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Rapid fluid pressure changes in unsaturated media due to perturbations at or near the earth-atmosphere interface are commonly attributed to preferential or bypass flow. An alternative mechanism for the rapid propagation of pressure perturbations in unsaturated media is the kinematic response, which results from the nonlinear relationship between unsaturated hydraulic conductivity and water content. The relationship between pressure wave velocities and fluid velocities is described using kinematic wave theory, presented for the Brooks - Corey and van Genuchten -Mualem formulations. The kinematic mechanism predicts fluid pressure pulse velocities to be substantially faster than unsaturated fractured rock tracer velocities for both formulations. A hydraulic form of the advection-diffusion equation based on Richards' Equation is presented that uses the hydraulic diffusivity and kinematic velocity to predict the hydraulic response in unsaturated fractured rock to pressure head perturbations. Pressure pulse velocity monitoring may be an additional tool for estimating unsaturated hydraulic properties in low permeability media.

Groundwater flow and contaminant transport through the unsaturated zone continue to receive attention as former nuclear weapons development sites are being characterized for determining decommissioning options, and geologic sites are being considered for deep disposal of nuclear and hazardous waste. The ability to make decisions with regard to cleanup, site suitability, and anticipated performance of disposal or storage facilities is dependent upon the characterization and modeling of unsaturated flow and transport features, events, and processes. Hazardous materials may be mobilized by infiltrating water and move downward to affect groundwater resources. These contaminants may also move upward or laterally by capillary movement or as vapor to the accessible environment. Substantial experience exists with respect to near-surface partially saturated porous media, traditionally the domain of the soil scientists and geotechnical engineers, but does not exist for fractured rock in either near-surface or deep, complex, unsaturated systems that are now being characterized and modeled. The ability to represent these complex systems composed of both a matrix and a fracture component is being tested through a variety of field experiments and comparisons to natural analogues. The present focus is on evaluating conceptual flow and transport models and quantifying the spatial and temporal parameters for these models using laboratory and field methods, and environmental tracer analyses. Modeling of these dynamic and transient systems has followed two paths, porous equivalency and discrete fracture models. In general, characterization methods and modeling are in the confirmation stage with the greatest lack of knowledge being the interaction between fracture and matrix properties for flow and transport.