HAZELWOOD, Mo. (AP) — The Army Corps of Engineers says it has discovered “low-level” radioactive contamination in residential yards that back up to Coldwater Creek in St. Louis County.

A Corps spokesman says homeowners have been notified, but he couldn’t give an exact number of affected properties because some samples are still being validated. In the places where contamination was confirmed, it’s several inches beneath the soil surface and isn’t dangerous unless it’s exposed.

Residents who pushed for additional testing near the creek’s floodplain tell the St. Louis Post-Dispatch that they aren’t surprised by the results.

The Corps is working to remove waste from the county’s early nuclear weapons program. It has identified radioactive contamination on private commercial property, but it’s the first time it has found contamination on residential properties.