Darke County, Ohio

Arsenic: 11 of 19 sampled wells (58%) above the EPA limit of 10 µg/L. Samples 1998-05-20 to 2020-07-30; 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

11 of 19 sampled wells (58%) had a latest result above the EPA limit of 10 µg/L.

Median (latest per well): 12 µg/L
90th percentile: 25.1 µg/L
Highest: 67.5 µg/L
Samples: 29, 1998-05-20 to 2020-07-30
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 Ohio. Certified labs in Ohio.
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.