Updated · Rapid City, South Dakota

Numbers to remember: EPA action level 4.0 pCi/L. EPA also says consider fixing between 2 and 4. WHO reference level ≈ 2.7 pCi/L (100 Bq/m³). Outdoor air is often around 0.4 pCi/L.12

Why “safe” is the wrong word

Radiation risk models treat radon as a carcinogen without a bright line of absolute safety. “Safe” in homeowner language usually means “within a widely accepted action framework.” EPA chose 4.0 pCi/L balancing risk reduction and the practicality of measuring and fixing homes nationwide.1

How to decide in the 2–4 pCi/L band

Ask:

  • How many hours per day does your family spend in the basement or lower level?
  • Does anyone smoke or formerly smoke?
  • Are children or long-term occupants in the home?
  • Is mitigation priced reasonably for your foundation type?

In Zone 1 markets like Rapid City, many owners mitigate in the 2–4 range—especially before finishing a basement—because systems are proven and costs are predictable. See mitigation cost.

Units: pCi/L vs Bq/m³

U.S. reports use picocuries per liter. Multiply pCi/L by 37 to approximate Bq/m³. A 4.0 pCi/L result is about 148 Bq/m³.

Sources

  1. U.S. EPA. Citizen’s Guide to Radon.
  2. World Health Organization. Indoor radon handbook — 100 Bq/m³ reference level.

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