Appendix B
Methodology and sources
For Canada, see C-NRPP sources and verification. The source details below describe our US directory.
We list only people and firms that appear as currently credentialed on an official state file, or as currently certified on the NRPP or NRSB public finder. We do not list anyone whose source status is expired or unknown. City pages use the city printed on that record. We do not turn a ZIP-radius search into a city graph.
This site is not endorsed by EPA, NRPP, NRSB, or the state agencies whose files we check. Credential status can change between our monthly refresh and the day you hire someone. Follow the source link on each listing.
Table B.1
Sources we check
| Body | Last checked | Official page |
|---|---|---|
| CA CDPH | August 29, 2026 | cdph.ca.gov |
| CO DORA | September 11, 2026 | data.colorado.gov |
| IA HHS | August 29, 2026 | hhs.iowa.gov |
| IL IEMA | August 29, 2026 | public.iema.state.il.us |
| IN IPLA | August 29, 2026 | mylicense.in.gov |
| KS KDHE | August 29, 2026 | kdhe.ks.gov |
| ME DHHS | August 29, 2026 | pfr.informe.org |
| MN MDH | August 29, 2026 | radon.web.health.state.mn.us |
| NE DHHS | August 29, 2026 | dhhs.ne.gov |
| NRPP | August 29, 2026 | nrpp.info |
| NRSB | August 29, 2026 | nrsb.org |
| PA DEP | August 29, 2026 | pa.gov |
| RI RIDOH | August 29, 2026 | datahealth.ri.gov |
For which agency credentials radon work in each state, and the official page where you check a number, see radon credentials by state.
Colorado source-data notice
Required by the Colorado Information Marketplace terms of service:
The data made available here has been modified for use from its original source, which is the State of Colorado. THE STATE OF COLORADO MAKES NO REPRESENTATIONS OR WARRANTY AS TO THE COMPLETENESS, ACCURACY, TIMELINESS, OR CONTENT OF ANY DATA MADE AVAILABLE THROUGH THIS SITE. THE STATE OF COLORADO EXPRESSLY DISCLAIMS ALL WARRANTIES, WHETHER EXPRESS OR IMPLIED, INCLUDING ANY IMPLIED WARRANTIES OF MERCHANTABILITY, OR FITNESS FOR A PARTICULAR PURPOSE. The data is subject to change as modifications and updates are complete. It is understood that the information contained in the Web feed is being used at one's own risk.
NRPP and NRSB
Where a state does not publish a current roster with credential numbers, we list people who currently appear as certified on the NRPP or NRSB public finder. We skip laboratories and inspector-only credentials. We do not use those national programs in states that already have a .gov file on this site. A national certification is not a state license.
| State credential | NRPP or NRSB | |
|---|---|---|
| What it is | License or certification on a state file | National certification |
| On this site when | The state publishes a current roster we import | The state has no .gov roster on this site |
| A national certification is a state license? | Not applicable | No |
EPA how-to
How can you find a qualified radon service provider in your area?
Geography we do not invent
California CDPH publishes certification numbers and expiration dates, not city or county. Those people appear on the California state hub and on listing pages, not on city URLs. Illinois, Colorado, and Minnesota listings with an out-of-state mailing city stay on the state hub for the same reason. Iowa, Kansas, Nebraska, Rhode Island, Indiana, and Maine follow the same rule.
Maps and ZIP search
ZIP search looks up a US ZIP, then opens the city or county page we already publish for that state. If the ZIP city is not on the roster, we open the nearest place in that state that has listings. We do not create a page for a ZIP in a state we have not imported. Maps use Census city or county centroids. Official files almost never include a street, so pins are labeled approximate. We do not invent an office address.