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Monitoring of groundwater quality is divided among different state, federal, and local entities. In 1996 the
then-TNRCC (now known as the Texas Commission on Environmental Quality or TCEQ) began a water quality assessment program for aquifers as part of the Water Quality Inventory conducted by the
TNRCC under the Clean Water Act.* In 1996 one major aquifer (the Trinity) one minor aquifer (the Dockum, in the High Plains) and two local aquifers (the Rio Grande Alluvium and Laredo formations) were analyzed using both agency data as well as data from the Texas Water Development Board and others. Since 1990 the TWDB has begun a groundwater monitoring program that attempts to cover all the major and minor aquifers within six years. In a typical year, the TWDB conducts samples in 800 to 1,000 different sites, while other entities—such as groundwater conservation districts, the U.S. Geological Survey, and the TCEQ—conduct about 900 samples per year.* Currently, the TWDB maintains a database of ambient groundwater monitoring data for over 51,000 water wells. By the 2002 Draft Water Quality Inventory, some 30 major, minor and local aquifers were analyzed at some basic level, largely using data from the TWDB *. While the vast majority of sampled groundwaters had levels of contaminants below the Maximum Contamination Limits used for drinking water
regulations, certain contaminants -- such as flouride (176 out of 2914 wells), nitrate (792 out of 2,943 wells), selenium (95 out of 3,275 wells), chloride (481 out of 2,931 wells), flouride
(639 out of 2,582 wells), sulfate (643 out of 2,931 wells) and dissolved solids (643 out of 2,928 wells) -- had significant numbers of wells with samples at or above MCL levels. * Most of these high levels of constituents are probably due to naturally-occuring rather than human-made contamination and most occured in the western parts of the State. However, the majority of this groundwater quality monitoring data provides very little information about anthropogenic (i.e., human-made) sources of constituents such as heavy metals, petroleum products, or pesticides. Among the aquifers most affected by high levels of nitrate, sulfate and total dissolved solids include the Ogalalla and Dockum aquifers in the Texas Panhandle; the Cenozoic Pecos Alluvium, Capitan Reef Complex and Rustler aquifers in West Texas; and the Blaine and Lipan aquifers in North and West-Central Texas. In East Texas, many of the wells sampled did have high levels of nitrate in the Gulf Coast Aquifer. *.
In addition, at least four state agencies—the TCEQ, the Railroad Commission, the Texas Department of Health,
and the Texas Department of Licensing and Regulation —require monitoring at nearly 8,700
industrial, agricultural, and municipal facilities statewide for permit and operational requirements. The majority -- 98 percent -- are under the jurisdiction of the TCEQ. Among the programs that require groundwater monitoring include the Municipal Solid Waste Program, the State Superfund, the State Oilfield Cleanup Fund, the Bureau of Radiation Control, and Surface Mining and Reclamation Regulations. Most of this monitoring is self-reported. Most "human-made" groundwater contamination from regulated facilities occurs in heavily population areas of the state like Houston, Dallas, Fort Worth, San Antonio and El Paso -- often contaminating local, shallow water zones, rather than major or minor aquifers.
Finally, the TCEQ has ranked the aquifers' vulnerability to contamination using a model known as the DRASTIC
index. This index looks at both hydrological and geological components of the aquifers to gauge the potential for groundwater pollution.
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MAJOR AQUIFER VULNERABILITY RATING
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Shaded Areas: Outcrop (That Part of a water bearing rock layer which appears at the land surface)
Ruled Areas: Downdip (That Part of a water bearing rock layer which dips below other rock layers)
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Source: Texas Water Development Board
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AQUIFER
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VULNERABILITY RATING
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1. Ogallala North
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Low
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1. Ogallala South
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Medium
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2. Seymour
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High
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3. Hueco-Mesilla Bolson
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Low
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4. Cenozoic Pecos Alluvium
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Medium
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5. Edwards-Trinity (Plateau)
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Medium
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6. Trinity
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Medium
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7. Edwards (Austin & San Antonio)
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High
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8. Carrizo-Wilcox
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Medium
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9. Gulf Coast
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Medium
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Source: Texas Natural Resource Conservation Commission, State of
Texas Water Quality Inventory, 12th ed. (Austin: TNRCC, 1994).
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