About Arsenic and Uranium

Arsenic is a naturally occurring element that is widely distributed in the Earth’s crust. Some areas of the United States contain unusually high natural levels of arsenic in rock, and this can lead to unusually high levels of arsenic in soil or water. We see higher-than-normal concentrations of Arsenic in the groundwater in many areas in the Lake Helena Watershed.

See the Arsenic map provided by the Water Quality Protection District on our Maps Page.

From the Agency of Toxic Substances and Disease Registry:
“Soils in the vicinity of arsenic-rich geological deposits, some mining and smelting sites, or agricultural areas where arsenic pesticides had been applied in the past may contain much higher levels of arsenic. The concentration of arsenic in natural surface and groundwater is generally about 1 part in a billion parts of water (1 ppb), but may exceed 1,000 ppb in contaminated areas or where arsenic levels in soil are high. Groundwater is far more likely to contain high levels of arsenic than surface water.”


The drinking water standard is 10 ppb. We see concentrations much higher than this drinking water standard in the Helena Area.

Arsenic map provided by the Water Quality Protection District:

How can Arsenic affect my health?

  • inorganic arsenic is a known human carcinogen; exposure can cause increased risk of cancer
  • circulatory problems
  • skin damage
  • View this website to get more details about arsenic.

    Uranium is a naturally occurring element that has been in rocks since the earth was formed. Not all rocks contain uranium, but there are some places in Montana where uranium is in the bedrock and in valley fill sediments that have eroded from the bedrock of the adjacent upland or mountainous areas. Uranium breaks down (decays) very slowly into other elements including radium and radon gas. These other elements are part of a sequence formed through a transformation (decay) process that begins with the most prevalent form of “natural” (unprocessed) uranium (U-238).

    From the Agency of Toxic Substances and Disease Registry:
    “Typical concentrations in soil are a few parts per million ppm. Some rocks contain high enough mineral concentrations of uranium to be mined. The rocks are taken to a chemical plant where the uranium is taken out and made into uranium chemicals or metal. The remaining sand is called mill tailings. Tailings are rich in the chemicals and radioactive materials that were not removed, such as radium and thorium.”

    Uranium map provided by the Water Quality Protection District:

    How can Uranium affect my health?

  • The chemical properties of uranium in drinking water are of greater concern than its radioactivity. Most
    ingested uranium is eliminated from the body; only a very small amount is absorbed and carried through
    the bloodstream. Studies show that drinking water with elevated levels of uranium can affect the kidneys
    over time. Bathing and showering with water that contains uranium is not a health concern as uranium is
    not readily absorbed through the skin.

  • How do I know if there is arsenic or uranium in my groundwater?

  • If you live in the City of Helena, East Helena, or know that you get water from a Public Water Supply (PWS), your water goes through treatment and must meet the drinking water standards for human health
  • If you are on a private well, it is up to YOU to test your well annually

  • Stop by the County Builidng (316 N Park, Helena 59623). Come to the second floor, Room 220 to obtain a well-water test kit through the Well-Educated Program. This is a state-wide program through Montana State University’s Extension Office: All are welcome to come pick up a test kit, no matter where you live. We serve as a centralized, local distributor of these test kits. Check out their website : MSU Well Educated Program

    Visit Our:
    Well Test Kits Page

    What do I do if I find arsenic or uranium at high concentrations in my water?

  • We recommend installing a Point-Of-Use Treatment System, though it depends on the ways in which you are using your water supply (for drinking, agriculture, etc.)
  • Feel free to give the Water Quality Protection District a call at any time if you have questions

  • Phone: (406) 457 – 8584