Well water in Guilford County, North Carolina
In Guilford County, 4% of 4,698 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).
4,700 private wells tested 1998 to 2019 in state summaries; 70 individual samples from 70 wells, 1985 to 2007. 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 Guilford 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 | |
|---|---|---|---|---|---|---|---|
| Nitrate 1985 to 1996 | 13 | 69% | 8% | 0.4 | 12 | 10 mg/L EPA limit | |
| Radon 1996 to 2007 | 70 | 96% | no limit | 745 | 6,300 | 2,000 pCi/L health guideline |
Sampled fewer than 10 times, too few to summarize: Lead (4), Radium (226 + 228) (4), Uranium (2), E. coli (2), Arsenic (1), Sodium (2), Manganese (1).
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What this means
Among homeowners in Guilford County who sent a sample to the state lab, the health-based limits most often exceeded were uranium (8% of 12 wells), lead (4% of 4,698 wells), and arsenic (<1% of 4,700 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.
Manganese and iron 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 Guilford County
- Volatile organic compounds (VOCs)3,212 leaking underground storage tank sites on record locally.
- Manganese18% of 4,698 local wells tested were above the North Carolina groundwater standard.
- Iron14% of 2,307 local wells tested were above the North Carolina groundwater standard.
- Uranium8% of 12 local wells tested were above the EPA limit.
- Lead4% of 4,698 local wells tested were above the North Carolina groundwater standard.
- Arsenic<1% of 4,700 local wells tested were above the North Carolina groundwater standard.
- Copper<1% of 2,307 local wells tested were above the North Carolina groundwater standard.
- Coliform bacteriaRecommended for every private well, every year.
- RadonMedian local reading is 745 pCi/L.
Contamination sources on record in Guilford County
NC DEQ records 3,212 leaking underground storage tank sites in Guilford County, among 3,212 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.
- 3,212
- 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
- Uranium
- Point-of-use reverse osmosis; Anion exchange; Whole-house anion exchange
- Manganese
- Oxidizing filter (greensand, birm) whole-house; Water softener (low levels); Point-of-use reverse osmosis
- Iron
- Oxidizing filter whole-house; Water softener (low levels); Aeration plus filtration
- Nitrate
- Point-of-use reverse osmosis; Anion exchange; Distillation
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Common questions
Is there arsenic in well water in Guilford County?
Arsenic was detected in 0% of 1 public well samples in Guilford County, and 0% were above the EPA limit of 10 ug/L. Arsenic has no taste or smell; a lab test is the only way to know your level.
How high is radon in well water in Guilford County?
The median radon level across 70 public samples in Guilford County was 745 pCi/L, with a high of 6,300 pCi/L. New Hampshire recommends treatment above 2,000 pCi/L.
How often should I test a private well in Guilford 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: 99 samples in Guilford 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 8 contaminants in Guilford County, up to 4,700 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: 3,212 regulated sites located in Guilford 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.