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Potential for Establishing Nonvertical Flow within the Vadose Zone

Silliman, S.E., Fisker, E., Pescatore, J.
Vadose zone journal 2011 v.10 no.1 pp. 425-436
laboratory experimentation, lysimeters, mathematical models, permeability, sediments, unsaturated flow, vadose zone
Laboratory experiments and numerical studies are used to study the potential to induce water flux in the vadose zone, which is characterized by significant horizontal components of the water velocity. Specifically, a question is addressed as to whether water can be injected or withdrawn from lenses or layers of fine sediments (bordered by coarse sediments), thus establishing flow in those portions of the vadose zone commonly associated with higher moisture contents and a higher mass of dissolved contaminants. Laboratory experiments provided the base-line proof of concept of the ability to induce horizontal components to flow in unsaturated sediments through use of suction-cup lysimeters, but were limited to ideal media and short distance scales (<0.5 m). A numerical model was used in combination with published moisture retention and relative permeability parameters for a variety of sediment types to study conditions under which such horizontal flow components might be induced over substantially greater distances (e.g., 10 m). While these numerical results support arguments that flow induction is theoretically possible, induced flow will generally result in slow transport velocities such that application will likely be limited either to short flow distances (e.g., less than a meter) or long-term (>50 years) time scales, and only with thorough knowledge of subsurface heterogeneity. Implications of this work beyond the present study may include continuing discussions of constructed capillary barriers and development of improved technologies for removal of water from the vadose zone.