Radiocolloid Transport in Saturated and Unsaturated Fracturesby H. E. Nuttall,
Abstract: Studies have shown that radionuclides and toxic materials can attach to colloidal particles in groundwater or are themselves colloids. Since these contaminated particles can migrate several miles, toxic colloids present a potential environmental problem: they can rapidly transfer toxic materials through groundwater and pollute drinking water aquifers. Present in this paper is a colloid transport model for single fractures and the resulting simulations of colloid transport in both saturated and unsaturated fracture flow regimes. Results indicated that colloid diffusion rate in the direction normal to flow was an important parameter which was the rate controlling step in the process of colloids diffusing to the fracture wall and being captured. Colloid diffusion is an important parameter because the rate is approximately three orders of magnitude lower for colloids than for molecular species. An analysis of the average fluid velocities for saturated versus unsaturated cases showed that for the same fluid thickness, maximum and average velocities of unsaturated flow case were four times greater than that of the saturated case. In the unsaturated case where colloids migrate irreversibly to the air/water interface, migration rate will be six times the average rate of a saturated fracture. Therefore, unsaturated flow can potentially enhance colloid migration in comparison to the saturated case. A study of various rock/water boundary conditions was also performed and the results showed that irreversible capture was necessary to fully stop colloid propagation.
Subject Headings: Colloids | Cracking | Fluid flow | Water pollution | Fluid velocity | Toxicity | Unsaturated flow | Diffusion (fluid)
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