Well water in Onslow County, North Carolina
In Onslow County, 3% of 234 private wells tested between 1998 and 2019 had lead above the North Carolina groundwater standard (15 ug/L), according to the NC State Laboratory of Public Health (NCWELL).
234 private wells tested 1998 to 2019 in state summaries; 20 individual samples from 12 wells, 1948 to 2024. Data refreshed September 9, 2026.
What homeowner tests found
NCWELL private well summaries: private wells tested and reported to the state, 1998 to 2019. Shares are against the level the state applies to each contaminant, named in the last column; several are stricter than EPA.
What individual samples found
Each row summarizes every public sample for that contaminant inside Onslow County. Above limit means above the EPA maximum contaminant level; where EPA has no enforceable limit, the row shows a health guideline or nuisance level instead.
| Contaminant | Samples | Detected | Above limit | Median | Highest | Limit | |
|---|---|---|---|---|---|---|---|
| Uranium 2002 to 2024 | 20 | 20% | 0% | 0 | 0.152 | 30 ug/L EPA limit | |
| Radium (226 + 228) 2013 to 2021 | 13 | 62% | 0% | 0.07 | 1.6 | 5 pCi/L EPA limit |
Sampled fewer than 10 times, too few to summarize: Nitrate (5), E. coli (7), Fluoride (2), Lead (2), Copper (2), PFOS (1), PFOA (1), Radon (8), Sodium (2), Chloride (2), Manganese (2).
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What this means
Among homeowners in Onslow County who sent a sample to the state lab, the health-based limits most often exceeded were lead (3% of 234 wells) and arsenic (<1% of 234 wells). These are ordinary wells tested by their owners, so the shares are the best available picture of a typical well here, with one caveat: people test more often when they suspect a problem.
Iron and manganese exceed the state's advisory level in a sizable share of wells; these are mostly a taste, staining or diet issue rather than a toxicity one.
What to test for in Onslow County
- Volatile organic compounds (VOCs)836 leaking underground storage tank sites on record locally.
- Iron56% of 157 local wells tested were above the North Carolina groundwater standard.
- Manganese26% of 234 local wells tested were above the North Carolina groundwater standard.
- Lead3% of 234 local wells tested were above the North Carolina groundwater standard.
- Arsenic<1% of 234 local wells tested were above the North Carolina groundwater standard.
- Coliform bacteriaRecommended for every private well, every year.
- RadonMedian local reading is 143 pCi/L.
- NitrateAbove the limit in 1 of 5 local samples; too few to quote a rate.
- FluorideDetected in 100% of local samples.
Contamination sources on record in Onslow County
NC DEQ records 836 leaking underground storage tank sites in Onslow County, among 836 regulated sites in total. Groundwater does not follow property lines, so a well within a few hundred feet of one of these is worth testing for what that site could release.
- 836
- leaking underground storage tank sitesGasoline and heating oil that leaked from tanks move through groundwater as benzene, MTBE and other volatile organic compounds.
Treatment that fits the local profile
- Iron
- Oxidizing filter whole-house; Water softener (low levels); Aeration plus filtration
- Manganese
- Oxidizing filter (greensand, birm) whole-house; Water softener (low levels); Point-of-use reverse osmosis
- Fluoride
- Point-of-use reverse osmosis; Activated alumina; Distillation
- Chloride
- Point-of-use reverse osmosis; Distillation
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Common questions
How high is radon in well water in Onslow County?
The median radon level across 8 public samples in Onslow County was 143 pCi/L, with a high of 1,710 pCi/L. New Hampshire recommends treatment above 2,000 pCi/L.
How often should I test a private well in Onslow County?
Test for bacteria and nitrate every year. Test once for arsenic, uranium, radon, fluoride, manganese and PFAS, then again every three to five years or after any change in taste, color, or plumbing.
Sources
- USGS Water Quality Portal: 67 samples in Onslow County. Data from the Water Quality Portal, a service of USGS, EPA and USDA; groundwater samples collected by USGS and cooperators. Retrieved September 3, 2026.
- NCWELL private well summaries: summaries for 7 contaminants in Onslow County, up to 234 wells each. County summaries of private well tests run by the NC State Laboratory of Public Health, 1998 to 2019, compiled by the UNC Superfund Research Program (NCWELL database). Counts are tests, not distinct wells; since 2008 every new well is tested once, so most tests are unique wells. Shares are against the NC 2L groundwater standard where one exists (manganese 50 ug/L, lead 15, iron 300) and otherwise the EPA limit. Medians are not used because more than half of results sit at the reporting limit for most analytes. Retrieved September 9, 2026.
- NC DEQ regulated sites: 836 regulated sites located in Onslow County. Underground storage tank incidents from the North Carolina Department of Environmental Quality UST Section. Retrieved September 9, 2026.
Non-detects count as samples and are treated as zero when computing medians. Exactly at the limit counts as not above it. A sample belongs to the town containing the well's reported coordinates.