Perth Laboratory – Public Seminar Series 2009

Case studies of uranium transport and retardation in unconsolidated aquifers

Dr James A. Davis
U. S. Geological Survey

Thursday 5 March 2009 at 3.30pm, CSIRO Auditorium

Abstract

Three contaminated field sites in the USA have been investigated to determine which processes have the largest influence on the fate and transport of uranium (U). The sites differ in their hydrological, geochemical, and microbiological characteristics, and these differences have important impacts in regard to remediation by natural attenuation. At the Hanford (Washington) site, U contamination in the vadose and saturated zones of a shallow aquifer was caused by disposal of wastes from spent nuclear fuel rod processing. Uranium is present entirely as U(VI) at this site, and its fate and transport are governed primarily by complex hydrologic, desorption, and dissolution processes. The Naturita and Rifle (Colorado) sites are locations where U mills operated during the period of 1940-1970, with tailings piles and other mill operations leading to U contamination of shallow aquifers. Uranium is present as U(VI) and U(IV) at these sites, with the Rifle site showing a larger spatial regime with iron-reducing conditions and complex biogeochemical interactions. U fate and transport at the Naturita site can mostly be described by groundwater flow coupled with U(VI) surface complexation equilibrium, although uncertainty exists due to a poorly known initial boundary condition and small spatial regime at the downgradient end of the site where iron-reducing conditions occur.

About the speaker

James A. Davis is a geochemist whose research focuses on geochemical processes occurring at mineral surfaces and their effects on water quality in natural aqueous systems. He has a doctorate in Environmental Engineering and Sciences from Stanford University and currently holds the position of Senior Research Scientist with the U.S. Geological Survey, Water Resources Division, in California. Dr Davis serves on a number of national and international committees and working groups relating to geochemistry. In 2000 he received the Distinguished Service Award from the U.S. Department of Interior for outstanding scientific contributions. He is noted as author of one of the 10 most cited articles in journal history, Environmental Science and Technology, 2001.

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