Capillary pressure. Difference in pressure across the interface between two fluids.
Conduit flow. Water movement through discrete passages that are large enough for turbulent flow to occur--typically greater than 5 millimeters across.
Diffuse flow. Laminar water movement in granular or fractured media through networks of small, interconnected openings.
DNAPL. An acronym for denser-than-water nonaqueous-phase liquids.
DNAPL pool. A contiguous accumulation of DNAPL with a hydrostatically level upper surface. In the absence of capillary forces, the upper surface of a pool is typically flat and horizontal. DNAPL pools are typically greater than a few millimeters in depth.
Karst. Landscape in which chemical dissolution has enlarged joints, fractures, bedding planes, or other openings in soluble, underlying bedrock; may be characterized by sinkholes, caves, and disappearing streams.
Macropore. A crack, pipe, fissure, or other opening in soil or regolith greater than 1 millimeter across; formed by plant growth, animal activity, shrinking or swelling due to changing temperature or moisture content, mass movement, and numerous other processes; macropores form preferential flow paths for water and other fluids.
Matrix diffusion. Molecular diffusion of a dissolved chemical from a fracture into pores within adjacent rock or soil.
Regolith. Unconsolidated earth material including soil, residuum from weathered bedrock, and sediments.
Residual DNAPL. Isolated blobs or ganglia of DNAPL held in porous or fractured media following free drainage. Residual DNAPL masses are distinguished from pools by (1) their discontinuous nature; (2) their relatively small size--typically less than a few millimeters in any dimension; and (3) the dominance of capillary, rather than hydrostatic, forces in determining the shape and location of their free surfaces.
Residual saturation. Fraction of the pore space in a porous granular or fractured medium that retains residual DNAPL immediately after free drainage has occurred.
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