State Water Resources Research Institute Program

Project ID: 2009OR115B
Title: Colloidal transport in variably saturated porous media: A detailed evaluation of colloid mobilization mechanisms
Project Type: Research
Start Date: 3/01/2009
End Date: 2/28/2010
Congressional District: 5th
Focus Categories: Groundwater, Solute Transport, Radioactive Substances
Keywords: Groundwater, Unsaturated Zone, Colloids, Imaging
Principal Investigator: Wildenschild, Dorthe
Federal Funds: $ 7,810
Non-Federal Matching Funds: $ 37,322
Abstract: Until some two decades ago, it was believed that only the soil water and gaseous phases were mobile and could facilitate the transport of chemicals through the subsurface soil region above the water table, also known as the vadose zone. It is now generally accepted that part of the soil is also mobile, and that soil colloids facilitate chemical transport. Colloids are defined as particles of sizes between 1 nm and 1µm in diameter, and are ubiquitous in natural groundwater systems. Colloids include clays, organic macromolecules, bacteria and viruses (biocolloids). Colloid-facilitated transport is particularly important from a contaminant transport perspective due to the ability of these particles to form stable connections with various pollutants (e.g. heavy metals, pesticides, pharmaceuticals, radionuclides and other highly sorbing contaminants) that are otherwise considered to have limited mobility in the subsurface (e.g. McCarthy and Zachara, 1989; Ryan and Elimelich, 1996; Grolimund et al, 1996; deJonge et al., 1998; Kersting et al., 1999, Tolls, 2001; Hanselman et al., 2003). As a result transport of soil colloids have been studied quite widely, under saturated conditions, in batch, or under otherwise simplified conditions.

Nevertheless, differences in the deposition behavior of colloids, in 2-D and column displacement studies have frequently been reported (Schijven and Hassanizadeh, 2000; Gao et al., 2006), and the deposition and mobilization mechanisms are vastly different for saturated and unsaturated systems: straining, for instance, is anticipated to be even more important in unsaturated than in saturated systems (Bradford et al., 2006). At present our ability to predict the transport and fate of colloids and biocolloids in natural subsurface environments is limited by our understanding of the colloidal deposition and mobilization process. Though the state of knowledge has increased dramatically, much is still uncertain about the fundamental processes governing colloidal transport in both saturated and unsaturated environments, in particular pertaining to how colloids are remobilized during infiltration events.

Because mobilization is a central concern in many contamination situations, this proposal focuses on pore scale mobilization processes, such as air-water interface scour, film thickening, and detachment from soil-water interfaces. Failure to account for mobilization and associated colloid-facilitated transport can severely underestimate the transport potential and risk assessment for such pollutants (Simunek et al., 2006). The proposed project will leverage a larger grant currently pending with NSF which will further support our collaboration with Dr. Lis W. de Jonge at University of Aarhus in Denmark. Dr. de Jonge is one of the world leaders in the area of colloid transport and has technologically advanced laboratory facilities for colloid transport research. The proposed request for funding is entirely focused on providing a state-of-the-art research experience for a PhD student by supporting her during Spring term 2009 so she can carry out high-resolution imaging of colloidal processes in unsaturated media, and travel for her to work in and collaborate with Dr. Lis W. de Jonge's group during the Summer of 2009.

Progress/Completion Report, 2009, PDF

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