Evaluation of Colloid Transport and Dynamics using Light Transmission

Colloidal transport through porous media has been mainly studied in column experiments from which data analysis was limited to the evaluation of effluent breakthrough curves and/or destructive sampling at the end of the experiments. The internal processes occur within a "black box" where direct observation is not possible, and are therefore often poorly understood. A nondestructive, noninvasive method has been developed that allows for quantitative measurement of colloid distribution with unprecedented two-dimensional spatial and temporal resolution. This technique is well-suited to observing the effects of saturation transitions and physical heterogeneities on colloidal transport. The potential of this novel technique had been explored by investigating the effect of particle size and concentration on flow dynamics under saturated and unsaturated conditions. In saturated-flow experiments, deviation from the classical advection-dispersion behavior is observed. In unsaturated systems, colloidal accumulation at the capillary fringe interface and a high deposition rate of microspheres to the unsaturated media are readily observed. The experimental system is limited to translucent porous media and fluorescent colloids and is only semiquantitative in variably saturated media; nevertheless, it holds great promise for elucidating many complex mechanisms that control or influence colloid transport in the subsurface. Future experiments utilizing this technology will address phenomena of colloid transport at the interface between the saturated and unsaturated zones, at the interface between different matrix properties, and under conditions of matrix heterogeneity.