This website compiles USGS resources and data related to principal aquifers including Aquifer Basics, principal aquifers maps and GIS data, and the National Aquifer Code Reference List.
An aquifer is a geologic formation, a group of formations, or a part of a formation that contains sufficient saturated permeable material to yield significant quantities of water to wells and springs. The areal and vertical location of major aquifers is fundamental to the determination of groundwater availability for the Nation.
A principal aquifer is defined as a regionally extensive aquifer or aquifer system that has the potential to be used as a source of potable (drinkable) water. For study or mapping purposes, aquifers are often combined into aquifer systems.
A two-dimensional map representation of the principal aquifers of the Nation is shown below. This map, which was derived from Ground Water Atlas of the United States data (published as part of the National Atlas in 1998, revised 2003) indicates the areal extent of the uppermost principal aquifers on a national scale.
National Aquifer Code Reference List
The principal aquifers shown on the 2003 map above, with some additions, were used as the first National Aquifer reference list in the USGS National Water Information System (NWIS) in the Aggregate Water Use Data System (database released in August 2001). To learn more, visit the National Aquifer Code Reference List.
Learn more about aquifers
For an overview of principal aquifers: The principal water-yielding aquifers of North America can be grouped into five types by rock type and location: unconsolidated and semiconsolidated sand and gravel aquifers, sandstone aquifers, carbonate-rock aquifers, aquifers in interbedded sandstone and carbonate rocks, and aquifers in igneous and metamorphic rocks. The pages below contain descriptions and maps of these main aquifer types:
- Unconsolidated and semiconsolidated sand and gravel aquifers
- Sandstone aquifers
- Sandstone and carbonate-rock aquifers
- Carbonate-rock aquifers
- Igneous and metamorphic-rock aquifers
- Other rocks
These pages, formerly hosted at our Aquifer Basics website, provide a general summary of information published in the Ground Water Atlas of the United States.
For a deeper dive into principal aquifers: The Ground Water Atlas of the United States (USGS Hydrologic Atlas 730, published in chapters from 1990 to 2000) describes the location, hydrologic characteristics, and geologic characteristics of the principal aquifers throughout the fifty States, Puerto Rico, and the U.S. Virgin Islands. The groundwater information summarized in the Atlas was collected over many years by the USGS and other partner agencies, and provides key descriptive information in a regional and national context. The Ground Water Atlas of the United States is available online as an HTML website, as downloadable PDFs, and or available for purchase through the USGS Store.
Download aquifer GIS data
Principal aquifers (shallowest extents)
This dataset, published in 2003, contains the shallowest principal aquifers of the conterminous United States, Hawaii, Puerto Rico, and the U.S. Virgin Islands, portrayed as polygons. The map layer was developed as part of the effort to produce the maps published at 1:2,500,000 in the printed series Ground Water Atlas of the United States. The published maps contain base and cultural features not included in these data. Please note that the maps do not show the entire extent of an aquifer, only its subcrop or outcrop area. Refer to the metadata for a complete description of the files and how they were generated.
Aquifers of alluvial and glacial origin
This dataset, published in 2002, represents the extent of the alluvial and glacial aquifers north of the southern-most line of glaciation. Aquifers are shown in the States of Maine, Vermont, New Hampshire, Connecticut, Massachusetts, Rhode Island, New Jersey, New York, Pennsylvania, Ohio, Indiana, Michigan, Wisconsin, Illinois, Minnesota, Iowa, Missouri, Kansas, Nebraska, South Dakota, North Dakota, and Montana. These data delineate the areal extent of the alluvial and glacial aquifers as defined in The Ground Water Atlas of The United States. Refer to the metadata for a complete description of the files and how they were generated.
Hydrogeologic unit boundaries (framework) and groundwater recharge data
Additional hydrogeologic and groundwater recharge data is available through the Regional Groundwater Availability Studies of the National Water Census.
Aquifers with available data:
- Central Valley
- Columbia Plateau
- Denver Basin
- Floridan
- Great Basin Carbonate
- Hawaiian
- High Plains
- Lake Michigan Basin
- Mississippi Embayment
- North and South Carolina Atlantic Coastal Plain
- Northern Atlantic Coastal Plain
- Pennsylvanian and Mississippian Aquifers of the Appalachian Plateaus
- Upper Colorado River Basin
- Williston and Powder River Basins
Below are other webpages associated with principal aquifers.
National Aquifer Code Reference List
Unconsolidated and semiconsolidated sand and gravel aquifers
Sandstone aquifers
Sandstone and carbonate-rock aquifers
Carbonate-rock aquifers
Igneous and metamorphic-rock aquifers
Minor aquifers, confining units, and areas identified as "not a principal aquifer"
- Overview
This website compiles USGS resources and data related to principal aquifers including Aquifer Basics, principal aquifers maps and GIS data, and the National Aquifer Code Reference List.
An aquifer is a geologic formation, a group of formations, or a part of a formation that contains sufficient saturated permeable material to yield significant quantities of water to wells and springs. The areal and vertical location of major aquifers is fundamental to the determination of groundwater availability for the Nation.
A principal aquifer is defined as a regionally extensive aquifer or aquifer system that has the potential to be used as a source of potable (drinkable) water. For study or mapping purposes, aquifers are often combined into aquifer systems.
A two-dimensional map representation of the principal aquifers of the Nation is shown below. This map, which was derived from Ground Water Atlas of the United States data (published as part of the National Atlas in 1998, revised 2003) indicates the areal extent of the uppermost principal aquifers on a national scale.
Sources/Usage: Public Domain.This principal aquifers map is available for download as a PDF or available for purchase from the USGS Store. National Aquifer Code Reference List
The principal aquifers shown on the 2003 map above, with some additions, were used as the first National Aquifer reference list in the USGS National Water Information System (NWIS) in the Aggregate Water Use Data System (database released in August 2001). To learn more, visit the National Aquifer Code Reference List.
Learn more about aquifers
For an overview of principal aquifers: The principal water-yielding aquifers of North America can be grouped into five types by rock type and location: unconsolidated and semiconsolidated sand and gravel aquifers, sandstone aquifers, carbonate-rock aquifers, aquifers in interbedded sandstone and carbonate rocks, and aquifers in igneous and metamorphic rocks. The pages below contain descriptions and maps of these main aquifer types:
- Unconsolidated and semiconsolidated sand and gravel aquifers
- Sandstone aquifers
- Sandstone and carbonate-rock aquifers
- Carbonate-rock aquifers
- Igneous and metamorphic-rock aquifers
- Other rocks
These pages, formerly hosted at our Aquifer Basics website, provide a general summary of information published in the Ground Water Atlas of the United States.
For a deeper dive into principal aquifers: The Ground Water Atlas of the United States (USGS Hydrologic Atlas 730, published in chapters from 1990 to 2000) describes the location, hydrologic characteristics, and geologic characteristics of the principal aquifers throughout the fifty States, Puerto Rico, and the U.S. Virgin Islands. The groundwater information summarized in the Atlas was collected over many years by the USGS and other partner agencies, and provides key descriptive information in a regional and national context. The Ground Water Atlas of the United States is available online as an HTML website, as downloadable PDFs, and or available for purchase through the USGS Store.
Download aquifer GIS data
Principal aquifers (shallowest extents)
This dataset, published in 2003, contains the shallowest principal aquifers of the conterminous United States, Hawaii, Puerto Rico, and the U.S. Virgin Islands, portrayed as polygons. The map layer was developed as part of the effort to produce the maps published at 1:2,500,000 in the printed series Ground Water Atlas of the United States. The published maps contain base and cultural features not included in these data. Please note that the maps do not show the entire extent of an aquifer, only its subcrop or outcrop area. Refer to the metadata for a complete description of the files and how they were generated.
Aquifers of alluvial and glacial origin
This dataset, published in 2002, represents the extent of the alluvial and glacial aquifers north of the southern-most line of glaciation. Aquifers are shown in the States of Maine, Vermont, New Hampshire, Connecticut, Massachusetts, Rhode Island, New Jersey, New York, Pennsylvania, Ohio, Indiana, Michigan, Wisconsin, Illinois, Minnesota, Iowa, Missouri, Kansas, Nebraska, South Dakota, North Dakota, and Montana. These data delineate the areal extent of the alluvial and glacial aquifers as defined in The Ground Water Atlas of The United States. Refer to the metadata for a complete description of the files and how they were generated.
Hydrogeologic unit boundaries (framework) and groundwater recharge data
Additional hydrogeologic and groundwater recharge data is available through the Regional Groundwater Availability Studies of the National Water Census.
Aquifers with available data:
- Central Valley
- Columbia Plateau
- Denver Basin
- Floridan
- Great Basin Carbonate
- Hawaiian
- High Plains
- Lake Michigan Basin
- Mississippi Embayment
- North and South Carolina Atlantic Coastal Plain
- Northern Atlantic Coastal Plain
- Pennsylvanian and Mississippian Aquifers of the Appalachian Plateaus
- Upper Colorado River Basin
- Williston and Powder River Basins
- Science
Below are other webpages associated with principal aquifers.
National Aquifer Code Reference List
This list of national principal aquifer codes and names are fixed values assigned by the National Water Information System (NWIS). Aquifers are identified by a geohydrologic unit code - a three-digit number related to the age of the formation, followed by a 4 or 5 character abbreviation for the geologic unit or aquifer name.Unconsolidated and semiconsolidated sand and gravel aquifers
Unconsolidated sand and gravel aquifers are characterized by intergranular porosity and all contain water primarily under unconfined, or water-table, conditions. They are grouped into four categories: basin-fill, blanket sand and gravel, glacial-deposit, and stream-valley aquifers. Semiconsolidated aquifers consist of semiconsolidated sand interbedded with silt, clay, and minor carbonate rocks...Sandstone aquifers
Sandstone aquifers are more widespread than those in all other kinds of consolidated rocks. Groundwater movement in sandstone aquifers primarily is along bedding planes, but joints and fractures provide avenues for the vertical movement of water. Sandstone aquifers can be highly productive and provide large volumes of water.Sandstone and carbonate-rock aquifers
In scattered places in the United States, carbonate rocks are interbedded with almost equal amounts of water-yielding sandstone. In most places where these two rock types are interbedded, the carbonate rocks yield much more water than the sandstone.Carbonate-rock aquifers
Aquifers in carbonate rocks are most extensive in the eastern U.S. Most of the carbonate-rock aquifers consist of limestone, but dolomite and marble locally yield water. The water-yielding properties of carbonate rocks vary widely; some yield almost no water and are considered to be confining units, whereas others are among the most productive aquifers known.Igneous and metamorphic-rock aquifers
Igneous and metamorphic-rock aquifers can be grouped into two categories: crystalline-rock and volcanic-rock. Spaces in crystalline rocks are microscopically small, few, and generally unconnected. However, because these aquifers extend over large areas, large volumes of water can be withdrawn. Volcanic-rock aquifers have a wide range of chemical, mineralogic, structural, and hydraulic properties...Minor aquifers, confining units, and areas identified as "not a principal aquifer"
Aquifer maps often include large-to-small areas that are designated "minor aquifer," "not a principal aquifer," or "confining unit.” These are usually areas are underlain by low-permeability deposits and rocks, unsaturated materials, or aquifers that supply little water because they are of local extent, poorly permeable, or both. - Publications
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