Is radon high in ZIP 99163?

Moderate. The model's predicted long-term basement average for ZIP 99163 is 2.2 pCi/L (SD 0.05), with above-ground floors at 1.1 pCi/L. That is close to the average US ZIP code (2.2) and close to the Whitman County average of 2.2. It ranks 15 of 16 ZIPs in the county.

Do I need to test my home in 99163?

Yes. 99163's predicted average falls in the EPA's 2-4 pCi/L "consider fixing" band, and a meaningful share of individual homes in such areas test above 4. Test with a short-term kit and confirm anything at 2 or higher with a long-term test.

What EPA radon zone is ZIP 99163 in?

ZIP 99163 lies mostly in Whitman County, which the EPA classifies as Radon Zone 2 (moderate potential (2-4 pCi/L)). Zones are county-wide and date from 1993; the ZIP-level prediction above is from a 2001-2021 model built on millions of tests.

Radon levels in ZIP 99163

ModerateEPA Zone 2

ZIP 99163 (Whitman County, Washington): predicted long-term basement average of 2.2 pCi/L (model estimate), close to the average US ZIP (2.2) and about 1.4× the Washington average (1.6). This is the most populous ZIP in Whitman County.

Test ZIP 99163 - the EPA says "consider fixing" in this range

The predicted basement average here is 2.2 pCi/L, in the 2-4 pCi/L band where the EPA recommends considering mitigation. Plenty of individual homes in a moderate area test above 4. Start with a short-term test; if it comes back at 2 or higher, follow up with a long-term test or a continuous monitor.

Get a short-term test kit →Or track it with a continuous monitor

Already tested at 4 pCi/L or higher? Find a certified mitigation professional (EPA). A mitigation system typically runs $800-$2,500 installed.

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Predicted (model estimate). The pCi/L figures on this page are long-term area averages from a peer-reviewed national model built on millions of real radon tests (2001-2021). They describe the typical home in this area - not your home, which can be several times higher or lower. The EPA radon zone is a separate, 1993 county-level classification. How the numbers work.

2.2 ± 0.05

pCi/L predicted basement mean (model SD)

1.1 ± 0.08

pCi/L predicted upstairs mean

1.7 ± 0.06

pCi/L predicted typical screening test

How 99163 compares

Within Whitman County, ZIP 99163 ranks #15 of 16 ZIPs by predicted basement level; the county average is 2.2 pCi/L and its ZIPs run from 2.1 to 2.5. The county is EPA Radon Zone 2. About 31,404 people lived in this ZIP at the 2010 Census.

Above-ground floors are predicted at 1.1 pCi/L, below the action level, while basements sit in the 2-4 band. If you spend time in a finished basement, test there first.

Other ZIP codes in Whitman County

991112.4
991612.4
991702.2
991712.3
990332.4
991302.3
991132.5
991432.3
991582.3
991252.3
991792.3
991282.3
990172.2
991762.2
991362.1

ZIP 99163 radon questions

Is radon high in ZIP 99163?: Moderate. The model's predicted long-term basement average for ZIP 99163 is 2.2 pCi/L (SD 0.05), with above-ground floors at 1.1 pCi/L. That is close to the average US ZIP code (2.2) and close to the Whitman County average of 2.2. It ranks 15 of 16 ZIPs in the county.
Do I need to test my home in 99163?: Yes. 99163's predicted average falls in the EPA's 2-4 pCi/L "consider fixing" band, and a meaningful share of individual homes in such areas test above 4. Test with a short-term kit and confirm anything at 2 or higher with a long-term test.
What EPA radon zone is ZIP 99163 in?: ZIP 99163 lies mostly in Whitman County, which the EPA classifies as Radon Zone 2 (moderate potential (2-4 pCi/L)). Zones are county-wide and date from 1993; the ZIP-level prediction above is from a 2001-2021 model built on millions of tests.

ZIP pages are generated for ZIPs predicted at or above 2.5 pCi/L and for the most populous ZIP in each county; all other ZIPs appear in their county table. Methodology.