DAYTON, Ohio — Routine groundwater testing by the Ohio Environmental Protection Agency has detected elevated levels of arsenic and several other contaminants in a well that supplies raw water to the city of Dayton, according to a report released Thursday.

Sampling conducted in April from Well 10R in the Dayton Miami Wellfield revealed arsenic concentrations at 12.6 micrograms per liter, exceeding the U.S. EPA's maximum contaminant level (MCL) of 10 µg/L for drinking water. While the data reflect ambient groundwater—untreated and not yet distributed to the public—the results raise concerns about the quality of source water in Montgomery County.

The testing, part of Ohio EPA’s Ambient Ground Water Quality Monitoring Program, also showed elevated levels of manganese, iron, sodium, and strontium. Manganese was measured at 163 µg/L, more than triple the EPA’s secondary drinking water standard of 50 µg/L, while iron reached 1,090 µg/L—over three times the EPA’s aesthetic guideline.

The agency emphasized that the results do not indicate a violation of drinking water standards, since they do not represent finished water. However, local officials and public health advocates say the findings underscore the need for closer scrutiny of potential contamination sources in the Great Miami aquifer, which serves hundreds of thousands of Ohioans.

Low levels of certain PFAS compounds, including PFBS and PFHxS, were also detected but remained below proposed federal limits.

Residents with concerns were advised to contact their local drinking water inspector for further information.