248, p. 90-100.

Principal Investigators

Katie Walton-Day
Colorado Water Science Center

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