The American residential radon industry — federal regulations, contractor certification, mandatory disclosures, the EPA action level of 4 pCi/L — exists because of one Pennsylvania home. In December 1984, a routine radiation screening at the Limerick Nuclear Generating Station in Pottstown, Berks County led investigators to a Boyertown house testing at approximately 2,700 pCi/L. That single discovery, made by accident, transformed how Americans think about indoor radon.
The discovery: Stanley Watras and the Limerick alarms
Stanley Watras was a construction engineer working at the Limerick Nuclear Generating Station in late 1984. The plant was still under construction. On the morning of December 19, 1984, Watras triggered the radiation monitors as he entered the plant — not as he left. The alarms detected contamination on his clothes and skin.
This was operationally impossible by conventional plant logic. Entering radiation monitors are calibrated for plant workers carrying contamination out after exposure inside. Watras hadn't been inside the plant yet that day. The contamination had to be coming from elsewhere — and the only place he'd been was his Boyertown home.
The Boyertown reading: 2,700 pCi/L
Investigators from the plant operator and the Pennsylvania Bureau of Radiation Protection visited the Watras family home in Boyertown. They placed continuous radon monitors in the basement.
The result: approximately 2,700 pCi/L indoor radon — about 675 times the EPA action level of 4 pCi/L (which didn't exist as a regulatory threshold yet) and roughly 2,000 times the average US indoor radon level. Per EPA risk modeling done later, the Watras family's chronic exposure at that level was equivalent to smoking approximately 200 packs of cigarettes per day for lung cancer risk.
The reading remains the highest US residential indoor radon level ever recorded.
What caused the Watras home's extreme reading
The Watras home sat directly over the Reading Prong — a band of uranium-bearing Precambrian gneiss and granite that runs from Reading, PA northeast through Lehigh, Northampton, Bucks, Montgomery, and Chester counties (then continuing into New Jersey and New York). The Reading Prong is among the most uranium-rich rock formations in the eastern United States.
The Watras home was built directly on Reading Prong bedrock with minimal soil overburden. Foundation cracks, sump pits, and basement-floor penetrations allowed unusually efficient gas transport from the uranium-rich rock directly into the basement. The basement was finished and used as living space — meaning the family was exposed to the elevated radon for years before the Limerick alarms accidentally revealed the problem.
For a deep dive on Reading Prong geology and why eastern Pennsylvania has uranium-rich soils across multiple counties, see our companion post Reading Prong Geology: Why Eastern Pennsylvania Has Uranium-Rich Soils.
The federal response: EPA radon program created
The Watras Incident was made public in 1985 and triggered immediate federal action. Within four years:
- 1986: EPA published the first Citizens Guide to Radon and established the EPA Map of Radon Zones methodology.
- 1988: Congress passed the Indoor Radon Abatement Act, establishing a federal goal of reducing indoor radon to outdoor-air levels.
- 1988: EPA established the 4.0 pCi/L action level that remains the US regulatory standard today.
- 1988: EPA created the National Residential Radon Survey (later SIRS) which produced the first state-level radon rankings (placing Iowa #1, Pennsylvania #3).
- 1989: The first national radon contractor proficiency programs launched (NRPP and NRSB predecessors).
The Pennsylvania response: Title 25 Pa. Code Chapter 240
Pennsylvania moved faster than the federal government. PA was the first state to enact a radon-specific contractor certification law — Title 25 Pa. Code Chapter 240 (the Pa. Radon Certification Act). Under Chapter 240, anyone performing radon testing, mitigation, or laboratory analysis in Pennsylvania must hold an active PA DEP Bureau of Radiation Protection certification.
The Pa. Radon Certification Act predates the federal radon program. Pennsylvania built the regulatory infrastructure first — driven directly by the Watras discovery and the recognition that the Reading Prong geological footprint extends across millions of Pennsylvania homes.
Why the Watras Incident still matters in 2026
Three lasting consequences:
- Federal radon framework exists. The 4 pCi/L action level, the EPA Citizens Guide, the Radon Map of EPA Zones, the federal Indoor Radon Abatement Act — none of these existed before December 1984.
- Pennsylvania has the strictest radon contractor framework in the US. Title 25 Pa. Code Chapter 240 + dual-credential requirement (NRPP/NRSB + PA DEP) is more rigorous than nearly any other state's framework.
- Reading Prong testing is still essential. The geological conditions that produced 2,700 pCi/L at the Watras home still produce elevated readings across Berks, Lehigh, Northampton, Bucks, Montgomery, and Chester counties today. Stanley Watras's home is mitigated, but neighboring homes still face the same geological reality.
What this means for Pennsylvania homeowners today
If you live anywhere on the Reading Prong — particularly Berks, Lehigh, Northampton, Bucks, Montgomery, or Chester counties — your home's baseline radon expectation should be: test, expect elevated, mitigate. PA DEP reports that approximately 40% of Pennsylvania homes tested have radon levels above the EPA action level, but the percentage is far higher in Reading Prong counties.
Use our Pennsylvania radon calculator to map your test result against EPA guidance and estimate mitigation cost based on your city. For the geological deep dive, see Reading Prong Geology. For real estate transaction implications, see Pennsylvania Real Estate Seller Disclosure Law (68 Pa. C.S. §§ 7301-7315) Explained.
If your reading is elevated, work with an NRPP + PA DEP-certified mitigator under Title 25 Pa. Code Chapter 240. Verification details and the three-step credential check process are documented on our PA Radon Certification page.
Sources: Pennsylvania Bureau of Radiation Protection historical records, EPA Indoor Radon Abatement Act of 1988, Limerick Nuclear Generating Station operator reports (Philadelphia Electric Company / Exelon), published 1985-1986 reporting on the Watras Incident, PA DEP Title 25 Pa. Code Chapter 240.