Clay County, Minnesota

Arsenic: 51 of 100 sampled wells (51%) above the EPA limit of 10 µg/L. Nitrate: 2 of 125 sampled wells (2%) above the EPA limit of 10 mg/L as N. Samples 1965-09-09 to 2025-07-30; 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

51 of 100 sampled wells (51%) had a latest result above the EPA limit of 10 µg/L.

Median (latest per well): 10.585 µg/L
90th percentile: 49 µg/L
Highest: 73 µg/L
Non-detects: 17 wells' latest result was "not detected" with no detection limit reported; they are counted as below the limit.
Samples: 128, 1993-05-11 to 2025-07-30
Source: Water Quality Portal (USGS, EPA, NWQMC), siteType=Well, downloaded 2026-10-18

Nitrate

2 of 125 sampled wells (2%) had a latest result above the EPA limit of 10 mg/L as N.

Median (latest per well): 0.007 mg/L as N
90th percentile: 0.271 mg/L as N
Highest: 17.7 mg/L as N
Non-detects: 44 wells' latest result was "not detected" with no detection limit reported; they are counted as below the limit.
Samples: 128, 1965-09-09 to 2015-06-18
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.