A Three-Dimensional Field Study of Solute Transport Through Unsaturated, Layered, Porous Media 2. Characterization of Vertical Dispersion

Solute plumes were created in an unsaturated field soil with either flux application or by leaching an initial resident distribution (see Ellsworth et al., this issue). The spatial variance of the plumes initially increased with time between the soil surface and a depth of 2.5m, within which the soil was a nearly structureless loamy sand. Below this depth, the plumes were observed to compress in the vertical direction as they moved into, and through, a region of subangular blocky structure and loam texture (between 2.5 and 4.0m depth). As the solute moved below the layer of fine texture, the plume variance again increased with time. Using a transformed advection-dispersion equation description, two constant, field-averaged transport coefficients V*, and D*, were determined in a scaled coordinate system from the moment equations. These two constant parameters were then used to predict the observed local, or plot scale, transport. Results indicate that the two constant parameters describe transport reasonably well at each plot site and over all sampling depths