Every source we cite.

The county-level Zone 1 / 2 / 3 classification map. Source of every "your EPA radon zone" value in the dossier. Published once in 1993; the underlying geology has not been re-mapped at the federal level since. Available via the EPA Radon Zones page (epa.gov/radon/find-information-about-local-radon-zones-and-state-contact-information).

The technical risk assessment behind the EPA's headline "21,000 lung cancer deaths a year" figure. Table A-1 in this document is the source of the lifetime lung-cancer mortality per 1,000 by exposure level cited in every dossier. Built on BEIR VI dose-response modelling and updated with the Iowa Radon Lung Cancer Study evidence.

Defines the 4.0 pCi/L action level, describes short-term and long-term testing, and sets the EPA's recommended cadence (test, mitigate above 4 pCi/L, retest after mitigation, retest every two years or after major construction).

The EPA's mitigation guide. Names sub-slab depressurization, sub-membrane depressurization, drain-tile suction, and block-wall suction as the standard residential techniques and quotes effectiveness (50–99% reduction) and typical cost ranges ($800–$2,500 for SSD).

The EPA's framework for real-estate transactions: when to test, who pays, how to negotiate post-test, and how disclosure interacts with state law. Source for our selling-with-high-radon guide.

The 5,694-home national survey that produced the log-normal distribution of US indoor radon levels we use to calibrate per-county likelihood estimates. National geometric mean: 0.67 pCi/L; arithmetic mean: 1.25 pCi/L.

The current single-family residential mitigation standard. Defines design criteria for sub-slab depressurization, fan sizing, piping diameter, exhaust placement, monitoring requirements, and post-mitigation testing. The reference document for every "mitigation system" claim in the dossier.

The measurement protocol for multi-family buildings (apartments, condos). Source for the placement and timing guidance in our apartments and condos guide.

The measurement standard for large buildings. We do not write large-building dossiers, but we cite it where readers ask about radon testing in schools and commercial buildings.

One of the two recognised certification bodies for US radon professionals (measurement and mitigation). We link to the NRPP "Find a Pro" directory; we do not vet, recommend, or take referral fees from any listed professional.

The second recognised US certification body for radon measurement and mitigation professionals. Same use as NRPP — directory pointer only.

The pooled-miner-cohort risk assessment that underlies the EPA's residential radon risk numbers. BEIR VI's dose-response models are the basis of Table A-1 in EPA-402-R-03-003.

The case-control study of 413 lung-cancer cases and 614 controls in Iowa that produced the first major residential epidemiological evidence directly supporting the BEIR VI miner-cohort extrapolations. Source for the case-control evidence cited in our lung-cancer risk numbers guide.

Pooled analysis of 13 European case-control studies (7,148 cases, 14,208 controls) showing a linear dose-response relationship between residential radon and lung cancer with no apparent threshold. Strengthens the EPA's linear-no-threshold modelling.

Pooled analysis of seven North American case-control studies, including the Iowa study, with similar conclusions to the European pooling.

Public-facing summary of radon health effects and mitigation guidance. Source for the cost-range cross-check used against EPA-402-K-10-005.

NIH/NCI overview of radon as a Group A human carcinogen. Cross-reference for the "second leading cause of lung cancer" framing.

The Surgeon General's national health advisory urging all homeowners to test for radon. Frequently cited alongside the EPA action level.

Colorado state-wide and county-level screening averages. Used to refine Front Range county estimates (Boulder, Larimer, Jefferson, Adams, Arapahoe).

PA state-wide and county-level data. Berks, Lancaster, Centre, and Chester counties have particularly granular state data we use to override the 1993 EPA map.

Iowa state-wide screening surveys. Iowa has among the highest state-wide indoor radon averages in the US (≈ 8.5 pCi/L statewide) due to glacial till geology.

We pull state-published screening averages and use them as the county-level override where the state data is more recent than EPA-402-R-93-071.

USGS data on dissolved radon concentrations in US groundwater. Source for the "radon in well water vs. soil-gas radon" comparison in our well-water guide.

The proposed (never finalised) EPA drinking-water rule proposing 300 pCi/L as the maximum contaminant level for radon in community water systems served by groundwater, with a 4,000 pCi/L alternative MCL if states adopt a multimedia mitigation program.