Paper No. 22
Presentation Time: 9:00 AM-6:00 PM
EXPERIMENTAL CHARACTERIZATION OF CHROMIUM FATE AND TRANSPORT IN SANDIA CANYON, LOS ALAMOS NATIONAL LABORATORY, NEW MEXICO
DING, Mei1, LONGMIRE, Patrick
2, VANIMAN, David
3, BROXTON, David E.
4, REARICK, Michael
2, SPALL, Brian N.
5, WARE, Stuart D.
6, KATZMAN, Danny
7, BARGAR, John R.
8 and WEBB, Samuel M.
9, (1)Ees-14, Los Alamos National Lab, Los Alamos, NM 87545, (2)Earth and Environmental Sciences Division, Los Alamos National Laboratory, Mail Stop D469, Los Alamos National Laboratory, Los Alamos, NM 87545, (3)Hydrology, Geochemistry, and Geology Group, Los Alamos National Laboratory, P.O. Box 1663, Los Alamos, NM 87545, (4)Earth Environmental Sciences Division, Los Alamos National Laboratory, Los Alamos, NM 87545, (5)School of Earth and Environmental Sciences, Washington State University, Webster Physical Science Building 1228, Pullman, WA 99164-2812, (6)EES-14, Los Alamos National Lab, Los Alamos, NM 87545, (7)Water Stewardship Program, Los Alamos National Laboratory, MS M992, Los Alamos, NM 87545, (8)Stanford Synchrotron Radiation Lightsource, 2575 Sand Hill Rd, Menlo Park, CA 94025, (9)Stanford Synchrotron Radiation Laboratory, Stanford Linear Accelerator Ctr, Building 137, MS 69, 2575 Sand Hill Road, Menlo Park, CA 94025, mding@lanl.gov
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 Kd values. Additionally, higher Kd 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.
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