Radon levels in Contra Costa County, California
LowEPA Zone 2Predicted long-term basement average of 1.4 pCi/L (model estimate) across 39 ZIP codes - about 24% below the US average of 1.8, close to the California average of 1.5. Ranked #55 of 58 California counties.
Test Contra Costa County, CA once anyway - radon varies house to house
The predicted basement average here is 1.4 pCi/L, below the EPA's 2 pCi/L "consider fixing" threshold. That's good news for the area - but the EPA still recommends every home be tested, because foundation cracks, soil pockets and ventilation make one house very different from its neighbor. One inexpensive kit settles it.
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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.
1.4 ± 0.06
pCi/L predicted basement mean (model SD)
0.7 ± 0.08
pCi/L predicted upstairs (above-ground) mean
1.2-1.6
range of ZIP-level basement predictions in the county
What this means for Contra Costa
The typical Contra Costa County home is predicted below 2 pCi/L, the lowest band. That is the best case an area can show - but it describes the average house, and the ZIP-level predictions within the county still span 1.2 to 1.6 pCi/L.
Note that the EPA classifies Contra Costa County as Zone 2 while the newer model predicts 1.4 pCi/L. The zone map predates two decades of test data; where they disagree, we grade on the model but show both. County figures weight each ZIP by its 2010 Census population, so they describe where people live rather than empty land.
Comparable California counties: Del Norte County (1.4), Marin County (1.4), San Joaquin County (1.4), Solano County (1.4). The state's highest is Mono County at 2.7 pCi/L.
ZIP codes in Contra Costa County
Predicted basement and upstairs means by ZIP (model estimate). ZIPs whose land is mostly in this county.
| ZIP | Basement | Upstairs | Grade |
|---|---|---|---|
| 94565 | 1.3 ± 0.07 | 0.7 | Low |
| 94509 | 1.4 ± 0.06 | 0.7 | Low |
| 94806 | 1.4 ± 0.06 | 0.8 | Low |
| 94513 | 1.5 ± 0.06 | 0.8 | Low |
| 94553 | 1.4 ± 0.06 | 0.7 | Low |
| 94521 | 1.4 ± 0.06 | 0.7 | Low |
| 94531 | 1.3 ± 0.06 | 0.7 | Low |
| 94804 | 1.4 ± 0.06 | 0.7 | Low |
| 94582 | 1.5 ± 0.06 | 0.8 | Low |
| 94520 | 1.3 ± 0.06 | 0.6 | Low |
| 94561 | 1.4 ± 0.06 | 0.7 | Low |
| 94583 | 1.4 ± 0.06 | 0.8 | Low |
| 94523 | 1.4 ± 0.06 | 0.7 | Low |
| 94526 | 1.5 ± 0.06 | 0.8 | Low |
| 94801 | 1.4 ± 0.07 | 0.7 | Low |
| 94549 | 1.3 ± 0.06 | 0.8 | Low |
| 94518 | 1.3 ± 0.06 | 0.7 | Low |
| 94598 | 1.4 ± 0.06 | 0.7 | Low |
| 94803 | 1.4 ± 0.06 | 0.8 | Low |
| 94547 | 1.3 ± 0.06 | 0.7 | Low |
| 94530 | 1.2 ± 0.07 | 0.6 | Low |
| 94506 | 1.5 ± 0.06 | 0.9 | Low |
| 94597 | 1.3 ± 0.07 | 0.7 | Low |
| 94596 | 1.3 ± 0.06 | 0.8 | Low |
| 94519 | 1.4 ± 0.06 | 0.8 | Low |
| 94564 | 1.4 ± 0.06 | 0.7 | Low |
| 94563 | 1.3 ± 0.06 | 0.8 | Low |
| 94595 | 1.3 ± 0.06 | 0.7 | Low |
| 94556 | 1.5 ± 0.06 | 0.8 | Low |
| 94507 | 1.4 ± 0.06 | 0.8 | Low |
| 94805 | 1.3 ± 0.06 | 0.7 | Low |
| 94505 | 1.6 ± 0.06 | 0.8 | Low |
| 94517 | 1.3 ± 0.05 | 0.8 | Low |
| 94708 | 1.4 ± 0.06 | 0.8 | Low |
| 94572 | 1.4 ± 0.07 | 0.7 | Low |
| 94525 | 1.4 ± 0.07 | 0.8 | Low |
| 94514 | 1.6 ± 0.06 | 0.9 | Low |
| 94528 | 1.4 ± 0.07 | 0.9 | Low |
| 94548 | 1.6 ± 0.06 | 0.7 | Low |
If your test comes back at 4 pCi/L or higher
Mitigation is a routine job: a fan-driven pipe that vents soil gas from under the slab to above the roofline, typically $800-$2,500 installed (typical range; local quotes vary). Use certified professionals: EPA find-a-professional. Read the full mitigation guide.
Contra Costa County radon questions
- Is radon high in Contra Costa County, California?
- Low. The model predicts a long-term basement average of 1.4 pCi/L in Contra Costa County (about 24% below the US average of 1.8 and close to the California average of 1.5). That is below the EPA's 2 pCi/L "consider fixing" threshold, though individual homes still vary. Ranked 55 of 58 California counties.
- Should I test for radon in Contra Costa County?
- Yes, once. The EPA recommends testing every home regardless of area, and the model's ZIP-level predictions in Contra Costa County already range from 1.2 to 1.6 pCi/L. A short-term kit costs little and settles the question for your house.
- What does EPA Radon Zone 2 mean for Contra Costa County?
- Zone 2 - moderate potential (2-4 pCi/L). The zone map dates from 1993 and classifies whole counties. The newer model's predicted average of 1.4 pCi/L does not line up with Zone 2, which is common - the EPA itself says high-radon homes exist in every zone. Neither replaces a test of your own home.
- How much does radon mitigation cost in Contra Costa County?
- A standard active sub-slab depressurization system typically runs $800-$2,500 installed nationally; California quotes vary with foundation type (slab, crawlspace, basement), home size and local labor. Get two or three bids from certified mitigators listed by your state radon program or the EPA's find-a-professional page.
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