Groundwater is water that exists underground in saturated zones beneath the land surface. The upper surface of the saturated zone is called the water table.
Contrary to popular belief, groundwater does not form underground rivers. It fills the pores and fractures in underground materials such as sand, gravel, and other rock, much the same way that water fills a sponge. If groundwater flows naturally out of rock materials or if it can be removed by pumping (in useful amounts), the rock materials are called aquifers.
Groundwater moves slowly, typically at rates of 7-60 centimeters (3-25 inches) per day in an aquifer. As a result, water could remain in an aquifer for hundreds or thousands of years. Groundwater is the source of about 40 percent of water used for public supplies and about 39 percent of water used for agriculture in the United States. (
https://www.usgs.gov/faqs/what-groundwater)
The documents below present detailed information about groundwater.
Groundwater chemistry and water quality
Oregon's Susceptibility Analysis Procedures: Provides a summary of Oregon's approach to the evaluation of the relative potential of an aquifer becoming contaminated from activities at the surface.
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Groundwater Training Manual: Contains basic information about groundwater hydrogeology (i.e., the origin, occurrence and movement of groundwater). Also discussed are groundwater contamination and protection, well construction, and data that water systems should consider collecting.
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Natural Factors Influencing the Composition of Groundwater: Describes natural compositional variations (and causes) that might occur in groundwater. Groundwater is not constant in its chemical and physical characteristics. Seasonal changes in taste, odor and appearance are also common.
Potential minerals and substances in groundwater
Well information