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EXPERIMENTAL EVALUATION OF CHEMICAL TRANSPORT IN WATER‐SATURATED POROUS MEDIA: 1. NONSORBING MEDIA

Dispersion profiles of 2,4-dichlorophenoxyacetic acid were measured experimentally to evaluate a theoretical dispersion model previously developed by the investigators and to evaluate the effect of pore size on dispersion. The chemical being dispersed along a column made up of glass beads was initially present only in the pore water of a 1 cm long section at the front of the column. After leaching for a period of time, the column was sectioned and the concentration in each section was obtained and compared with a predicted concentration. Four porous media systems consisting of glass beads with particle diameters of <30, 28–53, 105–149, and 149–210 μm obtained by dry sieving were used. Corresponding predominant pore radii were 4.5, 8.2, 19.5, and 36.2 μm. The corresponding dispersion coefficients were found to be 0.53, 0.69, 1.41, and 2.05 cm2/day, repectively. Using these values, theoretical dispersion profiles were calculated. The theoretical distributions of the chemical in the columns were found to be in good agreement with the experimentally determined distributions. The values of the dispersion coefficients were in agreement with values reported in the literature and could be related to pore size, diffusion coefficient, and flow rate.