National Aquifer Code Reference List

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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.

National aquifers, or principal aquifers of the United States, are defined as regionally extensive aquifers or aquifer systems that have the potential to be used as a source of potable (drinkable) water. The first publication of the core of the national aquifer list in a comprehensive manner was the Ground Water Atlas of the United States (USGS Hydrologic Atlas 730, published in 2000) published as part of the National Atlas in 1998, revised 2003. A two-dimensional map representation of the principal aquifers was derived from this data and published as part of the National Atlas in 1998 (revised 2003). 

Aquifers shown on the 2003 Principal Aquifers map, 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 (AWUDS, database released in August 2001). In 2005, the “national aquifer” information was added to NWIS, allowing users to search by national aquifer code and name from the reference list below. 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).

National Aquifer Reference List 

Entries in italics are no longer valid.
To learn more about a specific aquifer, visit the Principal Aquifers website for an overview, or access more extensive information from the Ground Water Atlas of the United States.

 
Aquifer Name Code Valid States
Ada-Vamoosa aquifer N300ADAVMS  Oklahoma
Alaska unconsolidated-deposit aquifers N100AKUNCD  Alaska
Alluvial aquifers N100ALLUVL  Arkansas, Colorado, Delaware, Kansas, Kentucky, Louisiana, Maryland, Missouri, Montana, Nebraska, New Jersey, North Dakota, Ohio, Oklahoma, South Dakota, Tennessee, Texas, Utah, Virginia, West Virginia, Wyoming 
Arbuckle-Simpson aquifer  N400ABKSMP  Oklahoma
Basin and Range basin-fill aquifers  N100BSNRGB  Arizona, California, Idaho, Nevada, New Mexico, Oregon, Utah 
Basin and Range carbonate-rock aquifers  N400BSNRGC  Arizona, California, Idaho, Nevada, Utah 
Biscayne aquifer  N400BISCYN  Florida
Blaine aquifer  N400BLAINE  Oklahoma, Texas 
California Coastal Basin aquifers    N100CACSTL California
Cambrian-Ordovician aquifer system    S300CAMORD Illinois, Iowa, Michigan, Minnesota, Missouri, Wisconsin 
Castle Hayne aquifer    N400CSLHYN North Carolina
Central Oklahoma aquifer  N300CNRLOK  Oklahoma
Central Valley aquifer system  S100CNRLVL  California 
Coastal lowlands aquifer system  S100CSLLWD  Alabama, Florida, Louisiana, Mississippi, Texas 
Colorado Plateaus aquifers  N300COPLTS  Arizona, Colorado, New Mexico, Utah, Wyoming 
Columbia Plateau basaltic-rock aquifers   N600CMBPLV  Idaho, Oregon, Washington
Columbia Plateau basin-fill aquifers    N100CMBPLB  Idaho, Oregon, Washington
Denver Basin aquifer system    S300DNVRBS  Colorado
Early Mesozoic basin aquifers  N300ERLMZC  Connecticut, Maryland, Massachusetts, New Jersey, New York, North Carolina, Pennsylvania, Virginia 
Edwards-Trinity aquifer system    S500EDRTRN  Arkansas, Oklahoma, Texas
Floridan aquifer system  S400FLORDN  Alabama, Florida, Georgia, South Carolina 
Hawaii volcanic-rock aquifers  N600HIVLCC  Hawaii
High Plains aquifer  N100HGHPLN  Colorado, Kansas, Nebraska, New Mexico, Oklahoma, South Dakota, Texas, Wyoming
Intermediate aquifer system    S500INTRMD  Florida 
Jacobsville aquifer    N300JCBSVL  Michigan, Wisconsin
Kingshill aquifer (Virgin Islands)  N400KNGSHL  Virgin Islands 
Lower Cretaceous aquifers    N300LCRTCS  Iowa, Kansas, Minnesota, Montana, Nebraska, North Dakota, South Dakota, Wyoming
Lower Tertiary aquifers      N300LTRTRY Montana, North Dakota, South Dakota, Wyoming
Marshall aquifer    N300MRSHLL Michigan 
Mississippi embayment aquifer system    S100MSEMBM  Alabama, Arkansas, Illinois, Kentucky, Louisiana, Mississippi, Missouri, Tennessee, Texas 
Mississippi River Valley alluvial aquifer  N100MSRVVL  Arkansas, Illinois, Kentucky, Louisiana, Mississippi, Missouri, Tennessee 
Mississippian aquifers  N500MSSPPI  Alabama, Illinois, Indiana, Iowa, Kentucky, Maryland, Missouri, Ohio, Pennsylvania, Tennessee, Virginia, West Virginia 
New York and New England crystalline-rock aquifers    N600NECRSN  Connecticut, Maine, Massachusetts, New Hampshire, New York, Rhode Island, Vermont
New York and New England carbonate-rock aquifers    N400NYNECB  Connecticut, Maine, Massachusetts, New Jersey, New York, Pennsylvania, Vermont
New York sandstone aquifers  N300NYSDSN  New York 
North Coast Limestone aquifer system (Puerto Rico)  N400NCSTLM  Puerto Rico 
Northern Atlantic Coastal Plain aquifer system    S100NATLCP Delaware, District of Columbia, Maryland, New Jersey, New York, North Carolina, Pennsylvania, Virginia 
Northern Great Plains aquifer system (no longer valid)    S500NGRTPL Montana, North Dakota, South Dakota, Wyoming 
Northern Rocky Mountains Intermontane Basins aquifer systems    S100NRMTIB  Idaho, Montana, Washington, Wyoming 
Ordovician aquifers    N400ORDVCN  Kentucky, Tennessee
Other aquifers  N9999OTHER  All
Ozark Plateaus aquifer system      S400OZRKPL  Arkansas, Illinois, Kansas, Missouri, Oklahoma
Pacific Northwest basin-fill aquifers    N100PCFNWB  California, Idaho, Nevada, Oregon, Utah, Washington, Wyoming
Pacific Northwest volcanic-rock aquifers    N100PCFNWV  California, Idaho, Montana, Nevada, Oregon, Utah, Washington, Wyoming
Paleozoic aquifers  N500PLOZOC  Minnesota, Montana, North Dakota, South Dakota, Wyoming 
Pecos River Basin alluvial aquifer    N100PCSRVR  New Mexico, Texas
Pennsylvanian aquifers  N300PNSLVN  Alabama, Georgia, Illinois, Indiana, Kentucky, Maryland, Michigan, Ohio, Pennsylvania, Tennessee, Virginia, West Virginia 
Piedmont and Blue Ridge carbonate-rock aquifers    N400PDMBRC  Maryland, New Jersey, North Carolina, Pennsylvania 
Piedmont and Blue Ridge crystalline-rock aquifers  N400PDMBRX  Alabama, Delaware, District of Columbia, Georgia, Maryland, New Jersey, New York, North Carolina, Pennsylvania, South Carolina, Tennessee, Virginia, West Virginia 
Puget Sound aquifer system  S100PGTSND  Washington 
Rio Grande aquifer system  S100RIOGRD  Colorado, New Mexico, Texas 
Roswell Basin aquifer system    S400RSWLBS New Mexico 
Rush Springs aquifer    N300RSHSPG  Oklahoma 
Sand and gravel aquifers (glaciated regions) N100GLCIAL  Connecticut, Illinois, Indiana, Iowa, Kansas, Kentucky, Maine, Massachusetts, Michigan, Minnesota, Missouri, Montana, Nebraska, New Hampshire, New Jersey, New York, North Dakota, Ohio, Pennsylvania, Rhode Island, South Dakota, Vermont, Wisconsin
Seymour aquifer  N100SYMOUR  Texas 
Silurian-Devonian aquifers  N400SLRDVN  Illinois, Indiana, Iowa, Kentucky, Michigan, Missouri, Ohio, Tennessee, Wisconsin 
Snake River Plain basaltic-rock aquifers  N600SKRVPV  Idaho, Oregon 
Snake River Plain basin-fill aquifers N600SKRVPB  Idaho, Oregon
South Coast aquifer (Puerto Rico)    N300STHCST  Puerto Rico
Southeastern Coastal Plain aquifer system  S100SECSLP  Alabama, Georgia, Mississippi, South Carolina, Tennessee 
Southern Nevada volcanic-rock aquifers  N600SRNVDV  Nevada 
Surficial aquifer system      S100SURFCL Alabama, Florida, Georgia, North Carolina, South Carolina
Texas coastal uplands aquifer system S100TXCLUP  Louisiana, Texas 
Upper carbonate aquifer N400UPCRBN  Iowa, Minnesota
Upper Cretaceous aquifers N300UPCTCS  Montana, North Dakota, South Dakota, Wyoming
Valley and Ridge aquifers N500VLYRDG  Alabama, Georgia, Maryland, New Jersey, New York, North Carolina, Pennsylvania, Tennessee, Virginia, West Virginia
Valley and Ridge carbonate-rock aquifers (no longer valid)    N500VLRDGC  Alabama, Georgia, Maryland, New Jersey, Pennsylvania, Tennessee, Virginia, West Virginia
Willamette Lowland basin-fill aquifers N100WLMLWD  Oregon, Washington
Wyoming Tertiary aquifers  N300WYTRTR  Wyoming 

Code components: 

  • N or S, where N = aquifer, S = aquifer system

  • 3 digit number = rock type (4 digits used for "Other" to fill out the code) 

  • 100-- Sand and gravel aquifers 
    200--Semiconsolidated sand aquifers (not used) 
    300--Sandstone aquifers 
    400--Carbonate-rock aquifers 
    500--Sandstone and carbonate-rock aquifers 
    600--Igneous and metamorphic-rock aquifers 
    9999--Areas that are not a national aquifer 

  • 6 character identifier derived from the aquifer name using the code derivation procedure also used for GWSI geohydrologic unit names. (Note that the National Aquifer Code uses a different numeric component than the geohydrologic unit names.)

 

History of the National Aquifer Code Reference List

  • First publication of the core of the national aquifer list in a comprehensive manner was the Ground Water Atlas of the United States (HA 730 A-H), published in 13 chapters over the period 1990-2000, James A. Miller, editor. 
  • A single combined map (Principal Aquifers of the 48 Conterminous United States, Hawaii, Puerto Rico, and the U.S. Virgin Islands) was published as part of the National Atlas in 1998, revised 2003. 
  • Aquifers shown on the 2003 Principal Aquifers map, with some additions, were used as the first National Aquifer reference list in NWIS, released in AWUDS v. 1.0 for the national compilation of water-use data for the year 2000 (database released in August 2001). Water-use data collected using this list of aquifers will be published in Circular 1279, Estimated Withdrawals from Principal Aquifers in the United States, 2000. The additions were: 
    • Alluvial aquifers--consist of stream-valley aquifers and other aquifers of unconsolidated alluvial materials, not included in another named national aquifer, south of the limit of Quarternary continental glaciation and east of the Rocky Mountains. Note that alluvial aquifers north of the limit of continental glaciation are included in Sand and gravel aquifers (glaciated regions).
    • Intermediate aquifer (Florida) 
    • New England crystalline-rock aquifers 
    • (in error) Northern Great Plains aquifer system 
  • Some revisions to the lists of valid States, this code, and reference list were added to the NWIS Site File and to NWISWeb with the release of NWIS 4.5 in 2005; see the WMA Technical Memo "NWIS 4.5 -- Assigning National Aquifer Codes in the Ground Water Site Inventory (GWSI) for the NWIS 4.5 Release." 
  • Revisions to the reference list since it was first used by NWIS: 
    • Northern Great Plains aquifer system was removed: this umbrella term includes four national aquifers but is not considered a national aquifer itself. The component aquifers are Lower Tertiary, Upper Cretaceous, Lower Cretaceous, and Paleozoic. The appropriate component aquifer should be used instead of Northern Great Plains. (February 2005) 
    • Valley and Ridge carbonate-rock aquifers were removed: these now should be included in Valley and Ridge aquifers. (March 2005) 
    • Surficial aquifer system: removed the following States from the valid list: Delaware, Maryland, New Jersey, Virginia. The surficial aquifer in the Coastal Plain of these States should be included in the Northern Atlantic Coastal Plain aquifer system. Surficial deposits of glacial origin (New Jersey) should be included in Sand and gravel aquifers (glaciated regions). Surficial deposits which are not of glacial origin may be coded as Alluvial aquifers. You may need to request the addition of Alluvial aquifers to the list of aquifers valid in your State. (March 2005) 
    • The name of N600NECRSN was changed from "New England crystalline-rock aquifers" to "New York and New England crystalline-rock aquifers" to better reflect the geographic extent (January 2015).