HR: 0830h
AN: H51A-02    [Abstracts]
TI: Identification of Physical and Chemical Mass Transfer Processes by a Tracer Flush Experiment
AU: * Scheibe, T D
EM: tim.scheibe@pnl.gov
AF: Pacific Northwest National Laboratory, P.O. Box 999, MS K9-36, Richland, WA 99352 United States
AU: Brooks, S C
EM: brookssc@ornl.gov
AF: Oak Ridge National Laboratory, Environmental Sciences Division, P.O. Box 2008, Oak Ridge, TN 37831 United States
AU: Kamolpornwijit, W
EM: kamolpornwiw@ornl.gov
AF: Pacific Northwest National Laboratory, P.O. Box 999, MS K9-36, Richland, WA 99352 United States
AU: Fang, Y
EM: yilin.fang@pnl.gov
AF: Pacific Northwest National Laboratory, P.O. Box 999, MS K9-36, Richland, WA 99352 United States
AU: Roden, E E
EM: eroden@bsc.as.ua.edu
AF: The University of Alabama, Department of Biological Sciences, Tuscaloosa, AL 35487 United States
AB: A small-scale field tracer test with a long pulse injection (48 hours) was performed in a highly heterogeneous aquifer. Diffusive/dispersive mass transfer between a highly conductive gravel layer and adjacent saprolitic materials was hypothesized as a significant solute transport process. Some solutes of interest (e.g., uranium) are also strongly impacted by sorption to aquifer solids. In addition to observations of injected tracer breakthrough, we also measured concentration histories of several background groundwater constituents at monitoring wells, including sorbing (uranium) and non-sorbing (chloride, nitrate) solutes. As expected, the concentrations of these constituents decreased as the tracer pulse flushed the accessible aquifer pore space. However, the form of the inverse relationship between tracer and ambient solute concentrations was indicative of chemical and physical non-equilibrium between groundwater in advection-dominated zones (gravel) and that in relatively immobile pore space (saprolites). The observations were compared to field-scale transport simulations with and without mass transfer mechanisms included. These comparisons demonstrate that the response of background solutes to a tracer flush can be used to quantify field-scale mass transfer rates. This information is being used to design and evaluate experiments aimed at development of a distributed biologically-active microbarrier between advection- and diffusion-dominated pore regions.
DE: 1829 Groundwater hydrology
DE: 1831 Groundwater quality
DE: 1832 Groundwater transport
DE: 3210 Modeling
SC: Hydrology [H]
MN: 2005 Joint Assembly