Contaminant Guide

Radium in Well Water

Radium is a naturally radioactive element that dissolves from deep rock formations into groundwater. It is most prevalent in the deep sandstone aquifers of Michigan, Wisconsin, Illinois, Iowa, and Texas. Radium poses a cancer risk — primarily bone cancer and leukemia — and the EPA's MCLG is zero, as no safe level of radionuclide exposure has been established.

What is radium in well water?

Radium (Ra-226 and Ra-228) is a radioactive element formed by the decay of uranium and thorium in rock. It dissolves naturally into deep, confined groundwater — particularly in sandstone aquifers that have long contact time with radium-bearing rock. You cannot detect radium by taste, smell, or appearance.

Where is it most common?

Radium in well water is most prevalent in the Cambrian-Ordovician sandstone aquifer system underlying Michigan, Wisconsin, Illinois, Iowa, and parts of Texas. This confined aquifer is deep (often 500–2,000+ feet), ancient, and naturally enriched in radium from uranium-bearing minerals. Some Texas wells drawing from the Ogallala Aquifer also show elevated radium.

Health effects

  • Bone cancer (osteosarcoma) — Radium chemically mimics calcium and deposits in bone, where it irradiates bone marrow over years. Studies of radium dial painters (1920s) first established the bone cancer link; osteosarcoma is the primary documented health effect.
  • Leukemia — Bone marrow irradiation from radium-226 and radium-228 deposits increases leukemia risk with chronic exposure.

The EPA limit: MCL = 5 pCi/L, MCLG = 0

The radium MCL is expressed as 5 pCi/L combined Ra-226 + Ra-228 — measured in picocuries per liter (a radioactivity unit), not micrograms per liter, because the health risk is radiological rather than chemical. The MCLG is 0: no safe level of radionuclide exposure exists. If your well water contains any detectable radium, there is some risk — the MCL sets the regulatory limit, not a health threshold.

Testing

Radium testing requires a certified radiological laboratory. Ra-226 is measured by radon emanation or alpha spectrometry; Ra-228 by gamma spectroscopy or beta counting. Results are in pCi/L. Standard chemical water tests do not measure radium — you must specifically request radionuclide analysis. If you are in Michigan, Wisconsin, or Illinois and draw from a deep sandstone well, radium testing is strongly recommended.

Find a certified radiological lab and learn how to collect a sample

Treatment

  • Ion exchange water softener — radium is a divalent cation (Ra²⁺) and is removed by standard cation exchange resin along with hardness minerals (calcium and magnesium). If you already have a water softener for hardness, it is likely also removing radium. This is the most cost-effective treatment for the Upper Midwest where radium and hardness co-occur.
  • Reverse osmosis (RO) — removes radium at point of use; effective but does not protect the rest of the plumbing.
  • Greensand filtration with manganese oxidation — removes radium by co-precipitation with manganese; used in whole-house systems.
  • Lime softening — effective at municipal scale; not practical for residential use.

Compare radium treatment systems for private wells

Regulatory framework

MCL: 5 pCi/L (combined Ra-226 + Ra-228). MCLG: 0. Radionuclides Rule (2000). The MCL is a radioactivity-based standard, not a mass-concentration standard. A separate MCL of 15 pCi/L applies to gross alpha activity (excluding uranium and radon).

Note: radium MCL does not appear in µg/L in regulatory documents. To convert: 1 pCi/L Ra-226 ≈ 3.7 × 10⁻³ dpm/L; the mass concentration equivalent at 5 pCi/L is approximately 0.08 ng/L (sub-ppb), far below ICP-MS detection range.

Detection

Ra-226: radon emanation method (Ra-226 decays through Rn-222; radon is purged and counted by liquid scintillation or proportional counting) or alpha spectrometry after co-precipitation with barium sulfate. Ra-228: gamma spectroscopy (measures Ac-228 progeny) or beta counting after separation. Both require specialized radiochemistry labs; analysis time is 1–3 weeks. Certified radiological laboratory required for regulatory compliance.

Geochemistry

Radium mobility in groundwater is controlled by the same redox and ion-exchange chemistry governing barium and strontium (Group 2 elements). Radium is most mobile in reducing, low-sulfate groundwater; sulfate inhibits mobility through co-precipitation with barite (BaSO₄). Deep confined aquifers with long residence times accumulate radium from in-situ uranium-thorium decay and desorption from aquifer minerals. Radium-226 (half-life 1,600 years) and Ra-228 (5.75 years) have different source rocks and occurrence patterns; testing both is important.

Data access

Access our data API and methodology

References

  1. Ayotte, J.D., Gronberg, J.M., & Apodaca, L.E. (2011). Trace elements and radon in groundwater across the United States, 1992-2003. USGS Scientific Investigations Report 2011-5059. https://pubs.usgs.gov/sir/2011/5059/
  2. Chowdhury, S., & Champagne, P. (2009). Risk from exposure to radon and natural radionuclides in groundwater. Environmental Pollution, 157(3), 749-758. https://doi.org/10.1016/j.envpol.2008.11.028