Validation of stochastic flow and transport models for unsaturated soils: a comprehensive field study

This document describes a comprehensive field study for evaluating the effects of site variability on flow and transport of contaminants in the unsaturated zone. The field study is designed to measure the variability of key hydraulic properties within the unsaturated zone of an undisturbed field soil. A large trench, 5 m wide x 6.5 m deep x 25 m long, will be used to observe the transport of contaminants. Flow of water-coincident contaminants through the unsaturated zone will be monitored, and comparisons will be made between predicted and field-measured values. In addition, a controlled lysimeter test has been initiated to look at the effects of well-defined layering on transport processes. The stochastic model of Gelhar will be tested using the field and lysimeter test data. In this model, the fluctuations of measured hydraulic parameters are assumed to represent statisically homogeneous random fields. The mean values of these parameters and their covariance functions will provide sufficient statistical characterization to evaluate the flow and transport processes at the site soley on the basis of these measured hydraulic properties. The data set will also be useful in testing other models that are available for performance assessments of low-level waste sites and in addressing the effects of spatial variability on transport of contaminants in the unsaturated zone