Geological Society of America

T251 Contaminant Hydrogeology: Contaminant Fate and Transport in Geological Systems (Posters)

Wednesday, 21 October 2009
9:00 AM - 6:00 PM
Hall A

EXPERIMENTAL CHARACTERIZATION OF CHROMIUM FATE AND TRANSPORT IN SANDIA CANYON, LOS ALAMOS NATIONAL LABORATORY, NEW MEXICO

Paper number: T251-21
Program: Technical Sessions
Time: 9:00 AM – 6:00 PM

Authors

Mei Ding Presenting Author
Los Alamos National Lab, Los Alamos, NM
Samuel M. Webb
SLAC National Accelerator Laboratory, Menlo Park, CA
Patrick Longmire
Los Alamos National Laboratory, Los Alamos, NM
David Vaniman
Los Alamos National Laboratory, Los Alamos, NM
David E. Broxton
Newport News Nuclear, Los Alamos, NM
Michael Rearick
Los Alamos National Laboratory, Los Alamos, NM
Brian N. Spall
Washington State University, Pullman, WA
Stuart D. Ware
Los Alamos National Lab, Los Alamos, NM
Danny Katzman
Los Alamos National Laboratory, Los Alamos, NM
John R. Bargar
Stanford Synchrotron Radiation Lightsource, Menlo Park, CA

Abstract

Routine groundwater monitoring conducted in 2005 led to the identification of significant chromium (Cr) contamination within the regional aquifer at Los Alamos, New Mexico. Site-specific Cr(III, VI) transport data are needed to refine both conceptual and numerical models for Cr fate and transport within the contaminated vadose zone and regional aquifer. We conducted sorption, column flow-through transport experiments, and X-ray absorption spectroscopy measurements for Cr(III, VI) speciation and oxidation state of surface Cr complexes reacted with vadose zone and regional aquifer materials.

The results of sorption and flow-through experiments suggest that vadose zone and regional aquifer materials have differential retention capacities for Cr(VI), reflecting large variations of measured sorption coefficients of K_d values. Additionally, higher K_d values tend to be associated with crushed rocks and reduced particle size samples, having increasing surface areas and exposed fresh mineral surfaces acting as chemical reductants containing Fe(II). X-ray absorption near edge spectroscopy measurements suggest that reduction of Cr(VI) to Cr(III) occurred after Cr(VI) containing solution was exposed to alluvial and rock materials. These results indicate natural attenuation of anthropogenic Cr occurs within the Sandia Canyon wetland, vadose zone and regional aquifer. The reduction capacities for Cr are substantial within the wetland and are moderate within vadose zone basalts and regional aquifer clastic sedimentary rocks.