The Outagamie County Sheriff’s Office discovered the trays in a ditch on Tuesday morning, near Appleton International Airport, according to WLUK. The mail was returned to the U.S. Postal Service, and an investigation is underway.

“The United States Postal Inspection Service immediately began investigating, and we reserve further comment on this matter until that is complete,” USPS spokesman Bob Sheehan told WLUK.

The U.S. Postal Inspection Service told the Washington Examiner that it is aware of the mail, including absentee ballots, found in a ditch and is investigating the incident. The department declined to comment further.

The Outagamie County Sheriff’s Office told the Washington Examiner that the mail discovered was “mail going to the post office.”