GROUNDWATER AND NATURALLY OCCURRING URANIUM

HISTORICAL PERSPECTIVE

There are many shallow uranium deposits along the lower coastal plain of Texas that are commonly associated with oil and gas resources. Where uranium is present, the surrounding rock and groundwater register as radioactive because of the natural uranium decay process.

In 2003, the Environmental Protection Agency (EPA) established a Maximum Contaminant Level (MCL) for uranium concentrations in drinking water of 30 μg/liter (approximately 30 parts per billion - equivalent to 30 grains of salt in a billion grains of sugar). To ensure compliance with the new MCL in Texas, the EPA and the Texas Commission on Environmental Quality (TCEQ) mandated that public drinking water supplies be tested for uranium concentrations. Many Texas water wells have naturally occurring uranium concentrations above the EPA drinking water standard. This phenomenon was documented during testing that was conducted by a government program initiated in the 1970’s. The program’s goal was to assess the uranium concentration in groundwater samples collected throughout the United States, not to evaluate water quality, but to look for naturally occurring uranium mineralization for energy supplies. In fact, out of more than 17,000 wells sampled in Texas, a total of 435 wells were identified as having uranium concentrations above EPA standards.

NATIONAL URANIUM RESOURCE EVALUATION (NURE)

In 1973, the Atomic Energy Commission initiated the National Uranium Resource Evaluation (NURE) program, whose primary goal was to identify uranium resources in the United States. One objective of the NURE program was to systematically sample and analyze groundwater across the United States to determine the presence and levels of uranium and other chemical constituents. Many Texas wells were sampled during the program and the analysis was performed at one of four premier government laboratories: Lawrence Livermore Laboratory, Los Alamos Scientific Laboratory, Oak Ridge Gaseous Diffusion Plant or Savannah River Laboratory.

The enormous amount of data generated by the NURE program has been incorporated into a database that is available to the public through the US Geological Survey (USGS). The database allows users to access information concerning the natural occurrence of uranium in groundwater.

NATURALLY OCCURRING URANIUM IN TEXAS WELLS

Naturally occuring wells in Texas.

In Texas, 17,726 samples of groundwater were collected during the NURE program. Funding for the program was discontinued before all 254 counties in Texas were sampled.  Of those sampled, 84 counties had at least one groundwater sample with uranium concentrations above the MCL of 30 μg/liter. Presidio County had the most, with 57 out of 466 wells sampled (12%) having uranium concentrations above the drinking water standard.

As previously mentioned, the NURE program identified 435 wells in Texas with naturally occurring uranium concentrations that did not meet the EPA drinking water standard. Figure 1 shows the locations of these wells. Wells with elevated uranium concentrations occur in three distinct geographical regions. One region is in West Texas, northwest of Big Bend National Park. The second region is in North Texas in the southeast portion of the panhandle. The third region is in an arc along the Coastal Bend of South Texas. In West Texas and in the southeast portion of the panhandle, economically mineable concentrations of uranium have not been identified. Along the coastal bend of South Texas, economically extractable uranium deposits were identified as early as the 1950’s and development of the resources has been ongoing for nearly 40 years.

URANIUM FOUND IN GROUNDWATER PRIOR TO EXISTENCE OF MINES

Naturally occurring uranium concentrations above the EPA MCL drinking water standard Outcrop of geologic formations along the Gulf Coast

It is noteworthy that along the South Texas Coastal Bend, where oil, gas and naturally occurring uranium are prevalent in the geologic formations, significant concentrations of uranium were also found in many of the major drinking water aquifers during the NURE sampling. In the 1970’s, the NURE program identified over 113 wells across the Coastal Bend Region with naturally occurring uranium concentrations above the EPA MCL drinking water standard. Figure 2 shows the location of these wells in South Texas. These natural indicators of uranium mineralization, in part, led mining companies to conduct exploration activities aimed at finding economically viable uranium deposits.  Figure 3 is a map of South Texas showing the outcrop of geologic formations along the Gulf Coast.  In certain locations within these formations are aquifers that not only support fresh water supplies but also contain natural occurrences of uranium above the EPA MCL. Also illustrated on the map are the locations of historic uranium mines and NURE wells with elevated uranium concentrations.

The NURE data confirmed that uranium mining takes place in areas where groundwater contained concentrations of uranium above the EPA drinking water limit prior to the existence of the mines. The NURE sampling program also showed many areas in the Coastal Bend and throughout Texas that contain naturally high levels of uranium in groundwater that are not associated with uranium mines. It is incorrect to assume that elevated uranium concentrations in groundwater samples collected near uranium mines are a result of mining activities because the NURE program was generally in operation before many of mining operations began. Actually, the converse is true: mines are located in these areas because economically viable quantities of uranium exist in the subsurface sediments, and it is these sediments that contribute to the naturally occurring uranium concentrations in the groundwater.

Since the NURE testing was completed in the 1970s, thousands of new wells have been drilled, and because the public does not routinely analyze for uranium, there is a strong possibility that many more wells with elevated levels of uranium exist today.

CONTAMINATION CLAIMS UNFOUNDED

Recent claims that groundwater in Texas has been contaminated in areas near uranium mining activities is unfounded. Instead, new EPA MCL standards for uranium concentrations in drinking water have created a misconception that uranium concentration in the drinking water has actually increased, but the study of water quality from the historic NURE data set serves to dispel this misconception. Uranium has been in some Texas water a long, long time.

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