Groundwater in aquifers between layers of poorly permeable rock, such as clay or shale, may be confined under pressure.
What is the difference between a confined and an unconfined (water table) aquifer?
A confined aquifer is an aquifer below the land surface that is saturated with water. Layers of impermeable material are both above and below the aquifer, causing it to be under pressure so that when the aquifer is penetrated by a well, the water will rise above the top of the aquifer.
A water table--or unconfined--aquifer is an aquifer whose upper water surface (water table) is at atmospheric pressure, and thus is able to rise and fall. Water table aquifers are usually closer to the Earth's surface than confined aquifers are, and as such are impacted by drought conditions sooner than confined aquifers.
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Related
How important is groundwater?
Groundwater, which is in aquifers below the surface of the Earth, is one of the Nation's most important natural resources. Groundwater is the source of about 37 percent of the water that county and city water departments supply to households and businesses (public supply). It provides drinking water for more than 90 percent of the rural population who do not get their water delivered to them from...
If the ground filters water, is groundwater always clean?
Water drawn from a well was once precipitation that fell onto Earth's surface. It seeped into the ground and, over time, occupied the porous space in some subsurface material. Big particles that are in surface streams, such as leaf chunks, will not be seen in groundwater. So, yes, big particles are filtered out by the ground, along with some minerals and chemicals that are too small to see. But...
What is groundwater?
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...
What is the Ground Water Atlas of the United States?
This Ground Water Atlas of the United States is a series of USGS publications that describe the location, the extent, and the geologic and hydrologic characteristics of the important aquifers of the Nation. The series consists of 13 chapters that describe the regional groundwater resources that collectively cover 50 States, Puerto Rico, and the U.S. Virgin Islands. Learn more: Principal Aquifers...
How can I find the depth to the water table in a specific location?
The depth to the water table can change (rise or fall) depending on the time of year. During the late winter and spring when accumulated snow starts to melt and spring rainfall is plentiful, water on the surface infiltrates into the ground and the water table rises. When water-loving plants start to grow again in the spring and precipitation gives way to hot, dry summers, the water table falls...
What determines if a well will go dry?
A well is said to have gone dry when water levels drop below a pump intake. This does not mean that a dry well will never have water in it again, as the water level may come back through time as recharge increases. The water level in a well depends on a number of things, such as the depth of the well, the type (confined or unconfined) of aquifer the well taps, the amount of pumping that occurs in...
Flowing artesian well in Brunswick, Georgia, USA
Groundwater in aquifers between layers of poorly permeable rock, such as clay or shale, may be confined under pressure.
Collecting a groundwater-level measurement in Freeport, Texas
USGS hydrologist Jason Ramage collects a groundwater-level measurement using a steel tape in Freeport, Texas.
A new interactive web application illustrates how groundwater, sediment compaction and land-elevation change are related in the Houston-Galveston region in Texas.
USGS hydrologist Jason Ramage collects a groundwater-level measurement using a steel tape in Freeport, Texas.
A new interactive web application illustrates how groundwater, sediment compaction and land-elevation change are related in the Houston-Galveston region in Texas.
USGS Scientists Collecting Water-Quality Samples from Shallow Groundwater under Ashumet Pond
U.S. Geological Survey (USGS) scientists collecting water-quality samples from shallow groundwater under Ashumet Pond, Cape Cod, Massachusetts.
U.S. Geological Survey (USGS) scientists collecting water-quality samples from shallow groundwater under Ashumet Pond, Cape Cod, Massachusetts.
PubTalk 9/2011 — Tracking the Nation's Groundwater Reserves
--issues facing current and future water supplies
by William Alley, USGS Office of Groundwater
--issues facing current and future water supplies
by William Alley, USGS Office of Groundwater
Real-time Groundwater Streamgage equipment set up
Real-time Groundwater Streamgage equipment set up
Real-time Groundwater Streamgage equipment set up
What is "artesian well water"?
Listen to hear the answer.
Artesian Well Investigations
Artesian well investigations in South Dakota (circa-July 1957).
Artesian well investigations in South Dakota (circa-July 1957).
Related
How important is groundwater?
Groundwater, which is in aquifers below the surface of the Earth, is one of the Nation's most important natural resources. Groundwater is the source of about 37 percent of the water that county and city water departments supply to households and businesses (public supply). It provides drinking water for more than 90 percent of the rural population who do not get their water delivered to them from...
If the ground filters water, is groundwater always clean?
Water drawn from a well was once precipitation that fell onto Earth's surface. It seeped into the ground and, over time, occupied the porous space in some subsurface material. Big particles that are in surface streams, such as leaf chunks, will not be seen in groundwater. So, yes, big particles are filtered out by the ground, along with some minerals and chemicals that are too small to see. But...
What is groundwater?
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...
What is the Ground Water Atlas of the United States?
This Ground Water Atlas of the United States is a series of USGS publications that describe the location, the extent, and the geologic and hydrologic characteristics of the important aquifers of the Nation. The series consists of 13 chapters that describe the regional groundwater resources that collectively cover 50 States, Puerto Rico, and the U.S. Virgin Islands. Learn more: Principal Aquifers...
How can I find the depth to the water table in a specific location?
The depth to the water table can change (rise or fall) depending on the time of year. During the late winter and spring when accumulated snow starts to melt and spring rainfall is plentiful, water on the surface infiltrates into the ground and the water table rises. When water-loving plants start to grow again in the spring and precipitation gives way to hot, dry summers, the water table falls...
What determines if a well will go dry?
A well is said to have gone dry when water levels drop below a pump intake. This does not mean that a dry well will never have water in it again, as the water level may come back through time as recharge increases. The water level in a well depends on a number of things, such as the depth of the well, the type (confined or unconfined) of aquifer the well taps, the amount of pumping that occurs in...
Collecting a groundwater-level measurement in Freeport, Texas
USGS hydrologist Jason Ramage collects a groundwater-level measurement using a steel tape in Freeport, Texas.
A new interactive web application illustrates how groundwater, sediment compaction and land-elevation change are related in the Houston-Galveston region in Texas.
USGS hydrologist Jason Ramage collects a groundwater-level measurement using a steel tape in Freeport, Texas.
A new interactive web application illustrates how groundwater, sediment compaction and land-elevation change are related in the Houston-Galveston region in Texas.
USGS Scientists Collecting Water-Quality Samples from Shallow Groundwater under Ashumet Pond
U.S. Geological Survey (USGS) scientists collecting water-quality samples from shallow groundwater under Ashumet Pond, Cape Cod, Massachusetts.
U.S. Geological Survey (USGS) scientists collecting water-quality samples from shallow groundwater under Ashumet Pond, Cape Cod, Massachusetts.
PubTalk 9/2011 — Tracking the Nation's Groundwater Reserves
--issues facing current and future water supplies
by William Alley, USGS Office of Groundwater
--issues facing current and future water supplies
by William Alley, USGS Office of Groundwater
Real-time Groundwater Streamgage equipment set up
Real-time Groundwater Streamgage equipment set up
Real-time Groundwater Streamgage equipment set up
What is "artesian well water"?
Listen to hear the answer.
Artesian Well Investigations
Artesian well investigations in South Dakota (circa-July 1957).
Artesian well investigations in South Dakota (circa-July 1957).
Updated Date: March 11, 2024