What is Groundwater?

Groundwater is part of the Earth's water cycle that flows underground. Annually, Portage County receives an average of 31 inches of water from rain and snowmelt.4, 7, 8  Up to 29 inches of this water soaks or infiltrates into the ground and follows the path of least resistance through air pockets between soil and rock particles.

Water first passes through  the zone of aeration or unsaturated zone (the white layer in the diagram).  In this zone,  a mixture of air and water fills the spaces between the rock and soil particles. From here, water is taken up by plant roots, discharged into a body of water, or flows down to the next zone, which is the zone of saturation or saturated zone (the blue area in the diagram). Here all the spaces between particles are completely filled with water. The top of this zone is called the water table. Contrary to popular belief, groundwater is not an underground river or lake. Rather, it is all the water below the water table stored in subsurface void spaces. An aquifer is the geologic material that stores, transports, and yields groundwater to wells.

In Portage County, the depth to groundwater varies from less than a foot to over a hundred feet and the average amount of time groundwater is underground is 30 years, unless it is pumped out sooner by wells.⁶ 

(Italicized words defined in the glossary.)

water cycle  |  groundwater movement  |  groundwater storage  |  groundwater uses  |  contaminants  | protection actions  |  glossary
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