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ADVECTION/CONVECTION/DIFFUSION
Advection is transport by mass flow of a medium; for example, water. Convection
describes bulk water transport (i.e., flux) through porous media. Diffusion is the
net transport of solutes within the liquid, solid or gas phase resulting from random
(Brownian) motion of individual molecules in response to a concentration or other
gradient.
BIOREMEDIATION The CBE
research program addresses how biofilms "biotransform" organic contaminants to
less harmful forms. This process, which can occur either in the subsurface (i.e., in situ) or in engineered reactor systems, is
referred to as "bioremediation."
DISPERSION Net transport
(mixing) resulting from differential advection through soil pores of varying diameters.
HYDRAULIC CONDUCTIVITY The
proportionality factor (L t ^ -1) relating water flux density to a hydraulic gradient.
Highly dependent on wetness for a given set of soil conditions.
IN SITU In its
original place; i.e., not removed from its original or "natural" position.
Having its native physical, chemical, and biological properties intact.
PORE (WATER) VELOCITY The
ratio of soil water flux density ("Darcy velocity") to volume water content.
Describes the mean velocity of liquid phase transport through soil pores.
POROUS MEDIA Any solid
phase possessing pore space (e.g., soil, aquifer matrix).
VADOSE ZONE The
unsaturated region between the soil surface and water table.
VAPOR PHASE The gaseous
phase in soil pores, or that fraction of the total porosity not occupied by the liquid
(normally water) phase.
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