The EPA uses numerous mathematical models to predict and analyze the movement of water and dissolved contaminants in the saturated and unsaturated zones of the subsurface environment. The usefulness of these models, and the accuracy with which model predictions can be made, depends greatly on the ability to reliably characterize the hydraulic properties of the unsaturated zone. The report discusses several theoretical models which may be used to quantify the unsaturated soil hydraulic properties involving the soil water retention and hydraulic conductivity functions. The report includes a computer program which predicts, among other things, the unsaturated hydraulic conductivity from independently measured soil water retention data. Several examples illustrate the applicability of the model to different types of hydraulic data. The information in the report should be of interest to all those concerned with the development of improved methods for predicting or managing water and contaminant transport in partly saturated soils.

Research report. "U.S. Salinity Laboratory, U.S. Department of Agriculture." Shipping list no.: 92-168-P. "December 1991." "EPA/600/2-91/065." Includes bibliographical references (pages 52-55). Contract Number: DW12933934.