What Is a Safe Radon Level? York County Readings vs. the EPA Action Level

Radon is measured in picocuries per liter (pCi/L), a unit of radioactivity per volume of air. Outdoor air averages about 0.4 pCi/L. The U.S. EPA sets its action level at 4.0 pCi/L — the point at which it recommends fixing the home — and says homeowners should consider mitigating between 2.0 and 4.0. The World Health Organization is stricter, recommending action at 100 Bq/m³, which works out to about 2.7 pCi/L. No level is risk-free; the EPA estimates radon causes about 21,000 lung cancer deaths a year in the United States, making it the second-leading cause after smoking and the leading cause among people who have never smoked.

York County is an EPA Zone 1 county — the highest of three radon-potential zones, defined by a predicted average indoor level above 4.0 pCi/L. Pennsylvania as a whole is one of the worst radon states in the country, and DEP test records for York-area ZIP codes show average basement readings roughly double the action level, with about a third of tested homes exceeding 4.0. The reason is the bedrock: the limestone and dolomite of the York valley, the slate and schist of southern York County, and the shale to the north all contain trace uranium that decays into radon and vents upward through the soil.

Your own result depends on your house, not the county average. Two identical homes on the same street can differ by a factor of ten depending on slab cracks, sump pits, foundation type, how tight the house is and how the HVAC runs. A reading of 1.8 in East York and a reading of 22 in Red Lion are both normal outcomes here.

Reading your test: below 2.0 pCi/L, no action needed — retest in two years. 2.0 to 3.9, mitigation is optional but worth considering, especially if anyone in the home smokes or if children sleep on the lowest level. 4.0 and above, mitigate. Above 10, mitigate soon; above 20, treat it as a priority. Short-term tests run in winter tend to read higher than summer because the house is closed and the stack effect is stronger; if a summer test comes in at 3.5, a winter test may exceed 4.

A properly installed active system in York County typically brings a home from 8–20 pCi/L down to 0.5–2.0. If you have a system and haven't seen a follow-up number in more than two years, test again — a failed fan is silent.