This is a dataset containing what the Texas Water Development Board (TWDB) in Austin, Texas considers the 9 Major aquifers of Texas.
To update the delineations for the major aquifers of Texas for the purpose of adding them to the 1991 Water Plan.
Lines were digitized from the Bureau of Economic Geology's Geologic Atlas Sheets (GAT) at 1:250,000 scale. Work started in January 1990 and was completed in May 1990. All digitizing was done at the USGS office in Austin, Texas using Arc/Info.
REVISIONS MADE TO THE MAJOR AQUIFERS FOR THE 2007 STATE WATER PLAN: The Edwards aquifer southern boundary has been updated based on new geochemical data. The boundary of the 1,000-mg/L line of equal dissolved solids concentration has been revised and moved both to the north and south of the previous boundary. More information on the new aquifer boundary can be found in the Texas 2007 State Water plan at http://www.twdb.state.tx.us/home/index.asp. In general, the Pecos Valley aquifer is defined by: (1) the occurrence of structural highs that have the potential to form barriers to groundwater flow and (2) the spatial extent of the Pecos Valley sediment. The Pecos Valley aquifer boundary differs from its former boundary in two ways. First, we revised the aquifer boundary, extending the aquifer into New Mexico to coincide with perceived hydrologic boundaries. Second, the old aquifer boundary excluded parts of Loving, Winkler, Ward, Pecos, and Crane counties where the alluvium is thin. This presents a problem to modeling groundwater flow because it incorrectly restricts access to the Pecos River, the main discharge zone. The new aquifer boundary better represent the geology as indicated by the 1:250,000 maps of the Geologic Atlas of Texas by including these areas of thinner alluvium. More information on the new aquifer boundary can be found in the Texas 2007 State Water plan at http://www.twdb.state.tx.us/home/index.asp. Aware of reports that not all of the mapped Seymour Aquifer held water, TWDB reviewed well information to determine which parts of the aquifer hold water and which parts do not. This review was done prior to developing the groundwater availability model for the Seymour Aquifer. In the process of developing the model, additional changes were made to the aquifer’s extent. Therefore, TWDB has changed the boundary so that only those sediments that are known to hold groundwater are part of the Seymour Aquifer More information on the new aquifer boundary can be found in the Texas 2007 State Water plan at http://www.twdb.state.tx.us/home/index.asp. The Trinity Aquifer extends beneath the Edwards (Balcones Fault Zone) Aquifer ending in the subsurface toward the west in eastern Uvalde County. This subsurface boundary in Uvalde County appears to coincide with the Sabinal River and, therefore, has a great amount of sinuosity and detail. Groundwater in the Trinity Aquifer in Uvalde County presumably flows beneath the Edwards (Balcones Fault Zone) Aquifer toward the south, in the same direction of the Sabinal River, which is probably why TWDB chose the river as the subsurface boundary of the aquifer. However, the boundary has much greater detail than what is known about the groundwater flow line. Therefore, TWDB has smoothed the shape of this line to better reflect the knowledge of its position. More information on the new aquifer boundary can be found in the Texas 2007 State Water plan at http://www.twdb.state.tx.us/home/index.asp. * The Edwards-Trinity Aquifer (outcrop) lines in West Texas were adjusted to lie adjacent to the updated Pecos Valley aquifer lines. Also, a small part of the outcrop was reclassified to subcrop in order to show the adjusted outcrop of the Pecos Valley aquifer which lies on top of the Edwards-Trinity in northern Pecos County. Also, a small part of the Ogallala aquifer in West Texas (specifically Andrews and Ector counties) was adjusted to lie adjacent to the updated Pecos Valley and Edwards-Trinity aquifer lines.
Time Period of Content
Time Period Information
Range of Dates/Times
Maintenance and Update Frequency
West Bounding Coordinate
East Bounding Coordinate
North Bounding Coordinate
South Bounding Coordinate
Theme Keyword Thesaurus
Place Keyword Thesaurus
There are no restrictions nor legal prerequisites for accessing the data set.
There are no restrictions nor legal prerequisites for using the data set after access is granted.
Point of Contact
Contact Person Primary
Texas Water Development Board
mailing and physical address
1700 North Congress Avenue P.O. Box 13231
State or Province
Contact Voice Telephone
Contact Facsimile Telephone
Contact Electronic Mail Address
Hours of Service
Data Set Credit
Mark Hayes, GISP (9 original aquifers) 1990 Peter George and Dr. Robert Mace, Geologists (Trinity aquifer revisions) 11/2006 Mark Hayes, GISP (Edwards and Edwards-Trinity aquifers revision) 11/2006 Ian Jones, Hydrologist (Pecos Valley aquifer revision) 11/2006 Cindy Ridgeway, Hydrologist (Seymour aquifer revision) 11/2006
Native Data Set Environment
Microsoft Windows XP Version 5.1 (Build 2600) Service Pack 2; ESRI ArcCatalog 220.127.116.110
Data Quality Information
The Texas Water Development Board (TWDB) has identified and characterized 9 major and 21 minor aquifers in the state based on the quantity of water supplied by each. A major aquifer is generally defined as supplying large quantities of water in large areas of the state. Minor aquifers typically supply large quantities of water in small areas or relatively small quantities in large areas. The major and minor aquifers, as presently defined, underlie approximately 81 percent of the state. Lesser quantities of water may also be found in the remainder of the state.
Horizontal Positional Accuracy
Horizontal Positional Accuracy Report
Horizontal positional accuracy is tested by visual comparison of hard copy check plots to the source materials and verifying the location of the data on-screen relative to other data layers in the same geographic area.
Bureau of Economic Geology (BEG) at the University of Texas, Austin, Texas
Geospatial Data Presentation Form
vector digital data
Geologic Atlas Sheets (GAT)
Bureau of Economic Geology, University of Texas, Austin, Texas
Source Scale Denominator
Type of Source Media
Data was digitized from paper geology maps from the Bureau of Economic Geology (BEG) at the University of Texas, Austin, Texas
Arclines were digitized in Arc/Info using GAT 1:250,000 paper maps from the Bureau of Economic Geology (BEG) at the USGS office in Austin, TX. Lines were delineated where necessary by geologists at the Texas Water Development Board, Water Supplies Section. Digitizing was done using an Altex digitizing tablet and a 'PRIME' server. Data was transferred to 9mm tape by the USGS and given to the GIS section of the TWDB for further conversion into Arc/Info format. Arclines were then grouped and coded by aquifer (number). Data was projected to Lambert Conformal Conic (custom) projection (in meters) using Arc/Info. Data was then built as a line cover and then as a polygon cover, labels were created as well as additional fields for further descriptive purposes.