HR: 1330h
AN: H22A-0904    [PDF]
TI: Understanding Subsurface Colloid Behavior: A New Visualization Technique and the Application of Geo-Centrifuge Modeling
AU: Yoon, J S
EM: jyoon1@mit.edu
AF: Massachusetts Institute of Technology, Department of Civil and Environmental Engineering Room 1-353, Cambridge, MA 02139 United States
AU: * Culligan, P J
EM: culligan@civil.columbia.edu
AF: Columbia University, Department of Civil Engineering and Engineering Mechanics 610 S.W. Mudd Building, New York, NY 10027 United States
AU: Germaine, J T
EM: jgermain@mit.edu
AF: Massachusetts Institute of Technology, Department of Civil and Environmental Engineering Room 1-353, Cambridge, MA 02139 United States
AB: Subsurface colloid behavior has recently drawn attention because colloids are suspected of enhancing contaminant transport in groundwater systems. To better understand the processes by which colloids move through the subsurface, and in particular the vadose zone, a new technique that enables real-time visualization of colloid particles as they move through a porous medium has been developed. This visualization technique involves the use of laser induced fluorescent particles and digital image processing to directly observe particles moving through a porous medium consisting of soda-lime glass beads and water in a transparent experimental box of 10.0cm�27.9cm�2.38cm. Colloid particles are simulated using commercially available micron sized particles that fluoresce under argon-ion laser light. The fluorescent light given off from the particles is captured through a camera filter, which lets through only the emitted wavelength of the colloid particles. The intensity of the emitted light is proportional to the colloid particle concentration. The images of colloid movement are captured by a MagnaFire digital camera; a cooled CCD digital camera produced by Optronics. This camera enables real-time capture of images to a computer, thereby allowing the images to be processed immediately. The images taken by the camera are analyzed by the ImagePro software from Media Cybernetics, which contains a range of counting, sizing, measuring, and image enhancement tools for image processing. Laboratory experiments using the new technique have demonstrated the existence of both irreversible and reversible sites for colloid entrapment during uniform saturated flow in a homogeneous porous medium. These tests have also shown a dependence of colloid entrapment on velocity. Models for colloid transport currently available in the literature have proven to be inadequate predictors for the experimental observations, despite the simplicity of the system studied. To further extend the work, the visualization technique has been developed for use on the geo-centrifuge. The advantage that the geo-centrifuge has for investigating subsurface colloid behavior, is the ability to simulate unsaturated transport mechanisms under well simulated field moisture profiles and in shortened periods of time. A series of tests to investigate colloid transport during uniform saturated flow is being used to examine basic scaling laws for colloid transport under enhanced gravity. The paper will describe the new visualization technique, its use in geo-centrifuge testing and observations on scaling relationships for colloid transport during geo-centrifuge experiments. Although the visualization technique has been developed for investigating subsurface colloid behavior, it does have application in other areas of investigation, including the investigation of microbial behavior in the subsurface.
DE: 1829 Groundwater hydrology
DE: 1831 Groundwater quality
DE: 1832 Groundwater transport
DE: 1875 Unsaturated zone
DE: 1894 Instruments and techniques
SC: Hydrology [H]
MN: 2003 Fall Meeting