MINOR AQUIFERS IN TEXAS
In Texas, a minor aquifer is defined as one that supplies large quantities of water in small areas or small quantities of water in large areas. The Texas Water Development Board recognizes and names 15 such aquifers. These aquifers, which are in rocks that range in age from Pleistocene to Cambrian, are the Lipan, the Igneous, the Nacatoch, the Blossom, the Woodbine, the Rita Blanca, the Edwards-Trinity (High Plains), the Dockum, the Rustler, the Capitan Reef Complex, the Bone Spring-Victorio Peak, the Marathon, the Marble Falls, the Ellenburger-San Saba, and the Hickory (fig. 130). Two additional minor aquifers mapped by the Texas Water Development Board are considered to be principal aquifers and are discussed in previous sections of this chapter. The first is the Brazos River alluvial aquifer, which is part of the alluvial aquifers along major streams. The second is the Blaine aquifer, considered to be a major aquifer because of its large areal extent.
Some freshwater and moderately saline water withdrawn from the minor aquifers, particularly in the western part of the State, is used almost exclusively for irrigation and livestock watering purposes and some is used in oilfield water-flooding operations and mining activities. Water flooding is a secondary recovery operation in which water is injected into an oil reservoir to force additional oil into producing wells.
The Lipan aquifer consists mostly of the Leona Formation of Pleistocene age, but locally includes the underlying Choza Formation and the Bullwagon Dolomite Member of the Vale Formation, which are in the Permian Clear Fork Group. The aquifer is mostly in Tom Green County, but also is in small parts of Runnels and Concho Counties. The Leona Formation, which is the most productive part of the Lipan aquifer, consists of gravel, conglomerate, sand, silty clay, and caliche. The thickness of the aquifer ranges from a few feet to about 125 feet. Well yields are highly variable, and range from about 100 to 7,000 gallons per minute. Water from the Lipan aquifer gen-erally has a dissolved-solids concentration of between 1,000 and 3,000 milligrams per liter.
Most recharge to the aquifer is from local precipitation and return flow from applied irrigation water. Ground water is discharged by seepage to the Concho River and its major tributaries and by springflow, evapotranspiration, and withdrawals from wells. During 1985, reported withdrawal from the aquifer in Tom Green County was about 15 million gallons per day, about 95 percent of which was used for irrigation.
Water-yielding intrusive and extrusive igneous rocks of Tertiary age are in Brewster, Jeff Davis, and Presidio Counties. Ground water is in the fissures and fractures of lava flows, tuffs, and related igneous rocks, including the Petan Basalt, the Tascotal Formation, the Barrel Springs Formation, the Cottonwood Spring Basalt, the Sheep Canyon Basalt, and the Crossen Trachyte. The igneous rocks supply small to large volumes of water of chemical quality that is suitable for public supplies, irrigation, and other uses. About 4 million gallons per day was withdrawn from the igneous rocks during 1985; of that, about 60 percent was used for public and domestic supplies.
The Nacatoch aquifer consists of the Nacatoch Sand that lies beneath the Corsicana Marl and above the Neylandville Marl; the three formations are in the Upper Cretaceous Navarro Group. The southeastward-dipping aquifer extends from the Limestone-Navarro County line northeastward to the Red River. The aquifer consists of unconsolidated to consolidated, massive, glauconitic, calcareous sand and mudstone that locally are as much as 500 feet thick. The Nacatoch aquifer is generally unconfined in the outcrop area and confined where it dips beneath younger formations. The depth to the top of the aquifer in downdip areas where the aquifer contains fresh to slightly saline water is as much as 800 feet in southwestern Bowie County.
Wells completed in the Nacatoch aquifer yield as much as 500 gallons per minute; flowing wells are in Bowie and Red River Counties. Generally, water in the aquifer has dissolved-solids concentrations that range from 400 to 1,000 milligrams per liter. Pumpage in excess of annual effective recharge has caused water levels to decline since the beginning of development. About 4.5 million gallons per day was withdrawn from the Nacatoch aquifer during 1985, about 59 percent of which was used for public and domestic supplies.
The Blossom aquifer consists of the Blossom Sand of the Upper Cretaceous Austin Group. The aquifer is overlain and confined downdip by the Brownstown Marl, and underlain and confined by the Bonham Marl, both of the Austin Group. The aquifer extends from the middle of Lamar County eastward through Red River County into the northwestern corner of Bowie County. The Blossom Sand is locally as much as 400 feet thick, and consists of fine to medium sand interbedded with sandy and chalky marl.
The aquifer yields water of usable quality to wells located mostly in aquifer outcrop areas; in part of Red River County, however, water with a dissolved-solids concentration of less than 3,000 milligrams per liter extends downdip for about 6 miles south of the outcrop. Slightly more than 1 million gallons per day was withdrawn from the Blossom aquifer during 1985. About 98 percent of the water withdrawn was used for public and domestic supplies.
The Woodbine aquifer consists of the Templeton, the Lewisville, the Red Branch, and the Dexter Members of the Upper Cretaceous Woodbine Formation, and is present in an area that extends from northern McLennan County in the south to the Red River in the north. The aquifer consists of fine to coarse ferruginous sand and sandstone, clay, shale, and sandy shale and some lignite and gypsum. The aquifer is hydraulically connected to overlying alluvium along the Red River. The thickness of the aquifer ranges from a few feet in outcrop areas to about 700 feet near the downdip limit of slightly saline water in Fannin County. Maximum depth to the top of the aquifer is about 2,000 feet below land surface. In downdip areas, the Woodbine aquifer is confined above by shales of the Upper Cretaceous Eagle Ford Group and below by the Buda Formation or the Grayson Marl and the Mainstreet Limestone, all of Cretaceous age.
Recharge to the aquifer is by precipitation that falls on aquifer outcrop areas and by seepage from lakes and streams where there is a downward gradient to the aquifer. Water moves through the aquifer from the outcrop in an east-southeast direction and generally follows the dip of the beds. Water from the aquifer in the outcrop area has an average dissolved-solids concentration of about 550 milligrams per liter; the concentration increases downdip to more than 3,000 milligrams per liter. Locally, the water has objectionable concentrations of iron, sodium, and chloride.
Wells completed in the Woodbine aquifer yield from about 100 to about 700 gallons per minute. A large cone of depression on the potentiometric surface of the aquifer is located near the middle of Grayson County and is the result of withdrawals for public supply. About 16 million gallons per day was withdrawn from the Woodbine aquifer during 1985. The principal use of the water was for public and domestic supply (49 percent), followed by withdrawal for agricultural (primarily irrigation) use (39 percent).
RITA BLANCA AQUIFER
The Rita Blanca aquifer, which is in the extreme northwestern corner of the Panhandle, consists of all geologic formations that are below the Miocene Ogallala Formation and above the Triassic Dockum Group in Dallam and Hartley Counties and that contain fresh to slightly saline water. The formations that compose the aquifer are mostly in the subsurface and include the Romeroville, the Mesa Rica, and the Lytle Sandstones of Cretaceous age, and equivalents of the Morrison Formation and the Exeter Sandstone of Jurassic age.
The aquifer consists mostly of fine- to medium-grained sandstone, with some shale, clay, conglomerate, and limestone. The thickness of the Rita Blanca aquifer is locally as much as 250 feet. In places, the aquifer is hydraulically connected to the overlying High Plains aquifer and the underlying Dockum aquifer, and the total thickness of water-yielding rocks in such places is accordingly much greater. Well yields as large as 500 gallons per minute are possible. About 4.5 million gallons per day was withdrawn from the aquifer during 1985, 98 percent of which was used for irrigation.
EDWARDS-TRINITY (HIGH PLAINS) AQUIFER
The Edwards-Trinity (High Plains) aquifer consists of sand and sandstone of the Trinity Stage and the younger limestone of the Fredericksburg and the Washita Stages, all of Cretaceous age. Despite its name, the aquifer is not part of either the Edwards-Trinity or the High Plains aquifers discussed previously in this chapter as principal aquifers. The aquifer underlies parts or all of 14 counties in the central part of the Southern High Plains. The aquifer is hydraulically connected to the overlying High Plains aquifer in many places. The average saturated thickness of rocks of the Trinity Stage is estimated to be 30 feet, and those of the Fredericksburg and the Washita Stages are estimated to be 20 feet. In most places, the sand and sandstone of the Trinity Stage are separated from the younger limestone strata by clay, marl, and shale beds. Water in the Trinity rocks is confined, as opposed to water-table conditions in the carbonate rocks. Regional ground-water movement is generally to the east-southeast and follows the dip of the rocks.
Yields of wells completed in the aquifer range from 50 to more than 1,000 gallons per minute; the largest yields are reported from wells in Hale and Lubbock Counties. Yields are largest where the water is in solution cavities, fractures, joints, and bedding planes in the carbonate rocks.
Water from the Edwards-Trinity (High Plains) aquifer usually is slightly to moderately saline and moderately to extremely hard, but the chemical quality is suitable for irrigation and secondary oil recovery. Withdrawal from the aquifer during 1985 was about 11.4 million gallons per day. About 89 percent of the water withdrawn was used for irrigation.
The Dockum aquifer comprises all water-yielding units within the Dockum Group of Triassic age. The aquifer is in a large area that extends from the northwestern corner of the Panhandle southward to the northern part of the Edwards Plateau, and then westward into the Trans-Pecos area. In places, the Dockum aquifer is hydraulically connected to overlying aquifers, including the High Plains, the Pecos River alluvium, the Edwards-Trinity, the Edwards-Trinity (High Plains), and the Rita Blanca aquifers.
The Santa Rosa Formation, which is the most productive part of the Dockum aquifer, consists principally of interbedded shale, sand, sandstone, and conglomerate. The saturated thickness of the aquifer is as much as 700 feet in the Edwards Plateau area. Yields of wells completed in the aquifer are generally less than 300 gallons per minute. Dissolved-solids concentration of the water ranges from less than 100 to more than 4,000 milligrams per liter. About 33 million gallons per day was withdrawn from the Dockum aquifer during 1985, about 40 percent of which was withdrawn for mining and thermoelectricpower uses. Withdrawals for public and domestic supplies and agricultural (primarily irrigation) uses were about 29 percent each.
The Rustler aquifer consists of water-yielding rocks of the Rustler Formation of Permian age. The rocks consist of dolomite; limestone; anhydrite; gypsum; a basal zone of sand, sandstone, siltstone, and shale; and minor amounts of halite or rock salt. Solution openings are in the dolomite, limestone, anhydrite, and gypsum. The aquifer crops out in eastern Culberson County and dips toward the east-southeast where the farthest downdip occurrence of usable-quality water is in Pecos County. In places, the aquifer is hydraulically connected to the overlying Pecos River Basin alluvial aquifer. In other downdip areas, the Rustler aquifer is confined by the overlying Permian Dewey Lake Red Beds. Maximum thickness of the aquifer is about 500 feet.
Most wells completed in the Rustler aquifer yield less than 300 gallons per minute; one well in Pecos County, however, had a reported yield of 4,400 gallons per minute. The dissolvedsolids concentration of the water generally ranges from 2,000 to 6,000 milligrams per liter, with the principal ions being calcium and sulfate. The water is not suitable for human consumption, but is used for irrigation, livestock watering, and oilfield water-flooding operations. About 300,000 gallons per day was withdrawn from the Rustler aquifer during 1985. About 81 percent of the water withdrawn was used for agricultural purposes, and most of the remainder was used for oilfield water-flooding.
CAPITAN REEF COMPLEX AQUIFER
The Capitan Reef Complex aquifer consists of reef, fore-reef, and back-reef facies of Permian rocks that were deposited around the margin of the Delaware Structural Basin. The principal water-yielding formations are the Capitan Limestone and the underlying Goat Seep Limestone of the reef zone; also included in the aquifer are permeable zones in the limestone shelf facies immediately adjacent to the reef zone-the Tansil, the Yates, the Seven Rivers, the Queen, and the Grayburg Formations. The arc-shaped aquifer is about 10 to 14 miles wide and extends from northwestern Culberson County southeastward to Jeff Davis County and northward from Brewster County to northwestern Winkler County.
The aquifer generally contains highly mineralized water, except where it crops out in mountainous areas in Culberson, Brewster, and Pecos Counties. In an area along the Culberson-Hudspeth County line, the aquifer has been penetrated by wells to depths greater than 1,000 feet. Water levels range from about 100 to more than 200 feet below land surface. Wells completed in the aquifer commonly yield more than 1,000 gallons per minute; the yield from one well is estimated to be as great as 6,000 gallons per minute. The water is a calcium-magnesium bicarbonate type and has dissolved-solids concentrations that range from 850 to 1,500 milligrams per liter.
In a mountainous area of southeastern Culberson County, well depths range from 350 to about 1,700 feet, and water levels range from 280 to 1,000 feet below land surface. Wells completed in the aquifer in this area yield as much as 400 gallons per minute. The calcium-magnesium-bicarbonate water has a dissolved-solids concentration that ranges from 1,000 to 2,500 milligrams per liter.
About 200,000 gallons per day was withdrawn from the Capitan Reef Complex aquifer during 1985. About 81 percent of the water withdrawn was used for agricultural (primarily irrigation) purposes.
BONE SPRING-VICTORIO PEAK AQUIFER
The Bone Spring-Victorio Peak aquifer consists of the Bone Spring Limestone and the Victorio Peak Limestone of Permian age. The aquifer underlies an area in northern Hudspeth County. Water is in joints, fractures, and solution cavities in the limestone formations. The thickness of the aquifer is as much as 2,000 feet. The wide range in aquifer hydraulic conductivity is reflected in the yields of wells completed in the aquifer; yields range from about 150 to more than 2,200 gallons per minute.
The chemical quality of the water in the aquifer also is extremely variable. The water is generally not suitable for municipal and domestic supplies, but is used for irrigation. In 1948-49, water withdrawn from the aquifer for use in an intensively irrigated area had dissolved-solids concentrations of 1,100 to 1,800 milligrams per liter. By 1968, the dissolvedsolids concentration in most of the water in the same area ranged from 3,000 to 5,000 milligrams per liter, which amounts to almost a threefold increase for many of the wells. The increased dissolved-solids concentration was probably caused by the concentration of salts in the return flow of applied irrigation water as a result of evapotranspiration and the leaching of additional salts from overlying shallow alluvial deposits. Further increases in the dissolved-solids concentration of the ground water were reported for the 1970's.
About 82 million gallons per day was withdrawn from the Bone Spring-Victorio Peak aquifer during 1985. More than 99 percent of the water withdrawn was used for irrigation.
The Marathon aquifer consists of tightly folded and faulted rocks of the Gaptank Formation and the Dimple Limestone of Pennsylvanian age; the Tesnus Formation of Pennsylvanian and Mississippian age; the Caballos Novaculite of Mississippian, Devonian, and Silurian age; and the Maravillas Chert, the Fort Pena Formation, and Marathon Limestone of Ordovician age. The aquifer underlies an area in north-central Brewster County.
The Marathon Limestone is the most productive part of the aquifer and is the source of municipal supply for the town of Marathon. The upfolded Marathon Limestone is at or near land surface, and water in the aquifer is under unconfined conditions in fractures, joints, and cavities. Maximum thickness of the aquifer is about 900 feet, and well depths are commonly less than 250 feet. Wells completed in the aquifer yield from less than 10 to more than 300 gallons per minute.
Water from the Marathon aquifer is very hard, but otherwise is generally suitable for most uses. The dissolved-solids concentration ranges from 500 to 1,000 milligrams per liter. About 700,000 gallons per day was withdrawn from the aquifer during 1985, of which about 81 percent was used for public supply.
MARBLE FALLS AQUIFER
The Marble Falls aquifer consists of the Marble Falls Limestone of Pennsylvanian age, which crops out along the flanks of the Llano Uplift, primarily in McCulloch, San Saba, Lam-pasas, and Burnet Counties. Water is in joints, fractures, and cavities in the limestone, which is locally as much as 600 feet thick. The aquifer is highly permeable in places, as indicated by wells that yield as much as 2,000 gallons per minute and the presence of large springs that issue from the aquifer.
The chemical quality of the ground water is generally suitable for most purposes. About 900,000 gallons per day was withdrawn from the Marble Falls aquifer during 1985. About 59 percent of the water withdrawn was used for agricultural purposes, and the remainder was used equally for public and industrial supplies.
ELLENBURGER-SAN SABA AQUIFER
The Ellenburger-San Saba aquifer consists of the Tan-yard, the Gorman, and the Honeycut Formations of the Ellenburger Group of Ordovician age, and the San Saba Limestone Member of the Wilberns Formation of Ordovician and Cambrian age. The aquifer is a sequence of limestone and dolomite beds that crop out in a circular pattern around the Llano Uplift and dip radially into the subsurface away from the center of the uplift. The maximum thickness of the aquifer is about 2,000 feet. Water is in fractures, cavities, and solution channels and is commonly under confined conditions. The aquifer is highly permeable in places, as indicated by wells that yield as much as 1,000 gallons per minute and springs that issue from the aquifer, which maintains the base flow of streams in the area.
Although the ground water is hard, the dissolved-solids concentration is minimal in most places. Fresh to slightly saline water extends downdip to depths of approximately 3,000 feet below land surface. About 4.4 million gallons per day was withdrawn from the Ellenburger-San Saba aquifer during 1985. The water was used about equally for public supply and for agricultural (primarily irrigation) purposes.
The Hickory aquifer consists of the Hickory Sandstone Member of the Riley Formation of Cambrian age, which crops out in a circular pattern around the Llano Uplift and dips radially into the subsurface from the center of the uplift. The aquifer is underlain by Precambrian rocks and is overlain and separated from the Ellenburger-San Saba aquifer by the Cap Mountain Limestone and the Lion Mountain Sandstone Members of the Riley Formation. The Hickory aquifer is locally as much as 500 feet thick, and is extensively faulted. Wells completed in the aquifer commonly yield between 200 and 500 gallons per minute; a few wells yield more than 1,000 gallons per minute.
Dissolved-solids concentrations of the ground water commonly range from 300 to 500 milligrams per liter. Water that contains a dissolved-solids concentration of less than 3,000 milligrams per liter extends downdip to a maximum depth of about 5,000 feet below land surface. About 25.5 million gallons per day was withdrawn from the Hickory aquifer during 1985. About 82 percent of the water withdrawn was used for agricultural (primarily irrigation) purposes. Most of the remainder was used for public supply.