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Radon Levels in Rio Grande County, Colorado

EPA puts Rio Grande County in Zone 2, its middle radon zone, and only 11 radon tests from it are on file with CDC (2023). Homes with elevated levels occur in all three zones, so only a test measures yours.

Data checked By Radon411Methodology

How to test this homeFind a certified tester

  • Share at 4+ pCi/L

    37.5%

    9.5 pts below CO

    Rio Grande
    37.5%
    Colorado
    47.0%

    216 tests, 2008 to 2017

  • Median result

    3.0pCi/L

    Below action level

    Rio Grande
    3.0 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2008 to 2017

  • Tests reported

    216

    30th of 50 by tests

    Rio Grande
    216
    Jefferson
    11,723

    Reported to CDC before any fix, 2008 to 2017

  • EPA radon zone

    Zone 2

    Moderate potential

    1. 1
    2. Zone 2
    3. 3

    1 highest, 3 lowest

    EPA predicts 2 to 4 pCi/L indoors

  • Rank in Colorado

    46 of 50

    Lowest quarter

    Rio Grande
    37.5%
    Kit Carson
    71.4%

    By share, of 50 with 30+ tests

Read a result for Rio Grande County

Starts at Rio Grande County's median, 3.0 pCi/L

3.0pCi/L

EPA’s own thresholds; the figures are the area’s, never this home’s.

EPA’s reading of 3.0 pCi/L

Between 2 and 4 pCi/L

  1. Under 20 to 1.9 pCi/L
  2. 2 to 4consider a fix
  3. 4 and aboveEPA says fix it

This result is between 2 and 4 pCi/L. EPA recommends considering a fix when the level is between 2 and 4 pCi/L. Rio Grande County's median reported result, 2008 to 2017.

Interpret this readingWhat a fix costs

The data

Rio Grande County, At a glance

Rio Grande County at a glance

Predicted: EPA radon zone

EPA Zone 2: moderate predicted potential

Rio Grande County is a county: EPA's forecast for it as a whole is an average indoor of 2 to 4 pCi/L (75 to 150 Bq/m³). It describes no single address, and homes above EPA's are found in every zone, this one included.

USGS geologic potential: Moderate across 100% of the county's area

Predicted: EPA Map of Radon Zones

Measured: tests reported to CDC

Radon tests reported for Rio Grande County, 2023

Share of reported tests at or above 4 pCi/L, by year, Rio Grande County
Share of reported tests at or above 4 pCi/L, by year, Rio Grande County
YearShare of reported tests at or above 4 pCi/L
20145.3%
201554.2%
201621.1%
201716.7%
201844.4%
201925.7%
202071.4%
202121.1%
202219.0%
202336.4%

2023: 36.4%. Across these years the share ran from 5.3% to 71.4%. Each column counts radon tests reported to CDC that year, not homes.

What these figures count

Only 11 tests were reported to CDC for Rio Grande County over 2023, 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: 2023. Measured data period: 2005 to 2023 (every CDC figure on file).

How to read these figures

Rio Grande County, Compared

Rio Grande County radon figures, compared

Calculated by Radon411

In Rio Grande County, about 4 in 10 reported tests over the 2008 to 2017 laboratory totals (81 of 216) were at or above EPA's action level. Against the national pool of 35.7%, the gap is 1.8 points higher. Across 63 Colorado counties pooled together, 47.0% of tests reached that level, so Rio Grande County runs 9.5 points below its state.

The newest figure, in 2023, counts only 11 tests (36.4% at or above 4 pCi/L), too few to compare, so this reading uses the 216-test figure.

Of 2 neighbours with a figure, none reported a larger share at or above 4 pCi/L; the spread is 26.6% (Alamosa County) to 31.2% (Archuleta County). By share, Rio Grande County is 46th of 50 Colorado counties with 30 or more tests for the same period.

Half the tests came in under 3.0 pCi/L and half over it; the single highest reached 50.0 pCi/L. Below the action level, 60 tests (27.8%) came in under 2 pCi/L, against 31.4% statewide, and 75 tests (34.7%) fell between 2 and 4, against 21.5% statewide.

Zone 2 on EPA's map (predicted average between 2 and 4 pCi/L) and a 37.5% share point the same way here. USGS geology rates 100% of the county's land moderate radon potential.

The busiest year on file was 2019, with 35 tests reported; the quietest, 2017, had 6.

Rio Grande County against Colorado, the United States and nearby counties, 2008 to 2017, laboratory
AreaTestsAt or above 4 pCi/LMedianDifference from Rio Grande County
Rio Grande County21637.5%3.0 pCi/LThis county
Colorado, pooled63 counties, pooled96,36747.0%Not pooled+9.5 points
United States, pooled2,661 counties, pooled2,013,54435.7%Not pooled−1.8 points
Kit Carson Countyhighest in the state4271.4%5.3 pCi/L+33.9 points
Prowers Countylowest in the state13731.4%3.0 pCi/L−6.1 points
Mineral County, COborders it1471.4%13.1 pCi/L+33.9 points
Saguache County, COborders it2653.8%4.2 pCi/L+16.3 points
Archuleta County, COborders it60031.2%2.3 pCi/L−6.3 points
Alamosa County, COborders it7926.6%2.1 pCi/L−10.9 points
Conejos County, COborders it1315.4%2.4 pCi/L−22.1 points
Where Rio Grande County's reported results fell, 2008 to 2017, laboratory, beside Colorado and the United States
ResultRio Grande County testsRio Grande County shareColorado shareU.S. shareAgainst Colorado
Under 2 pCi/L6027.8%31.4%39.6%−3.6 points
2 to 4 pCi/L7534.7%21.5%24.7%+13.2 points
4 pCi/L and above8137.5%47.0%35.7%−9.5 points
Rio Grande County ranked among the 50 Colorado counties with 30 or more tests, by share at or above 4 pCi/L, 2008 to 2017, laboratory
CountyRankTestsAt or above 4 pCi/LMedian
El Paso County40 of 508,52042.1%3.2 pCi/L
Denver County41 of 508,02141.8%3.3 pCi/L
Adams County42 of 504,76541.4%3.0 pCi/L
Phillips County43 of 505440.7%3.5 pCi/L
Douglas County44 of 507,35839.0%2.6 pCi/L
Montezuma County45 of 5017037.6%3.1 pCi/L
Rio Grande County46 of 5021637.5%3.0 pCi/L
Mesa County47 of 502,63235.8%2.9 pCi/L
Prowers County48 of 5013731.4%3.0 pCi/L
Archuleta County49 of 5060031.2%2.3 pCi/L
Alamosa County50 of 507926.6%2.1 pCi/L
Rio Grande County radon tests by year, against Colorado's pooled share
YearTestsAt or above 4 pCi/LMedianHighestColorado, pooledChange from the row before
20231136.4%3.7 pCi/L15.0 pCi/L38.9%+17.4 points
20222119.0%1.3 pCi/L26.2 pCi/L38.6%−2.1 points
20211921.1%2.0 pCi/L336.6 pCi/L47.3%−50.3 points
2020771.4%5.2 pCi/L9.3 pCi/L41.9%+45.7 points
20193525.7%1.7 pCi/L12.9 pCi/L44.1%−18.7 points
2018944.4%3.7 pCi/L50.8 pCi/L44.2%+27.7 points
2017616.7%2.3 pCi/L9.5 pCi/L41.0%−4.4 points
20161921.1%2.7 pCi/L39.5 pCi/L38.5%−33.1 points
20152454.2%4.0 pCi/L11.2 pCi/L47.2%+48.9 points
2014195.3%2.0 pCi/L5.4 pCi/L46.5%First on file

Pooled shares: Radon411's sum of CDC's county counts for one period.

Rio Grande County, State data

Colorado's own radon test data

Measured

What Colorado's own agencies publish about radon tests in Rio Grande County, with their period. These are not CDC's figures and are never added to them.

MeasuredState figures, not CDC's

What Colorado CDPHE reports for Rio Grande County

Radon data (county results): radon test results received from radon testing labs, primarily short-term household tests taken by the homeowner. Period: 2005-2025.

Share over 4 pCi/L

37.1%

159 of 428 tests

Median result

2.7 pCi/L

Highest result

336.6 pCi/L

Tests behind these figures

428 tests

  • CDPHE says these data do not give actual radon levels in homes that have not been tested.
  • When possible, only tests conducted before a mitigation system was installed are used.
  • Some counties have very small numbers of test results, and their summaries may be less representative.
  • These figures describe tests reported to Colorado CDPHE in this area. They count a different set of tests than CDC's figures and are not a reading of any one home.

Measured: Colorado CDPHE data, 2005-2025.

Rio Grande County, Geology

The ground under Rio Grande County

Predicted

USGS's geologic map puts all of Rio Grande County's mapped land in one class: moderate radon potential. All of it lies in the area the map calls San Juan Volcanic field, to which USGS gives a radon index of 11, in the moderate band (9 to 11).

USGS's geologic areas under Rio Grande County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
San Juan Volcanic fieldVolcanic rocks, rhyolite, tuff, basaltModerate11100%

Names, descriptions and indexes: U.S. Geological Survey, Geologic Radon Potential Map (2025). Shares: Radon411, from the map cut to the boundary.

Rio Grande County beside the ground around it

Across Colorado 74.8% of the land is rated high; none of Rio Grande County's is. Of the 5 counties that border it, 3 have more high-potential ground, Saguache County the most at 17.0%.

Share of land by USGS radon potential: Rio Grande County, the 5 counties bordering it and Colorado
AreaEPA zoneLow potentialModerate potentialHigh potential
Rio Grande CountyZone 2None100%None
Conejos CountyZone 2None95.3%4.7%
Alamosa CountyZone 2None91.9%8.1%
Mineral CountyZone 2None100%None
Saguache CountyZone 2None83.0%17.0%
Archuleta CountyZone 2None100%None
Colorado64 counties, pooled by land areaVariesNone25.2%74.8%

The map rates the ground, not the air in any home.

Local help

Rio Grande County, Local resources

Radon testing and mitigation in Rio Grande County

What Colorado's program says
Licensing of radon professionals
Listed contractors are certified by the National Radon Proficiency Program or the National Radon Safety Board, and must be licensed by the Colorado Department of Regulatory Agencies.
Disclosure when a home is sold or rented
As of August 7, 2023, landlords in Colorado are required to disclose radon information when a tenant signs a lease agreement.

What it means

Rio Grande County, Questions

Questions about radon in Rio Grande County

Are radon levels high in Rio Grande County?

In 2023, 36.4% of the radon tests reported to CDC for Rio Grande County, Colorado were at or above 4 pCi/L, and the median reported pre-mitigation result was 3.7 pCi/L. Of 50 Colorado counties with 30 or more tests for the same period, 45 reported a higher share; pooled, the state comes to 47.0%.

Which counties border Rio Grande County?

Rio Grande County borders 5 counties: Conejos County, Alamosa County, Mineral County, Saguache County and Archuleta County.

Products

Rio Grande County, Products

Testing a home in Rio Grande County

In Rio Grande County, 37.5% of 216 tests reported to CDC over the 2008 to 2017 laboratory totals reached 4 pCi/L, against 47.0% pooled across Colorado. In Zone 2 a short-term kit (2 to 90 days) is the quick first check in Rio Grande County; a long-term test tells the year-round average.

Test kits and monitors3

See every kit and monitor

Best radon monitors for Rio Grande County homes, compared

Explore

Rio Grande County, Bordering counties

Counties bordering Rio Grande County

Calculated by Radon411

Rio Grande County, Cities and towns

Cities and towns in Rio Grande County

About 11,087 people live in Rio Grande County by the Census Bureau's estimate for July 1, 2025, 451 fewer than in 2020 (−3.9%). That works out to 12 people per square mile of land. Its largest town, Monte Vista, has 4,005 residents, 36.1% of the total. CDC's 216 reported tests for 2008 to 2017 work out to 19.5 per 1,000 residents (2025 estimate), close to Colorado's 16.0.

From Monte Vista to South Fork, CDC publishes no figure by town: each reads Rio Grande County's.

The cities and towns in Rio Grande County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
Monte Vista4,005−5.9%36.1%
Centerextends beyond Rio Grande County1,890−3.5%Counted whole
Del Norte1,396−4.1%12.6%
South Fork506−2.1%4.6%

4 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). A place that extends beyond Rio Grande County is counted whole, so it has no share.

Rio Grande County, Homes

Homes in Rio Grande County

Of Rio Grande County's 6,574 homes, 74% are detached houses, against 62% across Colorado; 12% are mobile homes. Half of its homes were built before 1981, close to Colorado's 1987: 29% date from before 1960 and 18% from 2000 or later. 68% of occupied homes are lived in by their owner (Colorado: 66%); in the rest a tenant can run a test, but a fix is the landlord's to make.

Homes in Rio Grande County, Colorado, 2019 to 2023
HomesRio Grande CountyColorado
Housing units6,5742,545,124
Detached houses74%62%
In buildings of 5 or more7%22%
Mobile homes12%4%
Built before 196029%16%
Built since 200018%31%
Middle year built19811987
Owner-occupied68%66%

Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.