This is a dataset containing what the Texas Water Development Board (TWDB) in Austin, Texas considers the 21 Minor aquifers of Texas.To update the delineations for the minor 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. The Yegua Jackson aquifer was digitized and added to the original dataset in 2001. REVISIONS MADE TO THE MINOR AQUIFERS FOR THE 2007 STATE WATER PLAN: The boundary of the Blaine aquifer was revised based on current information from well yields, groundwater levels, and groundwater chemistry. It was extended farther south to include most of the larger outcrops of the Blaine Formation. The boundaries of the Blaine Formation are based on the digital Geological Atlas of Texas (see TNRIS). The downdip extent of the aquifer, west of the exposure of the Blaine Formation, includes wells that produce groundwater with total dissolved solids of 10,000 ppm or less. The subsurface boundary along parts of the aquifer to the east includes all wells that draw water from the aquifer, and is not defined in terms of groundwater salinity. 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 Bone Springs–Victorio Peak aquifer is defined on the east by the center line of the Salt Basin, the original, pre-development discharge for groundwater flow in the area. Its southern boundary coincides with the Bitterwell Break, a Tertiary normal fault, out of the Salt Basin. This feature reportedly corresponds to a groundwater divide. Moving westward, the southern boundary transfers from the Bitterwell Break to the Babb Flexure, a structural hinge or bend in the rocks. To the northwest, the boundary follows a flow line based on the area’s potentiometric surface. The northern extent of the aquifer in Texas is defined by the state line with New Mexico. 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 revised boundary for the Igneous aquifer encloses contiguous Tertiary igneous rocks. Large exposures of pre-Tertiary, mainly Cretaceous, age rocks were kept outside of the boundary. It is defined to include the majority of wells drawing from Tertiary igneous rocks. For the most part, the boundary follows that defined by the USGS. However, the revised boundary excludes the northernmost extension of the USGS boundary in Culberson County since that area consists of mostly Permian rocks, and includes areas of Tertiary rocks that are within a LBG-Guyton boundary in the northeast part of the study area. We included an area in the southwest part of the proposed boundary because that area appears to contain Tertiary igneous rocks overlain by Quaternary sediments. 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 revised boundary for the Lipan aquifer includes Quaternary alluvium, mainly Qau, outside the present boundary. By including more alluvium the Lipan aquifer is coincident with the boundary for the Edwards-Trinity Plateau aquifer to the north, west, and south. To the east the boundary remains essentially unchanged, occurring at the boundary between the Leona Formation and the Permian Clear Fork Group or Lueders Formation. The boundary of the GAM model, defined by the groundwater divide, is used to determine a subsurface limit for the Lipan aquifer to the south. The northern edge of the Edwards-Trinity Plateau aquifer defines the northern subsurface boundary. The contact between the Permian Clear Fork Group and the Lueders Formation is extended along strike to the south to delineate an eastern subsurface limit. 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. Minor adjustments to the eastern boundary of the 'Presidio-Redford' portion of the West Texas Bolsons aquifer were done to show the contact with the new Igneous aquifer boundary. Minor adjustments were also made to show the contact with a smaller portion of the 'bolsons'/Igneous boundary in western Jeff Davis and southern Culberson county.
