Updated · Rapid City, South Dakota

Use 4.0 pCi/L as a decision switch: at or above → plan mitigation. Between 2 and 4 → seriously consider it. Below 2 → maintain with periodic retesting.1

What the action level is

A national recommendation for when the cost and effort of mitigation are strongly justified by risk reduction. States and Tribes may amplify messaging; they do not rewrite physics.

The Origin and History of the 4.0 pCi/L Action Threshold

The U.S. Environmental Protection Agency established 4.0 pCi/L as the national action level in the 1980s following extensive residential radiation studies and epidemiological research on underground uranium miners. It is vital for homeowners to understand that 4.0 pCi/L is a technology- and feasibility-based public policy decision, rather than a purely medical safety cutoff.

When the EPA enacted the standard, 4.0 pCi/L represented the concentration that available radon mitigation technology could reliably and economically achieve across the vast majority of American housing styles without excessive equipment cost. Epidemiological risk modeling indicates that at 4.0 pCi/L over a lifetime exposure, approximately 7 out of 1,000 non-smokers and 62 out of 1,000 smokers could develop radon-induced lung cancer. Consequently, the EPA explicitly advises that homeowners consider remediating levels between 2.0 and 4.0 pCi/L to further reduce long-term radiation exposure.

What it is not

  • A guarantee of safety below 4.0
  • A building-code maximum for all situations
  • A substitute for professional judgment on real estate negotiations

Related reading

What is a safe radon level? · Radon and lung cancer

Sources

  1. U.S. EPA. A Citizen’s Guide to Radon (EPA 402/K-12/002). epa.gov/radon/citizens-guide-radon
  2. World Health Organization (WHO). WHO Handbook on Indoor Radon: A Public Health Perspective (100 Bq/m³ reference level). who.gov/publications/i/item/9789241547673
  3. South Dakota Department of Health. Understanding Radon Action Levels. doh.sd.gov/programs/radon
  4. ANSI/AARST. Soil Gas Mitigation Standards for Existing Homes. standards.aarst.org

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Need a local next step? Call (605) 600-6282 to talk through testing, real estate timing, or mitigation for your Rapid City–area home.