PROBABILISTIC MODELING OF MOISTURE FLOW IN LAYERED VADOSE ZONE - APPLICATIONS TO WASTE SITE PERFORMANCE ASSESSMENT

The problem of moisture flow through layers of statistically homogeneo us soils in the vadose zone is studied by a probabilistic approach. A random number generator is used to characterize the spatial variabilit y of hydraulic properties in such a way consistent with the probabilit y distribution function observed in field measurements. The water trav el time is calculated from the solution of the pressure head-based Ric hards' equation obtained by means of the Galerkin finite element metho d in conjunction with the backward Euler method for time advancement. Applications are directed toward burial sites at the Nevada Test Site (NTS) and at the Idaho National Engineering Laboratory (INEL). Uncerta inties in the travel time due to the uncertain soil properties are qua ntified by an appropriate statistical parameter deduced from the trave l times of the realizations simulated.