Groundwater Monitoring

Our aquifers hold one of the state's greatest resources, particularly as drought's more immediate effects on surface water resources become understood. As the state's population continues to grow in the coming decades and increases the demand on drought-depleted reservoirs, groundwater will only become more vital. It is critical to monitor this important resource in terms of both quantity and quality to understand resource availability, vulnerability, changing conditions, and conservation needs.

The Groundwater Monitoring Department monitors groundwater levels and groundwater quality in the 9 major and 22 minor aquifers of Texas. This includes both historical and current information staff collect each year from various types of wells that rely on voluntary access consent from landowners and other entities. We strive to maintain a consistent network of monitoring wells, finding replacement wells as needed, to develop a robust historical record and document changes in groundwater levels and groundwater quality over time.

Programs that are part of this department include the Groundwater Quality Program, Springs Monitoring Program, Water Level Program, and Recorder Well Program. The information collected by TWDB staff in these programs and by our cooperating partners, primarily Groundwater Conservation Districts, is vitally important to all Texans and made publicly available in the TWDB Groundwater Database. From a regional and often long-term perspective, such as that considered by public sector planners, private consultants, and researchers, management and conservation plans must be based on accurate groundwater data. From a localized and often near-term perspective, such as that taken by public water supply and private well owners, more immediate decisions must be based on real-time water level data in comparison to as much historical data as possible.

Groundwater Quality Program

The purpose of the groundwater quality sampling program is to monitor changes in the quality of groundwater over time and to establish as accurately as possible the baseline quality of groundwater occurring naturally in the state's aquifers. Although groundwater used for drinking purposes typically does not contain dissolved constituents in excess of their Maximum Contaminant Levels, which could pose health risks, it is important to monitor groundwater quality periodically over time to detect trends in the concentrations of these constituents. Certain constituents pose greater risks than others as listed in the Priority Contaminant Ranking in Groundwater in Texas.

Priority Contaminant Ranking in Groundwater

Rank 1 - Severe Health Threat

Bacteria: Bacteria can cause gastro-enteric illness and may indicate fecal contamination. Although it is often tested for in private wells when property with a well is sold, the analysis may not be performed at a certified lab
Nitrate, NO₃^-: The presence of NO₃^-/NO₂^- can indicate fecal contamination. Nitrate and nitrite can cause blue-baby syndrome.
Nitrite, NO₂^-: Nitrate and nitrite are immediate risks to young children and pregnant mothers.

Rank 2 - Moderate Health Threat

Arsenic: Arsenic has a health-based standard based on long term risk and occurs relatively frequently in Texas public water systems (most frequently of the constituents with primary drinking water standards).
Fluoride: Fluoride has a health-based standard based on long term risk and occurs relatively frequently in Texas public water supply systems (second most frequently detected in excess of primary standards).
Gross alpha, radium 226+228: Radionuclides (including emissions from uranium) naturally occur in several Texas aquifers. Analysis methods, identifying all three, are more expensive than for other constituents.
Uranium: Uranium may also cause metal toxicity in excess amounts, not related to emission of radionuclides. Analysis as a metal is separate from analysis for radionuclide emission.

Rank 3 - Minimal Health Threat

VOCs: Texas has naturally occurring and anthropogenic Volatile Organic Compounds (VOCs). Occurrence infrequently indicates explosion risk, with ingestion of lesser concern.
Pesticides: Pesticides are rarely detected and even more rarely detected at levels above the health-based standard based on long-term (2 liters/70 years) health risks.
Sulfate, SO₄^-: Sulfate can cause "traveler's diarrhea," but does not cause any health issues to people acclimated to the water--therefore a low concern for homeowner.
Manganese: Manganese causes no identified health concerns; instead, the element causes colored water, and is therefore of less concern for the homeowner.
Perchlorate: Although Texas has naturally occurring and anthropogenic perchlorate, occurrence is likely not high. EPA has still not set a standard based on perchlorate (ClO₄^-)'s long-term risks.
Radon: Radon is a much greater concern in air than in water, and radon detectors for air (similar to smoke detectors) are a much more efficient way of determining if a private residence is at risk from radon.

The TWDB tests for most of the dissolved inorganic constituents listed above including nutrients (nitrate/nitrite) and radionuclides. Bacteria in groundwater, while of the greatest concern for well owners using their well water for drinking, may be tested for inexpensively at many county health departments and numerous private analytical labs. Texas Agrilife Extension Service recommends that well disinfection be performed by professionals.

Primarily, the TWDB groundwater quality monitoring program consists of collecting samples directly from the aquifer, before treatment, in accordance with procedures established in the TWDB's Field Manual for Groundwater Sampling. Protocols outlined in this manual have been followed consistently since 1988 to ensure network continuity. Results from analyses sampled by other entities in cooperative agreements with the TWDB in which the TWDB's sampling protocols are followed are also entered in the TWDB Groundwater Database and coded appropriately, as are water quality data from certain other programs from a variety of state, local, and federal agencies that collect in Texas. The TWDB samples a representative number of wells from each of the state's 9 major and 22 minor aquifers, throughout their extent, once every four years.

No other state agency is equipped or mandated to monitor statewide ambient groundwater quality or obligated to sample using the TWDB's methods, although numerous other agencies collect data for their own purposes. In 2023 the Texas Groundwater Protection Committee conducted a survey of water quality data-collection programs administered by other agencies in Texas to help identify potential data gaps, monitoring needs, and opportunities for collaboration.

Springs Monitoring Program

The Springs Monitoring Program aims to document the springs of Texas and to monitor short and long-term changes in flow rate and water quality data.

Water Level Program

The TWDB measures groundwater levels annually in nearly 2,000 wells completed in 30 major and minor aquifers and located throughout the state. The majority of these wells are used for irrigation, household needs, and stock watering, although some are owned by small commercial water suppliers or used for industrial purposes. TWDB personnel measure depths to water in accordance with procedures outlined in the TWDB Water-Level Measuring Manual. Typically they use steel tapes, sometimes electric lines and sonic detectors, or even pressure gauges if the water is under artesian pressure and rises above land surface. Annual water levels are measured during cooler months when groundwater pumping is minimal and the water levels are most indicative of static or ambient conditions.

We cooperate with nearly 70 groundwater conservation districts, federal entities such as the US Geological Survey, and numerous additional municipalities to collect water-level measurements. Currently cooperators provide at least an additional 8,000 measurements annually that are entered in the TWDB groundwater database. They measure some wells more than once a year, depending on the needs of their specific programs, and provide water-level data to the TWDB. Of all wells measured, approximately 4,000 are considered part of an "ideal" water-level monitoring network by the TWDB, based on monitoring targets of one well per 25 to one well per 125 square miles per major and minor aquifer, and depending on amount of groundwater pumpage.

Recorder Well Program

As of September 1, 2024, the TWDB maintained 269 water-level recorders, solely or in cooperation with groundwater districts, in 113 counties at wells also equipped with satellite or cellular telemetry. These automatic recorders transmit near-real-time water level data via the Geostationary Operational Environmental Satellite or GOES system. TWDB receives this information and publishes daily water level data. The equipment at each site typically consists of dataloggers attached to water level recording devices, such as transducers or floats and pulleys; satellite transmitters; power sources, including solar panels; antennae; and equipment shelters.

Procedures for maintenance and troubleshooting are found in the TWDB's Field Manual for Automated Water Level Recorders. An ever increasing number of groundwater conservation districts have been able to purchase recorders and transmitters, install equipment with the help of TWDB staff, and publish data from their wells on the TWDB web site. The TWDB is currently actively seeking funding for installation of more recorders in the remaining counties in the state.