Radionuclides Rule

Radionuclides Rule

What are radionuclides?

Radioactive materials, also called radionuclides, are both naturally occurring and human-made. Radionuclides from naturally occurring sources can get into groundwater and surface waters in Montana. When radionuclides break down (decay), they create radiation. Radionuclides are a natural part of our environment, and small amounts of radiation are common in the air, water and soil.

How do radionuclides get into groundwater?

Most of the radionuclides found in Montana’s ground water occur naturally from the weathering and dissolution of rocks and minerals. The amount and type of radiation released during the decay process depends on the radionuclides present.  Radioactive materials are also used in medical diagnostics and treatments, electricity production, commercial products, research and nuclear weapons. Human activities, such as disposal of radioactive wastes, may increase the levels of radioactive materials in groundwater. 

What are safe levels of radionuclides in drinking water?

The US Environmental Protection Agency (EPA) has set maximum contaminant levels (MCLs), for radioactive substances in public drinking water systems. EPA defines an MCL as the maximum allowable level of a contaminant that may be present in drinking water without a high risk of causing health problems. DEQ uses these standards for public water systems. The table below shows the MCLs for radionuclides:


MCL’s in Drinking Water

Radium (-226 and -228)

5 pCi/L (combined)

Gross Alpha

15 pCi/L


30 µg/L

Elevated radionuclides in Montana

Montana’s community water systems are required to sample for radionuclides. The map below shows the concentrations of radionuclides that are above the MCL.


Health effects of radionuclides

Exposure to radiation can cause different types of health effects depending on the source of radioactivity, how much radiation you are exposed to (total dose), and how long you are exposed to the radiation. Drinking water that has radionuclide levels near the federal drinking water standards puts you in contact with very low doses of radiation every day. This exposure, when combined with other sources of radiation exposure, can slightly increase your lifetime risk of developing cancer or kidney problems.

For more information about radionuclides, contact Diane Jordan, Chemical/Radiological Rule Manager at (406) 444-6741.