The effects of the percolation phase transition on equilibration of porous media during drainage are shown to set on at moisture contents, θ, somewhat larger than the critical moisture content for percolation, θt. An algorithm is developed, which yields the typical upward curvature of log[h(θ)] curves at low moisture contents, where h is the hydraulic head, as well as a flattening of the curve of log[K(h)] for large h, where K is the hydraulic conductivity. Within certain approximations the procedure can be validated through solution of the associated differential equation. The procedure was tested against seven drainage curves from the USDOE Hanford site and found to be predictive. However, theoretical questions remain regarding, among other things, the implicit assumption that the interfacial tension measured is an equilibrium value, even though the moisture content is not. The motivation of the present research is to reduce ambiguities in the interpretation of dry-end pressure–saturation curves.

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