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privatewelldata / Counties / North Carolina

Onslow County, North Carolina

Arsenic: 0 of 10 sampled wells (0%) above the EPA limit of 10 µg/L. Nitrate: 4 of 46 sampled wells (9%) above the EPA limit of 10 mg/L as N. Samples 1941-09-03 to 2021-12-15; updated 2026-10-18. Source: Water Quality Portal (USGS, EPA, NWQMC), siteType=Well.

What wells in this county have measured for arsenic and nitrate. A local picture only: test your own well to know your water.

Arsenic

0 of 10 sampled wells (0%) had a latest result above the EPA limit of 10 µg/L.

Median (latest per well)
0 µg/L
90th percentile
0.2 µg/L
Highest
0.4 µg/L
Non-detects
6 wells' latest result was "not detected" with no detection limit reported; they are counted as below the limit.
Samples
14, 2002-04-02 to 2021-12-15
Source
Water Quality Portal (USGS, EPA, NWQMC), siteType=Well, downloaded 2026-10-18

Nitrate

4 of 46 sampled wells (9%) had a latest result above the EPA limit of 10 mg/L as N.

Median (latest per well)
0.019 mg/L as N
90th percentile
0.791 mg/L as N
Highest
Withheld for review: 2 wells' latest result was above 100 mg/L as N, far outside the usual range. They are still counted as above the limit.
Non-detects
16 wells' latest result was "not detected" with no detection limit reported; they are counted as below the limit.
Samples
55, 1941-09-03 to 2021-12-15
Source
Water Quality Portal (USGS, EPA, NWQMC), siteType=Well, downloaded 2026-10-18

Includes monitoring, research and private wells reported to the Water Quality Portal. Non-detects count only when the lab's detection limit is at or below the EPA limit. Method: data rules.

What to do next

  1. Test your own well. County numbers cannot tell you what is in your water. See which tests fit your well.
  2. Use a lab certified by North Carolina. Certified labs in North Carolina.
  3. Compare your results with the EPA limits (arsenic 10 µg/L, nitrate 10 mg/L as N). If a result is above a limit, contact your county or state health department.
  4. If a result is high: arsenic guide · nitrate guide · bacteria guide · salesperson checklist.
  5. Test again every year for bacteria and nitrate. Get a yearly reminder.