St. Louis County, Minnesota

Arsenic: 22 of 287 sampled wells (8%) above the EPA limit of 10 µg/L. Nitrate: 2 of 165 sampled wells (1%) above the EPA limit of 10 mg/L as N. Samples 1956-09-21 to 2025-10-22; 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

22 of 287 sampled wells (8%) had a latest result above the EPA limit of 10 µg/L.

Median (latest per well): 1.11 µg/L
90th percentile: 7.03 µg/L
Highest: 46.7 µg/L
Non-detects: 64 wells' latest result was "not detected" with no detection limit reported; they are counted as below the limit.
Samples: 419, 1976-02-24 to 2025-10-22
Source: Water Quality Portal (USGS, EPA, NWQMC), siteType=Well, downloaded 2026-10-18

Nitrate

2 of 165 sampled wells (1%) had a latest result above the EPA limit of 10 mg/L as N.

Median (latest per well): 0.01 mg/L as N
90th percentile: 0.82 mg/L as N
Highest: 56 mg/L as N
Non-detects: 64 wells' latest result was "not detected" with no detection limit reported; they are counted as below the limit.
Samples: 211, 1956-09-21 to 2009-10-28
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

Test your own well. County numbers cannot tell you what is in your water. See which tests fit your well.
Use a lab certified by Minnesota. Certified labs in Minnesota.
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.
If a result is high: arsenic guide · nitrate guide · bacteria guide · salesperson checklist.
Test again every year for bacteria and nitrate. Get a yearly reminder.