Short-term kitFirst Alert
RD1 short-term charcoal radon test kit
- Lab fee included
Method: Charcoal
In home: 2 to 4 days
Locations and reports
Radon Levels in Merced County, California
EPA puts Merced County in Zone 3, its lowest radon zone, and only 5 radon tests from it are on file with CDC (2008 to 2017, laboratory totals). Homes with elevated levels occur in all three zones, so only a test measures yours.
Data checked By Radon411Methodology
Highest bordering
23.0%
Tuolumne County
- Tuolumne
- 23.0%
- Santa Clara
- 9.2%
4 of 7 neighbours have 30+ tests, 2008 to 2017
Nearest county
14.7%
Madera County, 53 miles
- Madera
- 14.7%
- California
- 10.3%
Share at 4+ pCi/L, 34 tests, 2008 to 2017
Ground above low
34.8%
7.9 pts below California
- Merced
- 34.8%
- California
- 42.7%
Share of land USGS rates moderate or high potential
Tests reported
6
Too few for a share
- Merced
- 6
- Needed
- 30
2007 to 2016, laboratory
EPA radon zone
Zone 3
Lower potential
- 1
- 2
- Zone 3
1 highest, 3 lowest
EPA predicts under 2 pCi/L indoors
Read a result for Merced County
Starts at EPA's action level
EPA’s own thresholds; the figures are the area’s, never this home’s.
EPA’s reading of 4.0 pCi/L
At or above 4 pCi/L
- Under 20 to 1.9 pCi/L
- 2 to 4consider a fix
- 4 and aboveEPA says fix it
This result is at or above 4 pCi/L. EPA recommends fixing a home when the radon level is 4 pCi/L or higher.
The data
Merced County, At a glance
Merced County at a glance
Predicted: EPA radon zone
EPA Zone 3: lower predicted potential
USGS geologic potential: Low across 65% of the county's area
Predicted: EPA Map of Radon Zones
Measured: tests reported to CDC
Radon tests reported for Merced County, 2008 to 2017, laboratory
CDC holds 5 reported tests for Merced County over the 2008 to 2017 laboratory totals, with a median of 2.1 pCi/L: too few to describe a county (Radon411 reads a share from 30 tests up). Merced County beside the counties around it is how this page reads it.
What these figures count
Only 5 tests were reported to CDC for Merced County over 2008 to 2017 (laboratory totals), and tests are often run on homes being sold or already suspected of a problem: so few describe neither the county nor this house.
Measured: CDC tracking data. Figure above: 2008 to 2017, laboratory. Measured data period: 2005 to 2017 (every CDC figure on file).
Merced County, Compared
Merced County radon figures, compared
Calculated by Radon411CDC's largest figure for Merced County rests on 6 tests over the 2007 to 2016 laboratory totals, 0 of them at or above 4 pCi/L, so each test moves its share by 16.7 points and no rank or comparison is drawn from it. Results reached as high as 3.7 pCi/L, with a middle value of 2.0 pCi/L.
Of the counties bordering it, 4 have a figure over the 2008 to 2017 laboratory totals: Tuolumne County reported the largest share at or above 4 pCi/L, 23.0%, and Santa Clara County the smallest, 9.2%, with Madera County at 14.7% and Fresno County at 11.0% between. Farther out, San Joaquin County (60 miles away) at 14.9%, Calaveras County (70 miles away) at 17.6% and Santa Cruz County (72 miles away) at 21.9% have figures too. Pooled across 56 California counties, 10.3% of reported tests reached that level; across every county in the country with a figure, 35.7%.
Statewide for the same period, El Dorado County reported the highest share (30.3%) and Sonoma County the lowest (0.8%). EPA's 1993 map puts Merced County in Zone 3, its lowest label: a predicted county average under 2 pCi/L. USGS geology rates 65% of the county's land low radon potential.
Pooled shares: Radon411's sum of CDC's county counts for one period.
Merced County, Geology
The ground under Merced County
PredictedUSGS's geologic map splits Merced County: 65.2% of its land is low radon potential and 34.8% moderate. The map puts 65.2% of Merced County in the area it calls Great Valley and 22.7% in Southern Coast Ranges, with one smaller area beside them. USGS gives the first a radon index of 8, in the low band (5 to 8), and the second 9, in the moderate band (9 to 11).
| Area | The rock, in USGS's words | Potential | Radon index | Share of land |
|---|---|---|---|---|
| Great Valley | Quaternary alluvial gravel, sand, silt, clay. | Low | 8 | 65.2% |
| Southern Coast Ranges | Metamorphosed marine sedimentary rocks, ultramafic rocks, Triasic metamorphic rocks, Mesozoic granitic rocks, and a series of fault-bounded linear basins in which Teriary marine and continental sedimentary rocks were deposited. | Moderate | 9 | 22.7% |
| Sierra Nevada | Northern Sierra Nevada is underlain primarily by Paleozoic and Mesozoic metamorphic rocks. Granitic rocks predominate in the southern Sierrra Nevada , with lesser Mesozoic metamorphic rocks. | Moderate | 9 | 12.1% |
Names, descriptions and indexes: U.S. Geological Survey, Geologic Radon Potential Map (2025). Shares: Radon411, from the map cut to the boundary.
Merced County beside the ground around it
Across California 0.1% of the land is rated high; none of Merced County's is. Every one of the 7 counties that border it has more moderate-potential ground, Mariposa County the most at 100%.
The map rates the ground, not the air in any home.
Local help
Merced County, Local resources
Radon testing and mitigation in Merced County
- California Indoor Radon ProgramCalifornia Indoor Radon Program, run by California Department of Public Health, licenses or certifies radon professionals and offers free or discounted test kits, and answers questions about testing and mitigation in California.Visit the program’s page(opens in a new tab)
- Free and low-cost kitsThe program says:
Discounted test kits can be purchased through our partner laboratory, Alpha Energy, for $14.95.
- Compare kits
- Professionals in California4 professionals are listed in California.
What California's program says
- Phone
- 1-800-745-7236
- Radonprogram@cdph.ca.gov
- Licensing of radon professionals
The Radon Program certifies all radon service providers operating in California.
What it means
Merced County, Questions
Questions about radon in Merced County
Are radon levels high in Merced County?
Over the 2008 to 2017 laboratory totals, 0.0% of the radon tests reported to CDC for Merced County, California were at or above 4 pCi/L, and the median reported pre-mitigation result was 2.1 pCi/L. Of the counties bordering it, 4 have a figure over the 2008 to 2017 laboratory totals: Tuolumne County reported the largest share at or above 4 pCi/L, 23.0%, and Santa Clara County the smallest, 9.2%, with Madera County at 14.7% and Fresno County at 11.0% between.
Which counties border Merced County?
Merced County borders 7 counties: Stanislaus County, Mariposa County, San Benito County, Madera County, Santa Clara County, Fresno County and Tuolumne County.
Products
Merced County, Products
Testing a home in Merced County
No CDC figure names Merced County; the nearest county with one, Madera County (53 miles away), reported 14.7% of its tests at or above 4 pCi/L over the 2008 to 2017 laboratory totals, the only reading nearby until a test of this home. Zone 3 is the lowest label, yet homes at or above 4 pCi/L occur in every zone: a short-term kit (2 to 90 days) is the quick first check in Merced County.
Test kits and monitors3
See every kit and monitor
Long-term kit
RL116 long-term radon test kit
- Lab fee extra
Method: Alpha track
In home: 90 days to 12 months
Monitor
View Plus radon and air quality monitor
- C-NRPP 2024/25: Approved
- Battery
- Wi-Fi, Bluetooth
- Screen, app
Method: Alpha spectrometry
- See every kit and monitor Test kits and monitors
Test kits and monitors: 1 of 3
Explore
Merced County, Bordering counties
Counties bordering Merced County
Calculated by Radon411- Radon levels in Tuolumne CountyEPA zone 2
23.0%at or above 4 pCi/L
Median 1.4 pCi/L · 74 tests
- Radon levels in Mariposa CountyEPA zone 2
16.7%at or above 4 pCi/L
Median 1.3 pCi/L · 6 tests
- Radon levels in Madera CountyEPA zone 2
14.7%at or above 4 pCi/L
Median 1.4 pCi/L · 34 tests
- Radon levels in Stanislaus CountyEPA zone 3
11.1%at or above 4 pCi/L
Median 1.4 pCi/L · 27 tests
- Radon levels in Fresno CountyEPA zone 2
11.0%at or above 4 pCi/L
Median 1.5 pCi/L · 100 tests
- Radon levels in Santa Clara CountyEPA zone 2
9.2%at or above 4 pCi/L
Median 0.9 pCi/L · 793 tests
- Radon levels in San Benito CountyEPA zone 2
0.0%at or above 4 pCi/L
Median 0.7 pCi/L · 19 tests
Merced County, Cities and towns
Cities and towns in Merced County
Merced County is growing: the Census Bureau puts it at 297,260 residents on July 1, 2025, up 5.1% from 282,895 in 2020. That works out to 153 people per square mile of land. Its largest town, Merced, has 99,724 residents, 33.5% of the total. Together its 6 incorporated places hold 70.0% of those residents; the other 30.0% live outside any of them. Reported testing is thin here: 6 tests over 2007 to 2016, or under 0.1 for every 1,000 residents (2025 estimate), where California as a whole comes to 0.3.
From Merced to Dos Palos, CDC publishes no figure by town: each reads Merced County's.
| Place | Residents | Since 2020 | Share of residents |
|---|---|---|---|
| Merced | 99,724 | +10.2% | 33.5% |
| Los Banos | 49,614 | +8.5% | 16.7% |
| Atwater | 32,133 | +0.7% | 10.8% |
| Livingston | 14,690 | +3.5% | 4.9% |
| Gustine | 6,112 | −0.4% | 2.1% |
| Dos Palos | 5,697 | −1.0% | 1.9% |
6 incorporated places, as listed in the U.S. Census Bureau’s 2020 place reference files. Residents: U.S. Census Bureau population estimates for July 1, 2025 (Vintage 2025).
Merced County, Homes
Homes in Merced County
Of Merced County's 89,610 homes, 74% are detached houses, against 57% across California; 10% are in buildings of five or more homes. Much of Merced County is recent building: 28% of its homes have gone up since 2000 and the middle year built is 1984, against 1976 for California. 53% of occupied homes are lived in by their owner (California: 56%); in the rest a tenant can run a test, but a fix is the landlord's to make.
| Homes | Merced County | California |
|---|---|---|
| Housing units | 89,610 | 14,532,683 |
| Detached houses | 74% | 57% |
| In buildings of 5 or more | 10% | 24% |
| Mobile homes | 7% | 4% |
| Built before 1960 | 19% | 27% |
| Built since 2000 | 28% | 18% |
| Middle year built | 1984 | 1976 |
| Owner-occupied | 53% | 56% |
Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.