Technical Announcement

February 19, 2008

Rod Caldwell

406-457-5933

USGS Samples for Uranium and Other Radioactive Elements in Jefferson County Ground Water

The U.S. Geological Survey (USGS) recently sampled ground water in Jefferson County for uranium and other radioactive elements. Scientists with the USGS Montana Water Science Center, in cooperation with the Jefferson Valley Conservation District and Jefferson County, sampled 40 wells throughout Jefferson County last fall and released preliminary findings to Jefferson County officials on February 19, 2008.

Most of the wells included in the study provide water for human and/or domestic-animal consumption. The objectives of the USGS study were to evaluate the geologic setting in which elevated uranium concentrations occur in Jefferson County and to provide information about the occurrence and concentration of other radioactive elements which had not been studied previously.

The presence of uranium in area ground water had previously been documented by required monitoring of public-supply systems, information from private citizens, and a Montana Department of Health and Human Services biomonitoring study. Some of the previously reported uranium concentrations were greater than the drinking-water standard, or Maximum Contaminant Level (MCL) of 30 micrograms per liter (µg/L), set by the U.S. Environmental Protection Agency (USEPA) for public drinking-water supplies.

USGS scientists sampled 40 wells throughout Jefferson County in September 2007. Thirty of the wells were randomly selected to represent different geologic settings. Ten of the wells were selected in areas where elevated uranium concentrations had been previously reported. Uranium concentrations were higher than the USEPA MCL of 30 µg/L in 12 percent of the wells (see figure 1). Radon concentrations exceeded the proposed MCL of 4,000 picocuries per liter (pCi/L) in 41 percent of the wells. Samples from 12 of the 40 wells also were analyzed for radium, radon, gross alpha particle activity, and gross beta activity. In these wells, 67 percent of the samples exceeded the MCL of 15 pCi/L for gross alpha particle activity, 33 percent exceeded the MCL of 5 pCi/L for total radium, and 17 percent exceeded 50 pCi/L (approximately equivalent to the MCL of 4 millirem per year) for gross beta particle activity.

Figure 1. Concentrations of dissolved uranium in the ground water in Jefferson County, Montana.

Radioactive elements, or radionuclides, are unstable trace elements that naturally occur in rocks, soil, and ground water. These elements undergo radioactive decay through the emission of alpha particles, beta particles, or gamma rays to form more stable elements. For example, during decay of uranium, alpha and beta particles are emitted and radium and radon are formed as interim products; these, in turn, ultimately decay to a stable form of lead.

Nearly all of the wells that had radionuclide concentrations exceeding one or more USEPA drinking-water standards obtained water from rocks of the Boulder batholith. The Boulder batholith is one of the most extensive geologic units found in Jefferson County. These igneous rocks are known to contain uranium-bearing minerals in some areas. The Boulder batholith was intensively prospected for uranium in the 1950s, and some uranium ore was mined locally. However, it is important to note that not all the wells completed in the Boulder batholith had radionuclide concentrations that were above USEPA drinking-water standards.

Radioactive elements in water generally are colorless, ordorless, and tasteless and typically cannot be detected by our senses. According to the USEPA, some people who drink water containing radionuclides in excess of the specified MCLs over a lifetime may have an increased risk of cancer or, in the case of uranium, toxic effects to the kidneys. For example, the USEPA has estimated that the risk of contracting cancer is about 1 in 10,000 for people who, during their lifetime, consume 2 liters of water per day that contains 30 µg/L of uranium.

Private well owners who participated in the USGS study received results of their water-quality analysis and information about USEPA drinking-water standards. Well owners also were supplied with information about possible options for treating well water. Treatment options are available that can reduce concentrations of uranium and other radioactive elements in private wells.

Results from the USGS study identified two major topics for possible future evaluation. First, concentrations of radioactive elements in individual wells may vary over time and follow-up sampling would be needed to determine if concentrations are less than or exceed drinking-water standards part or all of the time. Second, some radioactive elements (including radium isotopes, gross alpha, and gross beta) were analyzed in samples from only a few wells; therefore, the occurrence of these elements throughout the county is not well documented. Additional sampling and analysis would better describe the extent and magnitude of radionuclide concentrations in ground water.

County and State health officials recommend that private well owners have the quality of their well water tested. To have private well-water samples tested for drinking-water quality, citizens may contact the Montana Department of Public Health and Human Services Environmental Laboratory at 406-444-2642 or a private laboratory. The Jefferson County Sanitarian, 406-442-4126, is available to answer questions regarding drinking-water quality and has bottles available for collecting samples for water-quality analysis.

Information on EPA drinking-water standards and other aspects of water quality can be obtained from the EPA “Safe Drinking Water Hotline” at 1-800-426-4791 or at http://www.epa.gov/safewater/.

For more information about this study contact Rod Caldwell at the U.S. Geological Survey, 3162 Bozeman Ave, Helena, MT 59601, e-mail at caldwell@usgs.gov or call 406-457-5933.

USGS provides science for a changing world. For more information visit www.usgs.gov.

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