Northern Guam geospatial information server

Phreatic zone

The phreatic zone (from Greek for "well" or "spring" and also known as the saturated zone) is part of the aquifer that lies beneath the vadose zone. Its upper boundary is the water table, beneath which all pores in the rock are filled with groundwater. Its lower boundary is irrelevant because phreatic zone includes groundwater in the aquifer lens as well as all the marine groundwater beneath.

The term phreatic surface generally coincides with the water table and indicates the location at which pore water is under pressure that is equal to atmospheric pressure. This means a pressure head of zero. The slope of the phreatic surface generally determines the direction of ground water movement in unconfined aquifers such as the NGLA.

Understanding the movement of water within the phreatic zone is important for evaluation of aquifer storage and internal transport, tracing of contaminant flow between recharge and discharge areas, and studies of interactions between the aquifer and nearshore ecosystems such as coral reefs.


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