The Remediation Technology Summit

February 26-28, 2019

Colorado Convention Center
Denver, CO

thomsonDr. Bruce M. Thomson
Regents Professor of Civil Engineering
University of New Mexico

Bruce Thomson is a Research Professor and Regents Professor Emeritus in the Department of Civil Engineering at the University of New Mexico (UNM). Dr. Thomson was Director of UNM’s Water Resources Program from 2006 to 2013. His areas of research include chemistry of inorganic contaminants, ground water contamination, and water resources management. He has served on numerous national, state and local advisory committees and is an elected member and chair of the Board of Directors of the Albuquerque Metropolitan Arroyo Flood Control Authority (AMAFCA). Dr. Thomson is a licensed professional engineer in New Mexico and one of the last practicing engineers who still knows how to use a slide rule.

PLATFORM PRESENTER - Heavy Metal Bands and Other Ignoble Species: The Rock Stars

Ground Water Remediation Following In-Situ Leach Mining of Uranium: Hydrodynamic, Chemical and Microbial Considerations

In-situ leach (ISL) mining, also called in-situ recovery (ISR), is the only method of mining uranium (U) currently practiced in the U.S. It involves circulating an oxidizing solution through U ore bodies to dissolve and transport U complexes to extraction wells which pump the solution to the surface. Soluble U is then recovered by ion exchange and the barren leachate is recirculated back through the ore body. ISL mining substantially changes the aqueous geochemistry of the aquifer near the ore body resulting in high concentrations of U and co-constituents.

Current methods of ground water remediation rely on aquifer flushing with clean water, however, field scale pilot testing in New Mexico and elsewhere has found this to be of limited effectiveness. Chemical and biological methods have been proposed to improve the performance of aquifer restoration. Two methods were investigated in this lab study of in-situ restoration methods; phosphate addition to achieve precipitation of U and other minerals, and stimulation of sulfate reducing microorganisms to achieve reduction and subsequent precipitation of U and other minerals. Restoration was simulated by passing a phosphate (chemical stabilization) or lactate solution (microbiological stabilization) through a set of columns containing U ore and simulated ISL leach solutions. The effluent composition of each column was monitored and found to be identical to that of control columns fed only ground water. The results are believed to be due to limited mixing between the contaminated ground water and the restoration fluids. Post treatment analyses of the columns by mineralogical (chemical stabilization) and microbial genetic analyses (microbiological stabilization) confirm the occurrence of intended reactions, however, most of the soluble U and other constituents was swept through the column by the restoration solution instead of becoming immobilized. These results have important consequences for other in-situ remediation activities in which a soluble restoration fluid is added to remove highly soluble contaminants.