The short answer
Radon, a natural gas from uranium-bearing rock, is found in most North Carolina Piedmont wells at some level. The main concern is the radon it releases into indoor air, not drinking it. The NC Radon Program recommends testing your home's air first, then testing the well if air levels are high, and considering water treatment mainly at higher radon-in-water levels.
Where radon in well water comes from
Radon is a gas produced naturally as uranium in rock breaks down. North Carolina's Piedmont and mountains have uranium-rich minerals in many rocks, especially granites and granitic gneisses, so groundwater picks up dissolved radon as it moves through fractures in the bedrock.[source] USGS reports that radon in domestic wells in the Piedmont and Blue Ridge crystalline-rock aquifers is among the highest in the nation.[source]
That sounds alarming out of context, so here's the context: radon in water matters mostly because it escapes into the air when you run water, especially in the shower and at the dishwasher. The NC Radon Program states plainly that breathing radon in air poses a greater risk than swallowing it in water.[source]
What NC studies found
1,010 pCi/L
Median radon in 115 sampled wells, western and central NC, 2009–2010
18 counties, including Gaston, Lincoln and Catawba.
14%
Of those wells above 4,000 pCi/L
EPA's proposed alternate level, which has not been adopted.
30%
Of USGS-sampled Piedmont and Blue Ridge public-supply wells above 4,000 pCi/L
Untreated well water, 60 wells.
The state study found radon in every one of its sampled wells, ranging from 50 to 21,390 pCi/L, and higher on average in wells drilled into granitic rocks than in metasedimentary rocks.[source] It also reported that 91% of wells were above EPA's proposed 300 pCi/L level. Neither the 300 nor the 4,000 pCi/L level has been enacted as a federal standard,[source] which is why state guidance below uses different numbers.
Uranium and radium, radon's relatives, were far less common in the same study: one of 37 wells was above the 30 µg/L uranium standard, and three were above the 5 pCi/L combined radium standard.[source] Those are different contaminants with different treatments, covered below. If you're in one of the sampled counties, our Gaston County and Lincoln County pages summarize other local well data, and our well testing schedule guide covers what else to check.
Radon in water vs. radon in air
The NC Radon Program's rule of thumb: 10,000 pCi/L of radon in water adds about 1 pCi/L of radon to the air in your home. Its goal is to keep combined indoor radon from soil and water at or below EPA's recommended level of 4 pCi/L in air.[source] Most indoor radon comes up from the soil under the house, which is why the program recommends that every home in North Carolina be tested for radon in air, well or not.[source]
| Radon in well water | Guidance |
|---|---|
| At or above 10,000 pCi/L | Consider water treatment together with a radon-in-air mitigation system[source] |
| Between 4,000 and 10,000 pCi/L | Water treatment is optional[source] |
| Any level, if air radon is elevated | Testing the water helps show whether plumbing is a pathway[source] |
How to test, in the right order
- Step 1
Test your air
Start with a radon-in-air test kit and follow its placement instructions. The NC Radon Program notes kits are widely available online and in home improvement stores.[source]
- Step 2
If air is elevated, test the water
Radon in water needs its own sample, collected carefully so the gas doesn't escape. Use a lab that offers radon-in-water analysis; our water testing service can arrange it.
- Step 3
Consider uranium too
Radon isn't on North Carolina's required test list for new wells, and neither is uranium.[source] If you're testing for one, it's sensible to ask about the other.
- Step 4
Decide with both numbers
Air radon decides whether you need an air mitigation system. Water radon decides whether water treatment is worth adding, using the guidance above.
Treatment categories
NC DHHS lists these options for radionuclides in well water, and each one targets a different contaminant:[source]
| Treatment | Radon | Uranium | Radium |
|---|---|---|---|
| Aeration system | Yes | Not listed | Not listed |
| Granular activated carbon | Yes | Not listed | Not listed |
| Surface and decay storage | Yes | Not listed | Not listed |
| Ion exchange | Not listed | Yes | Yes |
| Reverse osmosis | Not listed | Yes | Yes |
For radon, aeration systems bubble or spray the water so the gas is released and vented outside before water reaches your taps. Granular activated carbon tanks can also hold radon. Since radon in water matters mostly as an airborne issue, these are whole-house systems. For uranium or radium, the fix is different, often a point-of-use reverse osmosis system. Our radon and uranium treatment page explains how we match a system to your results.
These systems connect to your plumbing, and aeration systems also need venting. Clear Bridge Water supplies and sizes equipment; here's how licensed installation works.
Sources
- NC Department of Environment and Natural Resources, Division of Water Quality, Naturally-Occurring Radon-222, Total Uranium, Radium-226, and Radium-228 in Drinking Water Wells in Western and Central North Carolina, 2009–2010 (Groundwater Circular 2011-02) (2011)
- NC Department of Health and Human Services, NC Radon Program, Radon in Well Water (2026)
- NC Department of Health and Human Services, Environmental Health Section, 15A NCAC 18A Section .3800: Private Drinking Water Well Sampling (2008)