This is a dataset containing what the Texas Water Development Board (TWDB) in Austin, Texas considers the 9 Major aquifers of Texas. 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.
