Radon in Washington County is a geology story, not a scare story

Washington County, Tennessee, is EPA Radon Zone 1. That color means the predicted average indoor screening level is above 4 pCi/L. It does not mean every house on Indian Ridge is at 8, and it does not mean a Zone 2 house in Elizabethton is safe. The EPA drew the map in the 1990s from indoor data, geology, aerial radioactivity, soils, and foundation types. They still tell you to test the house you sleep in.

Johnson City, Kingsport, Bristol TN, and Jonesborough each have their own page for the houses and the water. This hub is the county and the rock.

Zone 1 here, Zone 2 next door

Look at a county map. Washington is red on the EPA sheet. Carter County and Unicoi County, immediately east and southeast, are Zone 2. Sullivan County, which holds Kingsport and Bristol TN, is Zone 1 again. Hawkins is Zone 1. You can drive from a Zone 1 ranch in Gray to a Zone 2 crawl in Elizabethton in twenty minutes. Radon does not read the county line.

Zone 2 is a milder predicted average (often talked about as 2 to 4 pCi/L). Individual Zone 2 homes still clear 4. If your sister in Unicoi "never tested because it's yellow," that is a family story, not a measurement.

Ridge-and-Valley, karst, and the shale people name-drop

Johnson City sits in the Valley and Ridge physiographic province. The ridges run northeast to southwest. The rock is folded and faulted sedimentary stuff: Knox Group carbonates (cherty limestone and dolomite) on a lot of the ridges, Chickamauga limestone and Conasauga shale in the valleys. Water dissolves the carbonates. You get karst: sinkholes, springs, solution openings, and soil-gas shortcuts.

Tennessee's groundwater reports have pointed at the Chattanooga Shale as a uranium-bearing unit that can feed radioactivity into nearby carbonates. In East Tennessee the same idea shows up as "shales in the Valley and Ridge can be a low-level source." You do not need a geology degree to use that sentence. You need to know why a county average can be high while your neighbor's kit is 1.2: the gas follows fractures and soil permeability, then the house.

Karst also means a well or spring is not a sealed bottle. A 2022 study of fifty springs across Carter, Greene, Hamblen, Sullivan, Unicoi, and Washington Counties found radon above the 300 pCi/L proposed drinking-water conversation level in 60 percent of samples. The authors called out a hotspot in northern Washington County and pointed at Knox Group and Chickamauga carbonates plus fault density. That is spring water research from ETSU folks, published in Geosciences. It is not a tap reading for your kitchen. It is why we ask about wells north of town.

Well water versus city water

If you're on Johnson City, Jonesborough, or another utility, the radon job is indoor air. Treated municipal water is not the usual driver of a 6 pCi/L living room.

If you're on a private well or a spring, especially in northern Washington County (think the Fall Branch, Boones Creek north, and the rural tracts toward Sullivan), radon in water can add to indoor air when you shower. The EPA has talked about 4,000 pCi/L in water as a rough "might matter to indoor air" conversation starter, and 300 pCi/L as a proposed drinking-water MCL that never became a national rule. We will not pretend those numbers are your well. Air test first. Water sample if you want the extra lab.

Jonesborough, 1779, and the housing mix

Jonesborough was founded in 1779. It is the oldest town in Tennessee and the county seat. The historic district is limestone, brick, and wood, with dirt crawls, fieldstone, and chimneys that predate plastic membranes. Those houses can be mitigated. They are not a 1998 Boones Creek slab. See the Jonesborough page.

The rest of the county is a mix the Zone map cannot see:

• Mid-century Johnson City ranches on dirt crawls with a couple of foundation vents
• Hillside walkouts toward Buffalo Mountain and the ridges
• Newer subdivision slabs that people assume are "tight enough"
• Split foundations where someone added a basement under a crawl house

Radon enters wherever the house touches soil: floor-wall joints, sumps, block cores, plumbing chases, and the entire dirt floor of a crawl. A "drafty old house" can be low. A tight new house can be high. Age is a pathway clue, not a result.

TDEC free kits versus a professional protocol

The Tennessee Department of Environment and Conservation will send a free short-term kit. Order from the Tennessee Radon Program or call their hotline at 1-800-232-1139. Run it 3 to 5 days. Mail it back immediately. Postage and lab are in the kit. That is a good first look if you already live there.

A professional test is different work:

• Closed-house conditions you can describe in a report
• Placement someone is responsible for
• A continuous monitor when a contract needs a time series
• A writeup a listing agent can forward

TDEC's own FAQ has said testers are not licensed in Tennessee and that you should look for national certification (they have named NEHA's radon program, which is the NRPP lineage, and NRSB). We agree. If you only need a screening number, use the kit. If you need a number that survives a negotiation, hire the protocol. Both can be true on the same street.

NRPP, NRSB, and the missing state license

Tennessee does not issue a state radon measurement or mitigation license. Anyone with a truck can say they "do radon." The state's own program points consumers to the National Radon Proficiency Program and the National Radon Safety Board. Those are exams, continuing education, and public directories. Ask for the credential. Look it up. If a bid comes in $400 cheaper and the name is not in either directory, you know what you are buying.

What to do with this page

Use the risk explainer if you want the geology translated into "what matters in my crawl." Then test. Then mitigate if the number earns a fan. We work Johnson City, Jonesborough, Kingsport, and Bristol TN from the same shop. Request a quote with the town and the foundation.