Unsaturated Zone
The unsaturated zone is the zone between the land surface and the regional water table. It includes the capillary fringe and may also include localized perched ground water. Pore-water pressure in the unsaturated zone is less than atmospheric, except for perched ground water. Except for the capillary fringe and perched ground water, pores in the unsaturated zone contain both water and air. The unsaturated zone differs from the saturated zone, in which pores contain water at greater than atmospheric pressure and are almost always completely filled with water. The unsaturated zone is also called the vadose zone and the zone of aeration.
The unsaturated zone is a major focus of many contaminated-site investigations because contaminants often have to pass through the unsaturated zone before they get to the ground-water resources or the surface environment. Furthermore, many contaminants are accidentally placed or intentionally disposed of in the unsaturated zone.
Unsaturated Zone Headlines
Toxics Program Unsaturated Zone Research
More Information
Related Fact Sheets
References
- Heath, R.C., 1983, Basic ground-water hydrology: U.S. Geological Survey Water-Supply Paper 2220, p. 84.
- Lohman, S.W., and others, 1972, Definitions of selected ground-water terms—revisions and conceptual refinements: U.S. Geological Survey Water-Supply Paper 1988, 21 p.
- Meinzer, O.E., 1923, The occurrence of ground water in the United States with a discussion of principles: U.S. Geological Survey Water-Supply Paper 489, p. 321.
- National Research Council, 2001, Science and Technology for Environmental Cleanup at Hanford: Washington, D.C., National Academy Press, 180 p.
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