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Texas Environmental Almanac, Chapter 2, Water Quality, Page 7



Like surface water, groundwater is vulnerable to contamination from a variety of sources. In Texas, all nine major aquifers and 20 minor aquifers have experienced some form of contamination. These contamination problems stem partly from development and industry and partly from overpumping, which causes infiltration of saline waters.

Despite these contamination problems, state laws do not protect groundwater to the extent that they do surface water. There are, for example, no groundwater quality standards to parallel those for surface water. The state does have standards in place for groundwater stored for drinking water, but apart from these public health standards, state law does not apply environmental standards to groundwater.

Clean groundwater is needed for more than drinking purposes. Agriculture depends heavily on groundwater for irrigation; in 1990, some 79 percent of all groundwater pumped was used for crop irrigation.(73) Poor or contaminated groundwater could jeopardize crops and threaten the health of livestock.

Clean groundwater is also essential to clean surface water. Groundwater is connected to surface water in the hydrological cycle and some aquifers actually feed area springs and rivers. For example, the Edwards Aquifer is the major source for Central Texas rivers through the Comal and San Marcos Springs. Poor quality water - or a lack of water - harms the springs and their aquatic life as well as downstream users.

Sometimes contamination occurs naturally. Saline water from deeper aquifers may reach aquifers that provide water for humans. Some groundwater may have naturally high background levels of nitrates, metals, iron, sulfate or chloride, all of which can give water an odd odor, color or taste.

Groundwater contamination has become a major public policy concern in recent decades, as citizens and public officials alike have learned how human activity has impacted water quality. Landfills for both hazardous and non-hazardous waste, improperly completed or abandoned water wells, oil- and gas-related wells, petroleum storage tanks, agricultural pesticides and leaking septic tanks are all potential sources for contaminants that can seep down to the aquifer. Deep petroleum, mining and injection wells can likewise directly pollute aquifers.


Diagram of Groundwater Contamination Routes

Source: Adapted from Environmental Protection Agency, Office of Water Supply and Solid Waste Management Programs, Waste Disposal Practices and Their Effects on Groundwater (Washington, DC: U.S. Government Printing Office, 1977).


It is difficult to ascertain how much groundwater contamination has resulted from human activities. The state does, however, track instances of contamination. The Texas Groundwater Protection Committee, which includes three state agencies that regulate activities that can cause groundwater contamination - the Texas Natural Resource Conservation Commission, the Railroad Commission of Texas and the Texas Department of Agriculture - reported 5,670 instances of groundwater contamination between 1989 and 1993 which had yet to be cleaned up.(74) These figures represent only the cases reported and confirmed.

Although the state conducts no comprehensive water quality assessment for aquifers, the Texas Natural Resource Conservation Commission 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.

Underground Storage Tanks

From 1989 through 1993, the source of groundwater contamination in 85 percent of the reported cases to the Texas Groundwater Protection Committee was an underground or above ground storage tank. Usually these were petroleum storage tanks used by gas stations. To date, 825 of the 5,718 documented cases (about 15 percent) have been successfully cleaned up.(75)

There are some 150,000 underground and 17,000 above ground storage tanks registered with the TNRCC. Most contain petroleum products like diesel fuel, waste oil and gasoline. A smaller number store regulated hazardous substances. Of the 5,718 cases of groundwater contamination reported since the state began monitoring the tanks in 1989, about a third are located in the Houston and Dallas metropolitan areas (see County Indicators for a complete list). (76)

In 1989, the Texas Legislature created a fee-supported reimbursement fund that enables the state to assume clean-up costs when the party responsible for contamination is unwilling or unable to pay or cannot be located. From 1990 to 1993, almost $200 million from this fund was spent on petroleum storage tank clean-up.(77) However, fee revenue has not been sufficient to pay for all the necessary clean-ups and the Legislature has had to appropriate emergency funds. Contamination from petroleum storage tanks has affected not only groundwater quality but also real estate values in some areas, as prospective buyers have considered clean-up costs and pollution liability.(78)


Injection Wells

Injection wells, where pressurized liquid waste or other fluids are injected into aquifers, are a major method of disposal for industrial and hazardous waste. Injection wells are also used to help recover oil, gas and minerals. For example, injection wells are used to inject fresh water into an underground oil field for secondary recovery of oil. Uranium and sulfur are often mined by injecting hot water into formations to loosen up these materials.

Injection wells are not a new technology. Beginning in the 1920s, deep wells were injected with superheated water to recover liquid sulfur. As far back as 1938, salt water extracted from the ground along with oil from an East Texas oil field was returned to the lower part of the formation via an injection well.(79)

Injection wells have been involved in a number of controversial lawsuits and permit battles, as well as high-profile groundwater contamination cases, usually resulting from improper handling of the waste at the surface prior to injection (see Waste chapter ). According to the Texas Natural Resource Conservation Commission, there have been no confirmed cases of groundwater contamination from the injection of hazardous and other industrial waste in the last five years. However, in the case of injection wells used for mining, the movement of mining fluids into groundwater is not considered a case of groundwater contamination so long as the facility cleans up the water and assures that it does not spread past the mining area. All groundwater contamination resulting from these activities has been cleaned up.

In Texas, 116 underground injection wells are currently used by generators of hazardous and non-hazardous waste or by owners or operators of hazardous waste management facilities. Approximately 65 other wells are in various stages of permitting by the Texas Natural Resource Conser- vation Commission or have stopped operations.(80) Together, Texas' industries injected approximately 14.8 million tons of hazardous waste on-site, and sent an additional 183,900 tons to Texas commercial facilities in 1991.(81)

Industrial and hazardous wasteManufacturing industry
Oil and gas wasteOil and gas exploration, development, production
Superheated waterBrine mining, sulfur and sodium, sulfate mining, uranium mining
Sewage disposalMunicipalities, individuals
Agricultural drainageAgriculture, particularly citrus production

Source: Texas Department of Water Resources,
Underground Injection Wells in Texas (Austin: TDWR, 1984).

The Railroad Commission of Texas has jurisdiction over injection wells used to inject oil and gas waste, a term that includes all waste incidental to drilling for production of oil, gas or geothermal resources. Most waste consist of saltwater, which is recovered along with natural gas during drilling. The Railroad Commission can also issue permits for wells to be used for secondary recovery or to store hydrocarbons. Some 12,475 salt-water disposal wells, 40,000 secondary-recovery wells and 545 hydrocarbon and gas storage wells are currently under the jurisdiction of the Railroad Commission.(82) In 1993, two cases of groundwater contamination related to Railroad Commission-permitted injection wells were documented in Runnels and Matagorda counties.

Another class of injection wells are those used for uranium or sulfur mining or for the recovery of brine (subsurface salt deposits). These wells can contribute to the contamination of groundwater by increasing its salinity.

Most of the 81 brine-mining facilities operating in Texas are located in the High Plains and Trans-Pecos regions. Thirty-four uranium mining sites, three sodium sulfate mining sites and six sulfur mining sites have been permitted in South Central Texas, near San Antonio. All of the uranium mines and 75 of the 81 brine mines are required to sample and monitor groundwater quarterly because of potential contamination.(83) In general, injection wells used in mining are not as deep as those used for injection of waste. They are thus more likely to impact near-surface water used for drinking.

Other types of wells used in Texas include wells to inject urban or agricultural runoff that has been stored in surface ponds; water used in air conditioning systems; human waste from septic tanks; and fresh surface water or treated wastewater to recharge depleted aquifers.

The Lower Rio Grande Valley is the major area of Texas where agricultural drainage wells are used. These wells help eliminate excess water from agricultural production. Because this part of the state is flat and has clay soils and high water tables, there is limited surface drainage. Agricultural drainage wells collect near-surface waters and drain them into subsurface formations. They dispose of waters containing nitrates, dissolved solids and pesticides, all of which have a high potential for contamination of groundwater.

These wells are used mainly in citrus production, which has been rapidly declining in the Valley.(84) Some 108 wells have been located in the Lower Rio Grande Valley counties of Hidalgo and Starr and in south-central Runnels County. Other agricultural drainage wells are located in Oldham County, where they could impact the Ogallala Aquifer.(85)

Other Wells

Groundwater may also be affected by the thousands of Texas wells drilled for water or for oil and gas exploration. When improperly drilled or cased, or when the casing has corroded, old oil, gas, and water wells serve as conduits for contamination of the aquifers below. Improperly completed and abandoned water wells may allow direct access from the surface to groundwater for contaminants such as pesticides, or they may facilitate the comingling of groundwater from one aquifer to another. Additionally, they can be a safety hazard to humans and livestock.

There are an estimated 600,000 individual water wells in Texas, of which 150,000 are conservatively estimated to be abandoned.(86) The Texas Water Development Board estimates that about 20,000 new wells are drilled each year, most of which are not properly inventoried.(87) Currently, all new wells must meet specific casing and construction standards and abandoned wells must be plugged. This plugging activity is overseen by the Water Well Drillers Team, since 1993 a division of the Texas Natural Resource Conservation Commission. About 150 wells per month are plugged by individual landowners and reported to the Water Well Drillers Team.(88) However, abandoned water wells are considered one of the greatest sources of pollution of groundwater within Texas and may rank first in priority for mitigation by the state.(89)

In addition to water wells, an estimated 1.5 million holes have been drilled in this century for oil- and gas-related activities. About 1 million of these remain improperly plugged.(90) Abandoned oil wells are channels for the upward movement of brine - saltwater often found in oil-bearing zones - and paths to contamination by oil and gas, drilling fluids and other contaminants. Salt water from abandoned oil wells has contributed to pollution in the upper portions of the Colorado River.(91) These wells must be plugged to prevent the contamination of aquifers by salt water and oil waste.

The Railroad Commission of Texas has regulated the oil industry since 1901 when pipelines were designated as a form of interstate transport on a par with railroads. Currently, 367,188 oil and gas wells across the state are registered with the Railroad Commission, about 86,000 of which are not currently producing.(92) Some 30,210 of these wells may need to be plugged in the coming years to prevent contamination of aquifers.

To address the large number of unplugged wells, the Texas Legislature in 1984 created an Abandoned Well Plugging Fund, which has spent $54 million and has helped plug approximately 7,500 wells over the past ten years.(93)

Other Oil and Gas Industry Impacts

The EPA estimates that about one million tons of hazardous waste is produced each year in American oil fields.(94) The disposal of this waste has the potential to affect groundwater. Until 1969, when the Railroad Commission adopted its no pit rule - also known as Statewide Rule 8 - oil companies typically disposed of salt water and chemicals in open pits, creeks and roads. The chemicals used during the oil-well drilling process and disposed of in these pits include such highly toxic elements as barium, arsenic and cadmium.

Today, the storage and disposal of major oil and gas waste requires a permit or authorization. Statewide Rule 8 identifies three types of oil field pits: prohibited pits, authorized pits and authorized pits through a permit. Authorized activities include land farming, where toxic materials are mixed with soils; burial; road-spreading; commercial hauling, treatment and disposal; and the use of pits such as reserve pits, fresh mining water pits and others. Other pits such as saltwater disposal pits, brine pits, drilling fluid storage and disposal pits, and gas plant evaporation and retention pits require a permit from the Railroad Commission.(95) There are currently 76 land farming facilities permitted for disposal of oil and gas waste and 4,979 lined pits permitted for storage or disposal of such waste.

In 1993, the Railroad Commission reported 20 new cases of groundwater contamination due to hydrocarbons, crude oil, chlorides and hydrochloric acid. These cases added to the 44 cases from previous years which had not yet been cleaned up.(96) Contamination from oil and gas activities may in fact be higher; the Railroad Commission monitors only 75 groundwater monitoring wells associated with 53 disposal sites out of more than 5,000 permitted sites.(97)


Hazardous Waste

Another serious threat to groundwater in Texas comes from abandoned hazardous waste sites. Many of these sites are regulated through the federal Superfund program, which designates abandoned hazardous waste sites for clean-up by placing them on a National Priorities List. States may also designate hazardous waste sites on a state Superfund list. Texas now has 30 federally designated Superfund sites on the National Priorities List, and 42 sites proposed or listed on the state Superfund registry (See Waste section for more detail). All of these sites are subject to groundwater monitoring by the Texas Natural Resource Conservation Commission. Seven sites on the federal Superfund list, and eight on the state Superfund list are directly related to the production of oil and gas. Twenty-five of the federally designated sites and 13 of the state sites show contamination of groundwater by such constituents as arsenic, lead, chromium and PCBs.

In addition to these Superfund sites, industrial and municipal hazardous-waste disposal facilities have been responsible for 456 cases of groundwater contamination in Texas between 1989 and 1993, none of which has yet been cleaned up.(98) Another 38 abandoned hazardous waste disposal sites not designated as Superfund sites by either the state or the federal government have been the source of confirmed groundwater contamination. Municipal solid waste facilities have been linked with another 24 cases of contamination. Superfund sites, hazardous waste sites and municipal landfills are discussed more fully in the section entitled Waste.


As they have degraded surface water, agricultural and forestry activities have also degraded groundwater quality in Texas. Unauthorized discharges and runoff from Confined Animal Feeding Operations (CAFOs) have been responsible for nitrate contamination of shallow groundwater. (However, excess nitrate in groundwater can be caused by other sources, such as poorly designed or old septic tanks.) The primary causes of agriculture-related groundwater contamination are runoff from Confined Animal Feeding Operations, pastures and barnyards; excessive nitrogen fertilization of crop land; and land-clearing and other agricultural practices which change soil composition, altering its ability to filter out pollutants.

Agricultural chemicals such as pesticides and herbicides are also a major concern for groundwater protection. From 1987 to 1990, the Texas Department of Agriculture (TDA), which regulates pesticide use, surveyed water wells for pesticide residues in 11 counties. The Texas Department of Agriculture discovered 75 cases of pesticide-contaminated groundwater. The pesticides found included arsenic, dicamba, atrazine and prometon. In addition to these data, the Texas Natural Resource Conservation Commission since 1991 has kept an Inter-agency Pesticide Database, which compiles the results of sporadic groundwater monitoring for pesticides statewide. An additional 24 cases of pesticide contamination of groundwater were listed in this database, seven of which were identified in 1993.(99)

Other risks to groundwater from agricultural activities include contamination by nitrates and arsenic. High nitrate levels are sometimes caused by infiltration from fertilizers and animal waste. Contamination by arsenic, which the Texas Water Development Board found in three Panhandle counties (Howard, Martin and Reagan) between 1972 and 1989, could be caused by arsenic-based pesticides, by naturally occurring arsenics or a combination. These high levels of arsenic were mainly found in wells pumping from the Ogallala aquifer, which is the major source of drinking and irrigation water for the Panhandle and High Plains region of Texas.


Texas Environmental Almanac, Chapter 2, Water Quality, Page 7


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