Radon Levels & Zone Map in Butte County, CA
Direct Answer for basement and lowest-level tests: Butte County is classified as EPA Zone 3 (Low Risk). Predicted average indoor screening levels are below 2.0 pCi/L. However, the EPA recommends testing all homes regardless of zone - elevated readings have been found in every state.
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Direct Answer
What radon risk level should homeowners assume in Butte County?
Butte County is currently categorized as EPA Zone 3 (Lower Predicted Average Risk). Testing is still recommended because home-level variance can be high.
| Evidence | Value |
|---|---|
| Area | Butte County, CA |
| EPA Zone | Zone 3 |
| Primary Recommendation | Perform direct radon testing in the lowest livable level |
Your Radon Reading
Enter your home's measured level or use the Butte County average
Safe Range
Your reading is within the safe range. Both the EPA (4.0) and WHO (2.7) thresholds are not exceeded. Mitigation is not needed right now. We recommend periodic monitoring with a digital radon detector.
Get a Home Radon Monitor (~$30)Elevated - Consider Action
Your reading is below the US EPA action level (4.0 pCi/L), but this range still warrants follow-up testing. The World Health Organization uses 2.7 pCi/L as a tighter reference point.
If this level persists on confirmatory testing, planning mitigation is reasonable, especially for homes with frequent basement use, children, or pending real-estate transactions. Scroll down to see your estimated cost.
Verify with Long-term Monitor (~$150)Warning: Action Required - EPA Threshold Exceeded
At 1.5 pCi/L, this reading is above the EPA action level. Prompt mitigation planning is recommended after confirmatory testing.
Typical mitigation systems reduce radon by 80-99%. See your itemized cost estimate below.
Understanding Radon Levels: Complete Reference
Below 2.0 pCi/L - Acceptable Range
Below both the EPA (4.0) and WHO (2.7) action levels. No mitigation needed. The average outdoor radon level is approximately 0.4 pCi/L. Periodic monitoring is still recommended, as levels can change over time due to seasonal variations, changes in home ventilation, or foundation settling.
-4.0
2.0 - 4.0 pCi/L - Elevated, Consider Action
Exceeds the World Health Organization's reference level of 2.7 pCi/L but falls below the US EPA action threshold. The EPA states that homeowners should "consider fixing" homes in this range, especially if the home has a basement used as living space, if children are present, or in connection with a real estate transaction. Practical next step: run a confirmatory long-term test, then compare mitigation quotes if levels remain elevated.
-8.0
4.0 - 8.0 pCi/L - Action Recommended
Exceeds the EPA action level of 4.0 pCi/L. The EPA and Surgeon General strongly recommend mitigation within a few months. At this level, prioritize confirmatory testing and contractor planning. Standard sub-slab depressurization systems typically reduce indoor levels by 80-99%.
Above 8.0 pCi/L - Urgent Action Required
At these levels, the EPA recommends expedited mitigation - ideally within weeks, not months. Occupants should minimize time in lower-level rooms until the system is installed. Use a certified mitigator and request priority scheduling to shorten high-exposure time. Many mitigators offer priority scheduling for homes above 8.0 pCi/L.
Why Radon is Still Relevant in Butte County
Butte County is classified as EPA Zone 3, with predicted average indoor screening levels below 2.0 pCi/L. This does not mean radon is absent - it means the statistical average is low.
The EPA has documented elevated radon readings in every state and in homes in every zone classification. Local geological anomalies - pockets of granite, shale intrusions, or fractured bedrock - can create localized high-radon areas even within an otherwise low-risk county.
The Surgeon General and EPA recommend testing all homes, regardless of geographic zone. A simple short-term test kit ($15-$30) provides results within a few days and can give you peace of mind.
Radon & Health: What the Science Says
lung cancer
from radon
4.0 pCi/L
Radon is a Class A carcinogen - the same classification as asbestos and tobacco smoke. The National Academy of Sciences estimates that radon causes approximately 21,000 lung cancer deaths annually in the United States, making it the leading environmental cause of cancer death.
Unlike smoking, radon exposure is involuntary and often invisible. There is no safe level of radon - risk increases linearly with exposure. The good news: radon mitigation systems are highly effective, typically reducing indoor levels by 80-99% within hours of activation.
Source: US Environmental Protection Agency, "A Citizen's Guide to Radon" (EPA 402/K-12/002). National Academy of Sciences, Biological Effects of Ionizing Radiation (BEIR VI) Report, 1999.
Step 1: Test Your Home
Testing is the only way to know your home's radon level. Zone data tells you the regional risk, but your home could be significantly higher or lower than the county average.
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Already Know Your Level?
If your test shows 4.0 pCi/L or higher, get an itemized cost estimate specific to Butte County - including regional labor rates and permit requirements.
Get Mitigation Cost Estimate ->CA Radon Regulations
California requires sellers to complete the Transfer Disclosure Statement (TDS), which covers known environmental hazards including radon.
California does not require specific radon licensing. Look for NRPP or AARST-certified professionals.
How to Test for Radon in Butte County
Buy a Test Kit
Purchase a short-term charcoal test kit online or from a local hardware store. Cost: $15-$30. Place it in the lowest livable level of your home.
Wait 2-7 Days
Keep doors and windows closed (except normal entry/exit) during the test period. Avoid running whole-house fans. Mail the kit to the lab provided.
Read Your Results
If results are below 4.0 pCi/L, re-test every 2 years. If above 4.0, use our cost calculator to see mitigation options.
Related Radon Resources for Butte County
Explore Other CA Counties
Sources & Methodology
Radon zone classifications for Butte County are sourced from the EPA's Map of Radon Zones, which uses geological surveys, indoor radon measurements, and soil permeability data to assign each county a risk tier.
Disclaimer: Zone data represents county-level averages and cannot predict the radon level in any specific home. Testing is the only reliable method to determine your home's radon concentration. This content is for informational purposes and is not medical advice.
Page Content Last Reviewed: 2026-04-09
Editorial and Data Transparency
- Author
- RadonVerdict Editorial Team (Data and Content Team)
- Last Reviewed
- 2026-04-09
- Data Retrieved At
- 2026-02-24
Primary Sources
- US Census Bureau, 2018-2022 American Community Survey 5-Year Estimates (retrieved 2026-02-24)