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ARS Home » Research » Publications at this Location » Publication #126428
Title: TRANSPORT AND FATE OF COLLOIDS IN PHYSICALLY HETEROGENEOUS POROUS MEDIA

Author
item Bradford, Scott
item BETTAHAR, MEHDI - US SALINITY LAB POST DOC
item SIMUNEK, JIRKA - UC RIVERSIDE, DEPT ES
item Van Genuchten, Martinus

Submitted to: International Workshop by Danish Institute of Agricultural Science
Publication Type: Proceedings
Publication Acceptance Date: 10/20/2002
Publication Date: N/A
Citation: N/A

Interpretive Summary: Colloids particles such as disease causing bacteria and viruses pose a serious threat to food and water supplies in the United States. Most research to date on colloid transport and fate has been conducted in uniform soil systems. Natural soil systems are much more complex due to variations in soil texture (size). This manuscript reports on research designed to explore the role of variations in soil texture on colloid transport and fate. Our data indicates that colloid mobility is significantly affected by the colloid and soil size, and soil texture variations. This information will provide scientists and engineers with an improved understanding of colloid transport and fate in natural soils systems, and should therefore facilitate the accurate assessment of contaminant potential and the development of more efficient remediation strategies.

Technical Abstract: Soil column experiments were conducted to explore the influence of physical heterogeneity(various soil combinations of a cylindrical soil lens embedded in the center of a larger cylinder of matrix soil)on the transport and fate of colloid particles in saturated porous media. Colloid migration was found to strongly depend upon colloid size and the physical heterogeneity. Pore straining of colloids lead to a decrease in the peak effluent concentration and an increase in the inlet mass removal when the mean grain size of the matrix sand decreased or the size of the colloid increased. In heterogeneous systems, colloid retention was sometimes enhanced by presence of relatively stagnant flow zones and diminished by flow bypassing of finer textured soils. The transport differences between conservative tracers and colloid particles tended to increase in heterogeneous systems as a result of flow bypassing, pore straining, and size exclusion. Depending upon the colloid and soil size, size exclusion sometimes resulted in earlier colloid breakthrough and less concentration tailing compared to bromide. Transport parameters obtained from homogeneous experiments were used in conjunction with a first-order attachment/detachment advection dispersion transport model to simulate the heterogeneous experiments. Simulations provided a reasonable description of tracer transport, but tended to overestimate the colloid transport potential, thus suggesting that the model should be refined to more realistically account for pore straining, size exclusion, and the velocity dependence of the attachment/detachment coefficients.